Metalworking Industry

METALWORKING INDUSTRY A. Hot metal processing includes casting (see Foundry Production), forging, and heat treatment. Forging (blacksmithing). Workpieces are heated in a forge (for small pieces) or in large coal, oil, or gas furnaces to a temperature of 750-950°. Small pieces are removed from the forge by the blacksmith with tongs, while large pieces are extracted from the furnace and transported by special cranes to a steam hammer or press. The heated workpiece is then subjected to manual forging (by the blacksmith and striker) or mechanical forging under a hammer or press. The hammer's operation is controlled by a special machine operator. Either so-called free forging (without dies) or die forging (in mass production) is used. Additionally, metal is processed using hydraulic and steam-hydraulic presses, as well as forging machines. Forging operations include welding, in which the ends of two heated white-hot parts are placed together and joined under hammer blows ('welded'), with the heating temperature being higher than for forging. Heat treatment changes the properties of metals under the influence of heat without the participation of external mechanical forces; it changes the internal structure of the metal without changing the shape of the object being processed. One of the main operations of heat treatment is steel hardening, which consists of heating the products in hardening furnaces to a temperature of 750° to 1,200° and then rapid cooling in water, oil, and other baths. Products are heated in special furnaces. Heating is also used in baths with molten lead or certain salts (for example, barium chloride) and in electric furnaces. Cooling is done by immersing the products in liquid or blowing with a stream of cold air. Liquids are arranged according to their hardening ability as follows: mercury, acidified or salty water, ordinary river water, water with lime impurities, lard, kerosene, petroleum, vegetable oil (linseed, rape), stream of cold air. After hardening, products have high hardness but are also very brittle; both hardness and brittleness are reduced by tempering, however brittleness is reduced much more than hardness. Tempering is achieved by reheating the products to 250-450°. Annealing aims to reduce the hardness of materials resulting from hardening or mechanical processing, as well as to eliminate harmful tensions that have occurred in the material after mechanical and thermal processing. Annealing consists of heating to 750-1,000° and slow cooling. Cementation is the enrichment of the iron surface with carbon (case hardening), which aims to give iron products considerable surface hardness (case-hardened layer) in combination with the toughness and non-brittleness of the rest of the mass (soft iron). B. Cold mechanical processing consists of removing chips from the workpiece on various machines: lathes, vertical lathes, boring machines, milling machines, planing machines, slotting machines, drilling machines, and various special machines. Workers operating these machines are engaged in setting up the workpiece on them, securing and setting up the tool, adjusting the machine, monitoring the lubrication and cooling of the cutting tool during operation, and monitoring the movement (feed) of the tool necessary to obtain a certain chip depth. With automatic feed, the worker usually monitors the operation of several machines. To obtain parts with high precision, products after mechanical processing go to grinding (turning and polishing), which consists of removing thin layers of metal (in the form of dust) with emery carborundum discs or cloth wheels lubricated with polishing pastes, etc. C. Cold manual processing and assembly. Products from the mechanical shop go to cold metal processing departments by hand to locksmiths and to assembly shops. Locksmithing is the cold processing of metal primarily by hand. With the help of a series of fairly simple tools, the locksmith removes a larger or smaller layer of metal from a metal product using so-called finishing operations, which include scraping, filing, polishing, etc. Of all metal finishing operations, filing occupies the main place, being the most typical for a locksmith. In many cases, it takes up to 25-50% of the time of the entire work. Assembly operations include the preliminary assembly of various parts processed in hot and cold shops into 'units' by fitting, lapping, balancing, and connecting individual parts with screws, by welding, riveting, and soldering, and then the subsequent assembly of 'units' into the final complete product. In newly built mass production factories - automotive, tractor - assembly is carried out on a conveyor in the mechanical assembly shop. To fasten various parts together, welding (see Autogenous Welding, Electric Welding) or riveting is used. There are the following types of riveting: manual, pneumatic, hydraulic. In pneumatic chiseling, the pneumatic chisel makes 1,000 or more blows per minute. Despite the introduction of an increasing number of machines that perform various work on sheets and produce the bulk of the products, manual processing still plays a significant role in the work of a tinsmith with the help of a number of fairly primitive tools. The process of soldering is characteristic of tinsmithing. With soft (low-melting) solders, soldering is done with a heated soldering iron, with hard refractory solders - without a soldering iron, by direct heating of the soldering point. Before final assembly, individual metal parts or parts of them, in order to give them special qualities (greater strength, hardness) or better protection against corrosion, are coated with other metals (tin, chromium, nickel, etc.) by using electrochemical (galvanic) processes. After assembly, the final process is carried out - painting and varnishing of products with preliminary priming and puttying (see Painters). Somewhat separate are boiler production, in which methods of both hot and cold processing are used, and wire-drawing production. In boiler work, hot processing to give the sheet its final shape is done by a team of blacksmith-benders, and then by roller-sheet straighteners. Instead of riveting, welding is increasingly being used (see Autogenous Welding, Electric Welding). The wire used in wire-drawing production comes from rolling mills, where by rolling (see Metallurgy) in the hot state, iron wire is reduced to 4-5 mm, and copper wire to 8 mm. The reduction of wire in diameter (to 0.5-0.3-0.1 mm) and the increase in its length occur in the process of cold drawing or wire drawing through a drawing board in wire-drawing shops. Instead of the previously used immersion of wire in a special composition, which contained a large amount of sulfuric acid, soap powder can be recommended as a more hygienic (and economical) means for lubrication. Occupational hazards in M. p. mainly consist of high air temperature, sharp temperature fluctuations, the effect of radiant heat, excessive physical stress, dust and gas polluting the air, noise and vibrations, as well as the special danger of accidents. In the metalworking industry in the field of radiant energy (see) and high temperature, production processes of forge workers, workers in hot stamping, pressing, boiler-benders, near annealing furnaces, hardeners, heaters, etc. proceed. Furnaces, forges, and hot products are sources of heat transferred to the surrounding sphere (by conduction, convection, and radiation). The air temperature and radiation stress at the workplace vary depending on the size of the heat sources, the insulating properties of the furnace walls, the furnace temperature at which the product is heated, the location of the worker, and the degree of opening of the shutters. Radiant heat, measured by a Kalitin actinometer, ranges from 1 to 10 small calories per 1 cm² of skin per minute, depending on the measurement location, furnace temperature, and working moment of the furnace. The air temperature, measured by a thermometer protected from the effects of radiant energy, reaches approximately 25-35° (directly at the forge-35°, at the anvil-30°, at steam hammers-28-30°). Temperature fluctuations when measured with a psychrometer shielded from the effects of radiant heat at different heights from the floor and in different sides relative to the blacksmith are not large and generally do not exceed 3-4°. At the workplaces of crane operators, the temperature is 5-10° higher.

The harmful influence of high temperature in the forging and thermal shops of the metalworking industry, especially in old shops without heating, is intensified by uneven temperature inside the shop: 1) fluctuations in air temperature within the work area when a worker moves from the furnace or forge to the work station and back (approximately 35° near the furnace, 25° near the steam hammer). 2) More sharp fluctuations in temperature are connected with leaving the work area when moving from the furnace to the anvil, and from there to the rest area (approximately 35° near the furnace, and 7-8° in the middle of the shop). The air temperature in areas of the shop located 4-5 meters from the furnace, when there is no other source of heat formation, depends almost entirely on the outside air temperature and exceeds it by only a few degrees. The heat loss from the worker's body in hot shops, measured by the kata-thermometer in milli-calories, shows (with Hill's established optimal value for cooling the dry kata for metalworkers at 9.24 milli-calories) in summer time at a distance of 1½ meters from the furnace-H dry = 2.0-4.5 milli-calories, H humid = 23.0-26.0. The worker's subjective sensations are significantly worsened by the fact that work conducted in hot shops with insufficient mechanization is mostly heavy physical labor. Prolonged work in shops with high temperature in the presence of radiant energy causes overheating of the body, accompanied by a series of pathological changes. - Measures-see Radiant energy. Recently in hot shops, to ease the body's struggle with the influence of high temperature and radiant energy, air blowing of workers with colder (20-28°) air streams directed directly at the worker at their workplace is being used. A rational drinking regimen (salted water) is being introduced. In new buildings (single-story) of hot shops, provision is made for a roof that also serves the purpose of natural ventilation (aeration). Heavy physical strain when loading and unloading products from furnaces, at hammers, is eliminated by the widespread introduction of mechanization (cranes, hoists, lifting devices, etc.). Dust. Removal of metal from semi-finished products during their processing or during final finishing of products is associated with the formation of chips and is accompanied by the release of dust. Chips, fragments, and the resulting large heavy dust, settling immediately on the machine, pose only a danger of injury. Only dust particles smaller than 5-10 μ can penetrate into the pulmonary alveoli. The dust is mainly metallic. Processing of metal products on artificial grinding stones is one of the particularly harmful operations, as it is accompanied by the release into the air of the workroom of a significant amount of mixed silicate-metallic dust. The size of the products being processed, their material and quality (cast iron, steel, copper, hardened and unhardened), the duration of dusty operations, dry or wet method of processing, the quality of materials from which the stones are made, the size, strength, and graininess of the wheel, and mainly the power and type of dust extraction installation affect the amount of dust released into the air of the room, which varies within rather wide limits, from 0.5 to 100 mg in 1 m³ of air during deep grinding approaching to rough grinding, with average figures of 10.0 mg during dry processing and 4-5.0 mg during wet processing; during more precise grinding operations the average dust content is 2.0-4.0 mg (Pick and Taits). Polishing of metal products is also accompanied by the release of dust, but the dust content is less-2-10 mg. Dust during dry processing contains on average 60% metallic (from 35% to 80%) and 40% mineral (from 65% to 20%), during wet processing on average 60% metallic (from 35% to 80%) and 40% mineral dust (from 35% to 75%). The number of dust particles when collecting dust with the Owens instrument is less during wet processing of products compared to the dry method (dry processing gives 600-5,000 dust particles, wet processing gives 300-2,000 dust particles in 1 cm³). Measures to reduce dust content come down to installing local exhaust ventilation from grinding and polishing machines. A number of machines currently produced by our factories are equipped with dust extraction devices. A significant amount of dust is formed when grinding products with portable grinders. The dust content during wet grinding files on natural stones gives 16-20 mg in 1 m³. The wet method of processing metal on grinding and polishing wheels has a certain sanitary-hygienic advantage over the dry method of grinding and polishing metal. However, when processing large metal products, the air dust content even with the wet method on artificial stones reaches rather significant amounts, and therefore wet grinding of metal is not a completely harmless operation, as is commonly believed. On dusting in sandblasting apparatuses see Sandblasting apparatus. Gases and vapors. The most characteristic types of poisoning for the metalworking industry are the following: acute poisoning with carbon monoxide, sulfur dioxide, and chronic poisoning with lead. Carbon monoxide in the air of shops is either due to products of incomplete combustion in the thermal shop, etc., or due to generator gas containing CO as its main component. The presence of illuminating gas in the air is connected with its leakage during work on gas burners. Products of incomplete combustion are released from open and portable forges, from coke furnaces for pipe soldering, with insufficient draft from hardening furnaces, from the presence in the shop of forges with ignited charcoal, from oil furnaces, stoves, etc. Gas penetrates into the air of the shop from furnaces through poorly closing dampers, as well as when opening them for loading and unloading billets. The largest amount of gases enters during the reheating of cold furnaces and forges. Another source is the combustion of coal dust from contact of hot billets with the earth floor of the room, where billets remain until cooled. The cause of sulfur dioxide formation is the sulfur contained in coal in amounts depending on the type of coal (from 1% in Donets to 8% and more in Moscow region). Ventilation significantly reduces the presence of harmful gases in the air. Permissible concentrations (if it is not possible to completely prevent the entry of gases into the air): CO-not more than 0.02-0.03 mg, sulfur dioxide-0.02 mg per 1 liter of air. In newly built factories in the USSR, built using natural air exchange (aeration), only negligible concentrations of CO were found in samples. Measures to reduce gas concentrations: replacement of forges with furnaces, correctness of combustion in heating installations, ensuring normal draft from forges by installing hoods with natural exhaust ventilation, mandatory closing of furnace doors, aeration ensuring in forges with great heat a system of natural ventilation of shops (heat and gas removal by air exhaust through the roof skylight) of the 'Bouallo' type, wide trapezoidal, etc., air intake through windows arranged at various heights in the walls. Great importance for preventing CO poisoning is the implementation of mechanized fuel loading into furnaces, which eliminates the worker's presence in hazardous zones, and the installation of electric furnaces instead of open forges and furnaces for heating rivets. To detect illuminating gas in the room, and with it carbon monoxide, perfumization has been proposed (adding strongly odorous substances at the beginning of the gas pipeline, which makes it possible to notice gas leakage). Lead. Workers involved in lead soldering, turners who come into contact with lead during processing operations, workers when filing files manually or mechanically when using lead shims, when hardening tools in lead baths heated to 900°, tinsmiths when loading products into lead baths, are exposed to the influence of lead vapors or lead dust. During most of the main work in the manufacture of shot, workers are constantly in contact either with lead dust (cold work) or with lead vapors. A certain danger is represented by the soldering process when using soft solders containing ½ and ⅔ lead. Inhalation of lead compounds is dangerous for tinsmiths when tinning with tin mixed with lead. Measures to combat lead poisoning-see Lead. Arsine (see) is encountered in pickling departments and zinc-rolling mills when soldering with hydrogen. In thermal shops where tempering is done in salt and oil baths, vapors and gases of liquids present in the baths (barium chloride, cyanide salts) may be found in the air. Mercury is used in precision mechanical engineering factories in the production of tools. From chromium-plating baths, chromium anhydride is released, which can cause skin lesions, lesions of the upper respiratory tract (see Chromium). Measures to combat chromium poisoning: installation of rational edge ventilation at baths and covering the surface of the bath (electrolyte) with 'liquid pillows' of lower specific gravity, which, without interfering with the course of the chemical process in the bath, prevent particles of the released chromium from entering the work area.

The Leningrad State Institute of Applied Chemistry proposed using a fraction of purified kerosine with a boiling point from 200° to 270° for covering the electrolyte. Tests conducted by the Leningrad Institute of Labor Protection confirmed the presence of only traces of chromium in chromium-plating rooms (0.00 mg per 1 m³). In many workshops of the M. p., noise is observed from the operation of various machines, hammers, cranes, and chains during manual metal processing; the most characteristic 'noisy' workshops are the boiler and nail-making workshops. In the boiler workshop, due to riveting and chiseling, and in the nail-making workshop, due to impact nail-making machines, a sharp and extremely unpleasant noise is produced, which deafens everyone entering the workshop for the first time, and significant vibration is noted. M e r o p- r i y a t i y a: replacement of riveting with welding, and in extreme cases hydraulic riveting, which is completely noiseless (see below - noise). Individual protective earplugs are used to reduce the harmful effects of noise on the hearing of workers. Lubricating and cooling oils used in the operation of semi-automatic and automatic machines for the purpose of cooling the cutting tool, reducing friction during cutting, and removing chips formed during metal cutting, known under the names 'spindle oil' and 'frezol', cause skin diseases (rash elements) in workers operating these machines. Works by Leshchinskaya, Tait, Zenin and others have established that skin lesions are the result of the interaction of a number of factors of production and individual character. The first include the long-term circulation of oil without purification and its contamination with small particles of metal and a significant amount of microbes. The second include wearing irrational special clothing, insufficient washing of hands and the entire body. Measures to combat skin morbidity consist of enclosing machines in places where oils splash with shields, removing metal particles and bacteria from oils, and introducing a number of personal hygiene measures for workers in the form of rational, vulcanized special clothing, the provision of showers, washbasins, and clean rags for wiping hands soiled with oil. Severe physical stress, sometimes associated with uncomfortable body position, is noted in fitters-assemblers, laborers in assembly shops, drillers, benders, and stampers. The work of a fitter, as well as a marker and a filer, during manual marking is accompanied by strong pressure from the tools used on the palmar surface of the hand and fingers, especially during filing, scraping, chiseling, etc. The skin of the palmar surface usually calluses; compression of deeper parts (fascia, muscles, nerves) is possible. Extremely great physical stress (of the abdominal muscles) is characteristic of the non-mechanized work of stampers of utensils. Morbidity in the M. p. The most common diseases among workers in the M. p., directly related to production, are: disorders of heart activity (muscle strain at high t°), diseases of the digestive organs (high t°, excessive drinking of water), diseases of the respiratory system and especially the lungs under the influence of dust and gases, 'cold' diseases and in particular rheumatism, frequent accidents. In machine building, the disability due to illness of workers, calculated per 100 insured, decreased over 5 years (1929-1933) by 29^J/₀ in terms of cases and by 21% in terms of days. On average per worker in the M. p. in the USSR per year, the number of cases of temporary disability in 1933 was 1.31 with a loss of 10.91 days due to illness. The average duration of one illness was 8.3 days. Accidents. One of the main professional hazards of workers employed in the M. p. is the danger of injury. Injuries are observed from dangerous parts of machines, engines, and belt drives, as well as from flying particles of metal, especially during fine metal processing. Assembly work is associated with collapses and falls of both the parts being assembled and the workers themselves - with severe bruises, crushes, etc. Collapses, falls, and crushes are especially frequent among fitters, assemblers, and laborers. The danger of eye injury is particularly great for riveters, chasers, miners, hammerers, and grinders. Burns from HCl and molten metal are characteristic for tinsmiths and solderers. The number of injuries by profession (1932) varies greatly: among blacksmiths per 1,000 'full' workers - 466, among hammerers - 343, among turners - 287, among fitters - 246, among drillers - 351, among planers - 315, among millers - 308, among boiler-assemblers - 310, among boiler-riveters - 461, among coppersmiths - 229, among polishers - 548; in other occupations in production - 139. Eye injuries in the M. p. (in relation to the total number of injuries in a given profession) occupy an exceptionally large place: among turners - 69%, among blacksmiths - 44%, among boiler-makers - 57%, among fitters - 69%, among drillers and chippers - 60%, among grinders - 59%, among millers - 45%, among planers - 33%. The number of lost days due to eye injuries accounts for 12.5% of all lost days due to accidents. Legislation on labor protection in the metalworking industry in the USSR. Legislation on labor protection in the M. p. is collected in the 'Handbook on Safety Techniques and Industrial Sanitation in the Machine Building Industry' by S. A. Tait and I. G. Bekker. The socio-legal protection of labor in the M. p. is regulated by mandatory decrees of the USSR NKT on the reduced working day (of 10/XI 1928, №643, in Izv. NKT, №51-52, for 1928), on additional leave (of 30/IV 1929, № 156, in Izv. NKT, № 20-21, for 1929), on the issuance of milk (of 20/VI 1923, № 271/776), on the issuance of soap (of 20/IX 1923, № 80), on the restriction of the employment of women (of 10/IV 1932, № 119), adolescents (of 13/X 1932, № 186). Standards for special clothing for the M. p. were established by decree of the USSR NKT №8 of 23/I 1933. Particularly important mandatory decrees were published in Izvestia of the USSR NKT on the rules for the installation and maintenance of industrial enterprises (of 29/I 1926, №21/309), rules on safety measures in forging production (of 27/11 1926, № 50/323), in cold metal cutting production (of 20/11 1926, № 40/317), in boiler and copper boiler production (of 14/I 1926, № 8/304), during pneumatic painting (of 22/VI 1930, № 215).