Defects of sand inclusion and scab in steel casting and preventive measures

Sand inclusion refers to that there is a layer of metal lump or sheet on the surface of the casting, and a layer of molding sand or coating is sandwiched between the metal lump and the casting. Scarring is caused by a protruding scar on the part where the metal liquid flushes a piece of sand on the surface of the casting or where stirring or boiling occurs. The fallen sand is sandwiched in the scar block or other parts of the casting. During pouring, the moisture on the surface of the wet mold cavity migrates to the inside of the sand mold due to the high temperature baking of the molten steel, forming a water condensation area with low strength, which is easy to cause the surface of the mold cavity to desquamate and cause the defects such as steel casting scab, sand inclusion, etc.

Precautions for sand inclusion and scarring:

  1. Strictly control the properties of molding sand and core sand.
  2. The pouring time should be as short as possible; the design of the pouring system should make the molten metal enter the mold cavity smoothly and the impact force is not large; the layout of the inner gate should be properly distributed to avoid local overheating of the mold, and cover the lower mold surface as soon as possible.
  3. Inclined casting can be used for large flat plate casting;
  4. The air hole on the mold can help to remove water vapor and other gases, make the water condensation area move backward and reduce the water content, and reduce the effect of gas pressure on the cavity surface.
  5. Avoid pressing the big plane back and forth with the pressure spoon to prevent layering during the modification.
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