We all think that galvanized screws won't rust, but that's not the case. After galvanizing, screws don't become completely rust-proof-they just delay the onset of rust. Therefore, the requirements for their surface treatment during use are crucial. Only surface treatments that match the environmental conditions can optimize the rust resistance of galvanized screws. Of course, galvanized screws aren't the best in terms of corrosion resistance among all surface treatments, but they have the largest market share among fasteners with surface treatments. Compared to Dacromet and hot-dip galvanizing, galvanizing is the most widely used.
Before production, relevant technical parameters for galvanized screws are clearly specified in the drawings, including wire drawing dimensions, mold size, thread standards, and even strict requirements for packaging. Only by documenting these standards can implementation be ensured; verbal instructions alone cannot achieve standardized production.
But why do galvanized screws still rust even when produced according to standards? In fact, surface galvanizing of screws is a conventional process. For better rust resistance, galvanizing is indeed inferior to hot-dip galvanizing or Dacromet treatment. If design permits, these two treatments-with longer rust prevention periods-can be chosen instead. The primary purpose of galvanizing screws is rust prevention, with additional benefits of moderate aesthetics and ease of installation. Their corrosion resistance is mainly suitable for indoor fixed environments, providing basic rust protection. If a galvanized screw is used in a highly corrosive environment like a coastal area, it will likely become severely rusted within a year.
Thus, rusting of galvanized screws isn't entirely a quality issue. (Of course, if galvanized screws frequently rust in normal environments, it's definitely a problem with the galvanizing process; in harsh environments where galvanizing is clearly unsuitable by design, rusting is another matter.) The root cause must be found in the design, which must align with actual usage requirements.
If screws rust before use, we need to check if they were improperly handled. Sometimes, after transporting screws from the galvanizing plant to the warehouse, their surface temperature hasn't cooled down yet. If sealed in packaging immediately, temperature differences between the inside and outside of the package cause moisture condensation. This condensation is highly corrosive to the screw surface, leading to rust in a short time. Therefore, the timing and process of packaging and warehousing are also critical.
Storage environment is another key factor. Storage areas for galvanized screws must have ventilation facilities. For example, in Wuxi, Jiangsu, the plum rain season from May to June brings severe indoor humidity. Storing galvanized screws in such humid conditions will cause them to rust quickly.
The final reason for rusting relates to the manufacturer. If a galvanized screw manufacturer has inadequate technology, resulting in defects in the zinc coating on the threads, rusting will inevitably occur.
