Welded Elbow

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 the 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.


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

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


(2) Check whether the overlap of the weld is normal, and whether there is a decrease in the overlap or cracking on the drive side. 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 is reduced and cannot bear the large tension. In particular, the cracking phenomenon on the driving side will cause stress concentration, and the cracking will become larger and larger, and finally break.


(3) 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 bad.


(4) Check whether the pressure of the welding wheel is reasonable. If the pressure is not enough, the actual current will decrease due to excessive contact resistance. Although the welding controller has a constant current control mode, the increase in resistance exceeds a certain range (usually 15%). , it will exceed 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.


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 welding wheel pressure 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 power grid voltage fluctuates, other measures must be taken to solve the welding seam.

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