Steels are the most common materials. They have good technological properties. Products are obtained as a result of pressure and cutting processing.

The advantage is the ability to obtain the desired set of properties by changing the composition and type of processing. Steels are divided into carbon and alloy.

The influence of carbon and impurities on the properties of steels

Carbon steels are basic. Their properties are determined by the amount of carbon and the content of impurities that interact with iron and carbon.

Carbon influence.

The effect of carbon on the properties of steels is shown in Fig. 10.1

Fig. 10.1. The influence of carbon on the properties of steels

As the carbon content in the steel structure increases, the amount of cementite increases, while the proportion of ferrite decreases. Changing the ratio between the components leads to a decrease in ductility, as well as an increase in strength and hardness. Strength increases to carbon content of approx. 1%, and then it decreases, as a coarse network of secondary cementite is formed.

Carbon affects viscous properties. Increasing the carbon content increases the threshold of cold brittleness and reduces toughness.

Electrical resistance and coercive force increase, magnetic permeability and magnetic induction density decrease.

Carbon also affects technological properties. An increase in carbon content worsens the casting properties of steel (steels with a carbon content of up to 0.4% are used), workability by pressure and cutting, and weldability. It should be taken into account that steels with low carbon content are also difficult to cut.

Influence of impurities.

Steels always contain impurities, which are divided into four groups. 1. Permanent impurities: silicon, manganese, sulfur, phosphorus.

Manganese and silicon are introduced during the steelmaking process for deoxidation; they are technological impurities.

Manganese content does not exceed 0,5…0,8 %. Manganese increases strength without reducing ductility, and sharply reduces the red brittleness of steel caused by the influence of sulfur. It helps reduce iron sulfide content FeS, since it forms a manganese sulfide compound with sulfur MnS. Manganese sulfide particles are located in the form of separate inclusions, which are deformed and appear elongated along the rolling direction.

Being located near the grains, it increases the temperature of transition to a brittle state, causes cold brittleness, reduces the work of crack propagation, increases the phosphorus content for each 0,01 % increases the threshold of cold brittleness by 20…25ºС.

Phosphorus has a tendency to segregate, so in the center of the ingot, individual areas have a sharply reduced viscosity.

For some steels it is possible to increase the phosphorus content to 0,10…0,15 %, to improve machinability.

Sulfur reduces ductility, impairs weldability and corrosion resistance.

The sulfur content in steels is 0,025…0,06 %. Sulfur is a harmful impurity that gets into steel from cast iron. When interacting with iron, it forms a chemical compound - sulfur sulfide FeS, which, in turn, forms a low-melting eutectic with iron with a melting point 988ºС. When heated for rolling or forging, the eutectic melts and the bonds between the grains are broken. During deformation, tears and cracks occur at the locations of the eutectic, and the workpiece is destroyed - a phenomenon red brittleness.

Red brittleness – increased brittleness at high temperatures

Sulfur reduces mechanical properties, especially impact strength and ductility(ies), as well as endurance limit. It impairs weldability and corrosion resistance.

2. Hidden impurities- gases (nitrogen, oxygen, hydrogen) enter the steel during smelting.

Nitrogen and oxygen are found in steel in the form of brittle non-metallic inclusions: oxides ( FeO,SiO2,Al 2O 3) nitrides ( Fe 2N), in the form of a solid solution or in a free state, located in defects (cavities, cracks).

Interstitial impurities (nitrogen N, oxygen ABOUT) increase the threshold of cold brittleness and reduce the resistance to brittle fracture. Non-metallic inclusions (oxides, nitrides), being stress concentrators, can significantly reduce the endurance limit and viscosity.

Hydrogen dissolved in steel is very harmful, as it significantly embrittles the steel. It leads to the formation of floken.

Floken– thin cracks of an oval or round shape, having the appearance of spots in the fracture - silvery flakes.

Metal with flakes cannot be used in industry; during welding, cold cracks form in the deposited and base metal.

If hydrogen is in the surface layer, it is removed as a result of heating at 150…180 , better in a vacuum mmHg. Art.

Vacuuming is used to remove hidden impurities.

3. Special impurities, which are specially introduced into steel to obtain specified properties. Impurities are called alloying elements, and steels are called alloyed steels.

Purpose of alloying elements.

The main alloying element is chromium (0,8…1,2)%. It increases hardenability and helps to obtain high and uniform hardness of steel. The cold brittleness threshold of chromium steels is (0…-100) ºС.

Additional alloying elements.

Boron - 0.003%. Increases hardenability and also increases the threshold of cold brittleness (+20…-60) ºС.

Manganese – increases hardenability, but promotes grain growth and increases the cold brittleness threshold to (+40…-60) ºС.

Titanium (~0,1%) is introduced to refine grain in chromium-manganese steel.

Introduction of molybdenum (0,15…0,46%) in chromium steels increases hardenability, reduces the cold brittleness threshold to –20…-120 ºС. Molybdenum increases the static, dynamic and fatigue strength of steel and eliminates the tendency to internal oxidation. In addition, molybdenum reduces the tendency of steels containing nickel to become temper brittle.

Vanadium in quantity (0.1…0.3) % in chromium steels it refines the grain and increases strength and toughness.

The introduction of nickel into chromium steels significantly increases strength and hardenability, lowers the threshold of cold brittleness, but at the same time increases the tendency to temper brittleness (this disadvantage is compensated by the introduction of molybdenum into the steel). Chrome-nickel steels have the best range of properties. However, nickel is scarce and the use of such steels is limited.

A significant amount of nickel can be replaced with copper, this does not lead to a decrease in viscosity.

When chromium-manganese steels are alloyed with silicon, steels get chromansil (20ХГС, 30ХГСА). Steels have a good combination of strength and toughness, are well welded, stamped and machined. Silicon increases impact strength and temperature reserve of viscosity.

The addition of lead and calcium improves machinability. The use of hardening heat treatment improves the complex of mechanical properties.

Distribution of alloying elements in steel.

Alloying elements dissolve in the main phases of iron-carbon alloys (ferrite, austenite, cementite), or form special carbides.

The dissolution of alloying elements occurs as a result of the replacement of iron atoms with atoms of these elements. These atoms create stresses in the lattice, which cause a change in its period.

Changing the dimensions of the lattice causes a change in the properties of ferrite - strength increases, ductility decreases. Chromium, molybdenum and tungsten strengthen less than nickel, silicon and manganese. Molybdenum and tungsten, as well as silicon and manganese in certain quantities, reduce viscosity.

In steels, carbides are formed by metals located in the periodic table to the left of iron (chromium, vanadium, titanium), which have less complete d-electronic strip.

In the process of carbide formation, carbon donates its valence electrons to fill d electron band of the metal atom, while the metal's valence electrons form a metallic bond, which determines the metallic properties of carbides.

When the ratio of the atomic radii of carbon and metal is more than 0,59 Typical chemical compounds are formed: Fe 3C,Mn 3C,Cr 23C6,Cr 7C 3Fe 3W 3C– which have a complex crystal lattice and dissolve in austenite when heated.

When the ratio of the atomic radii of carbon and metal is less than 0,59 implementation phases are formed: Mo2C,W.C.V.C.TiCTaC,W 2C– which have a simple crystal lattice and are difficult to dissolve in austenite.

All carbides have high hardness and melting point.

4. Random impurities.

Classification and marking of steels

Steel classification

Steels are classified according to many characteristics.

1. By chemical composition: carbon and alloyed.
2. By carbon content:

a) low-carbon, with a carbon content of up to 0,25 %;
b) medium-carbon, with carbon content 0,3…0,6 %;
c) high-carbon, with a higher carbon content 0,7 %

1. According to the equilibrium structure: hypoeutectoid, eutectoid, hypereutectoid.

1. By quality. A quantitative indicator of quality is the content of harmful impurities: sulfur and phosphorus:

a) carbon steels of ordinary quality:
b) high-quality steel;
c) high-quality steels.

1. By smelting method:

a) in open hearth furnaces;
b) in oxygen converters;
c) in electric furnaces: electric arc, induction, etc.

1. By purpose:

a) structural – used for the manufacture of machine parts and mechanisms;
b) instrumental – used for the manufacture of various tools;
c) special – steel with special properties: electrical, with special magnetic properties, etc.

Steel marking

Alphanumeric designation of steels has been adopted

Carbon steels of ordinary quality (GOST 380).

Marked: St.2kp., BSt.3kp, VSt.3ps, VSt.4sp.

St – index of this steel group. Numbers from 0 before 6 — this is the conventional number of the steel grade. As the grade number increases, the strength of the steel increases and the ductility decreases. According to guarantees upon delivery, there are three groups of steels: A, B and C. For steels of group A, mechanical properties are guaranteed upon delivery; the index of group A is not indicated in the designation. For steels of group B, the chemical composition is guaranteed. For group B steels, both mechanical properties and chemical composition are guaranteed upon delivery.

The indices kp, ps, sp indicate the degree of deoxidation of the steel: kp - boiling, ps - semi-calm, sp - calm.

Quality carbon steels

High-quality steels are supplied with guaranteed mechanical properties and chemical composition (group B). The degree of deoxidation is generally calm.

Structural quality carbon steels. They are marked with a two-digit number indicating the average carbon content in hundredths of a percent. The degree of deoxidation is indicated if it differs from calm.

Steel 08 kp, steel 10 ps, ​​steel 45.

Tool quality carbon steels are marked with the letter U (carbon tool steel) and a number indicating the carbon content in tenths of a percent.

Steel U8, steel U13.

Tool high-quality carbon steels. They are marked similarly to high-quality tool carbon steels, only at the end of the mark they put the letter A to indicate the high quality of the steel.

Steel U10A.

Quality and high quality alloy steels

Designation is alphanumeric. Alloying elements have symbols, designated by letters of the Russian alphabet.

Designations of alloying elements:

X – chromium, N – nickel, M – molybdenum, B – tungsten, K – cobalt, T – titanium, A – nitrogen (indicated in the middle of the mark), G – manganese, D – copper, F – vanadium, C – silicon, P – phosphorus, P – boron, B – niobium, C – zirconium, Y – aluminum.

Alloy structural steels

Steel 15Х25Н19ВС2

At the beginning of the stamp there is a two-digit number indicating the carbon content in hundredths of a percent. Alloying elements are listed below. The number following the symbol of the element shows its content as a percentage,

If the number does not appear, then the content of the element does not exceed 1,5 %.

The specified steel grade contains 0,15 % carbon, 35% chromium, 19 % nickel, up to 1,5% tungsten, up to 2 % silicon.

To designate high-quality alloy steels, the symbol A is indicated at the end of the grade.

Alloy tool steels

Steel 9ХС, steel ХВГ.

At the beginning of the brand there is a single-digit number indicating the carbon content in tenths of a percent. If the carbon content is more than 1%, the number is not indicated,

All alloy tool steels are high quality.

Some steels have non-standard designations.

High-speed tool steels

P – index of this group of steels (from rapid – speed). Carbon content more than 1%. The number shows the content of the main alloying element - tungsten.

In the specified steel, the tungsten content is 18 %.

If steels contain an alloying element, then their content is indicated after the designation of the corresponding element.

Ball bearing steels

Steel ШХ6, steel ШХ15ГС

Ш – index of this group of steels. X - indicates the presence of chromium in the steel. The following number shows the chromium content in tenths of a percent, in the specified steels, respectively, 0,6 % And 1,5 %. Alloying elements included in the steel composition are also indicated. Carbon content more 1 %.

Permanent impurities

Permanent impurities (silicon, manganese, sulfur, phosphorus and gases) are always present in steel in a certain amount. Silicon and manganese are introduced during the smelting process (up to 0.4% sulfur and 0.1-0.8% manganese), and sulfur and phosphorus come from ores and secondary raw materials (up to 0.05%).

Silicon And manganese are present in any steel, remaining in it after deoxidation in small quantities in the form of useful impurities (they are deoxidizers). Manganese increases the strength of hot-rolled steel.

Sulfur And phosphorus– harmful impurities that make steel red-brittle (loss of ductility at 800 °C and above).

Steel with a high sulfur content cannot be hot-formed. In addition, sulfur worsens the mechanical properties of steel in a cold state and significantly reduces its viscosity. The only positive effect of sulfur on properties is improved machinability.

Phosphorus worsens the plastic properties of steel, reduces impact strength at room temperature, and especially at negative temperatures (gives steel cold brittleness). This effect is noticeable when the phosphorus content is above 0.1%. In some cases, phosphorus is useful: it improves the machinability of steel by cutting, and in the presence of copper, its anti-corrosion properties.

Sulfur and phosphorus in increased quantities are allowed only in steel with increased and high machinability, which has relatively low mechanical properties.

Gases ( oxygen, hydrogen, nitrogen) are usually harmful impurities, present in any steel in very small quantities, and they are called latent impurities. Gases are present in solid steel in the following forms: in a gaseous state (in pores, voids), in an α-solid solution; in the form of compounds, i.e. non-metallic inclusions (nitrides, oxides).

A large number of hydrogen in steel is dangerous, as this can lead to internal tears (flocks). Over time, the amount of hydrogen in steel decreases due to its release from the metal, which occurs due to the fact that hydrogen does not form compounds with iron. The release of hydrogen is accompanied by an improvement in the mechanical properties of steel, especially ductility.

Nitrogen and oxygen form brittle non-metallic inclusions that worsen the properties of the metal (decreasing viscosity and increasing the threshold of cold brittleness).

Random impurities

Random impurities are chemical elements that enter steel from ores of various deposits or from scrap, as well as due to varieties technological process.

The most common random impurities are nickel (up to 0.3%), chromium (up to 0.2%), copper (up to 0.1%). The content of random impurities is not allowed above a certain limit established by the technical specifications for each grade of steel, since very often the same elements that are useful in steel of one composition turn out to be harmful in another.

Special impurities

Special impurities (alloying elements) are introduced into steel in certain quantities in order to change its structure and properties (increasing strength, obtaining special physical and chemical properties, etc.). Alloying elements preferentially dissolve in the main phases of iron-carbon alloys (ferrite, austenite, cementite) or form special carbides.

Literature

1. Materials Science / Yu.T. Chumachenko, G.V. Chumachenko. – Rostov n/d: Phoenix, 2005. – 320 p.
2. Materials Science / O.V. Travin, N.T. Travina. M.: Metallurgy. 1989. 384 p.
3. Metallurgy / A.P. Gulyaev. M.: Metallurgy, 1986. 544 p.
4. Materials Science / A.M. Adaskin, V.M. Zuev. – M.: ProfObrIzdat, 2001. – 240 p.

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Introduction

Materials science is a science that studies the composition, methods of production, physical, chemical and mechanical properties, methods of thermal and chemical-thermal processing of materials, as well as their purpose.

The foundations of this science were laid in the 30s of the 19th century, when a general idea of ​​the structure of metals and alloys was developed, industrial methods for producing steel and the basics of heat treatment were developed. Since that time, metallurgy has begun to become increasingly important in resolving issues of the suitability of metals for certain purposes, the production of alloys with certain properties, giving them the necessary properties using thermal and chemical-thermal treatment, etc.

The foundations of the theory and scientifically based technology of heat treatment of steel were laid in the works of D.K. Chernov (1839-1921) on the metallography of iron and steel, which won international recognition. He also developed the theory of crystallization, created one of the most progressive hardening methods - isothermal, and pointed out the advantages of crystallization under pressure and centrifugal casting.

The largest discovery of the 19th century. became the periodic law of D.I. Mendeleev (1834-1907), which makes it possible to establish a connection between the properties, composition and structure of metals and to predict changes in both physicochemical and mechanical properties. Further successes in metallurgy are inextricably linked with the names of Soviet scientists N. A. Minkevich, S. S. Steinberg, N. T. Gudtsov, N. S. Kurnakov, A. A. Baykov, A. A. Bochvar, G. V. Kurdyumov and many others.

Currently, plastics and other non-metallic materials are widely used in the national economy, the creation of which became possible thanks to the work of A. M. Butlerov on the theory of the chemical structure of organic compounds; S.V. Lebedev, who substantiated industrial production synthetic rubber; V. A. Kargin, who performed structural studies of polymer materials, and others.

A variety of materials are used in shipbuilding, the number of which is growing every year.

The material is selected depending on the requirements for the vessel, structure or part (mechanical strength, durability, efficiency, reliability, etc.). Thanks to the right choice it is possible to increase the reliability and durability of the vessel, increase its speed and carrying capacity, reduce weight, reduce operating costs, reduce costs and increase labor productivity during construction.

Mastering materials science will help resolve the issue of the suitability of a material for certain purposes.

In the context of scientific and technological progress, the development of

its defining fields of science, technology and production. There is practically no branch of mechanical engineering, instrument making and construction in which welding and cutting of metals are not used. With the help of welding, permanent joints of almost all metals and alloys of various thicknesses are obtained - from hundredths of a millimeter to several meters.

The influence of harmful impurities of sulfur, phosphorus and non-metallic inclusions on the quality of steel

Steel is an alloy of iron and carbon, where carbon content is up to 2.14%. Steel always contains other elements - impurities that enter the alloy from natural compounds and from scrap metal during the deoxidation process: manganese, silicon, sulfur, phosphorus, nickel, copper, chromium, arsenic and others.

Impurities in steel are divided into permanent, random and harmful. The quality of steel is determined by the content of harmful impurities.

The main harmful impurities are sulfur and phosphorus. “Sulfur and phosphorus are the main enemies with which metallurgists of ferrous metals have to deal” (A.A. Baikov).

Harmful impurities also include non-metallic inclusions - gases (nitrogen, oxygen, hydrogen), with the exception of arsenic, they are present in all steels. These impurities are harmful primarily because an increase in their content reduces the resistance of rolled products to brittle fractures of various natures; these impurities have a particularly harmful effect on the properties of steels operated at low temperatures. One of the important tasks of modern metallurgy is to reduce their content to a reasonable minimum.

Sulfur (S) enters steel from cast iron (from ash and ore).

S - 0.035 - 0.06% (0.018% S - quality steel). Sulfur is insoluble in iron; it forms the compound FeS with iron. This compound forms a low-melting eutectic with iron with a melting point - Tm = 988? C.

The presence of eutectic causes red brittleness, i.e. brittleness at high temperatures. When heated to 1000-1200? C, the eutectic, located along the grain boundaries, melts and during deformation (OMD), tears and cracks appear in the steel. Sulfur forms with it

Euthemctic ( Greek yutektos -- easily melting) -- liquid system ( solution or melt), which at a given pressure is in equilibrium with solid phases, the number of which is equal to the number of components of the system.

Therefore, when steel blanks are heated for plastic deformation, the steel becomes brittle. During hot plastic deformation, the workpiece

is destroyed. This phenomenon is called red brittleness. One way

To reduce the influence of sulfur is the introduction of manganese. These inclusions are plastic and do not cause red brittleness.

Sulfur is removed from steel using manganese. Manganese has a greater affinity for sulfur than iron, and forms the MnS compound with a high melting point Tmelt = 1620? C:

FeS + Mn > MnS + Fe.

Sulfur and its compounds at room and low temperatures help reduce the impact toughness of steel, since the destruction of the metal occurs along sulfide inclusions (therefore, the impact toughness of the metal (KCU) decreases) (Fig. 5).

Figure 5. Effect of sulfur on the ductile properties of steel

Sulfur also reduces plasticity - d, w%.

Sulfur inclusions impair weldability and corrosion resistance. Sulfur facilitates machinability.

Phosphorus (P) is contained in the range of 0.025-0.045% P. It enters steel during the production process from ore, fuel, and fluxes.

Phosphorus occupies a special place among other elements, the presence of which negatively affects the quality of steel. On the one hand, phosphorus is an alloying element that greatly strengthens ferrite and increases the corrosion resistance of rolled products under atmospheric conditions; on the other hand, an increased content of phosphorus in steel causes the appearance of brittleness, a decrease in impact strength and resistance to brittle fracture, as well as an increase in the tendency to form crystallization cracks during welding.

Dissolving in ferrite, phosphorus greatly distorts the lattice and increases the strength and fluidity limits, but reduces ductility and toughness. The strong strengthening effect of phosphorus is explained by the fact that in ferrite it replaces iron atoms, and since its atom is larger than iron atoms, this leads to significant strengthening, but also to embrittlement. In addition, phosphorus prevents transverse microsliding, thereby increasing the tendency to microplane sliding, while the number of slip planes decreases, especially with decreasing temperature, and the tendency of iron to twinning also increases.

The more phosphorus in the steel, the more significant the decrease in viscosity.

Phosphorus significantly increases the threshold of cold brittleness.

Each 0.01% P increases the cold brittleness threshold of steel by 20 - 25? C (for carbon, each 0.1% has the same effect).

Phosphorus has a high tendency to segregation (heterogeneity of distribution). Phosphorus accumulates in the middle layers of the ingot, along the grain boundaries, greatly reducing the impact strength.

Phosphorus (P) - strengthens covalent (brittle) bonds and weakens metallic ones. As the temperature decreases, the fragility of the metal increases (cold brittleness) (Fig. 6). Phosphorus makes the steel easier to machine with cutting tools (creating brittleness). The combined presence of phosphorus and copper (P + Cu) in steel increases corrosion resistance.

Figure 6. Effect of phosphorus on the cold brittleness of steel (0.2% C, 1% Mn)

Hidden impurities:

This is the name given to the gases present in steel - nitrogen, oxygen, hydrogen - due to the difficulty of determining their quantity. Gases enter the steel during its smelting.

In hard steel they can be present, either dissolving in ferrite or forming a chemical compound (nitrides, oxides). Gases can also be in a free state in various discontinuities.

Even in very small quantities, nitrogen, oxygen and hydrogen greatly impair the plastic properties of steel. Their content in steel is allowed

0.2 - 0.4%. As a result of evacuation of steel, their content decreases and properties improve.

Oxygen (O2): forms non-metallic inclusions oxides - FeO, MnO, Al2O3, SiO2.

Nitrogen (N2): forms nitrides - Fe4N, Fe2N, AlN.

Oxygen and nitrogen in free form are located in cavities, cracks, etc. These inclusions significantly reduce impact strength, increase the threshold of cold brittleness and reduce ductility, while increasing the strength of steel (Fig. 7).

Figure 7. Effect of interstitial impurities of oxygen (a) and nitrogen (b) on the viscous properties of iron

Hydrogen (H2): During solidification, some of the hydrogen in the atomic state remains in the steel. When atomic hydrogen transforms into molecular hydrogen, the pressure increases to 150 MPa, forming ellipsoidal depressions - flakes, which are an irreparable defect. Flocks contribute to severe embrittlement of steel.

Hydrogen can be partially removed from the surface layer by heating to 150-180? C, best in a vacuum of ~ 10-2 - 10-3 mm. rt. Art. or heating to 800? C and holding, the hydrogen leaves and pure metal remains.

Processing steel with synthetic slag

The technology is used in large-capacity furnaces with a capacity of 60-200 tons in workshops that have a special furnace for smelting synthetic slag. Processing steel with synthetic slag is as follows. Before releasing steel from the melting unit, 3...5% of the weight of steel is poured into the casting ladle of liquid slag containing 55% CaO, 42% Al2O3, up to 3% SiO2 and 1% FeO. Up to 25% of cast iron, lime (1.5-3.5%) and iron ore (2-3%) are added to the filling. After melting, the bath is purged with oxygen. The oxidation slag is drained, ferromanganese is added to the metal, counting on the lower limit of manganese content in the steel being smelted, and ferrosilicon at the rate of introducing 0.15-0.20% silicon. Further they suggest not a large number of(~ 1% by weight of the metal) calcareous slag with the addition of lime, fireclay, and fluorspar. There is no recovery period as such; instead, short-term (~ 30 min) finishing is carried out, during which the steel is brought to the specified temperature and composition by introducing the necessary alloying additives. Slag deoxidation is not carried out.

Before releasing steel, 80-90% of the slag is drained from the furnace. Next, the steel is released into a ladle with synthetic slag poured into it, which ensures the refining of the metal from sulfur and non-metallic inclusions. During tapping, ferrosilicon and, if necessary, ferrotitanium and ferrovanadium are introduced into the ladle. Typically, synthetic lime-alumina slag (~ 55% CaO and 45% Al2O3) is used, which is poured into the ladle in an amount of 4-6%.

Then the smelted steel is released into the ladle from as high a height as possible with a powerful jet. As a result of intensive mixing of steel and slag, the surface of their interaction increases hundreds of times compared to that available in the furnace. Therefore, the refining processes are sharply accelerated and they no longer require 1.5...2 hours, as usual in a furnace, but approximately as much as it takes to release the melt.

Steel refined with synthetic slag has a low content of oxygen, sulfur and non-metallic inclusions, which provides it with high ductility and toughness.

Refining remeltings include: electroslag, vacuum-arc, plasma-arc, electron-beam, etc.

2. Based on the sketch of the part (Fig. 7), develop a sketch of the casting with model and foundry instructions, provide sketches of the model, core box and assembled casting mold (sectional view). Describe the sequence of making a mold using the hand molding method.

Part material - steel 45L

Type of casting delivery GOST 977-75.

Steel substitute: 35L, 55L, 50L, 40L.

admixture steel molding casting

Table 1 - Chemical composition of steel 45L

Main components and notations
Symbols in steel grade	Element designation according to the periodic table		Composition in the material %
Other components
		manganese
			No more than 0.3
			No more than 0.3
			No more than 0.3
			No more than 0.045
			No more than 0.04

processing of a metal workpiece by pressure by compression between the rotating rolls of a rolling mill to reduce the cross-section of the ingot or workpiece and give them the desired shape. At metallurgical enterprises it is carried out in two stages. First, the ingots are heated and rolled on crimping mills into a billet. The dimensions and shape of the workpiece depend on its purpose: for rolling sheet and strip metal, rectangular workpieces with a width of 400-2500 mm and a thickness of 75-600 mm, called slabs, are used; for high-quality metal - square-section blanks ranging in size from 600-5,600 mm to 400-5,400 mm, and for solid-rolled pipes - round-section with a diameter of 80--350 mm. Then the resulting billet is rolled into commercial steel products in three main types of mills: sheet, section and pipe. Steel sheets with a thickness of 4 to 50 mm and plates with a thickness of up to 350 mm are rolled on plate or armor mills, and sheets with a thickness from 1.2 to 20 mm are rolled on continuous mills, from where they come out in the form of long (more than 500 m) strips that are wound into rolls. Sheets less than 1.5-3 mm thick are rolled in a cold state. Rolling of high-quality metal is carried out with heating to 1100-1250 °C sequentially in several stages to gradually bring the cross-section of the initial workpiece closer to the cross-section of the finished profile. Pipe rolling is usually carried out in a hot state and includes three main operations. The first operation (piercing) is the formation of a hole in a workpiece or ingot; the result is a thick-walled pipe called a sleeve. The operation is performed on the so-called. piercing screw rolling mills. The second operation (rolling) is lengthening the sleeve and reducing the thickness of its wall; performed on various rolling mills: continuous, pilgrim, screw rolling, etc. The third operation is calibration (or reduction) of pipes after rolling; carried out on calibration mills. In order to reduce the wall thickness and diameter of the pipe, obtain higher mechanical properties, a smooth surface and precise dimensions, after hot rolling, pipes are cold rolled in special mills. After rolling is completed, the resulting products are cut into pieces of the required length and subjected to heat treatment, for example. annealing (if necessary), and checking their quality.

From ser. 20th century Rolling of steel billets is replaced by continuous casting (casting) on ​​special casting machines. Thanks to the use of continuous casting of steel, slabs and blooms are eliminated, the quality of rolled products is improved, and losses associated with the processing of ingots, reaching 15-20%, are eliminated.

Based on the sketch of the finished part (Fig. 21), develop a diagram of the technological process of its production using the hot die forging method using a steam-air hammer. When performing work you should:

1) describe the essence of the hot die forging process and indicate the scope of its application;

2) draw a diagram of the hammer and describe its operation;

3) establish the temperature range for stamping and the method of heating the workpiece;

4) draw up a drawing of the forging and determine its mass;

5) list all technological waste, determine the volume and length of the original workpiece;

6) select stamping transitions and provide a sketch of the tool,

7) list the technological process operations necessary to obtain this forging,

8) describe the mechanism of the stamping process

1. Hot die forging is the process of hot deformation in which the flow of metal is limited to the cavity of the die stream.

The flow of metal occurs as a result of the force of the machine-tool through the die on the workpiece. For any method of hot die forging, the tool is a stamp. The stamp always consists of two or more parts. The surfaces where the parts of the die come into contact with each other are called parting planes. On the parting planes there are cavities, which are like an imprint of the future forging, which are called streams. The workpiece heated to a plastic state is placed in the stream when the stamp is open. When the parts of the die come together, the metal of the workpiece begins to flow, fills the stream and takes the shape of the forging. Forgings produced by hot die forging have the shape of a finished part with small allowances on the surfaces to be machined. Hot die forging is advantageous in large-scale and mass production environments and is produced in forge shops. This method is widely used to produce forgings of various shapes weighing from 0.5 to 350 kg, and with specialized equipment it is possible to produce forgings weighing up to 1 ton.

The advantages of hot die forging are as follows:

uniformity and accuracy of forgings,

high performance,

possibility of producing forgings of complex configuration.

The main disadvantage of the process is the high cost of the stamp. Using hot die forging, it is possible to produce forgings from all metals and alloys that have ductility in a hot state.

These methods produce products made of metal, plastics and other materials of very different shapes and sizes with varying degrees of dimensional accuracy, mechanical and other characteristics and surface quality. Therefore, forging and stamping production is widely used in mechanical engineering and instrument making, in the production of objects consumer consumption and other sectors of the national economy. Producing products by forging and stamping makes it possible to bring the original shape of the workpiece as close as possible to the shape and dimensions of the finished part and thereby reduce or completely eliminate expensive operations with loss of metal into chips.

2. The main types of hammers for forging are driven - steam-air and pneumatic.

The main type of hammers are steam-air stamping hammers. In single-acting hammers (Fig. 9), steam (compressed air) serves only to lift the falling parts to the upper position. The working stroke (downward stroke) is performed in these hammers only under the influence of the weight of the falling parts.

Rice. 9. Diagram of a single-acting steam-air hammer: 1 - hole for air passage, 2 - working cylinder, piston, 3 - rod, 4 - female, 5 - upper striker (stamp), 7 - lower striker (stamp), 8 -- stamp pad, 9 -- chabot
Rice. 10. Diagram of a double-acting steam-air hammer:
1 - piston, 2 - rod, 3 - woman, 4 - upper firing pin (stamp), 5 - lower firing pin (stamp). 6 -- shabot

In double-acting hammers (Fig. 10), steam or compressed air not only lifts the parts to the upper position, but also presses on the piston from above during the working stroke. Thus, it increases the force of the impact, accelerating the falling parts to a higher speed.

In single-acting hammers, the working cycle begins with the supply of steam or compressed air from the line into the lower cavity of working cylinder 2 (see Fig. 9). Acting on piston 3, the energy carrier forces it to move upward. Connected to the piston 3 is a rod 4, to the lower end of which a head 5 is attached. An upper striker 6 is installed on the head 5. Thus, when steam or compressed air is introduced, all falling parts rise upward.

Near the top cover along the circumference of the cylinder there are holes L through which the air above the piston escapes into the atmosphere.
When piston 3, rising upward, reaches holes 1 and blocks them, a closed space appears above the piston. With the further upward stroke of the piston, the air in this space will be compressed. Thus, an air cushion is created, which ensures smooth braking of the piston in the upper position.

When the woman rises to a sufficient height, the steam distribution mechanism stops supplying energy to the cylinder and air from under the piston is released into the atmosphere. The pressure in the cylinder decreases sharply. Under the influence of their own weight, the moving parts fall down and the striker 6 hits the workpiece, which is placed on the lower striker 7 (stamp). It is fixed in a die pad 8 lying on a slab 9.

Single-acting hammers have a simple design and are reliable in operation. However, they have disadvantages: energy consumption is high, it is difficult to regulate the speed of movement of the hammer, and therefore the force of the blow; finally, to deliver a blow of the same force as that of a double-acting hammer, the mass of the moving parts of a single-acting hammer must be much greater. Therefore, single-acting hammers have recently been replaced by more advanced double-acting hammers. Air hammer. The most common design of such a hammer is shown in the following diagram. In the cast frame 10 there are two cylinders - compressor 9 and working 5, the cavities of which communicate through spools 7 and 6. Piston 8 of the compressor cylinder is moved by connecting rod 14 from crank 15, rotated by electric motor 13 through gears 11 and 12 (gearbox). When the piston moves in the compressor cylinder, the air is alternately compressed in its upper and lower cavities. Air, compressed to 0.2-0.3 MN/m, when you press the pedal or handle that opens the spools 7 and 6, enters through them into the working cylinder 5. Here it acts on the piston 4 of the working cylinder. Piston 4, made in one piece with a massive rod, is at the same time a hammer head, to which the upper striker 3 is attached. As a result, the falling parts 3 and 4 periodically move up and down and strike the workpiece laid on the lower striker 2, which is fixedly fixed on a massive hammer 1. Depending on the position of the controls, the hammer can deliver single and automatic blows of controlled energy, operate at idle speed, forcefully press the forging to the lower striker and hold the hammer suspended.

Pneumatic hammers are used for forging small forgings (up to approximately 20 kg) and are manufactured with a mass of falling parts of 50-1000 kg.

Diagram of a pneumatic hammer.

3. During hot deformation, the ductility of the metal is higher and the resistance to deformation is lower, so it is accompanied by lower energy costs. Heating of the metal during OMD affects the quality and cost of the product. Basic requirements for heating: it is necessary to uniformly heat the workpiece along its cross-section and length to the appropriate temperature in the minimum time with the least loss of metal into scale and economical fuel consumption. Improper heating causes various defects: cracks, decarburization, increased oxidation, overheating and burnout.

Slow heating reduces productivity and increases oxidation and decarburization of the workpiece surface. When overheated (heating above the optimal OMD interval), grain growth occurs, which reduces the mechanical properties. It is corrected by normal annealing by heating to the optimum temperature, holding and then slowly cooling with the furnace. In case of burnout, i.e. when heated to a temperature close to the melting point, grain boundaries melt and cracks appear, which is an irreparable defect.

Each metal and alloy has its own specific temperature range for hot pressure treatment, which is selected from tables depending on the grade of the alloy. So, for example, for carbon steels, the temperature of the beginning of hot deformation is selected according to the iron-cementite phase diagram at 100 - 200 °C lower than the melting temperature of the steel given chemical composition, and the temperature at the end of deformation is taken to be 50 - 100 °C higher than the recrystallization temperature.

Before pressure treatment, billets and ingots are heated in forges or furnaces. Furnaces differ from heating furnaces in their small size and are heated coal, coke or fuel oil, the metal is heated in them by direct contact with the fuel. They are used to heat small workpieces during hand forging. Furnaces for heating workpieces are divided into flame and electric, and according to temperature distribution - into chamber and methodical. In chamber furnaces - periodic heating furnaces - the temperature is the same throughout the entire working space. Methodical furnaces with a constantly increasing temperature of the working space from the place of loading of workpieces to the place of their unloading are continuous furnaces.

Mechanical properties at T=20 °C for 45L

Physical properties for 45L

			W/(m deg)		J/(kg deg)

Technological properties for 45L

Foundry and technological properties for 45L

Chemical composition in % for 45L

Ordinary casting steel is used for the production of frames, gears and rims, brake discs, couplings, casings, road wheels, sprockets, etc. - parts that require increased strength and high wear resistance and operate under static and dynamic loads.

Difficult to weld - to obtain high-quality welded joints, additional operations are required: heating to 200-300°C during welding, heat treatment after welding - annealing

Substitute: 35L, 55L, 50L, 40L

Mechanical properties in sections up to 100 mm (GOST 977-75)

Table 26 Melting and pouring temperatures of casting alloys

To obtain high-quality castings, molds are filled with

compliance with certain requirements, the indicators of which are:

a) melt temperature;

b) duration of mold filling;

c) the nature of the melt entering the mold;

d) the degree of filling of the sprue bowl with the melt;

e) jet height;

f) timely filling of the mold; preventing slag and non-metallic inclusions from entering the mold.

The temperature of pouring the melt into the mold is determined mainly by the design of the castings. The smaller the wall thickness and the larger the overall dimensions of the casting, the higher the temperature of the poured melt should be. In order to reduce shrinkage, massive castings are poured with a melt at a lower temperature.

3. Unified principles for standardization of admission and landing systems

A system of tolerances and landings is a set of series of tolerances and landings, naturally built on the basis of experience, theoretical and experimental research and formalized in the form of standards.

The system is designed to select the minimum necessary, but sufficient for practice, options for tolerances and fits of typical connections of machine parts, makes it possible to standardize cutting tools and gauges, facilitates the design, production and achievement of interchangeability of products and their parts, and also improves their quality.

Currently, most countries in the world use ISO tolerance and landing systems. ISO systems were created to unify national tolerance and fit systems in order to facilitate international technical connections in the metalworking industry. Incorporation of international ISO recommendations into national standards creates conditions for ensuring the interchangeability of similar parts, components and products manufactured in different countries. The Soviet Union joined ISO in 1977, and then switched to a unified system of tolerances and landings (USDP) and basic interchangeability rules, which are based on ISO standards and recommendations.

Basic standards of interchangeability include systems of tolerances and fits for cylindrical parts, cones, keys, threads, gears, etc. The ISO and ESDP tolerance and fit systems for standard machine parts are based on common design principles, including:

system of formation of landings and types of interfaces;

system of main deviations;

accuracy levels;

tolerance unit;

preferred fields of tolerances and landings;

ranges and intervals of nominal sizes;

normal temperature.

The system for forming fits and types of mates provides for fits in the hole system (SA) and in the shaft system (SV).

Fittings in a hole system are fittings in which various gaps and tensions are obtained by connecting different shafts to the main hole (Fig. 3.1, a).

Fitments in the shaft system are fits in which various gaps and interferences are obtained by connecting various holes to the main shaft (Fig. 3.1, b).

Rice. 3.1. Examples of the location of tolerance fields for landings: a - in the hole system; b - in the shaft system

For all fits in the hole system, the lower deviation of the hole EI = 0, i.e. the lower limit of the tolerance field of the main hole, always coincides with the zero line. For all fits in the shaft system, the upper deviation of the main shaft is es = 0, i.e., the upper limit of the shaft tolerance always coincides with the zero line.

The tolerance field of the main hole is set upward, the tolerance field of the main shaft is set down from the zero line, i.e., into the material of the part.

The system of main deviations is a series of main deviations of shafts in SA and holes in SV, designated respectively by lowercase and capital letters of the Latin alphabet, for example a, b, ..., zb, zc; A, B, …, ZB, ZC.

The value of the main deviation is determined by the corresponding letter and depends on the nominal size.

In the systems of tolerances and fits of different types of parts, a different number of main deviations is established; the largest number of them is contained in the system of tolerances and fits of smooth cylindrical parts.

Accuracy levels can be called differently: accuracy grades - for smooth parts, degrees of accuracy - for threaded parts and gears, or accuracy classes - for rolling bearings, but in any case they determine the required level of accuracy of parts to perform their functions. Accuracy levels are indicated, as a rule, by Arabic numerals; the smaller the number, the higher the accuracy level, i.e. more precisely a detail.

The tolerance unit is the dependence of the tolerance on the nominal size, which is a measure of accuracy, reflecting the influence of technological, design and metrological factors. Tolerance units in tolerance and fit systems are established on the basis of studies of the accuracy of machining of parts. The tolerance value can be calculated using the formula T = a·i, where a is the number of tolerance units, depending on the level of accuracy (quality or degree of accuracy); i - tolerance unit.

Preferred tolerance fields and fits are a set of tolerance fields selected from among the most frequently used in the production of products and fits or types of mates made up from them. These tolerance and fit fields constitute a series of preferred and recommended ones and should be primarily used when designing products.

Ranges and intervals of nominal sizes take into account the influence of the scale factor on the value of the tolerance unit. Within one size range, the dependence of the tolerance unit on the nominal size is constant. For example, in the system of tolerances and fits of smooth parts for the size range from 1 to 500 mm, the tolerance unit is equal; for the size range over 500 to 3150 mm, the tolerance unit is i = 0.004D + 2.1.

To construct tolerance series, each of the size ranges, in turn, is divided into several intervals. Since it is not economically feasible to assign a tolerance for each nominal size for all sizes combined into one interval, the tolerance values ​​are assumed to be the same. In the formulas for tolerance units in the ISO and ESDP systems, the geometric mean of the extreme dimensions of each interval is substituted as dimensions.

The sizes are distributed across intervals so that the tolerances calculated from the extreme values ​​in each interval differ from the tolerances calculated from the average diameter value in the same interval by no more than 5-8%.

The normal temperature at which the tolerances and deviations established by the standards are determined is assumed to be + 20 °C (GOST 9249-59). This temperature is close to the temperature of the working premises of industrial premises. Calibration and certification of all linear and angular measures and measuring instruments, as well as accurate measurements should be carried out at normal temperature, deviations from it should not exceed the permissible values ​​​​contained in GOST 8.050-73 ( State system measurements).

The temperature of the part and the measuring instrument at the time of control must be the same, which can be achieved by jointly keeping the part and the measuring instrument under the same conditions (for example, on a cast iron plate). If the air temperature in the production room, the controlled part and the measuring instrument are stabilized and equal to 20 ° C, there is no temperature measurement error for any difference in the temperature coefficients of linear expansion. Thus, to eliminate temperature errors, it is necessary to maintain normal temperature conditions in the premises of measurement laboratories, tool, mechanical and assembly shops.

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Sulfur creates the possibility of the formation of hot or crystallization cracks in the weld metal. Its content in metal and welding materials should always be strictly limited. This is achieved by introducing manganese into the weld pool. A general reduction in sulfur in the metal during welding is possible with highly basic slags. Oxygen-free fluoride fluxes help remove sulfur from metal as a result of the formation of volatile metal fluorides and solid sulfides. Sulfur is easily removed during electroslag welding and metal remelting.

Phosphorus being a harmful impurity in brooms that reduces their ductility. Thus, during the crystallization of steel, phosphorus forms a number of compounds with iron, distinguished by their fragility, the crystals of which can become the nuclei of cold cracks. The phosphorus content in the weld metal during arc welding is practically impossible to reduce, because it is removed in oxidative slags, and welding slags are reduced. The concentration of phosphorus in the weld is significantly reduced during electric slag welding

Oxygen a harmful impurity in the metal during welding, which reduces the plastic properties of the metal, therefore, for all types of welding, the process of deoxidation of the weld metal to an acceptable standard is provided.

When the metal of the weld pool crystallizes, nitrogen forms nitrides of varying degrees of stability. Iron nitrides Au4TbAy2T form brittle needle-shaped crystals, the destruction of which leads to the initiation of cold cracks. Of the industrial metals, only copper does not produce stable nitrides and therefore can be welded in a nitrogen atmosphere.

Hydrogen is a harmful impurity that causes hydrogen embrittlement.

Sources of hydrogen for metal welding:

1) hydrogen absorbed by the metal from the atmosphere of the arc charge (causes the appearance of pores and cracks)

2) Hydrogen, dissolved mainly metal

Protection of the weld pool from exposure environment

To protect the metal of the weld pool from exposure to air, a gas shield is created, which pushes the air away from the molten metal. As a result, the possibility of dissolving oxygen and nitrogen from the air in the liquid metal is reduced.

Shielding gases are formed during the combustion of electrode coating components (in manual arc welding) and fluxes (in submerged arc welding).

When welding in a shielded gas environment, the welding zone is protected from air with argon, helium, carbon dioxide, a mixture of gases, etc.

Protection of the weld pool from environmental influences:

Slag;

Gas;

Gas and slag;

Vacuum (used for welding structures made of titanium, molybdenum, vanadium and other chemically active and refractory metals)

Slag protection during arc welding is formed due to melting
fluxes, electrode coatings and flux cores. The most reliable slag protection is used in submerged arc welding. The formation of droplets during melting of the electrode and their transfer occurs in the volume of a gas bubble filled with metal and flux vapors. Interaction with atmospheric gases is practically eliminated.
Slag protection is less reliable when welding with coated electrodes and flux-cored wire. Drops of electrode metal pass through the open arc gap and interact with the atmosphere. The presence of a slag film on droplets does not always protect them from this interaction. When welding, along with slag protection, gas protection must also be created. In accordance with this, slag-forming and gas-forming components are introduced into electrode coatings and cores of flux-cored wire.

Slag protection.

Slag protection of the weld pool is implemented during automatic submerged arc welding. An electric arc moving along the weld is maintained in a confined space of molten flux, while the gases of the arc atmosphere (vapors of metal and flux components) maintain the pressure inside the flux cavity higher than the pressure of the surrounding atmosphere. As a result of the melting of flux and metal, slag is formed on the surface of the weld.

Slags are complex substances (mainly metal oxides) resulting from the melting of metal and flux. Slags are substances that are liquid at high temperatures and separate the metal surface from the action of air. Slags do not isolate the metal from the surrounding gaseous environment, but only replace the direct interaction of gases with the metal by diffusion.

Based on the type of interaction with the metal bath, slags are divided into oxidizing and reducing ones.

When welding, fused, granular, ceramic fluxes are used.

Fused fluxes are most widely used. According to their composition and purpose, fused fluxes are divided into aluminosilicate and fluoride.

Aluminosilicate fluxes are intended for welding steels. Fluoride for welding titanium and other non-ferrous metals.

Fluxes are divided according to physical properties:

According to the structure of the grains, they are glassy and pumice-like;

By the nature of the change in viscosity into long and short;

According to the nature of interaction with metal, they are divided into active and passive.

The main components of fluxes are: silicon oxide Si O 2, manganese oxide Mn O and calcium fluoride Ca F 2.

In the reduction zone of the weld pool, reactions occur that lead to alloying and, at the same time, oxidation of the metal of the weld pool by flux components:

Fe + (MnO) → + (FeO).

2 Fe + (SiO) → + 2 (FeO)

Parentheses indicate that the substance is in the flux or slag.

Square brackets indicate that the substance is in the weld.

In the same zone, oxidation of steel carbon occurs according to the equation:

+ (C) → + (CO);

and reduction of silicon with manganese:

2 + (SiO 2) → + 2 (MnO).

The metal enriched with silicon and manganese enters the low-temperature welding zone and as the temperature drops, these components begin to deoxidize (reduce) the metal:

+ → + (MnO),

2 → 2 + (SiO 2)

Ceramic fluxes additionally contain ferroalloys and free metals for additional alloying and deoxidation of the metal. The high deoxidizing ability of ceramic fluxes makes it possible to weld metal along the oxidized edges (rust) of the products being welded.

Gas protection

Currently, this welding process has become very widely used in the manufacture of structures of low-carbon, low-alloy, medium-alloy and high-alloy steels with high quality welded joints. In recent years, gas protection methods have been developed using various gas mixtures (Ar + He, Ar + O2, Ar + CO2, CO2 + O2, etc.), which expands the welding, technological and metallurgical capabilities of this welding method.

Of the inert gases, argon is the most widely used, since it is much cheaper than helium and also has better protective properties.

Sometimes argon-arc welding is used for hardened medium- or high-alloy steels.

Austenitic corrosion-resistant and heat-resistant steels (12Х18Н10Т, etc.) are well welded in an argon environment with both consumable and non-consumable electrodes.

Welding in a carbon dioxide environment is carried out using a welding head that moves the welding tool and feeds the electrode wire into the welding zone. With the help of a nozzle, a flow of carbon dioxide is created, washing the arc discharge zone and pushing the air atmosphere out of the welding zone. Welding can be carried out in automatic or mechanized mode.

In mechanized welding, the tool (torch, head) is moved by the welder’s hand, and the electrode wire is fed through a flexible hose using a separately installed mechanism.

The density of carbon dioxide is 1.96 kg/m3, so it displaces air well, whose density is 1.29 kg/m3. Carbon dioxide is supplied in cylinders in liquid form.

For welding, gas is used with a reduced content of harmful impurities - oxygen, nitrogen, carbon monoxide, moisture. The quality of welds depends not only on the purity of CO2, but also on its flow rate and the nature of the outflow from the nozzle under low pressure, ensuring a calm (laminar) nature of the outflow.

When welding in a carbon dioxide stream, the metal absorbs hydrogen in smaller quantities than with other types of welding.

Metal deposited during CO2 jet welding is cleaner in terms of slag inclusions, and therefore its plastic properties are slightly higher than when welding under a submerged arc layer.

Superheated water vapor is the cheapest protective medium, but is not currently used because with this method the metal absorbs large amounts of hydrogen. When hydrogen is absorbed, the metal sharply deteriorates its plastic properties, but they are restored after heat treatment or during “aging”, since diffusion-mobile hydrogen leaves the metal over time.

Gas and slag protection

Gas-slag protection is used for manual arc welding with thick-coated or high-quality electrodes.

Thanks to the development of coatings that melt together with the electrode metal, it was possible to dramatically improve the quality of the deposited metal and the welded joint as a whole, which ensured the use of manual arc welding in all industries and construction, and to develop a wide range of electrodes for welding various types of steels and many alloys.

The composition of the electrode coating is determined by a number of functions that it must perform:

protection of the welding zone from oxygen and nitrogen in the air;

deoxidation of the weld pool metal;

doping it with the necessary components;

arc discharge stabilization

Electrode coatings consist of a number of components, which can be divided into:

ionizing,

slag-forming,

gas-forming,

deoxidizers,

alloying,

Some components can perform several functions at the same time, for example, chalk, which, when decomposed, releases a lot of gas (CO2), calcium oxide forms slag, and calcium vapor has a low ionization potential and stabilizes the arc discharge.

An electric arc discharge occurs when the product touches and burns between the electrode and the weld pool.

The electrode rod melts faster than the coating and a depression (bushing) is formed at the end of the electrode, which directs the flow of gases and drops of metal into the weld pool.

Drops of metal pass through the arc gap, already covered with a thin layer of slag. The drop actively interacts with the slag and gases of the arc gap and, entering the bath, is freed from the slag, which floats up and is pushed back by the arc pressure.

The metal melting at the end of the electrode dissolves the deoxidizers present in the coating. In the crystallizing metal of the bath, intense diffusion occurs between the base metal and the electrode metal, but the concentration can vary significantly

An important indicator of the quality of weld metal is the formation of gases and the composition of non-metallic inclusions in the coating, which affect the strength properties of welded joints.

The weld metal composition is formed from the base metal, electrode wire and coating.

Course work

Subject:“The influence of harmful substances in the air of the working area on the human body”

Introduction

1. Classification of harmful substances and routes of their entry into the human body

1.2 Relationship between cause-and-effect indicators and factors influencing the employee’s health status.

1.3 Dust and its effect on the human body

1.3 Harmful chemical substances

1.5 Impact of meteorological conditions on the human body

2. Methods of protection from exposure to harmful and dangerous air factors

Conclusion

Bibliography

INTRODUCTION

Hazardous physical factors include: moving machines and mechanisms; various lifting and transport devices and transported loads; unprotected moving elements of production equipment (drive and transmission mechanisms, cutting tools, rotating and moving devices, etc.); flying particles of the processed material and tools, electric current, increased temperature of the surfaces of equipment and processed materials, etc.

Physical factors harmful to health are: increased or decreased air temperature in the working area; high humidity and air speed; increased levels of noise, vibration, ultrasound and various radiations - thermal, ionizing, electromagnetic, infrared, etc. Harmful physical factors also include dust and gas contamination in the air of the working area; insufficient lighting of workplaces, passages and passages; increased light brightness and pulsation of light flux.

Chemical hazardous and harmful production factors, according to the nature of their effect on the human body, are divided into the following subgroups: general toxic, irritating, sensitizing (causing allergic diseases), carcinogenic (causing the development of tumors), mutagenic (acting on the germ cells of the body). This group includes numerous vapors and gases: benzene and toluene vapors, carbon monoxide, sulfur dioxide, nitrogen oxides, lead aerosols, etc., toxic dusts formed, for example, during cutting of beryllium, leaded bronzes and brasses and some plastics with harmful fillers. This group includes aggressive liquids (acids, alkalis), which can cause chemical burns to the skin upon contact with them.

Biological hazardous and harmful production factors include microorganisms (bacteria, viruses, etc.) and macroorganisms (plants and animals), the impact of which on workers causes injuries or diseases.

Psychophysiological dangerous and harmful production factors include physical overload (static and dynamic) and neuropsychic overload (mental overstrain, overvoltage of hearing and vision analyzers, etc.).

There is a certain relationship between harmful and dangerous production factors. In many cases, the presence of harmful factors contributes to the manifestation of traumatic factors. For example, excessive humidity in the production area and the presence of conductive dust

(harmful factors) increase the risk of electric shock to a person (hazardous factor).

The levels of exposure of workers to harmful production factors are standardized by maximum permissible levels, the values ​​of which are specified in the relevant standards of the system of occupational safety standards and sanitary and hygienic rules.

The maximum permissible value of a harmful production factor is the maximum value of the value of a harmful production factor, the impact of which, with a daily regulated duration throughout the entire work experience, does not lead to a decrease in performance and illness both during the period of work and to illness in the subsequent period of life, as well as does not provide adverse influence on the health of the offspring.

1 Classification of harmful substances and routes of their entry into the human body

A person may be exposed to hazardous (causing injuries) and harmful (causing diseases) production factors during his work activity. Dangerous and harmful production factors are divided into four groups: physical, chemical, biological and psychophysiological.

Hazardous physical factors include: moving machines and mechanisms; various lifting and transport devices and transported loads; unprotected moving elements of production equipment; flying particles of the processed material and tools, electric current, increased temperature of the surfaces of equipment and processed materials, etc.

Chemical hazardous factors include: general toxic, irritant, sensitizing (causing allergic diseases), carcinogenic (causing the development of tumors), mutagenic (acting on the germ cells of the body). This group includes vapors and gases: benzene and toluene vapors, carbon monoxide, sulfur dioxide, nitrogen oxides, lead aerosols, etc., toxic dust. This also includes aggressive liquids (acids, etc.) that cause burns.

Biological hazards include microorganisms (bacteria, viruses, etc.) and macroorganisms (plants and animals), the impact of which on workers causes injury or illness.

Harmful production factors for human health are increased or decreased air temperature in the working area; high humidity and air speed; increased levels of noise and vibration. Harmful production factors also include dust and gas contamination in the air of the working area; insufficient lighting of workplaces, passages and passages; increased light brightness and pulsation of light flux.

The main sources of air pollution in industrial premises with harmful substances can be raw materials, components and finished products. Diseases that arise from exposure to these substances are called occupational poisonings (intoxications).

According to GOST 12.1.005-88, all harmful substances according to the degree of impact on the human body are divided into the following classes: I - extremely dangerous, 2 - highly dangerous, 3 - moderately dangerous, 4 - low-hazardous. The danger is established depending on the MPC value, the average lethal dose and the zone of acute or chronic action.

There are various classifications of harmful substances, which are based on their effect on the human body.

Generally toxic substances cause poisoning of the entire body. These are carbon monoxide, lead, mercury, arsenic and its compounds, benzene, etc.

Irritating substances cause irritation of the respiratory tract and mucous membranes of the human body. These substances include: chlorine, ammonia, acetone vapor, nitrogen oxides, ozone and a number of other substances.

Sensitizing substances act as allergens, i.e. lead to allergies in humans. Formaldehyde, various nitro compounds, nicotinamide, hexachlorane, etc. have this property.

The impact of carcinogenic substances on the human body leads to the emergence and development of malignant tumors (cancer). Chromium oxides, 3,4-benzpyrene, beryllium and its compounds, asbestos, etc. are carcinogenic.

Mutagenic substances, when exposed to the body, cause changes in hereditary information. These are radioactive substances, manganese, lead, etc.

Among the substances that affect the reproductive function of the human body, we should first of all mention mercury, lead, styrene, manganese, a number of radioactive substances, etc.

1 .2 Relationship between cause-and-effect indicators and factors influencing the employee’s health status.

The influence of production factors is not limited to their role as the cause of occupational or production-related diseases. It has been revealed that people who come into contact with toxic substances often suffer from general diseases (influenza, inflammation of the upper respiratory tract and lungs, disorders of the digestive system), that these diseases are more severe in them, the recovery process is slow, relapses of chronic diseases often occur, in these individuals, postoperative wounds heal slowly and exacerbation of the disease is often recorded. According to medical examinations, people who work with chemicals, regardless of their origin, complain of fatigue, irritability, insomnia, depressed mood, anxiety, lack of appetite, pain in joints and muscles. They do not tolerate both heat and cold well, they are infuriated by the noise and behavior of the environment, although they did not react to this when working with them.

The action of a number of factors in the working environment can lead to damage - disruption of the anatomical integrity or function of the human body, causing uncomfortable or extreme conditions in the work activities of workers.

Specific operating conditions significantly affect the mental and vital functions of the human body. If the influence of factors (taking into account their interaction) in specific conditions of activity is such that the normal implementation of mental and vital functions of the body is ensured, there is no high tension in the compensatory systems of the body and the specified work activity is successfully performed, then such conditions can be defined as favorable, and in the best cases, as optimal. If, due to these factors, high tension occurs in the body’s compensatory systems, then such conditions are defined as unfavorable or uncomfortable, and in the case of a pronounced adverse effect, as extreme. When designing workplaces of complex systems, which are intended, as a rule, to work in special conditions, the maximum tolerable values ​​of factors serve as the basis for calculating means and methods of protection and rescue in emergency situations.

The worker's stay in extreme conditions to perform the necessary activities is assumed when designing objects based on taking into account possible maximum permissible values ​​of factors. In this case, the duration of stay is determined by the characteristics of the harmful effects of factors on a person’s health, the possibilities of using protective equipment and their effectiveness, the complexity of the activity, etc.

However, a person may be associated with the need to carry out activities in extreme conditions not only occasionally (accidents, malfunctions, technological process features), but also constantly, due to the specifics of the profession. Factors of extreme conditions, in addition to the direct negative impact on the human body, can cause increased mental stress, which is associated with a feeling of fear, the experience of danger, etc.

The mechanism of action of the environmental temperature factor on the employee. The influence of the environmental temperature factor on a person is due to the presence of functional thermoregulation systems and the production of thermal energy in the body, the constant heat exchange of the body with the environment, and the targeted use of means of heat exchange regulation by a person in his daily life and activities. The temperature of a person’s internal environment is known to be maintained at approximately 37°C. Daily temperature fluctuations, as a rule, do not exceed 0.5°C. Deviations of human body temperature beyond the limits of below 25 and above 43°C are incompatible with life. At temperatures above 43°C, protein denaturation begins. At temperatures below 25°C, the intensity of metabolic processes, primarily in nerve cells, decreases to a low level. Preservation and further restoration of vital functions at lower body temperatures is possible only with the help of special measures.

Thermal energy in the body is produced mainly (95%) due to the occurrence of complex biochemical reactions, in which the starting materials are substances found in food. In comfortable conditions, in the absence of physical stress, for the normal implementation of vital functions, the human body must produce 1700-1800 kcal per time, or approximately 73 kcal/hour. These are the so-called main energy expenditures of the body of a middle-aged adult. They cannot be lower without disrupting the normal functioning of the body.

The heat generated in the body must be released externally. A person spends most of the thermal energy during work activities. Work in which the body's energy consumption is no more than 2500 kcal is assessed as easy. Working with the body's energy expenditure of close to 5000 kcal at a time is very difficult. For normal heat production, the human body must also be provided with food, the calorie content of which in the daily diet covers the body's expenses by approximately 20%.

Comfort of thermal conditions is assessed by a healthy person depending on microclimate conditions (ambient temperature, intensity of thermal and cold radiation, humidity, speed of movement and air pressure) and intensity of work. In addition, the feeling of thermal comfort significantly depends on climatic conditions, the properties of a person’s clothing and his physiology.

Extreme thermal conditions lead, if protective measures are not taken, to overheating or hypothermia of the body.

With high-intensity thermal effects, pain occurs, general well-being deteriorates, and working ability in general decreases. With thermal damage to the skin - a burn, depending on its severity, various disorders in the activity of vital functional systems of the body can appear, even leading to shock and death.

General prolonged overheating, against the background of an increasing decline in working capacity, leads to difficulties in performing physical and mental labor. At the same time, attention, coordination of confident movements, the process of thinking about the situation and making decisions slow down, and the time of sensorimotor reactions increases.

Painful symptoms of shortness of breath, interruptions in heart function, tinnitus, and dizziness occur. Without taking protective measures, not only a disruption of activity occurs, but also a serious breakdown in health with loss of consciousness and disruption of the functions of the vital systems of the body (the so-called “heat stroke”). A general breakdown in human activity and health also occurs as a result of the so-called “sunstroke,” which occurs when direct sunlight influences the unprotected head of a person. This is due to the ability of infrared solar radiation to penetrate the brain tissue, causing an overheating effect.

The local effect of cold can have a varied effect on the human body, depending on the duration of cooling and the depth of coverage of the tissues of one or another part of the body.

Deep local hypothermia can result in frostbite of parts of the body with tissue damage, including bone.

The general influence of cold, depending on its strength and duration, can cause hypothermia of the body, which first manifests itself in lethargy, then feelings of fatigue, apathy arise, chills and a drowsy state begin. If protective measures are not taken, the person falls into a deep, drug-like sleep, followed by depression of respiratory and cardiac activity and a progressive decrease in core body temperature. As medical practice shows, if the internal body temperature has dropped below 20 (C), then restoration of vital functions is almost impossible.

In case of disasters at sea, hypothermia becomes a direct cause of death for a significant part of the victims. The time during which a person retains consciousness and the ability to move at a water temperature close to 5 (C) rarely exceeds 30 minutes.

Measures to protect against hypothermia in industrial conditions include the creation of protective structures from the wind in open areas, heating of production premises, and designing work clothing with sufficient thermal resistance. Great importance It also has human adaptation to living in low temperatures.

Extreme conditions can occur due to a decrease or significant increase in the content of oxygen and (or) an increase in the content of carbon dioxide in the air

An oxygen content of less than 15% at normal atmospheric pressure cannot ensure life even with maximum activity of the respiratory system. But 100% oxygen content at normal pressure also acts as an extreme factor.

A special group consists of extreme conditions that are obtained due to the action of harmful gas impurities in the air. This may be contamination by components of those substances that are used or arise in the technological process, which are included in the burners and equipment. These are vapors of technical liquids, fuels and lubricants, fuels, battery gases, carbon monoxide, ozone, etc. (that is, combustion and electrification products); ammonia, hydrogen sulfide, etc. (products that are released during biochemical reactions); substances that are released from some synthetic materials that are used in mechanical engineering, construction, etc.

The effect of harmful gas impurities on the human body can lead to severe somatic damage and mental disorders, which depend on the toxic agent. Depression, euphoria, aggressiveness, etc. can dominate. Pain in various organs, severe headaches, and difficulties in perception and thinking often appear.

The pronounced toxic effect of many impurities occurs when their content is very small in the air that a person breathes.

Extreme conditions that are associated with the action of sound, light and other factors. The acoustic environment is an important component in the general environment of existence: a person exists in a world of sounds. The parameters of the acoustic environment can significantly determine the general condition of a person, his ability to work, and the success of his activities, especially if it is necessary to work with sound signals and recreate the language of another person.

Extreme conditions in the acoustic environment are created mainly when the sound pressure approaches the pain threshold, or at such noise levels that complicate the perception of sound signals. The pain threshold for sound pressure is approximately 130 dB. Already at 100 dB the noise will cause general fatigue, reduce productivity and quality of work, and at 110-120 dB it is oppressive. With equal noise levels of 110 dB, direct communication is impossible.

When designing workplaces, it is necessary to proceed from the fact that the unacceptable noise level reaches more than 80 dB and it requires the use of personal protective equipment for workers.

Protective measures include creating soundproofing of production premises, using sound-absorbing materials and personal protective equipment (ear plugs, headphones, etc.).

Extreme conditions that arise due to lighting factors in industrial premises associated with vision functions.

When assessing the influence of light, the light intensity is taken into account first of all, which is measured in candelas (cd); luminous flux (lm); brightness (cd/m2); illumination (lx).

Low lighting makes it difficult to recognize details and reduces the ability to recognize colors. Working in such conditions leads to the development of fatigue and errors. In industrial premises, levels of general illumination should range from 100 to 500 lux and higher (depending on the nature of the work). If a person works with luminous signals of low brightness, then equal illumination should be reduced by 0-2 0 times.

Insufficient ultraviolet radiation will cause CT so-called “light starvation”. Ultraviolet deficiency in adults manifests itself in decreased ability to work and illness; in children it can cause the development of rickets. Prevention of ultraviolet deficiency involves special procedures for ultraviolet irradiation or the introduction of an ultraviolet component into the light flux, which is formed indoors by different lighting sources.

Excess ultraviolet radiation can also lead to severe health and disability problems in workers. In industrial conditions, excessive ultraviolet radiation occurs during electric arc welding, during the operation of mercury-quartz and electric melting furnaces.

Ultraviolet damage to the body can manifest itself as symptoms of general intoxication, or local damage. Symptoms of general intoxication are caused by protein denaturation and excessive formation of active substances. Such metabolic symptoms include increased fatigue with symptoms of agitation and irritability, headache, and poor health.

Symptoms of local damage occur in the skin and in the organ of vision. Excessive ultraviolet irradiation of the skin causes dermatitis, pain, heartburn, and itching. All this can significantly complicate the work or lead to disruption.

When the eyes are affected, intense lacrimation, cutting pain in the eyes, sensation of a foreign body, decreased clarity of vision and photophobia are observed. These phenomena begin no more than 4-5 hours after irradiation, and can lead to a complete disruption of vision.

Under natural conditions, damage to the skin by ultraviolet rays is most often observed when the sun exposure regime is violated. There is a high probability of eye damage in high altitude conditions.

Measures to protect against the influence of ultraviolet radiation are reduced to the use of glasses, protective masks, and the use of work clothes. Development of radar, radio communications, heat treatment of metals, etc.

In some cases, extreme conditions are associated with the influence of radioactive radiation.

1.3 Dust and its effect on the human body

Dust is the most common unfavorable factor in the working environment. Many technological processes and operations in industry, transport, and agriculture are accompanied by the release of dust; large contingents of workers can be exposed to it. This is typical for the mining industry, mechanical engineering, metallurgy, building materials industry, textile industry, agro-industrial complex, etc.

When grinding and polishing surfaces, fine dust is released, and when woodworking, a large amount of sawdust, shavings and wood dust is released, dust is released during welding, gas and plasma cutting of metal, etc. Dust generated during the process abrasive processing consists of (30–40)% materials from the abrasive wheel, but (60–70)% from the material being processed.

Industrial dust not only has a negative effect on the human body, but sometimes also worsens the production environment (visibility, orientation) within the work area and at the same time leads to rapid destruction of the rubbing parts of the machine. In addition, dust can be explosive, produce static electricity, and can also carry germs.

The damaging effect of dust on the human body is largely determined by its physicochemical properties, toxicity, dispersity, i.e. the size of dust particles, as well as the concentration in the air of the working area. The degree of danger of dust also depends on the shape of its particles, their hardness, fibrousness, electrical charge, specific surface area and other properties.

Dust is divided into organic, inorganic and mixed. Organic dust includes dust of animal and plant origin, for example, cotton, wood. Inorganic dust includes mineral dust, for example, cement, quartz, asbestos, and metal. Dust, according to the degree of its grinding (dispersity), is divided into two groups: visible, with a particle size of more than 10 microns, and microscopic, less than 10 microns.

Dust particles are in continuous motion in the medium in which they are suspended. The rate at which dust settles from the air depends on the particle size. Large particles settle relatively quickly under the influence of gravity. Smaller dust particles, overcoming air resistance, fall at lower speeds, and the smallest, highly dispersed particles can move in the air for a long time. The latter circumstance is explained by the large ratio of the total surface of dust grains to their volume and mass.

Dust particles are charged with electricity, the magnitude of their charge is determined by the chemical composition of the substance. Non-metallic dust is charged positively, and metallic dust is negatively charged. Oppositely charged particles are attracted to each other, stick together, coagulate, increase in size and settle faster than other particles. With like charges, particles are repelled and their coagulation becomes more difficult.

The nature and effectiveness of dust depends on its charge. It is known that charged particles stay in the lungs longer than neutral ones, therefore, other things being equal, they are more dangerous to the body. The harmful effects of dust are also related to the solubility, hardness, and shape of dust particles.

According to the harmfulness of dust, they can be inert and aggressive. Inert dust (soot, sugar dust, etc.) consists of substances that do not have a toxic effect on the human body. Aggressive dust (dust of lead, arsenic, etc.) has toxic properties. Working in a dusty environment over time can lead to occupational diseases. Hard dust particles with sharp edges may cause eye injury, etc.

Dust can have fibrogenic, irritating and toxic effects on the human body.

Fibrogenic is the effect of dust in which the growth of connective tissue occurs in the lungs, which leads to disruption of the normal structure and function of the organ.

Dust from certain substances and materials (fiberglass, mica, etc.) has an irritating effect on the upper respiratory tract, mucous membranes of the eyes, and skin.

The toxic effect is caused by dust of toxic substances (lead, chromium, beryllium, etc.), which enters the human body through the lungs.

The harmfulness of dust is due to its ability to cause occupational diseases. The most severe diseases occur when dust gets into the lungs. These types of disease are collectively called pneumoconiosis (in Greek “pneumo” - lungs, “konis” - dust). They have many varieties (metaloconiosis, grain pneumoconiosis, asbestosis, talcosis, cementosis, kaolinosis, etc.).

Under the influence of dust, conjunctivitis, skin lesions, etc. develop.

The harmful effects of dust are aggravated by heavy physical labor, unfavorable meteorological conditions, and certain gases.

The decisive influence on the degree of damage to the human body by harmful chemicals and dust is their concentration in the air of the work area and the duration of exposure. In production environments, workers are often exposed to several harmful substances simultaneously. In this case, it is possible to sum up their effects, the independent harmful effects of each of them, or to reduce this impact due to the mutual neutralization of harmful substances.

The individual characteristics of a person are also of certain importance. It is known that when working in the same conditions, some people get sick more often than others.

Methods for protecting workers from harmful chemical production factors (dust) are also varied.

Enterprises whose production activities involve hazardous substances (dust) must have:

regulatory and technical documents on labor safety in the production, use and storage of hazardous substances have been developed;

complexes of organizational, technical, sanitary, hygienic and medical and biological measures were carried out.

The decisive direction in this work is the use of advanced production technologies that exclude human contact with harmful substances and dust (closed cycles, automation, integrated mechanization, remote control, continuity of production processes, automatic control of processes and operations, etc.).

Of great importance is the development of technological processes that exclude the use of harmful substances, providing for the replacement of harmful substances with less harmful ones. For example, lead white has been replaced by zinc; the most dangerous solvent - benzene - is replaced by less harmful solvents - organofluorine compounds of the methane and ethane group; methyl alcohol in the production of fatty acids is replaced by butyl alcohol; Instead of organic solvents, aqueous cleaning solutions, etc. are used to degrease parts and equipment.

Reducing dust emissions is facilitated by replacing dry methods of processing dust-producing materials with wet ones, producing final products in non-dusting forms, and using hermetic ventilated shelters with built-in sleeves with gloves when packaging and bottling bulk materials.

Reducing the entry of harmful substances (dust) into the air of the working area is facilitated by the correct selection of appropriate equipment and communications that do not allow the release of harmful substances into the air of the working area in quantities exceeding the maximum permissible concentrations during normal operation of the technological process, as well as by sealing the equipment. The use of closed technological cycles, continuous technological processes that exclude depressurization of equipment and communications, conducting processes in a vacuum, etc. also reduce the release of harmful substances into the air of the working area.

A good effect is achieved with a rational layout of industrial sites, buildings and premises, placement of production equipment in special booths with appropriate ventilation and removal of control and monitoring devices into the corridors.

The interior decoration of production premises is also of certain importance, because... A significant role in indoor air pollution has been established for the processes of desorption of chemicals adsorbed by construction and finishing materials.

It is important to use special systems for the capture and utilization of exhaust gases, the recovery of harmful substances and the purification of process emissions from them, the neutralization of production waste, wash water and waste water. Ensuring the cleanliness of the air supplied by forced ventilation to production premises is also achieved by landscaping the territory of the enterprise.

Of great importance in the complex of preventive measures are special training and instruction of service personnel, preliminary and periodic medical examinations of persons who have contact with harmful substances, their observance of personal hygiene rules, as well as therapeutic and preventive nutrition.

The use of personal protective equipment for the respiratory system, eyes, overalls, safety shoes, hand protection, as well as protective pastes and ointments helps protect workers from harmful substances and dust.

1.4 Harmful chemical substances

Vapors, gases, liquids, aerosols, chemical compounds, mixtures upon contact with the human body can cause changes in health or disease. Exposure to harmful substances on humans can be accompanied by poisoning and injury.

Currently, more than 7 million chemical substances and compounds are known, of which about 60 thousand are used in modern production; most of them are synthesized by humans and are not found in nature.

Chemically hazardous and harmful production factors include:

· toxic and poisonous gases;

· toxic and poisonous liquids.

Chemically negative factors in the production environment include:

Gas contamination of the working area, the sources of which are leaks of toxic and harmful gases from leaking equipment and containers, fumes from open containers during spills, emissions of harmful gases during depressurization of equipment, release of harmful gases during processing of materials, spray painting, drying of painted surfaces, galvanic treatment baths and etc.

Dust in the working area, the sources of which are the processing of materials with abrasive tools (sharpening, grinding, etc.), welding, gas and plasma cutting, processing of bulk materials, areas of knocking out and cleaning castings, processing of fragile materials, soldering with lead solders, soldering of beryllium with solders containing beryllium, areas of crushing and breaking of materials, pneumatic transport of bulk materials, etc.

Contact of poisons on the skin and mucous membranes, sources of which are filling containers, spraying liquids, spraying, painting, electroplating, etching.

The entry of poisons into the human gastrointestinal tract is caused by errors in the use of toxic liquids.

The study of the potential danger of the harmful effects of chemicals on living organisms is the subject of chemical and biological science - toxicology. Toxicology studies the mechanisms of the toxic action of chemicals, diagnosis, prevention and treatment of poisoning. Harmful substance, i.e. a chemical element or compound that causes disease in an organism is a central concept in toxicology. The field of toxicology that studies the effects of harmful substances on humans is called industrial toxicology.

In industry, harmful substances are found in gaseous, liquid and solid states. They are able to penetrate the human body through the respiratory, digestive or skin organs. The harmful effects of chemical substances are determined both by the properties of the substance itself (chemical structure, physicochemical properties, the amount entering the body - dose or concentration - a combination of harmful substances present in the body), and by the characteristics of the human body (individual sensitivity to a chemical substance, general condition health, age, working conditions).

Based on the degree of effect on the human body, harmful substances are divided into four hazard classes:

Extremely hazardous: MPC 10.0 mg/m3.

This classification is based on the average lethal concentration (MLC) and maximum permissible concentration (MPC).

Maximum permissible concentrations of harmful substances are concentrations that, when working daily for eight hours or another duration, but not more than 41 hours per week, during the entire working period, cannot cause illness or deviations in the state of health detected by modern research methods in the process of work or in long-term life spans of present and subsequent generations.

Sulfur dioxide (SO2) is a colorless gas with a pungent odor and a sweetish taste, does not burn and does not support combustion. It is found during the roasting and smelting of sulfur ores, in copper smelters, and in the production of sulfuric acid; used as a bleaching agent in the textile industry and a preservative in the food industry.

It dissolves well in water, alcohol, acetic and sulfuric acids, chloroform and ether.

Sulfur dioxide irritates the respiratory tract and causes necrosis of the cornea of ​​the eyes. Irritation is accompanied by a dry cough, burning and pain in the throat and chest, lacrimation, and with stronger exposure, vomiting, shortness of breath, and loss of consciousness. Death can occur from suffocation and sudden stoppage of blood circulation in the lungs.

First aid: fresh air, provide oxygen inhalation, rinse eyes, nose, rinse with 2% soda solution; heat on the neck area, mustard plasters, warm milk with Borjomi, soda, butter and honey.

Protection: industrial gas masks of brands "B" and "M", civil, children's and insulating gas masks.

Organic sulfur is converted into SO2 and H3S under the influence of anaerobic and aerobic heterotrophic microorganisms. SO2 released into the atmosphere during the combustion of mineral resources, especially coal, is the most dangerous component of industrial emissions, SO2 is formed through the interaction of geochemical and meteorological processes (erosion, sedimentation, leaching, rain , absorption) with biological processes. SO4 2- - similar to nitrate and phosphate, is reduced by autotrophs and included in proteins (part of a number of amino acids). The ecosystem does not require as much sulfur as nitrogen and phosphorus, therefore sulfur is not a factor limiting plant growth and animals. In sediments, iron and phosphorus sulfides are converted from insoluble forms to soluble forms. One cycle is regulated by another. Despite the fact that both oxidative and reduction processes occur in the sulfur cycle, some of the sulfur is removed from the cycle; reduction does not compensate for oxidation. This is aggravated by the conscious activity of man, who converts natural sulfides into sulfates, for example, in the production of sulfuric acid, smelting metals from sulfur ores. Sulfur compounds that enter the atmosphere technogenically from land almost entirely return to the earth's surface and have a detrimental effect on natural complexes.

As a result of the combustion of diesel fuel, a number of combustion products are formed. Their composition depends on the engine design, fuel supply system, power and workload. In first place are water (H2O) and harmless carbon dioxide (CO2). In addition, several more substances are formed in fairly low concentrations:

Carbon monoxide (CO);

Unburned hydrocarbons (CH);

Nitrogen oxides (NOx);

Sulfur dioxide (SO2) and sulfuric acid (H3SO4);

Solid soot particles.

If the engine is not overheated, during its operation many unreacted hydrocarbons are formed due to lack of oxygen. They appear as white or bluish smoke, and aldehydes (partially oxidized hydrocarbons) cause an unpleasant odor.

The predominant route of entry of harmful substances into the human body under industrial conditions is through inhaled air.

The toxicity of harmful substances is determined primarily by the concentration in the air of the working area. Therefore, maximum permissible values ​​are established for the content of harmful substances in the air of the working area - maximum permissible concentrations (MPC). MPC values ​​are determined in regulatory documents- state standards (GOST 12.1.005-88) and state regulations (GN 2.2.5.686-98) for almost all substances known and used in industry. MPCs are measured in mg/m3. The maximum permissible level of SO2 is 10 mg/m3. The condition for the safety of harmful substances is the ratio: Ed. SF and MPC mg/m3 were measured.

When there are several harmful substances of unidirectional action in the work area, the following ratio must be observed:

Based on the nature of their action, they are divided into:

Generally toxic - causing poisoning of the whole body (CO - carbon monoxide, benzene, mercury, lead, cyanides, arsenides - arsenic compounds);

Irritants (chlorine, ammonia, sulfur dioxide, acetone);

Sensitizing – allergens (formaldehyde, solvents and varnishes based on nitro compounds);

Carcinogenic – causing cancer (nickel, chromium compounds, asbestos, amines, etc.);

Mutagenic – affecting reproductive function (styrene, magnesium, mercury).

Control of harmful substances.

Laboratory control methods:

They are used when it is necessary to track extremely dangerous, highly hazardous substances. Pros: super accurate.

Disadvantages: complexity, duration, requires highly trained personnel.

Examples: spectral analysis, photometry, colorimetry, chromatography.

The methods are as follows: sampling is carried out (automatically or manually) in the area where the harmful substance is released, followed by qualitative and quantitative identification.

2. Methods of protection from exposure to harmful and dangerous air factors

Harmful and dangerous factors in production arise when there is a deviation from the standardized microclimate parameters, as well as when the permissible values ​​of dust and air pollution are exceeded. Long-term exposure to dust and gas levels exceeding permissible values ​​can lead to occupational diseases, and significant excess of permissible values ​​leads to acute poisoning.

Maximum permissible concentration of harmful substances in the air of a working area is a concentration that during daily (except for weekends) work is within

8 hours or another duration, but not more than 40 hours a week throughout the entire working experience, cannot cause diseases or health conditions detected by modern research methods during work or in the long-term life of the present and subsequent generations.

If the air of the work area simultaneously contains several harmful substances of unidirectional action, the sum of the ratios of their actual concentration in the indoor air to the maximum permissible concentration of each of them should not exceed one.

Gas concentrations are determined by a variety of standard methods based on chemical, diffusion and electrical principles.

In cases where the concentration of harmful impurities exceeds permissible standards, it is necessary to carry out special measures to clean the air in the work area. If due to the choice of technological processes it is not possible to ensure compliance with permissible standards, then various ventilation and air conditioning systems are used.

Ventilation and air conditioning in enterprises creates an air environment that meets occupational health standards. There are natural and artificial ventilation.

Natural ventilation provides air exchange in rooms as a result of the action of wind and heat pressure resulting from different air densities outside and inside the premises. Natural ventilation is divided into organized and unorganized.

Unorganized ventilation occurs through leaks in structures (windows, doors, wall pores). It is caused by the difference in air temperatures indoors and outdoors, as well as air movement due to wind.

Organized natural ventilation is carried out by aeration or deflectors. With natural ventilation, air circulation occurs through ventilation ducts located in the walls, lanterns and special air ducts. Aeration provides for ductless air exchange through windows, vents, transoms, etc., deflector ventilation - through channels and air ducts with special nozzles.

Artificial ventilation (mechanical) is achieved through the operation of fans or ejectors. It can be supply, exhaust and supply and exhaust.

With supply ventilation, air is supplied by a ventilation unit, and air is removed by lights or deflectors. It is used, as a rule, in rooms where there is excess heat and low concentrations of harmful substances. Exhaust ventilation pumps air out of rooms using a ventilation unit. It is used for ventilation of rooms with a high concentration of harmful substances in the air, as well as moisture and heat. The supply and exhaust ventilation system is carried out using separate ventilation systems, which must provide the same amount of air supplied and removed from the premises. In rooms where harmful substances are constantly released, exhaust ventilation should exceed supply ventilation by approximately 20%. In these cases, exhaust is carried out from places where harmful substances accumulate, and clean air is supplied to workplaces.

In cases where ventilation means are ineffective or during work where ventilation units cannot be used, and the concentration of harmful substances exceeds the maximum permissible concentration, personal respiratory protection equipment is used:

Conclusion

The task of protection from negative factors is to eliminate or reduce to acceptable limits the entry of harmful substances into the human body and contact with harmful or dangerous objects.

Therefore, the task of protection is to remove substances from the zone of their formation; minimizing their release into the air; cleaning polluted air from them before entering the air of the work area, enterprise territory, or the biosphere.

In order to choose means and methods of protection against negative factors, you need to know their main characteristics and effect on humans. It is almost impossible to completely eliminate the impact of negative factors on humans, both from a technical and economic point of view. Sometimes this is not advisable, since even in the natural environment a person is exposed to them - the air contains harmful substances emitted by natural sources.

In the work area, it is necessary to ensure such levels of negative factors that do not cause deterioration in human health or diseases. To avoid irreversible changes in the human body, it is necessary to limit the impact of negative chemical factors to maximum permissible concentrations.

Health is not only the absence of disease, but also physical, mental and social well-being. Health is a capital given to us not only by nature from birth, but also by the conditions in which we live and work.

Bibliography

1 Ecology and life safety: textbook. manual for universities / D.A. Krivoshein, L.A. Ant, N.N. Roeva and others; Ed. L.A. Ant. – M.: UNITY-DANA, 2000. – 447 p.

2 T.A. Hwang, P.A. Hwang. Fundamentals of ecology. Series "Textbooks and teaching aids". Rostov n/d: “Phoenix”, 2001. – 256 p.

3.Life safety. Tutorial. Ivanov et al., MGIU, 2001

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