Seamless elbow is a kind of pipe fitting used at the turn of the pipe. In the pipeline system used in all pipe fittings, the proportion of about 80%.
Usually, the elbow of different material or wall thickness choose different forming process. Manufacturers commonly used seamless elbow forming process has hot push, stamping, extrusion and so on.
- Hot push molding
The forming process of hot push elbow is a process of using special elbow push machine, mandrel and heating device to make the blank on the die move forward under the push of push machine. The deformation characteristics of the hot pushing elbow are that the diameter of the tube blank is determined according to the law of the volume unchanged before and after the plastic deformation of the metallic material. The diameter of the tube billet is smaller than that of the elbow, and the deformation process of the blank is controlled by the mandrel, so that the compressed metal in the inner arc can flow and compensate to the other parts which are thinned due to expanding, so as to obtain the elbow with uniform wall thickness.
Hot push elbow forming process has the characteristics of beautiful appearance, uniform wall thickness and continuous operation, which is suitable for mass production. So it is the main forming method of carbon steel and alloy steel elbow, and also used in the forming of stainless steel elbow with some specifications.
The heating methods of forming process include medium frequency or high frequency induction heating (heating ring can be multi-circle or single-circle), flame heating and reverberatory furnace heating, which heating method depends on the forming product requirements and energy conditions.
- Stamping forming
Stamping forming elbow is the earliest forming process used in the mass production of seamless elbow. It has been replaced by hot push method or other forming process in the production of commonly used elbow. But in some specifications of the elbow due to production quantity is small, wall thickness is too thick or too thin.
The product is still in use when there are special requirements. The pipe blank equal to the outside diameter of the elbow is used for forming the elbow, which is directly pressed by the press in the die.
Before stamping, the tube blank is placed on the lower die, the inner core and the end die are loaded into the tube, the upper die moves downward and begins to press, and the elbow is formed by the constraint of the outer die and the support of the inner die.
Compared with the hot pushing process, the appearance quality of stamping forming is not as good as the former. When forming, the outer arc of the stamping elbow is in the stretched state, and there is no excess metal in other parts to compensate, so the wall thickness of the outside arc is reduced by about 10%. However, due to the characteristics of single piece production and low cost, stamping elbow technology is mostly used for small batch, thick wall elbow manufacturing.
Stamping elbow points cold stamping and hot stamping two, usually according to material properties and equipment capacity to choose cold stamping or hot stamping.
The forming process of cold extrusion elbow is to use a special elbow forming machine, put the tube blank into the outer mold, and after the upper and lower die are combined, and the pipe blank moves along the gap reserved between the inner mold and outer mold under the push of the push rod to complete the forming.
The elbow made by the inner and outer die cold extrusion process has beautiful appearance, uniform wall thickness and small size deviation, so the stainless steel elbow, especially the thin-walled stainless steel elbows, is made by this process. The precision of inner and outer mold used in this process is high. The requirements of the wall thickness deviation of the tube blank are also harsh.
- Medium plate welding
Press the middle plate to make half of the elbow section and weld the two sections together. This process is generally used for more than DN700 elbow. In addition to the above three common forming processes, the forming process of seamless elbow also uses the tube billet extruded into the outer mold, and then through the tube through the ball shaping. However, this process is relatively complex, difficult to operate, and the forming quality is not as good as the aforementioned process, so it is rarely used.