Electric heating – Metal heating – By arc
Patent
1996-03-18
1997-08-05
Paschall, Mark H.
Electric heating
Metal heating
By arc
21912155, 21912139, 21912144, B23K 1000
Patent
active
056538952
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a plasma cutting method for cutting a workpiece such as of a steel material. More particularly, it relates to a plasma cutting method which is suitable for the cutting of a stainless steel sheet metal that is especially of a thickness not greater than 6 mm.
BACKGROUND ART
Customarily, an apparatus that is used for plasma cutting is constructed as shown in FIG. 1. More specifically, a plasma torch in such an apparatus is provided with a centrally positioned electrode 1 and a confining nozzle 4 that is arranged to surround the electrode with a spacing therefrom which defines a passage 3 for a plasma gas 2. And, there is provided a plasma power supply 9 which is connected across to the electrode 1 and a workpiece 5, and further to the confining nozzle 4 via a switch 16. A cutting operation using such an apparatus is carried out by passing a plasma gas 2 through the passage 3 while generating a plasma arc between the electrode 1 and the workpiece 5 to produce a high temperature plasma gas stream 6 that is narrowly pinched by means of the confining nozzle 4 so as to project onto a given portion of the workpiece material 5. That portion of the workpiece 5 is thereby molten and removed.
By the way, it is typical in the plasma cutting that a quality of cutting may be enhanced by selecting a suitable plasma gas 2 with respect to a workpiece material 5. For example, by using an oxygen gas in cutting a mild steel, it has been known that an operation can be performed to yield a smooth surface of cutting with a dross less attached thereto and yet at an elevated cutting rate.
Also, in cutting a stainless steel material, it has been known that an inert or a reducing gas such as a nitrogen, argon+hydrogen or nitrogen+argon+hydrogen gas can be used to give rise to a smooth cutting surface and, when the workpiece thickness is not less than 6 mm, with a dross less attached thereto and with a high quality of cutting.
However, in case the workpiece is a thin stainless sheet material that is of a thickness less than 6 mm, it has been recognized that such a high quality of cutting is no longer obtainable.
More specifically, if it is attempted to cut a stainless sheet material that is so thin with an inert or a reducing gas as the plasma gas, a large quantity of the dross will be attached to the cut workpiece surface and cannot at the least be peeled. As a result, a subsequent operation such as to grinding off the dross securely deposited onto the cut workpiece surface with a grinder has hitherto been required. Further, since a large quantity of the dross is adhered to the cut workpiece material, it has been found that a heat is conducted from the adhered dross into the workpiece material, thus giving rise to a large thermal deformation thereof. For those reasons, the use of an inert or a reducing gas as the plasma gas for cutting a stainless steel workpiece material has been found to be virtually impractical.
Also, although it is known that if a stainless sheet material is cut using an oxygen gas as the plasma gas, a considerable improvement can be achieved with respect to the problems of a dross that is tending to deposit onto a rear side of the workpiece material, it is also known that the cut surface of the workpiece is severely oxidized by the oxygen gas and consequently becomes blackened and rough. Also, if the cutting rate is set fast, a large amount of the dross will be blown up above the upper surface of a cutting portion of the workpiece material and will build up thereon, thereby reducing the quality of a resultant cut. Conversely, if the cutting rate is set slow, the input heat into the workpiece material will be enlarged, thus enlarging the thermal deformation thereof. Then, in addition, with the oxidation of the cutting surface being promoted, the quality of a resultant cut will still further be lowered. Thus, it has commonly be recognized that it is difficult to properly set the cutting rate.
As set forth above, if a stainless steel sheet material of a thickness
REFERENCES:
patent: 4125754 (1978-11-01), Wasserman et al.
patent: 5396043 (1995-03-01), Couch, Jr. et al.
Kananen Ronald P.
Komatsu Ltd.
Paschall Mark H.
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