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MOLD MATERIAL CASTING DEFECTS AND CAUSES
Foundry Mold material casting defects are related to the mold material, which is most commonly sand. Foundry can typically address these casting defects and causes by modifying the mold.
1. Cuts and washes
Cuts and washes are areas of excess metal. These appear when the molten metal erodes the molding sand.
A cut appears as a low projection along the surface of the drag face, decreasing in height as it extends from one side of the casting to the other.
Causes and prevention of cuts and washes
Cuts and washes can be caused by molten metal flowing at a high velocity, causing too much metal to flow through the gate.
Foundry can prevent cuts and washes easiest by:
- Designing the gating system properly
- Improving mold and core strength
- Adding more binders to the facing and core sand
2. Foundry Casting Fusion
Fusion occurs when sand grains fuse with molten metal. It appears as a thin crust with a brittle, glassy appearance firmly adhered to the casting.
Causes and prevention of fusion
Two main factors can cause fusion:
- Low refractoriness of clay or sand
- Too high pouring temperature of molten metal
Refractoriness is the ability of the molding material to resist the temperature of the liquid so it doesn’t fuse with the metal. Silica sand has the highest refractoriness.
Improving the refractoriness of the molding material and/or reducing the pouring temperature of the molten metal will help prevent fusion.