JPS59110465A - Plasma cutting method - Google Patents

Abstract

PURPOSE:To prevent the generation of a nitride layer at the cut end face and to decrease the blow hole in the stage of welding said part by using a gaseous mixture formed by mixing oxygen at a specific ratio or above with air as gaseous plasma and performing plasma cutting. CONSTITUTION:A gaseous mixture formed by mixing air and oxygen and regulating the mixing ratio of the oxygen with respect to the air at >=75% is used as gaseous plasma and plasma cutting is performed. Then, the amt. of the active gaseous nitrogen in the plasma jet is decreased and the generation of the nitride layer at the cut end face is suppressed. Not only the stage for removing the oxide layer prior to welding is omitted but also the defectless weld zone having no blow hole is obtd.

Description

[Detailed description of the invention] Pertains to aplasma cutting method.

Although air plasma cutting is used in a wide range of fields because of its high-speed cutting performance, it has drawbacks due to the use of air as a plasma gas, which will be explained with reference to FIGS. 1 and 2.

In FIG. 1, air inside a plasma cutting torch 1 becomes a plasma jet 2 and blows out from the plasma cutting torch 1, cutting a material 4 to be cut at high speed. At this time, a large amount of activated nitrogen gas exists within the plasma jet 2.

During cutting, a part of this active nitrogen diffuses and dissolves from the plasma jet 2 into the workpiece 4, leaving a thickness of 10 mm at the plasma cut end.
Make a nitride layer 3 of ~20 μm.

When welding the plasma cut end of the material 4 to be cut, a large number of blowholes are generated. FIG. 2 shows an example of a blowhole generated in the first bead of double-sided submerged arc welding. The blowhole 6 opens into the bath welding groove root gap 7 and extends into the weld metal 5. The blowhole 6 is created by the nitrogen in the nitrided layer 3 turning into a gas due to the welding heat input and blowing out into the root ganop 7 and at the same time partially blowing out into the weld metal gap of the weld metal 5.

It is believed that this occurs.

Therefore, in order to weld soundly parts cut by air plasma, the nitrided layer 3 at the cut end is necessary. : It is necessary to remove it with a grinder, which requires a lot of man-hours in the pre-welding process.

In order to eliminate the drawbacks of the conventional methods as described above, the present invention is characterized in that air and oxygen are mixed and a mixed gas having a mixing ratio of oxygen to air of 75 inches or more is used as a plasma gas. 1. According to the cutting method of the present invention, by mixing 75 or more oxygen into the plasma gas, the amount of active nitrogen gas in the plasma agent is reduced and the plasma cutting edge is The generation of a nitrided layer can be suppressed, and the step of removing the nitrided layer before welding can be omitted, and a sound welded part can be obtained.

The method of the present invention will be explained in detail with reference to Examples.

Using a plasma gas that is a mixture of air and oxygen.

FIG. 3 shows the relationship between the number of blowholes generated in the weld metal and the oxygen concentration in the plasma gas when the cut ends of plasma-cut steel materials are subjected to submerged arc welding and fillet downward welding.

According to FIG. 3, it can be seen that as the mixing ratio of oxygen to air increases, the number of blowholes decreases. It is also seen that when the oxygen mixing ratio becomes 75% or more, the number of blowholes decreases extremely.

The number of blowholes in this case is oxygen tool (pure oxygen)
The number of blowholes is almost the same as that in plasma cutting using B as the plasma gas, and the number of blowholes is not a problem at all in actual welding work. That is, a plasma cutting method using a mixed gas of air and oxygen with a mixing ratio of oxygen to air of 75% or more as a plasma gas is effective in preventing blowholes during welding work.

Therefore, in the method of the present invention, if plasma cutting is shifted using a mixed gas with an oxygen to air mixing ratio of 75 parts or more, the formation of a nitride layer on the cut end surface can be avoided and the number of blowholes can be greatly reduced when welding that part. Therefore, it is possible to obtain a healthy welded joint without any pretreatment for removing the nitrided layer.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the plasma cutting method, Fig. 2 is an explanatory diagram of a welded part of a plasma-cut material, and Fig. 3 is an illustration of the relationship between the oxygen mixing ratio with respect to air and the blowhole generation rate in an example of the method of the present invention. This is a diagram. 1 month 1 month 2 flashes ζ

Claims (1)

[Claims] Mix air and oxygen, and the mixing ratio of oxygen to air is 7.
A plasma cutting method characterized by using a mixed gas of 5% or more as a plasma gas.