Crucible made of fireclay bricks. Crucible: purpose, principles of melting, manufacturing, options, diagrams

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). The general line of development of large-scale metallurgy is to reduce the number of processing steps, up to the release of conditioned metal directly 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, remains of crystallites 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 with them chemical compounds, 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 they are removed from the hydrogen chamber and heated, 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 metal: it does not spoil the metal and does not give by-products with a strong excess of 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. Remember how the 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 the 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):

ceramic chemically neutral;
ceramic graphite;
graphite;
cast iron;
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 no energy absorption 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 amounts of lead into fishing weights, etc.

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 required strong recovery old oxidized metal, 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 used mainly 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 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 in an EMF from any homemade generator for, then installation on 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? aluminum alloys, see eg. 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:

Steel;
Ceramic neutral;
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

The composition of the mixture for forming a neutral ceramic crucible is 7 parts of fireclay clay, 1 part of finely ground fireclay (up to the 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.

To melt metals, special heat-resistant bowls called crucibles are used. They are very popular in jewelry workshops, laboratories and the metallurgical industry. But for a full-fledged process, it is not enough to acquire a simple object with a heat-resistant surface, because different iron requires its own product, which must correspond to the chemical composition and be suitable for a specific temperature regime. These facilities also produce a finished alloy, which remains to be given the correct shape.

Sometimes it happens that such devices may be needed in private business, but purchasing them is expensive. Therefore, it is more profitable to make a crucible with your own hands - you can save a significant share of the budget. Yes, the procedure will require certain skills and patience, but in the end you will get a vessel that is not inferior to factory analogues. It is also important to decide on the types of objects to be melted in order to make a suitable bowl. If you plan to work with different metals, it is recommended to create several products.

As an alternative, you can use an electric crucible, which you can do yourself without much difficulty. It has several uses, but the main one is gold refining.

General manufacturing steps

To begin with, the raw materials are prepared, and here everything depends on the model of the future tank. It is better to take components with a reserve, because the first thing is unlikely to work out. Also, for safety reasons, you should carry out production away from open fire, and choose a well-ventilated area.

It is safer to carry out work in a garage or special extension.
The second stage is mixing the materials and giving the casting the necessary parameters. For these purposes, plaster molds are used. Creating the outlines is not difficult, and such information is easy to find on the Internet. Then a homogeneous material is pasted over the outer part of the model, forming a future homemade refractory crucible. It is also important to give it the required depth and thickness.
And the last step is the drying process: the workpiece is placed in a cardboard box and covered with a lid. This will allow the casting to dry and remove excess water from it. Sometimes heat treatment may be required, however, the important point is to control the annealing temperature and protect the skin of the hands and face. If the heat is too intense, the item will burst and there is a chance of severe burns. Detailed instructions on how to make a crucible yourself and at home will be described in the following chapters.
Making a clay crucible
Here you can’t do without fireclay clay, which is sold in any building materials store. It tolerates extreme thermal effects very well, is cheap and there are unlikely to be any problems finding it. As a last resort, you can make a crucible from crushed fireclay bricks. You will also have to buy liquid glass and mix all the ingredients for a homogeneous base. The proportions look something like this:
7 units of clay;
3 units of fireclay;
10 spoons of liquid glass.

All components are added in stages: clay and fireclay are mixed until smooth, and water is gradually added to them. The main goal is to create a mixture that will not stick to your hands. When the required consistency is obtained, glass is added and everything is thoroughly mixed. The main thing here is to bring the object to a state where the plane stops cracking. The mixture is ready, and for storage it is recommended to use thick cellophane, or wrap it in 7-10 layers of film.
Before sculpting, you will have to remove any remaining air by hitting the substance about 8-12 times on a hard surface.

The mixed material is applied inside the model, its depth and thickness are formed. It is better to create a semicircular bottom, which will give a greater effect during future melting of iron filings. Also, the substance must be pressed tightly against the model so that air does not form between the planes, and for greater convenience it is recommended to wet your hands with water.
Afterwards, the tank is sent for drying: it is placed in a container made of cardboard or plastic and placed in a dry place. A few hours will be enough to remove any remaining moisture. Also, the product will settle a little, and it will be easy to remove it from the mold. A refractory vessel made of fireclay bricks will last for a long time of use, however, the last point of creation should be the firing procedure in a furnace and at T = 800 °C. And the thing can be used for its intended purpose. For ease of use, you will need a crucible furnace, which you can make yourself. For simple installation, you can weld a structure from several pipes to form a cylinder. Usually it is fixed on two parallel posts so that it does not touch the ground. And here the thickness of the walls (minimum 5 mm) and the stability of the product are taken into account (it must easily withstand T = 1600 °C or more).
How to make a graphite crucible
low overall weight;
resistance to hot alloys;
good thermal conductivity;
strength increases with increasing temperature.

If you take the easy route, you can take a graphite rod, and the crucible is almost ready. All that remains is to attach the bottom.
If the required tube is not found, everything can be done using two molds of different sizes, which are inserted one into the other, and the free space will allow you to give the desired dimensions. Initially, you need to pour the mortar into an empty container, and you should not spare it. The fact is that the powder will compact and settle. Next, add liquid glass (about 15 ml) and mix everything thoroughly. It is recommended to place the mixed mass in a large cylindrical container (you can use a plastic cup) and press a hole into a small one, leaving the bottom thick enough.
As a result, a vessel will come out, which is given time to dry. In this case, heat treatment will also be required to remove excess liquid. If all the steps were correct, then you will have a high-quality graphite crucible, made by yourself.
Assembling a cast iron crucible
This type is the worst, but sometimes it brings good benefits. All that is required is to place a cast iron glass of a smaller diameter in a metal bowl, and fill the free space with sand and clay.
Next, everything is heated in the oven until the mixture melts and takes on the same type of substance. Afterwards, the cup will harden, and iron can be melted in it. This is basic information on how to make a crucible at home and at minimal cost.

If you are going to do aluminum casting at home, then you will need not only the muffle furnace itself, but also a crucible for the muffle furnace. The good news is that all of this can be made very easily and at minimal cost. When I did and described the process in my Dimanjy TechnoBlog, I actually ended up with 0 rubles, because... all the materials were lying around and rusting near the barn, trying to end up in a landfill, and only mother laziness saved them from such a deplorable fate.

I also made the crucible for the muffle furnace myself from a regular piece of thick-walled pipe of a suitable diameter. But, as I later learned on the ChipMaker forum, I was a little hasty. And that's why.

The easiest way to make a crucible for a muffle furnace is to weld it from metal, or rather from a piece of pipe. But the fact is that the design of my muffle furnace is equipped with open conductive heating elements. And how come I didn’t get electrocuted during my first melting of aluminum at home! Intuitively, I very carefully inserted and removed the crucible from the working chamber of my muffle furnace. By the way, it is often called a “crucible furnace” precisely because non-ferrous metal is melted in a crucible. Now I need to modify the design of the stove, providing it with a special lid with an opening sensor, the signal from which would turn off the electricity from the heating elements, saving me from electric shock. But that’s not about that now.

As I said, making a metal crucible is very simple. We take a pipe of suitable diameter. It is very desirable to have a wall thickness of at least 4-5 mm, otherwise a thinner-walled crucible will quickly burn out, and during the melting process, liquid aluminum may flow out of the crucible, thereby short-circuiting the exposed spirals of the heating elements of the muffle furnace. To prevent this from happening, you can drill a drainage hole in the bottom of the muffle furnace. Then all the aluminum will flow out through it, burning our heels, but saving our mini-smelter from failure. By the way, this was also advised to me on the forum. I didn't think of this myself.

So, we take a pipe, clean it and weld it at one end with a metal plate, which we then lightly file with a grinder to give it a more or less rounded shape.

You can, of course, not clean it up. Then all this will burn on its own in the working chamber of the muffle furnace, but I didn’t really want to breathe it all in later, so I wasn’t lazy and polished

Then we saw off the pipe so that we get a glass of the required height - this will be our crucible.

As you can see from the picture, I attached a spout to my crucible and ground it a little with a grinder and polished it with a file. The spout is also very simple to make - it is a piece of metal corner cut at an angle. At what angle to cut - you can guess for yourself. Twist the piece of angle in your hands, mentally drawing the cutting plane of the angle grinder through it.

I also welded an M8 nut to the opposite side of my crucible. A handle is screwed into it for immersing and removing the crucible from the crucible furnace. Just a few turns of the handle are enough, and our crucible holds tightly, eliminating accidental tipping or spilling of molten aluminum into your slippers. Such safety measures are especially relevant for melting non-ferrous metals at home.

I made the handle from an ordinary piece of reinforcement, welding an M8 bolt on one side. The only drawback of such a crucible handle is the inconvenience of casting. But this can be easily corrected by welding an additional device onto our crucible so that it is convenient to intercept. When I do this I will update the post. Follow the updates on TechnoBlog Dimanjy

Many craftsmen make crucibles for melting metals with their own hands, they have perfected their technologies, and the quality of such products is quite good. If making a crucible with your own hands is a new thing for you, then this review will help you decide which path to take next: make the crucible yourself or buy it from a direct manufacturer without intermediaries.

Let's start with the fact that the materials for making a crucible with your own hands can be pieces of stainless steel pipes, cast iron, clay, fireclay chips, charcoal, graphite, etc. It would seem that the materials are cheap, the cost of a homemade crucible should also be low. However, in practice, when making a high-quality and cheap crucible at home, craftsmen are faced with a number of problems. In this review we will not dwell on graphite crucibles and their burnout problems when melting metals. Here we will dwell in more detail on the problems of making ceramic crucibles with our own hands. I will describe the most common of them:

The main problem is the heterogeneous composition of the clay masses. Different clay deposits are characterized by different compositions, and in order to obtain high-quality ceramic products, clays of a certain qualitative and quantitative composition are required.
Clays used to make ceramic crucibles shrink; different clays shrink differently. If you prepare crucibles in large batches and purchase one type of clay in large quantities, then this is not a problem. The shrinkage of the clay is calculated in advance, and the finished product is obtained in a given shape and the variation in overall dimensions is extremely small. But if ceramic crucibles are made from case to case, different batches of clay are used, then maintaining the required dimensions turns out to be problematic, and the percentage of defects increases.
Homemade ceramic crucibles can withstand a small amount of melting; when using sodium tetraborate (borax), homemade ceramic crucibles quickly become covered with microcracks and become unsuitable for further melting of metal.
Homemade crucibles are often not sufficiently dried, which is why, when the metal melts, additional stress appears in the body of the crucible and the crucible bursts.
Homemade ceramic crucibles are thick-walled and require more heating time; energy consumption increases when melting metal.

The best option for melting most metals is a ceramic crucible, but not every ceramic crucible is suitable for melting metal. Let's consider this issue in more detail. Let's start with the fact that ceramic crucibles, which are most often found on the Russian market, are divided into porcelain, corundum and quartz ceramic crucibles. are not suitable for melting many metals due to their relatively low fire resistance. fire-resistant and durable, but when melting metal there is one very important limitation: the corundum crucible cannot be sharply heated and cooled, the cooling rate of the corundum crucible is 2-3° S/minute. Suitable for melting metal under changing temperatures

A crucible made of quartz ceramics is inert towards metals, fireproof, chemically resistant, and can withstand sudden temperature changes. For an inexperienced person, making a high-quality crucible from sintered quartz ceramics will require unreasonably large amounts of time, material and energy for experimental work. Thus, for a beginner it is much more profitable not to make a crucible for melting metals with your own hands, but to buy it directly from the crucible manufacturer. Prices You can look at crucibles made of quartz ceramics.

A crucible is a special container that can withstand high temperatures and is designed for melting metals. Basically, the crucible is made in the form of a cylinder or cone, although some manufacturers make it in the form of a bowl or boat for more convenient pouring of liquid metal into molds. The crucible is created from refractory materials, most often graphite or cast iron. A simple crucible is ideal for melting not only ferrous metals, but even precious ones. The crucible is perfect for melting silver and gold.

Where to get a crucible for melting silver and gold

Buying a crucible for melting metals is not difficult, because there are many manufacturers involved in the creation of crucibles, but it is best to immediately purchase a ready-made induction installation with a crucible, so that there are no problems later, and the melting is carried out in a short period of time. Induction melting furnaces are assembled with an already installed crucible of the size required by the client. The melting furnace is configured with all the necessary characteristics and melts any metals, allowing you to obtain high-quality alloys.
You can also make a crucible with your own hands, but it is more suitable for individual use, for example, to melt a certain amount of lead and cast your own bullets (for hunters). To use this equipment on an industrial scale, it is best not to be independent and purchase ready-made induction equipment that has a crucible and is ready to begin the work process.

Materials for creating a crucible

It is very important to pay attention to the material from which the crucible is made, so that the metal that will subsequently melt in it does not enter into an unnecessary chemical reaction.
Typically, crucibles are made from:

Ceramic mixture. The ceramic mixture includes materials that have increased resistance to high temperatures - clay, boron compound, metal carbide and many others.
Black metal. The most refractory metal available today is cast iron, making it an excellent choice for creating a crucible.
Non-ferrous metal. As a rule, non-ferrous metal is rarely used to create a crucible, because such a container will not be cheap. However, it is worth noting that the following metals are perfect for these purposes: titanium, nickel, molybdenum, etc.
Non-metallic materials are used to create a crucible much more often than all the others listed above. The crucible can be created from: graphite, clay, quartz sand and other similar elements.

A simple crucible for melting silver and gold can be made independently using available containers from the above materials, but for its use on an industrial scale we recommend purchasing a ready-made installation.