Process flow of steel pipe fittings manufacturing
For sheet metal, common blanking methods include gas cutting, plasma cutting and punching. For bars, the common blanking methods are band sawing machine or bow sawing machine cutting, punching and shearing cutting.
For sheet metal, common blanking methods include gas cutting, plasma cutting and punching.
For bars, the common blanking methods are band sawing machine or bow sawing machine cutting, punching and shearing cutting.
② Forming (welding)
For the manufacturing process of all pipe fittings, forming is an indispensable process. Due to different forming processes of different products, the required space is long, which will be described in Section 15.2.4. Here, the heating and welding included in some forming processes are briefly introduced.
a. . Heating
In order to meet the requirements of material deformation in the forming process, it is necessary to heat the blank when using the hot forming method to manufacture pipe fittings. The heating temperature is usually determined according to the material and process needs.
When forming hot push elbow or hot bend elbow, medium frequency or high frequency induction heating is usually used, and flame heating is also used. This heating method is a continuous heating synchronized with the forming process of elbows or elbows. The tube blank is heated in motion and the forming process is completed.
When hot pressing elbows, hot pressing tees or forgings are formed, they are usually heated by reverberatory furnace, flame, induction or electric furnace. This heating is to first heat the tube blank to the required temperature, and then put it into the die for pressing or forging.
The pipe fittings with welds include two cases. One is the pipe fittings made of welded pipes. For pipe fitting manufacturers, the forming process of welded pipes is basically the same as that of seamless pipes. The forming process of pipe fittings does not include the welding process; The other is the welding process required by the pipe fitting manufacturer to complete the pipe fitting forming, such as the elbow that is assembled and welded after single piece pressing, the tee that is welded into the tube blank after using the steel plate reel and then pressed.
Welding methods of pipe fittings commonly include manual arc welding, gas shielded welding and automatic welding.
The manufacturer shall prepare the welding procedure specification to guide the welding work, and shall carry out the welding procedure qualification according to the corresponding specification requirements to verify the correctness of the welding procedure specification and assess the welding ability of the welder.
Welders engaged in pipe fitting welding operations shall pass the examination of the quality and technical supervision department and obtain the corresponding qualification certificates before they can engage in welding of relevant steel types (according to the regulations of some industries, welding pipe fittings used in some industries shall obtain the welder examination and welding procedure qualification specified by the industry, such as welding of marine pipe fittings shall obtain the welder examination and welding procedure qualification of the corresponding classification society).
③ Heat treatment
Heat treatment process is an important part of pipe manufacturing. Through the heat treatment steps of heating, heat preservation and cooling, the work hardening, residual stress, metal deformation defects, etc. generated during the forming process are reduced, so that the metal structure and properties of the formed pipe fittings are changed, and they are restored to the state before deformation processing or their properties can be improved.
Commonly used heat treatment equipment is reverberatory furnace, electric furnace, etc; The common control mode is that the thermocouple in the furnace is connected to the control device of the temperature time automatic recorder through the sensor.
The regulations on heat treatment are different in different pipe fitting product standards. Not all deformed pipe fittings shall be subject to heat treatment. Generally, when the forming temperature of low carbon steel pipe fittings is not lower than 723 ℃ (recrystallization temperature), heat treatment is not required, because its structure state is basically normalized under this temperature condition, and heat treatment shall be carried out when the temperature is lower than this temperature or higher than 980 ℃; The pipe fittings made of alloy steel or stainless steel, whether cold forming or hot forming, shall be subject to heat treatment.
Routine inspection of heat treatment is generally completed through hardness test.
④ Surface treatment
The surface treatment of pipe fittings is usually carried out by sand blasting, shot blasting, polishing, pickling and other methods to reduce the corrosion and scratches on the product surface, so that the product can reach a smooth surface and meet the requirements of subsequent processing and inspection.
The surface hardness of pipe fittings with shot blasting surface treatment will increase slightly.
Cutting processing is a process to complete the welding end, structural dimension and geometric tolerance processing of pipe fittings. For some pipe fittings, the cutting process also includes the processing of inner and outer diameters. Cutting is mainly completed by machine tools or general machine tools; For pipe fittings with too large size, when the existing machine tool capacity cannot meet the processing requirements, other methods can be used to complete the processing, such as the method of grinding after gas cutting used for large diameter elbows.
Appearance and dimension inspection of pipe fittings are usually conducted after cutting.
Non destructive testing is an important process to inspect the defects that may occur during the processing of materials and pipe fittings. Most pipe fitting product standards specify the requirements for nondestructive testing, but the requirements are not consistent. In addition to meeting the requirements of product standards and ordering requirements for non-destructive testing, some manufacturers with strict quality control also formulate non-destructive testing requirements according to materials, processing technology and internal quality control regulations to ensure the quality of products delivered.