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How to Deal with Pit and Hole Defects in Hot-rolled Seamless Steel Tubes?

Date:2019-06-21    keywords:seamless steel tube, hot-rolled
In the production of seamless steel tubes, regular holes and pits are mainly caused by uneven deformation. The key to solving the problem lies in reducing uneven deformation. In order to solve this problem, the hot rolling seamless steel pipe can be improved by finely adjusting the continuous rolling mill, appropriately reducing the deformation of the continuous rolling mill, uniformizing the billet and capillary temperature, and reducing the vibration of the continuous rolling mill. 

1. The approriate adjustment of the continuous rolling mill should follow the principle of equal flow and continuous flow, avoiding the reasonable amount of deformation while avoiding the rolling of the steel between the racks, and not allowing the holes of the previous mills to be overfilled or underfilled too. Seriously, the deformation of the rolling stock on each rolling mill should be relatively uniform. When the wear of the continuous rolls is severe, the influence of roll wear on the rolling is also considered.

2. In order to reduce the degree of longitudinal unevenness, the deformation amount of the continuous rolling mill can be appropriately reduced, and a small amount of deformation is advanced to the perforation. At the same time, the pore geometry is strictly controlled. Sometimes, the length of the capillary tube rolled out with the seven ejector pins is not uniform, and the problematic ejector rod is removed in time.

3. The uneven temperature of the billet and the capillary causes uneven deformation, because the deformation resistance of the rolled parts at different temperatures is different, the deformation resistance of the part with high temperature is low, and it is easy to be deformed; the deformation resistance of the part with low temperature is high and it is difficult to deform. The heating uniformity of the annular heating furnace is much worse than that of the step heating furnace, and there is a high requirement for improving the production efficiency. When the temperature is not good, the wall thickness deviation of the capillary tube is very serious, which will be It will have an adverse effect on the subsequent rolling deformation. It is also necessary to reduce the temperature drop during the transport of the billet and the capillary, especially the local temperature drop, so as to avoid local plasticity degradation, and holes or recesses may occur.

4. Reduce the vibration of the continuous rolling mill. When rolling, the rolling opportunity will have different degrees of vibration, especially the vibration of the mandrel is very severe, which is unfavorable for rolling, so it is necessary to reduce its influence. The speed of the continuous rolling mill and the speed limit can be adjusted to avoid the vibration frequency during rolling and the natural vibration frequency of the rolling mill.

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