Differences between hot-dip galvanized bolts and ordinary galvanized bolts
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Dear sea friends, I’ve run into a big problem recently. The company purchased a batch of hot-dip galvanized hex bolts, but upon receipt it was found that they could not be connected to threaded valves – only two or three threads would fit. Here, I would like to ask the experts: what is the difference in thickness between hot-dip galvanized bolts and ordinary galvanized bolts? Could anyone provide the relevant standards? Thank you in advance.
The galvanized coating is relatively strong. In the case of cold galvanizing, no heating is generally required, and the amount of zinc applied is small; such galvanized parts tend to peel off in humid environments. It can be seen that hot-dip galvanizing yields better results than cold-dip galvanizing; therefore, bolts are galvanized using hot-dip methods.
Typically, the thickness of an electro-galvanized layer is 5–15 μm, while that of a hot-dip galvanized layer is generally over 35 μm, and can even reach up to 200 μm. (Excerpt from Baidu Baike)
Why doesn’t the poster confirm whether the thread type is the same? If the thread pattern is different, it won’t fit no matter whether it’s zinc-plated or not; 2–3 mm of penetration is already quite good.
I also think it’s not an issue with the galvanizing thickness; such a thin layer wouldn’t prevent it from being screwed in. A mismatch in thread form might be the key.
The standards for threads are different; for NPT and RC threads, only 2-3 turns are possible.
The technical requirements for the purchase were incorrect; bolts with cold galvanizing should have been specified； Hot-dip galvanizing, due to the difficulty in accurately controlling the thickness of the coating, naturally makes it hard to tighten bolts.
Try applying some oil; it’s a red, paste-like substance
For nuts used with hot-dip galvanized bolts, drilled nuts should be chosen, as the thick zinc coating prevents the threads from being accessible. Secondly, when purchasing hot-dip galvanized bolts, it is best to choose those with a dull appearance, as such bolts generally do not suffer from zinc runoff.
If it’s really a problem with the galvanizing, then one can turn to an electroplating factory; if the thread specifications are incorrect, then the threads need to be measured carefully