Casings are prone to the following eight categories of typical defects during production, classified according to their causes and characteristics:
Porosity Defects
Porosity: Gas fails to escape in time, forming smooth-walled circular/pear-shaped pores (divided into invasive, precipitating, and reactive types). Commonly found subsurface or internally, reducing density and fatigue strength.
Shrinkage Cavities & Porosity: Caused by insufficient feeding during solidification shrinkage. Shrinkage cavities are concentrated large pores (mostly at hot spots/riser roots), while shrinkage porosity are dispersed micropores (microscopic level), severely affecting load-bearing capacity.
Sand Holes/Slag Holes: Sand-containing/slag-containing pores formed by molding sand falling off or molten slag being entrained. Sand particles are visible on the surface or there may be internal inclusions.
Surface and Forming Defects
Sand Adhesion: Molten metal seeps into the mold, causing difficult-to-remove sand particles to adhere to the surface (divided into mechanical/chemical sand adhesion), increasing cleaning difficulty.
Cold shuts & incomplete filling: Insufficient filling capacity leads to incomplete fusion of the metal flow (cold shuts have rounded corner gaps) or casting defects (incomplete filling), often occurring in thin-walled/far-end areas.
Sand inclusions/scalds: The surface of the sand mold arches and fractures due to heat, embedding into the casting, forming grooves or flaky protrusions.
Misalignment: Misalignment between upper and lower sand molds causes misalignment of the parting surface and dimensional deviations.
Cracks and Structural Defects
Cracks: Divided into hot cracks (formed at high temperatures, with a dark gray oxide fracture surface and rounded edges) and cold cracks (cracks caused by low-temperature stress, with a metallic luster and sharp edges), often originating from sharp corners, uneven cooling, or residual stress.
Segregation: Uneven distribution of chemical composition (such as impurities enriched at grain boundaries) weakens high-temperature performance and easily induces subsequent cracking.
Deformation/missing material: Uneven demolding stress or handling damage leads to geometric distortion or localized missing material.
Note: Some defects are repairable (e.g., minor porosity/sand holes repaired by welding, micro-crack penetration), but severe shrinkage cavities and through cracks usually require scrapping. Prevention hinges on optimizing smelting degassing, gating and riser design, molding sand strength, cooling control, and stress relief through heat treatment.
Of course, professional foundries will strictly avoid these defects. For example, Mulan Manufacturing Group. If you have large-volume custom casting needs, you can entrust Mulan Manufacturing Group with production. Mulan Manufacturing Group has 13 years of experience in casting production, shipping to Europe, America, Japan, and South Korea year-round, and possesses complete certifications. We look forward to your cooperation and inquiries.
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