Misruns

Misrun is a casting defect in which molten metal fails to completely fill the mold cavity, producing an incomplete or undersized section in the finished part. It is commonly observed in metal casting processes such as sand casting, die casting, and investment casting, but can occur in any molding process that relies on full fill of the cavity.

Causes of misruns include insufficient pouring temperature or metal fluidity, gating systems and runner layouts that restrict flow, and inadequate venting that allows air to become trapped. Premature solidification in thick sections, corners, or hot spots can also block further filling. Design errors in the mold or pattern, slag or inclusions, and issues with feeding systems can contribute as well.

Consequences typically involve compromised structural integrity and dimensional accuracy, leading to rejection or costly rework. Small misruns may be detected during finishing or inspection, while larger ones are evident on external surfaces or within the part.

Detection and prevention emphasize process control and design for fill. Visual inspection and non-destructive testing can identify misruns, though many are caught during quality checks after molding. Prevention focuses on proper gate and riser design, adequate venting, sufficient metal head pressure, and uniform wall thickness to promote even fill and solidification. Controlling pouring temperature, melt treatment, and mold temperature also helps maintain adequate fluidity and filling capability.

Remedies for a misrun typically involve scrap or re-melting and re-casting. In some cases, small, superficial misruns may be corrected through machining or welding, but these are limited and not universally applicable.