Electroplating of Hardware Screw Fasteners to Master Four Points to Control Quality
1. Appearance: Any surface defects such as local plating, burning, roughness, grayness, peeling, crust, and obvious stripes not only affect the aesthetics of hardware screw products but also may indicate potential issues with the electroplating process. These defects can lead to a reduction in the corrosion resistance and durability of the screws, shortening their service life. For example, peeling of the coating can expose the base metal to the environment, accelerating rusting and weakening the structural integrity of the fasteners.
2. Hydrogen embrittlement: To prevent hydrogen embrittlement, it is essential to control the processing conditions during pickling, alkaline washing, and plating. Using appropriate inhibitors during pickling can reduce the absorption of hydrogen atoms. Additionally, performing a baking treatment after plating can help to drive out the absorbed hydrogen. This baking process should be carried out at a specific temperature and for a certain duration to effectively remove hydrogen without affecting the properties of the fasteners. For instance, a baking temperature of around 190 - 230°C for 2 - 4 hours is commonly recommended for most metal screw fasteners.
3. Coating distribution: When dealing with screws of complex shapes, the coating distribution becomes even more critical. For example, in screws with irregular threads or intricate head designs, the electroplating method significantly affects the uniformity of the coating. Traditional electroplating may result in uneven coating thickness at different parts of the screw, while mechanical plating tends to provide a more uniform coating due to its unique deposition mechanism. However, hot dip galvanizing might deposit a thicker coating at certain recessed areas, which could potentially affect the fit and function of the screw in some applications. Understanding these differences helps manufacturers choose the most suitable electroplating method based on the specific requirements of the screw.
4. Coating thickness:In a highly corrosive marine environment, hardware screw fasteners used in shipbuilding or offshore structures require a thicker coating to ensure long-term performance. For example, screws exposed to seawater should have a coating thickness close to the upper limit of the recommended range, preferably around 12 um for economical electroplating or even thicker for hot dip galvanizing. On the other hand, screws used in indoor applications with relatively low corrosion risks can have a thinner coating, but still within the recommended thickness range to maintain a certain level of protection. This customization of coating thickness based on the application environment helps to optimize the cost and performance of the screw fasteners.
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