Common Non-Ferrous Casting Problems and Their Causes
Common Non-Ferrous Casting Problems and Their Causes
Shrinkage Cracks and Cavities: Cracks or cavities formed by the metal pulling itself apart while cooling in the mold.
Inadequate feeding of heavy sections or Inadequate gating requiring excessive pouring temperatures.
Too high or too low pouring temperatures.
Adjacent position of heavy and light sections. Lack of fillets.
Cold Shut: Lack of joining of metal where two streams meet, leaving a crack, or a weakness, which may result in a crack.
Inadequate gating. Restriction in the gate or runner.
Metal too cold. Improper Skimming allowing dross to enter sprue.
Wet sand. Low permeability of sand. Insufficient venting.
Wormy Surface: Elongated depressions near the gate, like worm tracks, Often filled with zinc oxide. Sometimes shows a fracture.
Inadequate gating.
Excessively high pouring temperature.
Inadequate venting and low permeability of sand.
Sand Wash: Rough lumps of metal at some points of casting and rough holes at other points.
Weak sand or weak areas of sand around gate. Sharp Corners at gate.
Too light/soft ramming Poor draw of pattern, leaving soft edges on mold.
Rough pattern surface, insufficient draft on patterns
Scab: A rough slightly raised surface on casting often with sand embedded.
Hard Ramming.
Sand too fine. Lack of permeability.
Core Blow: A smooth depression on inner surface of a cored casting or gas pocket above cored cavity.
Insufficient curing of core, moisture pickup after curing.
Inadequate venting from core prints.
Insufficient core print for venting.
Burning Into Sand: Rough sandy appearances of outer part of casting with some sand embedded in the surface.
Excessive metal fluidity as from too much phosphorus.
Sand too coarse, Sand too dry. Sand with too high permeability.
Excessive pouring temperature.
Weak or Discontinuous Structure: Minute cavities or voids between large crystals. In bronze, badly discolored fractures, granular in appearance.
Inadequate gating requiring high pouring temperature. Inadequate feeding of heavy sections.
Gassing during melting.
Excessive pouring temperature.
Burning Into Cores: Rough appearance of inner part of casting with sand imbedded. Metal fins penetrating into core holding grains of sand.
Excessive metal fluidity as from too much phosphorus.
Insufficient curing of core, poorly bonded cores.
Excessive pouring temperature.
Gas Holes: Holes under or near surface of casting. Inside of gas cavities untarnished.
Gas absorption during melting. Particularly hydrogen. Metal contaminated with sulfur dioxide while charging.
Too high pouring temperature.
Wet sand. Excessive build up of combustibles in sand. To much new sand in mix.
Tin or Lead Sweat: Spots, lumps, or a thin layer of white metal on the surface of the casting.
Inadequate venting.
Absorption of reducing gases during melting or holding. Silicon or aluminum contamination in charge.
Excessive pouring temperatures coupled with high phosphorus. Metal not properly stirred previous to pouring.
Misrun: An incompletely filled mold cavity. Lugs or corners not filled out. A smoothly rounded hole through the wall of the casting.
Inadequate venting.
Interruption of pour. Too slow pouring. Too cold of metal. Metal Gassed and made sluggish in melting.
Too small a Gate.
Rough or Pitted Surface: Rough surfaces on castings, some angular fairly deep pits but with no apparent sand wash or crush.
Careless molding leaving loose sand in cavity.
Coarse particles of cores or metal in molding sand.
Melting with highly fluid fluxes which cannot be skimmed off. Slag or dross allowed to enter sprue during pouring.
Solid Inclusions: Pieces of non-metallic materials or separate particles of metal showing in the walls of the casting when fractured or machined.
Molding sand not properly screened. Allowing small bits of metal to be adjacent to the mold wall.
Use of excessively fluid slags or fluxes.
Improper Gating.