Quite often, in the process of various production, it is required to produce heating, quenching or other heat treatment details. In this case, it is necessary not only to observe a certain temperature regime but also to exercise control of cooling. For these purposes, muffle furnaces are best suited.

They got their name thanks to a special device, which is a camera made of heat-resistant materials designed to protect the part from various influences. For example, it prevents the product from coming into contact with protects against impact environment and helps to maintain the temperature regime.

There is a muffle furnace, in which a device of this type is provided, where the muffle is installed permanently. It is quite practical and convenient, but after a certain period of operation it is subject to complete re-equipment, or the camera is replaced. Therefore, in large industries, where similar ones go without stopping, a fundamentally different type of devices is used, which have replaceable packing.

Such a muffle furnace works without interruption, and the parts are immersed in it together with the muffle. Therefore, a certain amount is required. Given the short service life, such enterprises usually organize the production of muffles themselves.

Chambers of such furnaces are made of various properties. If specific technological process requires rapid cooling, then thin-walled ceramics are used, when it is required to keep heat in the furnace for a long time after it is turned off, then a special or other packing made of heat-conducting and refractory material is used.

There are many heating methods that a muffle furnace uses. It can run on gas, wood, diesel or other liquid fuel, but most often they use electric heating elements. They allow the furnace to heat up evenly (cooling also occurs), to exercise precise control over the temperature during operation. At the same time, special pyrometric devices can be connected to them, thanks to which the entire heating and cooling mode can be performed automatically. To control the temperature, thermocouples made of special alloys are usually used, which are located inside the device.

The simplest muffle furnace is produced with a metal body, in which heating elements and control devices are installed. After that, its camera is made, which is installed inside. At home, clay is also used for this. They are the most readily available materials and have good technical characteristics.

Such a muffle furnace can last long enough, and replacing the chamber itself will not be difficult and will not entail special material costs. It should be noted that most industrial devices of this type have exactly the same assembly principle, although for different conditions the material of the muffle can be changed.

If you refer to Explanatory Dictionary Dahl, you will learn that the word "muffle" means a small refractory furnace with thin walls for processing metal, ceramic, porcelain products or parts, protecting them from the effects of combustion products (soot, soot, gas).

Muffle furnace Is such a special design for heating various metals up 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 production jewelry, smelting of non-ferrous metals, firing ceramics, smelting various elements from wax, firing casting molds, etc.

Muffle furnaces are gas and electric.

They differ in several ways:

- type of construction
- type of heating
- peculiarities protective function
- temperature regime

Exists muffle furnaces moderate, medium, high and ultra-high temperatures.

In moderate heating furnaces, the temperature regime ranges from 100 to 500 degrees Celsius. In medium-temperature ovens - 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 heating elements... The number of these elements directly depends on the dimensions of the furnace.

Heaters are of two types:

- open
- closed

Open heaters at a sufficiently high speed heat up the structure to the required temperatures, they are easy to change in case of breakdown or malfunction. The main disadvantage of these elements is that they are susceptible to corrosion and the development of harmful substances during thermal incandescence.

Heaters closed type are in the muffle itself, therefore harmful substances do not adversely affect them. But their disadvantage is that the oven warms up rather slowly, and if the element breaks down, the entire heating chamber will have to be replaced.

Closed-type muffle furnace device

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. ceramics have a high level of thermal conductivity and density, which prevents damage to the muffle under various influences on it.

The use of a ceramic muffle does not provide for a high-speed processing mode due to a long heating and cooling process. 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 heats up faster and does not require more electrical power.

On the harmful effect external environment The ceramic fiber heater responds more quietly than the fiber heater alone.

Fiber muffle is used much less frequently in furnaces for the following reasons:

- requires a lot of electricity
- gives off 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
For hardening metal in muffle furnaces, an increase in the cooling rate is used.

3. Vacation
This is the process required to give the material plasticity after the hardening process.

The firing process takes place especially often in muffle furnaces, especially when processing ceramics. If it is necessary to study the material for the presence of various impurities, the method of incineration or ashing is used. Muffle furnaces are widely used in blacksmithing, in laboratories for the determination of precious metals in ores, alloys, ingots, etc.

Ready-made muffle furnaces for home use

Muffle furnace PM-8

Scientists, laboratory assistants in 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 produced in two modifications:

- 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 it into an ordinary room outlet. The only drawback of the PM-8 is that its door gets very hot.

The Sicron 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 remelting metal.

Stove "SNOL". Such ovens are made by the most different sizes, but you are unlikely to find a price for it cheaper than 30,000 rubles.

The Shenpaz stove has gained a good reputation and feedback 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 stove on their own.

We assemble a furnace with heat treatment of products in air

1. Frame

For the manufacture of the body of the future stove, you can take the oven from the old gas stove or an electric furnace, after removing all plastic elements from them. Or you can weld the body using a sheet of metal 0.2 cm thick.

2. Thermal insulation

The efficiency of your structure depends on the quality of the thermal insulation layer. For the insulating layer, refractory (chamotte) brick is best suited, which can withstand t up to 1000 degrees.

It is better to use it as the outer layer of the case. Asbestos sheets should not be used because it emits harmful substances when exposed to high temperatures.

3. As heating elements your stove will have spirals wound from nichrome wire. Their thickness must be at least 0.1 cm.

Heating in the muffle furnace chamber

1.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, cut out a strip in the shape of a rectangle 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 must be of such a size that an insulating layer is located inside, plus a brick.

2. Take the basalt and lay it inside the case.

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. In the metal case, lower a brick pipe, and then a layer of thermal insulation.

6. Make wire grooves inside the brick layer.

7. From the wire you have, wind up 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 bottom to top 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 between two bricks ceramic tiles, 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 have a sequential inclusion
- the lower spiral is connected independently of the rest
- parallel connection of two circuits

Be sure to make grounding!

9. Further into the stove body with insulating layer we install the working chamber. In this case, do not forget to put a brick on the bottom of the case and grease it with clay. Drill a hole in the housing for the ceramic channels. From steel sheet make a lid and attach a refractory brick to it. Weld the handle and latch to this lid and degrease the surface.

Before using a self-assembled muffle furnace, it must be thoroughly dried by turning on the voltage until high level until steam is no longer emitted from the surface.

A muffle furnace is a chamber device with a horizontal discharge system, which is an essential criterion for the owner's safety during use. In certain cases, a mine version may be required, in which the muffle is made deaf and located vertically - this will not only significantly reduce the production time, but also allow heating objects without direct contact with air. In any case, the heating system, the chamber and the thermocouple, which controls the maintenance of the required temperature, remain the key elements of heating the furnace.

History of origin

At the end of the 17th - beginning of the 18th centuries. French coachman Jeanto began to invent the steering linkage, which received his name, but he did not succeed in starting practical tests, because the axes of the prototypes were constantly breaking. Jeanto, who was sure that the invention would bring him huge profits, was completely desperate, because the carriages put on his axle constantly overturned right during the trip. However, the matter made significant progress when a Russian nobleman visited Zhanto's workshop, wishing to order, by order of Peter the Great, a luxurious carriage from the best European craftsman as a gift to the khan from Bukhara.

Having tried the product for strength, the nobleman advised Zhanto to first perform cementing in a muffle with cattle horns crushed into powder, and only then proceed to hardening. Thanks to this method, the steel had to remain viscous on the inside, and on the outside it had to be covered with a hard hardened crust, which would last for many years before being worn out.

Despite the fact that the muffle kiln for firing ceramics has changed significantly over the past time, it continues to maintain its basic characteristics. A muffle is a container that is resistant to high temperatures and has an impermeable structure. In it, the part undergoes the necessary heat treatment due to the fact that it completely isolates it from external influences, while ensuring uniform heating from all sides.

Over time, the requirements for the quality of heat treatment increased significantly, which made it possible, at the beginning of the 19th century, to begin the mass use of furnaces on an industrial scale. To date, even a low-temperature muffle furnace has appeared, in which the elements undergo a hot curing procedure.

Application today

• Safe remelting of valuable metals to avoid impurities in their structure and prevent direct interaction with the flame.
• Artificial aging of metals.
• Firing ceramics.
• Getting a flat surface.
• Drying of materials with high degree thermal conductivity.
• Burning objects to the state of mineral components, for example, during body cremation.

The muffle furnace is also used for growing single crystals and high-temperature processing of medical equipment. Thanks to this, it is possible to destroy all harmful bacteria without damaging the tools themselves.

Is it better to make or buy?

If you want to create a device such as a muffle furnace with your own hands, be prepared for the volume of the muffle to not exceed 7 liters, and the work itself will be lengthy and time-consuming. Before starting work, make your choice suitable model which you will be guided by. They differ:

• Heating temperature - from 100 to 2000 ° C.
• Design.
• Processing mode.
• Heating type.

The undisputed sales leader is the PM-8 and PM-10 muffle furnaces - the muffle chamber does not exceed 6.5 liters. It is her prototype that most people choose for their own handicraft, because the main material used in the work is only heat-resistant ceramics.

It is produced in several versions, K and M, differing only in that the latter has digital control. The cost starts from 1 thousand dollars, while you can buy much more cheap option whose design will function as well as if you bought it from the store.

Despite the fact that this muffle furnace has excellent data, one significant drawback still exists - it is the door. It gets significantly hot during work, which is why the owner often gets burns.

How to start creating?

When starting the manufacture of such a structure as a muffle furnace with your own hands for the first time, it is best to give preference to a structure that will be used for minor work. You can significantly reduce the cost of the product by creating a small hole in the back wall of the muffle. It will be enough if you are not going to use a design such as a muffle furnace on an industrial scale.

First of all, decide on which fuel - gas or electricity - the muffle furnace will work. The price for a gas device will start at $ 1,000, however electrical system much easier to manage. In addition, you will need to purchase a high-quality temperature sensor (thermocouple) that monitors the degree of heating up to 1300 degrees. Mounting the sensor to the oven can be made of soft steel wire, carefully twisting it with pliers so that the ends do not touch each other.

For safety reasons, it is better not to try to make a muffle on your own, because if the design is incorrect, the product will simply lose its value after processing. It is best to purchase ceramic chemical glassware from a laboratory equipment store for the required type of discharge.

Secondary appointment

The muffle furnace allows you to quickly remove moisture from the material. At the same time, it does not matter at all whether it will be plain water or liquid element chemical composition in the material. In addition, small structures are very convenient to use when conducting cupelling (laboratory experiments), easily melting lead with gold or silver by oxidation with oxygen contained in the air of the structure to isolate precious metals in its purest form.

When choosing a muffle furnace, it is better to give preference to renowned manufacturers, which guarantee the quality of the product, which also provides high firing rates.

Master Kudel © 2013 Copying of site materials is allowed only with the indication of the author and a direct link to the source site

Muffle furnace made of ball screws (fireclay fiber board)

This is a description of a budget muffle furnace built on the basis of chamotte-fiber plates produced by the Aprelevsk Thermal Products Plant. This is what is called cheap and cheerful. In the spring of 2015, one plate costs 1,670 rubles. But you won't be able to buy one stove, they sell it in boxes. There are 4 pieces in a box. Therefore, we will proceed from this amount.
The dimensions of the slab are 500x500x100 mm. This size suits me, so I proceed from this size, although there are also larger standard sizes on sale. On this page I will describe the design of the muffle furnace itself, without a control unit. Because I have one temperature controller used in several ovens, I will devote a separate page to its description. The whole structure will dance from the size of the slabs, from the most optimal cutting of these slabs, taking into account the smallest deviation. So, taking into account the original size of the slabs, we got a muffle with an internal volume of 27 liters.

This figure schematically shows the location of the ballscrew slabs, as well as the scraps of these slabs. The dimensions of the oven are drawn in red, that is, the metal walls of the box. In one cage - 10 cm. That is, the full slab in this figure will be 5x5x1 cells. From 4 full slabs we get: - door, ceiling and both side walls. The back wall and under (bottom) of the oven are made of scrap. Thus, one box of plates was enough for everything.

Iron

Thus, the dimensions of the furnace body will be:
500 plate + 4 mm two thicknesses of an iron sheet + 6 mm two thicknesses of a corner 25x25. Total 510 mm.
Choose the height with legs yourself, based on your height.

The middle photo below shows the back cover of the oven and the door blank. Please note that the depth of the box will be the same as the width and height. This is because there will be a ventilated cavity at the back for switching the power supply of the heaters, as well as the low-current thermocouple.
All of the furnace control electronics will be in a separate housing, so I don't have to worry about cooling the furnace body. In the rear cavity of the oven there are perforations from the bottom, from the top, and also in the back cover. Therefore, the air freely walks in this cavity and the area of ​​the sites for connecting nichrome is quite large and therefore there is no need to install fans for cooling.

Cutting out ball screws

The processing of ball screws is not difficult at all. You can do this with the same tools as for wood, and even more so for metal.

In the first video, the ball screws of the slabs are cut. Two metal guides are taken and fixed on the pre-marked lines. If you have the knack, you can just hold it with your hand. In the first video, the task is complicated by the fact that the fireclay insert in the oven door is not with right angles, but beveled. But by pressing the lower guide to the table, and holding the upper one with your hand, you can cope with this task.

The second video shows how to mill grooves in a slab for laying heaters. To show how, I used a slab cut.

It should be noted that fireclay strongly blunts the instrument, and if hacksaw blade can be neglected, but it is better to use a cheap burr. The photo shows how a penny cutter for wood from the market worked. When milling a groove, remember to recess the cutter at an angle so that the heater does not fall out.

When marking grooves for heaters, the following considerations should be taken into account. If, when marking the hearth, the heaters should be evenly spaced (right figure), then when marking the sidewalls, the heaters should be shifted down so that, for example, when calcining the flask, they heat up more evenly. Because hot air will rise.
Air exchange in the muffle will take place on natural draft. At the bottom of the door and in the ceiling, 3/4 inch cut-off stainless pipes are welded. And then all this is mounted in the case. The body is pre-painted with heat-resistant paint

Electrician

Here I will not dwell on the calculation of spirals. I have previously painted simplified calculation of heaters made of nichrome and fechral. I will only indicate the data of the heaters for this particular oven. First of all, I made a calculation when all three heaters - right, left and connected in parallel. This is done on purpose. If suddenly some spiral burns out, then the two remaining ones will finish the calcination cycle according to the given program. With sequential switching on, the remaining one will not pull.
Heater data:
- right, left - Nichrome 0.7 mm Length 21.8 meters, R = 62.4 ohm, 775 VA.
-under- Nichrome 0.6 mm, 19 meters, R = 73 × 9 ohm, 654 VA.
Total = 2204 VA

The first photo shows the winding of a nichrome spiral.
A tube of suitable diameter is clamped into the drill. In this case, God has sent me a red label with a diameter of 8 mm. The end of the spiral is attached near the chuck. If you don't have the skill yet, then I recommend hand drill... If you have experience, then electric is better.
After the spiral is wound, it should be stretched to the required length. There is one trick for this. A piece of cambric is taken of a suitable diameter, approximately equal to the diameter of your spiral. In this case, God sent me a silicone tube with a diameter of 10 mm. The tube fits into the groove. and the length is noted. The coil is then evenly stretched at the ends of the coil to the length marked on the tube. Not in any way in pieces, in segments, but precisely at the ends. Otherwise, there will be no uniformity, and it will no longer be possible to squeeze back. Then the spiral fits into the grooves, and the ends are brought out through back wall through the drilled holes.

The installation of the electrical part can be carried out as it is more convenient for you, or as you are used to. For example, I did it in the same way as in the photo. These are, first of all, stainless steel tires. Even if they heat up, they still will not oxidize and will good contact... They are insulated from the aluminum frame with ceramic fasteners made from power transistor spacers. You can also use ceramics from old sockets, this is how I connected the thermocouple to the compensation wire (on the top left frame). The jumper could be made smaller: o). But it just was like that. Conclusions of nichrome were designed in mullite-silica tubes (MCR). If you haven't, don't be scary. Use some beads from an old iron. At worst, ceramic tubes from resistors, fuses. It's just that nichrome doesn't like contact with mortar based liquid glass with which I covered the cracks.

I would like to add that it is better not to fasten the parts of the lining with any mortar. Furnaces do not like rigid connections. Dry lapped surfaces are better. If the two walls were not made of segments, I would have done so.

Door

I first planned a rectangular door. But when cutting out the opening in the front wall, a piece of sheet iron formed, which the toad did not allow to be thrown out. Therefore, the door turned out to be a pyramid.

The ball screw insert sat on the same mastic. Processing the slab is just as easy. The second photo shows an inlet with a stainless insert.

In the first photo door hinge... You may not have one like mine. Nothing, the simple one will go from the market. The main thing is that first the door is made, then the stove is laid on the back, the door is superimposed, centered, a template is made of paper or cardboard, a traction is made according to the template, and only then it is welded to the door. The second photo shows traditional constipation. The weight of the ball is enough to tighten the door. The main thing is without fanaticism.

Total

Many builders claim that it is possible to make a muffle furnace even with wood. Well, if you manage to find firewood with a heat dissipation capacity of 14,000 kcal / kg, then you can still. But no - it makes no sense to put a hefty woodpile around a small muffle, most of the heat will go into emptiness, namely, to increase the entropy in the Universe.

In principle, the concentration of the generated heat required for the necessary kindling can be obtained by a room using coal or charcoal, but only in a furnace with a pressurization system. In this case, there is no point in fencing a whole furnace, it will only be enough to place a muffle inside the furnace as needed,

Muffle furnace

Buy or do it yourself?

It is recommended to make a do-it-yourself oven with a muffle with a volume of up to 5-7 liters. In the event that you take proper processing of such a furnace, then the work you will get is clearly not easy. For this reason, it is necessary at the beginning to see which of the ready-made muffle furnaces will definitely be useful for home use and what it will cost to buy them.

Ceramics for the muffle is required not simple, but with sufficient thermal conductivity. It is provided only by additives from rare metals. Therefore, it is better not even to try to make a muffle on your own.

How to make a muffle furnace on your own:

Nowadays, there are pragmatic craftsmen who like to engage in firing ceramics, homemade products or conduct various physical experiments.

• Refractory. First, we decide on the material of the refractory. The best cost will be fireclay brick... Asbestos boards and fiber can be used. The second layer of thermal insulation is perlite or basalt fiber.
• Frame. Convenient to use old refrigerator or a stove. If you can't find anything, you can weld or rivet from steel. The structure is quite heavy, the body from the refrigerator should be strengthened, especially the bottom. For example, weld it with a steel corner rectangular section... The body is lined with basalt wool. This wool can be used as a top layer when insulating roofs, the material is tough. It's even called hard rock wool.

We buy fireclay bricks at the construction market. It is needed for laying stoves and fireplaces. It is better to purchase a special refractory mixture for masonry as a bonding material.

Fitting and subsequent markup:

Lay it out on the floor side walls future camera so that the back stack is between the side ones. We simulate the thickness of the seams using a wire 3-5 mm in diameter. We adjust the brick to each other. We immerse each brick in a container with warm water for 30 seconds so that water fills his pores. We spread the bottom of the stove. After that we lay out the walls.

Sealing:

The tightness of the doors can be increased with silicone. After the silicone burns out, it should be replaced. It is important to lock the cooking compartment door tightly. In handicraft and semi-handicraft conditions, it is possible to create a screw locking device.

We are laying a heating coil in our future oven:

The heating element is made of nichrome or fechral wire. Its diameter is 1 millimeter, the spirals are 6 millimeters. You can take ready-made spirals, or you can wind it yourself.

Disadvantages of homemade muffles:

clay, even if chamotte, does not conduct heat well enough for uniform heating of the entire muffle. Also, to obtain the maximum firing of the workpiece, a temperature is needed not less, but much higher than the working one.

Where, then, can I get a muffle?

The best option is chemical and ceramic dishes, which can be purchased in stores with laboratory equipment. Shape and size - at choice, everything is usually supplied with lids.

Finally:

Currently, muffle furnaces, especially small-sized ones, are almost not common and they can only be found among the IP masters. And in vain, because these ovens can give a lot.