7. Rat Tail
Rat tails appear as irregular cracks or lines on the casting. These defects are caused by compression failure of the mold cavity surface when the molten metal is overheated. The molten sand expands due to the heat, causing the mold walls to move back and give way. During this process, small line marks appear on the surface of the casting. If this type of failure occurs multiple times during the casting process, you may notice small intersecting lines on the surface of the component.
Causes
• · Poor expansion ability of the sand.
• Improper mold design.
• Metal pouring temperature is too high.
Remedies
• Add combustible additives to the molding sand.
• Reduce the metal pouring temperature.
• Design the mold to be less hard to ensure sufficient expansion.
Casting Shape Defects
Incorrect casting shape can cause two types of defects: mismatch and flash.
1. No match
Mismatch is a casting defect that occurs due to misalignment of the lower and upper parts of the mold. This occurs if the upper and lower dies of the mold are not properly aligned before pouring the metal. There are two types of mismatch, mold shift and core shift. Mold shift is the result of mold misalignment and usually manifests as a horizontal shift. On the other hand, core shift occurs due to core misalignment and manifests as a vertical shift.
Causes
• Loose box pins.
• Wrong dowel pin pattern.
• Misplacement of the upper and lower parts of the mold can cause misalignment.
Remedies
• Ensure proper matching plate pattern alignment and installation.
• Use the correct mold box and seal pins.
2. Flash
Flash is any excess or unwanted material that appears as a thin, irregular shape on the parting line of a die cast part. Typically, it is a thin piece of metal that forms on the parting surface and turns into slag after remelting. Since flash usually has a large size, it can be seen through visual inspection.
Causes
• Inadequate clamping force.
• Insufficient cleaning of the parting surface.
• Injection speed and filling temperature are too high.
• Insufficient strength of mold material.
• Deformation or wear of hinges of casting machine.
Remedial measures
• Adjust casting parameters such as injection speed, filling temperature, clamping force, etc.
• Ensure regular maintenance of casting machine.
• Clean mold cavity and parting surface.
