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Muffle furnace from electric stove. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Ham Radio Technologies

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Raw clay products will become durable if they are fired. To do this, you need a furnace with a temperature of up to 950 ° C. Today we will tell you how to make a muffle furnace from a household electric stove. By the way, it can be used not only for firing ceramics, but also for heat treatment of steel products, tools, melting of many metals and alloys.

Look at fig. 1. A cylindrical cap is installed on the tile with the bottom up. It is he who forms the working chamber. The cap is shown in section, so the layers of which it is made are clearly visible. The inner layer is formed by a deep cup of refractory clay (chamotte). You can get clay in small boiler houses, where it is used to coat boilers. The cup is made in a cardboard form impregnated from the inside with paraffin or stearin so that the form does not stick. The thickness of the clay layer is up to 10 mm.

Muffle Furnace

When the clay dries, it will easily lag behind the wall of the mold. The finished cup should fit snugly on the hot plate. To avoid cracks, process the bottom edge with a file or knife, and then with sandpaper.

The outer layer of the cap forms a protective casing. Cut out a cylindrical shell and a cover from a steel sheet with a thickness of 0,5-0,8 mm. Tabs should be provided on the bottom of the cylinder - with them the cup will rest on the tile. The cover is fixed on the cylinder with three screws and nuts. Several small holes must be drilled in the lid to allow moisture to escape. For greater reliability of fastening, install on the U - shaped spacer plate. With its lower ends, it rests against a ceramic cup, and with a horizontal shelf - against the cover of the casing. All the remaining space between the cup and the casing must be tightly filled with asbestos chips. For convenience in operation, the oven must have a peephole with a closing shutter. The hole is formed by a tube of refractory clay with a diameter of 15-20 mm. On the casing, it remains to make two handles from wire with a diameter of 5-6 mm.

To give the cup the necessary thermal strength, it must be fired. Place the cap on the electric hot plate.

Attention! All further work with the included tiles requires compliance with safety regulations. The tile should stand on a thick asbestos-cement base or several tiles. If you do not find such a base, install the electric stove on a steel sheet resting on the table with ceramic rollers. The gap between the table and the sheet must be at least 20 mm. Now you can start firing the cup. For a short time (before heating the spiral), turn on the tile in the network, and then turn it off. Repeat this operation for two hours. Turn on the stove for a longer time (about three hours). During the firing process, the cup may warp a little, and then cracks form. During firing, fill the cracks with asbestos cord. When the inner surface of the fireclay cup warms up to 950 ° C, that is, it becomes bright orange in color (control is carried out through the peephole), firing is completed. Turn off the tile. After the casing has cooled down, the identified cracks should be removed with a file. The muffle furnace is ready.

And now we will briefly describe how ceramic products are made. Wipe the clay that you brought from the quarry through a fine metal mesh. Then add water and mix thoroughly. Leave the solution to stand for several days. This procedure is necessary so that all solid inclusions settle to the bottom. Only then will the composition of the clay become homogeneous. Drain the water, and carefully knead the clay with your hands on a plywood sheet until a lump of uniform viscosity is obtained. In order for the clay to retain its original qualities for a long time, it is kept in a plastic bag.

Muffle Furnace
Fig. 2

But here you fashioned products from clay. The clay is wet, it needs to be dried a little. For a few days, put the products on the bottom of the pan and cover it with a paper sheet. This technique will protect products from the appearance of microcracks, which will increase significantly after firing.

After drying, the surface of the products is corrected with a scraper and cleaned with sandpaper.

An interesting method of obtaining hollow clay products is casting in a plaster mold. A model-copy of the future product is molded from plasticine. The model is installed in a box and half-filled with plaster. Get the first half. After the plaster has hardened, the model is removed. The same operation is carried out with the second semi-form. Plasticine is removed from it, and both parts of the form are connected. A liquid clay solution is poured into the formed cavity. Gypsum will absorb water intensively. A layer of clay settles on the inner surface of the mold and exactly copies its shape. However, the model for such a casting must be made simple, otherwise it will not come out of the plaster mold and will have to be broken.

Put the finished clay figurines on an electric stove and cover with a cap. Within three hours, preliminary drying should be carried out, that is, the tile turns on and, as soon as the spiral heats up, turns off. And only after that the products are fired at a temperature of 900-950 ° C.

When firing in a muffle furnace, it is advisable to lay pieces of charcoal - the released carbon dioxide will protect the spiral from oxidation and increase its service life.

After firing, the products can be glazed. Pounded glass and silicate (office) glue will do. To prepare glass powder, make a special mortar from a massive cylindrical steel bar. A blind hole with a diameter of 30-35 mm and a depth of 70-100 mm should be drilled along the axis. Several pieces of broken glass are placed in the mortar and the glass is broken into powder by blows of a hammer on a steel pestle. Each product is pre-coated with a thin layer of silicate glue, and then rolled in glass powder. Glazes can be given a blue or green color if gouache "Cobalt" or "Chromium Oxide" is added to the glass powder. The last operation: the products are fired again at a temperature of 950 ° C.

Author: K. Skvortsov

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