Green sand quality control, including good critical visual inspection, helps avoid scrapped castings.
Excerpt from the July 2018 issue of Modern Casting by the AFS Institute
Quality control begins with prevention. Metalcasters can control five areas of green sand mold making in order to prevent mold defects:
- The selection of type of sand and clay and the amount of moisture needed to make the mold.
- Consistent mulling, using the right sequence of raw materials, and selecting the right temperature of the sand.
- The cleanliness and condition of horizontal and vertical patterns, as well as core placement.
- Selection of scrap metal and determining what can be reused and what must be discarded.
- Testing for quality ensures the part meets the requirement of the buyer. While casting can be tested many ways, one of the major casting quality tests used after the casting is made is visual inspection.
Nine common types of green sand casting defects can be visually identified:
- rough surfaces
- friable edges
- excess parting spray
- missing components
- loose sand
- sand contamination
Usually, the causes of defects include shrinkage, gas porosity, sand expansion, sand adherence, and weak sand strengths. The chart below shows the causes and possible remedies for green sand molding defects.
More specifics about each defect and aspect of green sand casting can be found in the article.
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