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Nowadays, induction furnaces are widely used in the metal smelting process. The current produced in the field of the inductor contributes to the heating of the substance, and this feature of such devices is not only basic, but also the most important. Processing causes the substance to undergo several transformations. The first stage of transformation is the electromagnetic stage, followed by the electrical stage, and then the thermal stage. The temperature generated by the stove is used practically without any residue, so this solution is the best among all others. Many may be interested in a manufactured stove. Next we will talk about the possibilities of implementing such a solution.

Types of furnaces for melting metals

This type of equipment can be divided into main categories. The first has a heart channel as its base, and the metal is placed in such furnaces in a ring manner around the inductor. The second category does not have such an element. This type is called a crucible, and the metal is placed inside the inductor itself. It is technically impossible to use a closed core in this case.

Basic principles

The melting furnace in this case operates on the basis of the phenomenon of magnetic induction. And there are several components. The inductor is the most important component of this device. It is a coil, the conductors of which are not ordinary wires, but copper tubes. This requirement is imposed by the design of the melting furnaces itself. The current that passes through the inductor generates a magnetic field that affects the crucible inside which the metal is located. In this case, the material plays the role of a secondary transformer winding, that is, a current passes through it, heating it. This is how melting occurs, even if you make an induction furnace yourself. How to build this type of furnace and increase its efficiency? This important question, to which there is an answer. The use of high-frequency currents can significantly increase the efficiency of equipment. For this, it is appropriate to use special power supplies.

Features of induction furnaces

This type of equipment has certain characteristic features, which are both advantages and disadvantages.

Since the distribution of the metal must be uniform, the resulting material is characterized by a good homogeneous mass. This type of furnace works by transporting energy through zones, while also introducing the function of focusing energy. Parameters such as capacitance, operating frequency and lining method are available for use, as well as regulation of the temperature at which the metal melts, which significantly facilitates the work process. The existing technological potential of the furnace creates a high melting rate; the devices are environmentally friendly, completely safe for humans and ready for use at any time.

The most noticeable disadvantage of such equipment is the difficulty of cleaning it. Since the slag is heated solely due to the heat generated by the metal, this temperature is not enough to ensure its full use. The high difference in temperature between the metal and the slag does not allow the waste removal process to be as simple as possible. As another disadvantage, it is customary to highlight the gap, due to which it is always necessary to reduce the thickness of the lining. Due to such actions, after some time it may become faulty.

Use of induction furnaces on an industrial scale

In industry, crucible and channel induction furnaces are most often found. In the first, melting of any metals in arbitrary quantities is carried out. Containers for metal in such variants can hold up to several tons of metal. Of course, in this case it is impossible to make induction melting furnaces with your own hands. Channel furnaces are designed for smelting non-ferrous metals different types, as well as cast iron.

This topic is often of interest to fans of radio design and radio technology. Now it is becoming clear that creating induction furnaces with your own hands is quite possible, and many people have managed to do this. However, to create such equipment it is necessary to implement the action electrical diagram, which would contain the prescribed actions of the furnace itself. Such solutions require the involvement of those capable of producing wave oscillations. A simple do-it-yourself induction furnace according to the circuit can be built using four electronic lamps in combination with one neon, which gives a signal that the system is ready for operation.

In this case, the AC capacitor handle is not located inside the appliance. Thanks to this, you can create an induction furnace with your own hands. The device diagram describes in detail the location of each individual element. You can make sure that the device is powerful enough by using a screwdriver, which should reach a red-hot state in just a few seconds.

Peculiarities

If you are creating an induction furnace with your own hands, the operating principle and assembly of which is studied and carried out according to the appropriate scheme, you should know that the melting rate in this case may be affected by one or more factors listed below:

Pulse frequency;

Hysteresis losses;

Generating power;

The period of heat release;

Losses associated with the occurrence of eddy currents.

If you are planning to build an induction stove with your own hands, then when using lamps you need to remember that their power should be distributed so that four pieces are enough. When using a rectifier, you will get a network of approximately 220 V.

Household use of stoves

In everyday life, such devices are used quite rarely, although similar technologies can be found in heating systems. They can be seen in the form of microwave ovens and In the environment of new technologies, this development has found wide application. For example, the use of eddy induction currents in induction cookers allows you to cook a huge variety of dishes. Since they take very little time to heat up, the burner cannot be turned on if nothing is standing on it. However, special utensils are required to use such special and useful cookers.

Build process

Do-it-yourself induction consists of an inductor, which is a solenoid made from water-cooled copper tube and a crucible, which can be made from ceramic materials, and sometimes made of steel, graphite and others. In such a device you can smelt cast iron, steel, precious metals, aluminum, copper, magnesium. Do-it-yourself induction furnaces are made with a crucible capacity from a couple of kilograms to several tons. They can be vacuum, gas-filled, open and compressor. The furnaces are powered by high, medium and low frequency currents.

So, if you are interested in making your own induction furnace, the scheme involves the use of the following main components: a melting bath and an induction unit, which includes a hearth stone, an inductor and a magnetic core. A channel furnace differs from a crucible furnace in that electromagnetic energy is converted into thermal energy in the heat release channel, in which there must always be an electrically conductive body. To make the initial start-up of a channel furnace, molten metal is poured into it or a template made of a material that can be straightened in the furnace is inserted. When the melting is completed, the metal is not completely drained, but a “swamp” remains, intended to fill the heat release channel for future start-up. If you are going to build an induction furnace with your own hands, then to make it easier to replace the hearth stone for the equipment, it is made detachable.

Furnace components

So, if you are interested in making a mini induction oven with your own hands, then it is important to know that its main element is the heating coil. When homemade version It is enough to use an inductor made of a bare copper tube, the diameter of which is 10 mm. For inductor used inner diameter 80-150 mm, and the number of turns is 8-10. It is important that the turns do not touch, and the distance between them is 5-7 mm. Parts of the inductor should not come into contact with its screen; the minimum gap should be 50 mm.

If you are planning to make an induction furnace with your own hands, then you should know that on an industrial scale, water or antifreeze is used to cool the inductors. When low power and short-term operation of the created device can be done without cooling. But during operation, the inductor gets very hot, and scale on copper can not only sharply reduce the efficiency of the device, but also lead to a complete loss of its performance. It is impossible to make a cooled inductor on your own, so it will need to be replaced regularly. You cannot use forced air cooling, since the fan housing placed close to the coil will “attract” EMF, which will lead to overheating and a decrease in the efficiency of the furnace.

Generator

When assembling an induction furnace with your own hands, the diagram involves the use of such important element, like an alternator. You should not try to make a stove if you do not know the basics of radio electronics at least at the level of a semi-skilled radio amateur. The choice of generator circuit should be such that it does not produce a hard current spectrum.

Using Induction Furnaces

This type of equipment is widely used in areas such as foundries, where the metal has already been cleaned and needs to be given a specific shape. You can also get some alloys. They have also become widespread in jewelry production. The simple principle of operation and the possibility of assembling an induction furnace with your own hands allow you to increase the profitability of its use. For this area, devices with a crucible capacity of up to 5 kilograms can be used. For small industries this option will be optimal.

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Crucible is a vessel for melting metal. As a rule, conversion metal is melted in crucibles, i.e. already brought to the required degree of quality for casting into a mold or refining (deep purification from impurities). General line the development of large-scale metallurgy - a reduction in the number of redistributions, up to the release of conditioned metal immediately from the melting furnace, but in industry crucible melting still retains significant importance, and in handicrafts and jewelry it dominates.

The crucible is not just a fairly heat-resistant vessel. His chemical composition and the design must correspond to the type of metal being melted and the melting mode. This article describes how to make a crucible with your own hands and what conditions it must satisfy for use at home or in a small workshop. For beginner metallurgists, you will first have to touch on the metal smelting process itself, because... The requirements for the crucible are determined mainly by its conditions.

A little about melting

In a deep vacuum, the high-purity metal being melted can be heated exactly to the melting temperature or slightly higher, and kept at it for some time so that tiny, literally a few atoms, crystallite remains melt. Then the metal can be allowed to cool slightly below its melting point - it will remain liquid, like a supersaturated solution without a seed crystal. If we now pour the metal, also in a vacuum, into a mold made of a chemically absolutely inert material, in which a seed crystal of the same metal is placed, then, observing all the subtleties of this technology, we will obtain a single-crystal casting with unique properties.

In amateur conditions, vacuum melting, alas, is not feasible. In order to properly make a crucible for melting metal yourself, you need to take into account a number of features of melting in a non-inert chemical gas environment. The melted metal, firstly, interacts with air, causing part of it to be lost to the formation of oxide, which is especially important when melting scrap precious metals: at its melting temperature (1060 degrees Celsius), even gold noticeably oxidizes. To compensate for oxidation to some extent, the crucible must create a reducing environment for the melt or be chemically inert if the metal melts clean open flame, see below.

Secondly, so that the metal in the crucible does not freeze until it is brought to the casting mold, so that the remnants of the original crystallites do not spoil the casting, and the melt acquires sufficient fluidity, the metal in the crucible is overheated. For example, the melting point of zinc is 440 degrees, and its foundry temperature is 600. Aluminum, respectively, 660 and 800. Since overheating of the metal after melting takes some time, degassing of the melt also occurs at the same time, this is the third thing.

Recovery

In metallurgy, atomic carbon C, carbon monoxide CO (carbon monoxide) and hydrogen H are used as reducing agents. The latter is most often an accidental guest, because for this purpose it is too active and is absorbed by metals without forming chemical compounds with them in large quantities, which spoils the casting material. For example, solid platinum at room temperature capable of absorbing up to 800 volumes of hydrogen. A platinum blank in a hydrogen atmosphere literally swells before our eyes, cracks and falls into pieces. If you take them out of the hydrogen chamber and heat them, hydrogen will be released back.

Note: in a similar way, but in smaller quantities, metals absorb/emit other gases, e.g. nitrogen. This is why degassing of the melt is required, see also below.

A noticeable proportion of hydrogen reduction occurs when heated with an open flame. gas burner, upon its contact with a less heated surface. The metal does not deteriorate - the absorbed hydrogen is released and burned later in the smelting process. But, if the crucible material is also prone to gas absorption, it may crack and burst during melting; this must be kept in mind.

CO reduction is noticeable if the metal in the crucible is melted by the open flame of a liquid (gasoline, kerosene, diesel) burner, for the same reasons. Liquid fuel burns much slower than gas, and its afterburning zone extends several cm from the burner nozzle. Recovery carbon monoxide- the purest, from the point of view of the metal: it does not spoil the metal and does not produce by-products with a strong excess of the reducing agent. Therefore, CO reduction is widely used in metallurgy when smelting metal from ore, but no one has yet figured out how to make a crucible furnace (see below), in which oxidation compensation would be completely provided by CO.

Atomic carbon is a reducing agent energetic enough to compensate for oxidation. It is also not difficult to create a reducing environment in a crucible using C: it is enough to introduce free carbon in one or another allotropic modification into the composition of its material or make the entire crucible from a heat-resistant and mechanically sufficiently strong allotrope C; graphite is one of them. When reducing C, there is a danger of carburization of the melt, but graphite releases very little atomic carbon when heated. If you heat the metal in a graphite crucible with a gas flame, then the excess C will immediately find a more “tasty” H for it and the danger of carburization will be reduced to zero. And for other heating methods (see below), you can select the dimensions, configuration of the crucible and the addition of graphite to its material so that there is simply no excess C under any conceivable melting mode. This is a very valuable property of graphite, keep it in mind too.

Note: the coefficient of thermal expansion of graphite TKR is negative, which significantly compensates for the thermal expansion of the crucible, increases its durability and increases its service life. Also valuable quality.

Excerpt

So, it’s clear why the melt in the crucible needs to be overheated and held. Although metal casting is a completely different topic, it still needs to be mentioned here that the melt holding time should be observed quite accurately. Chemically pure metals are almost never used in practice, for example. gold 9999 wears out very quickly; The exception is electrical copper and zinc for galvanizing, the cleaner they are, the better. Most often they use the so-called. eutectic alloys; eg steel is a eutectic of iron and carbon, and duralumin is a complex eutectic of several components. If the melt is allowed to sit, the structure of the eutectic in the casting will change and ready product will come out spoiled. The holding time is especially critical for bronze and brass: they need to be cast immediately, as soon as the play of the melt in the crucible apparently changes and becomes calmer. Do you remember how engineer Telegin in A. N. Tolstoy’s “Walking Through Torment” was worried that the bronze would not wear out?

In relation to the manufacture of a homemade crucible, degassing of the melt during exposure is significant in that at this time it (the crucible) experiences significant dynamic loads from bubbles of released gases and/or play of the melt itself. That is, make the crucible withstand a large number of thermal deformations and, if required, restoration, are small. Its material must also be viscous enough to withstand shock waves from bursting bubbles and shocks from melt jets. It is this circumstance that explains the low durability and reliability of homemade graphite crucibles (see below).

What to make from

Melting crucibles are made (see figure below):

1. ceramic chemically neutral;
2. ceramic graphite;
3. graphite;
4. cast iron;
5. steel.

Their comparative characteristics are:

• Ceramic neutral – used for melting scrap jewelry with preservation of the sample, because at indirect heating(see below) do not change the properties of the metal. You can do it yourself, but it’s a little complicated (see below) and is it worth it? A 50 g gold crucible costs up to 100 rubles in a jewelry store. Suitable for melting without any problems induction furnace(see below), because almost do not absorb the energy of the electromagnetic field (EMF). Resource – 10-30 melts.
• Ceramic graphite – suitable for melting any metal; at home up to 1.5-2 kg at a time. To use an induction furnace, its power for the same amount of metal will have to be increased by 1.5-2 times due to the absorption of EMF by conductive graphite. You can do it yourself, see below. Resource – up to 50 or more melts.
• Graphite - suitable for melting old, oxidized scrap non-ferrous and precious metals, because create a strong restorative environment. Melting silver with an open gas flame in a graphite crucible makes it possible to almost completely restore the original weight of the oxidized metal. You can’t do it yourself, see below. Resource – more than 100 melts.
• Cast iron - used mainly for melting red copper into oxygen-free copper, because actively absorb oxygen. The resource is up to 30 melts, and then the amorphous carbon leaves the cast iron and the crucible degrades.
• Steel - homemade cheap option for melting small quantities of aluminum and magnesium alloys and other chemically inert metals in the melt. Can be used for melting small quantities of lead into fishing sinkers and so on.

Note: graphite, cast iron and steel crucibles for use in induction furnaces (see below) are completely unsuitable, because completely absorb EMF energy.

About graphite crucibles

Graphite crucibles are made either turned from massive natural graphite (expensive), or sintered at high temperature made of graphite powder (cheaper, but still not very cheap). Hobbyists often try to make “graphite” crucibles from ground graphite with a kaolin binder, etc., but what they end up with is not graphite, but overly graphitized ceramic crucibles - fragile, withstanding no more than 10 melts and spoiling the metal due to excessive release of atomic carbon by finely dispersed graphite . A more or less rational way to use ground graphite in amateur crucible melting is to make a tabletop mini crucible furnace from it for ceramic neutral crucibles, see fig.

Cold welding for assembling this furnace should be used at a temperature of at least 800 degrees - the cheeks, which conduct electricity well, do not heat up above 400 during one melt. Graphite powder will not heat up much more without a crucible, but when the crucible is pressed into it, it will be hot spot over 1000 degrees due to compaction of the powder under the crucible.

If gold is melting, then after the melting is completed and the furnace has cooled, the graphite powder is poured out and shaken, because it gets baked. To melt silver and cupronickel, the powder is removed and shaken after 3-5 melts, so the furnace heats up faster. In any case, to maintain a reducing environment, the furnace is covered with a mica lid during melting.

Heating Methods

If you need to melt more than 150-200 g of metal at a time, then you will need to build a crucible furnace next to the crucible, otherwise the melt will be homogeneous and High Quality casting will be very difficult. The exception is low-melting and easily recoverable lead: up to 20-30 kg of it can be melted at a time at home. A relative exception is zinc for hot galvanizing; its melt in a crucible without a furnace can be up to 2-2.5 kg, but borax must be sprinkled on top of it so that the surface of the melt is completely covered with its fluidized layer. Steel fasteners are thrown into the melt through a layer of borax.

The optimal method in all respects for heating the crucible in a furnace is with gas, pos. 1 in Fig., but a gas crucible furnace is a rather complex structure, although it can easily be made independently. The most suitable crucible for gas oven– ceramic graphite, because its material has fairly high thermal conductivity. If there are particularly high requirements for metal purity, it is better to use a neutral ceramic crucible. When lower for fusible metals - cast iron, as it conducts heat better and thereby saves fuel. Graphite crucibles are placed in a gas furnace only if strong reduction of old oxidized metal is required, and the danger of carburization is insignificant, for example, when melting silver extracted from the earth for refining

For low-melting metals, the electric crucible furnace, pos. 2; it may be the so-called ohmic (with heating by a nichrome spiral) or induction, with heating from an electromagnetic oscillation generator, see below. Only ceramic neutral or, to a limited extent, graphite crucibles are suitable for induction furnaces.

If the crucible contains more than 2-2.5 kg of metal, then according to safety rules the crucible furnace must be made tiltable (item 3), because and 1 kg of melt spilled on the floor is already a big disaster. On the contrary, it is preferable to heat metal in small jewelry crucibles without a furnace, directly with the flame of a burner, pos. 4. In this case, the crucible is held throughout the melting process with a special spring grip, pos. 5 and 6.

Note: silver and its alloys, as well as lead for sinkers, can be melted at home in quantities of up to 15-20 g, using instead of a crucible... a food-grade stainless steel spoon, see fig. on right. For safety, then it is necessary to make gaskets for the jaws of the vice with longitudinal cuts under the handle of the spoon. The flame is exclusively gas; gasoline can burn a spoon.

Electric heating

Ohmic crucible furnaces are mainly used for smelting lead or tin. For more refractory metals, they turn out to be uneconomical, but up to 20 kg of lead can be melted at a time in a home crucible electric furnace; how to make your own electric crucible for melting lead, see for example. video:

Video: electric crucible for melting lead

Melting aluminum in a crucible turns out to be more profitable by induction due to its high electrical conductivity, but this trick no longer works with copper - its temperature and latent heat of fusion are much higher. In the induction melting method, the metal is heated by Foucault eddy currents, for which the crucible with it is placed in an EMF coil made of thick copper wire, powered by alternating current from an electromagnetic oscillation generator. How to make a generator with your own hands for inductively heating small amounts of metal, for example, for trinkets, is described in other materials, or, for example, see next. video guide.

Video: DIY induction heating

With an increase in the amount of melted metal, not only does the required power generator, but its optimal frequency also drops, this affects the so-called. surface effect (skin effect) in metal. If 100-200 g of aluminum can be melted into EMF from any homemade generator for, then installing 1.5-2 kg of duralumin or magnesium alloy is already a solid structure, see fig. on right. If you intend to work with aluminum, then think carefully - is it worth building something like this? Wouldn't it be easier to use a mini gas furnace for melting small quantities of aluminum alloys, see for example. video clip

Video: mini furnace for melting aluminum

Making crucibles

Now it's time to make your own melting crucible. From the above it is clear that it makes sense to make crucibles with your own hands:

1. Steel;
2. Ceramic neutral;
3. Ceramic graphite.

There is nothing special to say about steel crucibles - they are just a steel vessel with a welded handle. Steel crucibles are used for melting low-melting metals; sometimes - zinc for hot galvanizing with quality up to 3+. Steel crucibles for lead, tin and zinc are only suitable for melting one specific metal, because... after 1-2 melts they themselves are covered with it from the inside.

Ceramic neutral

Composition of the mixture for forming a ceramic neutral crucible – 7 parts fireclay clay, 1 part finely ground chamotte (up to fraction<1,5 мм) и 10 ст. ложек жидкого стекла (силикатного канцелярского клея) на 1 л сухой смеси. Молотый шамот в небольших количествах можно получить из кусков шамотного кирпича, растолченных в фаянсовой ступке (продаються в магазинах хозяйственных, медицинского оборудования и некоторых аптеках). Не жалко денег на крутизну – можно в сувенирном купить агатовую, они более стойкие. Если же вы собираетесь лить металл регулярно и довольно много, или делать тигли на продажу, то, возможно, лучше будет сделать для размола шамота цепную или шариковую мельницу.

Fireclay mill

Finely ground chamotte is part of the raw material for molding both neutral and graphite crucibles, and the quality and durability of the crucible largely depend on it, and crushing chamotte using artisanal methods is very labor-intensive and does not produce a completely good-quality material. The structure of a chain mill for mineral raw materials is shown in Fig. on right. Material – steel. Chains – 4; they are hung crosswise so that they sag horizontally by approx. by 1/3 of the tank diameter. An option instead of chains for 1 broken fireclay brick is 2-3 handfuls of balls from the bearing. New store-bought chains will cost more than chains, but old ones from broken bearings are quite suitable. Any drive: manual, electric. Both chain and ball mills are capable of grinding fireclay into dust like cement; To obtain certain fractions, the mill is stopped earlier. To prevent dust from forming, the mouth of the tank is covered with something during grinding. To grind a brick, simply drop it from a height onto a hard floor and load the resulting pieces into the mill.

Preparing the molding material

Mix dry clay with ground fireclay until completely homogeneous (uniform). The ideal option is to scroll 15-20 times in the same mill; if it is spherical, then you don’t have to throw balls into the tank. Unload the mixed mass and add a little water (1.5-2.5 parts), mixing by hand until it reaches the consistency: clenched in a fist, sticks together into a lump, but does not stick to the skin and is not pressed between the fingers. Add liquid glass, also stirring until completely homogeneous, this is the most labor-intensive step.

Deaeration

Just one remaining air bubble in the ceramic crucible mixture can cause the crucible to burst due to heating. Therefore, you need to knock the air out of the mass. To do this, lay a clean film on the hard floor; newspaper, as some manuals advise, is not necessary - the mass will accumulate from paper fibers.

To knock out the air, the entire lump of mass is thrown forcefully onto the floor many times. Practically - after the bubbles have stopped jumping out of the flopping mass, at least 10 more times.

Storage

For storage, the beaten mass is placed in a glass container with a hermetically sealed lid. In plastic, and especially when wrapped in several layers of film, the mass dries out in a few weeks and cannot be restored, but in glass in a cool place it is stored for more than six months.

Usage

Crucibles from the resulting mass are simply sculpted by hand or molded in a destructible plaster mold or in a collapsible one, as described below. The molded crucible is dried, and, which is absolutely necessary for this mass, after drying it is annealed in a muffle furnace for an hour or two at a temperature of 800 degrees. It is at this temperature that the liquid glass will melt and firmly bind the other components. Below - the crucible will collapse during the first melting; higher – during annealing. This is a very significant drawback of this technology, because Muffle furnace equipment is not cheap or simple, although. The maximum operating temperature of the resulting crucibles is up to 1600 degrees; resource, with high-quality grinding of chamotte - up to 30 melts.

Graphite

Manufacturing technology of graphite crucibles for melting any metals, incl. black scrap, using any heating method, is well described in an article by the author A. Ramir from 2006 (see dendrite-steel.narod.ru/stat-ramir-3.htm). A. Ramir, apparently, is self-taught, but even more credit to him - his products fully correspond to good industrial designs. However, firstly, his article was rewritten many times by rewriters who clearly did not cast metal in their lives. Secondly, you can’t always get to it in a search, and for some reason the drawings are not downloaded, although they seem to be freely distributed. Thirdly, there is something to add to A. Ramir’s materials, no offense to him. One of the rules of technology is that in a good design there is always something to improve. Therefore, we will repeat and supplement the main points of this publication.

Drawings of crucibles from the mentioned article are given in Fig.:

The maximum weight of melted steel is indicated in kg; it must be recalculated for another metal. The main difficulty in this case is the manufacture of the flask - the round shell of the mold. Its inner surface is conical, otherwise the finished crucible cannot be removed after molding, so A. Ramir used turned flasks.

Meanwhile, a flask for any of these forms can be made from a piece of plastic pipe. It is secured in 3 places, at the bottom, in the middle and at the top, with screw clamps, and heated from the inside with a hairdryer. By tightening the clamps, the surface is not completely conical, but the flask will be removed from the crucible. You just need to use worm-drive clamps (see figure on the right) or their homemade equivalents. Any other clamp will deform the pipe across. The flask from it will most likely come off the crucible, but it will not last long or will crack during the first melting.

The composition of the mixture used by the author is 7 volume parts of ground fireclay, 3 parts of pottery or oven clay and 1 part of ground graphite. A. Ramir also gives a recipe with 2 parts of graphite, but in terms of reducing power this is clearly too much, and the likelihood of cracking a crucible from a 7:3:1 mixture will be reduced to zero if the fireclay is crushed into dust in a mortar or ground in a mill (see above) .

It is necessary to soak the fireclay brick, as A. Ramir advises, only before crushing it using the artisanal method he described. The dry components are mixed until completely homogeneous in the specified sequence (fireclay, clay, graphite) and mixed with water with continuous stirring until the consistency is as described above. There is no need to knock the air out of this mass, because... it is de-aired during the molding process. The mixture is not stored, so it must be prepared immediately before making the crucible.

To form the inner surface of the crucible, you need to carve a block from hard wood (filled with gray in positions 1-5 of the figure), sand it and, very preferably, walk over it with leather until the surface is completely smooth. In the center of the surface of the block that forms the bottom of the crucible, drill a blind hole and insert a toothpick or, better, a round smooth plastic stick from an ear picker into it. The match that A. Ramir used is not the best option - when pulled out, it often breaks, and as a result the product is damaged.

Note: The use of any lubricants when forming a crucible is unacceptable - they will be absorbed into its material, and the crucible will burst from heating.

The mold is filled with the mixture in layers of 15 mm, and each layer is compacted with a wooden tamper. This is the most critical stage: bubbles and uneven compaction of the mixture are unacceptable. When approx. remains to the top of the flask. 12 mm, the mixture is compacted with an already turned lid with a hole for the rod in the center, pos. 2. The mixture is added in layers of 1-2 mm until the gap between the very tightly pressed lid and the upper edge of the investment box reaches 1-1.5 mm, pos. 3. If the gap is larger, part of the mixture can be taken away. Next, the lid is removed and the rod is carefully pulled out of the block using pliers, the lid is put back and the mold is turned over. A handle is attached to the bottom of the block with self-tapping screws and, carefully turning it back and forth, it is pulled out of the casting.

Note: If the rod is not inserted into the bottom of the block, it will be impossible to remove it without destroying the casting - the vacuum under the block will not work.

The formation of a crucible with a flat bottom (which is 1.2 kg) has its own peculiarities - you can’t just pull it out. Therefore, when the compacted mass rises to the flat top of the block, a circle of toilet or filter paper is placed on it.

Now the hole from the rod and minor defects in the inner surface of the crucible are sealed with the same mass. It must be completely smooth, otherwise the probability of destruction of the crucible during melting is quite high, so after correcting the defects it must be smoothed out. The best way to do this is to line it with toilet paper (item 4), insert a block (item 5), and turn it several times.

All that remains is to remove the flask. To do this, it, together with the crucible, is turned over again into the working (for the crucible) position, a round wooden block is placed and the flask is carefully pulled together, pos. 5 and 6. If the flask is plastic, then its protruding upper edge is slightly bent outward in several places with your fingers; Most likely, the flask will come off like clockwork after this.

And finally, the finished casting is dried. Equipment – ​​kitchen stove with oven. The casting is placed upside down on a baking sheet and placed in the oven. They heat for half an hour on the lowest gas, then another half an hour on medium (the temperature according to the built-in thermometer is about 150 degrees) and another 2 hours on full. After this, turn off the fire and leave the casting in the oven to cool until tomorrow morning. Do not open the oven during the entire drying period!

Before use, the crucible must be checked for hidden cracks. To do this, hold it by the bottom with your fingertips and tap it with your nails in a circle from top to bottom. Every knock should ring. If somewhere it doesn’t ring, it’s a defect, you can’t melt with this. Annealing is not required for a crucible manufactured using this technology. It rings everywhere - you can immediately melt in it.

What for?

A reader interested in home metallurgy “for general development” may have a question: why all this trouble? Not everyone wanders around with a metal detector in the forest after the rain, not everyone is keen on smelting damask steel at home, and not everyone has in mind hundreds of centners of old electronics, from which tens of grams of gold, platinum, and palladium can be extracted.

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Unlike industrial equipment, a homemade furnace for melting metal is a compact device. Such portable equipment can be used to smelt, harden or smelt non-ferrous metals.

A furnace for melting metal is a body made of fireclay bricks. The binding element is clay. The firebox is designed to burn coal. There is a hole at the bottom through which the air is blown into the inferno. At the bottom there is a cast iron grate called a grate. Coke or coal is laid out on it. It can be removed from the old stove. Sometimes refractory bricks are laid on edge when forming the body. The finished structure is fastened from the outside with a metal belt.

A furnace for melting metals must have a crucible. It can be an enameled or cast iron cauldron. The location of the crucible is next to the burning coke. To improve airflow, a fan is installed nearby. The equipment is used for steel smelting, but can be used as a furnace for cast iron smelting.

Electric furnaces for melting metal

The basis of such a stove is asbestos, which can be replaced with tiles. Electrodes installed in a melting furnace with your own hands must have a voltage of 25 V.

They are made in the following order:

• They are machined from the brushes of an electric motor.
• 6 mm holes are drilled into the assembly.
• A wire with a cross section of 5 mm is passed through them.
• A nail is driven in to secure the wiring.
• In order to improve contact with graphite, the file makes notches.

Mica is placed inside the furnace as a heat insulator. When connecting to the network, you need to use a step-down transformer. After production, the oven turns on and runs for some time in idle mode.

Muffle furnace

Muffle furnaces are often used for heat treatment of parts. Such equipment is characterized by a wide temperature range, from 20 to 1000 degrees.

A muffle furnace for hardening metal operates on different types of energy. However, at home it is better to use a unit that runs on electricity. Hardening is carried out in the furnace muffle.

A do-it-yourself muffle furnace is made in several stages:

• The muffle is made from fireclay bricks. Due to the round shape of the oven body, their corners are beveled. In each brick, grooves are selected where the spiral is laid.
• If the muffle furnace for melting is made from an oven, then the inside is lined with fire-resistant bricks. Grooves for the spiral are cut into the masonry.
• The chamber, made of refractory brick, is placed in a housing made of steel. Insulation is placed on the bottom. The gap between the side walls of the chamber and the housing is 4 cm, where the insulation is inserted. The top consists of 2 layers of metal and insulation.
• Holes are drilled in the housing, and the ends of the spiral are brought out through them, which are connected to the network cable.
• When using an oven, no insulation is required. It is already provided for in it.

Aluminum smelting

Making a furnace for melting aluminum with your own hands is a real thing. In industrial production, units with the name - rotary-type ovens - are very expensive.

To understand how to make a furnace for melting aluminum, you need to understand their operating principle. There are several types where non-ferrous metal is melted.

Mini oven

Take a car wheel and bury it in the ground so that the top cut does not protrude outward. A hole is made in the middle for the pipe. One end is passed into the hole, and the other is brought out. A cooler is placed on it to pump air. The smelter is filled with coals and aluminum scrap. Air is supplied and the temperature rises.

Metal tank

You can make a furnace for aluminum from a metal tank. For example, the body of a top-loading washing machine. The interior of the structure is lined with refractory bricks. A pipe for air supply is mounted below. Thus, portable equipment is obtained.

From the bottle

One of the unusual ways in which aluminum is melted. Nichrome wire is wound around the bottle. The surface of the bottle is first lubricated with oil. A mixture of liquid glass and clay is applied on top. Drying is carried out for a week. Then another layer of wire is wound and clay is applied. After 7 days, the bottle is removed and only the heat-resistant shell remains. Voltage is connected to the ends of the wire to glow the nichrome, and raw materials are loaded into the hearth.

Lead smelting

An electric furnace for melting lead consists of the following elements:

• A round casing made of stainless steel, inside of which there is insulation. It is attached with brackets to the wall.
• An industrial heating element is supplied from below.
• There is a rotary type valve on top.
• A sensor that is located 3 cm from the bottom.
• There is a temperature regulator on the side.

By setting the regulator to a certain temperature, we warm up the device. The lead inside melts. At the end of the melt, a mold is placed underneath and the valve opens. Molten lead fills the interior of the mold.

Copper smelting

At home, you can use foam concrete material to melt copper. 2 cylinders with a diameter of 100 mm are cut from such material. The height of one is 100 mm, and the second is 15. Laying one on top of the other, a hole with a diameter of 15 mm is drilled in the middle. In the larger cylinder, in the middle, a funnel-shaped hole is made to a depth of 85 mm. In the middle of the cylinder, on the outside, a groove is cut and tied with wire. It is needed to ensure that the part does not fall apart due to temperature.

An adapter is placed on the gas stove. A larger cylinder is placed on top so that the conical funnel is directed upward. The top is covered with a small cylinder with a hole. When lighting the burner, lower a piece of copper rod into a small hole until it touches the wall of the funnel. After a minute the rod will melt.

Melting gold and silver

A furnace for melting gold is easy to make at home. It is also applicable for smelting silver.

The operating procedure is as follows:

• A fireclay brick is taken and cut into 2 parts. Using a Pobedit drill with a diameter of 48 mm, a through hole is made in one half, in the middle. And in the second hole is drilled to half the height.
• A spiral is drawn through the hole and both halves are tightened with bolts, holes for which are drilled from the sides.
• A graphite crucible is installed on top.
• A metal frame is made and both halves are inserted into it.
• All side gaps are covered with clay.
• Voltage is applied to the removed ends of the spiral.
• Pieces of gold or silver are thrown into the crucible.
• During the heating process, the non-ferrous metal melts.

Making furnaces for melting metal with your own hands is a complex process, but doable. To do this, you need to study the characteristics of the types of equipment. Decide which one is most preferable to the given conditions. Manufacturing costs will quickly pay for themselves.

A homemade melting furnace can be made from graphite, cement, mica or tiles. The dimensions of the furnace depend on the power supply and the transformer output voltage.

The homemade melting furnace heats up gradually, but reaches significant heat. For this design, it is necessary to install a voltage of 25 V on the electrodes. If an industrial transformer is used in the design, then the distance between the electrodes should be 160-180 mm.

The process of making a homemade melting furnace

You can make a melting furnace with your own hands. Its dimensions will be 100x65x50 mm. In this design you can melt 70-80 g of silver or other metal. Such possibilities for a homemade melting device are very good.

Materials and tools:

• brushes from a high power electric motor;
• graphite;
• electrode rods used in arc melting furnaces;
• copper wire;
• nails;
• mica;
• cement tiles;
• brick;
• metal pan;
• carbon graphite powder;
• fine conductive wire;
• transformer;
• file.

To make a melting furnace with your own hands, you can use brushes from a high-power electric motor for the electrodes. They have excellent current carrying wire.

If you cannot purchase such brushes, you can make them yourself from a piece of graphite. You can use an electrode rod, which is used in arc melting furnaces.

On the sides of this rod, you need to make 2 holes with a diameter of 5 mm, then, to add strength, carefully hammer a nail of suitable size into it. To improve contact with graphite powder, using a file, it is necessary to make a mesh notch on the inner surface of these electrodes.

Mica is used to make the inner surface of the stove walls. It has a layered structure and therefore can be used as a good heat-insulating screen.

The outside surface of the structure must be covered with cement or asbestos tiles, which have a thickness of 6-8 mm. After installing the walls, they must be tied with copper wire.

A brick should be used as an insulating stand for the device. A metal tray is installed underneath. It should be enameled and have sides on the sides.

Then you need to make carbon graphite powder. It can be prepared from unnecessary rods. It is better to do the work with a file or hacksaw for metal.

When using a stove, graphite powder gradually burns out, so it needs to be topped up occasionally.

To operate the device, a step-down transformer with a voltage of 25 V is used.

In this case, the network winding of the transformer must have 620 turns of copper wire, which has a diameter of 1 mm. In turn, the step-down winding should have 70 turns of copper wire. This wire must have fiberglass insulation and a rectangular cross-section measuring 4.2 x 2.8 mm.

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How to make a transformer?

If you cannot buy a transformer with a high enough power, it can be made from several similar transformers with lower power. They must be designed for the same network voltage.

For this purpose, it is necessary to connect the output windings of these transformers in parallel.

Can be made. To do this, you need to prepare L-shaped metal plates with an internal cross-section of 60x32 mm. The network winding of such a transformer is made of enameled wire with a cross-section of 1 mm. It should have 620 turns. In this case, the step-down winding is made of wire having a rectangular cross-section with dimensions of 4.2x2.8 mm. It should have 70 turns.

After installing the furnace, it is connected to the transformer using a copper wire having a thickness of 7-8 mm. The wire must have external insulation so that a short circuit does not occur during operation of the oven.

When the oven is completely ready for use, it must be warmed up well. In this case, the organic substances in the structure should burn out. During this procedure, the room should be well ventilated.

The device will work without soot. After this, the operation of the furnace is checked. If everything works fine, then you can start operating the device.

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How is metal melted in a furnace?

Metal melting is performed as follows. Using a small spatula (in the center of the stove), you need to make a small hole in the graphite powder, put scrap metal there and bury it.

If the pieces of metal to be melted have different sizes, then first of all lay a large piece. After it melts, add small pieces.

In order to check whether the metal has already melted, you can rock the unit a little. If the powder ripples, it means the metal has melted.

After this, you need to wait until the workpiece has cooled, then turn it over to the other side and melt it again.

This procedure must be repeated several times until the metal takes the shape of a ball. In this case, it is considered that the melting of the metal was performed with high quality.

If you need to melt sawdust or metal shavings of inexpensive metals, you need to pour them into the powder well and perform normal melting.

More expensive or precious metals should be placed in a glass medicinal ampoule and melted together with this ampoule. In this case, a film of glass is formed on the surface of the molten metal, which can be easily removed by placing it in water.

Metals that melt easily should be placed in iron containers. If it is necessary to make an alloy of various metals, then the metal that melts less readily is put into the furnace first. After it melts, add fusible. For example, to obtain an alloy of copper and tin, you must first put copper into the powder, and then tin. To obtain an alloy of copper and aluminum, first copper is smelted, and then aluminum.

This device can melt metals such as tin, iron, copper, aluminum, nickel, silver, and gold. After melting the metal, it is forged. It is forged on an anvil using a hammer. In this case, it is necessary to frequently heat the workpiece on a fire until red-hot, and then hammer it again. After this, the metal is placed in cold water and then hammered again until the workpiece reaches the required dimensions.

Under no circumstances should metals such as lead, magnesium, zinc, cadmium, cupronickel be melted, since when they burn out, they form very toxic yellow smoke, which has a detrimental effect on human health. You cannot melt silver contacts from relays and other devices because they contain up to 50% cadmium.