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Why does the weld appear? How to prevent it?

Date: 18/02/2024

Virtual welding is one of the most common defects.

Sometimes after welding it seems that the front and back of the steel belt welded together, but in fact did not achieve the degree of integration, the strength of the combination surface is very low, the weld in the production line to go through a variety of complex processes, especially through the high temperature furnace area and high tension tension area, so the weld in the production line is very easy to "cause broken belt accident," It has great influence on the normal operation of the production line.


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


Analysis of the causes and steps of virtual welding can be carried out in the following order:


(1) First check whether the weld joint surface has impurities such as rust and oil, or uneven and poor contact, which will increase the contact resistance, reduce the current, and the welding joint temperature is not enough.


(2) Check whether the amount of overlap of the weld is normal, and whether the amount of overlap on the drive side is reduced or cracked. The reduction of the amount of overlap will make the joint area of the front and rear steel strips too small, so that the total force surface will be reduced and can not bear the greater tension. In particular, the phenomenon of driving side cracking will cause stress concentration, and the cracking will become larger and larger, and finally pull off.


(3) Check whether the current setting conforms to the process regulations, and whether the current setting does not increase correspondingly when the thickness of the product changes, resulting in insufficient current in the welding and poor welding.


(4) Check whether the welding wheel pressure is reasonable, if the pressure is not enough, it will be due to the contact resistance is too large, the actual current is reduced, although the welding controller has a constant current control mode, but the resistance increases beyond a certain range (generally 15%), it will exceed the limit of current compensation, the current can not increase with the increase of resistance and the corresponding increase, can not reach the set value. In this case, the system will issue an alarm when it is working properly.


In actual operation, if the exact cause of the virtual welding can not be analyzed for a while, you can clean the head and tail of the steel strip, increase the amount of welding overlap, appropriately increase the welding current and welding wheel pressure again, and pay close attention to the formation of the weld during welding, in most cases, you can deal with the problem in an emergency.


Of course, if there are control system problems, or grid voltage fluctuations, so that the weld welding must be taken other measures to solve.

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