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Homemade electric furnace for melting metals

Homemade electric furnace for melting metals

If you have a need for annealing metals, creating ceramics, smelting non-ferrous and precious metals, you can build yourself such a simple furnace. Most of these stoves cost a lot of money, according to the author, in his region the prices are around $ 600-12,000 per stove. In our case, the furnace cost only $ 120, not counting the temperature controller. This small oven can produce temperatures around 1100oC.

Going to homemade simply, all parts are not expensive, and they can also be quickly replaced if the furnace malfunctions.

Some craftsmen manage to make wedding rings in such furnaces, earrings, various talismans, brass knuckles and much more.


Materials and tools for homemade:


Materials:
- bolts and nuts (8x10, 1/4 inch);
- seven refractory bricks (they must be soft, since they will need to be grooved, dimensions 4 1/2 "x 9" x 2 1/2 ");
- a corner to create a frame;
- a square sheet of metal for the door (the author used aluminum);
- a heating element (you can buy ready-made spirals for the furnace, or wrap your own nichrome)
- heat resistant contact screws for attaching the spiral;
- a piece of good cable (must withstand at least 10A).

From the tools:
- a hand drill with a suitable nozzle for cutting grooves in a brick;
- wrench;
- pliers;
- a hacksaw;
- drill;
- nippers and more.

The process of making a homemade furnace:

Step one. Make the grooves
First you need to determine how wide the spiral is, depending on this, the depth and width of future grooves in the bricks is determined. Next, you need to draw them on the brick with a pencil. The author’s grooves have a shape in the form of the letter “U”, all grooves of this shape are two pieces, that is, they are cut on two bricks. On that brick, which will be located in the back of the furnace, you need to make two parallel grooves as in the photo. As a result, after the assembly of the furnace, the spiral will receive approximately a "P" -shaped shape.

Step Two Installation of a heating element
Before installing the heating element, you need to collect the bricks, having decided on the dimensions of the furnace. Most likely, the bricks that go to the floor of the furnace will have to be cut, since two such bricks will form too large a bottom. You can cut them off with a grinder with a disk for concrete, well, or even with an ordinary cutting disc.



Well, then you can install the spiral.Most likely, it must first be stretched to the desired length. If you will wind the spiral yourself, then you need to calculate how long and thickness the wire should be, there is a ton of information on the Internet for this.

Well, then you can lay the oven in the groove. To fix the spiral, the author uses metal brackets, under which holes will need to be made in the brick. Particular attention should be paid to connecting the spiral to the wire. Special screws with ceramic washers should be used here, and the screws must be taken more authentically. Otherwise, the insulation of the wire will either constantly burn and stink, or it will constantly burn due to high temperature.

Our people learned to make such contacts from old car candles when ancient electric stoves with an open spiral were used.

Particular attention should be paid to the choice of material from which the spiral is made. The maximum temperature that the furnace can give out will depend on this. The spiral must withstand high temperature loads. For such purposes, the author chose a wire of the NiCr type. Most of these wires are designed for temperatures of about 1340aboutC. If you require higher temperatures, you can choose other types of wires that are suitable for this.

Step Three Making the stove frame
To create a frame you will need a corner, you can use steel or aluminum. Four pieces of aluminum form the legs, and two more go to the bottom and support the weight of all the bricks. You can use not two corners, but four to create the lower support. However, this is not necessary, as a result, the design is still pulled together with bolts and nuts, these bolts hold the bricks below.

Two or one and a half bricks will need to be laid in the upper part of the furnace, as well as below. Well, how everything is going, you can see in detail in the photo.

Step Four Make the door
To create the door you will need a sheet of metal, the author used aluminum. First, you need to draw a square or quadrangle on the sheet, depending on the size and shape of the door. Next, this square must still be circled in a circle, stepping back you need a distance for fixing the refractory material. Well, then cut the pieces at the corners, as seen in the photo.

As a refractory material auto used a Kaowool stove. It must be cut to the size of the previously drawn square. Well, then the plate is laid on the sheet, and the remaining edges of the sheet are bent, thereby holding the plate.




That's all, now the door needs to be hinged with screws and nuts to the furnace, having drilled a couple of holes. As an insulating material, you can use other accessories. The latch for the door can be done, but not.

Step Five We supply electricity
To connect the spiral, you need to use a good wire with a thick core, which can withstand at least 10A. Among other things, the furnace is connected through a regulator, it will help maintain the temperature in a given state. You will also need a furnace thermometer, according to which it will be possible to more accurately monitor the temperature in the furnace.

It is important to remember that such a furnace consumes a lot of energy, so all wiring must be in good condition, and the machine must withstand the load that the furnace creates.

Step Six Testing the stove
Before starting, the oven must be installed away from substances and materials that can easily catch fire. It should not be included on a wooden floor or floor with linoleum. It should be brick, concrete and so on. Now the oven can be turned on and tested. It is important to remember what temperature the selected wire is designed to not overheat the spiral.





According to the author, his furnace was able to give out a temperature of 1260 degrees Celsius and showed excellent performance.
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9.7
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17 comments
They asked to make a regulator for a 2.5 kW heater. For a home-made moonshine (fashion now is). Made on TS122-25 ... As expected. There will be no fire goodgood

T143-500-13 will go for scrap iron
SKM100 GB125DN - will go for colored scrap
Understood, thanks.
Icon in the form of a folder "Uploading files and images to the server"
They made the UPI-5000-12-T furnace (10 years ago). This is for color.
For ferrous metals, thyristor furnaces were used

I just smashed such a furnace 10 years ago.
Bonus bucket of fast thyristors TB 143-320-12 and diodes. Plus liquid contact radiators.
Guys, I’m new here and I can’t understand how to insert pictures. The engine doesn’t insert the direct picture. Only a link does not require an extraneous resource.
Quote: Hambaker
We need a weak driver with an instantaneous output current per pulse of 5 amperes.
Therefore, IR in order to build up its IGBT strongly recommends using its own driver ICs, which are consistent with the characteristics of transistors.
They made the UPI-5000-12-T furnace (10 years ago). This is for color.
For ferrous metals, thyristor furnaces were used (and for a long time). The frequencies there are much lower than 500Hz, 1kHz. The capacities there are large for volumes of 0.4t ... 8t
The circuits that have been developed for furnaces are already applied to welding inverters.
The Ketayans were cheaper (weaker) and at what convenient frequency

Looking at the graphs of the dynamic characteristics in datasheets, it can be seen that with an increase in the control frequency (Miller's capacity) and an increase in the temperature of the crystal, the characteristics of the “Izht” (IGBT) fly away to nowhere.
To download a powerful one with a gate capacitance higher than 5000 pF and at a speed of 60 kHz, you need a weak driver with an instantaneous output current per pulse of 5 amperes. Plus, taking into account the stray capacitance of the installation, you need to adjust the values ​​of the forced dead time for key management. Resetting spurious inductance emissions is a separate task .And to coordinate the generator with the load is another task.
A separate problem is the cooling of what is uselessly heated, reducing efficiency.
Type of radiators on IGBT and water cooling of the coil itself ... (Here is the answer for the efficiency - the excess heat of the inevitable losses in the inductor through the radiators and other cooling systems is discharged into the environment. Unlike resistance furnaces, in which, even the smallest ones try to exclude losses.
The difficulty was what they were doing at the allowed frequency of 66 kHz.
The difficulty is that they do not melt such a frequency.
P.S. I'm in the subject, if that.
We developed (at one time) a 12 kW induction furnace. The difficulty was what they were doing at the allowed frequency of 66 kHz. And these are high-frequency (expensive) IGBT transistors, etc. The Ketayans were cheaper (weaker) and at what convenient frequency nea . On the Internet, I was asked at what frequency do household Ketai tiles work. Measured - ~ 30kHz
Perhaps the most compelling argument in favor of the author’s design is simplicity and reliability at a low price.
An inductive heater of the same power and reliability "do it yourself" will cost ... I can’t even tell how much. For the final result greatly depends on the level of knowledge in the field of power electronics and the availability of appropriate measuring instruments for setting up and running the assembled unit.
There have not yet been enthusiasts to stir up induction melting in the kitchen?
The cheapest thing is to remake the inverter welder. First of all, you need power. Unlike heating a magnetic milk pan (household induction with others just will not turn on) to a boil, we are going to melt the metal ...
Here and about the secondary circuit try to retell something. It's funny. Actually, in the coil there is a core with "losses" .... Jewelers (real) have induction furnaces. And about efficiency. At the household level. Here put boil water (milk!) On an electric stove 1 kW. You will wait a long time until it all warms up ... (and the milk "runs away") derisive Yeah, economical. On the induction (Chinese) tile, it boils at a time and turns off - immediately the milk "drops" and does not run away. And the base (glass ceramic) is cold !! Only the pan is hot!
Remember, my boss wanted to melt silver for crafts. We didn’t have gas, but there was an ordinary muffle furnace (up to 1000s). I expressed doubt about the possibility. But, the beginning is a stove up to 1000, and silver - 960s. Through the air (without blasting)? ... The end of the working day is already over, but the stove has not warmed up. The chief says, but let him warm until morning. In the morning I come to work, beg. (gloomy) says - you know, the mold (graphite) fell apart, and the silver did not melt. smiles
Well, experience is also a necessary thing ... yes
Author
And respect to the author. He made this stove for his needs and shared his ideas. Those who need it will find something necessary. And add it to their design. Otherwise, we are not friends.


Bravo. The true spirit of the enthusiast)
The efficiency of the muffle furnace is determined only by losses to the environment.
The article provides a sample of a resistance furnace. It has the highest efficiency of converting heat generated from power consumption. For this, alloys with high resistivity and resistance to high temperatures were developed. Such as nichrome, fechral and others.
So gold and copper in such furnaces melt without problems. (Moreover, to melt gold, the lid with spirals does not need to be wrapped, it has been checked. yes The volumes are not the same.) One drawback is the operating temperature of the heater. Of the most common nichrome (1100 gr.) And fechral (1400 gr.)
And metal is melted in induction furnaces.
But here everything is not so rosy. The efficiency is even lower and not very stable in the process. It is mainly used for melting small (up to 300 kg) batches of non-ferrous metals and their alloys.
To ferromagnets (in ferrous metallurgy) induction melting is practically not used. For technological reasons, the operation of the inductor. ("I will explain on the fingers:
The “furnace” of the inductor is an oscillatory circuit in which the primary winding of a kind of transformer serves as the inductance, the secondary winding of which is the heated part itself. In simple terms, this part is a short-circuited coil in which all the heat of the short circuit is released. And in order for most of the power supplied from the generator to transmit the parts, the natural resonance frequency of the oscillating circuit should be as close as possible to the generator frequency. And the resonance frequency depends on the value inductance (and it is from the core-melting material) and its size. There are no problems with non-ferrous metals as a melting material. The magnitude of the inductance depends little on temperature. And ferromagnets, when heated to a certain temperature, sharply lose their magnetic properties (Curie point) and radically change the magnitude of the inductance and, in turn, the resonance frequency of the entire oscillatory circuit of the inductor, which again sharply reduces the efficiency)
But induction heating in technological processes of heat treatment of parts made of ferrous alloys is widely used. Sometimes this is the only way to achieve the desired results. (The same surface hardening).
That's just all this is not a garage option.
And respect to the author. He made this stove for his needs and shared his ideas. Those who need it will find something necessary. And add it to their design. Otherwise, we are not friends.
Author
Well, as far as I observed when melting aluminum or lead, the lower layer melts first, then this red-hot layer melts the rest due to heat exchange ... Well, of course, the metal is heated not by air, but by heating the bottom of the tank in which it melts.

I honestly don’t know by air ...
Not so simple in the smelting of metals. What is offered to melt? Through the hot air? In 1000 deg.? And what is the heat capacity of air and what is metal?
He wanted to make a young man a ring out of silver contacts. He took the ceramic tile
scratched the groove. On top of the imposed contacts in a circle (grooves). And he asked a friend at the factory to melt (fuse) into a ring with a gas burner (propane-butane). Sprinkled with brown. And nothing happened! Metal (silver) melted into a wide drop. And it doesn’t lock into a ring ... From a gas jet, rushing with heat, but there is no ring smiles
It turns out this is not the case. The factory craftsmen took a collapsible form of graphite. Contactees were poured around the circumference. Warm up a gas burner form. And that's it. A ring (blank) is ready for turning in size. ok
Author
Che, gold melts just above 1000, aluminum 660 .. Copper 1085. But the author, according to him, issues 1260
This is a muffle furnace. Suitable for firing ceramics, etc. Efficiency is low. Temperature up to 900gr (1100gr. If everything is covered with spirals ... and the lid). And metal is melted in induction furnaces.

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