JPH01133676A - Plasma cutting method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for cutting a material to be cut, such as a steel plate, using a plasma arc blown out from a plasma torch.

[Conventional technology]

Plasma cutting is performed using plasma torch 1 as shown in Figure 3.
A plasma arc 12 is blown out from zero to cut a material to be cut 14 such as a steel plate. Figure 3(a) is a side view, (
b) is a view seen from the rear in the direction of travel, with some parts omitted or broken to clearly show the cut portions. Arrow F indicates the cutting direction (torch advancing direction). Material to be cut 1
If the plate thickness of 4 is thick (and the cutting speed is fast, the plasma arc 1
As shown in the figure, the blade 2 generally enters the material to be cut vertically at first, but then gradually slopes, and finally passes through the material to be cut with an increasingly downward slope. The first vertical portion is caused by the fact that the plasma arc flame is ejected vertically downward, and also by the fact that the arc current flows in this portion and the material to be cut is also heated by the current. (The sloping part is due to the fact that there is no electric current heating, only heating by the high temperature flame. If the plate thickness is thin or the cutting speed is slow, the plasma arc will penetrate vertically through the material to be cut.)

If the cutting speed is slow, the plasma arc flame that exits the material to be cut will be vertically downward as shown in Figure 4 (a), and the angle of inclination ±θ from the perpendicular is not large; if the cutting speed is very slow, it will be tilted. The corner will be tilted forward in the cutting direction. If the cutting speed is high, the cutting speed will move significantly backwards as shown in Figure 4 (b).
(-θ is large).

The material to be cut is melted by the plasma arc flame, the molten metal is blown away, and the heated state advances as the torch advances and the cutting progresses. It tends to accumulate and eventually solidify. The molten metal that collects on the bottom surface and eventually solidifies is called dross. This dross 16 is generated when the plasma arc flame that pulls out the material to be cut is tilted greatly backwards as shown in Figure 4 (b), and as shown in Figure 4 (a), dross 16 is generated when it is vertical. do not. FIG. 3(C) is a view of the cut part of the material to be cut 14 viewed from below, where 18 is a hole opened by the plasma arc flame 12 penetrating the material to be cut, and 20 is the hole to be cut by the plasma arc flame. Indicates the position of incidence on the material.

[Problem that the invention seeks to solve]

When the molten metal collects on the underside of the cut and solidifies, the molten metal on both sides of the cut tends to bind together and become a single body, causing the underside of the cut to recombine with dross. In other words, although it should have been cut, it cannot be cut and recombination occurs.

FIG. 3(C) shows a state in which the lower surfaces of the cuts have been recombined with dross.

In order to prevent recombination due to dross on the lower surface of the cut, it is necessary to reduce the thickness of the plate and reduce the cutting speed, but both of these will lead to a decrease in the cutting ability of the plasma torch.In other words, if there is no recombination due to dross, If you had it, you would be able to cut thicker materials at a higher speed, but if you had this, you would only be able to cut thinner materials at a slower speed.

Plasma cutting machines that use oxygen or air as the operating gas are dross-free only when the thickness of the plate is 20 to 25 mm or less, and if the thickness is larger than that, the amount of dross attached is so large that it is almost never used. It is.

With an oxygen plasma cutting machine with an output of 250A, the maximum cutting thickness is 40m when cutting steel plates at room temperature, and the maximum thickness is 40m when cutting steel plates at room temperature.
) The maximum cutting thickness of the steel plate is 55n+. In the case of cutting any steel plate, if the plate thickness is 30W or more, there is a large amount of dross attached, and even if the steel plate is cut, it cannot be separated due to recombination due to the dross.

The common thing about the dross adhesion phenomenon when cutting steel plates with a thickness of 15 fins or more with oxygen-based and argon-based plasma cutting machines is that the dross-free cutting speed is approximately 70% of the maximum cutting speed.
% or less, and if this is the case as shown in Figure 4(a), the inclination angle θ of the plasma arc flame is within the range of ±15°, dross-free.If θ exceeds 115°, the inclination angle will crack. The amount of dross increases proportionally, and when θ becomes -30° or more as shown in FIG. Generally, cutting is performed in the state shown in FIG. 4(a).

The present invention aims to improve the above-mentioned problems and improve the cutting ability by removing dross.

[Failure to solve the problem]

In the present invention, an aftergas nozzle is provided on the cutting line at the rear in the direction of movement of the plasma torch, and a high-speed gas flow is ejected from the nozzle to blow away the molten metal that accumulates on the lower surface of the cut, resulting in dross adhesion and recombination of the cut part by the dross. to prevent

FIG. 1 shows an outline of a plasma torch used for cutting according to the present invention. Reference numeral 28 denotes an aftergas nozzle, which is attached to the plasma torch 10 by a mounting base 24 and positioned slightly below the plasma arc 12 at the rear in the traveling direction. When cutting is performed along a curve such as a circular arc, the direction of torch movement rearward changes according to the curve.
to the torch 10 to allow the torch 10 to rotate about its central axis, or the torch 10 does not rotate and the mount 24 allows the mount 24 to rotate about the torch 10. 2
2 is after gas hose, 26 is after gas nozzle 2
8 setting adjustment knob.

Further, 30 indicates an aftergas flow.

In principle, any type of aftergas may be used, but experiments have shown that better results can be obtained by changing the type of gas depending on the material of the material to be cut or the quality of the cut surface. For example, for mild steel materials, it is efficient to use oxygen gas or air and spray it onto the molten metal (molten mild steel in this case) to cause an oxidation reaction and use the heat of the reaction (dross can be removed well) . Ar gas, N2 gas, or air is used for non-ferrous materials, but Ar gas has the best surface quality.

The target position for aftergas spraying is as shown in Figure 2.
A point l behind the point where the plasma arc flame 12 passes through the lower surface of the workpiece 14, and the ejection angle α is -10° to -15°.
It should not be vertical (it should be tilted backwards).The dimension l will vary depending on the cutting speed, and if the speed is slow, it will be about 8 to 10 mm.
m, preferably about 12 to 20 mm near the maximum cutting speed. The point is to blow away the dross bridging the lower surface of the cut, and the target position is point A in Figure 3(C). If this position approaches the position where the plasma arc flame passes through the material to be cut, the plasma arc flame and/or the heating section will be cooled by the aftergas, which is not preferable. The aftergas flow 30 generates a plasma arc 12 in the material to be cut.
Keep it away from you. According to the experiment, the ejection angle α is -10”
The amount of residual dross is the lowest at about -15°. The purpose of tilting the aftergas flow 30 backward is to avoid disturbing the plasma arc 12 as much as possible.

The aftergas nozzle 28 is indicated by arrow F+ in FIG.

As shown by F2, it is possible to move forward or backward in the cutting direction, so that the distance β can be optimally set according to the drag gain delay D that changes depending on the relationship between plate thickness and cutting speed (
.

[Effect]

If a gas jet nozzle is installed on the rear cutting line of the plasma torch and the gas from the nozzle blows off the dross that adheres to the lower surface of the cut material, it is possible to increase the cutting speed and/or increase the thickness of the material to be cut. The cutting ability of the plasma torch can be increased.

〔Example〕

When cutting a 5011 diameter circular cutout of a 50mm thick steel plate made of high temperature material at approximately 700°C using 02 gas, conventional plasma cutting without aftergas requires a cutting speed of 6.
Although the cutting was possible at 00 m/win, there was a lot of dross attached, and about 1 in 5 cuts the cut part was reattached due to dross.
The cut material did not fall off when pulled out. However, by using aftergas, cutting was possible even at a cutting speed of 900 w/min, and there were no errors in the removal of the cut material.

〔Effect of the invention〕

As explained above, according to the present invention, since the dross generated at the cut portion is blown away by the aftergas, there is no recombination of the cut portion due to dross, and the cutting ability of the plasma torch can be improved.

[Brief explanation of the drawing]

FIGS. 1 and 2 are explanatory diagrams of a torch used in the present invention, and FIGS. 3 and 4 are explanatory diagrams of conventional plasma cutting. In Fig. 1, 14 is the material to be cut, lO is the plasma torch, and 12
28 is a plasma arc, and 28 is an aftergas nozzle. Applicant: Nippon Steel Welding Industry Co., Ltd. Representative Patent Attorney Minoru Aoyagi 12

Claims (1)

[Claims] In a method of cutting a material to be cut using a plasma arc blown out from a plasma torch, an aftergas nozzle is provided on the cutting line at the rear in the direction of movement of the plasma torch, and the aftergas nozzle is provided on the lower surface of the material to be cut during plasma cutting. A plasma cutting method characterized in that a material to be cut is cut by advancing a plasma torch while blowing away attached dross by a high-speed gas flow from the aftergas nozzle.