The limited mandrel continuous rolling mill (MPM) was developed on the basis of the long mandrel continuous rolling mill and is the third generation of the continuous rolling mill. MPM-generally consists of 11 two-high rolling mills. Due to the long mandrel continuous rolling mill (MM), the mandrel moves with the tube. After rolling, the mandrel must be drawn out from the steel pipe by an extractor. This method requires a large number of mandrels. Difficulties in mandrel production, storage and storage have restricted the development of the MM method and the possibility of using it to produce large-diameter pipes (above φ168mm).
To solve this problem, people developed the MPM method. The process is as follows: push the pierced and extended capillary tube to the front desk of MPM, insert the lubricated mandrel into the capillary tube and quickly send it into the rolling mill until the front end of the mandrel reaches the front and rear positions of the 7th stand, and then The capillary is sent to the rolling mill for rolling. During rolling, the mandrel will move forward with the pipe at a limited speed, and the front end of the mandrel must reach the 8th stand at least at the same time as the front end of the capillary tube. When all the capillary tubes are rolled, the front end of the mandrel extends about 4m from the centerline of the 8th stand. The tube rolled out of the MPM then enters the tube stripper. After rolling, the tail of the capillary tube is pulled out of the 8th frame by the tube stripper, and the mandrel quickly returns to its original position. After replacing the mandrel again, roll the next tube. During the rolling process, the mandrel does not need to be cooled, but 4 to 5 mandrels are used as a group to realize external cooling cycle.
Compared with MM, MPM has the following characteristics: (1) Reduce tool consumption and reduce mandrel consumption to about 1 kg per ton of steel pipe. (2) Improved pipe quality. Due to the rolling properties of the constrained mandrel rolling tube, it is conducive to metal extension, reduces the transverse deformation, and avoids the "slub" defect of the MM continuous rolling tube, so that the internal and external surface quality and dimensional accuracy of the tube are improved improve. (3) Rolling pressure and power consumption are 1/3 lower than MM. (4) The stripping machine is eliminated, the process flow is shortened, the final rolling temperature of the continuous rolling mill is increased, and the reheating furnace before sizing and reducing can be omitted. (5) The variety has been expanded. Compared with MM, large tubes and thicker or thinner tubes can be rolled. (6) The elongation coefficient can reach 6-10, and thicker capillary tubes can be used, which creates conditions for using continuous casting billets as raw materials. However, the production rate of MPM is much lower than that of MM, and only two steel pipes can be rolled per minute. As a result, the development of MPM is restricted.
