This article introduces the production process and equipment of the
seamless steel pipe factory, and the seamless steel pipe is produced by piercing and other methods to produce seamless steel pipes or other metal pipes and alloy pipes. The outer diameter of the seamless pipe ranges from 0.1 to 1425mm, and the wall thickness ranges from 0.01 to 200mm. In addition to circular tubes, there are also various special-shaped section tubes and cross-section tubes.
Production method of seamless pipe:
There are many ways to produce seamless pipes. According to the delivery requirements, seamless steel pipes can be produced by hot rolling (about 80-90%) or cold rolling and cold drawing (about 10-20%). The blanks for hot-rolled pipes include round, square or polygonal ingots, slabs or continuous casting billets, and the quality of the billets has a direct impact on the quality of the pipes.
There are three basic processes for hot-rolled pipes:
①Pierce the ingot or billet into a hollow thick-walled capillary on the piercing machine;
②Thin the capillary tube on the stretching machine, and extend it into a barren tube close to the wall thickness;
③Roll into the required finished tube on the finishing mill. The rolling mill series is expressed by the maximum outer diameter of the steel pipe produced (see rolling mill).
(1) Automatic rolling tube production
One of the ways to produce seamless steel pipes. The production equipment consists of piercing machine, automatic pipe rolling machine, leveling machine, sizing machine and reducing machine.
(2) Continuous rolling pipe production
The production equipment consists of piercing machine, continuous pipe rolling mill and tension reducing machine. After the round billet is pierced into a capillary tube, it is inserted into a mandrel, and is continuously rolled through a two-roller mill with 7 to 9 roll axes arranged at 90° to each other. Pull out the mandrel after rolling, and then carry out tension reduction after reheating, and the steel pipe can be rolled up to 165m long. The annual output of the 140mm continuous pipe rolling unit is 400,000 to 600,000 tons, which is 2 to 4 times that of the automatic pipe rolling unit. The feature of this unit is that it is suitable for producing steel pipes with an outer diameter of 168mm or less, and requires large equipment investment, large installed capacity, mandrel rod length of 30m, and complex manufacturing. The limit-moving mandrel continuous pipe mill (MPM) appeared in the late 1970s. During rolling, the external force forces the mandrel to move at a speed lower than that of the steel pipe, which can improve the metal flow conditions. Short mandrels are used to roll long pipes and large-diameter steel pipes.
(3) Cyclic rolling tube production
Polygonal and round steel ingots or continuous casting slabs are used as raw materials. After heating, they are pierced into cup-shaped blanks by hydraulic pressure, and then rolled into capillaries by two-roll cross-rolling extension machines. A section of steel pipe is rolled out by the roll turning once. The cycle rolling mill is also called the Pilger rolling mill. Periodic rolling pipe production uses steel ingots as raw materials, which is suitable for rolling large-diameter thick-walled steel pipes and variable-section pipes.
(4) Three-roll rolled tube production
It is mainly used to produce thick-walled pipes with high dimensional accuracy. The pipe produced by this method has a wall thickness accuracy of ±5%, which is about twice as high as that of pipes produced by other methods. In the 1960s, due to the invention of the new three-roll skew rolling mill (called Transval mill), this method developed rapidly. The feature of the new rolling mill is that when rolling to the tail, the entrance rotary frame is quickly turned to change the rolling angle, so as to prevent the tail from forming a triangle, so that the ratio of the outer diameter to the wall thickness of the production variety is expanded from 12 to 35, which can not only produce thin-walled pipes , also increased production capacity.
(5) Pipe jacking production
The traditional method is that the billet is extended into a cup-shaped capillary through hydraulic piercing and cross-rolling, and the long mandrel is inserted into the bottom of the capillary cup by a push rod, and sequentially passes through a series of roller formworks with gradually decreasing holes, and is rolled into a tube. This production method requires less investment in equipment, can be used for continuous casting billet, and can produce extra large and thick tubes with a diameter of 1070mm and a wall thickness of 200mm, but the production efficiency is low, the wall thickness is relatively thick, and the tube length ratio is short. After the new technology of CPE method appeared, the tube blank was pierced into a waste tube by cross rolling, and then rolled and extended into a tube after closing, which overcomes some shortcomings of the traditional method and has become a method with better economic benefits in the production of seamless tubes.
(6) Extrusion tube production
First, the peeled round billet is perforated or expanded, and then heated by induction heating or salt bath, and the inner surface is coated with lubricant and sent to the extruder, and the metal is extruded into a pipe through the annular gap between the die hole and the mandrel. . It is mainly used to produce high-temperature alloy pipes with low plasticity, special-shaped pipes and composite pipes, non-ferrous metal pipes, etc. This method produces a wide range, but the yield is low. In recent years, due to the improvement of mold materials, lubricants, extrusion speed, etc., the production of extruded pipes has also developed.
(7) Rolling tube production with guide plate
Also known as Diesel (Diessel) method. After piercing, the capillary tube with a long mandrel is rolled into a thin-walled tube on a guide plate rolling mill. The rolling mill is similar to the two-roll cross-rolling piercing machine, except that the fixed guide plate is changed to an active guide plate. Due to the production of long mandrels, the inner wall of the pipe is smooth and free of scratches; however, the cost of tools is large and the adjustment is complicated. It is mainly used to produce carbon steel pipes for general purposes with an outer diameter of 150mm or less. It is used less at present, and there is no great development prospect.
(8) Spinning tube production
The flat or hollow blank is processed into thin-walled pipes by one or more times of spinning on the spinning machine. The pipe has high precision, good mechanical properties, and a wide range of sizes, but low production efficiency. It is mainly used in the production of non-ferrous metal pipes, but is also increasingly used in the production of steel pipes. In addition to the production of living utensils, chemical containers and machine parts, spinning pipes are mostly used in the military industry.
In the 1970s, the powerful spinning method has been able to produce large-diameter extremely thin round pipes and special-shaped pipe fittings with a diameter of 6000mm and a ratio of diameter to wall thickness of more than 10,000.
(9) Production of cold-rolled and cold-drawn pipes
It is used to produce small-diameter thin-walled, precision and special-shaped pipes. Production is characterized by a multi-process cycle process. The elongation rate can reach 6-8 by cold rolling with a periodic cold rolling mill. In the 1960s, it began to develop in the direction of high speed, multi-line, long stroke, and long tube billet. In addition, the small roll cold rolling mill has also been developed. It is mainly used to produce ultra-thin precision pipes with a wall thickness of less than 1mm. The cold rolling equipment is complicated, the tool processing is difficult, and the variety and specification change is not flexible; usually a combination of cold rolling and cold drawing is used, that is, the wall is first reduced by cold rolling to obtain a large amount of deformation. , and then obtain a variety of specifications by cold drawing.
Production equipment for seamless steel pipes:
1. Perforator
Commonly used two-roll cross-rolling piercing, the round tube billet is pierced and rolled into a hollow thick-walled tube (capillary tube), and the axes of the two rolls form an inclination angle with the rolling line. In recent years, the inclination angle has increased from 6° to 12° to 13° to 17°, which speeds up the perforation speed. To produce steel pipes with a diameter of 250mm or more, secondary perforation is used to reduce the wall thickness of the capillary. New technologies such as perforation with active rotating guide plate, perforation with back thrust, axial discharge and circular top welding have also been developed to a certain extent, thereby strengthening the perforation process and improving the quality of the capillary.
2. Automatic pipe rolling machine
Roll thick-walled capillary into thin-walled barren tube. Generally, after 2 to 3 passes, the wall thickness of the finished product is rolled, and the total elongation is about 1.8 to 2.2. Since the 1970s, single-hole grooved rolls, double-stand tandem rolling mills, double-groove tracking rolling and spherical plugs have been used. Technology has improved production efficiency and realized the mechanization of rolling tubes.
3. Even machine
The structure is similar to that of a puncher. The purpose of leveling is to eliminate the internal and external surface defects and the ovality of the waste pipe, and reduce the unevenness of the transverse wall thickness. In recent years, the three-roll leveling machine has been adopted, which has improved the deformation and leveling efficiency of the leveling machine.
4. Sizing machine
It is composed of 3 to 12 frames, and the reducing machine is composed of 12 to 24 frames, and the reduction rate is about 3 to 28%. The tension reducing machine that appeared in the 1950s can control the wall thickness with proper tension while adjusting the roll speed and reducing diameter. The new tension reducing machine generally uses three-roller type, with 18 to 28 racks, the maximum diameter reduction rate reaches 80%, the wall reduction rate reaches 44%, and the exit speed reaches 18mm per second. The tension reducing machine has the disadvantage of thickening at both ends, which can be eliminated by "sudden electrical control at the head and tail ends" or micro tension reducing.
5. Automatic pipe rolling unit
There are four commonly used series with outer diameters of 100mm, 140mm, 250mm and 400mm, and the production of steel pipes with outer diameters of 17-426mm. The feature of the unit is that the main deformation is realized on the punching machine, the specification changes are more flexible, and the production variety range is wider. Due to the development of continuous rolling tube technology, units below 140mm are no longer built.
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