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Why does virtual welding occur?
 Apr 14, 2022|View:435


Why does virtual welding occur? How to prevent it?

Virtual welding is the most common defect. Sometimes it seems that the front and rear steel strips are welded together after welding, but in fact it does not reach the level of integration, the strength of the joint surface is very low, and the welding seam has to go through various complicated processes on the production line, especially it has to go through the high temperature furnace area and the high tension tension leveling area, so the virtual welding seam is very easy to cause a belt breakage accident on the production line, which has a great impact on the normal operation of the production line.

The essence of virtual welding is that the temperature of the joint surface of the weld during welding is too low, the size of the nugget is too small or even not melted, but it has reached a plastic state, and it is barely combined after rolling, so it looks welded, in fact not fully integrated.

In actual operation, if the exact cause of the virtual welding cannot be analyzed for a while, the head and tail of the steel strip can be cleaned, the welding overlap amount can be increased, the welding current and the pressure of the welding wheel can be appropriately increased, and the welding can be performed again. Pay close attention to the formation state of the weld, and in most cases, the problem can be dealt with in an emergency. Of course, if there is a problem with the control system, or if the grid voltage fluctuates so that the weld is soldered, other measures must be taken to solve it.

The reasons and steps to analyze the virtual welding can be carried out in the following order:



First check whether there are impurities such as rust, oil stains, etc. on the joint surface of the welding seam, or unevenness and poor contact, which will increase the contact resistance, reduce the current, and the temperature of the welding joint surface is not enough.



Check whether the overlap of the welding seam is normal, and whether there is a reduction or cracking of the overlap on the drive side. The reduction of the amount of overlap will make the joint area of the front and rear steel belts too small, so that the total force surface is reduced and cannot bear the large tension. In particular, the cracking phenomenon on the driving side will cause stress concentration, so that the cracking will become larger and larger, and finally it will be broken.



Check whether the current setting complies with the process regulations, and whether the current setting does not increase accordingly when the thickness of the product changes, so that the welding current is insufficient and the welding is defective. Check whether the pressure of the welding wheel is reasonable. If the pressure is not enough, the actual current will decrease because the contact resistance is too large. Although the welding controller has a constant current control mode, but the resistance increases beyond a certain range (usually 15%), the actual current will decrease. Exceeding the limit of current compensation, the current cannot increase correspondingly with the increase of resistance, and cannot reach the set value. In this case, an alarm will be issued when the system is working normally.