What is the purpose of shot blasting in preparation for coating?

• A. It cools the steel rapidly to prevent warping.
• B. It cleans the air around the site.
• C. It applies primer coating.
• D. It cleans and roughens the surface to improve coating adhesion and remove mill scale, oil, and corrosion products.

Answer: (D)

The key idea is preparing the metal surface so the coating can bond effectively. Shot blasting uses abrasive media hurled at the steel to strip away contaminants such as mill scale, oil, dirt, and corrosion products, and to roughen the surface to create an anchor pattern. That combination—cleanliness plus a rough texture—lets the primer and the topcoat adhere much more securely, improving the coating’s long-term performance and resisting peeling or blistering.

This isn’t about cooling the metal, cleaning the air at the site, or applying primer. Cooling isn’t the goal of shot blasting, and while it may generate some heat, the purpose isn’t temperature control. It doesn’t purify the air, and primer is applied after blasting as a separate step to begin the coating system.