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 for firing ceramic products, metal smelting, cupellation, creation of single crystals, etc. In medicine, they are used to disinfect instruments.
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
By design features 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:
- gas;
- electrical.
Of course, a gas furnace will bypass in operation 3-4 times cheaper than an electric one, due to fuel savings, but such a furnace, firstly, is prohibited by law to manufacture and use, and secondly, it is technically extremely difficult to make a muffle furnace with your own hands on gas.
Due simple materials the stove can be made in any convenient form, including one that is ideal for the interior of the room.
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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 tool, including wire cutters;
- 2mm nichrome wire.
and materials:
- 2.5 mm steel sheet or used oven body;
- corner;
- fittings;
- basalt wool;
- refractory fireclay bricks;
- refractory solution;
- silicone sealant.
Essential elements
Frame
Ideally, the body is suitable as the basis of a homemade muffle furnace for fusing or cupellation electric oven or a miracle stove, since it already has all the necessary insulation. It will only be necessary to remove or remove all plastic elements.
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If it was not possible to find such an oven, the body can be welded from a sheet previously cut into blanks. Weld all sidewalls, clean wire brush or grinder seams and cover with a primer.
The manufacture of the case from sheets, although a little more complicated, but 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 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 for a muffle furnace - it working temperature 1300 degrees, and he is "friends" with the air.
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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.
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Some forums on the manufacture of muffle furnaces recommend using asbestos for masonry. It's really flame retardant 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 resemblance metal barrel, the sides and bottom of which should be reinforced with reinforcement 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.
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
- Basalt (stone) wool is laid out along the perimeter of the structure.
Why is this type 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 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.
- 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.
When the bricks are cut and assembled, tighten them with wire and check how symmetrical the structure is.
- Making a 6 mm spiral from 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 of such high temperatures(more than 1000 degrees) - 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.
- Unroll the bricks and cut into inside at a slight angle grinder furrows 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.
- Bring out the ends of the spiral and connect them to a 25 A machine.
- 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 for full power, but do not close the lid - if evaporation begins somewhere, turn off and leave 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, “plant” fireclay bricks - 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
For the manufacture of such a simple device, you only need the usual electric hob, 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.
Safety
- It is possible to work with the stove only on condition that there is grounding.
- It is forbidden to start work if there are chips or cracks on the body.
- It is forbidden to touch the device during operation.
- It is strictly forbidden to touch the running coil.
- During operation, the oven requires constant supervision.
Despite the relative ease of manufacture, such a device is not very common among home craftsmen. This is due to 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 to use 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
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.
According to the type of heating elements, muffle furnaces are divided into:
- electrical;
- gas.
By purpose, they are divided into:
- for melting metal;
- for firing ceramics;
- for melting glass;
- for hardening metal;
There are also industrial and home-made muffle furnaces.
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.
At self-fulfillment muffle furnace, you can give it the desired shape and volume, decorate it in a style suitable for the interior.
The main parts of the structure
List of materials and tools for assembling the structure
- grinder (machine for grinding and cutting materials) with cutting wheels for metal;
- welding machine;
- sheet steel >2mm thick;
- metal corners;
- fireclay fire-resistant brick;
- refractory mixture;
- heat-resistant silicone;
- basalt thermal insulator (cotton wool, density 200 kg / m 3) or perlite;
- goggles and respirator;
- nichrome (fechral) wire with a cross section of 1 mm;
- wire cutters 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.
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 bar). We take out the bricks and lay them out again on 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 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, we insert three thin long pieces between two adjacent bricks ceramic tiles with thin wire channels sawn into them.
The use of such ceramic leads in the future will make it easy to produce repair work muffle furnace.
Electrical switching with three power levels
- for the first stage of power, it is necessary to connect two coil circuits in series;
- the second stage implies a separate connection of the lower spiral;
- the third stage of power is the 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 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 by increasing or decreasing the mains voltage.
Important! To make sure that the oven is completely dry, turn it on at maximum power and make sure that there is no steam evaporating from the oven surfaces.
The door must be tightly closed while the oven is in operation.
Video - homemade muffle furnace
Muffle furnace
View of the muffle of the electric muffle furnace PM-8.
Muffle furnace- a heating device designed to heat a variety of materials to a certain temperature. The main feature of this furnace is the presence of the so-called. a muffle that protects the material being processed and is the main working space of the muffle furnace (the muffle protects the material or product from contact with fuel and its combustion products, including gases). Muffle furnaces with replaceable muffles and a stationary heating chamber operate according to the following principle. A muffle with a cage is loaded into a constantly heated furnace. After heating to a predetermined temperature and holding, the muffle is removed from the furnace for cooling and another one is installed in its place.
Types of muffle furnaces
Muffle furnaces are divided according to the type of heating:
- Electric muffle furnaces - are a kind of chamber electric resistance furnaces
- Gas muffle furnaces
By protective processing mode:
- Air: heating in air (general purpose)
- With protective gas atmosphere: heating in a special gas environment (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)
Electric muffle furnaces
Materials for muffle furnaces
Materials intended for the production of muffle furnaces:
- Structural steels: mild steels general purpose for the construction of heat-insulating casings, supports, doors, etc.
- Refractory materials: high alumina refractory muffles, electrical insulation, doors, etc. Foamed refractory fillings for thermal insulation of furnaces
- Materials for electric furnace heaters:
- Alloys of the type: nichrome, fechral in the form of wire, tape and rods
- Tungsten: wire, tape and rods
- Molybdenum: wire, tape and rods
- Tantalum: wire, tape and rods
- Platinum and platinum alloys: wire, tape, rods
- Lanthanum chromite: rods, tubes and profiles
- Yttrium chromite: rods, tubes and profiles
- Scandium chromite: rods, tubes and profiles
Areas of use
The main areas of use of muffle furnaces:
- Heat treatment of metals (quenching, annealing, tempering, normalization)
- Metal smelting
- Firing of ceramic products
- Burning (ashing)
- Assay analysis (cupellation)
- Drying
- Growing single crystals
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See what the "Muffle Furnace" is in other dictionaries:
MUFFLE FURNACE- a chamber furnace of indirect heating, in which the heated product (material) is located in (see) and does not come into contact with combustion products or environment. M. p. is used, for example. in the chemical-thermal treatment of metals and ceramics in ... ...
From the word muffle. The furnace in which the muffles are placed. Explanation of 25,000 foreign words that have come into use in the Russian language, with the meaning of their roots. Michelson A.D., 1865 ... Dictionary of foreign words of the Russian language
muffle furnace- a thermal furnace in which the heated material is located in a closed thin-walled muffle chamber, which ensures its protection from contact with fuel combustion products (in fuel muffle furnaces) or air (in ... ...
muffle furnace- mufelinė krosnis statusas T sritis chemija apibrėžtis Laboratorinė elektrinė krosnis, kurioje pasiekiama 1200 °C temperatūra. atitikmenys: engl. muffle furnace rus. muffle furnace … Chemijos terminų aiskinamasis žodynas
flame or electric a furnace in which the product is heated inside a closed thin-walled chamber of the muffle. The product in M. item is protected from direct influence of a flame. The gas of a controlled composition can be supplied to the muffle (see Controlled Atmosphere). M... Big encyclopedic polytechnic dictionary
MUFFLE FURNACE- industrial heating flame or electric furnace, in which the heated product is inside the closed chamber of the muffle. The product in the muffle furnace is protected from direct exposure to the flame, oxidizes less and is not contaminated with soot and ... ... Metallurgical Dictionary
muffle furnace- A thermal furnace in which the heated material is located in a closed thin-walled muffle chamber, which ensures its protection from contact with the products of fuel combustion (in a fuel muffle furnace) or with air (in an electric muffle furnace) ... Technical Translator's Handbook
BAKE- building various designs made of stone, brick, metal or an engineering device that serves for industrial million domestic purposes, when it is necessary to obtain and use heat (convection, radiant radiation, etc.) for space heating ... Great Polytechnic Encyclopedia
FURNACE MUFFLE- a thermal furnace in which the heated material is located in a closed thin-walled muffle chamber, which ensures its protection from contact with the products of fuel combustion (in a fuel muffle furnace) or with air (in an electric ... Metallurgical Dictionary
electroslag remelting furnace- an indirect resistance furnace with a liquid heat carrier in the form of molten synthetic slag, which refines the remelted metal; used in special electrometallurgy, in mechanical engineering ... ... Encyclopedic Dictionary of Metallurgy
For almost every one of us, a muffle furnace is an unnecessary device. And such furnaces are needed exclusively for people of those professions that are associated with smelting, firing ceramics or manufacturing jewelry. In addition, single crystals can be created using muffle furnaces, 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, not everyone can afford. But if something has been preserved in your memory from a physics course at school (we are talking 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. So, according to the design features, such furnaces are:
- cylindrical;
- tubular;
- horizontal (this is the easiest 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 another classification. According to the type of heating element, the described devices can be:
- electric;
- gas.
Application gas ovens it is much cheaper, but you cannot do it 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 custom-made muffle furnace can be of any size and shape, and it can be made in a style that would ideally suit a particular home design.
Now - directly to the manufacturing process!
Option number 1. Production of a vertical muffle furnace
This option is the most convenient to use, so let's start with it. The manufacturing procedure itself (subject to the availability of high-quality instructions, of course) is not difficult. Traditionally, work begins with the preparation of everything necessary.
Stage 1. Equipment and supplies
To create an oven vertical type the following list of equipment/materials will be required.
- Bulgarian, "metal" circles to her.
- Plastic glasses.
- Wire cutters.
- Respirator.
- Welding machine.
- refractory mix.
- Nichrome wire (diameter 0.1 cm).
- Sealant based on silicone.
- Steel sheet (its thickness should be 0.25 centimeters).
- Refractory brick.
- Stone mineral wool.
- Metal corners.
Also, the preparation stage includes familiarity with the basic structural elements device. There are several of them, let's take a look at them.
Note! Asbestos cannot be used for thermal insulation, since it can release carcinogens during heating.
Now a little about the manufacture of the case for the future stove. To do this, you need a sheet of metal, from which a piece of rectangular shape of the required size is cut. This rectangle is folded into a "pipe", and the seams are welded with welding machine. The finished cylinder is painted with fire-resistant paint, then, when it dries, a circle pre-cut from metal is welded on one side (this will be the bottom). After that, the body is strengthened with reinforcing bars. It is important to calculate the volume of the case in advance - after all, you still need to place layers of thermal insulation in it.
Note! If an electric oven is used as the body, then the bottom in this case will be reinforced with corners.
Stage 2. Direct production of the furnace
Now let's get down to making it. Algorithm necessary action given below.
Step 1. Internal surfaces the hulls are laid out with stone mineral wool.
Step 2 After that, thermal insulation is arranged - it, as noted above, is made of refractory bricks. The procedure is as follows: inside the cylinder, seven bricks are joined so that a pipe is formed. Subsequently, this pipe will serve as a working chamber.
All bricks must be folded in a row and marks should be made on them, according to which they will be trimmed. After that, the bricks are cut so that their shape as a result allows them to be folded into a hollow tube. To simplify the work, each of the bricks is desirable to be numbered. When the cutting is completed, the pipe should be assembled and pulled together with wire. Then it is checked for symmetry, if necessary, the position of the bricks is adjusted.
Note! Brick needs to be cut outdoors or, alternatively, in a well-ventilated area. Moreover, do not forget about personal protective equipment - glasses, a respirator, etc.
Step 3 The nichrome wire is twisted into a spiral, the diameter of which is 0.6 centimeters, by winding it onto any base (it can be, for example, a pencil). Next, the bricks are removed from the cylinder and re-stacked in a row.
Step 4 The spiral should be attached 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 from the bottom to the very top of the structure. The coils should not touch, otherwise there is a risk of a short circuit, and the muffle furnace can fail with your own hands!
Step 5 Between two bricks, it is necessary to insert 3 strips made of ceramic tiles (the ends of the spiral will be removed with their help), in which polypropylene channels are made under the wire. Thanks to these channels, repair work will subsequently be greatly simplified.
Step 6 The whole structure is installed in a steel cylinder. It is important that before this another brick was laid on the bottom, covered with a special refractory adhesive. Also, a couple of holes are drilled in the body in the required places in order to bring out the ceramic channels.
Note! The inclusion of the spiral is allowed only after the entire structure has completely dried, otherwise it - the spiral - will be damaged.
Step 7 The cover 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 laid on top of the cover. After that, it is necessary to weld the handle, the iron latch, as well as the canopy. The edges of the circle, which are in contact with the body, are treated with fire-resistant silicone. Tellingly, silicone can only be applied to degreased surfaces.
Step 8 The design is almost ready, it remains only to make a trial run. But before that, it is necessary to install the device in a ventilated and warm place so that it is completely dry. The use of any heating devices is prohibited, because of this, the masonry may crack. When the structure is dry, the spiral must be connected to the machine. After that, the power and the desired temperature are adjusted.
Note! To check how dry the masonry is, the device turns on at full power. In this case, it is necessary to observe whether steam comes out of the surface.
In the course of further operation, the lid must be tightly closed without fail. Now let's get acquainted with another manufacturing option - this time horizontal.
Video - Muffle Furnace
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Option number 2. Creating a horizontal structure
The manufacturing procedure is in many ways similar to that described above, but there are significant differences. The body can be made from old oven, washing machine or, alternatively, sheets of steel (the thickness of the latter should be at least 0.2 centimeters). The procedure consists of two stages, we will 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 nichrome wire.
- Iron corners.
- Stone wool.
- Refractory brick.
- Scissors for cutting metal.
- Abrasive saw.
- Flame retardant adhesive.
If there is nothing to use as a case, it will again have to be made from scratch. To do this, you need to cut out the walls from the sheets of steel the right sizes and weld them into a single structure. After that, the top and bottom are welded. Outside, the bottom is reinforced with metal elements, legs made from corners are welded at the corners. Now you can proceed to the next step.
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Stage 2. Manufacturing instructions
Step 1. The base of the body is laid with a 10 cm 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 dimensions is laid over the corners. A similar procedure is done with the walls of the case.
Step 2 Now we proceed directly to laying and connecting our device.
Note! Before starting work, the refractory brick should be lowered into water for half a minute so that it does not absorb liquid from the working solution.
Brick laying starts from the bottom, a fire-resistant adhesive mortar is used (it is kneaded 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 the brick walls, a new mortar is used - this time it is necessary to add cement. The proportions should be as follows: for each kilogram of the finished mixture there should be about 300 grams of cement. Laying is possible only after installation is completed. stone wool And metal sheets. Although you can do without a thermal insulation layer, but only on condition that the bricks are laid flat.
Step 4 Bricks are laid from top to bottom, while the dressing of the seams is observed. If necessary, they are cut with a grinder.
Step 5 After laying the walls, you can proceed to the upper part of the body. Here, the extreme bricks must be laid on the ribs of the side walls, and a slight rise must be observed. For the manufacture of the central part, the bricks are cut to a trapezoidal shape and fixed to the mortar.
Step 6 One brick is attached to the door. At the end of laying, he must create a protrusion that will enter the inside of the body when the muffle furnace is closed with his own hands. Next, the hinges are welded, and the door itself is rubbed. It is important that the gaps between the body and the door are minimal.
Step 7 Further along the perimeter of the door, a heat-resistant seal is laid, which will prevent leakage of thermal energy during operation. The end bricks are covered with grease, and the protrusion of the door around the perimeter is processed silicone sealant. Next, the door should be covered so that the silicone takes the desired shape. Excess grease is removed with alcohol. This will be a kind of sealant, which in the future needs to be updated periodically.
Step 8 Let's start making a spiral. To do this, the wire is wound onto some kind of base (in the same way 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 that, the wire is brought out and bolted to a ceramic plate.
Step 10 It remains only to take care of the switch. On the one hand, it is equipped with two contacts - zero and phase, and on the other with three. The switch is attached in such a way that the toggle switch is located outside, wires are connected. As a result, in the first mode, the circuits will function sequentially, in the second, only one circuit (the one below) will work. Finally, in the third mode of operation, both circuits will work simultaneously.
Video - Homemade muffle stove
Option number 3. Making a simple muffle furnace
The most primitive kiln for firing small pottery is the one shown in the image below. As you can see, to make such a design, you only need a clay pot and an electric stove.
A refractory brick is placed under the stove, a thyristor regulator is used to adjust the power, or, alternatively, LATR. Tellingly, the thermocouple does not have to be placed inside the pot - with such small sizes, the procedure can also 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 start the countdown - this can take from four to twelve hours, depending on the specific product. If overshoot is observed, then the power should be reduced.
If the design will have big sizes, then the muffle should also be large (see the following picture), ideally a barrel made of faience. A small hole must be made in the bottom (use a diamond drill for this) under the thermocouple and the release of excess air.
The base is assembled "dry" from the same refractory bricks, fixing is done using a frame made of metal corners. From the inside, several annular grooves are made (always 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 the device is installed and covered with a muffle. The gap between the muffle and the shell should be covered with asbestos. The procedure for firing products is no different from that described above, the only difference is that the temperature will be controlled 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 its own hands, the ceramics will simply burn out.
Option number 4. Making a miniature muffle
If it is planned to run small jobs, 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 inner diameter, it can vary between 20 and 38 millimeters. It is difficult to say a specific figure, since the electroporcelain tubes are different, there are different sizes (much depends on the manufacturer).
Note! For 220 volts, the resistance should be about 900 ohms, for 100 volts - about 450 ohms, and for 150 - about 340-360 ohms. You should not try to speed up the heating by reducing the resistance, since such a device will still not be able to give 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 enamelled copper bus is also suitable - the enamel will additionally insulate.
After mounting the heat sinks, power cables are connected to the resistor. The heat sinks themselves are insulated with a special glass tape, and the turns in this case should overlap by 1/2. The insulating layer is treated with a heat-resistant varnish.
The final stage of work is putting on the shell and stuffing 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. Everything, do-it-yourself resistance muffle furnace is ready for operation!
Video - Large and powerful oven
If you refer to Explanatory Dictionary Dahl, you will find out that the word “muffle” means a small refractory furnace with thin walls for processing metal, ceramic, porcelain products or parts while protecting them from exposure to combustion products (soot, soot, gas).
Muffle furnace- this is such a special design for heating various metals to a certain temperature, you can buy it in a store or do it yourself.
The muffle is the main space for metal processing and an obstacle for its direct contact with fuel. The main purpose of muffle furnaces is the production of jewelry, melting of non-ferrous metals, firing of ceramic objects, melting of various elements from wax, firing of casting molds, etc.
Muffle furnaces are gas and electric.
They differ in several ways:
- construction type
- type of heating
- features of the protective function
- temperature regime
There are muffle furnaces of moderate, medium, high and ultra-high temperatures.
In furnaces of moderate heating, the temperature ranges from 100 to 500 degrees Celsius. In furnaces of medium temperatures - from 400 to 800 degrees. High-temperature mode - this indicator is from 400 to 1400 gr., And ultra-high up to 2000 gr.
The type of furnace heating is determined by the presence of heating elements. The number of these elements directly depends on the dimensions of the furnace.
Heaters are of two types:
- open
- closed
Open heaters heat up the structure to the required temperatures at a sufficiently high speed, they are easy to change in case of breakage or malfunction. The main disadvantage of these elements is that they are susceptible to corrosion and the production of harmful substances during thermal incandescence.
Heaters closed type are located in the muffle itself, therefore harmful substances do not adversely affect them. But their minus is that the heating of the furnace is quite slow, and if the element breaks down, it will be necessary to replace the entire heating chamber.
The device of the muffle furnace of the closed type
The main types of muffles used in stoves are ceramic, ceramic fiber and fibrous. The ceramic muffle furnace is used in a wide variety of industries, as ceramics has a high level of thermal conductivity and density, which prevents damage to the muffle under various influences.
The use of a ceramic muffle does not provide for high-speed processing due to the long process of heating and cooling. Ceramic fiber combines the positive properties of ceramics and fibers: it has the same density level as ceramics, but with such a muffle, the furnace warms up faster and does not require more electrical power.
On bad influence The ceramic-fiber heater reacts more calmly to the external environment than just a fibrous one.
Fiber muffle is used in furnaces much less frequently. the following reasons:
- requires a lot of electricity
- emits harmful gases
- very brittle
Where are muffle furnaces used?
1. Annealing, the purpose of which is the formation of a homogeneous structure as a result of heat treatment
2. Hardening
To harden metal in muffle furnaces, an increase in the cooling rate is used.
3. Vacation
This is the process necessary to give the material plasticity after the hardening process.
Especially often in muffle furnaces, the firing process is carried out, especially when processing ceramics. If it is necessary to examine the material for the presence of various impurities, the method of burning or ashing is used. Muffle furnaces are widely used in blacksmithing, in laboratories for the determination of precious metals in ore, alloys, ingots, etc.
Ready-made muffle furnaces for home use
Muffle furnace PM-8
Workers of science, laboratory assistants of various fields know the PM-8 muffle furnace with a chamber volume of 6.5 liters. The chamber of this furnace is made of heat-resistant ceramics, therefore it is very reliable and durable.
PM-8 is available in two versions:
— PM-8K with relay control
— PM-8M with digital control
The price for these muffle furnaces is 20 and 23 thousand rubles, respectively. In the heating mode, the power of such a furnace is about 2.4 kW, i.e. it can be used by plugging into an ordinary room outlet. The only disadvantage of the PM-8 is that its door is very hot.
The Sikron muffle furnace has about the same price as the PM-8. It is good to burn ceramics in it, but this furnace is not suitable for melting metal.
Furnace "SNOL". These ovens are manufactured by different sizes, but you are unlikely to find a price for it cheaper than 30,000 rubles.
The Shenpaz oven has gained a good reputation and good reviews from gold dentists.
How to make a muffle furnace with your own hands
Given the increased demand for muffle furnaces and their high cost, many would like to build this structure on their own. It is impossible to make a muffle at home, because. it is prohibited by law. But many can assemble an electric muffle furnace on their own.
We assemble a furnace with heat treatment of products in the air
1. Frame
To make the body of the future stove, you can take the oven from the old gas stove or an electric furnace, having previously removed all plastic elements from them. And you can weld the body using a sheet of metal 0.2 cm thick.
2. thermal insulation
The efficiency of your design depends on the quality of the thermal insulation layer. For the insulating layer, refractory (fireclay) bricks are best suited, which can withstand t up to 1000 degrees.
It is better to use as the outer layer of the case. Asbestos sheets should not be used because it releases harmful substances when exposed to high temperatures.
3. As heating elements your stove will have spirals wound from nichrome wire. Their thickness should be at least 0.1 cm.
Heating in the muffle furnace chamber
What you need to have to assemble the oven1. welding machine
2. grinder or angle grinder with cutting wheels
3. steel sheet 0.2cm thick
4. metal corner
5. refractory brick
6. basalt wool
7. nichrome wire
8. refractory mixture
9. respirator
10. scissors for cutting metal
Stages of work on the manufacture of the stove
1. We make a metal case from iron sheets.
Using the angle grinder, we cut out a strip in the shape of a rectangle of the required size and weld the seam. To this cylinder we weld the bottom, previously cut out of steel in the shape of a circle. The body should be of such a size that a heat-insulating layer is located inside, plus a brick.
2. Take the basalt and place it inside the hull.
3. Now you need to join the bricks in the amount of 7 pieces in the form of a pipe - this is the future heating chamber of your stove.
First, lay out the brick in one row and make a markup, along which you will cut the brick. To make it easier to assemble the pipe, number each brick.
4. When finished cutting, assemble the brick, wrap the pipe with wire. Remember to use a respirator when cutting.
5. Lower the brick pipe into the metal case, and then the thermal insulation layer.
6. Make grooves for the wire inside the brick layer.
7. From the wire you have, wind a spiral (0.6 cm thick), for convenience, you can use, for example, a ballpoint pen.
8. We lay out the bricks in a row, mark the places for the grooves. The wire should be located from the bottom up in a spiral throughout the chamber.
7 bricks with spiral grooves
In order to stick the ends of the wire out and connect them, insert 3 pieces of ceramic tiles between two bricks, in which narrow channels for the wire have already been cut out in advance.
When connecting spirals, consider 3 power levels:
- the contours of the spirals are connected in series
- the lower spiral is connected independently of the others
— parallel connection two circuits
Be sure to ground!
9. Next, install the working chamber into the body of the stove with a heat-insulating layer. At the same time, do not forget to put a brick on the bottom of the case and smear it with clay. Drill a hole in the housing for the ceramic channels. Make a cover from a steel sheet and fix a refractory brick on it. Weld a handle, a latch to this cover and degrease the surface.
Before using a self-assembled muffle furnace, it must be thoroughly dried by turning on the voltage to the very high level until no more steam comes out of the surface.
