Elbow process and formation principle
Seamless elbow: An elbow is a type of pipe used for turning a pipe. Among the total pipe fittings used in the piping system, the proportion is the largest, about 80%. Generally, different forming processes are selected for bends of different materials or wall thicknesses. At present, the seamless elbow forming process commonly used in manufacturing plants has hot push, stamping, extrusion and the like.
Hot push forming
The hot push elbow forming process uses a special elbow pusher, a core mold and a heating device, so that the blank placed on the mold moves forward under the push of the pusher, 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 of the volume change of the metal material before and after plastic deformation. The diameter of the tube blank used is smaller than the diameter of the elbow, and the deformation process of the billet is controlled by the core mold to compress the inner arc. The flow of the metal compensates for other portions that are thinned by the expansion of the diameter, thereby obtaining an elbow having a uniform wall thickness.
The hot-bending elbow forming process has the characteristics of beautiful appearance, uniform wall thickness and continuous operation, and is suitable for mass production. Therefore, it is the main forming method for carbon steel and alloy steel elbows, and is also applied to some specifications of stainless steel elbows. Forming.
The heating process of the forming process includes medium frequency or high frequency induction heating (the heating coil can be multi-turn or single turn), flame heating and reverberatory furnace heating, and the heating method is determined by the forming product requirements and energy conditions.
b. stamping forming
Stamping forming elbow is the earliest forming process for mass production of seamless elbows. At present, it has been replaced by hot pushing or other forming processes in the production of elbows of common specifications, but in some specifications of elbows The production quantity is small, the wall thickness is too thick or too thin. The product is still in use when it has special requirements. The stamping of the elbow is performed by using a tube blank equal to the outer diameter of the elbow, and is directly press-formed in the mold using a press. Schematic diagram of stamping elbow forming
Before the stamping, 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 is moved downward to start pressing, and the elbow is formed by the constraint of the outer 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 the stamping elbow is formed, the outer arc is in a stretched state, and no other parts of the metal are compensated, 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 for the manufacture of small batches and thick-walled elbows.
Stamping elbows are divided into cold stamping and hot stamping. Cold stamping or hot stamping is usually 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, the blank is reserved along the inner and outer molds under the push of the push rod. The gap moves to complete the forming process. Figure 15-8 is a photograph of a stainless steel elbow of a manufacturing plant before and after extrusion.
The elbow manufactured by the inner and outer mold cold extrusion process has beautiful appearance, uniform wall thickness and small dimensional deviation, so the stainless steel elbow, especially the thin-walled stainless steel elbow forming, is mostly manufactured by this process. The precision of the inner and outer molds used in this process is high; the wall thickness deviation of the tube blank is also demanding.
c. Other forming methods
In addition to the three conventional forming processes described above, the seamless elbow forming process also employs a forming process in which the tube blank is extruded into the outer mold and then passed through the tube blank. However, this process is relatively complicated, troublesome to operate, and the forming quality is not as good as the aforementioned process, so it is less used.
American American Standard Pipe Fittings Standard
American standard
Forged steel butt welded pipe parts manufactured by ASME/ANSI B16.9
ASME/ANSI B16.11 socket weld and thread forged pipe fittings
ASME/ANSI B16.28 steel butt welding small radius elbow and turning back
ASME B16.5 pipe flange and flange fittings
MSS SP-43 forged stainless steel butt welded pipe fittings
MSS SP-83 socket weld and threaded union
MSS SP-97 socket-welded, threaded and butt-welded, integral reinforced header
ASME B16.3-1998 malleable cast iron threaded pipe
4. Chinese pipe fittings standard
GB/T12459-2005 steel butt welding seamless pipe fittings
GB/T13401-2005 steel plate butt welded pipe fittings
SH 3408 steel butt welding seamless pipe fittings
SH 3409 steel plate butt welded pipe fittings
SH 3410 forged steel socket welding pipe fittings
GB/T10751-1995 marine steel pipe butt welding head
Pipeline standard
1The former Ministry of Labor [1996] No. 140 document pressure pipeline safety management and supervision regulations*
2 National Quality Inspection Pot [2002] No. 235 pressure vessel pressure pipe design unit qualification permit and management rules
Notice of the No. 3 Technical Supervision Bureau of Panfa [1999] No. 143 on Strengthening the Safety Supervision and Management of Liquefied Petroleum Gas Stations
4 Quality Technical Supervision Pot Word [1999] No. 59 on the implementation of the "Notice on Strengthening the Safety Supervision and Management of Liquefied Petroleum Gas Stations"
5 former Ministry of Labor [1996] No. 276 steam boiler safety technical supervision procedures*
6 former Ministry of Labor [1997] No. 74 document hot water boiler safety technical supervision procedures*
7 former Ministry of Labor [1993] No. 356 text organic heat carrier furnace safety technical supervision procedures*
8 Quality Technical Supervision Bureau Panfa [1999] No. 154 Pressure Vessel Safety Technology Supervision Regulations*
9 GB4962-1985 Hydrogen Safety Technical Regulations
10 GB6222-1986 Gas Safety Regulations for Industrial Enterprises
11 GB11984-1989 Chlorine Gas Safety Regulations
12 GB13348-1992 Liquid petroleum products electrostatic safety regulations
13 SY6186-1996 Oil and Gas Pipeline Safety Regulations
14 SY5737-1995 Petroleum Pipeline Safety Regulations
15 DL/T561-95 Guidelines for Water Vapor Chemical Supervision in Thermal Power Plants
16 DL/T709-1999 Pressure Pipe Safety Inspection Technical Regulations
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