JINGBANG has been engaged in the screw industry for more than 10 years. Occasionally, we will receive feedback from customers that the mechanical screws break during the assembly process. It is suspected that the material, heat treatment, structure and other problems of the screw. Today, the editor will make a comprehensive report on the problems often encountered on this production line. analysis.
First of all, when a mechanical tooth screw breaks, it is easy to conclude that the quality problem of either the screw or the nut is not objective and one-sided. The so-called no right to speak without investigation is like going to see a Chinese medicine doctor when you are sick. Same. The fracture of the mechanical tooth screw during the assembly process depends on the location of the fracture and the situation. Generally, the fracture of the screw shaft and the root (the junction of the head and the shaft) are common. Then we will analyze these two situations separately. one time.
1.Fracture of the rod: The qualified mechanical screw and the qualified nut hole can be easily screwed to the bottom in theory and in practice (the anti-loosening treatment is another matter). If the screw shaft breaks during the assembly process, there must be a problem with the fit of the two parts. In addition, the actual assembly torque exceeds the threshold of the corresponding material screw. Generally, there is a problem with the structure of the screw or nut hole. The probability of the two parts having a problem and assembly at the same time is very low, but this possibility is also possible. The judgment method is very simple, assemble a batch by hand or standard assembly torque to find out the stuck screws and remove them, then use the go-no-go gauge to test and analyze the two parts separately. The common problems of screws are poor thread teeth, such as oblique teeth, rotten teeth, and nut holes. In addition to poor structure, it is common that there are residues in the holes that block the track, and there are also secondary surface treatments that do not protect the screw holes and cause powder accumulation on the screw teeth. Oil plugging, usually blind hole is the most common. It is necessary to mention here that even if the hole is blocked and cannot be screwed in, the shaft of the machine screw will not break easily under the standard assembly torque. It is necessary to check whether the torque setting meets the standard, and whether the production line personnel have adjusted and increased the torque value without permission. It is also necessary to check whether the assembly tool is qualified, and whether it will be automatically protected after reaching the set torque. If the screw is blocked and twisted within the standard torque range, it is necessary to check the torque of the screw.
2.Root fracture: Root fracture is when the mechanical screw is screwed to the bottom and the assembly torque quickly reaches the peak value when the screw and the parent part form a clamping force. In this case, it is generally necessary to check whether the torque of the electric batch tool is set reasonably, and whether the groove of the screw is too deep, so that the wall is too thin to withstand the tension and pinching force formed by the peak torque of the standard assembly. If there is no problem with the assembly torque and screw structure, it is necessary to consider whether the design of the screw (non-standard) is reasonable, and whether the heat treatment process is standardized (either hard or soft). If it is a high-strength screw, it is generally above 10.9 (including 10.9 and 8.8) The upper limit of grade heat treatment has reached the 10.9 standard screw) If the galvanized series involves the problem of hydrogen embrittlement fracture.