How to make a crucible or melting furnace with your own hands. Do-it-yourself crucible for a muffle furnace Chamotte clay crucible

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 it is 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

It is not difficult to buy a crucible for melting metals, 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 later there are no problems, and melting is carried out in a short period of time. Induction melting furnaces are assembled with an already installed crucible of the volume required by the customer. The melting furnace is configured with all the necessary characteristics and melts any metals, allowing you to get 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 start the workflow.

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 be melted in it does not enter into an unnecessary chemical reaction.
As a rule, crucibles are created from:

1. Ceramic mixture. The composition of the mixture of ceramics includes materials with increased resistance to high temperatures - clay, boron compound, metal carbide, and many others.
2. Black metal. The most refractory metal today is cast iron, so it is great for creating a crucible.
3. Nonferrous metal. As a rule, non-ferrous metal is rarely used to create a crucible, because such a container will turn out to be expensive. However, it is worth noting that the following metals are perfect for this purpose: titanium, nickel, molybdenum, etc.
4. 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 improvised containers from the above materials, however, for its use on an industrial scale, we recommend purchasing a ready-made installation.

Almost every item has several types and purposes. This truth also applies to ovens.

There are furnaces for heating rooms, for cooking, and there are special devices for melting metals or for storing them already in molten form.

Such devices are called crucible melting furnaces. They have a specific purpose and therefore the list of enterprises where they have found their application is quite small. These are mainly factories and laboratories. But what to do if you need to melt metal for any purpose at home? It is very expensive to buy such equipment, but it is quite possible to make it yourself. This requires minimal knowledge in this area, desire and time.
A crucible furnace is a container made of refractory material in which metal is melted by heating to a certain temperature. The main materials from which the crucibles are made:
- ceramics;
- graphite;
- cast iron.
Crucible furnaces are used both in factories where more metal products are made, and in small enterprises, for example, for the manufacture of jewelry.
Ceramic ovens are the best option. When metals are melted in a ceramic crucible, no changes occur in the substance itself. Therefore, in such crucibles, even base metals or alloys of cobalt, chromium or palladium can be melted without problems.
Graphite crucibles. Such furnaces are characterized by a long service life and high resistance to oxidation, which makes them universal for melting all metals and especially alloys based on zinc and brass. In addition, they are often used in induction furnaces. Graphite crucibles can withstand very high temperatures, such as eight hundred degrees to melt aluminum.
Cast iron crucibles are perhaps the worst of the three listed. They have high reactivity, rapid oxidation and interaction with other metals, and cast iron does not resist high temperatures well. For these reasons, cast iron crucibles are very rare, but inexpensive and readily available.
This article will discuss how to make three types of homemade crucibles.

Crucible furnaces. Assembly of the inductor
The heating element of the crucible arms at home is usually an inductor. It has a cylindrical shape with a cavity inside. A self-made crucible with metal shavings is placed in this cavity. The inductor is made of refractory material, inside it is a wire winding, most often copper wire is used. With the help of a special generator, a current is supplied to this winding, which creates an electromagnetic field. Which, in turn, creates an eddy current in the crucible and in the metal placed in it. They melt the chips. The inductor itself is assembled from 4 vacuum tubes connected in parallel. Such an inductor can be connected to a conventional outlet.
There is another option for assembling an inductor with your own hands from an electromagnetic core and two winding layers. The first layer is 10 turns of copper wire with a thickness of 4 mm, and the second is one turn, the material for which is a metal plate with a cross section of 15 * 5 millimeters. The electromagnetic core has a U-shape and is a set of steel plates. The first winding is made around the plates, which is placed in an insulated case, the secondary winding connects the core and metal bars, between which there must be a distance equal to the size of the crucible. The whole structure is placed in the furnace body.
So, it turns out the furnace in which the inductor is located. Wires go from the inductor to the outlet. A crucible is placed in this furnace in such a way as to enclose the bars. If it is placed correctly, a buzz will be heard, indicating that tension has appeared and melting has begun. If there is no sound, then with the help of the handle you need to move the crucible until the circuit is completely closed.

Assembling the cast iron crucible
A metal casing is taken and a glass made of cast iron is placed in it. Between them, a mixture of sand and clay is poured. A handle is attached to the side. After one or two heatings, the mixture will melt and harden. The crucible is ready. Chips are poured into it and placed in an inductor.

Making a crucible from clay
You can make a crucible of chamotte clay. This is an inexpensive option and also has high resistance to high temperatures. Such clay is used when laying stoves and can be bought at any hardware store. Chamotte clay can withstand temperatures up to 1600 degrees Celsius.
So, you will need fireclay clay (sold in bags in hardware stores), liquid glass (sold there) and ground fireclay. It can be bought or made from fireclay bricks.
In order to make a mixture from which a crucible will be molded in the future, 7 parts of clay, 3 parts of fireclay and 10 tablespoons of liquid glass are taken per liter of dry mixture. Chamotte and clay are mixed until smooth. After that, water is slowly added. In order not to spoil the workpiece, you can pour out part of the mixture, and in the case of a large amount of water, add dry powder. You need to knead until the clay stops sticking to your hands.
Only after the clay of the desired consistency is mixed, glass can be added. When adding glass, you need to carefully knead everything until the clay stops cracking. It is best to add glass in a lump of clay and roll it into a roll, then fold it several times and repeat the procedure until it stops cracking. The material for the crucible is ready. Until the moment when it is used, it must be stored in several layers of cellophane.
There is clay, now to make a crucible you need to take a mold, the easiest way is to use a plaster mold. How to make such a form can be found on any site for gypsum modeling. So, directly making the crucible. Before starting sculpting, you need to beat off all the air from the clay, for this you can lay a newspaper on the floor and throw a lump on it several times with force, ten times will be enough. Now a lump of clay is taken and carefully pressed into the bottom of the mold, after which the walls of the product are formed in small lumps. Their thickness can be controlled along the edge of the mold. It is very important to carefully press the clay into the mold so that air cushions do not form there. After the crucible is fashioned, you need to make a smooth inner surface. To do this, it is enough to moisten the clay with water.
After that comes the drying time. The form with clay is placed in a cardboard box and covered with a lid. After about seven hours, all the water from the clay will evaporate and the shape of the future crucible will “sit down” a little, so getting it out of the mold is not particularly difficult. After that, the crucible continues to dry in the same box, as it dries, all defects will be eliminated by themselves and the pot will become gray in color. Sometimes small cracks may appear. They can be covered with wet clay. Next, the pots are fired at a temperature of 800 degrees in a muffle furnace. After firing, the crucible is ready for use.

graphite crucible
Graphite is a material that has many unique properties. Positive qualities of graphite:
- resistance to molten metals;
- increase in strength with increasing temperature;
- high heat resistance and thermal conductivity;
- low specific gravity.
To make a crucible from this material you will need:
- graphite powder;
- solid graphite;
- felt;
- graphite tube;
- fireclay mortar;
- magnesite.
Some of these materials can be used as independent units. For example, a graphite tube is in fact already a crucible, it is enough just to make a bottom in it.
The principle of manufacturing from all materials is the same. Consider the example of a mortar. Two forms are made. Can be rolled from thick paper to make it easier to remove later. The outer mold has the configuration of a hollow cylinder, while the inner one is just a cylinder. A small cylinder is inserted into a larger one. The mixture will be poured between them. The form is placed in a plastic cup and mortar powder is poured into it. You need to fall asleep with a slide, as he will sit down when you need to tamp. 15 cubes of liquid glass are poured into this powder using a syringe. Everything is mixed and the consistency of shortcrust pastry is obtained. Small portions are stuffed into the form.
The result is something like a cup turned upside down. To prevent the form from sticking to the table, it is best to do the entire procedure on cellophane. Then the form is turned upside down and the inner cylinder is removed. It is also best to glue it initially with cellophane or tape. Then, during extraction, the shape of the crucible will not suffer.
After the crucible has dried up, it must be placed in the inductor and heated. This must be done at low temperatures, since all the water should evaporate, despite the fact that outwardly it seems as if it is not there at all. If the crucible is not preheated and immediately begins to melt in it, then it will most likely burst. After warming up, when tapping on the crucible, it will make a ringing sound. This indicates that the crucible is well made.
Following the instructions presented, you can quite easily get a homemade melting furnace that will last no less than a purchased one. The main thing is not to rush, to be careful in work and not to violate manufacturing technologies.

• Date: 04/30/2018
• Category: Magic tools, weapons, devices and armor - Mod Thaumcraft 3, 4, 5, 6
• Views: 2455

How to create

To create this device, we will need an ordinary boiler. We pick up a magic wand and press RMB pointing at the boiler. I want to note that in Thaumcraft 3, when using a wand, 25 vis will be spent, and in Thaumcraft 4, in turn, any wand will do and no magic will be spent from it.
Now we will need to pick up a bucket and collect lava there. Since fire and lava are sources of heat for the crucible. In version 4 of Thaumcraft, you can also use nithor or flowing lava.
In Thaumcraft 4.1, you can improve the crucible using thaumothy, now the tool does not require water. But note that it needs warmth.
It remains to dig a hole and pour lava into it. Putting a cauldron directly on the lava will not work, put any block nearby and put the cauldron. Roughly it all looks like this:

Usage

First, fill it with water (we take a bucket of water in our hands). The water in the crucible must boil after a certain time due to the heat source. Using the thaumonomicon, you now need to find out the necessary aspects for the item you need or to perform a transmutation, after which you will need to throw the items with aspects into boiling water. Further actions depend on the version of the mod.
In Thaumcraft 3, to get a craftable item, you will need to use a magic wand with the required number of charges. If you throw more aspects into the crucible, an equal number of items will be created accordingly or transmutations will be carried out.
In Thaumcraft 4, after you throw aspects into the cauldron, you need to throw the main ingredient (catalyst) and if there are enough aspects in the crucible to complete the reaction, then you will get the desired item. For example, to get nitor, you must add aspects such as Lux, Potentia and Ignis (3 pcs each) to the cauldron, and light dust will serve as the main ingredient. As long as there are enough Aspects in the Cauldron, each Light Dust thrown will yield a new Nithor. If at least one aspect is missing, then the decomposition of light dust will begin.

Important: Essences in Thaumcraft 4 tend to degrade quickly, so we do not recommend loading a huge amount of essences for mass crafting in order to avoid pollution, damage and waste of essence. Essence degradation will make the crafting process of the item impossible or difficult. For example, Lux can turn into Aer or Ignis. The time after which this process will begin is 5-10 seconds.

Improvement

It is possible to "upgrade" the functions of the crucible using auxiliary elements in the game. In Thaumcraft 3, up to 4 stills can be added to a crucible (right-click). They are needed to collect unnecessary aspects for operations.

In Thaumcraft 4, you can add mystical fur to the crucible to speed up the process of boiling water. In this version, stills are not added, but an alchemy furnace is used to separate essences.

Features and facts

• If the player somehow stands on the crucible, he will begin to receive damage in the form of half a heart, at this time the “Corpus” aspect will automatically be added to the crucible.
• If you put on "revelation glasses", you will be able to see all the aspects that are in the crucible. They will show above the crucible.
• With the “Shift” key held down and RMB on the crucible with a magic stick, all aspects in it will turn into an aura, while at the same time turning into damage. If there are stills next to the crucible, then the aspects will go there. Well, if all aspects do not fit into cubes, then, accordingly, the remaining ones will turn into damage.

" News

We make a mini-smelter for melting aluminum | We make a mini smelter for melting aluminum

For melting metals, special heat-resistant bowls are used, called crucibles.

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 fit a specific temperature regime. Also, in these facilities, a finished alloy is produced, which remains to be given the correct shape.

DIY crucible

Sometimes it happens that such devices may be needed in a private matter, but their purchase is an expensive pleasure.

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 down in order to make a suitable bowl. If you plan to work with different metals, it is recommended to create several products.
Smelter, crucible, do it yourself

Material selection

Here, a serious role is played by refractory components, which include:

Ceramics - the average option, great for personal use. In this ware there are no reactions that can change the structure of the metal, and it is excellent for cobalt, chromium and palladium. Clay is a substance that is used in the manufacture of crucibles for jewelers. This component has a high fire resistance and can withstand up to +1600 °C. If a person wants to create jewelry in his own room, but does not know what to make dishes for remelting, then this option is definitely the best. Graphite is great for melting galvanized and brass alloys, and its main advantage is durability. As for the operating temperature, it should not exceed +800 °C. Cast iron. Crucibles from this substance are rare, and belong to budget categories. Still, dressings of this kind will have disadvantages in the form of rapid oxidation, low resistance to heat and fast production (up to 30 heats).

Varieties of homemade crucibles
Crucible for lead DIY

As an alternative, you can adopt an electric crucible, which is done by hand without much difficulty. It has several uses, but the main one is gold refining.

General manufacturing steps

To begin with, raw materials are being prepared, and it all depends on the model of the future tank.

It is better to take components with a margin, because the first thing is unlikely to work out.

Also, for safety reasons, you should carry out production away from open flames, and choose a well-ventilated area.

It is safer to work in a garage or a special extension.

The second stage is the mixing of materials and giving the casting the necessary parameters. For these purposes, plaster molds are used.

Creating outlines is not difficult, and such information is easy to find on the Internet.

Then, the outer part of the layout is glued with a homogeneous matter, forming a future home-made refractory crucible. It is also important for him to give the required depth and thickness.

Clay crucible in the process of drying

And the last step is the drying process: the blank 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 crucial point is to control the annealing temperature, and protect the skin of the hands and face.

If there is too much heat, the object 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 not do without fireclay type clay, which is sold in any building materials store.

It perfectly tolerates extreme thermal effects, it is cheap and there are hardly any problems with finding it. In extreme cases, 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 like this:

7 units of clay; 3 units of fireclay; 10 spoons of liquid glass.

Clay crucibles

All components are added in stages: clay together with fireclay are mixed to a homogeneous consistency, 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 advised to use thick cellophane, or wrap it in 7-10 layers of film.

Before sculpting, you will have to remove the remaining air by hitting the substance about 8-12 times on a hard surface.

The mixed material is applied inside the layout, its depth and thickness are formed.

It is better to create a semicircular bottom, which will give a greater effect in the future melting of iron shavings.

Also, the substance must be pressed tightly against the layout so that air does not form between the planes, and for greater convenience, it is recommended to wet your hands with water.

After 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 is enough to remove residual 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 need a crucible furnace, which is done by hand.

For simple installation, a structure of several pipes can be welded 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 (at least 5 mm) and the stability of the product are taken into account (it must easily endure 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 go the easy way, then you can take a graphite rod, and the crucible is almost ready. It remains only to attach the bottom.

Graphite crucibles in various sizes

If the necessary tube is not found, everything can be done using two molds of different sizes, which are inserted one into one, and the free space will allow you to give the desired size.

Initially, you need to fill the mortar into a free container, and you should not feel sorry for it. The fact is that the powder will compact and settle. Next, liquid glass is added (about 15 ml.

) and mix thoroughly.

As a result, a vessel will come out, which is given time to dry.

In this case, heat treatment will also be required, due to which excess liquid will be removed.

If all the steps went correctly, then there will be a high-quality do-it-yourself graphite crucible.

Assembling the cast iron crucible

This type is the worst, but sometimes it is of good use. 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.

After the cup will harden, and iron can be melted in it.

This is the basic information on how to make a crucible at home and at minimal cost.

Please select a piece of text and press Ctrl+Enter.

Source: http://promts.net/view/2011546598-tigel-svoimi-rukami/

Melting furnaces: types and arrangement of crucibles, making a do-it-yourself crucible from graphite, clay or cast iron

Almost every item has several types and purposes, as well as stoves.

There are furnaces for heating rooms, for cooking, and there are special devices for melting metals or for storing them already in molten form. Such devices are called crucible melting furnaces.

They have a specific purpose and therefore the list of enterprises where they have found their application is quite small. These are mainly factories and laboratories.

But what to do if you need to melt metal for any purpose at home? It is very expensive to buy such equipment, but it is quite possible to make it yourself. This requires minimal knowledge in this area, desire and time.

A crucible furnace is a container made of refractory material in which metal is melted by heating to a certain temperature. The main materials from which the crucibles are made:

Crucible furnaces are used both in factories where more metal products are made, and in small enterprises, for example, for the manufacture of jewelry.

Ceramic ovens are the best option. When metals are melted in a ceramic crucible, no changes occur in the substance itself.

Therefore, in such crucibles without problems even base metals or alloys can be melted cobalt, chromium or palladium.

Graphite crucibles.

Such furnaces are characterized by a long service life and high resistance to oxidation, which makes them universal for melting all metals and especially alloys based on zinc and brass. In addition, they are often used in induction furnaces. Graphite crucibles can withstand very high temperatures, such as eight hundred degrees to melt aluminum.

Cast iron crucibles are perhaps the worst of the three listed.

They have high reactivity, rapid oxidation and interaction with other metals, and cast iron does not resist high temperatures well.

For these reasons cast iron crucibles are very rare but they are inexpensive and readily available.

This article will discuss how to make three types of homemade crucibles.

Crucible furnaces

The heating element of the crucible arms at home is usually an inductor. It has a cylindrical shape with a cavity inside. A self-made crucible with metal shavings is placed in this cavity.

Inductor made from refractory material, inside it is a winding of wire, most often copper wire is used.

With the help of a special generator, a current is supplied to this winding, which creates an electromagnetic field. Which, in turn, creates an eddy current in the crucible and in the metal placed in it. They melt the chips.

The inductor itself is assembled from 4 vacuum tubes connected in parallel. Such an inductor can be connected to a conventional outlet.

There is another option for assembling an inductor with your own hands from an electromagnetic core and two winding layers.

The first layer is 10 turns of copper wire with a thickness of 4 mm, and the second is one turn, the material for which is a metal plate with a cross section of 15 * 5 millimeters.

The electromagnetic core has a U-shape and is a set of steel plates.

The first winding is made around the plates, which is placed in an insulated case, the secondary winding connects the core and metal bars, between which there should be a distance equal to the size of the crucible. The whole structure is placed in the furnace body.

So, it turns out the furnace in which the inductor is located. Wires go from the inductor to the outlet. A crucible is placed in this furnace in such a way as to enclose the bars.

If it is placed correctly, a buzz will be heard, indicating that tension has appeared and melting has begun.

If there is no sound, then with the help of the handle you need to move the crucible until the circuit is completely closed.

Making a crucible from clay

You can make a crucible of chamotte clay. This is an inexpensive option and also has high resistance to high temperatures.

Such clay is used in laying stoves And you can buy it at any hardware store.

Chamotte clay can withstand temperatures up to 1600 degrees Celsius.

So, you will need fireclay clay (sold in bags in hardware stores), liquid glass (sold there) and ground fireclay. It can be bought or made from fireclay bricks.

In order to make a mixture from which a crucible will be molded in the future, 7 parts of clay, 3 parts of fireclay and 10 tablespoons of liquid glass are taken per liter of dry mixture. Chamotte and clay are mixed until smooth.

After that, water is slowly added. In order not to spoil the workpiece you can sprinkle some of the mixture, and in case of a large amount of water - add dry powder.

You need to knead until the clay stops sticking to your hands.

Only after the clay of the desired consistency is mixed, glass can be added.

When adding glass must be thoroughly mixed until the clay stops cracking.

It is best to add glass in a lump of clay and roll it into a roll, then fold it several times and repeat the procedure until it stops cracking.

The material for the crucible is ready. Until the moment when it is used, it must be stored in several layers of cellophane.

There is clay, now to make a crucible you need to take a mold, the easiest way is to use a plaster mold. How to make such a form can be found on any site for gypsum modeling. So, directly the manufacture of the crucible.

Before starting modeling, you need to beat off all the air from the clay, for this you can lay a newspaper on the floor and throw a lump on it several times with force, ten times will be enough.

Now a lump of clay is taken and carefully pressed into the bottom of the mold, after which the walls of the product are formed in small lumps. Their thickness can be controlled along the edge of the mold.

Highly it is important to carefully press the clay into shape so that air pockets do not form there. After the crucible is fashioned, you need to make a smooth inner surface.

To do this, it is enough to moisten the clay with water.

After that comes the drying time. The form with clay is placed in a cardboard box and covered with a lid.

After about seven hours, all the water from the clay will evaporate and the shape of the future crucible will “sit down” a little, so getting it out of the mold is not particularly difficult.

After that, the crucible continues to dry in the same box, as it dries, all defects will be eliminated by themselves and the pot will become gray in color. Sometimes small cracks may appear.

Graphite is a material that has many unique properties. Positive qualities of graphite:

• resistance to molten metals;
• increase in strength with increasing temperature;
• high heat resistance and thermal conductivity;
• small specific gravity.

To make a crucible from this material you will need:

• graphite powder;
• solid graphite;
• felt;
• graphite tube;
• fireclay mortar;
• magnesite.

Some of these materials can be used as independent units. For example, a graphite tube is in fact already a crucible, it is enough just to make a bottom in it.

The principle of manufacturing from all materials is the same. Consider the example of a mortar. Two forms are made. Can be rolled from thick paper to make it easier to remove later.

External the shape is a hollow cylinder, and the inner one is just a cylinder. A small cylinder is inserted into a larger one. The mixture will be poured between them.

The form is placed in a plastic cup and mortar powder is poured into it. You need to fall asleep with a slide, as he will sit down when you need to tamp. 15 cubes of liquid glass are poured into this powder using a syringe.

Everything is mixed and the consistency of shortcrust pastry is obtained. Small portions are stuffed into the form.

The result is something like a cup turned upside down. To prevent the form from sticking to the table, it is best to do the entire procedure on cellophane.

Then the form is turned upside down and the inner cylinder is removed. It is also best to glue it initially with cellophane or tape.

Then, during extraction, the shape of the crucible will not suffer.

After the crucible has dried up, it must be placed in the inductor and heated.

It is necessary do at low temperatures, since all the water should evaporate, despite the fact that outwardly it seems as if it is not there at all.

If the crucible is not preheated and immediately begins to melt in it, then it will most likely burst. After warming up, when tapping on the crucible, it will make a ringing sound. This indicates that the crucible is well made.

Following the instructions presented, you can quite easily get a homemade melting furnace that will last no less than a purchased one. The main thing is not to rush, to be careful in work and not to violate manufacturing technologies.

© When using site materials (quotes, images), the source must be indicated.

A crucible is a vessel for melting metal. As a rule, pig metal is melted in crucibles; already brought to the required degree of quality for casting into a mold or refining (deep cleaning from impurities). The general line of development of large-scale metallurgy is to reduce the number of redistributions, up to the release of conditioned metal immediately from the melting furnace, but crucible melting still retains significant importance in industry, and dominates in handicrafts and jewelry.

The crucible is not just a sufficiently heat-resistant vessel. Its chemical composition and 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 meet for use at home or in a small workshop. Based on beginner metallurgists, you will first have to touch on the process of metal smelting itself, because. requirements for the crucible are determined mainly by its conditions.

A little about melting

In a high vacuum, high-purity remelted metal can be heated exactly to the melting point or slightly higher, and kept at it for some time, so that tiny, literally a few atoms, remnants of crystallites melt. Then the metal can be allowed to cool slightly below the melting point - it will remain liquid, like a supersaturated solution without a seed crystal. If now the metal is poured, also in 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 chemically gaseous environment. The remelted metal, firstly, interacts with air, which is why part of it is lost to the formation of oxide, which is especially important when remelting precious metal scrap: at its melting temperature (1060 degrees Celsius), even gold is noticeably oxidized. In order to compensate for oxidation to some extent, the crucible must create a reducing environment for the melt or be chemically inert if the metal is melted with a 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 remains 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 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 third.

Recovery

In metallurgy, mainly atomic carbon C, carbon monoxide CO (carbon monoxide) and hydrogen H are used as reducing agents. 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 can absorb up to 800 volumes of hydrogen. A platinum blank in a hydrogen atmosphere literally swells before our eyes, cracks and breaks into pieces. If they are taken out of the hydrogen chamber and heated, hydrogen will be released back.

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

A significant proportion of hydrogen reduction occurs when heated by an open flame of a gas burner, when it comes into contact with a less heated surface. It doesn’t come to damage to the metal - the absorbed hydrogen is further released and burns out during the melting process. But, if the material of the crucible is also prone to gas absorption, it can crack and burst during melting, this must be borne in mind.

CO recovery is noticeable if the metal in the crucible is melted by an open flame of a liquid (gasoline, kerosene, diesel) burner, for the same reasons. Liquid fuel burns much more slowly than gas, and the zone of its afterburning extends several cm from the burner nozzle. Reduction with carbon monoxide is the cleanest, 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, the reduction of CO 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.

The atomic carbon reducing agent is energetic enough to compensate for the oxidation. It is also easy 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 to make the entire crucible from a heat-resistant and mechanically sufficiently strong allotrope C; such is graphite. When C is reduced, there is a danger of carburizing 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 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 choose the dimensions, configuration of the crucible and the addition of graphite to its material so that there will simply be no excess C under any conceivable melting mode. This is a very valuable property of graphite, also keep in mind.

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 the service life. It's also a valuable asset.

Excerpt

So, why the melt in the crucible needs to be overheated and held is understandable. Although metal casting is a completely different topic, it still needs to be mentioned here that the melt holding time must 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 galvanization, the purer the better. Most often use the so-called. eutectic alloys; e.g. steel is a eutectic of iron with carbon, and duralumin is a complex eutectic of several components. If the melt is allowed to stand, the structure of the eutectic in the casting will change and the finished product will be spoiled. The exposure time is especially critical for bronze and brass: they must be poured immediately, as soon as the play of the melt in the crucible apparently changes, it becomes calmer. Do you remember how the engineer Telegin in A. N. Tolstoy's "Walking Through the Torments" was worried that the bronze would not over-age?

With regard to the manufacture of a self-made crucible, degassing of the melt during holding is significant in that at this time it (the crucible) experiences significant dynamic loads from bubbles of evolving gases and/or the play of the melt itself. That is, to make the crucible withstanding a large number of thermal deformations and, if required, reducing, little. Its material must also be sufficiently viscous to withstand shock waves from bursting bubbles and shocks from melt jets. It is this circumstance that explains the low durability and reliability of self-made graphite crucibles (see below).

What to do

Melting crucibles are made (see figure below):

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

Their comparative characteristics are as follows:

• Ceramic neutral - used for the remelting of scrap jewelry with the preservation of the sample, because. with indirect heating (see below), the properties of the metal do not change. You can do it yourself, but it’s difficult (see below) and is it worth it? A 50 g crucible for gold costs up to 100 rubles in a jewelry store. Suitable for melting in an induction furnace (see below) without any problems. almost do not absorb the energy of the electromagnetic field (EMF). Resource - 10-30 swimming trunks.
• Ceramic graphite - suitable for melting any metal; at home up to 1.5-2 kg at a time. For use in 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 electromagnetic fields by conductive graphite. You can do it yourself, see below. Resource - up to 50 or more melts.
• Graphite - suitable for remelting old, oxidized scrap of non-ferrous and precious metals, because. create a strong restorative environment. The melting of silver with an open gas flame in a graphite crucible makes it possible to almost completely restore the initial weight of the oxidized metal. Do not do it yourself, see below. Resource - more than 100 swimming trunks.
• Cast iron - are used mainly for remelting red copper into oxygen-free, because. actively absorb oxygen. The resource is up to 30 heats, and then amorphous carbon leaves the cast iron and the crucible degrades.
• Steel - a home-made cheap option for melting small amounts of aluminum and magnesium alloys and other metals that are chemically inert in the melt. May be used to melt small amounts of lead into fishing sinkers, 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 either machined from massive natural graphite (expensive), or sintered at high temperature from graphite powder (cheaper, but still not very cheap). Amateurs often try to make "graphite" crucibles from ground graphite on a binder of kaolin, etc., but these are not graphite, but excessively 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 it into a desktop mini crucible furnace for ceramic neutral crucibles, see fig.

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

If gold is melted, then after the end of melting and cooling of the furnace, graphite powder is poured out and shaken up, because. he bakes. 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 keep the reducing environment, the furnace is covered with a mica cover during melting.

Heating methods

If it is required to melt more than 150-200 g of metal at a time, then a crucible furnace will also need to be built to the crucible, otherwise it will be very difficult to achieve melt homogeneity and high casting quality. The exception is low-melting and easily recoverable lead: up to 20-30 kg can be melted at a time at home. A relative exception is zinc for hot-dip galvanizing, its melt in a crucible without a furnace can be up to 2-2.5 kg, but borax must be poured over it so that the melt mirror is completely covered with its fluidized layer. Steel fasteners are thrown into the melt through a layer of borax.

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

For fusible metals, the most economical is often an 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. In the induction furnace, only ceramic neutral or, to a limited extent, graphite crucibles are applicable.

If the crucible is more than 2-2.5 kg of metal, then the crucible furnace, according to safety rules, must be made tipping (pos. 3), because and 1 kg of melt spilled on the floor is already a big problem. Metal in small jewelry crucibles, on the contrary, is preferably heated without a furnace, directly with a burner flame, pos. 4. In this case, the crucible is held all the time during melting with a special spring grip, pos. 5 and 6.

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

Electric heating

Resistive 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 domestic crucible electric furnace; how to make an electric crucible for melting lead, see for example. video:

Video: electric crucible for melting lead

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

Video: do-it-yourself induction heating

With an increase in the amount of remelted metal, not only the required power of the generator increases, but also its optimal frequency decreases, this affects the so-called. surface effect (skin effect) in metal. If 100-200 g of aluminum can be melted into an EMF from any home-made generator for, then the installation of 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 it to fence something like that? Wouldn't it be easier to get a mini gas furnace for melting small amounts of aluminum alloys, see for example. video clip

Video: mini aluminum melting furnace

Making crucibles

Now it's time to make your own melting crucible. From the foregoing, 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 - it's just a steel vessel with a welded handle. Steel crucibles are used for remelting 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 the formation of a ceramic neutral crucible is 7 parts of fireclay clay, 1 part of finely ground fireclay (up to a 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.

Chamotte mill

Finely ground chamotte is a raw material for forming both neutral and graphitized crucibles, and the quality and durability of the crucible largely depend on it, and crushing chamotte by handicraft methods is very laborious and does not produce a completely benign material. The device of a chain mill for mineral raw materials is shown in fig. on right. Material - steel. Chains - 4; they are suspended crosswise so that they sag horizontally by approx. 1/3 of the tank diameter. Option instead of chains for 1 broken fireclay brick - 2-3 handfuls of balls from the bearing. New purchased ones will cost more than chains, but old ones from broken bearings are quite suitable. Drive any: manual, electric. Both chain and ball mills are capable of grinding chamotte into dust like cement; to obtain certain fractions, the mill is stopped earlier. The mouth of the tank, so as not to get dusty, is covered with something for the time of grinding. It is enough to throw a brick for grinding from a height onto a hard floor and load the resulting pieces into a mill.

Preparation of the molding material

We mix dry clay with ground fireclay until complete homogeneity (homogeneity). The ideal option is to scroll 15-20 times in the same mill; if it is spherical, then the balls can not be thrown into the tank. We unload the mixed mass and add a little water (1.5-2.5 parts), mixing by hand, until the consistency: clenched in a fist, sticks together into a lump, but does not stick to the skin and does not squeeze between the fingers. We add liquid glass, also stirring until completely homogeneous, this is the most time-consuming step.

Deairing

Only one air bubble remaining in the mass for a ceramic crucible can cause the crucible to burst from heating. Therefore, air must be knocked out of the mass. To do this, a clean film is laid on a hard floor; newspaper, as advised in some manuals, is not necessary - the mass will be filled with paper fibers.

To knock out the air, the whole lump of mass is thrown to the floor with force many times. Practically - after the bubbles stopped popping out of the flopping mass, at least 10 more times.

Storage

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

Usage

Crucibles from the resulting mass are simply molded by hand or molded in a destructible plaster mold or in a collapsible form, as described below. The molded crucible is dried, and, which is absolutely necessary for a given 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 liquid glass will melt and firmly bind the remaining 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 and not simple, though. The maximum operating temperature of the obtained crucibles is up to 1600 degrees; resource, with high-quality grinding of fireclay - up to 30 heats.

graphite

Manufacturing technology of graphite crucibles for melting any metals, incl. black scrap, with 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 all the more honor to him - his products are quite consistent with good industrial designs. However, firstly, his article was rewritten many times by rewriters who obviously did not cast metal in their lives. Secondly, you can’t always get to it in the search, and for some reason the drawings are not downloaded, although they seem to be in free distribution. Thirdly, there is something to add to the materials of A. Ramir, no offense to him. One of the rules of technology says: in a good design there is always something to improve. Therefore, we repeat and supplement the main points of this publication.

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

In kg, the maximum weight of the remelted steel is indicated; for another metal it needs to be recalculated. 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 intercepted with screw clamps in 3 places, at the bottom, in the middle and at the top, 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 only need to use worm clamps (see the figure on the right) or their homemade counterparts. Any other clamp deforms the pipe across. The flask from it will most likely come off the crucible, but it will not last long or will crack at the first melting.

The composition of the mixture used by the author is 7 volume parts of ground chamotte, 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 ability this is a clear overkill, and the probability of crucible cracking from a mixture of 7: 3: 1 will be reduced to zero if fireclay is crushed into dust in a mortar or ground in a mill (see above) .

Soaking fireclay bricks, as advised by A. Ramir, is necessary only before crushing in the artisanal way described by him. 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 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, it is necessary to carve a block out of hard wood (filled with gray in pos. 1-5 of the figure), sand it and, it is highly desirable, walk over it with leather until the surface is completely smooth. In the center of the block surface that forms the bottom of the crucible, a blind hole is drilled and a toothpick or, better, a round, smooth plastic stick from an ear picker is inserted into it. The match used by A. Ramir is not the best option - it often breaks when pulled out, and the product goes into marriage from this.

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

The form is filled with the mixture in layers of 15 mm, and each layer is rammed with a wooden tamper. This is the most critical stage: bubbles and uneven compaction of the mixture are unacceptable. When approx. 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 flask 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 blockhead with pliers, the lid is put back and the mold is turned over. A handle is attached to the bottom of the blockhead with self-tapping screws and, carefully turning it back and forth, they pull it out of the casting.

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

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

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

It remains to remove the flask. To do this, it, together with the crucible, is turned over again to the working (for the crucible) position, a round wooden chock is substituted 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 the fingers; most likely, the flask after that will come off like clockwork.

And, finally, the finished casting is dried. Equipment - cooker 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 that, the fire is turned off and the casting is left in the oven to cool until tomorrow morning. Do not open the oven during the drying time!

The crucible must be checked for hidden cracks before use. To do this, holding it with your fingertips at the bottom, tap your nails in a circle from top to bottom. Each knock should be answered by ringing. If somewhere it doesn’t ring - marriage, you can’t melt with this. Annealing for a crucible made using this technology is not required. It rings everywhere - you can immediately melt in it.

What for?

A reader who is 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 rain, not everyone is keen on smelting damask steel at home, and not everyone has centners of old electronics in mind, from which tens of grams of gold, platinum, and palladium can be extracted.