Operating temperature of a home muffle furnace. Stages of work on the manufacture of the stove. Classifications of such furnaces

Today, muffle furnaces are in demand at enterprises of various types. They are indispensable for testing, acceleration chemical processes and other works with metal, ceramics, glass, etc. If you want to buy a muffle furnace, please note that using the equipment is allowed only after reading the manufacturer's instructions.

Muffle furnaces can have different loading chamber volumes and opening types

Electric muffle furnace - what is it?

A muffle furnace is equipment that allows you to create optimal conditions for laboratory research and production processes associated with heating materials and products. The vast majority of these units are powered by electricity. To ensure that Electric Furnaces optimally suit their purpose, they are made from high-quality materials.

When working with muffle furnaces, it is necessary to strictly adhere to safety regulations

History of muffle furnaces

Muffle furnaces were first used in France. Their appearance is associated with the name of the famous carriage maker Jeanto, whose family built carriages for the royal court and noble nobles. He invented the steering trapezoid at the end of the 17th - beginning of the 18th centuries, but its tests were constantly frustrated due to the breakdown of the experimental axles. The situation has changed in better side, when a Russian nobleman came to the master, who wanted to order the famous European carriage maker to make a luxurious carriage. It was supposed to be a gift from Peter the Great to the Khan of Bukhara.

After testing the axle's strength, this customer told Jeanto how to improve it. First, it was necessary to perform cementation in a muffle made from a material that included powdered cattle horns. And only after that carry out hardening. This processing technology allowed the steel to remain viscous on the inside, but have a hard, hardened crust on the outside.

The muffle furnace, designed by a French master, was called the axle construction system

Areas where muffle furnaces are used

The muffle furnace is used in many areas; its application is quite wide. The device is necessary for heat treatment, as well as storing a variety of samples and materials under certain temperature conditions.

Let's figure out why a muffle furnace is needed; the equipment is used for:

Hardening, tempering, melting and other operations with metals.
Thermal firing of ceramics.
Ashing and cremation.
Drying of all kinds of substances.
Analytical research.
Growing single crystals.
Production of jewelry and souvenirs.

Muffle furnaces are used when working with dental materials, precious metals and other types of materials

Main types of muffle furnaces

All types muffle furnace conditionally divided according to the following criteria:

Purpose (industrial, laboratory, jewelry, educational).
Type of construction (horizontal and vertical loading, tube furnaces).
Processing medium (air, gas, vacuum).
Weight (from 18 kg).
Working chamber volume (from 3 l).
Heating level (moderate, medium, high temperature).

If we take a closer look at the muffle furnace and what it is, then the models can be divided according to the type of heating into electric and gas.

Muffle furnaces can be used for laboratory and educational purposes, industrial, jewelry, etc.

Advantages and disadvantages of muffle electric furnaces

What is a muffle furnace? It is a heating technique that has a wide range of operating temperatures and ensures precise adjustment. In addition to the convenience of loading and unloading processed materials, the advantages of heat-generating devices include:

Uniform heating of materials without temperature changes.
Cooling rate of samples after heat treatment to proceed to the next production stages.

Sealed door closures minimize heat loss and increase efficiency

But a muffle furnace, the purpose of which is to expose surfaces to high temperatures, also has a number of features that some users consider disadvantages. These include:

Inability to use equipment at temperatures above 1300° C.
The relatively low thermal resistance of the muffle, which determines the number of thermal cycles withstandable (heating-cooling).
The need for additional electricity to heat the muffle itself.

Muffle furnaces are characterized by significant thermal inertia, which different cases considered as a plus or minus of equipment

How does an electric muffle furnace work?

The working capacity of an electric muffle furnace is the so-called muffle. This is a ceramic or fiber tank of a semi-cylindrical shape, the heaters in which are built into the walls, i.e. are internal or closed. There are electric furnaces for ceramics and porcelain with stationary muffles, as well as those equipped with a stationary heating chamber and a replaceable muffle. In any case, when the heating elements are closed, the processed materials and objects are protected from direct radiation from the heaters. And those, in turn, are protected from exposure to aggressive vapors and volatile substances released during heating.

Muffle furnace design

What does the design of an electric muffle furnace consist of?

An electric muffle furnace is a device consisting of several elements:

Working chamber. It heats up different substances and objects.
Housings. Performs protective and heat-insulating functions.
Heating elements. Ensure the performance of thermal operations.

The wire or tapes are located in the chamber; they can be partially or completely open or completely closed.

Operating principle of a muffle furnace

Considering the muffle furnace, its structure and principle of operation, we can say that over the past centuries the equipment has gone through many transformations and has changed. Only the essence of its functioning remained unchanged. Parts or substances placed in the muffle are isolated from external environment and are heated evenly on all sides.

Harmful substances that may be released from samples during heating are removed using a ventilation system. In addition, the ovens provide natural or forced convection

Heating elements of muffle electric furnaces

As can be seen in many photos, the muffle furnace performs heat treatment thanks to heaters. They can be different shapes and sizes. Depending on these indicators, it may be necessary different quantities work items. They are located around the entire perimeter of the loading block, and may differ:

Design(tubular, tape, spiral, etc.).
Manufacturing materials(nichrome, fechral, tungsten, chromite, etc.).
Arrangement method(closed, open).

The most common form of heaters is a spiral made of wire with excellent heat resistance and resistance.

Electric muffle furnace control system

A modern muffle furnace is a device that makes it possible to process various materials and is easy to use thanks to control modules. Today, mechanical, analog models are used less and less; they have been replaced by electronic and programmable thermostats. With their help you can quickly and clearly:

Set any thermal values.
Set gradients and switching times.
Monitor current thermal indicators.
Carry out heat treatment with high precision.
Set heating times and temperatures.
Determine the holding period and cooling time, etc.

Modern modules allow you to program even complex operating cycles of equipment

Buy a muffle furnace or make one yourself

It is quite possible to figure out how to use a muffle furnace on your own, but how to make this device is not entirely easy to understand. Having considered even an incomplete list of necessary starting materials and a schematic description of the construction process makes it clear that the independent manufacture of muffle furnaces is a rather complicated matter. The market offers big choice a variety of models, which allows you to find the best option.

What does it mean to have a muffle furnace made in strict accordance with technological requirements, workers of laboratories, workshops and workshops know - equipment not only speeds up many processes, but also allows them to be carried out with extreme precision.

Making a muffle furnace at home

How to make a muffle furnace with your own hands

Regardless of the design of the muffle furnace, the design of the device will consist of the following elements:

Muffle. It’s better to do it yourself and not try, because... you need ceramics with high thermal conductivity, which can only be provided by additives made of rare metals. Purchasing a ready-made product will help you get out of this situation. ceramic tableware at a laboratory equipment store.
Fireproof. As the first layer, you can put asbestos boards and fiber, as well as fireclay bricks, which will be the cheapest in cost. For the bond, it is better to take a fire-resistant mixture for masonry.
Frame. Many home-made refrigerators use old refrigerators, which must be strengthened, especially the bottom. This can be done by welding a steel rectangular angle.
A heating element. There are ready-made spirals, but if you wish, you can wind them yourself from nichrome or fechral wire.

Basalt wool is used for reliable cladding of the body

Tools and materials for making a muffle furnace

The use of a muffle furnace is relevant in various fields. Depending on the operating conditions and the type of samples being processed, the following are used for the production of equipment:

Structural steels. They are used to make the body (casing), support, door and some other elements.
High alumina materials and fire retardant fiber. They are used to construct working chambers - muffles.
Nichrome, fechral, tungsten, molybdenum, tantalum. These and other materials serve as the basis for the heating elements of a muffle furnace.
Fiber compressed blocks. They form a highly effective thermal insulating shell (lining).

A prerequisite for the materials used is environmental friendliness, heat resistance and impact resistance

The following tools are used to create an electric muffle furnace:

Drill and set of drills.
Grinder, cutting and grinding wheels.
Welding machine, electrodes, clamps and magnetic corners.
Hacksaw.
Screwdriver.
A tape measure, a metal ruler and a construction square.

To construct a muffle furnace you will need tools for working with metal and wood.

Step-by-step process for making a muffle furnace

Before you start designing, prepare a drawing of a muffle furnace, all the data in which will be derived using formulas and precise calculations. Make sure you have everything necessary components and devices. After preparation components begin their adjustment, among the many stages of which:

Laying bricks on the bottom and walls of the future muffle furnace.
Door seal, which can be done using silicone, and sometimes a screw locking device is created.
Heating coil gasket etc.

When choosing the optimal volume of the working chamber, consider the size of the objects that will be processed

Basic calculations for the manufacture of muffle furnaces

Based on what the muffle furnace is intended for, its optimal characteristics and capabilities are selected. In order for the unit to operate productively and safely, many calculations need to be made. You will need to determine:

1. Parameters of the electric heater of the electric muffle furnace

What does a muffle furnace look like - a chamber with a door, inside of which there is a heater. Whether the unit will function depends on whether you select the components correctly. Among other things, it is worth paying attention not only to the estimated power of the heater, but also to its:

Manufacturing materials.
Accommodation.
Constructions.

It is necessary to determine the cross-section and length of the wire that will be used to create the heater. For example, the minimum diameter for spirals from:

Nichrome– (7÷10) × d.
Fehrali– (4÷6) × d.

All calculations must be carefully checked to prevent rapid combustion of heaters and fire hazards.

2. Power and current of muffle furnace

In order for the muffle furnace, a description of the functioning of which can be found on various thematic forums, to fulfill all the assigned tasks, it is necessary to calculate:

Power. You can find the optimal indicator based on the volume of the furnace. The table below shows the recommended ratios of indicators.

Current strength. The formula used for calculation is: P÷U , where P is power, U is voltage.

The volume of the chamber is measured in liters, while the specific power is in watts

3. The optimal length of wire for an electric muffle furnace

Considering what the muffle furnace is used for, it is necessary to select the correct wire size. Having the meaning of its general and resistivity, used as heating coils, you can find the length of the conductor.

Resistance heating element(R), determined by the formula U÷I , where U is voltage, I is current.

The current power affects the choice of wire cross-section - if components with insufficient capabilities are used, too much current will quickly overheat them, melt them or cause burnout

4. Specific surface power of the electric muffle furnace

Some models of muffle furnace can produce different amounts of thermal power. A conductor generates a certain amount of energy over its entire area. It is possible to determine what this indicator should be so that the surface does not lose its operational and mechanical properties. It is not recommended to exceed the permissible value, otherwise the spiral will quickly fail. To avoid this, you need to make a miscalculation with the wire larger diameter or increase the length of the heating element.

The indicator is calculated βadd according to the formula: βeff × α , where βeff is the effective specific surface power, α is the efficiency coefficient of the thermal radiation of the spiral.

At the intersection of columns and rows the value βeff is formed

As you can see, the device and operation of the muffle furnace are complex system. You can learn more about the capabilities of the equipment from the specialists of the Labor company. Call us, we will select for you the optimal type of electric furnace for any purpose!

In the production of various ceramic or metal products requiring heat treatment, a muffle furnace is used. When processing products, a factory-made model or a home-made muffle furnace can be used in compliance with all safety requirements and regulations. A do-it-yourself muffle furnace must be equipped with heaters of sufficient power to perform various operations related to the heat treatment of products.

Production and use

Muffle furnaces are widely used in the production of various products. industrial enterprises, educational institutions, repair shops and jewelry workshops.

To carry out laboratory research, a Snol muffle furnace is used, with the help of which hardening, firing and heating are carried out various materials. Material processing performed with Cnol allows for the melting of metals, the production of dental prostheses, and the hardening of ceramics.

Cnol equipment is manufactured by JSC Napal located in Solnechnogorsk, Moscow region. The list of equipment includes models with a working chamber volume from 3 to 40 liters and includes models:

PM Cnol 10/10;
PM Cnol 10/11;
PM Cnol 6/10;
PM Cnol 3/10;
PM Cnol 30/13;
PM Cnol 40/118;
PM Cnol 7.2/13.

with a chamber operating temperature from 1050 to 1300 °C (depending on the model). To regulate the temperature regime, a special thermostat is used that allows you to change the temperature in the chamber. To perform technological operations associated with large formation of combustion products, a special pull out drobe, in which the Cnol muffle furnace is placed.

Industrial enterprises produce various muffle furnaces EKPS 50 3U, MIMP-10P, MP-2UM, EMP 12.1 M "Averon".

In production ceramic products muffle furnaces Naberthem (Germany) are used in more than 100 countries. In the list of equipment produced, a special place is occupied by models for firing ceramics with a working chamber volume from 16 to 2200 liters and a heating temperature of up to 1340 °C:

Top 16/R+B400 Naberthem ;
Top 45+B400 Naberthem ;
Top60L+B400 Naberthem ;
Top 80+B400 Naberthem ;
Top 130+B400 Naberthem ;
Top 160+B400 Naberthem ;
Top 190+B400 Naberthem ;
Top 220+B400 Naberthem.

Naberthem offers a wide range of laboratory equipment:

laboratory smelting;
soldering;
chamber (with fibrous or ceramic insulation);
agglomeration;
muffle;
for ashing;
for firing ceramics.

Types of muffle furnaces

Furnace models are divided according to 2 main characteristics:

the energy source used;
body designs.

Muffle furnaces use 2 main energy sources:

electricity;

When making a muffle furnace with your own hands, it is most advisable to use heating elements as a heating element, since when using gas, the requirements and standards for the device create significant difficulties during assembly.

Structurally, furnaces are divided into:

tubular;
vertical;
bell-shaped;
horizontal.

Heating or firing of products can be carried out in various environments, according to the technology used:

V gas environment;
in a vacuum;
in the air.

The most affordable and simple option for making a muffle furnace is heating products in air, which does not require additional equipment or financial costs.

Device

The oven consists of several main elements:

Cases.
Thermal insulating inner layer.
Thermal insulating outer layer (refractory bricks, ceramics).
Heating elements.
Control elements and electrical wiring.

The body is made of metal with a thickness of more than 2 mm, according to a pre-prepared diagram.

The thermal insulation of the inner layer is made of refractory bricks with a maximum operating temperature of up to 1000 °C.

For the outer insulating layer, perlite or basalt wool is used, which are good insulators. It is especially worth noting that materials containing asbestos are prohibited from being used, since toxic substances are released at high heating temperatures.

The heating element - spiral is made of nichrome or fechral wire with a diameter of 1 mm. Nichrome wire consists of nickel and chromium and has good anti-corrosion properties. Fechral wire contains the metals iron, aluminum and chromium and is much cheaper. Both types of wire are able to withstand heating temperatures and long-term operation without changing their characteristics.

Manufacturing process

The most acceptable option for making a muffle furnace with your own hands is vertical or horizontal model with the process occurring in air using electricity as an energy source.

The entire manufacturing process consists of the following operations:

Body parts are cut from sheet iron and welded together. The welds are cleaned, and the entire body is covered with fire-resistant paint in several layers.
A door is made of steel, which is welded to the body using hinges and a locking mechanism is installed.
External thermal protection made of perlite is installed.
The working chamber is assembled from refractory bricks without mortar. Markings are made for laying the heating coil in the grooves and special leads to the control unit and power supply.
Grooves are punched into the bricks for laying spirals.
A heating coil is made by winding nichrome wire onto a rod with a diameter of 6 mm.
The chamber is laid out inside the brick casing using mortar, observing the markings for laying the spirals and the diagram.
The oven is dried, the spiral is laid, electrical wiring and grounding are connected.
Thermal insulation is mounted on the door.

To regulate the heating temperature in the muffle furnace, 2 circuits are laid out of spirals, which, according to the connection diagram, can operate in three modes:

The first mode - two circuits of spirals are connected in series.
The second mode – the lower circuit of the spirals is connected.
The third mode - two circuits of spirals are connected in parallel.

The body is carefully insulated using clay, fire-resistant glue and heat-resistant silicone. After the masonry has completely dried and insulating materials The equipment is configured and tested in three operating modes.

For almost all of us, a muffle furnace is an unnecessary device. But such furnaces are needed exclusively for people in those professions that are associated with smelting, firing ceramics, or manufacturing jewelry. In addition, with the help of muffle furnaces it is possible to create single crystals, and in medicine they can be used for sterilization at high temperatures. The cheapest “store” version of the device costs about 30 thousand rubles, which, of course, is not affordable for everyone. But if you remember something from a physics course at school ( we're talking about mainly about thermodynamics), then you can make a muffle furnace with your own hands.

Classifications of such furnaces

There are several classifications of the described devices. Yes, according to design features There are such ovens:

cylindrical;
tubular;
horizontal (this is the simplest option);
vertical.

Moreover, heat treatment of products can be carried out not only in air, but also in a special gas or vacuum. But, characteristically, only air can be used at home.

There is one more classification. Based on the type of heating element, the devices described can be:

electrical;
gas.

Application gas ovens They are significantly cheaper, but you cannot do them yourself - this is prohibited by law. As for electrical appliances, they will cost more, but they have one important advantage - the user will be able to independently regulate temperature regime.

Note! A muffle furnace made by yourself can have any size and shape; it can be made in a style that would be ideal for a specific home design.

Now - directly to the manufacturing process!

Option #1. Manufacturing of vertical muffle furnace

This option is the most convenient to use, so let's start with it. The manufacturing procedure itself (subject to availability) quality instructions, of course) is not anything complicated. Traditionally, work begins with preparing everything necessary.

Stage 1. Equipment and consumables

To create a furnace vertical type The following list of equipment/materials will be required.

Grinder, “metal” circles for her.
Plastic glasses.
Wire cutters.
Respirator.
Welding machine.
Fireproof mixture.
Nichrome wire (0.1 centimeter in diameter).
Silicone based sealant.
Steel sheet (its thickness should be 0.25 centimeters).
Fire brick.
Stone mineral wool.
Metal corners.

The preparation stage also includes familiarization with the main structural elements of the device. There are several of these, let’s take a look at them.

Note! Asbestos cannot be used for thermal insulation, since it can release carcinogenic substances when heated.

Now a little about making the body for the future stove. To do this, you will need a sheet of metal from which a rectangular piece of the required size is cut. This rectangle is rolled into a “pipe”, and the seams are welded using welding machine. The finished cylinder is painted using fire-resistant paint, then, when it dries, a circle pre-cut from metal is welded on one side (this will be the bottom). After this, the body is strengthened using reinforcing rods. It is important to calculate the volume of the case in advance - after all, you still need to place layers of thermal insulation into it.

Note! If an electric oven is used as the body, then the bottom will be reinforced with corners.

Stage 2. Direct manufacturing of the furnace

Now let's begin the manufacturing itself. The algorithm of necessary actions is given below.

Step 1. The internal surfaces of the body are lined with stone mineral wool.

Step 2. After this, thermal insulation is installed - it, as noted above, is made of refractory bricks. The procedure is as follows: seven bricks are joined inside the cylinder so that a pipe is formed. Subsequently, this pipe will serve as a working chamber.

All bricks must be placed in a row and marks must be made on them according to which the cutting will be done. After this, the bricks are cut so that their shape allows them to be folded into a hollow pipe. To simplify the work, it is advisable to number each of the bricks. When the cutting is completed, the pipe should be assembled and tied together with wire. Then it is checked for symmetry, and if necessary, the position of the bricks is adjusted.

Note! You need to cut the brick outdoors or, alternatively, in a well-ventilated area. Moreover, do not forget about individual protective equipment- glasses, respirator, etc.

Step 3. Nichrome wire is twisted into a spiral, the diameter of which is 0.6 centimeters, by winding it onto any base (this could be, for example, a pencil). Next, the bricks are removed from the cylinder and re-laid in a row.

Step 4. The spiral should be applied to the bricks in order to mark future grooves. Using the mounting level, the correctness of each of the lines is checked. It should turn out so that the spiral runs from the bottom to the very top of the structure. The turns must not touch, otherwise there may be a risk short circuit, and a do-it-yourself muffle furnace can fail!

Step 5. Between two bricks you need to insert 3 strips made of ceramic tiles(with their help the ends of the spiral will be brought out), in which channels are made of polypropylene for the wire. Thanks to these channels, repair work will subsequently be significantly simplified.

Step 6. The entire structure is installed in a steel cylinder. It is important that before this, another brick is laid on the bottom, covered with a special fire-resistant glue. Also, a pair of holes are drilled in the body in the required places in order to remove the ceramic channels.

Note! Turning on the spiral is allowed only after the entire structure has completely dried, otherwise it - the spiral - will be damaged.

Step 7 The lid will be made from the same steel sheet. A circle is cut out according to the dimensions of the body; for greater reliability, another unit of refractory brick is placed on top of the lid. After this, it is necessary to weld the handle, the iron latch, and the canopy. The edges of the circle that come into contact with the body are treated with fire-resistant silicone. Typically, silicone can only be applied to degreased surfaces.

Step 8 The design is almost ready, all that remains is to carry out a test run. But before this, it is necessary to install the device in a ventilated and warm place so that it is completely dry. Application of any heating devices is prohibited, because this may cause the masonry to crack. When the structure is dry, the spiral must be connected to the machine. After this, the power and desired temperature conditions are adjusted.

Note! To check how dry the masonry is, the device is turned on at full power. In this case, you need to observe whether steam is emanating from the surface.

During further operation, the lid must be tightly closed. Now let’s take a look at another manufacturing option – this time horizontal.

Video - Muffle furnace

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Option #2. Creating a horizontal structure

The manufacturing procedure is in many ways similar to that described above, but significant differences still occur. The body can be made from an old oven, washing machine or, alternatively, steel sheets (the thickness of the latter should be at least 0.2 centimeters). The procedure consists of two stages, let's get acquainted with them.

Stage 1. Preparing everything you need

In addition to the body, to make a muffle furnace with your own hands you will need the following equipment.

Welding machine.
Individual protection means.
Bulgarian with circles.
1mm wire made of nichrome.
Iron corners.
Stone wool.
Fire brick.
Scissors for cutting metal.
Abrasive saw.
Fire retardant adhesive.

If there is nothing to use as a body, you will again have to make it from scratch. To do this, you need to cut out the walls from steel sheets required sizes and weld them into a single structure. After this it is welded top part and bottom. From the outside, the bottom is reinforced with metal elements, and legs made from corners are welded in the corners. Now you can proceed to further actions.

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Stage 2. Manufacturing instructions

Step 1. The base of the body is laid with a 10-centimeter thermal insulation layer. To avoid deformation processes, pieces of metal corners are laid on top of the insulation. A sheet of metal of the required size is laid on top of the corners. A similar procedure is performed with the walls of the housing.

Step 2. Now let's proceed directly to laying and connecting our device.

Note! Before starting work, the refractory brick should be immersed in water for half a minute so that it does not absorb liquid from the working solution.

Brick laying begins from the bottom, a fire-resistant adhesive mortar is used (it is mixed as required by the manufacturer's instructions). It is important that the width of the seams between the bricks does not exceed 5 millimeters.

Step 3. When forming brick walls, it is used new solution– this time it is necessary to add cement. The proportions should be as follows: for each kilogram ready mixture there should be about 300 grams of cement. Masonry can only be completed after installation has been completed. stone wool And metal sheets. Although you can do without a thermal insulation layer, but only on the condition that the bricks are laid flat.

Step 4. The bricks are laid from top to bottom, while bandaging the seams is observed. If necessary, they are trimmed using a grinder.

Step 5. After laying the walls, you can proceed to the upper part of the body. Here the outer bricks must be laid on the edges of the side walls, and a slight rise must be maintained. To make the central part, the bricks are cut to a trapezoidal shape and fixed with mortar.

Step 6. One brick is attached to the door. Upon completion of installation, he should create a protrusion that will fit inside the body when the muffle furnace is closed with his own hands. Next, the hinges are welded, and the door itself is ground in. It is important that the gaps between the body and the door are minimal.

Step 7 Next, a heat-resistant seal is placed around the perimeter of the door, which will prevent leakage of thermal energy during operation. The end bricks are covered with grease, and the door protrusion around the perimeter is treated with silicone sealant. Next, the door should be closed so that the silicone takes on the required shape. Excess grease is removed with alcohol. This will be a kind of seal that will need to be periodically updated in the future.

Step 8 We begin making the spiral. To do this, the wire is wound onto some kind of base (the same as in the previous method), after which grooves are made for the heating element under the resulting diameter of the spiral. The spiral fits into these grooves.

Step 9 Two circuits are created, which will allow further regulation of the temperature regime. After this, the wire is brought out and bolted to a plate made of ceramic.

Step 10 All that remains is to take care of the switch. On one side it is equipped with two contacts - zero and phase - and on the other three. The switch is attached in such a way that the toggle switch is located outside, and the wires are supplied. As a result, in the first mode the circuits will function sequentially, in the second only one circuit will work (the one located below). Finally, in the third operating mode, both circuits will operate simultaneously.

Video - Homemade muffle stove

Option #3. Making a simple muffle furnace

The most primitive kiln for firing small ceramic products is the one shown in the image below. As you can see, to make such a design you only need clay pot and electric stove.

A refractory brick is placed under the stove; a thyristor regulator or, alternatively, an LATR is used to regulate the power. Typically, the thermocouple does not necessarily need to be placed inside the pot - with such a small size, the procedure can be controlled visually: at dusk, the sides of such a pot will give off a red glow. When such a glow appears, it is necessary to begin the countdown - this can take from four to twelve hours, depending on the specific product. If overheating is observed, the power should be reduced.

If the design has big sizes, then the muffle should also be large (see the next picture), ideally a barrel made of earthenware. You need to make a small hole in the bottom (use for this diamond drill) under the thermocouple and release of excess air.

The base is assembled “dry” from the same refractory brick; fixation is carried out using a frame made of metal corners. Several annular grooves are made from the inside (necessarily with transitions), into which the heating element is placed.

The final stage is the outer shell using galvanization. The shell will be removable; it is put on only after installing the device and covering it with a muffle. The gap between the muffle and the shell should be filled with asbestos. The procedure for firing products is no different from that described above, the only difference is that the temperature will be regulated by a thermocouple. The dimensions of the barrel are significant, and the walls are thick. Therefore, even without a shell, at the moment when the muffle furnace lights up with your own hands, the ceramics will simply be burned out.

Option number 4. Making a miniature muffle

If you plan to carry out minor work, then a wire resistor (either PEV or PE) with a power of 50 to 150 watts can be used as a muffle. As for the internal diameter, it can vary between 20 and 38 millimeters. A specific figure It’s hard to say, since electroporcelain tubes are different, there are different sizes (much depends on the manufacturer).

Note! For 220 volts the resistance should be approximately 900 ohms, for 100 volts - about 450 ohms, and for 150 volts - about 340-360 ohms. You should not try to speed up heating by reducing the resistance, since such a device will still not be able to produce more than nine hundred degrees, but the resistor may burn out because of this.

Brass clamps will require a heat sink. It is made from strips of copper 0.2 centimeters thick (this is shown in the image below). An enameled copper busbar is also suitable - the enamel will additionally insulate.

After installing the heat sinks, the power cables are connected to the resistor. The heat sinks themselves are insulated with special glass tape, and the turns in this case should overlap by 1/2. The insulating layer is treated with heat-resistant varnish.

The final stage of work is putting on the shell and filling it with thermal insulation. The edges are pre-bent at an angle of 90 degrees so as not to damage the insulation of the heat sinks. That’s it, the do-it-yourself resistor muffle furnace is ready for use!

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Based on the type of fuel used, the muffle furnace can be of two types:

gas;
electric.

Important! It is not possible to make a gas stove yourself, since this is prohibited by current legislation.

Regarding the design, the following types of furnaces are distinguished:

Horizontal, which are the simplest;
Potted type or vertical;
Tubular;
Bell bells.

Heating of such furnaces can be carried out in a vacuum, air or gas environment. The muffle furnace that you will build with your own hands may only provide an air environment for processing products.

Important! In addition to saving money, making such a stove yourself is advantageous in that the master can create a design of the most convenient volume and shape for himself.

What does a muffle furnace consist of?

The operation diagram of a muffle furnace becomes clear when considering the main details of this design.

Let's look at what parts a muffle furnace includes:

Furnace body. In this case, it will be most convenient to use an old gas stove equipped with an oven, which will be used as the basis for the structure.

Advice! If used as a housing gas stove, then you must first dismantle all plastic parts. In the absence of a finished structure, the body is welded from sheet metal, more than two millimeters thick.

Inner layer, which is in direct contact with the surface of the firebox. It is very important, since the efficiency of the furnace structure depends on it. Fire-resistant fireclay bricks should be used as the inner layer.
Outer layer. It is designed to reduce heat loss from the oven. Can be used basalt wool or perlite.

Advice! It is undesirable to use asbestos as an external furnace layer, since when heated, this material releases carcinogenic substances into the atmosphere.

Elements involved in direct heating of the workspace. In muffle furnaces, such elements most often are spirals, which are twisted from fechral or nichrome wire, about 1 mm thick. By the way, nichrome wire is a more desirable option due to its corrosion resistance and high ductility. At the same time, fechral wire has a lower cost.

Drawing of a furnace with a rectangular muffle: 1 - regulating millivoltmeter; 2 — signal lamp; 3-fuse; 4 - switch; 5-control unit; 6- heating chamber; 7-body; 8-ceramic muffle; 9-heat. element; 10-thermal insulation; 11 — counterweight; 12-door; 13 — hole for control thermocouple; 14-hole for regulating thermometer.

You can take examples of dimensions, power and volume based on SNOL brand furnaces in the table below.

Furnace model	Volume, l	Temperature, °C	power, kWt	Number of phases	Width x Length x Height, mm.		Weight, kg
					Working chamber	Dimensions
SNOL 3/10	3	1050	1,8	1	150×200×100	425×530×520	30
SNOL 3/11		1150
SKV (SNOL) 6/10	6	1050	2,2		180×270×130	450×600×545	40
SKV (SNOL) 6/11		1150
SNOL 10/10	10	1050	4		200×300×180	470×620×595	50
SKV (SNOL) 10/11		1150
SNOL 3/10-V	3	1050	1,8	1	150×200×100	425×610×650	32
SNOL 3/11-B		1150
SKV (SNOL) 6/10-V	6	1050	2,2		180×270×130	450×680×675	42
SNOL 6/11-B		1150
SKV (SNOL) 10/10-V	10	1050	4		200×300×180	470×700×725	52
SNOL 10/11-B		1150

Abbreviation of the form SNOL used to designate the type electric ovens. C - resistance, refers to the type of heating elements (resistive type). N - chamber, with rectangular cross-section oven chamber. O - for processing parts/materials in air at normal pressure. L - laboratory, i.e. allowing temperature adjustment over a wide range.

How to make your own muffle furnace

A muffle furnace for ceramics has a similar manufacturing procedure, regardless of the horizontal or vertical layout. The only difference is the arrangement of the elements. Let us consider the process of manufacturing a muffle furnace for firing ceramics in more detail:

As mentioned above, the best option for the body is ready gas oven or a structure made from sheet metal. To do this, using a grinder, you need to cut a rectangular strip of the size suggested by the drawing. Next, it is bent into a radius, after which the seam is hermetically sealed. Thus, a cylinder is obtained.

Video about self-production muffle furnaces from a professional master

Advice! To prevent corrosion, the metal can be exposed with several layers of fire-resistant paint.

We weld the bottom to the resulting structure, for which you need to cut a circle of the required diameter from a sheet of steel.
To strengthen the bottom and walls of the housing, it is necessary to use reinforcement. The housing must be of such a size that it can easily accommodate thermal insulation and a fireclay brick structure.

Important! Can also be used as a structure body old refrigerator. In this case, it also needs to be strengthened by metal tubes and corners.

The inside of the body is lined with a thick layer of basalt wool.
Now we make a heat accumulator. To do this, you need to join 6-7 bricks, as in the photo below. This will be the working chamber of the future design. To make it, you need to cut the bricks at an angle so that they can be used to assemble a structure in the form of a pipe. Trimming should be done using a grinder.

Advice! For ease of use, the bricks can be numbered. After cutting, we assemble the structure. When cutting bricks, it is very important to ensure reliable protection for eyes and respiratory tract. Work must be carried out indoors with good ventilation, or even better - outdoors.

We make a spiral from a coil of wire, the diameter of which should be about 6 mm. For these purposes, nichrome or fechral wire is excellent, which can be wound on a thin metal rod or pencil.
The bricks used to make the working chamber are laid out on a flat surface. It is necessary to make special grooves in them to accommodate the spiral. A grinder is used for this.

Important! The wire must be laid in brick construction in a spiral. It is very important that the turns do not touch each other. Otherwise, a short circuit may occur.

To extend the ends of the wire outside the chamber, it is necessary to prepare three long and thin pieces of ceramic tiles. Thin channels for the wire are first sawed into them, after which these sections are inserted between adjacent bricks. Such ceramic terminals can significantly facilitate the operation of equipment in the future, allowing repair work to be carried out simply and quickly.

Three pieces of tile allow you to use the oven at three power levels. To do this, you will need to include different spiral contours:

To turn on the first power stage, it is necessary to turn on two spiral circuits in series.
To operate the device in the second mode, you need to separately connect the lower spiral.
The third stage involves parallel connection two circuits.

Advice! The inclusion of spirals must necessarily provide for grounding!

Now that the design of the working chamber is completely ready, it must be wrapped in a layer of thermal insulation and placed in the furnace body. The camera is installed on a brick, which will act as its bottom. It is pre-coated with fireproof glue or clay.
To remove the ceramic channels outside the body, it is necessary to drill holes in it in the appropriate places.

Sheet steel is also used to make the lid. It is necessary to cut a circle to fit the size of the oven. A latch, canopies and handles are welded onto the lid. To seal the structure, it is necessary to apply a layer of silicone along the edges of the lid and on the adjacent walls of the structure. To do this, the surfaces are pre-degreased.

After the structure is completely dry, you can connect the wire to electricity through a stabilizer. At this stage, the furnace undergoes testing, during which the power of the muffle furnace is adjusted to obtain the required operating temperature at each stage.

Advice! To make sure that furnace design completely dry, it is turned on maximum power and check for the presence of fumes. If there is no steam coming from the surface of the oven, this means that it is completely dry.

Conclusion

An analogue of the PM 8 stove can be easily made at home. Wherein homemade design has excellent technical characteristics and is able to compete with factory-made analogues.

A muffle furnace is a heating device, inside of which there is a special casing - a muffle. It separates the internal workspace from the firebox (heaters). Thus, inner chamber protects the working area from carbon monoxide, and heated parts from interaction with these gases. How is the muffle constructed and is the muffle made?

The muffle protects the heating zone from gases or evaporation products of the heating elements. This creates conditions for heat treatment of parts, to saturate their surface with certain elements (carbon, nitrogen, chromium). The muffle is also used for melting gold and firing clay products.

In addition to its protective properties, the inner chamber ensures uniform temperature distribution throughout work area. This creates the same conditions for heat treatment of parts on the pallet.

Among the disadvantages of muffles it is worth noting low speed heating up to high temperatures, which means the complexity of high-speed heat treatment modes in such furnaces. In addition, heating the muffle itself requires additional energy consumption, which means that muffle furnaces are more expensive to operate than furnaces without a muffle.

Muffle furnaces: scope of application

Let us list the scope of application of muffle furnaces:

1. Metallurgical production and research in metallurgical laboratories. In muffle furnaces different sizes carry out heat treatment of parts made of various alloys - hardening and annealing, tempering and aging. Also in muffles, the surface is saturated with carbon, nitrogen, aluminum, silicon, and other elements (cementation, nitriding, cyanidation, diffuse metallization - chrome plating, aluminizing).

2. Remelting of gold and non-ferrous alloys, in which the saturation of the alloy with foreign impurities is unacceptable. In such remelting, it is necessary to limit the contact of the alloy with combustion products or with oxidation products of heating elements.

Melting metal in a muffle furnace

3. Firing of ceramics - used in the production of ceramic products (dishes, sculptural decorations made of clay). High-temperature firing ensures the strength of the ceramic surface and its water resistance.

4. Drying electrically conductive materials and elements.

Drying materials in a muffle furnace

5. Sterilization of instruments (in medicine).

Sterilization of instruments in medicine

6. Burning (cremation).

Features of a muffle furnace for melting metals

How muffle furnaces work: design

Main structural element furnaces - muffle. Parts for heat treatment (or gold for remelting, medical instruments for heat treatment, ceramics for firing) are loaded into its chamber. The muffle is made from a chemically inert material.

The muffle chamber is located inside the furnace. In this case, the space between the outer casing and the inner chamber is filled with a heat insulator. High-quality thermal insulation determines the efficiency of the device, as well as its safety (it limits the strong heating of the casing and prevents the possibility of getting burned on it).

The heating elements are located outside the muffle or in its walls. They heat the inner chamber, which in turn transfers heat to the workspace. The operation of the heating elements is controlled by the regulator. It controls the temperature and heating time, the entire heat treatment process. The level of automatic control affects the price of the heating device. The more regulatory functions, the more expensive the stove.

Muffle: design and materials

The following materials are used to make the inner chamber:

ceramics;
ceramic fiber;
corundum;
fireproof (fireclay) brick.

The choice of material for making the muffle is determined by the operating conditions and purpose of the furnace. For example, a muffle made of refractory fibers is used for heating in a neutral environment. Corundum chambers - can be used in chemical environments. But the ceramic muffle is universal. Due to its inertness, it is used for various tasks (melting, heat treatment, roasting).

The same housing can be loaded with muffles from different materials(for different heating and processing purposes). Thus, the inner chamber is a replaceable element, which can be in the form of a pot or a cap, loaded from the side or from the top. Structurally, muffles are divided into the following groups:

Bell-type (they are loaded from above in the form of a bell, and after heating they are separated from the hearth).
Potted (also loaded from above, but have the form of a container and are not separated from the hearth).
Simple (the cage is loaded from the side of the furnace).

Heating elements

To heat the walls of the inner chamber, heating elements are installed. They use wire made of heat-resistant metal or alloy. When current passes through the wires, they heat up and generate heat. To increase the recoil area, the wire is wound in the form of a spiral.

There are also open and closed heaters. Open heaters have more high speed heating, if damaged, they can be easily replaced with new ones. But at the same time, they oxidize faster (due to heating) and fail more often.

Closed heaters are located inside the walls of the muffle. They are protected from oxidation, therefore more durable. Disadvantages: longer heating time and higher repair costs (in case of breakdown, the entire muffle must be replaced).

Types of muffle furnaces

Muffle furnaces are classified according to several criteria. They are divided according to the method of heating:

electrical;

gas.

By type of protective atmosphere:

Air (the muffle limits the mixing of air between the workspace and the heaters).
Vacuum (a rarefied space is created inside the muffle - a vacuum).
Furnaces with a special atmosphere - the space inside the muffle is filled with a special gas (inert, nitriding, reducing, etc.).

The operating temperature inside the oven can vary from +400ºC to 2500ºC. Based on this criterion, muffle furnaces are classified into types:

For moderate heating - up to 500ºC.
For medium temperatures - up to 900ºC.
For high temperatures - up to 1400ºC.
For extremely high temperatures - up to 2000-2500ºC.

Note: The heating temperature determines the price of the stove. The hotter the oven heats, the higher its cost. In addition, the prices of muffles depend on the size and functional equipment (presence of thermocouples, type of heaters, automation).

You can assemble it yourself at home simple design ovens. In this case, the do-it-yourself muffle furnace will operate on electricity. The main element - the muffle - can be made of clay or folded from.

For a clay muffle, a blank is made from cardboard or plywood. The resulting box is covered with a layer of clay 1 cm thick, dried until hardened (3-5 days) and fired in a coal oven. The firing temperature is 700-800ºC. This is enough to vitrify the clay structure and create a strong inner chamber.

DIY muffle furnace

The resulting ceramic muffle is wrapped with wire (nichrome or fechral, 1 mm in diameter) - it will work as a heating element. In order to secure the wire to the casing, it is covered with a second layer of clay (which is also dried and fired in a coal oven). The ends of the wire for further connection to the electrical network are left open.

To fold the fireclay muffle, grooves are made in each brick (for the location of heating coils). After stacking the bricks, spiral wire is placed in the grooves. To secure it in the grooves, the spiral is coated with clay or reinforced with wire.

The finished inner chamber is placed in a metal casing. It is welded from steel sheets with a thickness of 2 mm or more. Holes are left in the body for connection to the heating wire.

The finished muffle is placed inside the casing, the contacts are connected and thermal insulation is made. Basalt wool or asbestos chips are used as an insulating material (asbestos is more harmful option, when it is heated, carcinogens are released).

Note: This do-it-yourself muffle furnace allows you to fire ceramic products. For metallurgical annealing or remelting of non-ferrous alloys, an industrial furnace is required.

Self-production of a muffle furnace

SNOL stoves: prices and models

The manufacturer of electric furnaces SNOL offers various heating furnaces and chambers. Muffle versions of SNOL are laboratory electric furnaces for heat treatment of parts in an air environment. They are equipped with electric spiral heaters and a rectangular inner chamber. Scope of application of SNOL furnaces: thermal and chemical-thermal treatment, heating of samples, calcination.

The SNOL model range provides furnaces with different operating temperatures and different working space volumes. The operating temperatures of SNOL are 100-1300ºC. In custom-made models, operating temperatures can be higher - up to 1600ºC. The volume of the working chambers is 3, 6 or 10 liters. Semi-closed and closed heaters are used. In versions with a working chamber volume of 3 and 6 l, the heaters are located with three sides. In versions with a 10 l chamber there are heaters on 4 sides of the inner chamber.

Muffle furnace SNOL

The muffle material is ceramic or fiber. There are SNOL models in which the inner chamber is made of of stainless steel, made of brick. The modular design of the oven allows you to quickly and easily replace any element if necessary.

The quality and reliability of operation of SNOL heating devices is ensured by Japanese programmable thermostats and fechral heaters.

Prices for SNOL stoves are affordable.

A muffle furnace is a device necessary for the operation of a metallurgical laboratory. It is also in demand in jewelry and ceramic production, used in medicine (for instrument processing). The design is simple. For annealing ceramic products, you can make a muffle with your own hands. For more critical types of chemical-thermal treatment, it is better to purchase a factory-made oven. This will guarantee its quality and safety.

Description of the operation of the muffle furnace Snol-7.2/1100