JPH06292971A - Plasma arc cutting gas - Google Patents

Abstract

PURPOSE:To prolong a service life of an electrode and reduce the cost of consumables for cutting work by mixing a specified quantity of oxygen in inert gas or gaseous carbon dioxide in plasma arc cutting gas. CONSTITUTION:The plasma arc cutting gas for air plasma cutting uses gas mixed with oxygen by about 20% in inert gas or gaseous carbon dioxide. Consequently, since nitrogen gas is not contained in orifice gas, nitriding on the cut surface is not generated. Since the quantity of oxygen is little as about 20%, the service life of the plasma cutting torch electrode 7 is prolonged and expenses of the electrode and the loss time at the time of exchange are reduced. Since gaseous carbon dioxide is used for the orifice gas, gas expenses are reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma arc cutting gas used for cutting steel sheets.

[0002]

2. Description of the Related Art Conventionally, oxygen cutting, which is a mixture of combustible gas and oxygen, has been mainly used for cutting steel sheets, but in recent years, an air plasma arc cutting machine utilizing a high-speed jet stream in a plasma arc has been used for shipbuilding steel sheets, etc. It has come to be used frequently for cutting.

FIG. 1 is an explanatory view showing the structure and operation of a conventional general plasma arc cutting torch.

In the figure, reference numeral 1 is a nozzle having a funnel-shaped tip. An electrode support cylinder 6 is provided in the nozzle 1 via a working gas swirling and inner cylinder fixed ring 12 made of an insulator, and a water-cooled outer cylinder having a watertight structure with the nozzle 1 on the outer peripheral surface of the nozzle 1. Two are connected. A cooling water supply pipe 3 and a cooling water discharge pipe 4 are connected to the water cooling outer cylinder 2.

The electrode support tube 6 is attached to the tip of the energizing pipe 8, and the tip of the electrode cooling water conduit 9 is inserted into the electrode support tube 6, and the tip of the electrode support tube 6 is inserted. A bar electrode 7 made of a pure metal of hafnium (Hf) or zirconium (Zr) or an alloy of both metals is installed therein. A connecting ring 13 made of an electrical insulator is provided between the nozzle 1 and the energizing pipe 8,
A working gas supply pipe 5 is connected to the nozzle 1 portion between the connecting ring 13 and the working gas swirling and inner cylinder fixed ring 12.

An electrode cooling water supply pipe 10 and an electrode cooling water drain pipe 11 are connected to the electrode cooling water conduit 9.

The nozzle 1 is connected to a pilot arc power source 16 via an electric wire 18b ', and the energizing pipe 8 is connected to the electric wire 18b.
a is connected to the plasma power source 17 via
It is connected to the pilot power source 16 via a and 18a '. Further, the plasma power source 17 is connected to the material 15 to be cut via an electric wire 18b.

In this way, the electrode support cylinder 6 and the material to be cut 1
5, a pilot plasma 14a and a plasma arc (or arc) 14b are generated. It should be noted that, in the figure, the hatched arrows indicate the flow direction of the cooling water, and the arrows indicate the direction of the working gas.

In the above structure, before the plasma arc is generated, cooling water is first introduced from the nozzle cooling water supply pipe 3 and the electrode cooling water supply pipe 10 into the plasma torch, and the nozzle 1 and the electrode support cylinder (chip) 6 are connected. The cooling of the rod electrode 7 is started.

Next, the working gas is introduced from the working gas supply pipe 5 into the torch and discharged from the tip of the nozzle 1. At this time, the working gas becomes a swirling flow by the working gas swirling and inner cylinder fixed ring 12 and is supplied to the nozzle tip.

Next, the pilot arc power supply 16 is operated to generate a small current pilot arc 14a between the rod electrode 7 and the nozzle 1, as shown in the figure. The working gas supplied to the tip of the nozzle 1 becomes a swirling plasma flow due to the heat generated by the pilot arc 14a, and extends downward from the nozzle 1 as the pilot plasma 14b. After the pilot plasma 14b comes into contact with the material 15 to be cut, the pilot power supply 16 is turned off, and at the same time, the plasma power supply 17 is operated to move the arc 14a between the rod electrode 7 and the material 15 to be cut to generate a large current (100- 250A)
Shed. As a result, the plasma arc 14 is generated and the material 15 to be cut is cut.

In air plasma cutting, since the working gas is air, nitrogen in the air reacts with the cut surface of the steel material, so-called nitriding occurs.

When this cut surface is welded, this nitride layer causes blowholes and cannot be used. Further, this nitrided layer is very thin and disappears if the cut surface is lightly grinded, but blinder cutting is not conceivable when a large amount of steel plates for shipbuilding or the like is processed.

Therefore, an oxygen plasma cutting method using only oxygen without using air as a working gas is applied.

The electrode material of the conventional plasma arc cutting torch is hafnium (Hf) or zirconium (Z).
r) pure metal or an alloy of both metals,
In addition, the rear part of the plasma arc generation side is directly cooled to suppress the temperature rise of the electrode material, and measures are taken to extend the life of the electrode.

[0016]

However, when only oxygen is used as the plasma working gas, there is a problem that the life of the plasma torch electrode is significantly shortened due to the oxidation reaction. Therefore, in the cutting work of the actual machine, the frequency of electrode replacement is high, the work efficiency is poor, and the electrode cost is very high as a consumable item. FIG. 2 shows the state of wear of the tip portion of the rod electrode 7. As shown in the figure, the wear 19a to 19d of the electrodes is lost by oxidation. In addition, the structure of the plasma torch is problematic because the electrodes are water-cooled and removal is very complicated when the electrodes are consumed, and it takes time to replace them.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a gas for plasma arc cutting capable of extending the life of the electrode and greatly reducing the cost of consumables due to the cutting work. To do.

[0018]

The structure of the plasma arc cutting gas according to the present invention for achieving the above object is a plasma arc cutting gas used for air plasma cutting,
It is characterized by using an inert gas or carbon dioxide gas mixed with oxygen at about 20%.

The contents of the present invention will be described below.

In the present invention, the working gas for plasma arc cutting used for air plasma cutting is, for example, an inert gas such as argon or carbon dioxide gas containing approximately 20 oxygen.
% Mixture is used.

Here, in the present invention, mixing approximately 20% of oxygen with an inert gas or carbon dioxide is equivalent to the amount of oxygen in the air, and in consideration of cutting treatment and consumption of electrodes and the like. The amount of oxygen is appropriately set, and the amount of oxygen is preferably about 15% to 25%. this is,
This is because if the oxygen content is 15% or less, the cutting becomes difficult and the cutting speed must be extremely slowed, and the cut surface is not clean. Further, the cutting is naturally good at 25% or more and 100% or more, but as the oxygen mixing amount increases, the consumption of the electrode becomes severe and both are not preferable. Therefore, the amount of oxygen added is about 2 which is the amount of oxygen in the air.
If it is set to about 0%, electrode consumption equivalent to that of EAR plasma can be obtained. At this time, in the present invention, since the nitrogen is not contained, nitriding of the cut surface does not occur.

Incidentally, 100% oxygen gas is used for plasma cutting of steel plates for shipbuilding, etc., where nitriding of cut surfaces is a problem.

From the viewpoint of the cutting speed, it was found that there is not much difference even if air containing only 20% oxygen is used. Also, good results can be obtained by mixing oxygen of about 20% with an inert gas such as argon gas. However, since argon gas is more expensive than oxygen or air, it is preferable to use carbon dioxide gas at low cost. Therefore,
The use of carbon dioxide gas, which is less expensive than oxygen, can reduce the consumption of the electrode and prevent nitriding, which is preferable for practical use.

[0024]

The preferred embodiments of the present invention will be described below.

Using the apparatus shown in FIG. 1, the carbon steel was cut under the conditions shown in "Table 1" below. As shown in Table 1, the cutting speed was 2 m / min in all cases.

[0026]

[Table 1]

The life of the electrode of the cutting torch under the above conditions was about 100 minutes in the case of 100% oxygen, but about 240 minutes (4 hours) in the case of 80% carbon dioxide containing 20% oxygen.
And the life has been improved.

[0028]

When the plasma working gas of the present invention is applied to the cutting of a steel sheet, 1) the working gas does not contain nitrogen, so that nitriding of the cut surface does not occur. 2) Since the amount of oxygen is as small as about 20%, the life of the plasma cutting torch electrode is increased, and the cost of the electrode and the loss time during replacement are significantly reduced. 3) Do not use expensive gas such as argon as the working gas,
Gas cost is reduced because carbon dioxide is used. From the above effects, a large amount of steel plates are cut in shipbuilding or the like, so that a great effect can be expected.

[Brief description of drawings]

FIG. 1 shows a cross-sectional view of a typical plasma cutting torch.

FIG. 2 is a diagram showing a situation in which electrodes are dropped and consumed.

[Explanation of symbols]

 1 Nozzle 6 Electrode Support Cylinder 7 Electrode 14a Pilot Arc 14b Plasma Arc 19a-19d Electrode Consumption

Claims (1)

[Claims] 1. A plasma arc cutting gas for use in air plasma cutting, characterized in that an inert gas or carbon dioxide gas mixed with oxygen at about 20% is used.