Elbow is a kind of pipe fittings used for pipe bend. Up to 80% of all fittings used in piping systems. Usually, different forming processed are selected for different material or wall thickness of elbow. At present, the commonly used seamless elbow forming processes in manufacturers including Hot Pushing, Stamping, Extrusion etc.
A. Hot Pushing Forming
The hot push elbow forming process uses a special elbow push machine, a core mold and a heating device, so that the blank set on the mold moves forward under the push of the push machine, and heated, expanded and bent during the movement the process of the deformation characteristic of the hot push elbow is to determine the diameter of the tube blank according to the law that the volume of the metal material does not change before or after plastic deformation. The diameter of the tube blank used is smaller than the diameter of the elbow. The metal flow is compensated to other parts thinned by the expansion, so as to obtain an elbow with a uniform wall thickness.
The hot push elbow forming process has the characteristics of nice 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 elbows. And also used in the forming of stainless steel elbows of certain specifications.
The heating method of the forming process is medium frequency or high frequency induction heating (Multi-turn or single-turn of heating coil),Flame heating and reverberatory furnace heating, and heating method to use depends on the forming product requirements and energy situation.
B. Stamping of forming
Stamping of forming Elbow is the earliest forming process applied to mass production of seamless elbow. At present, it has been replaced by hot pushing or other forming processes in the production of commonly used elbows, but in some elbows, the production quantity is too small, the wall thickness is too thick or too thin, the product is still in use when there are special requirements. The stamping forming of the elbow adopts a tube blank equal to the outer diameter of the Elbow, which is directly pressed in the mold using a press. Compared with the hot push process, the appearance quality of stamping forming is not as good as the former. The outer Arc of the stamping elbow is in a stretched state during forming, and there is no excess metal in other parts to compensate, so the wall thickness at the outer Arc is about 10% thinner.
Stamping elbows are divided into cold stamping and hot stamping. Usually, cold stamping or hot stamping is selected according to material properties and equipment capabilities.
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. Gap movement to complete the forming process.
The elbow manufactured by the internal and external cold extrusion process has beautiful appearance, uniform wall thickness and small size deviation. Therefore, this process is mostly used for the forming of stainless steel elbows, especially thin-walled stainless steel elbows. The internal and external molds used in this process have high precision requirements; the requirement of wall thickness deviation is also very strict.
C. Other Forming methods
In addition to the commonly used forming process, seamless elbow forming also adopts the tube blank extrusion to the outer die then through the tube blank ball shaping forming process. However, this process is relatively complex,troublesome to operate and the forming quality is not as good as the previous process, so it is rarely used.
