What are the processing methods of stainless steel pipe fittings

First, what are the processing methods of stainless steel pipe fittings?

Stainless steel pipe fittings are a new type of pipe fittings with relatively wide applications. Generally speaking, there are several processing methods:

1. Forging method: Use a forging machine to punch and stretch the top of the steel pipe or a part of it to reduce the outer diameter. The more commonly used forging machines are rotary, connecting rod, and roller.

2. Roller method: Place a core in the stainless steel pipe, push the outside with a roller, and process the round edge.

3. Stamping method: Use a tapered core on the punch press to expand the pipe end to the required specification size shape.

4. Bending forming method: There are three common methods, one method is called the stretching method, another method is called the stamping method, and the third method is the roller method, which has 3-4 rollers, two fixed rollers, and one adjustment roller. Adjust the fixed roller spacing, and the finished pipe fittings are bent.

5. Rolling method: Usually no mandrel is required, which is more suitable for the inner round edge of thick-walled pipes.

6. Bulging method: One method is to place rubber in the tube and compress it with a punch to make the steel tube bulge out; the other method is hydraulic bulging forming, filling liquid in the middle of the steel tube, and the liquid pressure bulges the steel tube into the required shape. Most of the production of corrugated pipes uses this method.

Second, the production process of stainless steel pipe fittings

Generally speaking, the process of manufacturing stainless steel pipe fittings includes cutting, forming, heat treatment, surface treatment, cutting, non-destructive testing, surface protection, and marking in order.

1. Cutting: The materials used for stainless steel pipe fittings are usually steel pipes, stainless steel plates, and stainless steel bars. The cutting method is selected according to the characteristics of the materials and the form of the blanks used in the product. The shape, size, and other requirements of the blanks are also carried out according to the process regulations of different products. For stainless steel pipes, the commonly used cutting methods are cutting with a band saw or bow saw, gas cutting, and plasma cutting. For stainless steel plates, the commonly used cutting methods are gas cutting, plasma cutting, and punching. For stainless steel bars, the commonly used cutting methods include cutting with a band saw or bow saw and punching and shearing.

2. Forming: Also called welding, this process is indispensable for the production and forming of all stainless steel pipe fittings. The following introduces heating and welding in some forming processes.

(1) Heating: To meet the requirements of stainless steel material deformation in the forming process, the blank must be heated during forming. The heating temperature is generally determined by the material and processing requirements. When hot-pushing elbows or hot-bending pipes are formed, medium-frequency or high-frequency induction heating methods are generally used, and flame-heating methods are also used. This type of heating process is a continuous heating process that is synchronized with the elbow or pipe-forming process. The pipe blank is heated and the forming process is completed during movement. When hot-pressing elbows, hot-pressing tees, or forgings are formed, reverberatory furnace heating, flame heating, induction heating, or electric furnace heating are generally used. This type of heating process is to first heat the stainless steel pipe blank to the required temperature, and then put it into the mold for pressing or forging.

(2) Welding: There are two situations. One is the pipe fittings produced by welded pipes. The forming process of welded pipes is the same as that of seamless pipes. The pipe fitting forming process does not include the welding process. The other is that the pipe fitting manufacturer completes the welding process required for pipe fitting forming, and then rolls the stainless steel plate into a pipe blank and welds it into a tee, etc. for pressing.

3. Heat treatment: This process is an important part of stainless steel pipe fitting production. After the heat treatment steps of heating, insulation, and cooling, the work hardening, residual stress, metal deformation defects, etc. formed in the forming process are removed, so that the metal structure and properties of the stainless steel pipe fittings after forming are changed, and the state before deformation processing is restored or the performance is improved and enhanced. The heat treatment equipment commonly used is the reverberatory furnace, electric furnace, etc., and the control method is that the thermocouple in the furnace is connected to the control device of the temperature-time automatic recorder through a sensor. The provisions for heat treatment in different pipe fitting product standards are not the same. Not all deformed pipe fittings need to be heat-treated. Generally speaking, for low-carbon steel pipe fittings, when the final forming temperature is not less than 723°C, there is no need to perform heat treatment. Because its final organizational state under this temperature condition is usually normalized, heat treatment is required when the temperature is lower than this temperature or higher than 980°C. Alloy steel or stainless steel pipe fittings must be heat treated regardless of whether they are cold-formed or hot-formed. The effect of conventional heat treatment is usually determined by hardness test.

4. Surface treatment: The methods are sandblasting, shot blasting, grinding, pickling, etc., to remove rust and scratches on the surface, improve surface smoothness, and meet the needs of subsequent processing and inspection. The surface hardness of stainless steel pipe fittings after shot blasting will increase slightly.

5. Cutting: It is a process to complete the welding end, structural dimensions, and form and position tolerance processing of stainless steel pipe fittings. For some pipe fittings, cutting processing also includes the processing of inner and outer diameters. Cutting is usually done by special machine tools or general machine tools. For pipes that are too large, when the existing machine tool capacity cannot meet the processing requirements, other processes can be used to complete the processing, such as the method of grinding after gas cutting used for large-diameter elbows. Usually, the appearance and size inspection of stainless steel pipe fittings are carried out after cutting.

6. Nondestructive testing: Nondestructive testing is an important process for detecting defects that may occur in the processing of stainless steel materials and pipe fittings. Most stainless steel pipe fittings product standards have some provisions for nondestructive testing requirements, but the requirements are also different. In addition to nondestructive testing by stainless steel standards and ordering requirements, some manufacturers with strict quality control also formulate nondestructive testing requirements based on materials, processing technology, and internal quality control regulations to ensure the quality of the final product. In actual work, the determination of the qualified level of nondestructive testing of stainless steel pipe fittings should be based on the clear provisions of the ordering requirements or standards. Since the surface of stainless steel pipe fittings is usually in the original tube, plate, or forging state, for the nondestructive testing of the surface quality of stainless steel pipe fittings, if there is no clear grade requirement, it can be graded as II, and defects such as interlayers and cracks that are not easy to determine the depth should be regarded as unqualified. For the non-destructive testing of the internal quality of pipe fittings, if there is no clear grade requirement, the radiographic test should be grade II, and the ultrasonic test should be grade I. To avoid the possibility of defects in stainless steel pipe fittings during heat treatment, the final non-destructive testing of stainless steel pipe fittings should be carried out after heat treatment.

7. Surface protection: Use the method of passivation after pickling for stainless steel pipe fittings. The main purpose of surface protection of stainless steel pipe fittings is corrosion prevention, and it is also necessary to achieve the effect of a beautiful product appearance. Generally speaking, the ordering party puts forward specific requirements for surface protection, and the manufacturer completes the surface protection of stainless steel pipe fittings according to the requirements of the ordering party.

8. Marking on stainless steel pipes: Marking is an indispensable part of the product and is the basis for achieving traceability requirements. Generally speaking, the standards for stainless steel pipes make some provisions for the content and method of marking. The marking of stainless steel pipe fittings usually includes the manufacturer's trademark, name, material grade, specifications, and other contents of the ordering requirements. The marking mainly includes marks, such as steel stamps, engravings, electro-etching, etc., and there are also non-sexual marks, such as spray printing, labels, etc. In addition to the above conventional production process flows, to control the quality of raw materials, the manufacturer must also complete the inspection of raw and auxiliary materials to ensure the accuracy of the materials used. To meet some special requirements, it is also necessary to conduct inspections and tests such as metallographic structure, intergranular corrosion, ferrite, etc. to ensure that the quality of the final product meets the use requirements.