JPS61293668A - Crater processing method for plasma welding - Google Patents

Abstract

PURPOSE:To form a normal bead on the welding terminal part and to prevent a welding defect by gradually reducing the welding current after reducing it with gradations at the welding terminal part and by increasing the flowing quantity by changing the center gas from argon to helium as well. CONSTITUTION:The center gas is changed from argon gas to helium gas by opening a solenoid valve 9 and by closing solenoid valve 11 on reaching to a welding terminal part. It makes to reduce the key hole forming function as the center gas by reducing the mass of the center gas. The reason why the flow of the helium gas is increased is for displaying the reducing function of the arc of the center gas. The reason why the welding current is gradually reduced at the helium gas changing time is to make the heat gain same before and after the center gas shifting due to the heat again becoming large with the same current value and the helium gas ionization voltage being higher compared to that of argon gas. The current value is gradually reduced thereafter to obtain a good terminal bead.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for treating craters in plasma welding.

[Prior Art] In plasma welding, a deep crater is usually left at the end of the weld because a back wave is produced through a keyhole and a bead is formed.

In straight welding, auxiliary plates were attached to the starting and ending ends, and the welding was done so that craters would occur at the auxiliary plates, and the auxiliary plates were removed after welding was completed. However, when welding the entire circumference of a pipe, craters inevitably remain at the welded joint. Therefore, crater treatment becomes a major problem when welding the entire circumference of pipes.

As shown in Figure 4, the conventional crater treatment method in plasma welding is to keep the flow rate of argon gas (center gas) that penetrates the pool and form the keyhole unchanged, and increase the welding current to the required level at the terminal end. It's lowering.

[Problem to be solved by the invention This is almost the same as crater treatment in TIG welding,
In the case of plasma welding, there is a problem that either a keyhole remains due to the center gas or the pool is disturbed by the center gas, making it impossible to form a normal bead.

Therefore, in the past, it took a long time to repair the weld end, which resulted in a decrease in welding efficiency and a tendency for defects to occur in the weld end.

The present invention aims to provide a crater treatment method that can solve these problems.

[Means for Solving the Problems] The present invention is characterized in that the welding current is reduced in stages at the welding end and then gradually reduced, and the center gas is switched from argon to helium to increase the flow rate. be.

[Function 1] Eliminates keyholes at the weld end, reduces dents, and provides a good bead.

[Example] The present invention will be described in detail below with reference to the drawings.

In FIGS. 1 and 2, 1 indicates a torch and 2 indicates a center gas source.

In plasma welding, in addition to the shielding gas that shields the weld pool as described above, a high-pressure center gas for forming a keyhole is ejected. That is, the torch 1 for plasma welding is provided with an outlet 4 for a center gas ejected from the periphery of an electrode 3, which narrows the arc and penetrates the weld pool, and an outlet 5 for a shield gas ejected from the periphery. The shield gas outlet 5 is connected to a shield gas source (not shown) by a shield gas hose 6, and the center gas outlet 4 is connected to the center gas source 2 by a center gas hose 7.

The center gas hose 7 branches into two parts, one of which is connected to an argon gas source 10 via a solenoid valve 11, and the other to a helium gas source 8 via a solenoid valve 9.
, 11 are opened, but not both at the same time.

Next, the present invention will be explained in detail using FIG.

FIG. 3 shows changes in the welding current value and center gas flow rate. When reaching the welding end, the current value is changed stepwise by a required value, and then gradually decreased. Next, during actual welding, the center gas closes the solenoid valve 9 and opens the solenoid valve 11 to blow out argon gas. When the welding end is reached, the solenoid valve 9 is opened and the solenoid valve 11 is closed to switch the center gas from argon gas to helium gas and increase the flow rate of the center gas by the necessary amount (5 to about 10 times).

In plasma welding, the keyhole is filled by a flow of metal molten by an arc plasma. Therefore, for crater treatment, it is necessary to gradually reduce the keyholes and dents caused by the center gas, as well as to reduce the amount of molten metal, ie, the welding current.

Changing the center gas from argon gas to helium gas reduces the mass of the center gas and reduces its keyhole forming function as a center gas, and increasing the flow rate of helium gas is due to the arc narrowing function of the center gas. It is something that allows you to demonstrate your abilities.

Also, the reason why the welding current is gradually reduced when switching to helium gas is that helium gas has a higher ionization voltage than argon gas, and the amount of heat input is larger at the same current value, so it is necessary to keep the amount of heat input the same before and after switching to the center gas. I'm here to do something. Thus, if the current value is gradually decreased, a good termination bead can be obtained.

In the above embodiment, the current value is decreased continuously, but it may be decreased gradually in steps.

[Effects of the Invention] As described above, according to the present invention, a normal weld without a crater is formed at the end of the weld, and repair work at the end of the weld is greatly reduced, and the occurrence of weld defects is prevented. It can be prevented.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of an apparatus for carrying out the present invention, Fig. 2 is a detailed view of part A in Fig. 1, Fig. 3 is a line section showing changes in welding current and center gas over time, and Fig. 4 is It is a diagram showing changes over time in welding current and center gas in a conventional example. 1 is a torch, 8 is a helium gas source, 9 is a solenoid valve, 10 is an argon gas source, and 11 is a solenoid valve.

Claims (1)

[Claims] 1) A crater treatment method for plasma welding, which comprises reducing the welding current stepwise and then gradually at the welding end, and at the same time switching the center gas from argon to helium and increasing the flow rate.