How and with what to cut metal correctly. Heating of metal by welding current Self-resistance of the part

Have you ever faced the need to cut or cut something metal with your own hands? If yes, then you probably have a question how to do it. Of course, you can always use a good old hacksaw, but what if we are not talking about a thin galvanized sheet, but, for example, a thick-walled pipe?

Here, a hacksaw, of course, can help out, but a disproportionate amount of time and effort will be spent. And this means that a more radical approach is needed, and in this article we will talk about how to cut metal and what is the best way to do it.

We cut metal with a grinder

It is not known for certain why this instrument was so named. The main version is that Bulgaria was the first producing country, but in fact this is just a version.

When choosing how to cut metal, most people prefer the grinder, because, unlike gas equipment, its price is much lower, and no specific skills are needed to work with it.

On the other hand, many people are very afraid to work as a grinder, because of its high power and danger. In fact, there is nothing complicated, the main thing is to strictly observe safety precautions and not neglect even the smallest things.

In working with metal, there can be no trifles at all, and all cutting tools for metal represent a certain danger. The safety instructions for working with a cutting tool are relevant both for large angle grinders with a power of more than two kilowatts, and for very small ones, which, despite their compact size, can cause considerable harm to health.

This tool cuts metal by rotating an abrasive disc, the thickness of which may vary depending on the metal to be sawn. The thinner the wall steel product, the thinner metal cutting disc will be used.

We will not talk about the importance of safety in this article. This is always a priority issue, but if you do not have experience with a grinder, then especially for you we will give a few subtleties that you need to know about so as not to harm your health.

A few important points

So:

For safety reasons, the rotation of the disk should occur in the direction of the cut, that is, in the direction of the one who cuts the metal, but, as a rule, this position is not very convenient, and it is much easier when the flow of sparks is directed forward. In principle, there are no significant restrictions here, it all depends on the personal convenience of the tool operator.
When cutting metal, use only appropriate discs. Discs on stone or wood have a lower density, and upon contact with a steel surface, they quickly scatter, and fragments can damage you or others.

Don't work without protective cover. It directs the sparks to the side, and they will not fly in your face. Also, it is the only salvation in case the disc bites and shatters.
Do not cut metal away from you. So it is much more likely that a disk bite will occur. The direction of the cut must always be in the direction of the cutter.
Keep the tool straight. Cutting at an angle will cause the disc to warp and break, and fragments flying out at such a speed can cause significant harm to health.

Never clean the surface with a cutting disc. For stripping, there are special discs that differ in thickness and density.
Some types of grinders use only their own branded discs. This is due to the difference in the number of revolutions, so if you are the owner of a branded tool, use discs only under this brand.

Never use discs of a different size. Each size is designed for a tool with a certain number of revolutions. So, if you put a disk of small or medium size on a large grinder, it will simply burst.
Don't save. If a crack appears on the disc, or you did not notice it when buying, immediately throw it into the trash. Accidental cracking at the time of cutting can end very badly for you. Remember, the price of a disc is not worth your life and health.

Always keep a close eye on what is ahead of you at the time of work. Sparks flying out from under the grinder can ignite wood, plastic, and other combustible materials. Moreover, you can’t work as a grinder near gasoline or gas.
Before cutting metal with a grinder, make sure it is properly positioned. When cutting, the cut off part must be overhanging, otherwise the disc may be bitten.

Important! Never be afraid of an instrument, no matter how dangerous it looks or how loud it makes. Knowing how to cut metal correctly, you are guaranteed not to get injured.

So, we figured out the grinder, but this is far from the only tool for cutting metal. And below we will consider other options, but for now we recommend that you watch the video in this article, which talks about cutting metals and cutting tools. And in the meantime, we're moving on.

Other metal cutting tools

Of course, you can cut anything with a grinder, the main thing is to choose the right disk for it. But this option is not always the most convenient and practical. Here are just a few moments when it is more expedient to cut metal with another tool.

If the material is zinc coated. Due to the high speed, the grinder simply burns the coating, and there is not a trace of it left.

Painted material, it is also better to cut metal with scissors. They will save the coating and will not burn it.

It is more expedient to cut metal with a hacksaw if it is in tension, for example, if it is a heating pipe closed in a system circuit.

Metal with a thickness of more than 10 millimeters, it is better to cut with a gas cutter, as a grinder may simply not be able to cope with it.

Important! We intend not to tell in this article how to cut metal with a cutter, since this requires special knowledge and experience. Under no circumstances should you try to start the cutting torch yourself. This could result in a propane explosion or fire.

This is far from full list moments when it is better to refuse to use a grinder, but all of the situations listed are very common in everyday life. So what do you use for work?

Let's take a look at the most popular and affordable alternative metal cutting tools:

Cutting torch. It is difficult to call this tool affordable, but we could not leave it unattended, since in some cases, this is the only tool that is able to cope with the task. For example, when cutting thick metals, only a laser can be an alternative to a cutter, and such a tool is not available for domestic needs.

Hacksaw for metal. This tool, as a rule, is in the arsenal of any home master. Cutting metal with a hacksaw is long and problematic, but in some hard-to-reach places it is possible to crawl only to her.

Metal shears. Of course, you won’t cut the pipe with such a tool, but if you need, for example, to bite off a drywall profile, then better option just can't be found. They are easy and safe to work with and will not attack zinc or paint.

Press scissors. This tool is designed for cutting wire or rebar. Depending on the size, scissors can cut a bar with a diameter of up to 20 millimeters, and it is much more convenient to work with them than with a grinder.

As you can see, the choice is very rich, and you should choose a tool depending on specific situation. Of course, it is difficult to compete with a grinder, but it is not always possible to use it, and then alternative options will come to the rescue.

And in conclusion, I would like to remind you once again - always follow the safety precautions and use the means personal protection. No job is worth risking your health or even your life.

Heating of metal by welding current. Joule-Lenz law. Electrical resistance of metal.

All current-carrying elements are heated by electric current, and the amount of heat generated in any section of the electrical circuit with active resistance R=R(t), which is a function of t and τ at a current I=I(t) depending on time t, is determined by Joule's law -Lenza:

This is a general formula that does not show or determine specific temperatures in the joint area when it is heated by welding current.

However, it must be remembered that the value of R and I largely depends on the duration of the flow of this current.

Contact machines are structurally manufactured in such a way that the greatest amount of heat is released between the electrodes.

Seam spot welding has the largest number of electrode-electrode sections, the total amount of resistance is the sum of the resistance of the electrode-part + detail - detail+ detail + electrode - detail

Ree \u003d 2Red + Rdd + 2Rd

All components of the total resistance Ree continuously change during the thermal cycle of welding.

Contact resistance - Rdd is the largest in value, because. contacting is carried out along microprotrusions and the area of physical contact is small.

In addition, oxide films and various contaminants are present on the surface of the part.

Because We mainly weld steels and alloys with significant strength, then the complete collapse of microroughnesses occurs only when they are heated by welding current to temperatures of about 600 degrees C

The resistance in the electrode-part contact is much less than Rdd, because softer and more highly thermally conductive material of the electrodes is actively introduced between the protrusions of the microroughness of the parts.

The increased resistance in the contacts is also due to the fact that there is a sharp curvature of the current line in the contact areas, which determines a higher resistance due to an increase in the current path.

Contact resistance Rdd and Red largely depends on surface cleaning for welding.

By measuring 2 plates, 3 mm thick, very strongly compressed 200N according to the ammeter-voltmeter scheme, we obtained the following values:

Cleaning surfaces with a circle and grinding: 100 µOhm

Conclusion: grind

In practice, etching is used (when welding large surfaces), surface treatment with metal brushes, sandblasting and shot blasting.

At resistance welding they try to use cold-rolled steel on the surface of which there may be oil residues.

If there is no rust on the surface, then it is enough to degrease the surfaces to be welded.

The contact resistance of clean but oxide-coated parts decreases with increasing compression forces. This is due to the greater deformation of the microprotrusions.

We turn on the current, the highest density of the streamline is concentrated on juvenile surfaces. Current through the contacts, formed during the deformation of microprotrusions.

At the initial moment of time, the current density in the material of the part is less, because The current lines are distributed relatively evenly, and in the part-to-part contact, the current flows only through the conduction zones, therefore, the current density is higher than in the bulk of the part and heat generation and heating in this area are more significant.

The metal in contact will become ductile. It is deformed under the action of welding force, the area of conductive contacts will increase and when t=600 degC is reached (in hundredths of a second), the microprotrusions are completely deformed, the oxide films are partially destroyed, partially diffuse into the mass of the part, and the role of the contact resistance Rdd will cease to be paramount in the heating process. .

However, by this moment the temperature in the part-part contact area will be the highest, the resistivity of the material ρ will be the highest, and the heat release will be more intense anyway in this zone.

With sufficient current densities for the duration of its flow, it is there that the melting of the metal begins.

The appearance of a melting isotherm precisely in the part-part contact will be facilitated by the smallest heat removal from this area, the part's own resistance.

Intrinsic resistance of the part

S-section of the conductor

Coefficient A increases the spreading of the streamline into the mass of the part, while there is an increase in the real spreading area

dk - spreading diameter

A \u003d 0.8-0.95, depends on the hardness of the material, and in more from resistivity.

From the ratio dk / δ \u003d 3-5 A \u003d 0.8

It is obvious that the resistance of the part depends on the thickness, this is taken into account by the coefficient A and on the specific electrical resistance part material ρ, it depends on the chemical composition.

In addition, resistivity depends on temperature.

ρ(t)=ρ0*(1+αp*T)

In the process of welding with the flow of current, t is measured from contact to tmelt and above

Tmelt=1530 degC

When tm is reached, the resistivity increases abruptly.

αρ - temperature coefficient

αρ=0.004 1/degC - for pure metals

αρ=0.001-0.003 1/degC- for alloys

The value of αρ decreases with increasing degree of ligation.

With an increase in temperature, the metal, both in contact and in the bulk under the electrodes, is deformed, the contact area increases, and if the working surface of the electrodes is spherical, then the contact area can increase by 1.5-2 times.

Graph of the change in resistance during the welding process.

At the initial moment of time, the resistance of the part increases due to an increase in temperature and an increase in electrical resistivity, then the metal becomes plastic and the contact area begins to increase due to the indentation of the electrodes into the surface of the part, as well as an increase in the size of the contact area part-part.

The total resistance will decrease as the welding current is switched off. However, this is true for welding carbon and low alloy steels.

For welding high temperature Ni and Cr alloys, the resistance may even increase.

Electric and temperature field.

The Joule-Lenz law Q \u003d IRt shows heat generation in current-carrying elements, and heat removal processes are still taking place.

Thanks to the active cooling of the electrodes and the increase in heat removal in them, we obtain a lenticular shape of the cast core.

But such a shape is not always possible to obtain, especially when welding dissimilar, different thickness materials and thin parts.

Knowing the nature of the temperature field in the welding zone, it is possible to analyze:

1) Dimensions of the cast core.
2) Size of the HAZ (structure)
3) The magnitude of the residual stresses, i.e. connection properties.

Temperature field - a set of temperatures at various points of the part at a certain point in time.

Points with the same temperature connected by a line are called an isotherm.

The size of the pure core on the microsection indicates the melting isotherm along the boundaries of the cast core.

Ultimately, the temperature and the size of the melting isotherm, i.e. cast core, mainly affects the resistance of the part.

The founder - Gelman, took two parts 2 + 2mm, polished, etched and got a cast core; I took the parts and got a cast core too.

However, the difficulties that arise when welding heterogeneous thicknesses force us to investigate the distribution of thermal fields in the welding zone.

The current density is the number of charges passing for 1 second through a small area perpendicular to the direction of movement of the charges, divided by the length of its surface.

Basic methods and ways of converting electrical energy into heat are classified as follows. There are direct and indirect electrical heating.

At direct electric heating the conversion of electrical energy into thermal energy occurs as a result of the passage electric current directly over the heated body or medium (metal, water, milk, soil, etc.). At indirect electric heating electric current passes through a special heating device ( heating element), from which heat is transferred to a heated body or medium by conduction, convection or radiation.

There are several types of conversion of electrical energy into thermal energy, which determine electrical heating methods.

The flow of electric current through electrically conductive solids or liquid media is accompanied by the release of heat. According to the Joule-Lenz law, the amount of heat Q \u003d I 2 Rt, where Q is the amount of heat, J; I - silatoka, A; R is the resistance of the body or medium, Ohm; t - current flow time, s.

Resistance heating can be carried out by contact and electrode methods.

contact method It is used for heating metals both according to the principle of direct electric heating, for example, in electric contact welding machines, and according to the principle of indirect electric heating - in heating elements.

Electrode method It is used for heating non-metallic conductive materials and media: water, milk, succulent fodder, soil, etc. The material or medium to be heated is placed between the electrodes, to which an alternating voltage is applied.

Electric current, flowing through the material between the electrodes, heats it. Ordinary (non-distilled) water conducts electric current, since it always contains a certain amount of salts, alkalis or acids, which dissociate into ions that are carriers of electric charges, that is, electric current. The nature of the electrical conductivity of milk and other liquids, soil, succulent feed, etc. is similar.

Direct electrode heating is carried out only on alternating current, because D.C. causes electrolysis of the heated material and its deterioration.

Electrical resistance heating has found wide application in production due to its simplicity, reliability, versatility and low cost of heating devices.

Electric arc heating

In an electric arc that occurs between two electrodes in a gaseous medium, electrical energy is converted into thermal energy.

To start the arc, the electrodes connected to the power source are touched for a moment and then slowly moved apart. The resistance of the contact at the moment of dilution of the electrodes is strongly heated by the current passing through it. Free electrons, constantly moving in the metal, with an increase in temperature at the point of contact of the electrodes, accelerate their movement.

As the temperature rises, the speed of free electrons increases so much that they break away from the metal of the electrodes and fly out into the air. As they move, they collide with air molecules and split them into positively and negatively charged ions. There is an ionization of the air space between the electrodes, which becomes electrically conductive.

Under the influence of the source voltage, positive ions rush to the negative pole (cathode), and negative ions- to the positive pole (anode), thereby forming a long discharge - an electric arc, accompanied by heat generation. The temperature of the arc is not the same in its various parts and is with metal electrodes: at the cathode - about 2400 ° C, at the anode - about 2600 ° C, in the center of the arc - about 6000 - 7000 ° C.

There are direct and indirect electric arc heating. Main practical use finds direct arc heating in electric arc welding installations. In installations indirect heating the arc is used as a powerful source of infrared rays.

If a piece of metal is placed in an alternating magnetic field, then a variable e will be induced in it. d.s., under the action of which eddy currents will arise in the metal. The passage of these currents in the metal will cause it to heat up. This method of heating a metal is called induction. The device of some induction heaters is based on the use of the phenomenon of the surface effect and the proximity effect.

For induction heating, industrial (50 Hz) and high frequency (8-10 kHz, 70-500 kHz) currents are used. The most widespread is induction heating of metal bodies (parts, blanks) in mechanical engineering and in the repair of equipment, as well as for hardening metal parts. The induction method can also be used to heat water, soil, concrete and pasteurize milk.

Dielectric heating

The physical essence of dielectric heating is as follows. In solids and liquid media with poor electrical conductivity (dielectrics) placed in a rapidly changing electric field, Electric Energy turns into heat.

Any dielectric has electric charges bound by intermolecular forces. These charges are called bound as opposed to free charges in conductive materials. Under the influence electric field bound charges are oriented or displaced in the direction of the field. The displacement of bound charges under the action of an external electric field is called polarization.

in variable electric field there is a continuous movement of charges, and, consequently, the molecules associated with them by intermolecular forces. The energy expended by the source on the polarization of the molecules of non-conducting materials is released in the form of heat. Some non-conductive materials have no a large number of free charges, which create, under the action of an electric field, a small conduction current, which contributes to the release additional heat in the material.

During dielectric heating, the material to be heated is placed between metal electrodes - capacitor plates, to which a high-frequency voltage (0.5 - 20 MHz and higher) is supplied from a special high-frequency generator. The dielectric heating installation consists of a high-frequency lamp generator, a power transformer and a drying device with electrodes.

High-frequency dielectric heating is a promising heating method and is mainly used for drying and heat treatment of wood, paper, food and feed (drying grain, vegetables and fruits), pasteurization and sterilization of milk, etc.

Electron beam (electronic) heating

When a stream of electrons (electron beam) accelerated in an electric field meets a heated body, electrical energy is converted into thermal energy. A feature of electronic heating is the high density of energy concentration, which is 5x10 8 kW/cm2, which is several thousand times higher than with electric arc heating. Electronic heating is used in industry for welding very small parts and smelting of superpure metals.

In addition to the considered methods of electric heating, it is used in production and everyday life. infrared heating (irradiation).

If you know how to harden metal correctly, then even at home you can increase the hardness of metal products by two to three times. The reasons why this is necessary can be very different. Such a technological operation, in particular, is required if the metal must be hardened enough to be able to cut glass.

Most often, it is necessary to harden the cutting tool, and heat treatment is performed not only if it is necessary to increase its hardness, but also when this characteristic needs to be reduced. When the hardness of the tool is too low, its cutting part will jam during operation, but if it is high, the metal will crumble under the influence of mechanical loads.

Few people know that there is an easy way to check how well a steel tool is hardened, not only in production or at home, but also in a store when buying. In order to perform such a check, you need a regular file. They are carried out along the cutting part of the purchased tool. If it is hardened badly, then the file will seem to stick to its working part, and in the opposite case, it will easily move away from the tested tool, while the hand in which the file is located will not feel any irregularities on the surface of the product.

If, nevertheless, it turned out that you had a tool at your disposal, the quality of hardening of which does not suit you, you should not worry about this. This problem is solved quite easily: you can harden metal even at home, without using sophisticated equipment and special devices. However, you should be aware that low-carbon steels cannot be hardened. At the same time, the hardness of the carbon and easy enough to increase even at home.

Technological nuances of hardening

Tempering, which is one of the types heat treatment metals is carried out in two stages. First, the metal is heated to high temperature and then cooled. Various metals and even steels belonging to different categories differ from each other in their structure, so their heat treatment modes do not match.

Heat treatment of metal (hardening, tempering, etc.) may be required for:

its hardening and increase in hardness;
improving its plasticity, which is necessary when processing by plastic deformation.

Many specialized companies harden steel, but the cost of these services is quite high and depends on the weight of the part that needs to be heat treated. That is why it is advisable to do it yourself, especially since you can do it even at home.

If you decide to harden the metal on your own, it is very important to properly carry out such a procedure as heating. This process should not be accompanied by the appearance of black or blue spots on the surface of the product. The fact that the heating is happening correctly is evidenced by the bright red color of the metal. Shows well this process a video that will help you get an idea of how much to heat the metal being heat treated.

As a heat source for heating to the required temperature of a metal product that needs to be hardened, you can use:

a special oven powered by electricity;
blowtorch;
an open fire that you can make in the yard of your house or in the country.

The choice of heat source depends on the temperature to which the metal to be heat treated must be heated.

The choice of cooling method depends not only on the material, but also on what results are to be achieved. If, for example, it is not necessary to harden the entire product, but only its separate section, then cooling is also carried out pointwise, for which a jet of cold water can be used.

The technological scheme, according to which the metal is hardened, may provide for instantaneous, gradual or multi-stage cooling.

Fast cooling, using one type of cooler, is optimal for hardening steels in the carbon or alloy category. To perform such cooling, one container is needed, which can be a bucket, a barrel, or even an ordinary bath (it all depends on the dimensions of the object being processed).

In the event that other categories or if, in addition to hardening, tempering is required, a two-stage cooling scheme is used. With this scheme, the product heated to the required temperature is first cooled with water, and then placed in mineral or synthetic oil, in which further cooling takes place. Under no circumstances should an oil coolant be used immediately, as the oil may ignite.

In order to correctly select the hardening modes for various steel grades, one should be guided by special tables.

How to harden steel over an open fire

As mentioned above, it is possible to harden steel at home, using an open fire for heating. Naturally, such a process should begin with a fire, in which a lot of hot coals should form. You will also need two containers. Mineral or synthetic oil must be poured into one of them, and ordinary cold water into the other.

In order to extract red-hot iron from a fire, you will need blacksmith tongs, which can be replaced with any other tool of a similar purpose. After everything preparatory work completed, and a sufficient amount of hot coals has formed in the fire, you can put objects that need to be hardened on them.

By the color of the coals formed, one can judge the temperature of their heating. So, coals are hotter, the surface of which has a bright White color. It is also important to monitor the color of the fire flame, which indicates temperature regime in its interior. It is best if the fire flame is painted crimson, not white. In the latter case, indicating a too high temperature of the flame, there is a risk not only of overheating, but even of burning the metal to be hardened.

The color of the heated metal must also be carefully monitored. In particular, black spots should not be allowed to appear on the cutting edges of the machined tool. The blue color of the metal indicates that it has softened a lot and become too ductile. It cannot be brought to such a state.

After the product is calcined to the required degree, you can proceed to the next stage - cooling. First of all, it is lowered into a container with oil, and this is done often (with a frequency of 3 seconds) and as sharply as possible. Gradually, the intervals between these dives increase. As soon as the red-hot steel loses the brightness of its color, you can start cooling it in water.

When cooling metal with water, on the surface of which droplets of hot oil remain, care should be taken, as they can flare up. After each dive, the water must be shaken to keep it cool at all times. To get a better idea of the rules for performing such an operation, a training video will help.

There is certain subtleties during cooling of hardened drills. So, they cannot be lowered flat into a container with coolant. If you do it this way, then Bottom part a drill or any other metal object that has an elongated shape will cool first, which will lead to its compression. That is why it is necessary to immerse such products in the coolant from the side of the wider end.

For heat treatment of special grades of steel and smelting of non-ferrous metals, the possibilities of an open fire will not be enough, since it will not be able to provide heating of the metal to a temperature of 700–9000. For such purposes, it is necessary to use special furnaces, which can be muffle or electric. If it is quite difficult and expensive to make an electric furnace at home, then with muffle-type heating equipment this is quite feasible.

Self-made chamber for hardening metal

A muffle furnace, which is quite possible to make yourself at home, allows you to harden various grades of steel. The main component that will be required for the manufacture of this heating device is refractory clay. The layer of such clay, which will cover the inside of the furnace, should be no more than 1 cm.

Scheme of a chamber for hardening metal: 1 - nichrome wire; 2 - the inner part of the chamber; 3 - outer part of the chamber; 4 - back wall with spiral leads

In order to give the future furnace the required configuration and the desired dimensions, it is best to make a mold from cardboard impregnated with paraffin, on which refractory clay will be applied. Clay, mixed with water to a thick homogeneous mass, is applied to the wrong side of the cardboard form, from which it itself will lag behind after complete drying. Hardware, heated in such a device, are placed in it through a special door, which is also made of refractory clay.

The chamber and the door of the device after drying in the open air are additionally dried at a temperature of 100 °. After that, they are fired in a furnace, the temperature in the chamber of which is gradually brought up to 900 °. When they have cooled after firing, they must be carefully connected to each other using locksmith tools and sandpaper.

On the surface of a fully formed chamber, a nichrome wire is wound, the diameter of which should be 0.75 mm. First and last layer such winding must be twisted together. When winding the wire around the chamber, a certain distance should be left between its turns, which must also be filled with refractory clay in order to exclude the possibility short circuit. After the layer of clay applied to provide insulation between the turns of nichrome wire dries, another layer of clay is applied to the surface of the chamber, the thickness of which should be approximately 12 cm.

The finished chamber, after complete drying, is placed in a metal case, and the gaps between them are filled with asbestos chips. In order to provide access to the inner chamber, doors finished from the inside are hung on the metal body of the furnace. ceramic tiles. All existing gaps between structural elements sealed with refractory clay and asbestos chips.

The ends of the nichrome winding of the camera, to which it is necessary to supply electrical power, are output from the rear side of it. metal frame. To control the processes occurring in the internal part muffle furnace, and also measure the temperature in it using a thermocouple, in its front part it is necessary to make two holes, the diameters of which should be 1 and 2 cm, respectively. From the front of the frame, such openings will be closed with special steel curtains. Homemade construction, the manufacture of which is described above, allows you to harden metalwork and cutting tools, working elements of stamping equipment, etc.

The process of hardening steel allows you to increase the hardness of the product by about 3-4 times. Many manufacturers carry out a similar process at the time of production, but in some cases it must be repeated, since the hardness of the steel or other alloy is low. That is why many are wondering how to harden metal at home?

Methodology

In order to carry out work on hardening steel, it is necessary to take into account how such a process is performed correctly. Hardening is a process of increasing the hardness of the surface of an iron or alloy, which involves heating the sample to a high temperature and then cooling it. Despite the fact that at first glance the process under consideration is simple, various groups metals differ in their peculiar structure and characteristics.

Heat treatment at home is justified in the following cases:

If necessary, reinforce the material, e.g. cutting edge. An example is the hardening of chisels and chisels.
If necessary, increase the plasticity of the object. This is often necessary in the case of hot forging.

Professional hardening of steel is an expensive process. The cost of 1 kg of increasing the surface hardness costs about 200 rubles. It is possible to organize hardening of steel at home only taking into account all the features of increasing the surface hardness.

Process features

It is possible to carry out hardening of steel, taking into account the following points:

Heating must be even. Only in this case the structure of the material is homogeneous.
Heating of steel should take place without the formation of black or blue spots, which indicates a strong overheating of the surface.
The sample must not be heated to the extreme state, since the changes in the structure will be irreversible.
The bright red color of the metal indicates the correctness of the heating of the steel.
Cooling must also be carried out evenly, for which a water bath is used.

Equipment and features of the process

Special equipment is often used to heat the surface. This is due to the fact that it is quite difficult to heat steel to the melting point. At home, the following equipment is often used:

electric furnace;
blowtorch;
thermal furnace;
a large bonfire that is built around to redirect the heat.

When choosing a source of heat, one should take into account the fact that the part must be completely placed in the furnace or fire on which heating is carried out. It will be correct to select equipment also according to the type of metal that will be processed. The higher the strength of the structure, the more the alloy is heated to impart plasticity.

In the case when it is necessary to harden only part of the part, jet hardening is used. It provides for a jet of cold water to hit only a certain part of the part.

A tub of water or a barrel, as well as a bucket, is often used to cool the steel. It is important to take into account the fact that in some cases gradual cooling is carried out, in others fast and abrupt.

Increasing hardness on an open fire

In everyday life, hardening is often carried out on an open fire. This method is only suitable for a one-time surface hardening process.

All work can be divided into several stages:

first you need to make a fire;
at the time of making a fire, two large containers are prepared that will correspond to the size of the part;
In order for the fire to give more heat, you need to provide a large amount of coal. they give a lot of heat for a long time;
one container should contain water, the other - engine oil;
should be used special tools, with which the hot workpiece will be held. on the video you can often find blacksmith tongs, which are most effective;
after preparation necessary tools you should put the object in the very center of the flame. at the same time, it is possible to bury the part in the very depths of the coals, which will ensure that the metal is heated to a melting state;
coals that have a bright white color are hotter than others. the process of melting metal must be monitored closely. the flame should be crimson, but not white. if the fire is white, then there is a possibility of overheating of the metal. in this case performance deteriorate significantly, and the service life decreases;
the correct color, uniform over the entire surface, determines the uniformity of heating of the metal;
if darkening occurs of blue color, then this indicates a strong softening of the metal, that is, it becomes excessively ductile. this should not be allowed, since the structure is significantly violated;
when the metal is fully heated, it should be removed from the hotbed;
after that, the red-hot metal should be placed in a container with oil with a frequency of 3 seconds;
the final stage can be called immersion of the part in water. At the same time, shaking of water is periodically carried out. This is due to the fact that the water quickly heats up around the product.

When performing work, attention should be paid to caution, as hot oil can harm the skin. In the video, you can pay attention to what color the surface should be when the desired degree of plasticity is reached. But for hardening non-ferrous metals, it is often necessary to exert a temperature in the range of 700 to 900 degrees Celsius. It is practically impossible to heat non-ferrous alloys on an open fire, since it is impossible to reach such a temperature without special equipment. An example is the use of an electric furnace, which is capable of heating the surface up to 800 degrees Celsius.