A shift is a misalignment between two mating surfaces leaving a small clearance between them and changing their relative location. (i)Modify sand composition to increase the strengthħ. (i)Low green strength in moulding sand core. This is caused by the dropping of sand from the cope or other overhanging projections into the mould. DROP: An irregularly shaped projection on the cope surface of a casting is called the drop. (i)Ensure proper directional solidification by modifying gating,risering and chilling.Ħ. voids on the surface or inside the casting. SHRINKAGE: Metal shrink as they solidify.If this shrinkage is not compensated by providing risers etc. MISRUN and COLD SHUTS: When the metal is unable to fill the mould cavity completely and thus leaves an unfilled portion it is called misrun.Ī cold shut occurs when two metals streams do not fuse together properlyĥ. (ii)Use sand with proper refractoriness propertyĤ. (i)Pour metal at a proper lower temperature (ii)Excessively high temperature of molten metal FUSION: Sand may fuse or stick to the surface with a resultant rough glossy appearance. (ii)Reduce moisture and increase the permeabilityģ. (ii)Decrease in solubility solidification As molten metal solidifies, many small voids distribute quite uniformly throughout the metal due to the release of gases which results in porosity. hydrogen is responsible for pinhole porosity. POROSITY:This defect occurs in the casting in the form of pinhole porosity or gas porosity. (iv)Moulds should not be rammed excessively hardĢ. (iii)Low permeability and excessive fine grain sands These are entrapped bubbles of gas with smooth walls These may occur in a cluster or there may be one large smooth depression. These appear as cavities (holes)in a casting. BLOW HOLES: These are also called “ sand blows”. There are “23 defects” that commonly occur in casting, their possible causes and effective remedies are discussed below:ġ.
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