- Seamless elbow
The elbow is a pipe fitting used at the turn of a pipe. In the pipeline system used in all pipe fittings, the largest proportion, about 80%. Usually, the elbow of different material or wall thickness choose different forming process. Manufacturers commonly used seamless elbow forming process has hot push, stamping, extrusion and so on.
- Hot push forming
The forming process of hot push elbow is a process of using special elbow push machine, mandrel and heating device to make the blank on the die move forward under the push of push machine. The deformation characteristics of the hot pushing elbow are that the diameter of the tube blank is determined according to the law of the volume unchanged before and after the plastic deformation of the metallic material. The diameter of the tube billet is smaller than that of the elbow, and the deformation process of the blank is controlled by the mandrel, so that the compressed metal in the inner arc can flow and compensate to the other parts which are thinned due to expanding, 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, which is suitable for mass production. So it is the main forming method of carbon steel and alloy steel elbow, and also used in the forming of stainless steel elbow with some specifications.
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 reverberatory furnace heating, which heating method depends on the forming product requirements and energy conditions.
- Stamping forming
Stamping forming elbow is the earliest forming process used in the mass production of seamless elbow. It has been replaced by hot push method or other forming process in the production of commonly used elbow. But in some specifications of the elbow due to production quantity is small, wall thickness is too thick or too thin.
The product is still in use when there are special requirements. The pipe blank equal to the outside diameter of the elbow is used for forming the elbow, which is directly pressed by the press in the die.
Before stamping, the tube blank is placed on the lower die, the inner core and the end die are loaded into the tube, the upper die moves downward to press, and the elbow is formed by the constraint of the outer die and the support of the inner die.
Compared with the hot pushing process, the appearance quality of stamping forming is not as good as the former. When forming, the outer arc of the stamping elbow is in the stretched state, and there is no excess metal in other parts to compensate, so the wall thickness of the outside arc is reduced by about 10%. However, due to the characteristics of single piece production and low cost, stamping elbow technology is mostly used for small batch, thick wall elbow manufacturing.
Stamping elbow points cold stamping and hot stamping two, usually according to material properties and equipment capacity to choose cold stamping or hot stamping.
The forming process of cold extrusion elbow is to use a special elbow forming machine, put the tube blank into the outer mold, and after the upper and lower die are combined, and the pipe blank moves along the gap reserved between the inner mold and outer mold under the push of the push rod to complete the forming.
The elbow made by the inner and outer die cold extrusion process has beautiful appearance, uniform wall thickness and small size deviation, so the stainless steel elbow, especially the thin-walled stainless steel elbows, is made by this process. The precision of inner and outer mold used in this process is high. The requirements of the wall thickness deviation of the tube blank are also harsh.
- Medium plate welding
Press the middle plate to make half of the elbow section and weld the two sections together. This process is generally used for more than DN700 elbow.
- Other forming methods
In addition to the above three common forming processes, the forming process of seamless elbow also uses the tube billet extruded into the outer mold, and then through the tube through the ball shaping. However, this process is relatively complex, difficult to operate, and the forming quality is not as good as the aforementioned process, so it is rarely used.
Require control of the radius of curvature. Let’s say the radius length is 1.5D, then the radius of curvature must be within the required tolerance range. Since most of these pipes are used for welding, in order to improve the welding quality, The ends are slotted, leaving a certain angle, with a certain edge, this requirement is more stringent, the edge thickness, the angle and the range of variation are specified, the geometric size is more than the pipe. Elbow surface quality and mechanical properties and pipe is basically the same. For ease of welding, the steel material of the pipe to be connected is the same.
China is already the world’s largest producer and consumer of materials of construction. The main building materials products such as cement, flat glass, building and sanitary ceramics, stone and wall materials have ranked first in the world for many years. At the same time, the quality of building materials continues to improve, energy and raw material consumption decreased year by year, a variety of new building materials continue to emerge, building materials products continue to upgrade. Cangzhou pipeline equipment manufacturing base thick. The existing production enterprises more than 3200, including large-scale (sales income of more than 5 million yuan) 222 enterprises, employing 124,000 people. The main products are various kinds of special steel, stainless steel, carbon steel and other caliber seamless steel pipe, low in high pressure boiler tube, oil drilling pipe and other steel pipe; All kinds of three-way, four-way, valve, reducing pipe and other elbow pipe fittings; All kinds of stainless steel flange, forging flange; All kinds of pipe rack, meter, oil blowout preventer and other pipe fittings; All kinds of polyethylene pipes, polypropylene pipes and other plastic pipes, a total of 16 categories, more than 370 varieties, 3500 kinds of specifications. The main manufacturing process is hot-rolling straight seam welding, spiral double-face embedded arc welding, forging, pressing, intermediate frequency pushing, cold forming, hot extrusion, etc., with a maximum diameter of 2020mm. Products are widely used in municipal, petrochemical, West-to-East gas transmission, shipbuilding and nuclear power and other engineering fields, the annual design processing capacity of 25 million tons. In 2010, the industrial added value of enterprises above designated size reached 13 billion yuan, an increase of 31.7% year on year, accounting for 16.1% of the total added value. The pipeline equipment manufacturing industry in Cangzhou is striding forward to the goal of “three highs” (on the scale, on the level and on the equipment) and “three heights” (high-end, high voltage and high added value), and urged the capacity of pipeline equipment manufacture to reach 30 million tons. Cangzhou will become a well-known “pipeline equipment manufacturing and R & D base” and “pipeline and equipment capital.” “Eleventh Five-Year Plan” infrastructure investment has been chess to the plate, highway, railway and other infrastructure construction investment explosion growth and ordinary civil construction investment steady growth, so that the construction industry is in the boom upward stage. At the same time, under the background of building an energy saving society and strengthening the independent innovation ability of the country, energy saving and technology innovation will be the hot spot of the industry. Plastic pipe fittings and pipes set off a pipe fitting boom again.