The first generation of continuous rolling mill is a full-floating mandrel continuous rolling mill (MM (Mandrel Mill) for short), generally equipped with 7-9 racks, and a tension reducer at the rear. The speed of the mandrel is not controlled during the rolling process. The mandrel is driven by the friction force of the rolled metal to freely follow the pipe through the rolling mill. The running speed of the mandrel is uncontrolled; the running speed of the mandrel varies with the rolling process. The biting and throwing steel of each rack fluctuates, which causes the fluctuation of the tube wall thickness; after rolling, the mandrel is rolled out with the waste tube to the output roller table after the continuous rolling mill. When rolling thin-walled tubes, the full length of the mandrel is almost in the waste tube. The waste tube with the mandrel is moved horizontally to the stripping line, and the core rod is drawn out from the waste tube by the stripping machine for cooling and lubrication and recycling.
The features of the floating mandrel continuous rolling mill are: (1) The continuous rolling mill consists of 7 to 9 two-high rolling mills. Generally, the racks are arranged at 45° from the horizontal plane, and adjacent racks are arranged at 90° to each other. (2) Each rack is independently driven by a DC motor with high adjustment accuracy. The transmission device is arranged on both sides of the rolling mill. The latest rolling mill is driven by two or three DC motors in series to directly drive each roll or drive two rolls through a gear seat. (3) The combination of the continuous tube rolling mill and the high-efficiency tension reducer greatly expands the variety and specifications of tubes produced by the continuous tube rolling mill, while there are only one or two tube billet specifications, which significantly simplifies the production process and Improve the operation rate. (4) The maximum pipe diameter produced by the floating mandrel continuous rolling mill is 168mm, which is limited by the weight of the long mandrel (about 30m). After the steel tube is rolled, the temperature of the mandrel is very high (170-250℃). Due to the on-line recycling, the mandrel must be cooled to 70-80℃. The limited mandrel continuous pipe rolling mill can roll pipes with a maximum diameter of 426mm. (5) The newly put into production units are equipped with electronic computers for process control. From the tube blank loading into the heating furnace to finishing and cutting the tube, all have been automated. (6) Use water-soluble smokeless lubricant to lubricate the mandrel. (7) Using online normalizing technology, etc.
