Seamless pipe production methods are many. Seamless steel pipe can be produced by hot rolling (about 80% ~ 90%) or cold rolling, cold drawing (about 10% ~ 20%) according to delivery requirements. There are round, square or polygon ingot, rolled billet or continuous casting billet for hot rolling tube. The quality of billet has a direct influence on the tube quality.
There are three basic processes for hot rolling pipes:
The ingots or billets are pierced into hollow thick-wall capillary tubes in the piercing machine;
The capillary is thinned in the extender to extend to a hollow tube with wall thickness;
The required finished pipe is made by rolling on the finishing mill. The series of pipe rolling mill is expressed by the maximum outside diameter of the pipe produced.
Methods of Manufacturing Seamless steel pipe:
(1) Automatic tube rolling production of seamless steel pipe one of the ways. The production equipment consists of piercing mill, automatic pipe rolling mill, sizing machine, sizing mill and reducing mill.
Continuous pipe rolling production The production equipment consists of a piercing mill, a continuous tube rolling mill and a stretch reducing mill. The round billet is pierced into a capillary and inserted into a mandrel. The rolling mill is continuously rolled through a two-high rolling mill in which the axes of 7-9 rollers are mutually arranged at 90 °. The mandrel drawn after rolling is reheated for tension reducing. It can be rolled to 165m steel pipe. The annual output of 140mm continuous pipe rolling mill is 40 ~ 600 thousand tons, which is 2 ~ 4 times of that of automatic tube rolling mill. This unit is characterized by suitable for the production of steel pipe diameter 168 mm below, equipment investment, large installed capacity, mandrel up to 30m, complex processing and manufacturing. The MPM (Continuous Pipe Rolling Machine) with Restricted Mandrel appeared in the late 1970s. During rolling, the external force forces the mandril to move at a speed less than that of the steel tube. The metal flow condition can be improved.
(C) Polygonal and circular ingots or continuous casting billets are used as raw materials in the production of periodic tube rolling, After heating, it is perforated into cup-shaped blank by water pressure, and then it is rolled into a capillary by a two-high cross rolling extender. Then, a section of steel pipe is produced by rolling through the roller on a periodic pipe rolling mill with holes and grooves of varying diameter. The pipe rolling mill is also called Pilger mill. Steel ingots are used as raw material in the production of periodic tube rolling, which is suitable for rolling large diameter thick wall tubes and variable section tubes.
Three high rolling pipe production is mainly used to produce thick wall pipe with high dimensional precision. The wall thickness precision of the pipe produced by this method is ± 5%, which is about one time higher than that produced by other methods. The process flow is shown in Figure 4. The invention of the new three-high skew rolling mill (called Transval rolling mill) in the 1960s led to the rapid development of this method. The new rolling mill is characterized by rapidly turning the inlet rotating frame to change the rolling angle when the rolling reaches the tail. The ratio of the outer diameter to the wall thickness of the production variety is expanded from 12 to 35. Not only can the thin-wall tubes be produced, but also the productivity is increased.
The traditional method of pipe jacking is to extend the billet into cup-shaped capillary by hydraulic perforation and skew rolling. The long mandrel is inserted into the bottom of the capillary cup by a push rod, and the pipe is formed by top rolling through a series of gradually decreasing holes and grooves. This method has less investment in equipment and can be used to produce extra large and extra thick pipes with diameters up to 1070mm and wall thickness to 200mm. But the production efficiency is low, the wall thickness is relatively thick and the pipe length is short. After the appearance of CPE process, the tube blank is pierced by skew rolling and extended by top rolling after closing. It overcomes some shortcomings of traditional method and has become a better method in seamless pipe production.
(6) The peeled round blank is first perforated or expanded in extrusion pipe production, After induction heating or salt bath heating, and the inner surface coated with lubricant into the extruder, metal through the die hole and mandrel annular gap is extruded into pipe (Figure 5). Mainly used for the production of low plastic superalloy pipe, special-shaped pipe and composite pipe, non-ferrous metal pipe and so on. This method produces a wide range but low yields. In recent years, due to the improvement of die materials, lubricants, extrusion speed, extrusion pipe production has also developed.
(7) The pipe rolling process is also called Diessel process. The pierced capillary with a long mandrel is rolled to thin wall tube on a guide plate mill. The mill is similar to the two-high cross piercing mill, but the fixed guide plate is changed into the active guide plate. Because of the long mandrel, the inner wall of the pipe is smooth and has no scratch. But tools are expensive and complex to adjust. Mainly used for the production of carbon steel pipe with external diameter of 150mm or less. At present, the use of less, there is no great prospects for development.
Spinning tube production Flat or hollow blank in a spinning machine through one or more spinning processing into thin-walled tube. The pipe has high precision, good mechanical properties, wide size range, but low production efficiency. Mainly used in the production of non-ferrous metal pipe, but also increasingly used in steel pipe production. In addition to the spinning pipe for the production of living appliances, chemical containers and machine parts, mostly used in military industry.
(9) Cold rolling, cold drawing pipe production for the production of small caliber thin wall, precision and special-shaped pipe. The production is characterized by a multi-process cycle process. The elongation can reach 6 ~ 8 (Fig. 6) when the pipe is cold rolled by a cycle mill. The development of high-speed, multi-line, long-stroke and long-billet began in 1960s. In addition, the small roller cold rolling mill has also been developed. It is mainly used for the production of very thin precision tubes with wall thickness less than 1mm. The cold rolling equipment is complicated, the tool processing is difficult and the variety and specification change is not flexible. Usually the combined process of cold rolling and cold drawing is adopted, that is, first cold rolling to reduce the wall to obtain large deformation, then cold drawing to obtain a variety of specifications.
Equipment for the production of seamless steel pipe
Punch
Round tube blanks are rolled into hollow thick-walled tubes (linings), with an angle of inclination to the rolling line formed by the axis of the two rollers. In recent years, the angle of inclination has been increased from 6 ° -12 ° to 13 ° -17 °, making the speed of perforation faster. In order to reduce the wall thickness of the capillary pipe, secondary perforation is used to produce the pipe with diameter over 250mm. Some new technologies, such as perforation with active rotating guide plate, perforation with back thrust, axial discharge and cyclic top welding, have also been developed, which strengthen the perforation process and improve the quality of capillary.
Automatic pipe rolling machine
The thick – walled capillary is rolled into thin – walled hollow. The total elongation is about 1.8 ~ 2.2 after 2 ~ 3 pass rolling to the wall thickness of finished product. Since 1970s, the production efficiency has been improved and the pipe rolling mechanization has been realized by the techniques of single slot roller, double stand tandem rolling, double slot tracing rolling and spherical head.
Uniform machine
The structure is similar to the piercer. The purpose of leveling is to eliminate defects in the internal and external surface area and eliminate the ovality of the pipe, and to reduce the uneven horizontal wall thickness. In recent years, the use of three-roller leveling machine has improved the deformation and leveling efficiency of the whole machine.
Sizing machine
The reducing mill is composed of 3-12 racks, and the reducing rate is 3-28%. The tension reducing mill, which appeared in the 1950s, controls the wall thickness by proper tension while adjusting the roller speed and reducing diameter. The new type tension reducing mill generally uses three rollers, has 18 ~ 28 frames, the maximum diameter reduction rate is 80%, the wall reduction ratio is 44%, and the outlet speed is 18 mm per second. Tension reducing mill has the disadvantage of thickening at both ends, which can be eliminated by “sudden electrical control at the end of the head and the tail” or by slight tension reducing.
Automatic pipe rolling mill
Commonly used series of external diameter of 100mm, 140mm, 250mm and 400mm four kinds, production diameter of 17 ~ 426mm steel pipe. The features of the unit are that the main deformation is realized on the piercer, the specification is flexible and the production variety is wide. Due to the development of continuous pipe rolling technology, the units below 140mm are no longer built.