What causes the combination screws to be tightened?

Xiaobian previously said that many screws are too tight to be taken down. This problem is a problem that many users have encountered, but I don't know if anyone has encountered the problem of screws not being tightened. This problem is definitely encountered by some people, but this situation is relatively rare. Generally, if you encounter such a problem, you can just change it directly, but if it is a screw problem, then we will definitely lose something. Then we will Let's find out what causes the combination screws to be undertightened?
First of all, we repeated the inspection test on the product at the construction site, and eliminated the situation that the product was not tightened due to grooves, pits, and oil on the surface of the combined screws, welding nuts, and washers. Through analysis and comparison with similar products with surface phosphating treatment, it is found that the problem that the batch of products cannot be tightened tightly enough to reach the pre-tightening force value lies in the surface treatment method and process. Because the oxide layer is too thick, the combined screw is not tight, so that the phenomenon of failing to meet the pre-tightening force value occurs.
 
    During the alkaline oxidation treatment of the combined screw, the higher the concentration of the oxidant in the solution, the faster the oxide film is generated, and the denser and stronger the film layer is. If the concentration of the alkali in the processing solution is added, the thickness of the obtained oxide film increases. Conversely, if the content of alkali is too low, the oxide film is weak. Properly increasing the temperature of the treatment solution can increase the density of the oxide film.

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