Three-roll and multi-roll cold-rolled tube methods for rolling finished seamless steel pipes

First, multi-roll cold-rolled tube mill
A cold-rolled tube mill composed of three or more rollers is called a multi-roll cold-rolled tube mill. Multi-roll mills are divided into three types: three-roll, four-roll, and five-roll. Generally, three-roll cold-rolled tube mills are used to roll tubes with a diameter of φ8~60mm, and four-roll and five-roll cold-rolled tube mills are used to roll tubes with a diameter of ф60~120mm.

There are holes and grooves with constant cross-sections on the rollers. The holes and grooves of the three rollers form a circular hole shape, which together with the core head in the middle form a ring-shaped gap. The rollers roll back and forth on three slides with special curved slopes. The curve of the slide is similar to the hole-shaped expansion curve of the two-roll cold-rolled tube mill.

When the hole shape is at the left end of the slide, the height of the slide curve is the smallest, the distance between the three rollers is the largest, the outer diameter of the circle formed by the hole shape is the largest, and the cross-section of the ring formed with the cylindrical core head is also the largest. When the roller moves from left to right, the outer diameter of the circle composed of three-hole patterns gradually decreases due to the gradual increase in the slide height. The tube billet undergoes plastic deformation under the pressure of the hole pattern and the core head, achieving a reduction in outer diameter and thinning of wall thickness.

After the roller moves to the front end, it starts to move in the opposite direction and enters the back-rolling process. After the roller returns to the left end limit position, the tube billet is turned over and fed with a certain amount of feed through the rotary mechanism and the feeding mechanism to start the next rolling cycle. The tube billet obtains the size requirements of the finished tube under repeated cycle rolling.

Second, the advantages and disadvantages of the multi-roller cold rolling tube method

1. The advantages of the multi-roller cold rolling tube method are:
(1) Since the metal deformation is uniform during multi-roller cold rolling, the outer diameter shrinkage rate during tube rolling is small, which is conducive to the thinning of the metal wall thickness. Therefore, multi-roller rolling is suitable for the production of tubes with particularly thin wall thickness. The ratio of the outer diameter to the wall thickness of the rolled tube can reach 100~250; it is more suitable for the production of some alloy tubes with poor cold processing performance.
(2) There is no or little relative sliding friction between the hole groove and the tube billet during the rolling process, and the metal deformation is uniform. Therefore, the wall thickness accuracy of the rolled tube is high and the surface roughness is low.
(3) Finished tubes can be directly produced through reasonable tool matching.
(4) The multi-roller cold rolling mill has a large number of rollers and a small roller diameter. Therefore, the total rolling pressure is small and the rolling power consumption is also low.
(5) Compared with the two-roller cold rolling tube method, the tool design and manufacturing are relatively simple, and the quality is easy to guarantee.

2. The main disadvantages of the multi-roller cold rolling tube method are:
(1) The hole groove of the hole type is cylindrical, rather than a variable cross-sectional size, and the rolling feed volume is small, so the production efficiency is low;
(2) The diameter reduction during tube billet rolling is small.
To improve production efficiency, multiple sets of rollers can be installed in the multi-roller rolling mill frame to realize the multi-line rolling method.