Seamless elbow: The elbow is a pipe fitting for the bend of the pipe. In all the pipe fittings used in the pipeline system, the proportion is the largest, about 80%. Usually, different forming processes are selected for elbows of different materials or wall thickness. Manufacturers commonly used seamless elbow forming processes are hot push, stamping, extrusion and so on.
Hot push forming: The hot push elbow forming process is the use of special elbow pushing machine, core die and heating device, so that the blank set on the mold moves forward under the push of the push machine, in the movement is heated, expanded and bent forming process. The deformation characteristic of hot push elbow is to determine the diameter of the tube billet according to the law of constant volume before and after the plastic deformation of the metal material. The diameter of the tube billet is less than the diameter of the elbow. The deformation process of the billet is controlled by the mandrel, so that the compressed metal flow in the inner arc is compensated to other parts that are thinned due to the expansion of the diameter, 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, suitable for mass production, so it has become the main forming method of carbon steel and alloy steel elbow, and is also used in the forming of some specifications of stainless steel elbow. The heating method of the forming process has medium frequency or high frequency induction heating (the heating ring can be multiple or single circle), flame heating and reflection furnace heating, which heating method depends on the requirements of the forming product and the energy situation.
Stamping forming: stamping forming elbow is the first used in the mass production of seamless elbow forming process, in the common specifications of elbow production has been replaced by hot push method or other forming process, but in some specifications of elbow due to the production number is small, the wall thickness is too thick or too thin. The product is still used when it has special requirements. The stamping form of the elbow is made of a tube blank equal to the outer diameter of the elbow, which is directly pressed in the die by a press. Before stamping, the tube blank is placed on the lower die, the inner core and end die are loaded into the tube blank, the upper die moves downward to press, and the elbow is formed by the restriction of the outer die and the support of the inner die. Compared with hot push process, the appearance quality of stamping is inferior to the former. The outer arc of the stamping elbow is in a stretched state when it is formed, and there is no excess metal in other parts to compensate, so the wall thickness at the outer arc is reduced by about 10%. However, because it is suitable for single piece production and low cost, the stamping elbow process is mostly used for the manufacture of small batch and thick wall elbows. Stamping elbow is divided into cold stamping and hot stamping two, usually according to the material properties and equipment capacity to choose cold stamping or hot stamping.
The forming process of the cold extrusion elbow is to use a special elbow forming machine to put the tube blank into the outer die. After the upper and lower die are closed, the tube blank is transported along the gap reserved by the inner die and the outer die to complete the forming process under the push rod. The elbow made by the internal and external die cold extrusion process has beautiful appearance, uniform wall thickness and small dimensional deviation, so the stainless steel elbow, especially the thin-walled stainless steel elbow, is manufactured by this process. The internal and external die used in this process requires high precision; The wall thickness deviation of the tube billet is also strict.
In addition to the above three commonly used forming processes, seamless elbow forming also uses the tube blank extrusion to the outer mold, and then through the tube blank ball shaping process. However, this process is relatively complex, troublesome to operate, and the forming quality is not as good as the above-mentioned process, so it is less used.