Electric heating – Metal heating – By arc
Patent
1997-08-12
1999-05-04
Paschall, Mark H.
Electric heating
Metal heating
By arc
21912143, 21912155, 21912157, B23K 1000
Patent
active
059001682
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a plasma cutting method for use with a plasma cutting machine and, more particularly, a plasma cutting method which is rendered capable of preventing an orifice portion of the nozzle from being oxidized and damaged when a cutting process is initiated.
BACKGROUND ART
A plasma torch which has previously been used in a plasma cutting machine is so constructed as shown in FIG. 1 of the drawings attached hereto, and is provided in its central portion with an electrode 1, inside of which there is formed a cooling chamber 8. Also, outside of the electrode 1 there is formed a plasma gas passage 2, and a nozzle 3 is disposed so as to surround the electrode 1 via the plasma gas passage 2. Also, outside of a forward end of the nozzle 3 there are formed a cooling chamber 9 and a secondary gas passage 4 along with a shield cap 5 surrounding the cooling chamber 9 and the secondary gas passage 4.
A cutting process with a plasma torch of such a construction is carried out by generating a plasma arc 7 that constitutes a main arc between the electrode 1 and a workpiece 6 while causing a plasma gas 20 to flow through the plasma gas passage 2. The plasma arc 7 is pinched and thereby narrowed and densified with an orifice 3a of the nozzle 3 and is elevated in temperature and accelerated therethrough so as to be flushed towards the workpiece 6 and so as to melt and remove a portion thereof for cutting it.
Then, a water coolant is circulated through the cooling chambers 8 and 9 which are provided in the interior of the electrode 1 and the exterior of the nozzle 3, respectively, so that they may both be cooled. Also, a secondary gas 21 is then flushed through the secondary gas passage 4 provided inside of the shield cap 5 so that the above mentioned plasma arc 7 may be surrounded by the secondary gas 21.
The procedure of generating a plasma arc 7 as mentioned above is set forth below. First, a high frequency voltage is applied across the electrode 1 and the nozzle 3 to cause a spark discharge between them, resulting in the occurrence of a pilot arc. Floating on a flow of the plasma gas 20, the discharge spot of the pilot arc on the side of the electrode 1 is moved to the center of the forward end thereof while the discharge spot on the side of the nozzle 3 passing through the orifice 3a thereof is moved to a region of the outlet thereof, eventually reaching the surface of the workpiece 6, and thus establishing a plasma arc 7.
At the same time, the electric power between the electrode 1 and the nozzle 3 ceases being supplied. The plasma arc 7 is then pinched and thereby narrowed and densified with the orifice 3a of the nozzle 3 to result in a high temperature and high velocity flushing jet stream, which acts to form a cut groove of a small width in the workpiece 6 and to allow cutting thereof to proceed.
Then, while both the electrode 1 and the nozzle 3 are exposed to an elevated temperature by the plasma arc 7, they are, as mentioned above, cooled by the water coolant or air. Also, the electrode 1 which will be elevated by a temperature of several thousand degrees due to the thermo electron emission, in order for its wear to be lowered, is composed of a high melting point material. Such a material, if the plasma gas 20 contains oxygen, may be hafnium and, if it is a non-oxidizing gas not containing oxygen, may be tungsten.
Also, in a prior art plasma cutting process, the kind of plasma gas 20 that has been employed is related to the material of the workpiece 6. Thus, if a mild steel material is to be cut, the plasma gas 20 makes use of oxygen. If a stainless material or an aluminum material is to be cut, the plasma gas 20 makes use of a non-oxidizing gas not containing oxygen. The non-oxidizing gas may be composed of a single component gas such as argon or hydrogen or a mixture thereof.
By the way, as mentioned earlier, it should be noted that in plasma cutting, a plasma arc 7 at a high temperature and with a high velocity is flushed out of the nozzle 3, thereby locally melting
REFERENCES:
patent: 5414237 (1995-05-01), Carkhuff
patent: 5424507 (1995-06-01), Yamaguchi
patent: 5591357 (1997-01-01), Couch, Jr. et al.
patent: 5653895 (1997-08-01), Shintani
patent: 5653896 (1997-08-01), Couch, Jr. et al.
Patent Abstracts of Japan, vol. 95, No. 6, Jul. 31, 1995 & JP 07060450A (Nippon Steel Corp), Mar. 7, 1995.
Patent Abstracts of Japan, vol. 10, No. 267 (M-516), Sep. 11, 1986 & JP 61 092782A (Koike Sanso Kogyo Co. Ltd), May 10, 1996.
Patent Abstracts of Japan, vol. 13, No. 289 (M-845), Jul. 5, 1989 & JP 01 083376A (Komatsu Ltd), Mar. 29, 1989.
Saio Katsuo
Yamaguchi Yoshihiro
Komatsu Industries Corporation
Komatsu Ltd.
Paschall Mark H.
LandOfFree
Plasma cutting method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Plasma cutting method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Plasma cutting method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1868160