Q1: Hot dipping process is used for coating a low melting point metal (e.g. Pb, Sn, Zn) on iron, steel & copper having relatively higher melting points. Which of the following is not a hot dipping process ?

ANS:C - Sheardising

Sheardizing is a hot-dipping process used to provide corrosion protection to iron and steel components by applying a layer of zinc-aluminum alloy onto their surfaces. The process is similar to galvanizing, but it involves the use of a zinc-aluminum alloy instead of pure zinc. Here's how the sheardizing process typically works:

1. Preparation of the Substrate: The iron or steel component to be coated is thoroughly cleaned to remove any surface contaminants, such as dirt, grease, or rust. This ensures good adhesion of the coating to the substrate.
2. Preheating: The cleaned substrate is preheated to a specific temperature, typically around 350-450°C (660-840°F). Preheating helps to promote the bonding between the substrate and the molten zinc-aluminum alloy.
3. Dipping: The preheated substrate is then immersed in a bath of molten zinc-aluminum alloy. The composition of the alloy may vary, but it typically contains a mixture of zinc and aluminum in specific proportions. The temperature of the alloy bath is maintained within a certain range to ensure proper coating adhesion and alloy composition.
4. Diffusion and Bonding: When the substrate is immersed in the molten alloy, diffusion and intermetallic bonding occur between the alloy and the surface of the substrate. This results in the formation of a metallurgical bond between the coating and the substrate, providing excellent adhesion and corrosion resistance.
5. Cooling and Solidification: After a specified period of time in the molten alloy bath, the coated substrate is removed and allowed to cool. As the substrate cools, the molten alloy solidifies to form a uniform and protective layer on its surface.
6. Post-Treatment (Optional): Depending on the specific application requirements, the coated component may undergo further treatments, such as quenching or passivation, to enhance its properties or appearance.

Sheardizing offers several advantages over traditional galvanizing processes, including improved corrosion resistance, better adhesion, and enhanced durability. It is commonly used in various industries, including automotive, construction, and manufacturing, for applications where corrosion protection is critical.