JPH09295156A - Plasma cutting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably provide the cut section of excellent quality free from any welding defects while performing the cutting at high speed by feeding the shield gas having the reducing effect around the plasma jet. SOLUTION: The air which is the plasma gas is fed from a rear part of a plasma torch 1 through a plasma gas feed passage 11. The voltage is applied to an electrode 2 and at the same time, the reverse voltage is applied to a nozzle. Discharge is generated between the electrode and the inner surface of a first nozzle 31 to form the pilot arc, and the air is turned into the plasma gas and ejected from orifices 31a, 32a. When the reverse voltage is applied to a work then, and the reverse voltage applied to the nozzle is shut off, the arc is transferred between the electrode and the work to form the plasma arc. Hydrogen is fed to a shield gas feed passage 43 as the shield gas through a shield gas feed pipe 12 behind the torch 1. The shield gas is turned by a passage hole 32b provided on a second nozzle 32.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma cutting method for cutting a non-ferrous metal by using a plasma arc, and more particularly to a method for reducing the oxidation of a cut surface without lowering the cutting speed.

[0002]

2. Description of the Related Art Oxidation of a cut surface has become a major problem because the cut surface is extremely susceptible to oxidation during plasma cutting of non-ferrous metal and the oxidized cut surface causes welding defects. Oxygen may be used as the plasma gas in cutting stainless steel, but it is not desirable to use oxygen because the oxidation is remarkable especially in non-ferrous metals.

For plasma cutting of non-ferrous metals, there are one that uses a rod electrode that simply uses a rod-shaped electrode material such as tungsten as an electrode, and one that uses a buried electrode in which an electrode material such as hafnium is embedded at the tip of the electrode. . Since the rod electrode is heavily worn by oxidation, it is cut with an axial flow plasma gas using an inert gas such as nitrogen or argon gas. On the other hand, in a plasma torch using an electrode in which hafnium is buried, an oxidizing gas can be used as the plasma gas because it is resistant to oxidation.Therefore, oxygen, air, nitrogen, etc. can be used as the plasma gas and Is turned to perform the cutting.

However, in these cutting methods, the plasma gas entrains the atmosphere, or the oxygen contained in the plasma gas oxidizes the cut surface. Therefore,
Generally, a cutting method is used in which a rod electrode is used and a reducing gas such as hydrogen is mixed with argon which is a plasma gas and used.

[0005]

However, when argon is used as the plasma gas, the cutting speed is reduced. Further, if the rod electrode is used, there is a problem that the cutting surface changes in an unstable manner depending on the tip shape of the rod electrode.

Therefore, a cutting method is used in which water is jetted so as to fit around the plasma gas using an embedded electrode to perform cutting, thereby preventing oxidation of the cut surface. However, the water shield prevents oxidation of the cut surface, but since water lowers the temperature of the plasma arc,
There is a problem that the cutting speed becomes slow.

[0007]

In order to solve the above-mentioned problems, a plasma cutting method according to the present invention uses an embedded electrode to convert air, nitrogen or a mixed gas containing these as plasma into a nozzle. In a plasma cutting method of cutting a non-ferrous metal by jetting a plasma jet while swirling from the tip, a shielding gas having a reducing action is added around the plasma jet.

The shield gas is preferably hydrogen, a mixed gas containing hydrogen, or a hydrocarbon gas.

Further, the shield gas is jetted so as to swirl around the plasma jet, and jetted so as to be parallel or inclined to the plasma jet, so that the influence of the shield gas on the plasma jet can be adjusted. it can. Further, by arranging a plurality of shield gases concentrically with the plasma arc, a higher effect can be obtained.

With the above construction, it is possible to cut a stable cut surface at high speed and without oxidizing the cut surface.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a plasma cutting method according to the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of a tip portion of a plasma cutting torch according to an embodiment of the present invention.

As shown in FIG. 1, the electrode 2 arranged inside the torch 1 so as to coincide with the axis is formed by embedding an electrode material 21 made of hafnium in the center of the tip. Hafnium has a high melting point of an oxide, and an oxidizing gas such as oxygen or air can be used as a plasma gas.
A gap is provided around the electrode 2 to form a plasma gas supply path 11.

A centering stone 10, which is a ceramic cylindrical member, is fitted around the outer periphery of the electrode 2 and has a function of insulating the electrode from the nozzle 3 described later. The centering stone 10 is provided with a plurality of plasma gas passage holes 10a having a predetermined angle with respect to the radial direction of the cross section of the torch 1, and the plasma gas supplied from the plasma gas supply passage 11 passes through the passage holes 10a. It is configured to turn.

A nozzle 3 having a double structure consisting of a first nozzle 31 and a second nozzle 32 is fitted around the centering stone. A plasma gas passage 33 is formed between the first nozzle 31 and the electrode 2, and a shield gas passage 34 is formed between the first nozzle 31 and the second nozzle 32. Concentric orifices 31a and 32a are formed at the tip portions of the first nozzle 31 and the second nozzle 32, respectively.

A shield gas passage hole 32b, which is a plurality of holes, is formed in the body of the second nozzle 32. The shield gas passage hole 32b is formed at a predetermined angle from the radial direction of the cross section of the torch 1, and the shield gas passing through the shield gas passage hole 32b is supplied to the shield gas passage 34 while swirling.

The cap 4 is composed of a first cap 41 and a second cap 42, and has a double structure to form a shield gas supply passage 43. The shield gas supplied from the rear of the plasma torch 1 is supplied to the shield gas passage hole 32b of the second nozzle 32 through the shield gas supply pipe 12 and the shield gas supply passage 43.

Next, the operation will be described. In this embodiment, air is used as the plasma gas and hydrogen is used as the shield gas.

The plasma torch 1 is a transfer type plasma cutting torch. First, air as a plasma gas is supplied from the rear of the plasma torch 1 via a plasma gas supply passage 11. The air is swirled by the plasma gas passage hole 10 a of the centering stone 10 and supplied to the plasma gas passage 33.

Next, a voltage is applied to the electrode 2 and simultaneously a reverse voltage is applied to the nozzle. Then, an electric discharge is generated between the electrode and the inner surface of the first nozzle 31, a pilot arc is formed, and air becomes a plasma gas and is ejected from the orifices 31a and 32a. After that, if a reverse voltage is applied to the work and the reverse voltage applied to the nozzle is cut off, the plasma gas is energized to move the arc between the electrode and the work, forming a plasma arc.

Here, since the plasma gas is swirled, the starting point of the plasma arc is stabilized, the series arc is prevented, and the generation of the plasma arc is stabilized.

Hydrogen is supplied to the shield gas supply passage 43 as shield gas from the shield gas supply pipe 12 behind the plasma torch 1. Shield gas is the second nozzle
It is swirled by a shield gas passage hole 32b provided in 32 and is ejected together with the plasma jet from the second orifice 32a through the shield gas passage 34. First orifice 31
By adjusting the shapes of a and the second orifice 32a,
It is possible to adjust whether the shield gas is jetted in parallel with the plasma gas or jetted so as to be inclined and hit.

By flowing the shield gas along the plasma jet, the outside air and the plasma jet are separated from each other to maintain the purity of the plasma gas and extend the reaching distance. The swirling has the effect of improving the quality of the cut surface by giving characteristics to the groove angle of the cut surface.

Since the cutting progresses by melting and burning, the cutting surface and its periphery are inevitably oxidized. However, by using hydrogen, which is a reducing gas, as the shield gas, the material to be cut that has been oxidized can be reduced, and defects will not occur when performing a welding operation later.

Further, the groove angle of the cut surface is characterized by swirling the shield gas, the jetting angle of the shield gas with respect to the plasma gas, the strength and absence of swirl of the swirl, the angle of adhering to the plasma gas, etc. are set. The effect of the gas on the plasma gas can be adjusted.

Although hydrogen is used as the shield gas, any gas having a reducing action such as a mixed gas containing hydrogen or a hydrocarbon gas can be used as the shield gas. Further, in the above-mentioned embodiment, the nozzle and the cap have the double structure, and the description has been given by using the plasma torch which ejects gas of two systems. However, if the present invention is applied to a plasma torch that ejects gas of three systems or more, it is possible to obtain the effect of further preventing oxidation.

[0026]

According to the plasma cutting method of the present invention, the oxidized cut surface can be reduced by using the gas having a reducing action as the shield gas. Therefore, since it is not necessary to mix the reducing gas with the plasma gas, the cutting speed can be maintained. Therefore, since it is possible to stably obtain a high-quality cut surface that does not cause welding defects while cutting at high speed, it is possible to improve quality and work efficiency at the same time.

The influence of the shield gas on the plasma jet can be adjusted by swirling or tilting the shield gas. Further, a higher reduction effect can be obtained by disposing a plurality of shield gases concentrically with the plasma arc.

[Brief description of drawings]

[Figure 1] Cross-sectional view near the tip of a plasma cutting torch

[Explanation of symbols]

 1 ... Plasma torch 11 ... Plasma gas supply path 10 ... Centering stone 12 ... Shield gas supply path 2 ... Electrode 21 ... Electrode material 3 ... Nozzle 31 ... First nozzle 31a, 32a ... Orifice 32b ... Shield gas 32 ... Second nozzle 33 … Plasma gas passage 34… Shield gas passage 4… Cap 41… First cap 42… Second cap

Claims (5)

[Claims] 1. An embedded electrode is used for air, nitrogen,
Alternatively, in a plasma cutting method in which a mixed gas containing these as the main components is made into plasma, and a non-ferrous metal is cut by ejecting while rotating a plasma jet from the nozzle tip,
A plasma cutting method characterized in that a shielding gas having a reducing action is added around the plasma jet. 2. The plasma cutting method according to claim 1, wherein the shield gas is hydrogen, a mixed gas containing hydrogen, or a hydrocarbon gas. 3. The plasma cutting method according to claim 1, wherein the shield gas is jetted so as to swirl around the plasma jet. 4. The plasma cutting method according to claim 1, wherein the shield gas is jetted so as to be parallel to or inclined with the plasma gas. 5. A plurality of shield gases are arranged concentrically with the plasma arc, according to any one of claims 1 to 4.
The plasma cutting method according to claim 1.