Please take a look and see if the fracture surface of this shaft is due to fatigue fracture
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This post was last edited by shuimufeng111 on 2019-8-27 at 15:43. The main shaft of the dryer that had been in use for 2 years suddenly broke, at the location indicated by the orange circle. I just took a picture of the fracture surface; please analyze whether it is fatigue fracture. The broken shaft on the other side has been replaced.
Strictly speaking, it is due to improper processing of the shaft tube and shaft head structures, as well as insufficient emphasis on welding; as a result, the designed lifespan cannot be achieved!
Stair steps inherently have stress concentrations, and microcracks are bound to occur during the manufacturing process; as a result, fatigue damage or even fracture is a common occurrence.
The last edit to this post was made by Daoting Tusuo123456 on 2019-8-28 at 08:56. There are indeed some issues with the design; the area that has been welded together has a thickness of only 10.5 mm, which results in too much stress being concentrated at that point. Why not extend part of the fitting into the inner hole of 248 (using an interference fit method)? I misread it – it seems that part of it is already extended inside. Then why weld in that 10.5-mm-thick 304 material there? If the stress isn’t fully relieved after welding, problems can easily occur
This shaft does not appear to be a single, integrated unit; it seems to be joined at this point. The highlighted area on the outer ring is the welding site. From the image, it seems that the welds in some areas are not fully complete. Logically speaking, such a large solid shaft should not have any problems under any operating conditions; it’s more likely that the blades inside the dryer are the ones that have issues.
This post was last edited by gjn1970 on 2019-8-28 at 11:09. In this design where the shaft is fitted into a hole and then fixed by welding, it is unreasonable to use welding; welding generates stress, and in principle welding should be avoided on shafts. Moreover, this stress acts precisely on the stress-concentrated area at the shoulder, which is also the main cause of fracture. It is likely a fatigue fracture – cracks first form, then continue to spread, and finally the shaft breaks suddenly under an impact load. The solution is to arrange three anti-rotation pins symmetrically at the shoulder part of the pin fit, and the problem can be resolved.