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Prevent Slag Hole Problem

Various sand casting defects often appear in iron castings. How to prevent these defects is a problem that sand foundries are extremely concerned about. This article describes some knowledge about the prevention of slag holes in this field based on practical experience.

Measures To Prevent Slag Holes

  1. Increase the temperature of molten iron, vermicular iron and alloy cast iron. If time permits, rest for a period of time before casting to make the residue float.
  2. To prevent the oxidation of molten iron, iron foundries should strictly control the amount of nodulizer and modifier.
  3. Design a reasonable gating system and set the filter into the chip to improve the ability to filter residues. When pouring, continuously use the best system on the casting slag ladle.
  4. When we cast sand-shaped ductile iron, the molten iron flows in the cavity of the cast iron. Due to the oxidation of molten iron or the reaction of various elements in molten iron with casting materials and sand cores, slag will be generated again. We often call it “secondary slag” (different from “primary slag”).

This defect usually only appears on the fractured surface and the surface of the finished sand casting by magnetic particle inspection. Such impurities mainly include oxides (magnesium oxide, silicon dioxide, iron oxide…) and sulfides (magnesium sulfide, iron sulfide, manganese sulfide…) and other impurities.

Measures to prevent secondary slag

  1. Strictly control the residual amount of magnesium in the molten iron, (generally the mass fraction is 0.035% ~ 0.055%, if the wall is thin, it should be controlled to the lowest; otherwise, it should be controlled at the highest.)
  2. Reduce the sulfur content of the original molten iron. If conditions permit, it is best to adopt some desulfurization methods to increase the processing temperature and pouring temperature. The molten iron after desulfurization greatly reduces the sulfur content, which can effectively reduce the “secondary slag.”
  3. Increase the rare earth content in the spheroidizing agent and reduce the magnesium content. It can help reduce the temperature of the molten iron surface and effectively reduce the “secondary slag hole.”

Slag hole will reduce the effective load-bearing range, cause stress to concentrate around the hole and reduce the fatigue and impact resistance of the casting. Foundries or individuals who want to buy sand castings should check carefully to avoid these defects.

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