Do you know the difference between hot pressing elbow and stamping elbow?

Elbow is a kind of pipe fittings used at the turning of the pipe. Hot push, stamping, extrusion and other processes are commonly used in the forming process of seamless elbow. Do you know the difference between hot pressing elbow and stamping elbow?

20210331022624 69645 - Do you know the difference between hot pressing elbow and stamping elbow?

Forming technology of elbow

Hot push forming technology of elbow

The forming process of hot push elbow is a process in which special elbow pusher, core die and heating device are used to make the blank set on the die move forward under the push of the pusher, and is heated, expanded and bent during the movement.
The deformation characteristics of hot push elbow are to determine the pipe blank diameter according to the rule that the volume is constant before and after plastic deformation of metal materials. The pipe blank diameter adopted is smaller than the elbow diameter. The deformation process of the blank is controlled by the core die, so that the metal flow compressed at the inner arc can be compensated to other parts which are thinned due to the expansion, so as to obtain the elbow with uniform wall thickness.
Hot push elbow forming technology has the characteristics of beautiful appearance, uniform wall thickness and continuous operation, which is suitable for mass production. Therefore, it has become the main forming method of carbon steel and alloy steel elbow, and also applied to the forming of some stainless steel elbows.
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 reflection furnace heating. The heating method adopted depends on the requirements of forming products and energy conditions.

Stamping process of elbow

Stamping elbow is the first process used in batch production of seamless elbow. It has been replaced by hot push or other forming processes in the production of elbow of common specifications. However, in some elbow, it has been produced in small quantity, too thick or too thin.
The product is still in use when it has special requirements. The elbow is formed by pressing the tube blank equal to the outer diameter of the elbow, and the press is used to press directly in the die. Before stamping, the tube blank is placed on the lower die, and the inner core and end die are installed into the tube blank. The upper die moves downward to press, and the elbow is formed by the constraint of the external mold and the support of the inner mold. Compared with the hot push process, the appearance quality of stamping is not as good as that of the former; when forming, the outer arc of the stamping elbow is in the tensile state, and no other parts of the excess metal is compensated, so the wall thickness at the outer arc is about 10% thinner. But because of the characteristics of single piece production and low cost, stamping elbow technology is mostly used in the manufacture of small batch and thick wall elbows.
The elbow is divided into two types: cold stamping and hot stamping, which usually choose cold stamping or hot stamping according to the material properties and equipment capability.

Cold extrusion forming technology of elbow

The forming process of cold extrusion elbow is to use special elbow forming machine, put the tube blank into the outer mold, after the upper and lower die is closed, and under the push rod, the tube blank moves along the gap reserved by the inner and outer die to complete the forming process.
The elbow made by cold extrusion process of internal and external mould is beautiful in appearance, uniform in wall thickness and small in size deviation. Therefore, this process is used for forming stainless steel elbow, especially thin-walled stainless steel elbow. The precision of internal and external die used in this process is high, and the deviation of wall thickness of tube blank is also very strict.

Other forming methods of elbow

In addition to the three common forming processes, seamless elbow forming also adopts the forming process of extruding the tube blank into the outer die and then through the ball shaping in the tube blank. However, this process is relatively complex, operation is difficult, and the forming quality is not as good as the above process, so it is less used.

The characteristics of the stamping elbow:

  • 1. it is the characteristic of stamping to finish processing by means of punch and stamping equipment. High speed pressure can reach hundreds or thousands of times per minute, and a stamping part can be obtained for each stroke. Therefore, stamping is easy to realize mechanization and automation, high production efficiency and convenient operation.
  • 2. stamping usually does not produce chips and waste materials, consumes less materials and does not require other heating equipment. The cost of stamping parts is lower. Therefore, stamping is a kind of material saving and energy-saving processing method.
  • 3. stamping can process parts with large-scale and more complex shapes, as well as the cold deformation and hardening effect of materials during stamping, as well as high strength and rigidity of stamping.
  • 4. in the process of stamping, because the die ensures the size and shape accuracy of the stamping parts, and generally does not damage the surface quality of the stamping parts, the stamping quality is stable, the interchangeability is good, and the service life of the die is generally long.

Small knowledge of stamping elbow:

Quenching can increase the strength and hardness of steel, so it is necessary to reduce the plasticity of the bend when quenching. Water, oil, alkali water and salt solutions are usually used as quenchants for quenching.

Common quality defects of stamping elbows

The plastic processing of stamping elbows often produces the following quality defects, especially in the bending process of pipe.

  • (1) The thickness of the wall becomes thinner and wrinkle is like the outside of the bending deformation area. The part with the largest thinning amount is at the maximum deformation, and the pipe rupture occurs when the thinning is too thin. From the perspective of deformation mechanics, it is a problem of excessive plastic ring tensile stress. If the inner side of the bending deformation area increases the wall thickness. If the deformation degree is too large, the inner wall will be unstable and thickened, and wrinkle will occur when it is serious. Therefore, instability is not only under the action of tensile stress, but also instability under the action of compressive stress. Such quality defects occur in the bending of pipe with larger wall thickness.
  • (2) If necessary measures are not taken (such as filling material or placing mandrel support in the pipe), the cross section of the pipe after bending is easy to become oval without internal support.

Therefore, it is very important to choose reasonable process methods and take necessary technological measures to prevent the above defects. The production practice shows that eliminating or minimizing the quality defects to meet the requirements of pipe fittings is the key to plastic processing of pipe.

What kind of conditions should stamping elbow, die press elbow and hot pressing elbow be selected respectively?

  1. Stamping elbow is generally used for forming elbows with wall thickness above Sch80.
  2. The elbow of die pressing is a bit different. As long as the elbow formed by mould can be molded elbow, as long as the elbow formed by mould can be called die pressing elbow, except shrimp bend or small diameter elbow made on site.
  3. Hot pressing elbow is one of the stamping elbows, only when the tube blank is hot when it is not overpressure. Generally, because the ability of direct cold stamping equipment is not enough or the surface defects of pipe fittings caused by cold pressing are too serious, hot pressing is used to form. Usually, the wall thickness is more than 16″ Sch100.

The difference between hot pressing elbow and stamping elbow

Different process flow

Hot pressing elbow is to heat the pipe, process it through professional equipment, and then cut and heat it to the pipe above the critical temperature. After holding for a period of time, it is quickly put into the quenchant to make the temperature suddenly decrease and cool rapidly at a rate greater than the critical cooling rate.
The stamping elbow is an elbow made of the same material as the pipe plate, and then stamping into a semicircular elbow by stamping die, and then assembling two half ring elbows to weld the formed elbow.

Different production time

The production time of hot pressed elbow is slow, and it needs to reach a certain temperature zero point.
Through stamping elbow, stamping is completed by stamping die and stamping equipment. Each stroke can get a stamping part, and the high-speed pressure can reach hundreds or thousands of times per minute. Therefore, the production efficiency of stamping bending head is higher and the time spent is less than that of hot pressed elbow.

Different production risk factors

Hot pressing elbow is an elbow formed under high temperature, which needs high temperature, which is likely to cause scald.
The stamping elbow of automatic machine stamping does not require too much labor.
OK, the above is about the characteristics of stamping elbow and the difference between hot pressing elbow and stamping elbow, do you know?

Source: China Steel Elbows Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@steeljrv.com

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