In the production process of welded elbows, if long-radius elbows are made, the specifications should be selected first, and the pipes should be put forward. The expansion rate, through theoretical calculation, is generally between 33% and 35%, so it is pushed back. 2 19mm short radius generally has an expansion rate of 50%. After selecting the raw materials, cut the materials according to the elbow specifications, and then consider the radius of curvature, such as a 90 elbow. Through its curvature, we can calculate how long it will take for the material to process a 90 elbow. It can be calculated theoretically and then cut with this length as the length. Finally, the material is hot pressed. Everyone may have seen the push machine, but it is actually very simple. It is a trumpet-shaped core head or mandrel, and the mandrel changes from thin to thick, and the pushing process is a process of bending and unwinding the belt. There is a bracket at the back to insert the blanking pipe section into the mandrel, and there is a memorial arch fixed mandrel at the back. There is a car in the middle, some of which are driven by hydraulic pressure and some by mechanical transmission, that is, lead screw transmission, and then push the car forward. The trolley pushes the tube along the mandrel, and there is an induction coil outside the mandrel. Heat the pipe, and then the car pushes the pipe down for processing. After pushing, the elbow should be shaped in this hot state. Because some elbows will be twisted after improper handling, which is not allowed. In addition, the outer diameter of the rear front end of the pusher is generally large, so it needs to be shaped with a shaping die. Plastic mold is actually a press, it should have a set of mold, two semi-circular arcs, one above and one below. After molding, the outer diameter meets the size requirements of finished products. The wall thickness is controlled by the wall thickness of raw materials. The wall thickness tolerance of elbow and pipeline is the same, which is 12.5%. In the process of advancing, the wall thickness should not be changed in general, but if there is wall reduction in some places due to tools, then some allowance should be added to the wall thickness when lifting materials. For example, the elbow wall thickness is 8. 18mm, and a pipe of about 8.5mm is usually hung. The outer diameter and wall thickness of the formed elbow have reached the requirements. Next, finish machining. After shot peening, the iron scales on the inner and outer surfaces of the elbow are removed, and the two ends are slotted and welded. After inspection, typing, painting and packaging, it can leave the factory. The above is the production method of elbow with seamless steel pipe below 24 ″. After 24 ",it is more than 600mm, the maximum bending head is between 2.032 m and 2.80 m, and it is made of steel plate. After the steel plate is cut as required, it is made into the shape of UOE, and it is also punched into a circle with a die. There are two halves, then they are spliced and welded. Because of the existence of weld, nondestructive testing must be carried out. Due to the existence of welding stress, heat treatment is needed. There are two processes for welding elbows: one is flaw detection, and the other is heat treatment. Other procedures are the same.

The manufacturing process of tee is basically the same. According to the different specifications of the tee, blanking should be carried out. Sand blasting should be carried out after blanking, and the oxide scale on the surface should be removed before molding. The forming method is hydraulic bulging. There is a die with a flat bottom and a flange hole at the top. After the pipe is put in, the pipe is fixed by a hydraulic cylinder, and both sides are filled with liquid to bulge inward, so that the pipe is extruded into a convex shape, and then the convex part is removed from the appropriate position and made into a groove. Shot peening must be done twice. Because there is work hardening during processing, heat treatment is also needed. The production process of pipe fittings is such a situation.

It needs to be explained again that cutting requires a pipe cutter and a sawing machine. For larger specifications, flame cutting is used. No matter which method is adopted, the pipe end must be straight, burr-free and accurate in length. Otherwise, in the process of pushing, the pipe end is easy to break. The technical problem in this respect lies in the tool design. If the design is good, the model is correct and basically meets the requirements. Some waste products are more, mainly tools. Design mainly depends on experience. It needs experienced workers to polish it continuously before it can be put into normal use. Tools are very important. In addition, the hydraulic incremental launching method is used now. Hydraulic propulsion speed is adjustable. The pushing speed and heating speed of big bend and small bend are different. In addition, the deformation of hydraulic jacking is relatively stable. Now there are not many methods of mechanical pushing, and heating is more important. Old-fashioned heating used gas stoves to heat pipes, but now they all use medium frequency heating. After 1970s, this heating method in China passed the standard. This method has better temperature control and uniform heating. The heating temperature is controlled by adjusting the number of coils. If you burn your mouth, it's hard to control. In addition, warm up before pushing. The mandrel is preheated before fixing the pipe. Adopting intermediate frequency heating technology is a great progress in elbow production, and the output and quality have been greatly improved.