For the board, common cutting methods include gas cutting, plasma cutting, and punching.
For bars, the common method of cutting is band saw or bow sawing, punching and cutting.
2 forming (welding)
Forming is an indispensable process for the manufacturing process of all pipe fittings. Due to the different forming processes of different products, the length of time required is longer and will be further described in Section 15.2.4. Here, a brief introduction will be made to the heating and welding included in the partial forming process.
In order to manufacture the pipe fitting by the hot forming method, in order to meet the requirements for material deformation in the forming process, the billet needs to be heated during forming. The heating temperature is usually determined by the materials and process needs.
When hot bending or hot bending is formed, it is usually a medium frequency or high frequency induction heating method, or a flame heating method. This heating method is continuous heating in synchronism with the elbow or elbow forming process, and the tube blank is heated during the movement and the forming process is completed.
When a hot press elbow, a hot press tee or a forging is formed, a method of heating by a reverberating furnace, a method of heating by a flame, a method of induction heating, or a method of heating by an electric furnace are generally employed. This heating is preceded by heating the tube blank to the desired temperature and placing it in a mold for pressing or forging.
The welded pipe fittings include two cases, one is a pipe fitting made of welded pipe. For the pipe fitting manufacturer, the forming process using the welded pipe is basically the same as the forming process using the seamless pipe, and the pipe forming process does not include the welding process; The other is a welding process required for the pipe fitting to be completed by the pipe manufacturing factory, such as an elbow which is assembled and welded after being pressed by a single piece, a tee which is welded into a tube blank after being rolled by a steel plate, and then pressed.
Commonly used methods for welding pipe fittings include manual arc welding, gas shielded welding, and automatic welding.
The manufacturer shall prepare welding procedure specifications to guide the welding work, and shall perform welding procedure qualification according to the corresponding specifications to verify the correctness of the welding procedure and evaluate the welding ability of the welder.
Welders engaged in pipe fitting welding shall pass the examinations of the quality and technical supervision department and obtain the corresponding qualification certificates before they can engage in the welding of relevant steel grades (according to the regulations of some industries, the welded pipe fittings used in some industries shall obtain the welder examinations prescribed by the industry and Welding procedure qualification, such as welding of marine pipe fittings, is to obtain the welder's examination and welding procedure qualification of the corresponding classification society.
3 heat treatment
The heat treatment process is an important part of the manufacture of pipe fittings. 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 eliminated, and the metal structure and properties of the formed pipe are changed, and the state before the deformation process or the performance can be restored. Improve and improve.
The commonly used heat treatment equipment is a reverberatory furnace, an electric furnace, etc.; the usual 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 heat treatment requirements in different pipe product standards are different. Not all deformed pipe parts are subjected to heat treatment. Generally, when the forming temperature of the pipe of low carbon steel material is not lower than 723 ° C (recrystallization temperature), heat treatment is not required, because the microstructure of the pipe is basically under this temperature condition. The upper part is in a normalized state. When the temperature is lower than this temperature or higher than 980 °C, heat treatment should be carried out; the tube of alloy steel or stainless steel should be heat treated whether it is cold forming or hot forming.
Routine testing of heat treatment is generally done by a hardness test.
4 surface treatment
The surface treatment of pipe fittings is usually carried out by sandblasting, shot blasting, sanding, pickling, etc. to remove rust, scratches, etc. on the surface of the product, so that the product can reach a smooth surface and meet the requirements of subsequent processing and inspection.
For pipe fittings treated with shot blasting, the surface hardness will increase slightly.
The cutting process is a process of completing the welding end portion, the structural size, and the shape tolerance processing of the pipe fitting. For the machining of some pipe products, the machining of inner and outer diameters is also included. Machining is mainly done by special machine tools or general-purpose machine tools. For over-sized pipe fittings, when the existing machine tool capacity cannot meet the machining requirements, other methods can be used for machining, such as the method of gas-cutting after large-diameter elbows.
The appearance and dimensional inspection of the pipe fittings are usually carried out after the cutting process.
6 Non-destructive testing
Non-destructive testing is an important process for testing defects in materials and fittings. The requirements for non-destructive testing are specified in most pipe fitting product standards, but the requirements are not uniform. In addition to non-destructive testing in compliance with product standards and ordering requirements, some manufacturers with strict quality control also develop non-destructive testing requirements based on materials, processing techniques and internal quality control regulations to ensure the quality of manufactured products.
The determination of the level of non-destructive testing of pipe fittings in actual work shall be determined in accordance with the requirements of the ordering requirements or standards. Since the surface of the pipe is basically the original pipe, plate or forging condition, for the non-destructive testing (MT, PT) of the surface quality of the pipe, if there is no clear grade requirement, it can be grade II, but regardless of the qualification level, for the interlayer and Cracks, which are difficult to determine depth, should be considered unqualified. For the non-destructive testing (RT, UT,) of the internal quality of the pipe fittings, if there is no clear grade, the radiographic testing shall be in accordance with Class II (for example, the inspection of welds), and the ultrasonic testing shall be in Class I.
In order to prevent possible defects in the product during the heat treatment, the non-destructive testing of the pipe should be carried out after the heat treatment.
Non-destructive testing of pipe fittings in China usually uses the JB/T 4730 specification. Personnel engaged in non-destructive testing shall obtain corresponding qualifications in accordance with relevant regulations.
7 Surface protection
The surface protection of carbon steel and alloy steel pipe parts is usually painted, and the stainless steel is passivated after pickling (for all surface-cut stainless steel pipe fittings, it is not necessary to passivate). The main purpose of the surface protection of the pipe fittings is to prevent corrosion and at the same time achieve the appearance of the appearance of the product. Usually, the ordering party puts forward specific requirements for surface protection, and the manufacturer completes the protection of the surface of the pipe fittings according to the requirements of the ordering party.
Marks are an integral part of the product and are the basis for achieving traceability requirements. In general, the content and method of the logo are specified in the product standard. The marking content of the pipe fittings generally includes the manufacturer's trademark or name, material grade, specifications, and other contents of the ordering requirements. The method of marking includes permanent markings such as stamping, engraving, electric erosion, etc.; non-permanent markings such as printing, labeling, etc.
In addition to the above-mentioned conventional manufacturing process, in order to control the quality of raw materials, the manufacturer shall also complete the inspection of the raw and auxiliary materials to ensure the correctness of the materials used; in order to meet the special requirements of the order or materials, such as metallographic organization, intergranular Corrosion, ferrite and other inspections and tests to ensure that the products provided meet the customer's requirements.