CA1167499A - Arcuate silicon carbide manufacturing plant - Google Patents
Arcuate silicon carbide manufacturing plantInfo
- Publication number
- CA1167499A CA1167499A CA000358200A CA358200A CA1167499A CA 1167499 A CA1167499 A CA 1167499A CA 000358200 A CA000358200 A CA 000358200A CA 358200 A CA358200 A CA 358200A CA 1167499 A CA1167499 A CA 1167499A
- Authority
- CA
- Canada
- Prior art keywords
- furnace
- load
- silicon carbide
- core
- plant
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/60—Heating arrangements wherein the heating current flows through granular powdered or fluid material, e.g. for salt-bath furnace, electrolytic heating
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/90—Carbides
- C01B32/914—Carbides of single elements
- C01B32/956—Silicon carbide
- C01B32/963—Preparation from compounds containing silicon
- C01B32/97—Preparation from SiO or SiO2
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F27—FURNACES; KILNS; OVENS; RETORTS
- F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
- F27B21/00—Open or uncovered sintering apparatus; Other heat-treatment apparatus of like construction
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Carbon And Carbon Compounds (AREA)
- Silicon Compounds (AREA)
- Furnace Details (AREA)
Abstract
Abstract of the Disclosure Disclosed is an electrical resistance furnace and manufacturing plant for the preparation of silicon carbide.
A resistance core of carbon is horizontally inserted within a load of silicious and carbon material. The core and load are of broken ring configuration and current is supplied to the resistance core by means of electrodes.
A resistance core of carbon is horizontally inserted within a load of silicious and carbon material. The core and load are of broken ring configuration and current is supplied to the resistance core by means of electrodes.
Description
I :3.87~9 ,, , ~ILICON CARBIDE FURNACE
Silicon carbide may be formed under various time-temperature conditions from mixtures of carbon and silica or siliccn. It can be formed as low as 525C. from silicon and carbon under special conditions ~rom a carbon riched alloy of silicon, aluminum and zinc. Silicon car-bide crystals have also been produced by gaseous cracking in at leas,t five vapor systems. It is produced primarily in batch type furnaces ranging up to 60 ft. long by 10 ft.
wide and holding up to about 200,000 lbs. of mix. The fuxnace walls consist of removable sections of cast iron frames lined with low grade-firebrick.
The mix is delivered to the furnace by a hopper and an overhead traveling ~rane or by conveyors. When the furnace is approximately 1/2 full, the loading is interrupt-ed temporarily so that a loose graphite core can be placed between the electrodes located at each end o~ the furnace.
The core is of uniform cross-section and may range up to 10 inches thick and 16 inches wide, depending upon the size of the furnace. Placing the balance of the mix above the core completes the loading operation. Power is applied at rates up to about 5,000 kw and at voltages ranging from 400 to 200 as the resistance o the charge changes during the heating period of about 1-1/2 days. The heated charge requires several days cooling to permit handling. Upon removing the si~ewalls, the loose covering falls away exposing the ingot. The covering is similar in composition to the original mix and is reused. The ingot is oval in cross-section and is encased in a crust of about 1 - 2 inches thick, This relatively thin crust forms because , ~
.
' ~ ~ 6~ e~
of the sharp temperature gradient at that position favors condensation of the oxide impurities. This concentration facilitates the effective disposal of the unwanted im-purities.
S The ingot proper, containing the commercial crystals of silicon carbide, is broken into large sections and removed from the furnace. The graphite core is recovered for reuse as a core material. The crystalline ingot is finally crushed and is screened to desired sizes. Depend-ing upon end use, the grain may be further treated by cleaning with acid or alkali, then washed with water and dried. The above-described process is well known as the Acheson process.
Such furnace installations usually require four to six furnaces for each transformer in order to utilize the transformer to its maximum efficiency, with one furnace heating, one being unloaded, one loading, and the remainder cooling. This requires very large capital investment in buildings and furnaces. The unloading of such furnaces is quite difficult and tedious because of the adjacent hot furnaces and because of the necessity of using large amounts of hand labor to remove the silicon carbide from the furnace due to the proximity of the adjacent furnaces and the difficulty of using mechanical unloading equipment in the restricted floor space available. This also requires that the furnaces be cooled an extraordinarily long time before unloading in order to get the temperature down to the point where the hand labor can be effectively used. A further problem arises in the loading of such furnaces because of the adjacent other furnaces. This means lengthy conveyor belts from the mixing bins to the furnaces or ouerhead cranes carrying successive bucket loads to the furnace.
Accordingly, it is among the objects of this invention to provide an improved furnace design utilizing Acheson principles.
Another object of the invention is to provide an improved silicon carbide manufacturing plant.
Still another object is to reduce operating costs.
A further object is to facilitate pollution control.
-Still a further object i5 to reduce electrical losses.
~et another object is to reduce the hazards attendant the operation of such ~urnaces.
Yet a further object is to improve material handling.
In the drawings:
Fig. 1 is a plan view of the improved silicon carbide manufacturing plant; and Fig. 2 is an elevation view of the plant.
In accordance with the p~esent invention, there is provided an electrical resistance furnace operated by direct electric heating for the preparation of silicon carbide from a load of silicious and carbonaceous materials.
The current is supplied by means of bus bars and electrodes through a resistance core of carbon horizontally inserted within the load. The core and the load are circular 1n configuration.
The electrical resistance furnace is situated in a heating enclosure only of a size sufficient to accommodate the operation. There is a means for loading and unloading the furnace. The entire top of the enclosure is sealed except for ductwork which leads to a dust collector.
Referring to Figs. 1 and 2, there is shown a furnace installation situated within a heating enclosure o~ buil~ing
Silicon carbide may be formed under various time-temperature conditions from mixtures of carbon and silica or siliccn. It can be formed as low as 525C. from silicon and carbon under special conditions ~rom a carbon riched alloy of silicon, aluminum and zinc. Silicon car-bide crystals have also been produced by gaseous cracking in at leas,t five vapor systems. It is produced primarily in batch type furnaces ranging up to 60 ft. long by 10 ft.
wide and holding up to about 200,000 lbs. of mix. The fuxnace walls consist of removable sections of cast iron frames lined with low grade-firebrick.
The mix is delivered to the furnace by a hopper and an overhead traveling ~rane or by conveyors. When the furnace is approximately 1/2 full, the loading is interrupt-ed temporarily so that a loose graphite core can be placed between the electrodes located at each end o~ the furnace.
The core is of uniform cross-section and may range up to 10 inches thick and 16 inches wide, depending upon the size of the furnace. Placing the balance of the mix above the core completes the loading operation. Power is applied at rates up to about 5,000 kw and at voltages ranging from 400 to 200 as the resistance o the charge changes during the heating period of about 1-1/2 days. The heated charge requires several days cooling to permit handling. Upon removing the si~ewalls, the loose covering falls away exposing the ingot. The covering is similar in composition to the original mix and is reused. The ingot is oval in cross-section and is encased in a crust of about 1 - 2 inches thick, This relatively thin crust forms because , ~
.
' ~ ~ 6~ e~
of the sharp temperature gradient at that position favors condensation of the oxide impurities. This concentration facilitates the effective disposal of the unwanted im-purities.
S The ingot proper, containing the commercial crystals of silicon carbide, is broken into large sections and removed from the furnace. The graphite core is recovered for reuse as a core material. The crystalline ingot is finally crushed and is screened to desired sizes. Depend-ing upon end use, the grain may be further treated by cleaning with acid or alkali, then washed with water and dried. The above-described process is well known as the Acheson process.
Such furnace installations usually require four to six furnaces for each transformer in order to utilize the transformer to its maximum efficiency, with one furnace heating, one being unloaded, one loading, and the remainder cooling. This requires very large capital investment in buildings and furnaces. The unloading of such furnaces is quite difficult and tedious because of the adjacent hot furnaces and because of the necessity of using large amounts of hand labor to remove the silicon carbide from the furnace due to the proximity of the adjacent furnaces and the difficulty of using mechanical unloading equipment in the restricted floor space available. This also requires that the furnaces be cooled an extraordinarily long time before unloading in order to get the temperature down to the point where the hand labor can be effectively used. A further problem arises in the loading of such furnaces because of the adjacent other furnaces. This means lengthy conveyor belts from the mixing bins to the furnaces or ouerhead cranes carrying successive bucket loads to the furnace.
Accordingly, it is among the objects of this invention to provide an improved furnace design utilizing Acheson principles.
Another object of the invention is to provide an improved silicon carbide manufacturing plant.
Still another object is to reduce operating costs.
A further object is to facilitate pollution control.
-Still a further object i5 to reduce electrical losses.
~et another object is to reduce the hazards attendant the operation of such ~urnaces.
Yet a further object is to improve material handling.
In the drawings:
Fig. 1 is a plan view of the improved silicon carbide manufacturing plant; and Fig. 2 is an elevation view of the plant.
In accordance with the p~esent invention, there is provided an electrical resistance furnace operated by direct electric heating for the preparation of silicon carbide from a load of silicious and carbonaceous materials.
The current is supplied by means of bus bars and electrodes through a resistance core of carbon horizontally inserted within the load. The core and the load are circular 1n configuration.
The electrical resistance furnace is situated in a heating enclosure only of a size sufficient to accommodate the operation. There is a means for loading and unloading the furnace. The entire top of the enclosure is sealed except for ductwork which leads to a dust collector.
Referring to Figs. 1 and 2, there is shown a furnace installation situated within a heating enclosure o~ buil~ing
2. A conveyor (not shown) brings the raw materials, silicious and carbonaceous, already properly mixed, from a main building to the enclosure. This conveyor discharges onto a series of conveyors (not shown) which discharges into a surge tank (not shown) located on the roof of the enclosure housing whichever furnace is to be charged. This surge tank empties onto a series of conveyors 6 located above the circular furnace to be formed. This stacker loads the furnace 8 with the proper charge of raw materials 10.
It also places the graphite core 12. The furnace design is an angle of repose furnace, preferably, and does not employ any sidewalls or gates to contain the furnace charge. How-ever, sidewalls may be employed if desired.
In loading the furnace, the bottom half is first formed and then stopped. Next the core 12 i5 laid on the mixture.
Then the furnace is topped off in a triangular-like i7 ~ (J ~
configuration. Manual means or other mechanical means may be employed to load the furnace if desired.
Once this is accomplished, an electrical power source, such as a transformer 14, is electrically connected to the electrodes 16 located at either end of the furnace, with bus bars 18. Because the furnace is almost a complete circle, and the transformer is located near the two endwalls 20 of the furnace, very short bus work runs are needed to make this connection. The transformer may serve the furnace shown and an adjacent furnace or furnaces 22 located in another heating enclosure 24, to start operations when the first furnace is being cooled. The power applied through the bus bars, electrodes and through the core, may be either AC or DC. The power is sufficient to provide a temperature to react the silicious and carbonaceous material to form silicon carbide.
Once the burn cycle is complete, the transformer 14 is disconnected and the cooling-unloading procedure begins.
The furnace is cooled and unloaded in stages. Initially, the furnace pile is allowed to cool, undisturbed, for several days~ At this time, a mobile shovel 26 or other equipment is brought into the enclosure. This equipment begins to unload the furnace by stripping the overburden pile in stages. This operation is done so that the hotter material below the surface of the pile is continuously ex-posed to air. Once the furnace overburden pile is removed and the silicon carbide ingot is exposed, it is allowed to cool for several days. The cooling of the ingot may be aided by a water spray. After the cooling period, the ingot is removed from the furnace by the same unloading equipment and taken to a central cleaning and sorting area.
Once the ingot is removed ~rom the furnace, the loading cycle may be repeated. All of the dust passes through duct 28 and are collected in a fume collector 30.
This setup reduces operating costs. Less manpower is required. The shorter bus bars required reduce cost of material and reduce electrical loss. Pollution control is readily achieved. The furnace is more easily loaded and unloaded. Hazard to workers is materially reduced since 7~9 they need not be in the plant heating enclosure when the furnace is in operation.
Merely by way of example, a small furnace of about 30 inch0s in diameter was built on a flat bed of refractory brick. A layer of sand, coke and recycled mix was then spread about 6 inches wide and 2 inches deep on the 30-inch circle. On the axis of the bed, a 1 inch by 1-1/4 inch graphite core was laid, each end being connected to a 2 inch graphite rod which, in turn, was connected to a 50 KVA
transformer. Six inches of mix were then added over the core, thus forming a triangular cross section of mix on a 30 inch diameter circle. After heating and cooling, a silicon carbide ingot of circular configuration having a uniform cross-section was recovered.
It is intended that the foregoing description and drawings be construed as illustrative and not in limitation of the invention.
It also places the graphite core 12. The furnace design is an angle of repose furnace, preferably, and does not employ any sidewalls or gates to contain the furnace charge. How-ever, sidewalls may be employed if desired.
In loading the furnace, the bottom half is first formed and then stopped. Next the core 12 i5 laid on the mixture.
Then the furnace is topped off in a triangular-like i7 ~ (J ~
configuration. Manual means or other mechanical means may be employed to load the furnace if desired.
Once this is accomplished, an electrical power source, such as a transformer 14, is electrically connected to the electrodes 16 located at either end of the furnace, with bus bars 18. Because the furnace is almost a complete circle, and the transformer is located near the two endwalls 20 of the furnace, very short bus work runs are needed to make this connection. The transformer may serve the furnace shown and an adjacent furnace or furnaces 22 located in another heating enclosure 24, to start operations when the first furnace is being cooled. The power applied through the bus bars, electrodes and through the core, may be either AC or DC. The power is sufficient to provide a temperature to react the silicious and carbonaceous material to form silicon carbide.
Once the burn cycle is complete, the transformer 14 is disconnected and the cooling-unloading procedure begins.
The furnace is cooled and unloaded in stages. Initially, the furnace pile is allowed to cool, undisturbed, for several days~ At this time, a mobile shovel 26 or other equipment is brought into the enclosure. This equipment begins to unload the furnace by stripping the overburden pile in stages. This operation is done so that the hotter material below the surface of the pile is continuously ex-posed to air. Once the furnace overburden pile is removed and the silicon carbide ingot is exposed, it is allowed to cool for several days. The cooling of the ingot may be aided by a water spray. After the cooling period, the ingot is removed from the furnace by the same unloading equipment and taken to a central cleaning and sorting area.
Once the ingot is removed ~rom the furnace, the loading cycle may be repeated. All of the dust passes through duct 28 and are collected in a fume collector 30.
This setup reduces operating costs. Less manpower is required. The shorter bus bars required reduce cost of material and reduce electrical loss. Pollution control is readily achieved. The furnace is more easily loaded and unloaded. Hazard to workers is materially reduced since 7~9 they need not be in the plant heating enclosure when the furnace is in operation.
Merely by way of example, a small furnace of about 30 inch0s in diameter was built on a flat bed of refractory brick. A layer of sand, coke and recycled mix was then spread about 6 inches wide and 2 inches deep on the 30-inch circle. On the axis of the bed, a 1 inch by 1-1/4 inch graphite core was laid, each end being connected to a 2 inch graphite rod which, in turn, was connected to a 50 KVA
transformer. Six inches of mix were then added over the core, thus forming a triangular cross section of mix on a 30 inch diameter circle. After heating and cooling, a silicon carbide ingot of circular configuration having a uniform cross-section was recovered.
It is intended that the foregoing description and drawings be construed as illustrative and not in limitation of the invention.
Claims (7)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A silicon carbide manufacturing plant comprising:
an electrical power source;
a heating enclosure;
an electrical resistance furnace disposed within the enclosure and operated by electric heating for the preparation of silicon carbide from a load of silicious and carbonaceous material;
the current being supplied by means of electrodes through a resistance core of carbon horizontally inserted within the load, said core and load being of broken ring configuration;
means for loading the furnace in said configuration;
means for unloading the furnace; and means for collecting gases.
an electrical power source;
a heating enclosure;
an electrical resistance furnace disposed within the enclosure and operated by electric heating for the preparation of silicon carbide from a load of silicious and carbonaceous material;
the current being supplied by means of electrodes through a resistance core of carbon horizontally inserted within the load, said core and load being of broken ring configuration;
means for loading the furnace in said configuration;
means for unloading the furnace; and means for collecting gases.
2. The plant of claim 1, in which the furnace is loaded with a device, mounted at the top of the enclosure.
3. The plant of claim 1, in which the cross-sectional configuration of the furnace is triangular.
4. The plant of claim 1, in which no sidewalls are present on the furnace.
5. In an electrical resistance furnace operated by electric heating for the preparation of silicon carbide from a load of silicious and carbonaceous material, the current being supplied by means of electrodes through a resistance core of carbon horizontally inserted within the load, the improvement comprising said core and load being of broken ring configuration.
6. The furnace of claim 5, in which the cross-sectional configuration is triangular.
7. The furnace of claim 5, in which no sidewalls are present.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US7976379A | 1979-09-28 | 1979-09-28 | |
| US079,763 | 1979-09-28 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1167499A true CA1167499A (en) | 1984-05-15 |
Family
ID=22152650
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000358200A Expired CA1167499A (en) | 1979-09-28 | 1980-08-13 | Arcuate silicon carbide manufacturing plant |
Country Status (9)
| Country | Link |
|---|---|
| JP (1) | JPS5824372B2 (en) |
| AU (1) | AU6165980A (en) |
| BR (1) | BR8006188A (en) |
| CA (1) | CA1167499A (en) |
| CH (1) | CH640199A5 (en) |
| IN (1) | IN154845B (en) |
| NL (1) | NL8004762A (en) |
| NO (1) | NO802864L (en) |
| NZ (1) | NZ194699A (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4399546A (en) * | 1979-09-28 | 1983-08-16 | Dresser Industries, Inc. | Silicon carbide furnace |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2630198C2 (en) * | 1976-07-05 | 1983-02-03 | Elektroschmelzwerk Kempten GmbH, 8000 München | Furnace with direct electrical resistance heating for the production of silicon carbide |
-
1980
- 1980-08-13 CA CA000358200A patent/CA1167499A/en not_active Expired
- 1980-08-18 NZ NZ194699A patent/NZ194699A/en unknown
- 1980-08-19 IN IN602/DEL/80A patent/IN154845B/en unknown
- 1980-08-22 NL NL8004762A patent/NL8004762A/en not_active Application Discontinuation
- 1980-08-22 AU AU61659/80A patent/AU6165980A/en not_active Abandoned
- 1980-09-25 CH CH719080A patent/CH640199A5/en not_active IP Right Cessation
- 1980-09-26 NO NO802864A patent/NO802864L/en unknown
- 1980-09-26 BR BR8006188A patent/BR8006188A/en unknown
- 1980-09-29 JP JP55135729A patent/JPS5824372B2/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5824372B2 (en) | 1983-05-20 |
| IN154845B (en) | 1984-12-15 |
| CH640199A5 (en) | 1983-12-30 |
| BR8006188A (en) | 1981-04-07 |
| NO802864L (en) | 1981-03-30 |
| NL8004762A (en) | 1981-03-31 |
| JPS5659615A (en) | 1981-05-23 |
| AU6165980A (en) | 1981-04-02 |
| NZ194699A (en) | 1982-12-21 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |