U.S. patent number 3,671,655 [Application Number 05/100,729] was granted by the patent office on 1972-06-20 for electrical transfer type plasma arc melting furnace.
This patent grant is currently assigned to Daido Seiko Kabushiki Kaisha, Aichi-ken, JP. Invention is credited to Kiyohide Hayashi, Masayoshi Onishi, Toshio Adachi.
United States Patent |
3,671,655 |
|
June 20, 1972 |
ELECTRICAL TRANSFER TYPE PLASMA ARC MELTING FURNACE
Abstract
An electrical transfer type plasma arc melting furnace with one
or more combined electrodes composed of a metal electrode having
direct contact with the scrap or molten metal, a electric carbon
electrode directly connected with the source and baked or unbaked
electrically conductive compounded refractory which is inserted
between the metal bar and the said carbon electrode arranged either
in the furnace hearth or in the furnace wall.
Inventors: |
Toshio Adachi (Nagoya, JP),
Masayoshi Onishi (Tokai, JP), Kiyohide Hayashi (Nagoya,
JP) |
Assignee: |
Daido Seiko Kabushiki Kaisha,
Aichi-ken, JP (N/A)
|
Family
ID: |
14385091 |
Appl.
No.: |
05/100,729 |
Filed: |
December 22, 1970 |
Foreign Application Priority Data
|
|
|
|
|
Dec 25, 1969 [JP] |
|
|
44/104607 |
|
Current U.S.
Class: |
373/18;
219/121.37; 219/121.52; 219/121.58; 313/231.01 |
Current CPC
Class: |
H05B
7/06 (20130101); H05B 7/00 (20130101) |
Current International
Class: |
H05B
7/00 (20060101); H05B 7/06 (20060101); H05b
007/00 () |
Field of
Search: |
;13/1,9 ;219/121P
;313/231 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Roy N. Envall, Jr.
Attorney, Agent or Firm: Stevens, Davis, Miller &
Mosher
Claims
1. An electrical transfer type plasma arc melting furnace with an
upper cathode and a lower anode characterized in that said anode is
a combined electrode composed of a metallic portion which directly
contacts the scrap or molten metal in said furnace, a carbon
portion which is connected to the electric source and an
intermediate portion which comprises a blend of
2. An electrical transfer type plasma arc melting furnace according
to claim 1 wherein said carbon portion is arranged either in the
furnace hearth or in the furnace wall.
Description
This invention relates to a combined electrode in a plasma arc
melting furnace operated by an electrical transfer type plasma
torch.
In a conventional transfer type plasma arc furnace, the cathode is
placed in the center of a plasma jet torch and molten metal
functions as the anode.
The plasma arc current flows between the plasma jet torch and
molten metal; therefore, the molten metal must be contacted to a
bottom electrode connected with an electrical source.
The said bottom electrode (ordinally made of graphite) which is
usually placed in the furnace hearth, is often broken by the
erosion caused by chemical reaction between the electrode and
molten metal, overheating of molten metal or electrical joule heat.
As, the said damage often appears at the early stage just after the
charge of scraps, a stable plasma arc cannot be maintained and the
plasma arc melting cannot be actually continued.
This invention may be fully understood by referring the attached
drawing, which shows a vertical section of a typical furnace
according to the present invention.
A metal electrode 3 is fixed in the cone shaped refractory 2 which,
for example, is made of baked or unbaked magnesia, and contacts
directly with scraps or molten metal 1.
Electrically conductive materials 8 comprising refractory and
carbon powder properly kneaded together are inserted between the
said metal electrode 3 and the graphite electrode 4.
According to the present invention, the above described defects can
be avoided and suitable electric conductivity can also be
maintained by preparing the combined electrode composed of the
metal electrode 3, compounded refractory 8 and the carbon electrode
4. This furnace, as shown in the drawing, has a furnace body 5, a
furnace cover 6, a plasma jet torch 7, a rectifier 9 and a
transformer 10, all of which are suitably arranged.
As described before, this furnace will not have such a direct
contact between the molten metal and the carbon electrode as seen
in any conventional transfer type plasma arc melting furnace.
Therefore, no increase of carbon content in the molten metal
results. Moreover, a relatively small power loss caused by possible
electric resistance of the metal electrode is incurred.
At the earlier stage of melting, plasma arc current can be
stabilized and also plasma arc melting can be smoothly carried
out.
These advantages accomplish a considerable reduction in melting
time and provides for suitable melting of ultra low carbon
steel.
Results shown in Table 1 indicate operational conditions between a
furnace of the present invention and a conventional furnace. The
data in the table highlights the advantages of the present
invention.
The metal electrode 3 keeps a solid form with its one part in
contact to the kneaded refractory 8 and semi-molten form with the
other part in contact to the molten metal 1. ##SPC1##
Though the metal electrode 3 which is in semi-molten form will be a
little lost after tapping, quicker melting operation can be
obtained by only exchanging the used metal electrode with a new
one.
* * * * *