Electric heating – Metal heating – By arc
Patent
1992-07-14
1994-03-22
Paschall, Mark H.
Electric heating
Metal heating
By arc
21912152, 21912145, 21912151, 219119, B23K 900, B23K 1000
Patent
active
052966682
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention concerns a gas-cooled cathode for a direct current (dc) arc torch. Direct current arc torches should not be confused with transferred arc devices, such as TIG welders, where the anode comprises a workpiece. A sheath is provided around the cathode of TIG welders and a very high flow of inert gas (not working gas) is pumped through the sheath to Provide an inert environment and prevent oxidation of the cathode and workpiece.
Direct current arc torches should also not be confused with intermittent arc devices such as are proposed for jet engines.
In direct current arc torches a working gas is heated by a dc arc to create a plasma which then passes out of the torch through a nozzle comprising its hollow anode. The device operates continually over long periods of time, and the plasma may be used to ignite fuel, such as pulverized coal, in steam raising boilers used to generate electric power. The plasma may also be used to stabilize combustion of the coal, and in many other applications, for instance in blast furnaces and to obtain process heat.
BACKGROUND ART
Conventional direct current arc torches are water-cooled, and passages for the water usually pass through both the cathode and anode. Cooling is essential since it prevents the cathode from reaching temperatures where it deteriorates due to melting or boiling. Also, heat radiation from the cathode at high temperatures will make it impossible to control the arc. Working gas is conventionally injected directly into the space between the anode and the cathode, through passages in the insulation which separates them.
The water-cooled arrangement involves the connection of water pipes to the torch, and because water conducts electricity, the water circuit is required to be electrically isolated. There is a potential safety hazard in these systems since if one of the water hoses comes uncoupled during use, a jet of hot, and possibly high voltage, water can be sprayed out in an uncontrolled fashion.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a gas-cooled cathode for a direct current arc torch. The cathode has a tip connected to a body. A gas passage for working gas passes through the body of the cathode, passes proximate the tip and exits the body adjacent the tip. The cathode is spaced apart from and insulated from the anode by means of a collar of insulating material.
All the working gas required to sustain the arc is supplied through the cathode and cools it on the way to the ntry of the anode.
A swirler surrounds the tip of the cathode, downstream of ports through which the working gas exits the body. Swirling the gas improves the stability of the arc in the region of the cathode, and rotates the anode root, which reduces erosion of the anode. In a highly preferred embodiment this swirler is made of metal and as the torch heats up to its operating temperature it expands and seals against the collar which insulates the cathode from the anode.
In a particularly advantageous embodiment of the invention the gas passage through the cathode communicates the tip such that working gas contacts the tip as it passes through the cathode.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described by way of example only, with reference to the accompanying drawings, in which:
FIG. 1 is a schematic section through the wall of a steam raising boiler in which an arc torch embodying the invention may be used;
FIG. 2a is a elevational and part sectional view of an arc torch embodying the present invention;
FIG. 2b is a cross-sectional view of the anode of FIG. 2a taken along the section lines IIb--IIb;
FIG. 3a is a elevational view of the cathode of FIG. 2a; and
FIG. 3b is an elevational view of the cathode tip of FIG. 3a.
BEST MODE FOR CARRYING OUT THE INVENTION
Referring first to FIG. 1, a typical steam raising boiler has an outer wall 1 and an inner wall 2 lined with water tubes 3. A cavity in the wall houses a direct current arc torch 4. A passage 5 extends from the outer wall 1 to s
REFERENCES:
patent: 3632951 (1972-06-01), Klasson
patent: 4266113 (1981-05-01), Denton et al.
patent: 4649257 (1987-03-01), Yakolevitch et al.
Foreman Craig
Vierboom Peter
Paschall Mark H.
The Electricity Commission of New South Wales
The University of Sydney
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