For the first post-weld expansion process, the primary problem is to control the accuracy of the tube and tube plate holes and their cooperation. When the gap between the tube and the tube tube hole is small enough, the expansion process will not damage the quality of the welded joint. However, the ability of the welded joint to withstand shearing force is relatively poor. Therefore, if the control fails to meet the requirements during the strength welding, the over-expansion failure or the expansion joint may damage the welded joint.
In the manufacturing process, there is a large gap between the outer diameter of the heat exchange tube and the tube hole of the tube sheet, and the outer diameter of each heat exchange tube and the tube tube hole gap are not uniform in the axial direction. When the expansion is completed, the center line of the pipe must coincide with the center line of the tube hole of the tube to ensure the joint quality. If the gap is large, the expansion of the tube will be large due to the rigidity of the tube. Damage, and even cause the weld to be desoldered.
Welding and expansion joints can be divided into first post-weld expansion and first expansion and post-weld according to the processing conditions. The advantages and disadvantages are as follows:
The first post-expansion welding manufacturing process requires high cleaning of the tubes and tube sheets, otherwise manufacturing defects are easily generated. However, the post-weld expansion requires less cleanliness of the tube sheets and tubes.
After the first expansion and after welding process, the welding has an adverse effect on the expansion joint, and it is easy to cause the expansion joint to relax. The gas generated during welding is not easy to be removed, and weld defects are prone to occur, and the first post-weld expansion can fundamentally avoid this.
From the aspect of weld quality and use effect, the first post-weld expansion process is also much better than the post-expansion post-welding process.
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