Surface hardening tvch. HDTV hardening equipment

Induction heating occurs as a result of placing the workpiece near a conductor of alternating electric current, which is called an inductor. When passing through the current inductor high frequency(TVCh) an electromagnetic field is created and, if a metal product is located in this field, then an electromotive force is excited in it, which causes the passage of an alternating current of the same frequency as the inductor current through the product.

Thus, a thermal effect is induced, which causes the product to heat up. The thermal power P, released in the heated part, will be equal to:

where K is a coefficient depending on the configuration of the product and the size of the gap formed between the surfaces of the product and the inductor; Iin - current strength; f is the current frequency (Hz); r - specific electrical resistance (Ohm cm); m is the magnetic permeability (G/E) of steel.

The process of induction heating is significantly affected by a physical phenomenon called the surface (skin) effect: the current is induced mainly in the surface layers, and at high frequencies the current density in the core of the part is low. The depth of the heated layer is estimated by the formula:

Increasing the frequency of the current allows you to concentrate a significant amount of power in a small volume of the heated part. Due to this, high-speed (up to 500 C/sec) heating is realized.

Parameters of induction heating

Induction heating is characterized by three parameters: power density, heating duration and current frequency. Specific power is the power converted into heat per 1 cm2 of the surface of the heated metal (kW / cm2). The heating rate of the product depends on the value of the specific power: the larger it is, the faster the heating is carried out.

The duration of heating determines the total amount of thermal energy transferred and, accordingly, the temperature reached. It is also important to take into account the frequency of the current, since the depth of the hardened layer depends on it. The frequency of the current and the depth of the heated layer are in opposite dependence (the second formula). The higher the frequency, the smaller the heated volume of metal. By choosing the value of the specific power, the duration of heating and the current frequency, it is possible to change the final parameters of induction heating in a wide range - the hardness and depth of the hardened layer during hardening or the heated volume during heating for stamping.

In practice, the controlled heating parameters are the electrical parameters of the current generator (power, current, voltage) and the duration of heating. With the help of pyrometers, the heating temperature of the metal can also be recorded. But more often there is no need for constant temperature control, since the optimal heating mode is selected, which ensures a constant quality of hardening or heating of HDTV. The optimal hardening mode is selected by changing the electrical parameters. In this way, several parts are hardened. Further, the parts are subjected to laboratory analysis with fixation of hardness, microstructure, distribution of the hardened layer in depth and plane. With subheating, residual ferrite is observed in the structure of hypoeutectoid steels; overheating produces coarse-acicular martensite. Signs of marriage when heating HDTV are the same as when classical technologies heat treatment.

During surface hardening of high-frequency current, heating is carried out to a higher temperature than during conventional bulk hardening. This is due to two reasons. Firstly, at a very high heating rate, the temperatures of the critical points at which pearlite transforms into austenite increase, and secondly, this transformation must be completed in a very short heating and holding time.

Despite the fact that heating during high-frequency hardening is carried out to a higher temperature than during normal hardening, overheating of the metal does not occur. This is due to the fact that the grain in the steel simply does not have time to grow in a very short period of time. At the same time, it should also be noted that, compared with volumetric hardening, the hardness after high-frequency hardening is higher by about 2-3 HRC units. This provides higher wear resistance and surface hardness of the part.

Advantages of hardening with high frequency currents

high process performance
ease of adjustment of the thickness of the hardened layer
minimal warpage
almost complete absence of scale
full automation of the entire process
the possibility of placing the hardening plant in the flow of machining.

Most often, high-frequency surface hardening is applied to parts made of carbon steel with a content of 0.4-0.5% C. These steels after hardening have a surface hardness of HRC 55-60. With a higher carbon content, there is a risk of cracking due to sudden cooling. Along with carbon, low-alloy chromium, chromium-nickel, chromium-silicon and other steels are also used.

Equipment for performing induction hardening (HDTV)

Induction hardening requires special technological equipment, which includes three main components: a power source - a high-frequency current generator, an inductor and a device for moving parts in a machine.

A high-frequency current generator is an electrical machine that differs in the physical principles of generating an electric current in them.

Electronic devices that work on the principle of vacuum tubes that convert direct current into alternating current of increased frequency - tube generators.
Electromachine devices operating on the principle of inducing electric current in a conductor, moving in a magnetic field, converting a three-phase current of industrial frequency into alternating current of increased frequency - machine generators.
Semiconductor devices operating on the principle of thyristor devices that convert direct current into alternating current of increased frequency - thyristor converters (static generators).

Generators of all types differ in frequency and power of the generated current

Types of generators Power, kW Frequency, kHz Efficiency

Lamp 10 - 160 70 - 400 0.5 - 0.7

Machine 50 - 2500 2.5 - 10 0.7 - 0.8

Thyristor 160 - 800 1 - 4 0.90 - 0.95

Surface hardening of small parts (needles, contacts, spring tips) is carried out using microinduction generators. The frequency generated by them reaches 50 MHz, the heating time for hardening is 0.01-0.001 s.

HDTV hardening methods

According to the performance of heating, induction continuous-sequential hardening and simultaneous hardening are distinguished.

Continuous sequential hardening used for long parts of constant section (shafts, axles, flat surfaces of long products). The heated part moves in the inductor. The section of the part, located at a certain moment in the zone of influence of the inductor, is heated to the hardening temperature. At the exit from the inductor, the section enters the sprayer cooling zone. The disadvantage of this heating method is the low productivity of the process. To increase the thickness of the glued layer, it is necessary to increase the duration of heating by reducing the speed of movement of the part in the inductor. Simultaneous hardening involves simultaneous heating of the entire hardened surface.

Self-tempering effect after hardening

After heating is completed, the surface is cooled with a shower or water flow directly in the inductor or in a separate cooling device. Such cooling allows hardening of any configuration. Dosing cooling and changing its duration, it is possible to realize the effect of self-tempering in steel. This effect consists in the removal of heat accumulated during heating in the core of the part to the surface. In other words, when the surface layer has cooled and undergone a martensitic transformation, a certain amount of thermal energy is still stored in the subsurface layer, the temperature of which can reach the low tempering temperature. After cooling stops, this energy will be transferred to the surface due to the temperature difference. Thus, there is no need for additional steel tempering operations.

Design and manufacture of inductors for HDTV hardening

The inductor is made of copper tubes through which water is passed during the heating process. This prevents overheating and burnout of the inductors during operation. Inductors are also made that are compatible with a hardening device - a sprayer: on the inner surface of such inductors there are holes through which coolant enters the heated part.

For uniform heating, it is necessary to manufacture the inductor in such a way that the distance from the inductor to all points on the surface of the product is the same. Usually this distance is 1.5-3 mm. When hardening a product of a simple shape, this condition is easily met. For uniform hardening, the part must be moved and (or) rotated in the inductor. This is achieved by using special devices - centers or hardening tables.

The development of the design of the inductor involves, first of all, the definition of its shape. At the same time, they are repelled from the shape and dimensions of the hardened product and the method of hardening. In addition, in the manufacture of inductors, the nature of the movement of the part relative to the inductor is taken into account. The economy and heating performance are also taken into account.

Cooling of parts can be used in three versions: water spraying, water flow, immersion of the part in a quenching medium. Shower cooling can be carried out both in sprayer inductors and in special hardening chambers. Flow cooling allows you to create an overpressure of the order of 1 atm, which contributes to a more uniform cooling of the part. To ensure intensive and uniform cooling, it is necessary that the water moves over the cooled surface at a speed of 5-30 m/sec.

The strength of elements in especially critical steel structures largely depends on the state of the nodes. The surface of the parts plays an important role. To give it the necessary hardness, resistance or viscosity, heat treatment operations are carried out. Strengthen the surface of parts by various methods. One of them is hardening with high-frequency currents, that is, HDTV. It belongs to the most common and very productive method during large-scale production of various structural elements.

Such heat treatment is applied both to the whole parts and to their individual sections. In this case, the goal is to achieve certain levels of strength, thereby increasing the life and performance.

The technology is used to strengthen the units of technological equipment and transport, as well as to harden various tools.

Essence of technology

HDTV hardening is an improvement in the strength characteristics of a part due to the ability of an electric current (with a variable amplitude) to penetrate the surface of the part, exposing it to heat. The depth of penetration due to the magnetic field can be different. Simultaneously with surface heating and hardening, the core of the node may not be heated at all or only slightly increase its temperature. The surface layer of the workpiece forms the necessary thickness, sufficient for the passage of electric current. This layer represents the depth of penetration of the electric current.

Experiments have proven that an increase in the frequency of the current contributes to a decrease in the penetration depth. This fact opens up opportunities for regulation and production of parts with a minimum hardened layer.

HDTV heat treatment is carried out in special installations - generators, multipliers, frequency converters, allowing adjustment in the required range. In addition to the frequency characteristics, the final hardening is influenced by the dimensions and shape of the part, the material of manufacture and the inductor used.

The following pattern was also revealed - the smaller the product and the simpler its shape, the better the hardening process goes. This also reduces the overall energy consumption of the installation.

copper inductor. On the inner surface there are often additional holes designed to supply water during cooling. In this case, the process is accompanied by primary heating and subsequent cooling without current supply. Inductor configurations are different. The selected device directly depends on the workpiece being processed. Some devices do not have holes. In such a situation, the part is cooled in a special hardening tank.

The main requirement for the process of HD hardening is to maintain a constant gap between the inductor and the workpiece. While maintaining the specified interval, the quality of hardening becomes the highest.

Strengthening can be done in one of the ways:

Continuous-series: the part is stationary, and the inductor moves along its axis.
Simultaneous: the product is moving, and the inductor is vice versa.
Sequential: Processing the various parts one by one.

Features of the induction installation

Installation for HDTV hardening is a high-frequency generator together with an inductor. The workpiece is located both in the inductor itself and next to it. It is a coil on which a copper tube is wound.

Alternating electric current when passing through the inductor creates an electromagnetic field that penetrates the workpiece. It provokes the development of eddy currents (Foucault currents), which pass into the structure of the part and increase its temperature.

The main feature of the technology– penetration of eddy current into the surface structure of the metal.

Increasing the frequency opens up the possibility of concentrating heat in a small area of the part. This increases the rate of temperature rise and can reach up to 100 - 200 degrees / sec. The degree of hardness increases to 4 units, which is excluded during bulk hardening.

Induction heating - characteristics

The degree of induction heating depends on three parameters - specific power, heating time, electric current frequency. Power determines the time spent on heating the part. Accordingly, with a larger value of time, less time is spent.

The heating time is characterized by the total amount of heat expended and the developed temperature. Frequency, as mentioned above, determines the depth of penetration of currents and the formed hardenable layer. These characteristics are inversely related. As the frequency increases, the volumetric mass of the heated metal decreases.

It is these 3 parameters that make it possible to regulate the degree of hardness and layer depth, as well as the volume of heating, in a wide range.

Practice shows that the characteristics of the generator set (voltage, power and current values), as well as the heating time, are controlled. The degree of heating of the part can be controlled using a pyrometer. However, in general, continuous temperature control is not required, as there are optimal HDTV heating modes that ensure stable quality. The appropriate mode is selected taking into account the changed electrical characteristics.

After hardening, the product is sent to the laboratory for analysis. The hardness, structure, depth and plane of the distributed hardened layer are studied.

Surface hardening HDTV accompanied by a lot of heat compared to the conventional process. This is explained as follows. First of all, a high rate of temperature increase contributes to an increase in critical points. Secondly, it is necessary to short term to ensure the completion of the transformation of pearlite into austenite.

High-frequency hardening, in comparison with the conventional process, is accompanied by higher heating. However, the metal does not overheat. This is explained by the fact that the granular elements in the steel structure do not have time to grow in a minimum time. In addition, bulk hardening has a lower strength of up to 2-3 units. After HFC hardening, the part has greater wear resistance and hardness.

How is the temperature chosen?

Compliance with technology must be accompanied by the correct choice of temperature range. Basically, everything will depend on the metal being processed.

Steel is classified into several types:

Hypoeutectoid - carbon content up to 0.8%;
Hypereutectoid - more than 0.8%.

Hypoeutectoid steel is heated to a value slightly higher than necessary to convert pearlite and ferrite to austenite. Range from 800 to 850 degrees. After that, the detail high speed cools down. After rapid cooling, austenite transforms into martensite, which has high hardness and strength. With a short holding time, fine-grained austenite is obtained, as well as finely acicular martensite. Steel gets high hardness and little brittleness.

Hypereutectoid steel heats up less. Range from 750 to 800 degrees. In this case, incomplete hardening is performed. This is explained by the fact that such a temperature makes it possible to preserve in the structure a certain volume of cementite, which has a higher hardness in comparison with martensite. Upon rapid cooling, austenite transforms into martensite. Cementite is preserved by small inclusions. The zone also retains fully dissolved carbon, which has turned into solid carbide.

Advantages of technology

Mode control;
Replacement of alloy steel with carbon steel;
Uniform heating process of the product;
Possibility not to heat the whole part completely. Reduced energy consumption;
High resulting strength of the processed workpiece;
There is no oxidation process, carbon is not burned;
No microcracks;
There are no warped points;
Heating and hardening of certain sections of products;
Reducing the time spent on the procedure;
Implementation in the manufacture of parts for high-frequency installations in production lines.

Flaws

The main disadvantage of the technology under consideration is the significant installation cost. It is for this reason that the expediency of the application is justified only in large-scale production and excludes the possibility of doing the work yourself at home.

Learn more about the operation and principle of operation of the installation on the presented videos.

Many critical parts work for abrasion and are simultaneously exposed to impact loads. Such parts must have a high surface hardness, good wear resistance and at the same time not be brittle, i.e., not break down under impact.

High surface hardness of parts while maintaining a tough and strong core is achieved by surface hardening.

Of the modern methods of surface hardening, the following are most widely used in mechanical engineering: hardening when heated high frequency currents (TVCh); flame hardening and hardening in an electrolyte.

The choice of one or another method of surface hardening is determined by technological and economic feasibility.

Hardening when heated by high-frequency currents. This method is one of the most efficient methods of surface hardening of metals. The discovery of this method and the development of its technological foundations belongs to the talented Russian scientist V.P. Vologdin.

High frequency heating is based on the following phenomenon. When an alternating electric current of high frequency passes through a copper inductor, a magnetic field is formed around the latter, which penetrates into the steel part located in the inductor and induces Foucault eddy currents in it. These currents cause the metal to heat up.

heating feature HDTV is that the eddy currents induced in steel are not distributed uniformly over the section of the part, but are pushed to the surface. The uneven distribution of eddy currents leads to its uneven heating: the surface layers heat up very quickly to high temperatures, and the core either does not heat up at all or heats up slightly due to the thermal conductivity of steel. The thickness of the layer through which the current passes is called the penetration depth and is denoted by the letter δ.

The thickness of the layer mainly depends on the frequency of the alternating current, the resistivity of the metal and the magnetic permeability. This dependence is determined by the formula

δ \u003d 5.03-10 4 root of (ρ / μν) mm,

where ρ is the electrical resistivity, ohm mm 2 /m;

μ, - magnetic permeability, gs/e;

v - frequency, Hz.

It can be seen from the formula that with increasing frequency, the depth of penetration of induction currents decreases. High frequency current for induction heating of parts is obtained from generators.

When choosing the current frequency, in addition to the heated layer, it is necessary to take into account the shape and dimensions of the part in order to obtain a high quality surface hardening and economically use electrical energy high frequency installations.

Copper inductors are of great importance for high-quality heating of parts.

The most common inductors have a system of small holes on the inside through which cooling water is supplied. Such an inductor is both a heating and cooling device. As soon as the part placed in the inductor heats up to the set temperature, the current will automatically turn off and water will flow from the holes of the inductor and cool the surface of the part with a sprayer (water shower).

Parts can also be heated in inductors that do not have choking devices. In such inductors, the parts after heating are dumped into the hardening tank.

Hardening of HDTV is mainly carried out by simultaneous and continuous-sequential methods. With the simultaneous method, the hardened part rotates inside a fixed inductor, the width of which is equal to the hardened section. When the set heating time expires, the time relay cuts off the current from the generator, and another relay, interlocked with the first one, turns on the water supply, which bursts out of the inductor holes in small but strong jets and cools the part.

With the continuous-series method, the part is stationary, and the inductor moves along it. In this case, sequential heating of the hardened section of the part, after which the section falls under the water jet of a showering device located at some distance from the inductor.

Flat parts are hardened in loop and zigzag inductors, and gear wheels with a small module are simultaneously hardened in ring inductors. Macrostructure of the hardened layer of a fine-modulus car gear made of steel grade PPZ-55 (low hardenability steel). The microstructure of the hardened layer is finely acicular martensite.

The hardness of the surface layer of parts hardened by heating with high-frequency current is obtained by 3-4 units HRC higher than the hardness of conventional bulk hardening.

To increase the strength of the core, the parts are improved or normalized before hardening.

The use of HDTV heating for surface hardening of machine parts and tools makes it possible to drastically reduce the duration of the heat treatment process. In addition, this method makes it possible to manufacture mechanized and automated units for hardening parts, which are installed in the general flow of machining shops. As a result, there is no need to transport parts to special thermal shops and the rhythmic operation of production lines and assembly lines is ensured.

Flame surface hardening. This method consists in heating the surface of steel parts with an oxy-acetylene flame to a temperature that is 50-60 ° C higher than the upper critical point A C 3 , followed by rapid cooling with a water shower.

The essence of the flame hardening process is that the heat supplied by the gas flame from the burner to the hardened part is concentrated on its surface and significantly exceeds the amount of heat distributed deep into the metal. As a result of such a temperature field, the surface of the part first quickly heats up to the hardening temperature, then cools down, while the core of the part practically remains unhardened and does not change its structure and hardness after cooling.

Flame hardening is used to harden and increase the wear resistance of large and heavy steel parts such as crankshafts of mechanical presses, large-modulus gears, excavator bucket teeth, etc. In addition to steel parts, parts made of gray and pearlitic cast iron are subjected to flame hardening, for example guides of the beds of metal-cutting machines.

Flame hardening is divided into four types:

a) sequential, when the hardening torch with the coolant moves along the surface of the fixed part being processed;

b) hardening with rotation, in which the burner with the coolant remains stationary, and the part to be hardened rotates;

c) sequential with the rotation of the part, when the part continuously rotates and a hardening burner with a coolant moves along it;

d) local, in which the fixed part is heated to a given quenching temperature by a fixed burner, after which it is cooled by a jet of water.

A method of flame hardening a roller that rotates at a certain speed while the burner remains stationary. The heating temperature is controlled by a milliscope.

Depending on the purpose of the part, the depth of the hardened layer is usually taken equal to 2.5-4.5 mm.

The main factors affecting the depth of hardening and the structure of the hardened steel are: the speed of movement of the hardening torch relative to the hardened part or part relative to the burner; gas flow rate and flame temperature.

The choice of hardening machines depends on the shape of the parts, the hardening method and the required number of parts. If you need to harden parts of various shapes and sizes and in small quantities, then it is more expedient to use universal hardening machines. In factories, special installations and lathes are usually used.

For hardening, two types of burners are used: modular with a module from M10 to M30 and multi-flame with replaceable tips having a flame width of 25 to 85 mm. Structurally, the burners are arranged in such a way that the holes for the gas flame and cooling water are arranged in one row, in parallel. Water is supplied to the burners from the water supply network and serves simultaneously for hardening parts and cooling the mouthpiece.

Acetylene and oxygen are used as combustible gases.

After flame hardening, the microstructure in different zones of the part is different. The hardened layer gets a high hardness and remains clean, without traces of oxidation and decarburization.

The transition of the structure from the surface of the part to the core occurs smoothly, which is of great importance for increasing the service life of parts and completely eliminates harmful phenomena - cracking and delamination of hardened metal layers.

The hardness changes according to the structure of the hardened layer. On the surface of the part, it is equal to 56-57 HRC, and then lowered to the hardness that the part had before surface hardening. To provide High Quality hardening, obtaining uniform hardness and increased core strength, cast and forged parts are annealed or normalized in accordance with ordinary conditions before flame hardening.

Surface forcalc in the electrolyte. The essence of this phenomenon is that if a constant electric current is passed through the electrolyte, then a thin layer is formed on the cathode, consisting of the smallest hydrogen bubbles. Due to the poor electrical conductivity of hydrogen, the resistance to the passage of electric current increases greatly and the cathode (part) is heated to a high temperature, after which it is hardened. As an electrolyte, an aqueous 5-10% solution of soda ash is usually used.

The hardening process is simple and consists in the following. The part to be hardened is lowered into the electrolyte and connected to the negative pole of a DC generator with a voltage of 200-220 v and density 3-4 a / cm 2, as a result of which it becomes the cathode. Depending on which part of the part is subjected to surface hardening, the part is immersed to a certain depth. The part heats up in a few seconds, and the current is turned off. The cooling medium is the same electrolyte. So, the electrolyte bath serves as both a heating furnace and a quenching tank.

Hardening plant for heating t. h. consists of a generator t. h.,

a step-down transformer, capacitor banks, an inductor, a machine tool (sometimes the machine tool is replaced by a device for driving a part or an inductor) and auxiliary service equipment (time relay, relay for controlling the supply of quench liquid, signaling, blocking and control devices).

In the installations under consideration, such t.v.h. generators at medium frequencies (500-10000 Hz) machine generators, and more recently thyristor-type static converters; at high frequencies (60,000 Hz and above) tube generators. A promising type of generators are ion converters, the so-called excitron generators. They keep energy losses to a minimum.

On fig. 5 shows a diagram of an installation with a machine generator. In addition to the engine generator 2 and engine 3 with exciter 1, the unit contains a step-down transformer 4, capacitor banks 6 and inductor 5. The transformer lowers the voltage to a safe one (30-50 V) and at the same time increases the current strength by 25-30 times, bringing it up to 5000-8000 A.

Figure 5 Figure 6

Table 1 Types and designs of inductors

On Fig. 6 shows an example of hardening with a multi-turn inductor. Hardening is carried out as follows:

The part is placed inside a fixed inductor. With the launch of the HDTV apparatus, the part begins to rotate around its axis and heat up at the same time, then liquid (water) is supplied with the help of automated control and cools down. The whole process lasts from 30-45 seconds.

HDTV hardening is a type of heat treatment of metal, as a result of which hardness increases significantly and the material loses its ductility. The difference between HDTV hardening and other hardening methods is that heating is carried out using special HDTV installations that act on the part intended for hardening with high-frequency currents. HDTV hardening has many advantages, the main of which is complete control of heating. The use of these hardening complexes can significantly improve the quality of products, since the hardening process is carried out in a fully automatic mode, the operator's work consists only in fixing the shaft and turning on the cycle of the machine.

5.1. Advantages of induction hardening complexes (induction heating installations):

HDTV hardening can be done with an accuracy of 0.1 mm

Ensuring uniform heating, induction hardening allows for an ideal distribution of hardness along the entire length of the shaft

The high hardness of HDTV hardening is achieved through the use of special inductors with water guides, which cool the shaft immediately after heating.

HDTV hardening equipment (hardening furnaces) is selected or manufactured in strict accordance with the technical specifications.

6.Descaling in shot blasting machines

In shot blasting machines, scale is removed from parts with a jet of cast iron or steel shot. The jet is created by compressed air with a pressure of 0.3-0.5 MPa (pneumatic shot blasting) or fast-rotating paddle wheels (mechanical cleaning with shot blasters).

At pneumatic shot blasting both shot and quartz sand can be used in installations. However, in the latter case, a large amount of dust is formed, reaching up to 5-10% of the mass of the cleaned parts. Getting into the lungs of service personnel, quartz dust causes an occupational disease - silicosis. Therefore, this method is used in exceptional cases. When shot blasting, the compressed air pressure should be 0.5-0.6 MPa. Pig-iron shot is produced by pouring liquid iron into water while spraying a jet of cast iron with compressed air, followed by sorting on sieves. The shot must have the structure of white cast iron with a hardness of 500 HB, its dimensions are in the range of 0.5-2 mm. The consumption of cast iron shot is only 0.05-0.1% of the mass of the parts. When cleaning with shot, a cleaner surface of the part is obtained, a greater productivity of the apparatus is achieved and better working conditions are provided than when cleaning with sand. To protect the environment from dust, shot blasting machines are equipped with closed casings with enhanced exhaust ventilation. According to sanitary standards, the maximum permissible concentration of dust should not exceed 2 mg/m3. Shot transportation in modern plants is fully mechanized.

The main part of the pneumatic installation is a shot blasting machine, which can be forced and gravity. The simplest single-chamber injection shot blasting machine (Fig. 7) is a cylinder 4, having a funnel for shots at the top, hermetically sealed with a lid 5. At the bottom of the cylinder ends with a funnel, the hole from which leads to the mixing chamber 2. Shot is fed by rotary valve 3. Compressed air is supplied to the mixing chamber through valve 1, which captures the shot and transports it through a flexible hose 7 and nozzle 6 on the details. The shot is under pressure of compressed air up to the outflow from the nozzle, which increases the efficiency of the abrasive jet. In the apparatus of the described single-chamber design, compressed air must be temporarily turned off when it is replenished with shot.

The high-frequency current is generated in the installation due to the inductor and allows heating the product placed in close proximity to the inductor. The induction machine is ideal for hardening metal products. It is in the HDTV installation that you can clearly program: the desired depth of heat penetration, hardening time, heating temperature and cooling process.

For the first time, induction equipment was used for hardening after a proposal from V.P. Volodin in 1923. After long trials and testing of high-frequency heating, it has been used for steel hardening since 1935. HDTV hardening units are by far the most productive method of heat treatment of metal products.

Why induction is better for hardening

High-frequency hardening of metal parts is carried out to increase the resistance of the upper layer of the product to mechanical damage, while the center of the workpiece has an increased viscosity. It is important to note that the core of the product during high-frequency hardening remains completely unchanged.
The induction installation has many very important advantages in comparison with alternative types of heating: if earlier HDTV installations were more bulky and inconvenient, but now this drawback has been corrected, and the equipment has become universal for heat treatment of metal products.

Advantages of induction equipment

One of the disadvantages of the induction hardening machine is the inability to process some products that have a complex shape.

Varieties of metal hardening

There are several types of metal hardening. For some products, it is enough to heat the metal and immediately cool it, while for others it is necessary to hold it at a certain temperature.
There are the following types of hardening:

Stationary hardening: used, as a rule, for parts that have a small flat surface. The position of the workpiece and the inductor when using this method of hardening remains unchanged.
Continuous-sequential hardening: used for hardening cylindrical or flat products. With continuous-sequential hardening, the part can move under the inductor, or it keeps its position unchanged.
Tangential hardening of workpieces: excellent for machining small parts that have a cylindrical shape. Tangential continuous-sequential hardening scrolls the product once during the entire heat treatment process.
An HDTV hardening unit is equipment capable of high-quality hardening of a product and at the same time saves production resources.