NL8004762A - SILICON CARBIDE OVEN. - Google Patents

Description

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Silicon carbide furnace.

Silicon carbide can be formed under various time temperature conditions from mixtures of carbon and silicon dioxide or silicon. It can already be formed at 525 ° C from silicon and carbon under special conditions from a 5-carbon alloy of silicon, aluminum and zinc. Silicon carbide crystals have also been produced by gaseous cracking in at least five vapor systems. It is mainly produced in batch-charged furnaces with dimensions up to 20 meters long by 3 meters wide and with loads up to approximately 90,000 kg of mixture. The oven walls consist of removable sections of cast iron frames lined with medium quality refractory bricks.

The mixture is delivered to the oven by a funnel and a high-mounted overhead crane or by conveyors.

When the oven is approximately half full, charging is temporarily interrupted so that a loose graphite core can be placed between the electrodes located at each end of the oven. The core has a uniform cross section and can have a thickness of up to 25 cm and a width of 40 cm, depending on the size of the oven. Applying the rest of the mixture above the core completes the loading operation. Energy is applied to values of about 5000 kW and at voltages ranging from 400 to 200 when the resistance of the fill changes during the heating period of about 1-1 / 2 days. Several cooling days of the heated charge are required to allow treatment. When removing the side walls, the loose covering is removed, exposing the 8004762 2 ingot. The coating is identical in composition to the original mixture and is reused. The cast is oval in cross-section and enclosed in a crust about 2.5-5 cm thick. This relatively thin crust 5 is formed because the large temperature gradient at this location promotes condensation of oxide contaminants. This concentration facilitates the effective removal of the unwanted contaminants.

The ingot itself, containing commercially available silicon carbide crystals, is broken into large pieces and removed from the oven. The graphite core is recovered for reuse as the core material. The crystalline casting is finally crushed and sieved to desired dimensions. Depending on the end use, the grains 15 can be further treated by cleaning with acid or alkali, then washed with water and dried. The method described above is known as the Acheson method.

Such furnace installations usually require four to six furnaces for each transformer to operate the transformer at its maximum efficiency, heating one furnace, discharging one, charging one and cooling the rest. This requires a very large capital investment in buildings and furnaces. Discharging such furnaces is very difficult and tedious because of the adjacent hot furnaces and because the use of a lot of manual labor is required to remove the silicon carbide from the furnace due to the proximity of the adjacent furnaces and the difficulty of a mechanical discharge device. ting to use with the available limited floor space. This also necessitates that the furnaces must be cooled for an extremely long time before discharge in order to bring the temperature down to the point where manual labor can be used effectively. A further problem arises with the loading of such ovens due to the adjacent other ovens. This means long conveyor belts from the mixing trays to the 35 ovens or high-mounted cranes carrying successive bucket loads to the oven.

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Thus, one of the objects of the invention is to provide an improved furnace design using the Acheson principles.

Another object of the invention is to provide an improved manufacturing plant of silicon carbide.

Yet another goal is to reduce machining costs.

A further aim is to facilitate the pollution control.

10 Another goal is to reduce electrical losses.

Finally, it is an object of the invention to reduce the hazards that arise in the operation of such ovens.

Another goal is to improve the material handling.

The invention will be elucidated hereinbelow with reference to the drawing.

Figure 1 is a top view of the silicon carbide fabrication device according to the invention.

Figure 2 is a side view of the manufacturing device.

According to the invention, an electric resistance furnace is provided which operates with a direct electric heater for the manufacture of silicon carbide from a batch of materials containing silicon and carbon. The current is supplied through rails and electrodes through a carbon resistance core that is horizontally inserted into the charge. The core and the load have a circular construction.

The electric resistance furnace is located in a heating enclosure that is only of a size sufficient for operation. There is a means for loading and unloading the oven. The entire top of the enclosure is sealed except for a channel construction that runs to a dust catcher 35.

With reference to Figures 1 and 2, an oven 8004762 4 installation located within a heating enclosure or building 2 is shown. A conveyor (not shown) brings the silicon and carbonaceous raw materials already properly mixed from a main building to the enclosure. . This conveyor discharges into a series of conveyors (not shown) which discharges into an overflow tray (not shown) located on the roof of the enclosure housing from which the oven is to be loaded. This overflow tray empties in a series of conveyors 6 located above the circular oven to be formed. This device loads the furnace 8 with the correct charge of raw materials 10. It also places the graphite core 12. The furnace design is preferably a rest angle furnace and uses no side walls or ports to contain the furnace charge. However, side walls can be used if desired.

When loading the oven, the bottom half is first formed and then stopped. The core 12 is then placed on the mixture. Then the top half of the oven is formed according to a triangle. Hand organs or other mechanical means can be used to load the oven.

Once this is accomplished, an electrical food source, such as a transformer 14, is electrically connected to the electrodes 16 located at each end of the oven, by means of the rails 18. Because the oven forms almost a full circle and the transformer is located near the two end-walls 20 of the furnace, very short rails are required to make this connection. The transformer can operate the shown oven and an adjacent oven or ovens 22 located in another heating enclosure 24 to begin operation when the first oven is cooled. The power applied through the rails, electrodes and through the core can be alternating current or direct current. The ability is sufficient to provide a temperature for the reaction of the silicon and carbonaceous material to form silicon carbide.

Once the combustion cycle is complete, transformer 14 is disconnected and the cool-discharge process begins. The oven is cooled and discharged in stages.

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First, the oven elements are allowed to cool undisturbed for several days. At that time, a movable digging device 26 or other device is brought within the enclosure. This device begins to discharge the furnace by stripping the ornate stack in steps. This operation is performed so that the warmer material below the surface of the stack is continuously exposed to the air. Once the overloaded stack has been removed from the oven and the silicon carbide ingot is exposed, cooling can take place for several days. The cooling of the ingot can be assisted by a water sprinkler. After the cooling period, the ingot is removed from the oven with the same discharge device and to a central cleaning and sorting area. Once the ingot has been removed from the oven, the loading cycle can be repeated. All dust passes through channel 28 and is collected in a vapor collector 30.

This arrangement reduces operating costs. Less manpower is needed. The shorter rails required reduce material costs and reduce electrical losses. A contamination control is easily obtained. The cooker is easier to load and unload. Operator hazards are significantly reduced as they do not need to be in the heater enclosure when the oven is operating.

Just by way of example, a small oven with a diameter of about 75 cm was built on a flat bed of refractory stone. A layer of sand, coke and recycled mixture was then spread over a width of about 15 cm and a depth of 5 cm on the circle of 75 cm. A graphite core of 2.5 cm x 3 cm was placed on the axis of the bed, each end being connected to a 5 cm graphite rod, which in turn was connected to a 50 kVA transformer. A 15 cm mixture was then added to the core thus forming a triangular cross section of mixture on a circle with a diameter of 75 cm. After heating and cooling, a silicon carbide ingot of circular construction with a uniform cross section was again obtained.

8004762

Claims (8)

1. Device for the production of silicon carbide, characterized in that the device contains an electric power source, a heating enclosure, an electric resistance furnace arranged within the enclosure and operating with electric heating for the production of silicon carbide from a charge of siliceous and carbonaceous material, the current being supplied by electrodes through a carbon resistance core introduced horizontally into the charge, the core and the charge being circular in construction, means for loading the furnace into the construction, means for discharging the furnace and means for collecting gases. 2. Device according to claim 1, characterized in that the oven is loaded by a device attached at the top of the enclosure. The device according to claim 1, characterized in that the cross-sectional construction of the furnace is triangular. 4. Device according to claim 1, characterized in that no side walls are present in the oven. 5. Electric resistance furnace operating with electric heating for the manufacture of silicon carbide from a charge of siliceous and carbonaceous material, the current being supplied by electrodes through a carbon resistance core which is horizontally introduced into the charge, characterized in that the core and the load have a circular construction. The device of claim 1, having the fSe ^ v / arl cross-sectional construction triangular. Device according to claim 1, characterized in that no side walls are present. 8. Device substantially as described in the description and / or shown in the drawing. 35 8004762