Analysis of the cause of crack in the frame of jaw crusher
Author:xixi Addtime:2019-07-15 Click:
The porosity and crack in the welding frame of jaw crusher are the main causes of the cracking of the frame, and the causes of the holes and cracks in the frame are as follows:
1 ) The ambient temperature is low : because the welding is in winter , the hoop temperature is lower than 0 ~ C . When welding at low temperature , the crack tendency is increased due to the faster cooling rate of the weld metal , especially Q345 , because its alloy element content is higher than that of low carbon steel , the hardening tendency is lower than that of low carbon steel , and the tendency to crack at low temperature is larger .
2)Crusher welding rod drying: due to the shell crusher frame welding, the welding seam is manual arc welding, the electrode used is low hydrogen type E5016. The welding rod is required to be dried for 2 days with 350% 40%, and it is easy to be used after heat preservation. However, by tracing the welding process, it is found that the drying temperature of the electrode is only about 200 ℃, so that the moisture adsorbed in the electrode coating and the crystalline water in the coating composition can not be removed, thus increasing the porosity and crack tendency caused by moisture.
3)Welding piece cleaning: the electrode E5016 is sensitive to water, oxidation, rust and oil stain on the surface of the welding piece, so it is necessary to clean the surface of the welding piece strictly in order to prevent the blowhole. However, the process is not strictly executed in the actual welding process, which makes the porosity and crack tendency increase.
4)restraint stress: the structure of the main welding seam of the frame is closed weld, and the welding sequence is straight through welding, which results in larger welding stress and restraint stress.
5）After heat, hydrogen elimination measures: low-alloy high-strength steel welding cold cracks, weld hydrogen is the main culprit. Preheating before welding and heat after welding can reduce cooling rate, prolong cooling time and release hydrogen more fully after welding, thus reducing hydrogen content in weld seam and reducing cold crack and material hardening. The heat after welding can not only make the hydrogen fully escape, but also reduce the residual stress and the hardening of the material to some extent. The preheating temperature can be compensated by choosing the appropriate post-heat temperature.
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