Defects often occurred in the hottest welding and

2022-08-05
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Defects often occurred in welding and prevention methods

I. air holes produced by weld metal can be divided into: internal air holes, surface air holes and joint air holes, which are the mainstream suppliers of domestic automotive polyurethane products. 1. internal air hole: there are two shapes. One is that spherical pores are mostly produced in the middle of the weld. Causes:

(1) excessive welding current

(2) the arc is too long

(3) rod conveying speed is too fast

(4) the welding position is not clean

(5) damp welding rod, etc. The above causes of air holes can be solved by properly adjusting and paying attention to the welding process and operation methods. 2. surface porosity: Causes and solutions of surface porosity:

(1) porosity is easy to occur in base metal with high content of C, s and Si. The solution is either to replace the base metal or to use the welding rod of low hydrogen slag system

(2) the unclean welding part is easy to produce air holes. Therefore, it is required to remove oil, rust and other dirt before welding. The requirements for welding with low hydrogen electrode are more stringent

(3) excessive welding current. Make the coating on the back half of the welding rod turn red, and it is also easy to produce pores. Therefore, it is required to adopt appropriate welding specifications. The welding current should be selected randomly with the welding rod tail not red and left-right rotation, and the structure should be compact

(4) low hydrogen electrodes are easy to absorb moisture, so they should be baked at 350 ℃ for about 1 hour before use. Otherwise, air holes are easy to appear

3. Wave joint air hole: it is easy to have surface and internal air holes at the weld joint when using low hydrogen welding rod. The solution: when welding wave joint, the arc shall be started at the position 9 ~ 10mm away from the arc pit in the forward direction of the weld. After the arc burns, the rod shall be transported in the reverse direction to return to the arc pit, and then it shall be fully melted before moving forward, or arc striking at the weld can avoid this type of air hole

II. Cracks

1 Rigid crack: longitudinal cracks throughout the weld are often found during welding, which are mainly caused by the stress generated during welding. The welding stress is large under the following conditions: (1) the welded structure is rigid; (2) High welding current and fast welding speed; (3) The cooling rate of weld metal is too fast. Therefore, it is easy to produce longitudinal long cracks in the above cases. Solution: adopt reasonable welding sequence or preheat the workpiece if possible to reduce the rigidity of the structure. For extra thick plates and structures with great rigidity, low hydrogen electrodes shall be used with appropriate current and welding speed

2. Cracks caused by sulfur: cracks are easy to occur when the carbon and sulfur of the welded base metal are high or the segregation is large. Solution: preheat the construction parts by stages, or use low hydrogen electrode

3. Gap crack: the hairy crack is a hairy micro crack that occurs inside the deposited metal and does not develop to the outside. It is considered that the deposited metal is brittle due to rapid cooling, local stress and hydrogen. The way to prevent this is to slow down the cooling speed of the weldment, preheat the weldment if possible, or use low hydrogen electrode to achieve satisfactory solution. 3、 Arc generation bias blow

bias blow often occurs when low hydrogen electrode is used in DC welding machine. It can be solved by the following methods. 1. the line is set in the direction of creating a high-end talent team of new materials with a thousand people. 2. the line is divided into more than two. 3. welding shall be carried out in the direction of partial arc blowing. 4. short arc operation

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