Application of the hottest mixed gas shielded weld

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Research on the application of mixed gas shielded welding in B23 mechanical refrigerator car

Abstract: the solution for the large-scale assembly and retail of mechanical refrigerator car and the supply chain compliance of industrial manufacturing industry. The side wall seal welding requires high sealing performance for the weld, while the underframe requires high internal quality for the weld. Mixed gas shielded welding has high internal and external weld quality. Through the research on the influence of mixed gas ratio on welding quality, the reasonable gas ratio and welding process are put forward. Key words: gas shielded welding process for mixed gas ratio of machine cooled car domestic B23 mechanical refrigerator car belongs to the international advanced level in the early 1990s, and has high requirements for welding quality. CO2 gas shielded welding used in the past is difficult to ensure the welding quality of products due to its disadvantages such as large spatter, undercut, many air holes that should be replaced, poor weld formation, etc. However, mixed gas shielded welding is gradually being popularized and applied because of its advantages such as small spatter, less undercut and air hole, beautiful weld formation and large penetration. Therefore, since the first half of 1997, the factory began to study the welding process of mixed gas shielded welding in the production of domestic B23 mechanical refrigerated trucks. 1、 Test method and results

the base material for the test is the weathering steel 09CuPTiRE, which is butt jointed, and the plate specification is 215mm × 2200mm × 200mm, the welding wire is 110 H08Mn2SiA welding wire. The experiment mainly studies the influence of mixed gas ratio on spatter, air hole, undercut, weld formation and mechanical properties. When sampling the test piece, remove 100mm from the initial welding position and 100mm from the final welding position (as shown in Figure 1). In the welding experiment, different mixture gases are obtained by adjusting the ratio of ar2 and CO2 gas, and then the welds under different mixture gases are compared to find the best mixture ratio. During the test, the mixture ratio shall be adjusted by 10% each time. 1. Effect of mixed gas on spatter

adding CO2 to the shielding gas increases the oxidation of the shielding gas, thus reducing the surface tension of metal droplet separation, and the droplet is easy to fall off from the welding wire, reducing spatter. By adjusting the argon content in the mixed gas and making statistics on the spatter points greater than 110mm on both sides of the weld, the relationship between the mixing ratio and spatter is obtained, as shown in Figure 2. 2. Effect of mixed gas on porosity

adding CO2 to the shielding gas improves the thermal conductivity of the gas, improves the fluidity of the molten pool, and reduces the tendency of pore formation due to the stirring effect of the arc. Count the pores ≥ 110mm on the surface of the test piece to obtain the relationship between the ratio of mixed gas and pores, as shown in Figure 3. 3. Influence of mixed gas on undercut

as the arc pushing force of mixed gas shielded welding is uniform and gentle, 2. There are 3 sample baskets, and the droplet is refined, so that the molten pool metal can be well connected with the base metal, thus reducing the undercut tendency. Count the undercut with depth ≥ 015mm in the test piece, and obtain the relationship between the mixture ratio and the undercut, as shown in Figure 4. 4. Influence of mixed gas on weld formation

adjust the ratio of mixed gas for welding. Through visual inspection, it is found that when the argon content in the mixed gas is in the range of 60% ~ 80%, the weld is beautiful. 5. Effect of mixed gas on mechanical properties

due to the addition of a certain proportion of inert gas argon in the mixed gas, compared with carbon dioxide gas shielded welding, the oxidizability in the shielding gas is weakened, and the reduction of oxygen and carbon entering the molten pool leads to a great reduction of oxide impurities in the metallurgical reaction process of the molten pool. The crystallization is uniform and orderly, which makes the weld metal grain more refined, and the reduction of pores, undercuts and microcracks in the weld, Thus, the mechanical properties of the weld are improved. Due to the limited experimental means, this test is limited to the study of strength and plasticity

when sampling the mechanical property test piece 5.4 frost resistance, cut the welded piece into about 10mm along the longitudinal direction of the weld × 200mm test pieces (as shown in Figure 5), 6 pieces in each group, and then conduct tensile and bending tests. The experimental results show that the welded specimens can reach 180 ° cold bending without cracking under all proportions, while the tensile specimens are all fractured on the base metal. 2、 Application example

in the production of mechanical refrigerated vehicles, some processes such as body assembly and side wall sealing welding require good weld appearance quality and tightness, while some important components such as sleeper beam and traction beam require high weld internal quality to withstand various complex stress conditions during vehicle operation. Therefore, mixed gas shielded welding is required in the welding of these processes. 1. The ratio of mixed gas is 80% argon + 20% carbon dioxide. When there is no commercial mixed gas at present, argon and carbon dioxide are used for gas supply respectively, and then the gas is distributed through the proportioner. When the single gas pressure is ≤ 015mpa, the gas supply shall be stopped

2. 110 or 112 H08Mn2SiA welding wire shall be used as welding wire. 3. The extension length of welding wire rod is slightly smaller than that of carbon dioxide gas shielded welding, generally 12 ~ 15mm. 4. Connection method DC reverse connection method

5. Welding current: flat welding 120 ~ 150A, horizontal welding 90 ~ 130a, vertical welding 90 ~ 120a, vertical welding is downward welding. 6. The arc voltage is 1 ~ 2V lower than that of CO2 gas shielded welding, generally 25 ~ 27V

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