Judgment and adjustment of tension between frames

Judgment and adjustment of tension between frames

The influence of inter frame tension on the size of rolled parts is a complex plastic mechanical process. If steel is pulled in the 1st and 2nd pass, i.e. tension is generated between the 2nd and 1st rolling mills, this tension reduces the resistance generated along the rolling direction, thereby increasing the flow of metal along the rolling direction and decreasing the flow towards the width direction, resulting in a smaller width dimension of the rolled piece. On the contrary, the stacking process can increase the width dimension of the rolled piece.

From the above analysis, it can be seen that when the tail of the rolled piece leaves the previous frame, the width increases again, indicating that there is tension between the previous frame and that frame, because once the tension disappears, the width of the rolled piece in that frame increases. The greater the width change, the greater the tension. In this way, the adjuster can determine whether there is tension between the stands by measuring or judging the changes in the width dimensions of the head and tail of the rolled piece and the width dimensions of the middle rolled piece. The variation in width dimension of the intermediate rolled piece can be determined by the width of the unrolled part on both sides (at the roll gap) of the rolled piece. There are two specific methods used on site: one is to observe with the naked eye, and the other is to use burnt wood marks to judge. The latter is suitable for smaller sized rolled parts.

The magnitude of tension between racks can be directly determined by the changes in motor load current on the main control panel. When the rolled piece bites into the first steel, the current value is a. If the current value remains unchanged after biting into the second frame, there is no tension. When the current value changes, if it is less than (or greater than) the value of a, it indicates the presence of steel pulling (or stacking) in the first and second frames.

After confirming the height of each rolled piece, the rolling mill can use its speed regulation to gradually eliminate tension. The tension shall be adjusted from the first frame to the rear frame by frame. If the adjustment starts from the last frame, it is possible to adjust the back, and when adjusting the first few frames, the tension relationship at the back can be disrupted again, causing accidents.

It is possible to increase the speed of the previous frame, but the increase should be small and progressive. While increasing the speed, observe whether the rolled parts of the frame have increased in the width direction. When increasing the speed, pay attention to observing whether there is a small amount of vertical loop produced in the rolled parts between these two frames. The speed continues to increase until the width of the rolled piece on the frame meets the requirements. If the size variation of a rolled piece in the width direction is irregular, it may be caused by local uneven steel temperature; If there is periodicity, it is possible that in the first few passes, one of the mill rolls may rotate eccentrically, or a piece of material may fall off the pass, commonly known as "shedding", causing inconsistent sizes of periodic incoming materials. The occurrence of the above situations should be dealt with according to specific reasons.

Generally speaking, the main method of adjusting tension is to adjust the speed of the rolling mill. However, before implementing this process, it is necessary to ensure that the height and size of the rolled parts in each stand meet the process requirements. It is not allowed to adjust the speed and roll gap at the same time. Performing both adjustments simultaneously will inevitably cause confusion in the adjustment.

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