Analysis of undercut defects of large steel castings

1. Manifestations of undercut defects

Undercut is the result of electric arc scouring or melting the base metal near the seam and failing to fill, as shown in the figure. Undercut defect is a common kind of welding defects. Local notch will increase the stress value, and serious undercut will affect the quality of castings and even produce crack defects.

2. Main measures to prevent undercut defects

In order to prevent undercut defects, the following measures shall be taken:

① Reasonably select the welding process parameters, and reasonably select the welding current, strip transportation speed, electrode angle, etc. according to the distribution position of defects, so as to ensure complete melting and sufficient molten metal filling in the molten pool. Most of the defects in large steel castings are “U” shaped defects. Take vertical welding defects as an example. In the welding process, pay special attention to ensure that the welding rod shall stay for 1 s ~ 3 s at both edges, and the included angle between the welding gun and the molten pool shall be controlled at 45 ° to ensure complete fusion. The welding current should not be too large and should be controlled at 180 a ~ 230 a;

② In the selection of welding rod specification, the spot defect or the part with defect width less than 25 mm shall be selected φ 3.2 mm or φ Repair welding with 4.0 mm electrode.

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