Hot-dip plating involves immersing pre-treated copper products into molten low-melting-point metal liquid (such as tin or aluminum), leaving them for a while before removing them and cooling them down. After cooling, a layer of metal coating will form on the surface.
1. Process principle and characteristics
(1) Principle: When clean copper products come into contact with molten metal, there will be infiltration, dissolution, and diffusion reactions, eventually cooling and solidifying to form a composite coating consisting of an alloy layer and a pure metal layer.
(2) Characteristics: The coating is relatively thick (from tens to hundreds of micrometers), has a long-lasting protective effect; it adheres particularly well to the substrate; it is suitable for large-scale continuous production (such as copper wires and copper strips); however, it requires a lot of coating metal and needs high-temperature heating, resulting in high energy consumption.
2. Hot-dip plating of copper and copper alloys
The melting point of copper is relatively high, so copper is rarely used as the coating metal for hot-dip plating. However, copper and copper alloys are often used as substrates for hot-dip plating with tin, aluminum, etc.
(1) Hot-dip plating of copper wire/copper strip with tin: This is mainly to make copper easier to weld and prevent oxidation. The process flow is: unwinding the wire → cleaning → pickling → water washing → post-treatment (using a special solution to prevent copper oxidation) → preheating → immersing in tin liquid → controlling the coating thickness → cooling → winding up.
(2) Key control points: The temperature of the tin liquid should be controlled at 240-280℃; the immersion time is very short, only a few seconds; the post-treatment agent is crucial and must be dried; the thickness of the alloy layer in the coating should be controlled well; it should not be too thick as it will make the coating brittle and affect subsequent use.
(3) Quality control: Ensure that the copper surface is clean and free of oxidation; the concentration of the post-treatment agent should be stable and the drying should be thorough; control the composition and temperature of the tin liquid; adjust relevant parameters to ensure uniform coating thickness.