Post-welding treatment and spatter avoidance for operation of Mechanical Structure

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In manufacturing field, carbon steel is one of most popular material types selected by metal working factories. Those are maturely cut by CNC Flame Cutting Equipment or Multi-strip Cutting Machine and welded by column and boom manipulator. As compared with carbon steel, high-strength structural steel with low-alloy has higher strength, but has good plasticity, toughness and appropriate for welding, it is widely used in the field of construction machinery. In the formation of low-alloy high-strength steel construction machinery structural parts, the welding method has the advantages of metallurgical bonding, high bonding strength, flexible and convenient operation, etc. Compared with riveting and bolt connection, it becomes an important processing method.

 

Construction machinery welding process includes three parts: preparation before welding, ongoing welding process, and post-welding treatment. Among them, the post-welding heat treatment is very critical, which can improve the structure of the weld, improve the comprehensive mechanical properties, and ensure and extend the service life of the structural parts. Post-welding treatment includes post-welding heat treatment, post-weld spatter removal, welding slag, etc.

 

1. Post-welding heat treatment

 

1) Post-welding heat treatment at low temperature

For welded joints with strength lower than 650MPa or less restrained, low-temperature post-heat treatment is adopted, that is, the entire weld is heated to 150-250 ℃ immediately after welding, and the temperature is kept for 1-2 hours.

 

2) Hydrogen elimination treatment

For welded joints with a strength higher than 650MPa or with a greater degree of restraint, dehydrogenation treatment should be performed to accelerate the diffusion rate and escape of hydrogen. The temperature of dehydrogenation treatment is between 300 ~ 400 ℃, and the time is 1 ~ 2h. The dehydrogenation treatment must be carried out immediately after the welding of the weldment is completed, and at the same time, it can also play a role in reducing the intermediate stress of the welding.

 

Due to the limitation of large workpieces and long production cycle, it is impossible to achieve overall heating, and local hydrogen elimination treatment can be used. Specific operation method: heat the welding seam and the surrounding 100mm uniformly to 300 ~ 350 ℃, keep it warm for 1.5 ~ 2h, slow cooling; slow cooling method is to cover (enclose) the welding seam insulation blanket, cool to below 50 ℃, and then air cool to Normal temperature. When a welding seam is stopped after being welded, it must be partially dehydrogenated immediately. When welding continues, preheating must be performed. The methods of preheating and dehydrogenation are the same as above.

 

When single-sided bevel welding is performed on plates with a thickness of ≥35mm, intermediate hydrogen removal treatment is required during the welding process. The hydrogen removal treatment method is the same as above; the welding is continued when it is cooled to 100 ~ 150 ℃, and must be carried out after welding Dehydrogenation treatment.

 

2. Splash and slag after welding

 

After welding is completed, only flat chisel and elastic grinding discs can be used to remove welding slag and spatter. Especially after the arm is welded, grinding machine is not allowed to grind.

 

By formulating reasonable post-weld treatment, it can optimize the welding quality and finally achieve the goals of high quality, high efficiency and low cost.

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