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DEFECTS IN CASTINGS Presented by N.SITHIVINAYAGAM ME MANUFACTURING ENGG METAL CASTING TECHNOLOGY

Defects in Castings-1

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METAL CASTING TECHNOLOGY

Presented by N.SITHIVINAYAGAM ME MANUFACTURING ENGG

The

Casting Defects may cause by Major three Region.The Casting design Technique in manufacture method Application of the technique workmanship

Shaping

faults arising in purring Inclusion and sand defects Gas defects Shrinkage defects due to volume contraction in the liquid state and during solidification. Contraction defects occurring mainly after solidification. Dimensional defects Compositional error and segregation.

DEFECT A casting that has solidified before completely filling mold cavity CAUSE low pouring temperature Low fluidity In adequate venting of mould Faulty pouring practice

REMIDIES Provide hotter metal at furnace spout; reduce heat losses in ladle by using flux coverage. Increase carbon and phosphorus Avoid excessive ramming and increase vent

DEFECTS Two portions of metal flow together but there is a lack of fusion due to premature freezing

CAUSE & REMIDIES

DEFECTS Depression in surface or internal void caused by solidification shrinkage that restricts amount of molten metal available in last region to freeze CAUSE Incorrect gating and feeding Unsuitable composition REMEDIES Use risers to feed heavy sections and ensure that they are fitted with hot metal. If using open risers, use feeding flux. If using blind risers, use feeding cores.

DEFECTS Balloon shaped gas cavity caused by release of mold gases during pouring

DEFECTS Formation of many small gas cavities at or slightly below surface of casting CAUSE They are caused by the absorption of Hydrogen and carbon monoxide when moisture content of sand is high or when steel is poured from wet ladles or is not sufficiently degasified .

REMIDIES This defect can be minimized by using good melting and fluxing practice. By reducing the moisture content of moulding sand increase its permieablity

DEFECTS When fluidity of liquid metal is high, it may penetrate into sand mold or core, causing casting surface to consist of a mixture of sand grains and metal

CAUSE & REMIDIES Remedies

Visual

inspection to detect obvious defects such as misruns, cold shuts, and severe surface flaws Dimensional measurements to insure that tolerances have been met Metallurgical, chemical, physical, and other tests concerned with quality of cast metal