JP2603837B2 - Plasma cutting method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for cutting a workpiece such as a steel plate by a plasma arc blown from a plasma torch.

[Conventional technology]

Plasma cutting is performed using a plasma torch as shown in Fig. 3.
Material to be cut such as steel plate by blowing out plasma arc 12 from 10
Cut 14 Fig. 3 (a) is a view from the side, (b)
Is a view seen from the rear in the traveling direction, but a part is omitted or broken so that a cut portion is clearly shown. Arrow F
Indicates a cutting direction (a torch advancing direction). If the thickness of the fractured material 14 is large and the cutting speed is high, the plasma arc 12 first enters vertically as shown in the figure, but eventually tilts, and finally, the downward inclination is strengthened. It is common to get out. The first vertical part is due to the plasma arc flame erupting vertically downward, and this part is due to the fact that the arc current flows and the workpiece is also subjected to current heating. The subsequent sloped portion is due to the fact that only the heating by the high-temperature frame is performed and there is no current heating. If the plate thickness is small or the cutting speed is low, the plasma arc penetrates the material to be cut vertically.

When the cutting speed is low, the plasma arc flame that escapes from the material to be cut is almost vertically downward as shown in FIG. 4 (a), and the inclination angle ± θ from the perpendicular is not large. If the cutting speed is very slow, the cutting head will tilt forward in the inclination angle + θ, that is, the cutting direction. When the cutting speed is high, the inclination is largely inclined backward (-θ is large) as shown in FIG. 4 (b).

The material to be cut is melted by the plasma arc flame, the molten metal is blown away, and the cutting progresses as the torch advances, but a part of the molten metal is cut below the cut portion of the material to be cut. And tend to solidify over time. The molten metal that accumulates on this lower surface and solidifies over time is dross
That. The dross 16 is generated when the plasma arc flame which escapes from the material to be cut is greatly inclined backward as shown in FIG. 4 (b), and is not generated when it is almost vertical as shown in FIG. 4 (a). FIG. 3 (c) is a view of the cut portion of the workpiece 14 viewed from below, wherein 18 is a hole opened by the plasma arc flame 12 penetrating the workpiece, and 20 is the plasma arc flame cut. Indicates the position of incidence on the part.

[Problems to be solved by the invention]

When the molten metal accumulates on the lower surface of the cut portion and solidifies, the molten metal on both sides of the cut portion tends to be connected and integrated, and in this case, the lower surface of the cut portion is recombined with dross. In other words, it should have been cut, but it cannot be cut and recombination will occur. FIG. 3 (c) shows a state in which the lower surface of the cut portion is rejoined by dross.

In order to prevent the lower surface of the cutting part from rejoining with dross, it is necessary to reduce the thickness of the plate and reduce the cutting speed,
In any case, the cutting ability of the plasma torch is reduced.
In other words, thicker materials can be cut faster without dross recombination, but thinner materials must be cut at lower speeds.

With oxygen or air as working gas and plasma cutting machine,
It is dross-free with a plate thickness of 20 to 25 mm or less. Above that, the adhesion of dross is so large that it is hardly practiced.

With a cutting machine using an oxygen plasma with a 250A output, the maximum thickness of a normal temperature steel sheet is 40 mm, and the maximum thickness of a high temperature (about 700 ° C) steel sheet is 55 mm. Regardless of the cutting of any steel plate, if the plate thickness is 30 mm or more, dross adheres very much, and once cut, it cannot be separated due to recombination by dross.

Oxygen-based and argon-based plasma cutting machines, plate thickness 15 mm
What can be said in common for the dross adhesion phenomenon in steel sheet cutting described above is that the dross-free cutting speed is approximately 70% of the maximum cutting speed.
In this case, as shown in FIG. 4 (a), the inclination angle θ of the plasma arc flame is within ± 15 °, dross-free,
It is. When θ exceeds −15 °, the dross amount increases almost in proportion to the inclination angle, and as shown in FIG. It becomes impossible to rejoin and separate. Therefore, conventionally, FIG.
In general, cutting is performed in the state described above.

An object of the present invention is to improve such a point and to improve the cutting ability by removing dross.

[Means for solving the problem]

In the present invention, an after gas nozzle is provided on a cutting line behind the traveling direction of the plasma torch, a high-speed gas flow is jetted from the nozzle, and the molten metal accumulated on the lower surface of the cutting portion is blown off,
Consequently, dross adhesion and reconnection of the cut portion by the dross are prevented.

FIG. 1 shows an outline of a plasma torch used for cutting according to the present invention. Reference numeral 28 denotes an after gas nozzle, which is attached to the plasma torch 10 by an attachment base 24, and is located slightly below the plasma arc 12 at the rear of the torch in the traveling direction. When the cutting is performed along a curved line such as an arc, the rear of the torch in the traveling direction changes according to the curved line.
10 to allow the torch 10 to rotate about its central axis, or the torch 10 does not rotate, and the mounting base 24 is
Make it rotatable around 10. 22 is an after gas hose,
Reference numeral 26 denotes a setting adjustment knob for the after gas nozzle 28. Numeral 30 indicates an after gas flow.

Any kind of after gas can be used in principle, but according to experiments, better results can be obtained by changing the kind of gas depending on the material of the material to be cut or the quality of the cut surface. For example, oxygen gas or air is used for mild steel, and this is sprayed onto a molten metal (in this case, molten mild steel) to cause an oxidation reaction, and the use of the reaction heat is efficient (dross can be removed well). . Ar gas, N ₂ gas, or air is used as the non-ferrous material, but Ar gas has the best surface quality.

As shown in FIG. 2, the target position of the after gas spraying is a point l behind the point where the plasma arc flame 12 has come off from the lower surface of the workpiece 14, and the injection angle α is −10 ° to −15 °. Try to lean backwards instead of vertically. The dimension l is slightly different depending on the cutting speed, and it is preferable that the size 1 is about 8 to 10 mm when the cutting speed is low and about 12 to 20 mm near the maximum cutting speed. The point is to blow off the dross that bridges the lower surface of the cut portion, and the target position is point A in FIG. 3 (c). If this position is brought close to the position where the plasma arc flame passes through the material to be cut, it is not preferable because the plasma arc flame and / or the heating section are cooled by the after gas. After gas flow
Reference numeral 30 is set apart from the plasma arc 12 in the material to be cut.
According to experiments, the ejection angle α is about −10 ° to −15 °, and the remaining amount of dross is the smallest. The after gas stream 30 is tilted backward in order to disturb the plasma arc 12 as little as possible.

The after gas nozzle 28 can be moved forward or backward in the cutting direction as shown by arrows F ₁ and F ₂ in FIG. ₂ , and the distance l is optimized according to the drag-in delay D that changes depending on the relationship between the thickness and the cutting speed. To be able to set.

[Action]

By providing a gas ejection nozzle on the cutting line behind the plasma torch and blowing off dross adhering to the lower surface of the cut portion of the material to be cut with the gas from the nozzle, the cutting speed is increased and / or the thickness of the material to be cut is increased. And the cutting ability of the plasma torch can be increased.

〔Example〕

By O ₂ gas, high-temperature material of approximately 700 ° C., the steel sheet having a thickness of 50 mm, the circular cut-out cutting diameter 50 mm, in the conventional plasma cutting without the after-gas, the cutting speed is 600 mm / min
However, there was much adhesion of dross, and the cut portion was recombined by dross about once every five times, and the cut material did not fall off. However, by using the after gas, it became possible to cut even at a cutting speed of 900 mm / min, and there was no mistake in dropping the cut material.

〔The invention's effect〕

As described above, according to the present invention, dross generated in the cut portion is blown off by the after gas, so that there is no recombination of the cut portion due to the dross, and the cutting capability of the plasma torch can be enhanced.

In addition, since the after gas is blown at a point behind the point where the plasma arc flame escapes from the lower surface of the workpiece, the after gas disturbs the plasma arc, and also cools the plasma arc and / or the heating unit, The advantage is that there is no problem.

[Brief description of the drawings]

1 and 2 are explanatory views of a torch used in the present invention, and FIGS. 3 and 4 are explanatory views of a conventional plasma cutting. In FIG. 1, reference numeral 14 denotes a workpiece, 10 denotes a plasma torch, 12 denotes a plasma arc, and 28 denotes an after gas nozzle.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-54-35155 (JP, A) JP-A-59-64165 (JP, A) JP-A-63-111268 (JP, U) 74114 (JP, B2)

Claims (1)

(57) [Claims] 1. A method for cutting a material to be cut by a plasma arc blown from a plasma torch, wherein an after gas nozzle is provided on a cutting line behind the plasma torch in a traveling direction, and after gas is supplied by a plasma arc flame. Aiming at a point behind the exit point and spraying at an injection angle of -10 ° to -15 ° with an inclination backward, the dross adhering to the lower surface of the cut portion of the material to be cut at the time of plasma cutting from the after gas nozzle. A plasma cutting method characterized by cutting a material to be cut by advancing a plasma torch while blowing off with a high-speed gas flow.