What must be dropped into the mold prior to adding the welding material?

• A. Water
• B. A Protective Cap
• C. Coal Slag
• D. The Metal Disk

Answer: (D)

A metal disk is used as a backing insert in this mold-welding setup. Dropping the disk into the mold before adding the welding material gives a solid base that defines the weld root and contains the molten metal, helping control penetration and maintain the correct dimensions. It acts like a tiny backing plate, giving the weld something to fuse against and preventing the material from leaking through the mold as it fills. Water would create steam and porosity, coal slag is a flux used on the surface rather than inside the mold, and a protective cap isn’t placed in the mold for this purpose. So the metal disk is the insert that makes the weld possible and consistent.