Which casting defect is produced when two streams of molten metal meet and do not fuse properly?

• A. A cold shut
• B. Blow hole
• C. Burst
• D. Flaking

Answer: (A)

When two streams of molten metal meet and fail to fuse, the result is a cold shut. This happens because the metal fronts solidify before they bond, so the joint remains unjoined or only loosely fused. You’ll often see a distinct seam or line on the casting, and in thicker sections the bond may be weak, creating a path for cracks to start.

Causes include pouring temperature that’s too low, metal that's too viscous or too cool to bond cleanly, restricted or turbulent flow that causes premature solidification, and oxide films or dirt on the metal surfaces preventing bonding. Remedies focus on keeping the metal hot enough and flowing smoothly: raise the pouring temperature within the alloy spec, optimize the gating and venting to promote steady, laminar flow, reduce chill near the joint, preheat the mold, and ensure metal cleanliness.

Other defects—like blow holes (gas porosity from trapped gases), bursts (mold or metal expansion issues), or flaking (surface scale from oxidation or improper heat treatment)—result from different mechanisms and aren’t caused by two fronts failing to fuse.