Seamless pipe elbow: an elbow is a type of pipe fitting used at the turn of the pipeline. Among all the pipe fittings used in the piping system, the proportion is the largest, about 80%. Generally, different forming processes are selected for pipe fitting elbows of different materials or wall thickness. Commonly used seamless pipe fitting elbow forming processes in manufacturing plants include hot pushing, stamping, and extrusion.
The hot push pipe fitting elbow forming process is to use a special elbow push machine, core mold and heating device, so that the blank sleeved on the mold moves forward under the push of the push machine, and is heated, expanded and bent during the movement. the process of. The deformation characteristic of the hot push pipe fitting elbow is to determine the diameter of the tube blank according to the law of constant volume before and after the plastic deformation of the metal material. The diameter of the tube blank is smaller than the diameter of the pipe fitting elbow, and the deformation process of the blank is controlled by the core mold, so that the inner arc is compressed The metal flow is compensated to other parts that are thinned due to diameter expansion, thereby obtaining an elbow with uniform wall thickness.
The hot push pipe fitting elbow forming process has the characteristics of beautiful appearance, uniform wall thickness and continuous operation, and is suitable for mass production. Therefore, it has become the main forming method for carbon steel and alloy steel elbows, and is also applied to certain specifications of stainless steel elbows. Is forming.
The heating methods of the forming process include medium-frequency or high-frequency induction heating (the heating ring can be multi-turn or single-turn), flame heating and reverberatory furnace heating. The heating method used depends on the requirements of the formed product and the energy situation.
Stamping pipe fitting elbow is the first forming process used in mass production of seamless elbows. It has been replaced by hot push or other forming processes in the production of commonly used elbows, but in some specifications of elbows due to the production quantity, the wall thickness is too thick or too thin.
The product is still used when there are special requirements. The stamping and forming of the elbow adopts a tube blank with the same outer diameter as that of the elbow, which is directly pressed in the mold by a press.
Before punching, the tube blank is placed on the lower mold, the inner core and the end mold are loaded into the tube blank, the upper mold moves downwards to start pressing, and the elbow is formed by the restraint of the outer mold and the support of the inner mold.
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 reduced by about 10%. However, due to its suitability for single-piece production and low cost, the stamping elbow process is mostly used in the manufacture of small batches and thick-walled elbows.
There are two types of stamping elbows: cold stamping and hot stamping. Cold stamping or hot stamping is usually selected according to the 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 mold. After the upper and lower molds are closed, under the push of the push rod, the tube blank follows the reserved The gap movement completes the forming process.
The elbow manufactured by the cold extrusion process of internal and external molds has beautiful appearance, uniform wall thickness and small size deviation. Therefore, this process is often used for forming stainless steel elbows, especially thin-walled stainless steel elbows. The inner and outer molds used in this process require high precision; the requirements for the wall thickness deviation of the tube blank are also strict.
Use the middle plate to make half of the elbow section with a press, and then weld the two sections together. This process is generally used to make elbows above DN700.
Other forming methods
In addition to the above-mentioned three commonly used forming processes, seamless elbow forming also adopts a forming process in which the tube blank is extruded to an outer die, and then the tube blank is passed through the ball. However, this process is relatively complicated, troublesome to operate, and the forming quality is not as good as the foregoing process, so it is rarely used
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