Plasma torch

Details Plasma torch Plasma torch

1998-10-30

2001-04-10

Walberg, Teresa (Department: 3742)

Electric heating

Metal heating

By arc

C219S121470, C219S121510

Reexamination Certificate

active

06215091

ABSTRACT:

CROSS REFERENCE TO RELATED ART
This application claims priority of Korean patent application No. 1998-20509 filed on Jun. 3, 1998, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1) Field of the Invention
The present invention relates to a plasma torch, more particularly, to a plasma torch that has high efficiency, the input power of which is more than 1 megawatt (MW), and the cathode of which has long life span.
2) Background of the Invention
in “UIE ARC PLASMA REVIEW 1998” which illustrates many kinds of plasma torches, among them two representative plasma torches will be explained.
FIG. 2
shows one of the transferred-solid type plasma torches of the prior art, a Daido Steel brand plasma torch. This is a scaled-up version of the torch design used for cutting and welding. The long tungsten cathode is recessed behind the copper nozzle and operates in the transferred mode with argon gas. The torch is available in sizes up to about 1 MW
FIG. 3
shows one of the non-transferred hollow type plasma torches of the prior art, an SKF brand, a SKF plasma torch. This design is segmented with a fixed length arc column with magnetic field coils at each end. The torch has two equal diameter copper electrodes, the capped rear electrode being connected negative. So the magnetic field makes a rotating arc root in the ups electrode and this results in long cathode life. The insulated segments between the electrodes stretch the length of the arc column to a larger length that will develop a higher arc voltage. Torches with power ratings from 100 kW to 8 MW are available. The SKF torch has a field coil for rotating the arc foot of the upstream electrode and thus can make more than 1 MW output. However efficiency of the torch is lower than the transferred type since temperature of the plasma rapidly reduces as it departs from the nozzle. To exchange the cathode, the whole assembly surrounding the cathode must be removed, which results in high exchange cost.
SUMMARY OF THE INVENTION
Therefore, it is one of the objects of the present invention to provide a plasma torch with a long life cathode and whose output is more than 1 MW.
It is another object of the present invention is to provide a plasma torch whose cathode can be easily exchanged.
It is still another object of the present invention is to provide a plasma torch whose cathode region has low pressure, which helps ignition at lower voltage.
To accomplish these objects, the present invention provides a plasma torch including
a body having a gas supplier for supplying plasma gas;
a cathode supporter for supporting the button-cathode;
a button-cathode for generating plasma arc, assembled to the front end of the cathode supporter by a bolting means; and
a hollow-cathode which surrounds the button-cathode, has a predetermined space from the button-cathode, is assembled to the cathode supporter, and is made of material with higher work function than the material for the button-cathode.
Preferably, the present invention also provides a plasma torch with multiple-solenoid coil surrounding the cathode. A moving peak current with flat current is applied to the multiple-solenoid coil in order to move arc foot on the surface of the button-cathode back and forth, which can prolong cathode life.
The button-cathode and the hollow-cathode are assembled by a bolting means, which enables easy exchange of the button-cathode which generates plasma arc and experiences wear.
The button-cathode of the invention is positioned so as to be surrounded by the hollow-cathode, which makes the pressure of the surrounding area of the button-cathode low, and thus makes ignition at lower voltage and enables stable flame of the plasma arc column generated at the button-cathode.
The plasma torch of the present invention has a hollow-cathode surrounding a hot button type cathode, so it can be called a hollow hot button-cathode torch.


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patent: 5688417 (1997-11-01), Cadre et al.
patent: 5717187 (1998-02-01), Rogozinski et al.

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