There are many ways to produce seamless steel pipes. According to the delivery requirements, seamless steel tubes can be produced by hot rolling (about 80-90%) or cold rolling and cold drawing (about 10-20%). The billet for hot-rolled tubes has round, square or polygonal ingots, rolled billets or continuous cast tube blanks, and the quality of the tube blank has a direct influence on the quality of the tube. There are three basic processes for hot-rolled pipe: (1) inserting the ingot or billet into a hollow thick-walled capillary tube on the punching machine; 2 rolling the capillary tube on the stretching machine to extend into a waste pipe close to the finished wall thickness; 3 rolling on the finishing mill The finished tube required. The rolling mill series is expressed in terms of the maximum outer diameter of the steel pipe produced. The German Mannesmann brothers first invented the two-roll cross-rolling piercing machine in 1885.
In 1891, the cycle rolling mill was invented. In 1903, the Swiss Ritteriefel invented the automatic pipe rolling machine (also called the head rolling). Pipe machine), and later appeared various types of extension machines such as continuous tube rolling mills and pipe jacking machines, and began to form a modern seamless steel pipe industry. In the 1930s, the quality of the steel pipe was improved by the use of a three-roll mill, an extruder, and a periodic cold-rolled pipe mill. In the 1960s, due to the improvement of continuous rolling mills, the emergence of three-roll punching machines, especially the application of tension reducing machines and continuous casting blanks, increased production efficiency and enhanced the ability of seamless pipes to compete with welded pipes.
In the 1970s, seamless pipes and welded pipes were moving in parallel, and the world’s steel pipe production increased at a rate of more than 5% per year. After 1953, China attached importance to the development of seamless steel pipe industry, and has initially formed a production system for rolling various large, medium and small pipes. Copper pipes are generally also used in the ingot blank rolling piercing, rolling mill rolling, coil stretching process. Automatic rolling pipe production One of the ways to produce seamless steel pipes. The production equipment consists of a punching machine, an automatic rolling mill, a leveling machine, a sizing machine and a reducer.
The punching machine is usually used for two-roll cross-rolling perforation. The round billet is rolled into a hollow thick-walled tube (capillary tube), and the axes of the two rolls form an inclined angle with the rolling line. In recent years, the tilt angle has been increased from 6° to 12° to 13° to 17°, which accelerates the piercing speed. The production of steel pipes with a diameter of more than 250mm uses secondary perforation to reduce the wall thickness of the capillary. New processes such as active rotating guide plate perforation, post-thrust perforation, axial discharge and cyclic top welding have also achieved certain developments, thereby strengthening the perforation process and improving the quality of the capillary.
Automatic tube rolling machine Roll thick-walled tubes into thin-walled tubes. Generally, after 2 to 3 passes, the thickness of the finished product is rolled to a total thickness of about 1.8 to 2.2. Since the 1970s, single-hole grooved rolls, stainless steel road brand double-stand tandem rolling mills, double-slot tandem rolling mills and Technologies such as spherical heads have improved production efficiency and achieved mechanization of rolling mills.1 inch square metal tubing
The sizing machine is composed of 3 to 12 frames, and the reducer is composed of 12 to 24 frames, and the reduction ratio is about 3 to 28%. The tension reducer that appeared in the 1950s controlled the wall thickness with appropriate tension while adjusting the roll speed and reducing the diameter. The new tension reducer is generally three-roller type, with 18 to 28 frames, the maximum diameter reduction rate is 80%, the wall reduction rate is 44%, and the export speed is 18 mm per second. The tension reducer has the disadvantage of thickening at both ends, and can be eliminated by “electrical control at the end of the head and tail” or micro-tension reduction.
Automatic rolling mills The commonly used series have outer diameters of 100mm, 140mm, 250mm and 400mm, and produce outer diameter 17~426mm steel pipes. The unit is characterized by the main deformation on the punching machine, the specification changes are more flexible, and the range of production varieties is wider. Due to the development of continuous rolling technology, units below 140 mm are no longer built.
The homogenizer structure is similar to the puncher. The purpose of the leveling is to eliminate the internal and external surface defects and the ellipticity of the waste pipe, and to reduce the unevenness of the lateral wall thickness. In recent years, the three-roller homogenizer has been used to improve the deformation and leveling efficiency of the homogenizer.