In this article I will talk about such an important and interesting unit as a muffle furnace.

The use of such furnaces is diverse, but the principle of operation is the same - heating various parts and materials to the required temperature and heat treatment. Is it known that jewelry workshops, ceramics studios or pottery workshops use muffle furnaces in their production.

I note that you can purchase a finished oven, but its cost is often very high. However, making a muffle furnace with your own hands is quick and easy enough if you have all the materials. You will also find informative information about all this in this article.

Muffle furnaces are equipment for heating various materials - ceramics, gold, silver, platinum, chemicals. By its nature, it has a wide spectrum and is used almost everywhere.

The electric muffle furnace is used for heat treatment of materials in many industries, mainly chemical laboratories and scientific institutes. The muffle in it is used mainly ceramic.

In technically obsolete furnaces, the scope of muffle furnaces is limited by a temperature maximum of 1150 degrees. This is due to the location of the heating elements behind the ceramic muffle, which does not allow the use of these units at a working space temperature of over 1150 degrees.

This is due to the need to increase the temperature on the heating elements, above their possible level of use.

To reduce the temperature transition between the temperature inside the muffle and the heater, the muffle is made of ceramic.

The principle of operation is also distinguished by a high consumption of electricity, since the massive muffle does not heat up quickly. This explains the use of fibrous muffles by some manufacturers. In such an oven, the heating elements are inside.

The principle of operation of the device is the elimination of direct radiation of heaters on the material that can be heat treated.

However, the fibrous muffle has a serious drawback: the fiber is unstable to gas evolution, which occurs especially actively during the firing of ceramics and metal processing. Salt release and oil burnout destroy the fiber.

The muffle furnace with remote heating control unit is a new branch in the development of electric resistance furnaces.

The working chamber is made of high-temperature and durable thermal insulation material.

The heaters are located in the grooves of the electric furnace, which facilitates their replacement and prevents them from closing when in contact with the charge.

It can be used at standard temperatures from 50 to 1250 degrees, but can be manufactured up to 1600 degrees.

Muffle furnaces are used for their intended purpose for roasting, hardening of metals and steel at high temperatures, various laboratory studies.

Today there is a wide variety of this type of furnaces, but each of them can be used for individual options for processing and hardening the material, namely:

• obtaining and creating special jewelry made of silver and gold;
• using high temperatures to melt precious metals and products with damage;
• creation of a stronger structure and firing of products based on ceramics;
• formation of the necessary product and smelting based on wax;
• hardening of metal products, production of molds for metal casting.

Varieties of muffle furnaces

Muffle furnaces are divided according to the type of heating:

• Electric muffle furnaces are a type of chamber electric resistance furnaces.
• Gas muffle furnaces.

By protective processing mode:

• Air: heating in air (general purpose).
• With a protective gas atmosphere: heating in a special gaseous medium (hydrogen, argon, helium, nitrogen, reducing gases, nitriding gases, etc.).
• Vacuum: heating in vacuum.

By design:

• Vertical loading (potted).
• Bell-type (with separation from the hearth).
• Horizontal loading (simple).
• Tubular (verification of thermocouples).

To buy a muffle furnace, you first need to decide for what purposes it will be used, what size of the workpiece, or chemical samples will be heated in it and to what temperature.

The size and temperature of the heating of the working chamber is very important. The price largely depends on these two parameters.

At present, there are many muffle furnaces on the market with a variety of names:

• laboratory muffle furnace;
• jewelry muffle furnace;
• dental muffle furnace;
• industrial muffle furnace;
• educational muffle furnace.

Of all the variety, it is not always possible to choose a muffle furnace according to the given parameters and at an affordable price.

Therefore, we will try to figure out what unites all these muffle furnaces and what are their differences.

Laboratory muffle furnace

Laboratory muffle furnace - used in the laboratory and carried out in it, many different tests with materials: heat treatment (heating, hardening, firing) of analytical work, laboratory chemical analyzes with maximum heating accuracy and control of the set temperature, so they are bought with program control and heating temperature from 1100 degrees.

Jewelry muffle furnace

The muffle furnace for jewelers is used for melting precious metals, so it can be categorized as a professional melting jewelry furnace.

Most often purchased, jewelry muffle for melting, silver, gold and platinum.

In order to choose a suitable jewelry melter for melting such metals, one must proceed from the melting point of gold, silver, platinum, etc.

When working with precious metals in a jewelry furnace, you do not need to save on cost and buy a jewelry furnace with 30 temperature control programs, PID (PID) automatic control.

Unlike a laboratory muffle furnace, a jewelry muffle furnace needs to be chosen according to slightly different technical parameters.

The jewelry muffle furnace should have a working chamber size of maximum 200×200×200 mm and a heating temperature of no more than 1200 degrees Celsius.

Since the jeweler works with a small amount of precious metal, it makes no sense to overpay for a large volume of the working chamber.

Dental muffle furnace

In dentistry, a muffle furnace is most often used for drying, firing, heating (orthopedic dentistry).

Muffle furnaces for ceramics are most often bought for dentistry with a heating temperature of 1100 to 1200 degrees Celsius. With working chamber size from 100×100×100 mm to 200×200×200 mm.

For such specialization, a muffle furnace with a small volume of the working chamber, from 100 × 100 × 100 mm to 200 × 200 × 200 mm, but more is possible.

Industrial muffle furnace

The differences between industrial muffle furnaces and all others are the size of the working chamber, not less than 200 × 200 × 200 mm and the heating temperature of the working chamber from 1400 degrees to 1750 degrees (it can be heated even higher, but when heated to 1800 degrees, the heating element quickly becomes unusable).

In this case, the price of the muffle does not depend on the size of the working chamber, but on the heating temperature.

In industrial production, they try to use muffle furnaces with the maximum temperature and equipment. the activity of such enterprises is very extensive and these units perform a lot of functions, in practice, the operation of such furnaces goes on in all respects.

Training muffle furnace

If you need a training muffle furnace designed for annealing, hardening and firing, then a muffle furnace with a maximum heating of the working chamber of 1100 degrees and with a standard working chamber size of 100 × 100 × 100 is suitable for you. Such furnaces are usually called “mini muffle furnace” or “small muffle bake".

To choose a muffle furnace, you need to consider what knowledge you want to achieve when working with a muffle furnace.

Muffle furnaces are very different from simple (at the level of using a household microwave oven) to complex muffle furnaces, which are controlled via a personal computer or laptop.

What is a muffle furnace for?

The muffle furnace is used:

For heat treatment.

The heat treatment of muffle furnaces includes (quenching, annealing, tempering, normalization, firing).

Heat treatment of metals and alloys in it is carried out in order to improve their service properties.

For annealing (homogenization and normalization).

The goal is to obtain a uniform grain microstructure and to dissolve the inclusions. The subsequent cooling is slow, preventing the formation of non-equilibrium structures such as martensite.

Dispersion hardening (aging).

After annealing, heating to a lower temperature is carried out in order to isolate particles of the hardening phase. Sometimes stepwise aging is carried out at several temperatures in order to isolate several types of hardening particles.

For hardening material.

Hardening in a muffle furnace is carried out with an increased cooling rate in order to obtain non-equilibrium structures such as martensite (hardness increase). The critical cooling rate required for hardening depends on the material.

For material issue.

Tempering in a muffle furnace is necessary to relieve internal stresses introduced during quenching. The material becomes more ductile with some decrease in strength.

For burning (ashing).

The method is used when there is a special task to examine objects of biological origin for the presence of manganese, copper and some other metals.

For drying.

Drying in a muffle furnace is the intentional removal of moisture (usually water, sometimes a liquid fraction of arbitrary chemical composition) from a material.

In muffle furnaces, firing is most often carried out.

When firing ceramic products in a muffle furnace, the most complex physical and chemical processes occur, as a result of which the ceramic mass - a mechanical mixture of mineral particles - becomes a stone-like material - strong, hard, chemically resistant, with aesthetic properties inherent only to it.

Firing of ceramic products is an important and final stage of the technological process of ceramic products, the final and important stage of any ceramic production.

Also, firing is used by jewelers for firing jewelry and art products made of non-ferrous metals.

When raw material is fired in a muffle furnace, an artificial stone material is formed, which, unlike clay, is not eroded by water and has a relatively high strength. This is due to the physicochemical processes occurring in clay under the influence of elevated temperatures.

When raw ceramic products are heated in a muffle furnace to 110 degrees, free water is removed and the ceramic mass becomes non-plastic. The total cost of roasting reaches 35-40% of the cost of commercial products.

The laboratory muffle furnace is intended for laboratory analyzes (cupellation).

Laboratory analyzes - oxidative melting of an alloy of lead with gold or silver in order to isolate them in their pure form.

Cupellation in a muffle furnace is based on the fact that lead and other base metals are easily oxidized by atmospheric oxygen at high temperatures, while gold and silver do not change.

DIY muffle furnace

The muffle furnace is an indispensable equipment for workshops engaged in jewelry or ceramics.

This device allows you to create the necessary temperature conditions for heating and melting metal, firing ceramics or joining enamels with glass.

A muffle furnace is also used in the manufacture of tiles, when hardening these products and strengthening the enamel layer. There are many other options for using such equipment.

Factory-made devices are quite expensive.

But it is quite possible to manufacture such equipment with the characteristics necessary for work and independently.

A do-it-yourself muffle furnace is quite often assembled by craftsmen engaged in one of the above types of work.

And in order for the device to function effectively, it is necessary not only to choose the right material and manufacture the high-temperature chamber itself, but also to correctly calculate the operating parameters of the electrical part, purchase the required components and make a competent installation.

A self-mounted apparatus of this plan opens up wide opportunities in terms of manufacturing high-quality items from non-ferrous metal (jewelry), wax and other materials that require a melt, and working with casting molds.

In order to make a muffle furnace, it is necessary to understand the principle of its operation. Fuel can be gas, coal, electricity and even wood.

In this case, it is better to make an electric unit yourself. It consists of a heating chamber and thermal insulation that saves heat. The accumulator of this heat is a refractory brick.

Heat treatment is carried out in a working chamber - a muffle, which is why the furnace got its name.

At home, any refractory form is used for the muffle, for example, porcelain, made of ceramic plates. It can also be made from fireclay clay or bricks.

It should be taken into account that the melting temperature of the mold must be higher than the melting temperature of the material used for heat treatment.

At home, a homemade muffle furnace is used to melt a small amount of metal or to harden a tool. That is why it is enough to make it small.

The undeniable advantages of the equipment include:

• Functioning from the home electrical network;
• Low cost of the product;
• Ease of use and compactness;
• Rapid heating to the required temperature;
• Possibility of repair;
• Durability;
• Access to the alternate use of several spirals, which increases the time of their operation.

Disadvantages of homemade design:

Each device is not without certain drawbacks, and a home-made device also multiplies them. Under the conditions of the goal, it is possible to sacrifice some requirements for the sake of fulfilling others. However, everyone should know the list of negative consequences.

• A self-made design is devoid of all guarantees, including safety guarantees.
• Evaporation of the metal from the heater coil can lead to the fact that it will be contained in the form of impurities in the composition of the processed precious metal.
• Home-made thermal insulation will not ensure the full concentration of heat in the furnace, so the body of a home-made stove is very hot and requires careful handling. By the way, this is the disadvantage of some factory models.
• Lack of a proper temperature control and regulation system may result in the furnace not being able to perform a specific heat treatment task.

When designing a high-quality and practical muffle furnace, it is important to take into account a number of aspects and criteria that will later allow it to be used for personal purposes, for various kinds of production solutions.

And if you decide to create a quality oven, you will need a special heat supply system placed inside the ceramics.

In this case, it is necessary to purchase fireclay bricks that can withstand high temperatures.

You can also make this product with your own hands, observing a number of technical requirements and features.

Creating a practical muffle furnace will require not only the availability of the appropriate material, but also the need to study in detail the design of this type of product.

In order to be able to create a high-quality furnace with your own hands, it is worth understanding what types it is divided into, taking into account the fuel and energy consumed, namely:

• gas;
• electrical.

This separation allows the use of various energy sources, which allow you to heat up the space inside the created structure.

At the same time, a furnace with installed elements for electric heating is more popular. This allows you to control the temperature inside the structure if it is necessary to process certain raw materials.

As noted earlier, a do-it-yourself muffle furnace can be made at home, powered by electricity or gas.

But do-it-yourself installation of gas equipment is expressly prohibited by current legislation, so the best option is to make an electric muffle furnace.

• vertical, it is potted;
• bell-shaped;
• horizontal, the simplest.

The main parts of the furnace design

When planning how to make a muffle furnace, the first step is to look for a suitable case. It can be a metal case from an old washing machine, a small refrigerator, a gas stove, etc.

The size of the case varies in the region of half a meter in width and length and about a meter or slightly lower in height.

In the absence of improvised materials, the body of the required dimensions can be welded from stainless steel sheets.

It is also important to strengthen the bottom of the furnace, since the structure will be heavy. To do this, you can use a corner or a pipe of small diameter. Legs can be made in the corners.

You should also strengthen the top of the case, the front part, where the door is, and the side edge on which you plan to weld the hinges for the door.

Thermal insulation layer.

This part of the design is extremely important. The efficiency of the furnace and the heat loss that it will incur depends on its quality.

The inner layer of thermal insulation is a refractory (fireclay) brick that can withstand temperatures up to one thousand degrees.

The outer layer, which reduces heat loss to the surrounding space, is made of perlite or basalt wool.

Asbestos is not safe to use; when it is heated, carcinogenic substances are released into the atmosphere.

Elements that directly heat the workspace.

The heating elements inside the muffle furnace are spirals twisted from nichrome or fechral wire. Thickness 1 mm. Nichrome (nickel-chromium) wire is very ductile and resistant to corrosion.

Fechral (aluminum, chromium, iron) wire is somewhat cheaper due to the absence of aluminum in the composition and also has the necessary properties for its use in a muffle furnace.

The process of creating a muffle furnace with your own hands

The main part of the furnace, the working chamber, or muffle, is made of refractory clay (chamotte), used for coating boilers. The size of the inner part of the furnace is 210x105x75 mm, and the wall thickness is 10 mm.

The muffle can be made from different materials:

Ceramic.

The temperature transition between chamber and heating element is reduced. This is very important for ceramics, as it cools more slowly than other materials, so if you do not pay due attention to the muffle, the furnace will be unusable.

Ceramic fiber muffle.

Advantages of fiber: the oven heats up quickly. Disadvantages - fragile material and under high temperature conditions, the release of harmful substances is possible.

1. The muffle is molded according to a pre-made form, made of cardboard, impregnated inside with paraffin or stearin so that the form does not stick.
2. Clay is applied from the inside. The thickness of the clay layer is up to 10 mm. If you sculpt from the outside, a crack may form: after all, clay shrinks quite a lot during drying. When the clay dries, it itself easily lags behind the walls of the mold. The ceramic element of the door should also be molded from the same clay.
3. After air drying, both clay parts are placed in a regular school muffle furnace (which is available in any secondary school). Then it is dried for two hours at a temperature of about 100 degrees.
4. Then they are fired, gradually raising the temperature to 900 ° C. The oven is then turned off and allowed to cool slowly along with the parts.
5. The fired muffle and the door element are adjusted to each other, carefully filing with a file and cleaning with sandpaper.
6. Then, 18 m of nichrome wire 0.75 mm thick are wound on top of the muffle, together with PEV 0.8–0.9 wire, in order to maintain the interval between turns.
7. To prevent the winding from untwisting, the first and last turns are shortened and twisted. Then remove the PEV wire. And so that a short circuit does not occur, the gaps between the turns are carefully coated with clay.
8. When it dries, a second coating is made with a thickness of 10–12 mm with clay mixed with asbestos chips.
9. The finished dried heating element of the furnace is placed in a metal case made of a steel sheet of millimeter thickness. Case size 270x200x180 mm.
10. Dry the finished muffle furnace with your own hands gradually in a well-ventilated place.
11. The drying time of the structure is from 5 days to several weeks.
12. In the case of intensive forced drying, the clay used in the manufacture of the furnace will crack, and such a device will not be used.
13. To check the quality of drying, the muffle furnace is turned on to a minimum and if there is no evaporation of moisture, then the device is completely dry.

It is important to remember that it is imperative to follow all safety regulations when manufacturing and using such a high temperature device.

Production of an electric muffle furnace

Consider building a small muffle furnace. The device will be connected to a network with a voltage of 220 V.

Materials for making the device are available in hardware stores and electrical departments.

To create a muffle furnace you will need:

• sheet steel 2-3 mm thick (2 sq. M);
• rolled steel with a section "corner" (3 m);
• heat-insulating material (basalt wool);
• fireclay bricks, 12 pieces;
• mortar (5-7 kg);
• thermocouple chromel-alumel;
• ceramic tube for thermocouple;
• nichrome spiral;
• fiberglass tubes for insulation of coil and thermocouple leads.

When choosing materials, they are guided by their quality: heat resistance, ability to withstand rapid heating and cooling. In order for the muffle to serve for a long time, you should not take a brick that has been in use for several years.

To prepare a mortar paste, you will need a ten-liter bucket and a stirrer.

When mixing the solution, use a respirator.

For installation, the following construction tools and equipment will be required:

• welding machine;
• electric drill;
• Bulgarian;
• a set of drills and drills for metal;
• stove-maker's tools: pickaxe hammer, trowel, small spatula, measuring tape;
• electrician's tools: pliers, wire cutters, round-nose pliers, metal ruler, a regular and Phillips screwdriver.

The workflow includes the following steps:

1. Mark and cut the steel sheet. Cut out the details of the casing and the details of the door.
2. Weld the casing and the door.
3. Hinges for the door and lock fastening are welded to the body.
4. A mortar is made from a mortar (according to the instructions on the package).
5. A mock-up of the furnace is made of bricks, determining where the spiral will be laid.
6. In bricks, grooves are made with a drill for laying a spiral. For work, a victorious drill is used.
7. The corner profile is cut with a grinder and a frame for bricks is welded from it.
8. A muffle of bricks is placed in the frame (on a mortar mortar).
9. The masonry is dried for 3-4 days.
10. In the walls of the muffle, a nichrome spiral is placed in the grooves. Having drilled a hole in the bricks, the contacts are brought out.
11. A ceramic tube and fiberglass protection are put on the thermocouple.
12. In the muffle, a hole is made for the thermocouple with a drill and inserted into the chamber.
13. The points of contact output are coated with a mortar solution.
14. The muffle is dried for 1-2 days.
15. A layer of mineral wool is laid on the back wall of the casing.
16. A muffle is installed in the casing. It is placed on a metal grid-stand so that the heavy stove does not compress the layer of cotton under it.
17. With a drill for metal, holes are drilled in the casing, the contacts of the spiral and thermocouple are brought out.
18. The gap between the muffle and the casing is tightly stuffed with basalt wool.
19. A layer of basalt wool is placed in the door and fastened with nichrome wire.
20. The door is installed on the casing, put the lock.
21. Cut out a piece of fireclay brick to fit the door. During firing, it is placed in the muffle in front of the door.

It is better to connect such a device to a reinforced outlet, such as the one into which the electric stove is turned on. Another option is to run a thick wire from the electrical panel. Also, to be sure, it’s a good idea to put an automatic switch (the so-called automatic switch).

And, of course, do not forget that with such an electric oven you need to exercise maximum caution.

Any mistake can lead to the most unpleasant consequences.

If you are not well versed in electrics, be sure to consult with a specialist before work. Never touch coils when switched on.

Do not forget about grounding and protective gloves for working with objects heated to such a high temperature.

Muffle Furnace for Ceramics

Pottery lovers know that for the manufacture of ceramic objects, they must be fired.

For this procedure, special ovens are used. They are designed exclusively for firing clay products.

Inside such units, a very high temperature is created (much more than 1000 degrees).

A ceramic kiln can be of various designs, differs in its capabilities, technical parameters, etc.

Special kilns for firing are manufactured industrially, among them there are also professional equipment. It costs very little.

However, it is not necessary to buy such ovens. They can be made with your own hands.

There are several classifications of kilns for roasting.

One of the most important criteria is the operating temperature.

• The highest category is equipment where heating is carried out up to 1400-2000 degrees.
• The next group is furnaces operating at a temperature of 900-1400 degrees.
• At moderate rates, furnaces of the third category (400-900 degrees) work.
• And the last group is characterized by a low-temperature regime (up to 500 degrees).

The most advantageous in operation are those furnaces where you can control the temperature.

Based on the energy sources used, kilns are divided into:

• electrical;
• gas;
• solid fuel.

Industrial designs are only of the first and second types.

As for wood-burning equipment, it can only be home-made stoves.

The use of solid fuel cannot provide heating to high temperatures.

Another important indicator of the operation of the furnace is its power.

For small units (chamber volume up to 50 liters), you should follow the rule: 100 W per liter. If the stove is large (100-500 liters), the ratio will be different: 50-70 watts per liter.

According to the configuration of the furnace are divided into three types:

• Bell-type.
• Tubular with vertical loading.
• Chamber with horizontal loading.

The advantages of tube ovens include a uniform distribution of heat in them.

The other two types are more suitable for mass production and firing of large items.

For insufficiently experienced craftsmen, kilns are suitable, where a viewing window is provided that allows you to visually monitor the firing process.

Modern kilns are equipped with refractory elements made of modern materials, which are characterized by low weight and low thermal conductivity. Heavy furnaces using fireclay are already a thing of the past.

The firing temperature of ceramics depends on the composition of the raw materials and the purpose of the finished product.

To get red products, a low-power oven heating up to 500 degrees is enough.

If dark red or cherry-colored ceramic is required, it must be fired at a temperature of 600-900 degrees.

Shades from orange to white can be obtained at a temperature of 900-1400 degrees.

In industrial ovens, the temperature can be adjusted, which allows the production of various products.

According to the energy source, solid fuel, electric or gas firing of ceramics can be.

You can only buy gas and electricity appliances, solid fuel ones are made independently.

Firing ceramic products at home can be done in quite simple ways: in a wood-burning stove or on a fire, on a gas or electric stove.

Before placing in the stove or on the fire, the product is placed in a container with sand. If a stove is used, the clay craft is placed in a cast-iron skillet and covered with a fireproof container. These methods are not suitable for the production of a large number of products.

The furnace can be muffle or chamber or muffle, depending on how the heating elements are located.

Heating elements are always located inside in a chamber electric stove.

A muffle furnace for firing ceramics can be with any source of energy, because a muffle is a container into which heat is transferred through the walls, combustion products do not get inside.

A cast-iron frying pan covered with a saucepan is the most primitive muffle chamber.

To make a pottery kiln with your own hands, you only need a clay flower pot and an electric stove.

Half of the fireclay brick is placed on the tile (so that the spiral does not come into contact with ceramics), the product is placed on it and closed with a pot.

A thyristor regulator is used to control the power.

Even in daylight, you will notice that shortly after switching on, the sides of the pot will glow with a dark red light.

From this point on, the firing countdown begins, from five to twelve hours, depending on what is fired.

If overshoot is observed, the power is slightly reduced.

Faience barrel stove

You can also make a larger oven from a faience barrel.

1. Stage one. First, a small hole is made at the bottom of the barrel with a diamond drill to release the expanded air.
2. Stage two. Next, you need to do under. To do this, a "foundation" of fireclay bricks is assembled on a small sheet of steel and connected with metal corners. Then, grooves for the spiral (no more than three or four) are made in the upper part of the barrel - the heating element of the required power will be laid in them.

Stage three. It remains only to make the outer shell of galvanized steel. It is made removable, since it will be put on only after covering the product with a muffle (barrel). The space between the muffle and the outer shell is covered with asbestos.

The firing procedure is no different from the previous version, but the temperature is adjusted using a thermocouple. The walls of the barrel are thick, until they light up (even without the outer shell), the ceramic product will be already burnt.

Muffle Furnace for Metal Hardening

A muffle furnace is a specialized design that allows you to heat various metals to the required temperature.

There are several ways to process metals using this device:

• Heat treatment: annealing, hardening, tempering, aging.
• Working with valuable materials, remelting metals when the use of open fire is unacceptable.
• To obtain an even surface tone, especially when processing ceramics (highly artistic), a muffle furnace is used.
• Drying of dielectrics.
• Cremation, incineration to mineral components.

Possible problems when creating a furnace

In the manufacture of the device, difficulties arise with the selection of material and the installation of a temperature control system.

Incorrectly selected materials lead to the rapid destruction of the muffle.

So, out of economy, some craftsmen use low-quality bricks, clay-sand mortar instead of fireclay. This leads to cracks in the muffle and heat loss.

The cracked muffle is temporarily sealed with a solution of fireclay clay. The camera must be removed and replaced with a new one.

If the furnace is connected to the mains without a thermostat, the temperature in the muffle is not controlled. This leads to damage to products that require firing at a given temperature.

To solve the problem, you should purchase a thermostat and electrical equipment, assemble the control unit and connect it to the heating elements of the muffle.

For ease of assembly, it is better to make it with removable front and rear covers that are fastened with screws. A door is attached to the front cover on a hinge, which should lean horizontally. A ceramic element is installed on the door with the help of two bolts through asbestos gaskets, and the gaps are sealed with clay.

The ends of the nichrome wire are brought out to the back cover of the case. Ceramic insulating "beads" should be strung on both terminals. The wire is attached to the pin connector. Such connectors, as well as insulating "beads" can be taken from old electrical appliances. A standard cord with a plug will be attached to the connector for inclusion in the electrical network.

All free space between the heating elements and the housing should be tightly packed with asbestos chips. In addition, a ground terminal must be provided in the design of the furnace.

For convenience of work, two small holes must be made in the heating chamber: one on the rear wall with a diameter of 10 mm - for installing a thermocouple, the other on a door with a diameter of 18–20 m - for observing the interior of the furnace during operation. Both openings must be provided with closing metal curtains.

A lining plate made of thin stainless steel 0.5–0.8 mm should be placed on the bottom of the working chamber.

The oven is rated for 220 VAC. It heats up to a maximum temperature of 950 degrees within an hour. The weight of the oven is about 10 kg.

How to choose the right oven

Manufacturers of muffle furnaces are constantly improving their products, as high competition in the market stimulates continuous customer satisfaction.

In order not to lose your customers and conquer new markets, you need to keep up with the times. At the same time, the pricing policy must be adequate, otherwise the level of sales will be low, regardless of the quality of the products.

In their manufacture, only modern environmentally friendly materials are used. Furnaces have a two-stage operation cycle, when heating occurs at the first stage, and the temperature obtained is stabilized at the second. The control unit allows you to remember the set settings during a power outage.

Very often, users purchase a thermocouple for a muffle furnace. This device is used to measure the exact temperature. Basically, it is necessary when the oven itself does not have a built-in thermometer and does not show the current temperature value.

For the safety of personnel, a fume hood is useful. This is a special element of technical furniture, inside which a working device is placed. It is necessary so that a person does not accidentally burn himself on a device that is very hot during operation.

The internal temperature of a muffle furnace can range from 400 to 2500 degrees Celsius, so even touching the outer surface can be quite unpleasant.

Of the rest of the additional equipment, muffles made of different materials are in great demand. They are used depending on the conditions of work with a particular material.

September 5, 2016

Many are interested in how to properly harden metal at home and in what cases is this process required? Hardening of products from this material is carried out if it is necessary to increase its strength. For example, to harden the edges for cutting kitchen utensils (knife, secateurs) or tools (chisel, chisel, etc.). In addition, the metal acquires a certain amount of plasticity, which facilitates the processing of the material. Blacksmiths are well aware of this rule. The article will describe how to harden metal at home.

What is hardening for?

Hardening of the metal contributes to an increase in the hardness of the product by about 4 times. In this case, an object made of this material can easily cut the glass surface. Hardening is required due to insufficient strength of the object or vice versa. In the first case, metal products will be crushed, and in the second, they will crumble.

Checking the level of hardening of a metal product

To check the level of hardening of a metal product, take a file and run the tool along the edge of the object to be cut, for example, an ax or a knife. If you feel that the file begins to stick or stick to the metal, then this indicates that the product is not hardened enough. At the same time, its edge will be soft and pliable.

If the tool easily moves away from the object and it feels like it is stroking it, and the hand does not feel irregularities, then this means that the metal is overhardened.

It is possible to harden metal at home. In this case, you should not turn to complex technologies. The process is done by hand.

It should be remembered that low-carbon steels are not subject to the process. But it is realistic to achieve an increase in the strength of products made of carbonaceous or tool materials.

How is hardening done?

Hardening technology involves two processes - heating a metal product to a high temperature and subsequent cooling.

Heat treatment of the surface is advisable if:

• there is a need to give the metal additional strength;
• an increase in the level of plasticity is required, for example, for subsequent hot forging.

The price of hardening a metal product at a professional level is 200 rubles. for 1 kg. Fire treatment of small parts is cheaper. The price for this service is 20 rubles.

How to harden metal at home? It is necessary to familiarize yourself with some of the nuances of this case.

Heating should be uniform. There should be no black or blue spots on the metal. Do not heat the product to the extreme temperature. The appearance of a bright red color indicates that the process is proceeding correctly.

What equipment is used for hardening?

For example, in order to harden metal at home in the form of a drill, an electric or thermal furnace, a soldering lamp, or a fire are used. What is suitable in a particular case depends on what temperature indicator is required for the material being processed.

Cooling of various tools

The rules for cooling instruments may be different. The process can be carried out in one or more steps. It all depends on the type of metal.

How to harden metal not over the entire surface, but only in a certain place? In this case, the jet type of hardening is used. It implies the direction of a jet of cold water on an object pointwise.

If the action is carried out with one cooler, then specialized devices are required in the form of a barrel or bucket. For this purpose, even a bath is used. This cooling method is suitable for objects based on carbon or alloy steel.

If a two-stage cooling scheme is required to lower the product temperature, then different media are used. This process provides metal tempering. Initially, drills or discs are cooled with water, then with machine or mineral oil. Cooling with its help is the second stage of the process, since there is a risk of ignition under the influence of high temperature.

Application of water for cooling

The main cooling liquid is water. If you add a little salt or soap to it, then the cooling rate will change. Therefore, the tempering tank cannot be used for hand washing. To ensure the same hardness index on the metal surface, the temperature of the liquid should be maintained at 20–30 °C. You can not often change it in the tank. It is forbidden to cool the product in running water.

The disadvantage of hardening with water is the appearance of many cracks on the surface of the metal. In this way, objects of a simple shape or cemented should be subjected to the process.

What is used to harden parts of complex shape?

How to harden metal of complex shape? For alloy steel, a fifty percent solution of caustic salt is used cold or heated to 50 - 60 ° C. Parts heated in a salt bath and hardened in it come out bright. The solution temperature must not exceed 60 °C.

The vapors that arise during hardening are harmful to health, so the bath must be equipped with a ventilation hood.

How is alloy steel hardened?

How to harden metal? At home, alloy steel is processed in a mineral oil bath. Thin objects made of carbon steel are hardened in the same way. The advantage of oil baths is that the cooling rate does not depend on the temperature of the oil. It will proceed equally quickly at any of its indicators.

How to harden metal in oil correctly? Water should not get into such a bath, as this can cause cracks to appear on the surface of a metal object. It is noted that if the oil is heated to a temperature of 100 ° C, then the ingress of water will not cause cracking of the product.

Cons of an oil bath

• During hardening, toxic gases are released.
• A plaque is formed on the subject.
• The oil may ignite.
• The quality of hardening in an oil bath gradually decreases.

How is metal tempered?

All hardened parts are tempered. This relieves internal stress. As a result of this process, the hardness decreases and the ductility of the material increases.

How to release hardened metal? Depending on the desired temperature, the process is carried out:

• in baths with oil;
• in baths with saltpeter;
• in furnaces with air circulation;
• in alkaline baths.

What determines the choice of tempering temperature?

How to loosen hardened metal correctly, what should be considered? An important factor is the tempering temperature. It depends on the type of steel and the required hardness index of the product. For example, a product for which an HRC indicator of 59 - 60 is required is tempered at a temperature of 150 - 200 ° C. In this case, the internal stress decreases, and the hardness practically does not change.

High speed steel is lowered at a temperature of 540 - 580 ° C. This process is called secondary hardening. Its result is an increase in the hardness of the product.

The metal is tempered to a tint color. It is heated on an electric stove, in ovens or hot sand. The oxide film that appears when heated is colored in different colors. In this case, the surface of the metal product is cleaned of scale, soot and oil.

After tempering, the metal is usually cooled in air. Chrome-nickel products are cooled in water or oil, since the slow cooling of these grades leads to temper brittleness.

How to harden steel over an open fire?

How to harden metal on fire? To easily carry out the process of hardening metal at home, you should build a fire and prepare two large-capacity containers. There should be a lot of hot coals in the fire.

Pour diesel or engine oil into one container, and clean water into the other. Better if it is a well. Initially, a tool is prepared with which the metal, heated to the limit, will be held. Blacksmith pliers are used. But if they are not, then you can use something similar.

After doing the preliminary work, metal drills or other tools are placed in the center of the flame on hot coals. White coals are much hotter than the rest. The hardening process must be observed carefully. The fire flame should be crimson. If the fire turns white, then there is a threat of overheating and even combustion of the metal.

It is necessary to ensure that the crimson color is evenly distributed over all areas of the fire. Black spots should not appear on the edge of a metal product. If blue spots appear on the material, this indicates excessive softening of the material and its excessive plasticity. This cannot be allowed.

After calcining a metal product in a fire, it should be removed from the hotbed. A red-hot object is lowered into a container of oil many times with an interval of 3 seconds. The time interval is gradually increased. You can't delay at this stage. The operation is carried out quickly and abruptly. The product is dipped in oil until its color is no longer bright and saturated.

Then the object is immersed in a bucket of water, which needs to be shaken a little. At this stage, you should be extremely careful, since drops of oil on a knife or ax can be dried when immersed in an aquatic environment. Drills should be lowered into the liquid with a thick end.

You already know how to temper metal correctly. If you follow all the recommendations, then the process will bring the desired effect.

When is an electric oven used?

At home, you have to harden products made of non-ferrous metals or steel. In this case, a very high temperature of up to 900 ºС and above will be required.

Only an electric or muffle furnace can heat a metal product to such an indicator. The latter can be made with your own hands, but it is impossible to make an electric one.

How to make a muffle furnace?

How to harden metal at home using a do-it-yourself muffle furnace? Such a device will become very necessary in the household. It will allow for heat treatment of metal products without unnecessary manipulations. Making a do-it-yourself oven requires refractory clay used for coating. From this material, a chamber is created with a thickness of not more than 1 cm. Its dimensions should be 210x105x75mm.

When sculpting a muffle furnace with their own hands, they resort to using a pre-prepared cardboard mold. So that it does not stick, it is impregnated with paraffin.

Clay is smeared on the form from the inside out. In this case, during drying, it will not shrink. When hardening, the material itself will move away from the edges of the mold. Refractory clay can become the basis of the furnace door.

A homemade muffle furnace should be allowed to dry in the open air. Then it is dried to the end in an oven at 100 ºС. The doors and chamber are fired gradually as the temperature rises to 900 ºС.

The parts should be allowed to cool without removing them from the oven. Then a door is attached to it. Its surface is polished with a file.

18 m of nichrome wire is wound on the camera. Its thickness should be 0.75 mm. The first and last turns must be twisted. To prevent a short circuit, the distance between the turns is coated with clay. On a dry layer of material it is necessary to spread another layer 12 cm thick.

A do-it-yourself muffle furnace is enclosed in a metal frame, the size of which is 270x200x180 mm.

For easy assembly of the case, it should be designed with two removable covers fixed with screws.

A door is attached to the front cover with a hinge. It should open horizontally. A ceramic part must be installed on this door using bolts and gaskets.

All gaps are covered with clay, and the edges of the wire are removed onto the back cover of the frame.

Then a connector and a standard cord with a plug are made. All holes between the heating parts and the frame are filled with asbestos chips.

To install a thermocouple and be able to monitor the process of metal hardening in the chamber, it is necessary to drill two holes. The diameter of the first should be 1 cm, and the second 2 cm. Closable metal curtains are attached to them.

The weight of a homemade muffle furnace is 10 kg. It heats up to a temperature of 900 ºС within an hour. With its help, you can facilitate the process of hardening drills, files, matrices and many other metal products.

Muffle equipment for metal hardening is not the only device. For this purpose, a chamber device, an electric or thermal oven, as well as a bath oven are used. Making a muffle furnace with your own hands is more profitable than buying ready-made equipment. For example, the average price of such a device on the market is 40,000 rubles.

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DIY muffle furnace

Muffle furnaces are a design, the heating elements of which allow you to achieve the temperature required for firing ceramics, melting metals, hardening steel in a personal workshop. Jewelers and other craftsmen whose workshop is at home understand the value of such a design. And given the high cost of factory-produced muffle furnaces, such a furnace, made independently, is of particular importance.

Classification of muffle furnaces

According to the type of heating elements, muffle furnaces are divided into:

But it is impossible to make gas-fired stoves at home, although gas is cheaper than electricity, since such experiments are prohibited by law. The electrical control of the furnace provides the convenience of temperature control.

By constructive type, muffle furnaces are divided into:

• - horizontal (the most simple);
• - vertical or pot type;
• - bell-shaped;
• - tubular.

Heating can be carried out in air, in a vacuum or in a gaseous medium. At home, it is only possible to design a furnace with heat treatment of products in an air environment.

With the independent implementation of the muffle furnace, it can be given the desired shape and volume, decorated in a style suitable for the interior.

The main parts of the structure

List of materials and tools for assembling the structure

1. - grinder (machine for grinding and cutting materials) with cutting wheels for metal;
2. - welding machine;
3. — sheet steel >2mm thick;
4. - metal corners;
5. - fireclay fire-resistant brick;
6. - refractory mixture;
7. — heat-resistant silicone;
8. - basalt thermal insulator (cotton wool, density 200 kg / m 3) or perlite;
9. - goggles and a respirator;
10. - nichrome (fechral) wire with a cross section of 1 mm;
11. - nippers or scissors for metal.

Muffle Furnace Construction Technology

The procedure for performing the work of a horizontal or vertical muffle furnace is similar, the difference lies in the arrangement of the elements of the furnace.

1. The body of the muffle furnace is made of sheet iron. We cut out a rectangular strip of the required size with a grinder, bend it into a radius and seal the seam with the help of welding. To prevent the formation of corrosion, you can cover the metal with several layers of refractory paint. We weld the bottom to the resulting cylinder. To do this, we cut out a circle of the required diameter from a sheet of steel, equal to the diameter of the cylinder. We strengthen the walls and bottom with metal fittings. The body is made of such a volume that it is possible to place a heat-protective layer and refractory bricks inside.

If an old refrigerator is used for the case, we similarly strengthen its bottom and walls with metal corners or tubes.

We lay out the inner part of the body with a thick layer of basalt wool.

For the manufacture of the internal thermal layer (heat accumulator) we use fireclay bricks (refractory). The task is to join the bricks in the amount of seven pieces in the form of a pipe, which will later serve as the working chamber of the furnace.

To do this, we lay out the brick in a row and make markings on each brick, along which we will cut. The shape of the bricks after cutting should allow all the bricks to be assembled in the form of a hollow tube. Pruning is done by a grinder. For convenience, the bricks are numbered. After trimming, we collect them together and fix them with wire, checking the correctness of the cut. If necessary, we correct the form, achieving accuracy.

Important! When cutting bricks, be sure to protect your eyes and respiratory organs from dust with goggles and a respirator. Work must be carried out outdoors or in a well-ventilated area.

We place the formed brick pipe in the body with a layer of thermal insulation.

But first, from a coil of nichrome or fechral wire, it is necessary to make a spiral with a diameter of about 6 mm. To do this, we wind the wire on the base (pencil, welding electrode or thin metal rod). We take out the bricks and again lay them out on a flat surface in a row.

We apply a spiral, make markings for future grooves, which we will cut out in bricks with a grinder. We check the correctness of the lines with a building level. Ultimately, inside the workspace, the wire will be laid in a spiral from the bottom to the top of the workspace. It is important that the turns do not touch each other, otherwise there will be a short circuit.

To bring the ends of the wire outside the working chamber and connect them to the machine, between two adjacent bricks we insert three thin long pieces of ceramic tiles with thin channels sawn into them for the wire.

The use of such ceramic leads in the future will make it easy to repair the muffle furnace.

Electrical switching with three power levels

• - for the first stage of power, it is necessary to turn on two circuits of the spirals in series;
• - the second stage implies a separate connection of the lower spiral;
• - the third stage of power - parallel connection of two circuits.

When turning on the spirals, grounding is mandatory!

We place the finished structure of the working chamber in a housing with a layer of heat-insulating material and one brick laid on the bottom, coating it with refractory (furnace) clay or refractory glue.

To bring the ceramic channels outside the case, we drill holes in it.

We make the cover from sheet steel, cutting it to the size of the furnace and fixing refractory bricks on it with furnace clay. From above we weld the heck, handles and canopies. For tightness, we apply a layer of heat-resistant silicone along the edges of the lid and on the adjacent walls of the muffle furnace, having previously thoroughly degreased the surfaces.

After the oven has completely dried, we connect the wire to an electric machine with a stabilizer and carry out a series of tests, adjusting the heating power of the spirals and the temperature in the working space, increasing or decreasing the mains voltage.

Important! To make sure that the stove is completely dry, turn it on at maximum power and check that there is no steam escaping from the stove surfaces.

The door must be tightly closed while the oven is in operation.

Video - homemade muffle furnace

Tempering metal at home: we harden steel correctly

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

Tempering metal at home

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

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

Dependence of steel hardness on heat treatment mode

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

Technological nuances of hardening

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

Heat treatment modes for some non-ferrous alloys

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

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

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

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

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

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

Tempering a knife on open coals

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

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

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

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

Cooling the knife blank in oil

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

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

Modes of heat treatment of high-speed steels

Modes of heat treatment of alloyed tool steels

Modes of heat treatment of carbon tool steels

How to harden steel over an open fire

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

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

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

Hot steel colors

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

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

Temper colors of steel

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

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

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

Self-made chamber for hardening metal

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

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

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

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

Clay heater with embedded nichrome coil

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

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

Finished homemade camera

The ends of the nichrome winding of the camera, to which it is necessary to supply electrical power, are output from the rear side of its metal frame. In order to control the processes occurring in the inside of the muffle furnace, as well as to measure the temperature in it using a thermocouple, two holes must be made in its front part, the diameters of which should be 1 and 2 cm, respectively. From the front of the frame, such openings will be closed with special steel curtains. A home-made design, the manufacture of which is described above, allows you to harden locksmith and cutting tools, working elements of stamping equipment, etc. at home.

Self-production of such a furnace (as well as other types of hardening equipment) allows you not only to get at your disposal a device that fully meets your needs, but also to save a lot, since serial models are quite expensive.

Do-it-yourself muffle furnace for firing ceramics

The term "muffle furnace" itself means nothing to most people. No, this is not another type of heating appliances that save on fuel. This is a device designed for firing ceramic products, smelting metals, cupellation, creating single crystals, etc. In medicine, they are used to disinfect instruments.

Photo 1 Muffle kiln

Despite its compact size, a household unit will cost 35-48 thousand rubles, which is quite expensive for making hand-made and ceramics. Therefore, many are looking for how to make a muffle furnace with their own hands. We offer to arm ourselves with a number of tools, recall the school physics course in thermodynamics and start manufacturing.

Varieties of muffle furnaces

According to the design features, the devices are divided into:

• tubular or cylindrical;
• horizontal or vertical.

By type of heat treatment composition:

• air;
• vacuum;
• based on inert gas.

Only an air muffle furnace can be made at home, therefore it is about it that the article will be discussed.

According to the features of thermoelectric heater:

Of course, a gas furnace will bypass operation 3-4 times cheaper than an electric one, due to fuel savings, but such a furnace, firstly, is forbidden by law to manufacture and use, and secondly, it is technically extremely difficult to make a muffle furnace with gas.

Due to simple materials, the stove can be made in any convenient form, including one that is ideal for the interior of the room.

Photo 2 Scheme of an industrial muffle furnace

Device manufacturing

In this case, we will tell you how to make a do-it-yourself vertical muffle furnace for firing ceramics.

To do this, you will need the following tools:

• angle grinder (grinder) and 1-2 circles;
• electric arc welding and electrodes;
• metalwork tools, including wire cutters;
• 2mm nichrome wire.

• 2.5 mm steel sheet or used oven body;
• corner;
• fittings;
• basalt wool;
• refractory fireclay bricks;
• refractory solution;
• silicone sealant.

Essential elements

Ideally, as the basis of a homemade muffle furnace for fusing or cupellation, the body of an electric oven or miracle stove is suitable, since it already has all the necessary insulation. It will only be necessary to remove or remove all plastic elements.

Photo 3 Old oven in the form of a muffle furnace body

If it was not possible to find such an oven, the body can be welded from a sheet previously cut into blanks. Weld all the sidewalls, clean the seams with a metal brush or grinder and cover with a primer.

The manufacture of the case from sheets, although a little more complicated, allows you to make the design that fits the size of a particular room.

A heating element

A key component of the device, since the temperature in the furnace and the heating rate depend on it. You will also need to make a thermostat for the muffle furnace with your own hands, or purchase a ready-made one. A nichrome wire will act as a heating element, the diameter of which is selected depending on the maximum temperature. The minimum and most consumable diameter is 1.5-2 mm.

Nichrome on a standard spiral can withstand 1100 degrees, but it is necessary to exclude air from entering, otherwise it will burn out. Fechral is best suited to a muffle furnace - its operating temperature is 1300 degrees, and it is “friendly” with air.

Photo 4 Heating element

Any electric muffle furnace, even the smallest, made by hand, when heated to 1000 degrees, consumes about 4 kW. Before use, check all wiring and set the automatic stabilizer to 25 A.

thermal insulation

The most important aspect of the work, which is responsible for the integrity and efficiency of the entire structure. Inside the muffle furnace, fireclay bricks are installed on fire-resistant glue. According to the size of the furnace, it is cut with a grinder. Basalt wool is used on top.

Photo 5 Flame retardant adhesive Terracotta

Some forums on the manufacture of muffle furnaces recommend using asbestos for masonry. It is indeed a fire-resistant material, but already at a temperature of 650 degrees +, it begins to release carcinogens.

Making a homemade muffle furnace

The first point can be skipped by those who use an old oven as a body.

How to make a body

Cut out a rectangle of the desired size from the sheet, bend it into a cylinder and weld the seam. Next, from the same sheet, cut out a circle of the appropriate diameter and weld it to the cylinder. You get a semblance of a metal barrel, the sides and bottom of which should be reinforced with fittings and corners.

The volume of the barrel is calculated in such a way that there is enough space for insulation (wool and bricks) and for fired materials.

Photo 6 Furnace body from a barrel

The body can also be rectangular - the shape does not affect the quality of the furnace and the heating efficiency. In the video, you will see how to make a rectangular muffle furnace with your own hands from similar materials.

Video 1 DIY muffle furnace with a description

Furnace thermal insulation

1. Basalt (stone) wool is laid out along the perimeter of the structure.

Photo 7 High temperature mats

Why is this type of mineral wool chosen? For several reasons:

• incombustibility - it is used even as a barrier to open fire. Cotton wool can withstand temperatures up to 1114 degrees, after which it begins to melt, but not burn;
• natural components - basalt, from which cotton wool is made, is an absolutely natural material, therefore, even when heated, it does not emit any harmful substances, unlike, for example, cotton wool made from slag;
• minimum thermal conductivity, which is only 0.032-0.048 W / m / K, which is even less than that of expanded polystyrene.

Cotton wool is attached to the body with special ceramic buttons.

Photo 8 We fasten cotton wool to the furnace body

1. This is followed by thermal insulation with fireclay bricks. Just such a material is required, since it consists of 75% refractory clay and will not burst during the operation of the furnace.

Take 7 bricks, number them for convenience, make them look like a pipe. Next, cut the ends with a grinder so that the pipe is as round as possible.

Photo 9 Marking the refractory of the muffle furnace

When the bricks are cut and assembled, tighten them with wire and check how symmetrical the structure is.

1. You make a 6 mm spiral of nichrome wire, for which you wind it on any round object that is suitable in diameter, you can even use a pencil.

Please note that the oven can only be operated with continuous temperature control. Otherwise, it's just an expensive, but very dangerous toy. The only real sensor option for such high temperatures (over 1000 degrees) is a thermocouple. You don’t need to look for platinum for this, this option is quite suitable:

• iron-constantan, 53 mV/deg, thermo EMF;
• nickel-iron, 34 mV/deg. thermo emf.

Photo 10 Heating coil gasket

1. Unwind the bricks and cut on the inside at a slight angle grinder grooves under the spiral. Check their evenness with a level and position them so that the turns go from the very bottom to the top. It is strictly forbidden to allow the turns to touch - there will be a circuit closure. After cutting the grooves, insert the spiral and assemble the entire structure again.

Photo 11 MP made by hand

1. Bring out the ends of the spiral and connect them to a 25 A machine.
2. Now you take the previously prepared steel cylinder, put fireclay bricks on the bottom of it, cut so as to completely cover the entire bottom, fill them with refractory glue. Next, place the assembled thermal structure and also fill the space between the barrel and the structure with a refractory compound.

Photo 12 The finished structure is placed in a steel case

You can turn it on only when the whole structure is completely dry. 3-5 days after manufacture, turn on the device at full power, but do not close the lid - if evaporation starts somewhere, turn it off and leave it for another day.

Cover making

• Cut out a circle from steel, identical in diameter to the already fully assembled structure.
• On top of the glue “sit down9raquo; fireclay brick - it will provide sufficient sealing.

• Weld handles on the sides so that it is convenient to lift and remove the lid, and a latch for closing.

• Cover the edge with refractory silicone, before that the surface must be degreased (even White Spirit will do).

Recall that when the oven is in operation, it must be closed. Excessive air ingress will lead to rapid wear of nichrome.

The simplest muffle furnace for ceramics

To make such a simple device, you only need an ordinary electric stove, a clay pot and a piece of fireclay brick.

• Put a piece of brick on the stove so that the ceramics being fired do not touch the spiral on the tile and cover it with a pot. The power is controlled by the thermostat.
• Now you are watching the pot - as soon as a red light begins to shine through its walls, you mark the time for firing. As a rule, it is 10-12 hours.

Pot muffle furnace

Safety

1. It is possible to work with the stove only on condition that there is grounding.
2. It is forbidden to start work if there are chips or cracks on the body.
3. It is forbidden to touch the device during operation.
4. It is strictly forbidden to touch the running coil.
5. During operation, the oven requires constant supervision.

Despite the relative ease of manufacture, such a device is not very common among home craftsmen. “Guilty9raquo; this high electricity costs. Someone thinks that it is possible to make a muffle furnace on wood - well, if you can find a log with a calorific value of 14,000 kcal / kg, then yes, it will work. Although it is still better as such “firewood9raquo; use a forge - it was in such conditions that the first such furnace in history was invented.

If you still have questions about how to make a muffle furnace with your own hands, watch the video instruction.

Video 2 DIY muffle furnace

Homemade muffle furnace

The history of the creation of this thermal furnace is very interesting. It was invented by a French court master named Jeantot in the early 19th century. He is also known as the person who introduced the concept of "steering linkage" (Jantot's trapezoid). If you want to know more, you can watch the video or find the necessary information on the Internet.

To date, the muffle furnace is designed for heating and roasting metals, ceramics and other materials. It is called muffle, since the main feature of the design is the presence of a muffle in its device (this refractory chamber protects the material being processed during firing and is the main working space). Nowadays, muffle furnaces have many areas of use. Some of them :

• Remelting of alloys and valuable metals, when the introduction of impurities is unacceptable;
• Heat treatment of metals (hardening, cementing, normalization, tempering);
• Firing of ceramic products (firing of art products in a muffle furnace gives an even surface tone);
• Burning (sometimes cremation);
• Growing single crystals;
• Drying of electrically conductive metals;
• Assay analysis (cupellation).

Hardening (muffle) furnaces are divided into types :

Type of heating:

By protective processing mode:

• Air (firing takes place in the air);
• With a gas protective atmosphere (roasting takes place in a special gaseous environment);
• Vacuum (firing takes place in a vacuum)

• Vertical loading;
• Horizontal loading;
• tubular;
• Bell-type.

Factory or homemade oven?

If you are thinking that it is time for you to get a stove, then first you should decide: do you want to buy it in a store or do it yourself. To date, there is a huge selection of this type of product: furnaces for firing ceramics, induction. electrical, hardening, etc. however, the prices are quite high: the cheapest induction furnaces cost about 30 thousand rubles. With your own hands, at home you can make a stove volume 5-7 liters. however, the manufacture of the unit will require a lot labor expended. time and materials.

And besides, a person without experience will not be able to build a quality stove at home. Also, there are many videos detailing all the pros and cons of homemade stoves. If you are relying on your own strength, let's look at what materials will be needed.

Materials intended for the production of muffle furnaces

So, we will need:

• Structural soft metals(become);
• Refractory and heat-resistant materials: muffles (it needs ceramics), doors, etc.;
• Materials for oven electric heaters.

Also, we will need tapes, wires and rods. from the following metals :

Tubes, rods and profiles from following chromites :

The choice of materials should be approached carefully. You can also watch videos with recommendations and links to specialized stores.

The device of the muffle hardening furnace

On top there is a cover with a connector and a ground terminal, there are handles on the sides. under cover the coating is located. then comes the winding. The space inside is occupied by asbestos chips, closer to the center there is a muffle (designed to protect substances during firing), there is also a spacer plate, then there is fireclay cup. curtain and fireclay tube. At the very bottom there is a round tile or a ceramic element (door) with valve .

The volumes of such furnaces can be very different, starting from 3 liters. ending with a few dozen. You can watch a video with reviews on various do-it-yourself muffle furnaces.

How to make at home

We will consider the simplest version of the hardening furnace, also, it is sometimes used for firing ceramics. We will need a household electric stove and a clay flower pot from ceramics (in the role of a muffle) of the desired size. Now you need a sub. It is usually assembled from bricks on a steel sheet and fastened with a frame from a corner. Closer to the edge make 2-3 ring and lay either a spiral or an electric stove. The shell is made of galvanized steel, it is removable, and it is put on only after the structure is firmly installed on the floor and covered with a muffle. The gap between the muffle and the shell is covered asbestos chips .

Temperature control is carried out by thermocouple. We have considered the simplest version of the muffle furnace. If you want to build a more complex and advanced one with your own hands, you can watch the video or find the necessary drawings.

In muffle furnaces, very high temperatures can be reached. Such units are used in workshops by jewelers, craftsmen who create tiles and other ceramics, they melt metals, work with glass and enamels.

Factory-made ovens are compact, have digital temperature controllers, but are quite expensive. Even the smallest stove with a 10 x 17 cm chamber will cost 23 - 39 thousand rubles. Larger ovens for working with ceramics (35 x 47 cm) already cost 60 - 75 thousand rubles.

But it is quite affordable to make a muffle furnace with your own hands. Of course, it will be inferior in quality, but you can make it the size you need for work, and its creation will cost much less. So, let's look at how to make a muffle furnace with your own hands for firing ceramics and other needs.

Cameras can work on:

1. Electricity.
2. Gaza.
3. Coal.

But it will not be possible to assemble a gas unit at home, since it is dangerous and prohibited by law. The charcoal version can only be operated with supercharging. But if there is such a hearth, then it is easier to place a muffle in it, rather than build a special furnace. The electric option will allow you to control the heating temperature and use a compact unit even in an apartment (the power of such devices is about 2.5 - 4 kW, so an ordinary socket with grounding and a reliable wire will do).

There are various types of ovens:

1. Horizontal.
2. Vertical (potted).
3. Tubular.
4. Bell-type.

The first option is the easiest to reproduce on your own.

How does a muffle furnace work? The main parts of the structure

The design of the furnace is a chamber (muffle), where the temperature is set from 20 to 1150 °C. The heating element is a nichrome wire twisted into a spiral. Two layers of thermal insulation allow you to keep heat for a long time (the more reliable it is and the less heat loss, the higher the efficiency of the product). The brick layer accumulates the temperature. You can use refractory fireclay bricks, or asbestos (however, its use is increasingly rejected due to the harmful substances that it releases when heated). The second layer is made of basalt fiber, or perlite.

All layers of the furnace are placed in a metal case.

The process of heating the workpiece occurs not due to direct radiation from the spiral, not under the influence of open fire, but by heating the muffle array. It creates the effect of an oven and ensures uniform heating.

Homemade muffle furnace in a metal case

As a housing for a furnace, they often use housings from obsolete equipment - an old oven, refrigerator, etc. If nothing suitable was found, they buy sheet metal and cook the housing from it.

The fact that the part is heated evenly, and without direct exposure to the infrared radiation of the spiral, gives:

• Melting of valuable metals without impurities.
• Obtaining an even shade of the surface of artistic ceramics.
• The possibility of drying conductive materials and much more.

Materials and tools for assembling the structure

Before you start making a muffle furnace with your own hands, you need to acquire a set of tools. For work it will be useful:

• welding and electrodes;
• Bulgarian;
• nippers and scissors;
• respirator, goggles;
• steel or body from the oven;
• metal corner;
• galvanized mesh with a cell of 2 x 2 cm;
• door - ready-made, or home-made;
• fireclay brick;
• refractory mixture;
• heat resistant silicone;
• perlite or basalt slab (roofing insulation 1 - 2 cm thick);
• nichrome wire 1 mm.

The thickness of the metal for the case should be 2 - 2.5 mm, since the final structure will be very heavy. For the same reason, if thin-walled household appliances are used, they must be reinforced with a steel corner.

Those who are going to fire ceramics will not need temperatures above 800 ° C, so they can make a muffle from any porcelain or earthenware or an old cistern.

Refractory masonry

Brickwork will be much more reliable, but it must be borne in mind that the spiral located inside the furnace will slowly evaporate, and these vapors will enter the product.

The manufacturing process of the refractory chamber

So for working with precious metals it is better not to use homemade units.

So, fireclay bricks and a mixture for mortar are purchased, which is not afraid of heat.

Fitting and marking

This action must be performed in order to be able to cut a groove in the wall of the muffle for the heater coil before the start of laying.

1. On a flat surface, the future side and rear walls of the refractory are laid out.
2. Bricks are adjusted, trimmed (it is important not to forget about the thickness of the seams, 3 - 5 mm, they can be imitated by wire).
3. After fitting, the bricks are numbered, markings are applied to their surface where the spiral will pass (at this stage, you need to make a spiral with your own hands).
4. In glasses and a respirator, grooves are cut by a grinder.

Finishing the stove with tiles is an expensive pleasure, but such decor brings a unique sophistication to the design of the room. To save money, you can try making them yourself. , read carefully.

You will find step-by-step instructions for assembling the Bubafonya oven.

The Russian stove is still relevant, and its construction is quite laborious. But if difficulties are not terrible for you and you want to make a stove with your own hands, step-by-step instructions for building will help you:. Consider the rules and stages of laying the furnace.

Making a spiral for a muffle furnace

You will need a base rod on which the wire will be wound. Its diameter should be approximately 5-6 mm, and the surface should be smooth. When the spiral is ready, it is applied to the brick blank and marks are made according to the resulting dimensions.

Later, when the masonry is ready, the winding will need to be carefully laid into the grooves and secured with the help of “staples” from the same wire. The ends of the staples are sealed into the seams.

Spiral heating element of the muffle furnace

Spiral outlets are located in the side or back wall. It is more convenient to fix them on a ceramic plate. The switch is mounted on the body, the spiral wires are connected to it. On the one hand, it will have two contacts ("+" and "-"). If you make two separate circuits, you get three power levels of the device:

1. Sequential connection of two circuits.
2. Only the bottom coil.
3. Parallel connection of two circuits.

RCD and grounding are a must. In order not to burn the spiral at the first connection, you need to wait for the masonry mortar to dry completely.

Camera

A heat-resistant mixture is diluted (instructions can be read on the package). The bucket is filled with water. The brick will be dipped into it for 20 seconds before being laid.

First, the bottom of the muffle is laid out, then the walls are erected. The ceiling is laid with a vault, with a castle brick.

Another option is when the chamber is made of bricks placed vertically and in a circle. It should look like a pipe.

Grooves are also applied, and on the sides, with the help of a grinder, a bevel is made.

When a ready-made body from the oven is used, it is reinforced with corners, then basalt insulation is glued to the inner walls (on heat-resistant silicone or special glue). Then, already fitted, numbered bricks with a groove are placed from the bottom up. They need to be laid very tightly (the thickness of the seams is not more than 5 mm).

Thermocouple

It is imperative to control the degree of heating in a closed muffle, but it is much more difficult to do this than, for example, in a blacksmith's furnace.

In high temperature conditions, only one type of sensor can work - a thermocouple (dissimilar conductive parts that are connected together).

Two ceramic tubes are made, from which two wires are brought out: one of aluminum, the other of an alloy of chromel (or nickel and iron).

One end of the wires is twisted together. Welding is not necessary, as the ends will soon burn anyway. They will need to "bite off" and twist the ends again. The other ends are connected to a regular household tester.

Door

There is also a layer of fire-resistant brick on the door. To fix it, a steel corner is welded, which will support the masonry.

The door is removed, placed on a flat surface. A mesh is attached to it.

Cement is added to the mortar, and a brick is laid out.

The door must be securely locked during melting work. It can be equipped with a screw or wedge mechanism.

Hinges from household appliances may not withstand the load of a door with a brick layer. It is better to replace them with more powerful ones.

Seal

It is unacceptable that the door does not fit snugly against the body of the furnace. She needs some extra sealing.

You can use a heat-resistant rubber band (used on ovens). And you can still the same silicone. The door in the places of contact is degreased, and a substance is applied to the oven itself, to which silicone does not stick (any grease).

Silicone is applied in a thick layer on the edges of the door, it closes. As a result, the seal will stick to the door, but the edge of the oven will remain clean.

The seal will burn through over time, so silicone should always be on hand to replace it.

Drying kiln

The main thing here is not to rush. The downtime period can take two weeks, but you should not resort to forced drying, otherwise cracks may form and the entire structure will have to be redone.

The furnace is placed in a dry ventilated room with positive temperatures.

You can check the readiness of the furnace by turning on the spirals to the weakest power mode. A dry unit will not emit steam.

Conclusion

If you still need a muffle furnace operating at temperatures above 1000 °, you can try to look for b. y. (they can serve for a very long time, there is practically nothing to break here, except for the thermocouple, which is regularly replaced). But the prices for used muffles do not drop much.

The presented project of a home-made muffle furnace is more suitable for work with t up to 900 ° C, which will suit ceramic artists.

Related video

The muffle furnace is mainly used for melting non-ferrous metals and firing ceramic products. The essence of its work is as follows, the workpiece is in a chamber closed from the source of combustion and combustion products, heat and heat pass into it through a wall or partition.

At home, it is quite possible to make such a furnace with air access to it, only in industrial production can one find a furnace where the heat treatment of products will take place in a chamber without air, that is, a vacuum or in a heated gas environment.

Industrial furnaces use such type of fuel as gas. In artisanal conditions, it is not recommended to make such a gas oven. In this article, we will consider a muffle furnace based on electrical energy.

Necessary materials

Materials needed directly for the manufacture of the furnace:

• fireclay brick
• spiral for one and a half kW
• heat-resistant clay or mortar

After its manufacture, it is placed in a casing. It can be welded from 2 or 3 mm steel sheets. Its dimensions are taken based on the size of the furnace. Also, in the form of a casing, you can use an old gas or electric oven, after removing all plastic parts and elements from it. The space between the oven and the casing is filled with an insulating material such as mineral wool.

Top-loading kilns are best suited for ceramic firing jobs. In furnaces where mainly work will be carried out with melting, hardening or other metal processing, the heating process of the product should be controlled by using a temperature sensor, loading into such chambers of workpieces is carried out horizontally.

Consider step by step an example of a muffle furnace

In this case, an old iron rectangular tank is used for the casing. It should be slightly modified and it will be fully suitable for its role. Having cut off the edge from the tank with a grinder, on which there is a round hole, 5-10 cm wide. We drill holes along the edges for fastening the door to the body on the curtains.

The work should begin with planning: Assemble the dry brick oven, make markings on it from the inside, in those places where the spiral will need to be laid. In the brick, according to the markings made earlier, with the help of a drill, using a pobedite drill, recesses should be made. In the illustration below, the drill is placed at an angle to the groove, this is how the desired result can be optimally achieved.

We put the prepared brick in the oven, from the corner you should make an external frame for it. We put a spiral into the grooves. We coat the entire structure with a mortar solution on water. All cracks should be sealed.

Next, you should make an electronic unit that will control the heating of the spiral. At what it will not be easy to heat up the oven, but it will be stepwise heating. For this, a step thermostat is used. A stand should be made under the muffle furnace to avoid losses at the bottom. The frame is cut out from the corner and welded at the corners, legs are welded onto it on the sides, also from the corners. A row of plates are welded on top.

We use special fiberglass heat shrink. It serves to protect the thermocouple, the characteristics of which are as follows: chromel-alumel (TXA) diameter 0.5 mm, length 1 m. We also use a ceramic tube with two holes for a thermocouple. You will also need a thick heat shrink to power the spiral. We put on a heat-resistant fiberglass cambric on the thermocouple, insert its end cap into a ceramic tube. At the top of the stove, a hole is made with an ordinary drill and a thermocouple must be inserted there and covered with a mortar. Let dry.

To connect, you will need a special heat-resistant wire for electric furnaces. The coated oven is hidden in a casing, its thermal insulation will be provided by basalt wool. At the top of the casing body, you need to make a hole for the output of power wires and a thermocouple to control it. Before the final packing in cotton wool, a test connection of the oven should be made.

The device itself is installed on a sheet of asbestos. Cotton wool should be laid with medical gloves. The control unit for the furnace. Next, we proceed to the manufacture of the furnace control unit.

The set of accessories consists of:

• housing (taken from a small switchboard)
• electromagnetic contactor (in this case still "Soviet")
• terminals (one ceramic for connecting the nichrome helix from the muffle furnace to the power wires, and more from fire-resistant plastic for the main switching)
• automatic 16A; bolts, nuts, engravers; thick wire and plug
• thermostat Profil-M-1K multi-stage single-channel

The thermostat can heat according to a complex schedule, you can set the time and temperature of heating in this interval.

This is what the finished device looks like.

Various materials are subjected to heat treatment in the muffle furnace. It can be used for firing, burning, hardening, smelting metals, glass, ceramics, wax. The versatility of the unit is provided by a large heating range: 20-1000ºC. The need to have a device leads to the decision to make it yourself, since the prices for such units are high in the distribution network. going to do-it-yourself muffle furnace fast enough if all the materials are prepared. Drying will take several days, as it will be necessary to lay fireclay bricks.

How does a muffle furnace work?

In order to make a muffle furnace, it is necessary to understand the principle of its operation. Fuel can be gas, coal, electricity and even wood. In this case, it is better to make an electric unit yourself. It consists of a heating chamber and thermal insulation that saves heat. The accumulator of this heat is a refractory brick. Heat treatment is carried out in a working chamber - a muffle, which is why the furnace got its name.

At home, any refractory form is used for the muffle, for example, porcelain, made of ceramic plates. It can also be made from fireclay clay or bricks. It should be taken into account that the melting temperature of the mold must be higher than the melting temperature of the material used for heat treatment. At home, a homemade muffle furnace is used to melt a small amount of metal or to harden a tool. That is why it is enough to make it small.

Materials for assembling a muffle furnace

To assemble the unit, you will need the following materials and equipment:

• Bulgarian,
• refractory brick,
• welding machine,
• metal case, for example, a bucket; sheet steel, if the case has to be made by hand,
• steel corners as stiffeners for the bottom of the hull (welded from the outside),
• thermal insulation, for example, asbestos sheets, chips, rope or basalt wool,
• wire with a cross section of 1 mm for a heating element spiral, for example, nichrome; it is better to buy a ready-made spiral.

First of all, they are determined with the body. The dimensions of the working chamber depend on its dimensions. This refers to the finished construction, for example, if using a steel bucket or an old gas oven. The body can be welded independently from sheet steel, then the muffle is first made, then it is determined what dimensions the body should have.

Also, a do-it-yourself muffle furnace can be made in a different way. The working chamber can be molded from fireclay clay or a ceramic pipe of medium diameter can be obtained. Depending on this, the technology of work will differ.

Making a spiral for a muffle furnace

Nichrome wire with a cross section of 1 mm is wound on a steel bar with a smooth surface. The sufficient diameter of the turns is 6 mm. It is necessary to ensure that they do not touch during winding. The spiral is laid in grooves prepared in bricks. Further, they should be prevented from falling out of these grooves when heated. To do this, you can make a thin putty of fireclay clay or use a wire. If a ceramic tube is used for the muffle, the wire is wound from its outer side. A distance of 2 mm between the turns must be observed.

Finishing the assembly of the muffle furnace

A brick or ceramic working chamber is placed in a steel or cast iron case, on the bottom of which a heat insulator is preliminarily laid. From the outside, the bottom is reinforced with steel corners, since fireclay bricks will make the structure heavier. Between the walls of the chamber and the body there should be a space of 4 cm. It is in it that the insulation is laid. The cover is made of 2 layers of metal and insulation between them. An opening handle should be provided.

Further, holes are drilled in the furnace body and the spiral leads are pulled out. In addition, it is necessary to make holes for the temperature sensor. The wires are connected to a separate cable. It is connected to a 20A machine for the safety of the mains. The connection of the leads and the cable can be made using a ceramic cartridge. In this way, it will be possible to avoid twisting the wires. The legs for the body are made of steel pipes. They are welded or screwed with bolts and nuts, but then the bottom of the stove must be raised so that the screws are outside.

If an old gas or electric oven was used to make the muffle furnace, then it is not required to insulate it. In its design, thermal insulation is provided by the manufacturer. It should be noted that such a unit is advantageous to manufacture if a medium-sized furnace is needed. Grooves for the spiral are made in the side and rear walls. The leads are connected to a switch located on the outside of the sealed door.