Welding technology treatment of welding ball valve

  Welding types mainly include: 1 Electrode arc welding; 2 Submerged arc welding (automatic welding); 3 Carbon dioxide gas shielded welding (automatic or semi-automatic welding); 4 MIG / MAG welding (GMAW; 5 TIG welding (tungsten inert gas shielded welding); 6 Plasma arc welding The principle and application of each method are different, because it is not the focus of this paper Point, so you can simply know, the following focuses on the welding technology treatment of welded ball valve: the welding of welded ball valve is actually different from the ordinary welding technology, because there are non-metallic sealing materials rubber and polytetrafluoroethylene plastic in the valve chamber, which cannot be heat treated after welding The thick wall and multi-layer welding process of welding ball valve is the process of repeated heating and cooling of metal materials Generally, its welding joints are designed as narrow gap thick wall submerged arc welding, and most of the valve bodies that use full welding are the welding joints with super thick cylinder shape Therefore, the stress concentration, residual stress and poor structure of the root gap of the valve body welding joint become the weak link in the valve body structure At present, there are two ways to deal with it: 1 Heat treatment technology; 2 It is the joint treatment; these two treatment methods will produce stress concentration several times of normal working stress, which also makes it difficult for engineers of manufacturers to handle It can be seen that how to solve the problem that the stress concentration, residual stress and poor organization of the root gap of the welded joint of the valve body of the welded ball valve become the Zui big problem of the valve welding The manufacturer of Quancheng brand all welded ball valve here summarizes the key points of the valve body welding technology as follows, hoping to help all friends who want to know about the ball valve welding technology! Now the welding process of the valve body is introduced as follows 1 Technical requirements for valve body (1) the valve body shall be free of deformation after welding, including upper and lower shaft flange (45 steel) (2) the heating area of the valve body shall not be too wide and the temperature shall not be too high, otherwise the sealing device in the valve body will be damaged (3) no weld beading (4) ensure that the pressure is above 10MPa 2 According to the above technical requirements, the weld structure is determined as non penetration weld Therefore, it is required that the butt joint form of the weld can ensure both assembly and non penetration After the test, Zui determines the weld form 3 The material of the valve body is zg15 Ⅱ, so the chemical composition of the valve body is tested before processing The test results are consistent with the test results during casting and meet the design requirements 4 The hydraulic press is used to refit the turning tire for positioning, and the surrounding two halves are fastened with bolts, and the adjustment is carried out for sealing test The outer part of the ball and the valve body meet the design requirements 5 Considering the technical requirements of the valve body, Zui finally chose MAG CO2 welding machine ER50-6 (Ø 1.0) welding wire is selected as welding material According to the principle of equal strength of welding materials, the ER50-6 (Ø 1.0) welding wire selected meets the requirements of zg15 Ⅱ The shielding gas is a mixture of 82% Ar + 18% CO2 5.1 due to the serious hardening tendency of the cast steel and 45 steel in the tack welding, it is necessary to preheat them before the tack welding The oxygen acetylene flame shall be used to evenly heat them to 75-100 ℃ (biased to 45 steel side) within the range of two times of the plate thickness on both sides of the weld, whichever does not affect the sealing device, and the far red outer line thermometer shall be used for measurement Before welding, the oxide skin and rust on both sides of the weld within 20 mm shall be polished with angle grinder to produce metallic luster Make 6 positioning points at the position 50 mm from both sides of the weld to the edge, and measure the distance between the two points with a caliper, so as to measure the shrinkage 5.2 due to the characteristics of large rigidity and poor plasticity of zg15 Ⅱ material, small welding parameters, i.e small welding heat input, should be adopted in the selection of welding specification for back cover welding On the premise of ensuring the weld quality, try to improve the welding speed and reduce the fusion ratio In terms of deformation, adopt the method of multi-layer, multi-channel and 6-SECTION symmetrical welding; pay attention to the use of calipers to measure the positioning points of each welding layer and control the shrinkage until the welding is completed Except for the later one of * and Zui, the other channels shall be stress relieved by hammering 6 After Zui completes the welding in the next step, there is no leakage at the welded junction through the pressure test (air tight), and the sealing surface meets the technical requirements After the X-ray flaw detection, the weld itself has no welding defects such as porosity, slag inclusion, lack of fusion, crack, etc., and the valve core rotation meets the technical requirements.