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INCREASE OF WEAR RESISTANCE OF DETAILS OF CARS BY TECHNOLOGICAL METHODS
The basic operational properties of details of cars - wear resistance, durability, corrosion stability are appreciably defined by a condition of their blanket defined by manufacturing techniques. In modern manufacture appointment and technological maintenance of parametres of a condition of surfaces of details is insufficiently proved, that results or in overestimate of requirements and rise in price of cars, or to their understating and reliability decrease.
There is enough considerable quantity of various technological methods of improvement of quality of surfaces of details. Most widespread of them are, galvanic and chemical methods of drawing of coverings, наплавка, a dusting, ionic implantation, laser processing. Providing increase of operational properties and as, improving a decorative kind of products, these methods at the same time are ecologically unsafe, polluting environment and representing complexity in recycling of a waste.
Methods of improvement of quality of details of cars
The big possibilities in technological quality management of a surface of details of cars have such progressive methods of processing, as versions of otdelochno-strengthening processing in which basis superficial plastic deformation (ППД) is put in pawn. Demanded parametres of quality of a surface and practically all major operational properties of details of cars can be provided by the hardening processes by their methods of superficial plastic deformation as much as possible showing potential possibilities of a material. Application of plastic deformation of a material allows to lower материалоемкость and to raise reliability and durability of products. Depending on appointment of a method and plastic deformations all these methods can be divided into three classes: 1) otdelochno-strengthening processing by superficial plastic deformation (накатывание, обкатывание, раскатывание, выглаживание, виброобработка, dynamic hardening, the electromechanical and combined processing of various surfaces of details of cars); 2) form-building processing by plastic deformation (накатывание teeths, шлицев, carvings, shaped surfaces); 3) otdelochno-strengthening processing by plastic deformation (калибрование external and internal surfaces of rotation and дорнование). Выглаживание make the tool which working element is diamond индентор, sliding on a processed surface. This method it is possible to process all kinds of surfaces from flat to the shaped.
Накатывание, раскатывание and обкатывание carry out the special tool. At pressure of a working element upon a processed surface there is its local plastic deformation in a contact place, presence various rotary and progress allows to process various surfaces 9 flat, cylindrical, shaped.
The combined processing
The special place among methods of improvement of quality of details of cars is occupied with the combined processing combining лезвийную and otdelochno-strengthening processing. Now for processing of external and internal surfaces of rotation enough wide circulation has received joint точение and обкатывание, carried out with application of the combined tools combining cutting and deforming elements. Advantages of joint processing by cutting and ППД various surfaces the combined tools in comparison with separate processing it is conclusive are proved in the modern literature [6]. Such method allows not only to raise quality of a surface, but also gives possibility to increase productivity, to lower labour input of processing that is essential advantage of the combined processing before other ways of improvement of quality of a blanket. However now in the spravochno-standard documentation data on a rational scope of the combined otdelochno-strengthening processing insufficiently full are presented. Hence, use of this method demands more detailed research and a substantiation of quality of the processed surface depending on properties of a processed material, modes of cutting, operational properties of processed details. Thus, all methods of processing by superficial plastic de-formation have ample opportunities in management in parametres of a condition of a blanket of details of cars, and consequently also their operational properties. Experience of modern mechanical engineering testifies, that at process combination лезвийной processings with ППД possibility along with increase of operational properties of produced production simultaneously is given to raise accuracy and productivity of technological process of processing as a whole.
The review of existing researches
Operational properties of details and their connections (wear resistance, rigidity and durability, tightness of connections, durability of plantings) define the basic indicator of quality of cars - reliability. Now there is a big number of mathematical dependences for definition of operational properties of details of cars and their connections described and works by Kragelskogo I.V. [11,12], Mihina N.M. [13]. However these dependences, as a rule, have empirical character, and the theoretical equations do not consider a blanket condition in all its geometrical and physicomechanical aspects. In Suslov's works And. Г [7, 34, 35], Bezjazychnogo V. F [33] results universal theoretical dependences for definition of operational properties of details with the account of parametres of a condition of a blanket (a roughness, a sinuosity, a macrodeviation and physicomechanical properties). Wear resistance - the operational property defining ability of blankets of details to resist to destruction at a friction-sliding, a friction-kachenii, and also at the micromovings caused by influence of vibrations. As a result of deterioration of details of cars the EFFICIENCY goes down, accuracy is lost, durability decreases, dynamic loadings which are a consequence of increase in backlashes in interfaces increase, noise raises at work. Researches [5, 7, 11-14, 30, 33-35] on influence on wear resistances of parametres of a condition and physicomechanical properties of a blanket testify to possibility of management of wear resistance of details of cars by a choice of rational methods of processing. Various researches such operational properties as fatigue durability [1, 2, 12, 15, 30, 33] are carried out. Fatigue durability is an ability of details of cars to resist to destruction during a certain time interval at action on them of sign-variable loadings. As a result of researches it is established, that destruction of details of cars for weariness of metal begins on their surface, and, means, is defined sheroho-vatostju and physicomechanical characteristics of a blanket. Besides, fatigue durability of details of cars depends not only on roughness size, but also in большей degrees from наклепа and residual pressure of a blanket. Tightness of connections defines their ability to keep gas or liquid leak. As a result of the spent researches [1, 2, 7, 30, 33-35] it was found out, that tightness of connections along with consolidation geometry, physicomechanical properties of its material and factors of external cart-action also depends on parametres of a roughness, a sinuosity, makroot-klonenija and degrees of hardening of contacting surfaces. Contact rigidity defines ability of blankets of the details which are in contact, to resist to action of the forces, aspiring them to deform. Contact rigidity makes considerable impact on toch-nost works of mechanisms, on accuracy of installation of details on machine tools, in prispo-soblenijah, on accuracy of processing and assemblage of details, in summary - on quality of machine-building products. As have shown researches [1, 2, 12,], rigidity also influences a game-taktnuju quality of a surface of interfaced details. Properties. The considerable quantity of researches concerning laws of formation of a blanket of details of cars is at present made. The analysis of the numerous factors influencing parametres of a blanket of details of cars is made, interrelations between these parametres are established at various methods of processing, ways of quality management of a surface [7, 8, 14] are revealed. The majority of researches of laws of formation of a blanket is devoted parametres of a roughness of a surface [7, 8]. Especially actual there is a necessity of the decision of this question for the combined variants of processing as the given problem is insufficiently studied in the existing literature, available works on technological maintenance of operational properties of details of cars at the combined processing have the isolated character, some do not meet modern requirements. All it causes necessity of more accurate substantiation of maintenance of demanded operational indicators of details of cars at a stage of konstruktorsko-technological preparation of manufacture with wide application for these purposes of the COMPUTER.
INFLUENCE OF PARAMETERS OF THE CONDITION OF THE BLANKET
DETAILS OF CARS ON OPERATIONAL PROPERTIES
WEAR RESISTANCE RESEARCH
Technological maintenance of operational properties of details of cars inseparably linked with parametres of a condition of a blanket of the details defining their operational properties. The major operational characteristics of details of cars - wear resistance, durability, tightness appreciably depends on a condition of their blanket defined in parametres of machining at manufacturing. For the successful decision of a problem of improvement of quality of cars it is necessary to consider theoretical aspects of influence of parametres of a condition of a blanket of details on their operational properties. Wear resistance is the major operational characteristic of details of cars. For the majority of cars a principal cause of refusals is achievement of maximum permissible level of deterioration of their most responsible details in this connection increase of wear resistance of details of cars is rather actual problem. Wear resistance of details of cars appreciably depends on a condition of their blanket defined in parametres of machining at manufacturing. The known equation [7] for calculation of intensity of wear process in normal deterioration at constant working conditions and physicomechanical properties of a material depending on blanket parametres can be presented:
Where tm - relative basic length of a profile at level of an average line; Ra - an average arithmetic deviation of a profile; Sm - an average step of roughnesses; Wz - sinuosity parametre; Hmax - the maximum macrodeviation. To - the constant factor depending on properties of a material of a detail and its conditions нагружения.
SOME KINDS OF TECHNOLOGY OF THERMAL AND HIMIKO-THERMAL PROCESSING OF THE STEEL
Kinds of thermal processing. Transformations into steels
Thermal processing name the processes connected with heating and cooling of metal, being in a firm condition, for the purpose of change of structure and properties without change of its chemical compound. The founder of the theory of processes of thermal processing is D.K.Chernov who has found out critical points of a steel. Thermal processing is characterised by key parametres: having heated up to certain temperature, endurance at this temperature, speed of heating and speed of cooling (drawing 1).
Drawing 1 Schedule of thermal processing of a steel.
Depending on temperature modes thermal processing is subdivided into following kinds: отжиг, normalisation, training, holiday, himiko-thermal processing (ХТО), thermomechanical processing (ТМО).
In звисимости from propensity to growth аустенитного grains at steel heating happen small - or coarse-grained. Fine-grained steels in the range of temperatures of heating 950... 1000°С almost do not change grain size. At coarse-grained steels grain growth begins at once after transition through a critical point. Necessity of strict observance of technological modes of the thermal processing, making solving impact on quality of products from here follows.
Possibility of hardening of steels by thermal processing is caused by presence аллотропических transformations into a firm condition. Cooling аустенит with various speeds and causing thereby various degree of overcooling, it is possible to receive disintegration products аустенита, sharply differing on a structure and properties.
2. Kinds отжига. Steel normalisation
Отжиг consists in heating of a steel above critical temperatures, endurance at the given temperature and slow cooling (usually together with the furnace). Depending on the requirements shown to properties of a steel, distinguish following kinds отжига: диффузионный (homogenization), full, incomplete (for zaevtek-toidnyh steels the Purpose отжига is called сфероидизацией) - to eliminate internal pressure to crush grain to give steels plasticity before the subsequent processing and to result structure in an equilibrium condition.
At isothermal отжиге a constructional steel heat up to temperature on 30... 50°С above a point on 50... 100°С, then the endurance and slow cooling in the fused salt to temperature a little below a point (680 follows. 700°С). At this temperature a steel subject to isothermal endurance at which there is a full transformation аустенита in перлит, with the subsequent cooling on air.
As steel normalisation is called having heated up доэвтектоидной steels above point Ac3 эвтектоидной there were points the Expert, заэвтектоидной there were points Ас1 on 30... 50°С, endurance and the subsequent cooling on air (see рисr 3).
After normalisation carbonaceous steels have the same structure, as after отжига, but перлит will be more disperse (the plate ферритоцементитной is more thin a mix).
The normalisation purpose доэвтектоидных and эвтектоидных steels the same, as full отжига. However after normalisation hardness and durability of a steel will be above, than at отжиге. Normalisation is applied to elimination of coarse-grained structure, alignment of mechanical properties. In заэвтектоидных steels normalisation eliminates цементитную a grid.
Normalisation-more a cheap and simple kind of thermal processing, than отжиг.
After отжига the carbonaceous steel (0,4 %) has following mechanical properties: 
в=550 МПа; d =20 %, y === 52 %, and after normalisation в=600 МПа;
d =22 %; y == 40 %,
On machine-building factories carbonaceous steels are delivered in a condition causing rather low hardness to provide good обрабатываемость with cutting. Constructional steels are delivered in отожженном or the normalised condition; tool steels - after sferoidizi-rujushchego отжига.
3 Training and steel holiday
After machining the product, as a rule, is exposed to strengthening thermal processing.
The most widespread kind of strengthening thermal processing of the carbonaceous steels, containing carbon more than 0,3 %, are training with the subsequent holiday.
Speed of heating and time of endurance of details depend on the sizes, weight of details, their configuration, a chemical compound of a material of details, on type of heating furnaces and heating environments.
At training as the cooling environment use water, sometimes with additives of salts, alkalis more often. To increase in cooling ability apply also the oils, the fused salts and metals. For training essential value has speed of cooling in the range of temperatures where аустенит less all is steady (650... 550°С). This interval of temperatures at training it is necessary to pass quickly. The great value has speed of cooling and in the range of temperatures 300... 200°С when in many steels there is a formation мартенсита (see drawing 2). In this area of temperatures slow cooling, in order to avoid occurrence of pressure and hardening cracks is required.
There are next ways of training. Training consists in one cooler that нагретую under training immerse a detail in the hardening environment (water, oil etc.) in which it is before full cooling. Apply to simple details from carbonaceous and the alloyed steels.
At training in two environments (faltering training) a detail at first immerse in быстроохлаждающую environment (water), and then quickly transfer to other environment (oil, saltpeter or on air) where it is cooled to a room temperature. Such training apply usually to processing of the tool from высоколегированной steels.
At step training нагретая the detail is cooled in the environment at temperature 230... 250°С (for example, in the hot oil, the fused salt, etc.), and then after small endurance it is cooled on air.
Isothermal training is made the same as also step, but endurance in the hardening environment more long. At such endurance there is an isothermal disintegration аустенита to formation бейнита (высокодисперсная a mix of ferrite and iron carbide).
The basic defects of training concern: underheating, an overheat, пережог, обезуглероживание, коробление, cracks, etc.
If steel heating was below a critical point speak about training with underheating. This defect исправимый for what a steel subject отжигу, and then spend training according to technological recommendations.
The overheat takes place when a steel heat up to the temperature much more exceeding the critical. Having overheated also it is possible to correct отжигом with the subsequent training.
Пережог steels can take place at a considerable overheat of a steel before training. Thus the steel becomes very fragile. This defect incorrigible (marriage).
Обезуглероживание and surface oxidation occurs at heating in ardent or electric furnaces without controllable atmospheres. To avoid these defects, it is necessary having heated up to conduct in special furnaces with protective (controllable) atmosphere, neutral in relation to a steel.
Steel training is accompanied by increase in its volume that leads to considerable internal pressure which are the reason of formation of cracks and коробления. Cracks are incorrigible defect, and коробления it is possible to eliminate the subsequent рихтовкой or editing. For the reasons specified above the tempered products and the tool subject to holiday.
Holiday name heating of a steel to temperature below point Д.1 with endurance at the given temperature and the subsequent cooling with the set speed (usually cool on air). The holiday purpose - reduction of hardening pressure, decrease in hardness and reception of necessary mechanical properties. The basic transformation at holiday - disintegration мартенсита, i.e. Allocation of carbon from пересыщенного a firm solution in the form of the smallest кристалликов iron carbide.
Depending on heating temperature distinguish three kinds of holiday.
Low holiday is made at 120... 150°С (holiday on released мартенсит). It apply after training of tools, цементованных and цианированных products, and also after superficial training. At low holiday residual hardening pressure decrease, hardness practically does not decrease.
Average holiday (holiday on троостит occurs at heating to temperatures 350... 450°С. Hardness Thus decreases. Average holiday is recommended for springs and springs.
High holiday (holiday on sorbite) is made at temperature 500... 650°С. Apply in mechanical engineering to products from a constructional steel for the purpose of maintenance of sufficient durability, viscosity and plasticity. The combination of training to high holiday on sorbite is called as improvement. This operation apply for среднеуглеродистых steels (0,35... 0,6 %С).
Gas-flame training consists in heating of a surface of steel products ацетиленокислородным a flame which temperature makes 2400... 3150 °С; thus the product surface quickly heats up to training temperature, and the core has not time to heat up. Fast cooling provides blanket training. A thickness of the tempered layer 2... 4 mm, hardness reach Н1^С50... 56.
Induction heating by currents of high frequency (ТВЧ) the most widespread productive and progressive method of superficial hardening. Its advantage is possibility of automation of process, absence of burning out of carbon and other elements, and also oxidations of a surface of a product. The essence of a way consists that under the influence of electromotive power (ЭДС) in metal there are electric vortical currents (Foucault's currents) which heat up metal to the necessary temperature.
Hardness of a blanket at heating ТВЧ a little above, than the hardness received at usual training. Training with use ТВЧ apply to steels with the maintenance of carbon more than 0,4 % to receive the set hardness.
Recently also superficial processing with use of heating by the laser is applied.
Under закаливаемостью understand ability began to get high hardness after training. Закаливаемость depends on the carbon maintenance in a steel: the more carbon, the above hardness.
Прокаливаемость - ability began to be tempered on certain depth. Прокаливаемость depends on a chemical compound of a steel, the sizes of a detail and cooling conditions. The more stability overcooled аустенита, the is more Прокаливаемость. The characteristic прокаливаемости is critical diameter, i.e. The maximum diameter cylindrical прутка which is calcinated completely in the cooling environment. So, for example, for carbonaceous steels at training in water critical diameter makes 10...... 20мм. The alloyed steels at training in oil depending on degree легирования can be calcinated in section to 250... 300 mm.
4. Thermomechanical processing of a steel
Thermomechanical processing (ТМО) is rather new method of the processing, allowing to raise mechanical properties of metal materials. TMO-IT set of operations of plastic deformation and the thermal processing, combined in one technological process which includes heating, plastic deformation and cooling. Thermomechanical influence leads to reception of a structural condition which provides increase of mechanical properties.
The optimum combination of plastic deformation and phase transformations leads to increase of density and more correct arrangement of imperfections of a crystal lattice of metal.
Distinguish two principal views ТМО: high-temperature thermomechanical processing (ВТМО) (drawing 7,) and низкотемпературную thermomechanical processing (НТМО) (drawing 7,).
At ВТМО deformation is made at temperature above temperature рекристаллизации (thus the steel has аустенитную structure). Degree of deformation 20...... 30 %. In avoidance рекристаллизации after deformation training (1150°С) with the subsequent низкотемпературным holiday (100 is immediately made...... 200°С).
НТМО it is applied only to the alloyed steels possessing considerable stability overcooled аустенита. At НТМО deformation is made below temperature рекристаллизации (400... 600°С), degree of deformation 75... 95 %. Training is made right after by deformations, and then follows низкотемпературный holiday (Ю0... 200°С).
Lacks НТМО are, first, necessity of use of the powerful equipment for deformation, secondly, became after НТМО have low resistibility to fragile destruction.
If at usual thermal processing the steel has time resistance at a stretching 2000... 2200 МПа after ТМО it reaches 2200... 3000 МПа, thus plasticity increases twice (lengthening with 3... 4 % raise to 6... 8 %).
5 Himiko-thermal processing of a steel
As himiko-thermal processing (ХТО) is called process of superficial saturation became various elements for the purpose of giving to it of corresponding properties. It differs from other kinds of thermal processing by that at this processing except structural changes there are changes of structure and a structure of a surface at the expense of diffusion in it of elements in an atomic condition from an environment at heats. A main objective - hardening of a surface of details, increase of hardness, wear resistance, durability lips-lostnoj, etc. And increase of firmness against influence of excited environments. Cementation, nitriding concern processes of himiko-thermal processing, цианирование, алитирование, chromium plating, silitsiro-vanie, борирование, etc.
ХТО it is characterised by three simultaneously proceeding processes. The first process - диссоциация - consists in disintegration of molecules and formation diffundi-rujushchego an element in an atomic condition.
The second process named absorption, represents interaction of atoms диффундирующего an element with a surface of a product and their penetration into an iron lattice. The third process - diffusion consists in penetration of atoms of the sated element into depth of metal.
Let's consider short some kinds of himiko-thermal processing.
As cementation is called process of saturation of a surface of a product by carbon. The purpose of cementation-giving of a surface of hardness at preservation of a soft core. Usually cementations subject details from низкоуглеродистой to a steel containing no more of 0,25 % With (a steel of marks 10, 15, 20, And 12, 15Х, 25ХГМ, etc.), working in the conditions of variable shock loadings and exposed to deterioration, for example teeths of automobile cogwheels, gear wheels, plugs, piston fingers etc. Temperature cementation 900... 970°С. A thickness of tsementovan th layer from 0,1 to 3... 4 mm.
Nitriding name saturation process became nitrogen. The nitriding purpose - to give surfaces high hardness, wear resistance, stability against corrosion and fatigue durability. Process consists in influence on an ammonia steel (gas nitriding) at temperature 500... 600°С. Образовашийся the free nitrogen which is in an atomic condition, influences a steel and forms with the elements entering into its structure (Сг, Ре, А1, etc.), the various nitrides possessing high hardness (to НRС 70). The nitrated layer keeps the hardness to 400... 600°С while hardness цементированного a layer with мартенситной structure remains only to 200... 250°С. A thickness of the nitrated layer 0,25... 0,75 mm,
Цианированием name saturation of a surface of products simultaneously carbon and nitrogen in the fused cyanic salts at temperature 820... 950°С.
Distinguish низкотемпературное and high-temperature цианирование. At низкотемпературном tsianirova-nii details heat up to 820... 860 °С in the fused salts containing МаСМ, during 0,5. 1,5 ч. Thus receive a layer in the thickness 150... 350 microns. Then make training directly from temperature цианирования with the subsequent низкотемпературным holiday (180...... 200°С). Hardness after thermal processing makes Н^С 58... 62. To such processing usually subject details from среднеуглеродистых steels and tools from fast-cutting steels.
For reception of thicker layer (500...2000 microns) apply high-temperature цианирование at 930...... 950°С in due course endurances 1,5... 6 ч. After such processing of a detail cool on air, make training and низкотемпературный holiday. A lack of this process is toxicity of cyanic salts. It causes to spend work in a special premise with observance of security measures.
Nitrocementation represents process of saturation of a blanket simultaneously carbon and nitrogen in the gas environment of nitrogen of 40 %, hydrogen of 40 % and оксида carbon of 20 % at temperature 850... 870 °С during 4... 10 ч. Appointment-increase of wear resistance, an endurance limit at a bend, hardness and corrosion firmness. After training and low holiday (160... 180°С) hardness of a blanket makes НRС 58... 60 and a thickness of a layer 0,2... 0,8 mm; they depend on temperature and endurance time.
Nitrocementation widely use in automobile and autotractor manufacture. Nitrocementation has certain advantages in comparison with gas cementation - lower temperature of process, decrease in deformation and коробления, etc.
Борирование consists in saturation of a blanket of products from low - and среднеуглеродистых steels 20, 40, 40Х, ЗОХГС and others a pine forest at heating in боросодержащей to environment. Борирование apply to increase of hardness, wear resistance, corrosion firmness and окалиностойкости hard loaded details (the oil equipment, stamps, compression moulds, etc.). Process is spent at temperature 850... 950°С during 2... 6 ч. The Blanket consists from боридов, a thickness of a layer 0,1... 0,2 mm, its hardness WELL 1800... 2000.
Диффузионная metallization - process диффузионного saturation of a surface of steel details by metals for the purpose of giving of their surface of heat resistance, corrosion firmness, hardness, wear resistance, etc. Диффузионная metallization can be carried out in firm, liquid and gaseous environments. For firm Диффузионной metallizations use ferroalloys with addition of chloride ammonia (0,5... 5 %). Liquid диффузионную metallization spend, immersing details in the fused metal (А1, 2п, etc.). Gas диффузионную metallization spend in gas · environments - chlorides of various metals. Superficial saturation is spent at temperatures 900... 1200 °С. Recently apply also multicomponent saturation of a surface of a steel (two and more components).
Let's consider short most often applied processes диффузионной metallizations.
Silitsirovanie-termodiffuzionnoe saturation of a surface of a product by silicon for the purpose of increase of corrosion firmness, heat resistance, wear resistance and кислотостойкости materials in aggressive liquid and gas environments. Силицирование apply, for example, to nests of valves, loose leaves of bearings, rotors of water pumps, shirts of cylinders, pipeline armature, pipes of ship mechanisms, etc.
Алитирование - process of saturation of a blanket became aluminium for increase окалиностойкости (heat resistance), corrosion and erosive firmness of a steel, чугунов and copper alloys. Алитирование carry out in порошкообразных mixes, in baths with the fused aluminium, in the gas environment and dispersion of liquid aluminium. The greatest distribution has received алитирование in powders, with saturation from a gas phase. On a surface the dense film оксида aluminium (А120з), protecting from oxidation алитированные products is formed. Алитирование make at 950...... 1050°С during 3... 12 ч. The thickness of a layer averages 0,2... 0,8 mm.
In particular, алитируют covers of thermocouples, details разливочных ladles, valves and other products working at heats. It is necessary to notice, that at use vacuum алитирования it is possible to receive coverings of high cleanliness.
Chromium plating - process of saturation of a blanket became chrome, corrosion firmness, hardness and wear resistance thus raises. The greatest application has received chromium plating in порошкообразных mixes феррохрома or chrome, chloride ammonium and оксида aluminium. Chromium plating is made at 1000...... 1050°С during 6... 12 ч. A thickness of a received layer no more than 0,2 mm. Chromeplate usually низкоуглеродистые steels: the layer structure consists of a firm solution of chrome in and - gland and contains 30... 40 % of chrome. At chromium plating sredne - and высокоуглеродистой became a received layer consists of chrome carbides. To chromium plating subject valves of compressors, matrixes of stamps for cold disembarkation, etc.
Цинкование it is most widely used in the technician. On a share of zinc coverings it is necessary about 60 % from the general surface of metal coverings. Zinc coverings well protect iron and its alloys from corrosion on air and in water. A thickness of a zinc covering 6... 36 microns depend on conditions of operation of products. The zinced sheets and strips are applied in housing construction (a roof, drainpipes), to manufacturing of capacities, in automobile and a railway transportation, etc.
Quality assurance of thermal and himiko-thermal processing includes the postoperative control of all details in the course of processing on hardness, structure and depth of the processed layer. The special attention at thermal processing should be turned on defects of details (a crack, коробление etc.). The control of small cracks in the tempered details make a method magnetic or рентгенодефектоскопии. In particular, this method is used for the control of springs, spring sheets, details of management of motor vehicles, etc. Some kinds of marriage цементованных the details, for example an insufficient thickness of a layer or the lowered maintenance of carbon on a surface, can be corrected by additional himiko-thermal processing on a special mode.
At thermal and himiko-thermal processing it is necessary to adhere to instructions on a labour safety strictly. The special attention should be turned on service of the furnaces working on gas and electric heating. At service of electric furnaces the basic attention needs to be turned on performance of rules of an electrosecurity. Workplaces should be provided by instructions on technics.
