Seamless Elbow: An elbow is a pipe fitting used at the bend of a pipeline. Among all the
seamless pipe fittings used in the piping system, the proportion is about 80%. Usually, different forming processes are selected for elbows of different materials or wall thicknesses. The seamless elbow forming processes commonly used in manufacturers include hot pushing, stamping, extrusion, etc. The hot push elbow forming process uses a special elbow push machine, core mold and heating device, so that the billet set 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 elbow is to determine the diameter of the tube blank according to the law that the volume of the metal material remains unchanged before and after plastic deformation. The metal flow is compensated to other parts that are thinned due to diameter expansion, so as to obtain an elbow with uniform wall thickness.
The hot push elbow forming process has the characteristics of beautiful appearance, uniform wall thickness and continuous operation, and is suitable for mass production, so it has become the main forming method of carbon steel and alloy steel elbows, and is also used in certain specifications of stainless steel elbows in the process of forming.
The heating methods in the forming process include medium-frequency or high-frequency induction heating (the heating ring can be multi-circle or single-circle), flame heating and reverberatory furnace heating. The heating method depends on the requirements of the formed product and the energy situation. Stamping elbow is the earliest forming process used in the mass production of seamless elbows. It has been replaced by hot push method or other forming processes in the production of elbows of common specifications, but in certain specifications of elbows due to the production quantity Less, wall thickness is too thick or too thin.
It is still used when the product has special requirements. The stamping forming of the elbow adopts a tube blank with the same outer diameter as the elbow, which is directly pressed and formed in the mold by a press.
Before stamping, the tube blank is placed on the lower die, the inner core and end die are put into the tube blank, the upper die moves downward to start pressing, and the elbow is formed through the constraint of the outer die and the support of the inner die.
Compared with the hot pushing process, the appearance quality of stamping is not as good as the former; when the stamping elbow is formed, the outer arc is in a stretched state, and there is no extra metal in other parts to compensate, so the wall thickness at the outer arc is about 10% thinner . However, due to the characteristics of single-piece production and low cost, the stamping elbow process is mostly used in the manufacture of small batches and thick-walled elbows.
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 mold. After the upper and lower molds are closed, under the push of the push rod, the tube blank is moved The gap movement completes the forming process.
The elbow manufactured by the cold extrusion process of the inner and outer molds has a beautiful appearance, uniform wall thickness, and small size deviation. Therefore, this process is often used for the forming of stainless steel elbows, especially thin-walled stainless steel elbows. The precision requirements of the inner and outer dies used in this process are high; the requirements for the wall thickness deviation of the tube blank are also relatively strict.
Middle plate welding
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. In addition to the above three commonly used forming processes, seamless elbow forming also uses a forming process in which the tube blank is extruded to the outer mold, and then the tube blank is passed through the ball to shape it. However, this process is relatively complicated, cumbersome to operate, and the forming quality is not as good as the aforementioned process, so it is rarely used
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