by clicking the arrows at the side of the page, or by using the toolbar.
by clicking anywhere on the page.
by dragging the page around when zoomed in.
by clicking anywhere on the page when zoomed in.
web sites or send emails by clicking on hyperlinks.
Email this page to a friend
Search this issue
Index - jump to page or section
Archive - view past issues
button in toolbar for more information.
Metal Casting Technologies : March 2007
METAL Casting Technologies March 2007 51 NAME & DESCRIPTION OF DEFECT CAUSES Run-outs and Bleeders • Weak molds or cores. Runouts and bleeders are defects which result in an incomplete casting. • Faulty flasks, improper clamping. Run-outs occur during pouring, usually when the mold cavity has not been • Rough mold handling. completely filled; while bleeders occur after pouring has stopped and the • Too high head pressure. mold cavity has been filled. • Lack of cope seal. • Weights are removed too soon. Scars, Seams, Plates • Interrupted metal flow during pouring. A scar is a minor or shiny mark on a casting surface where the casting does • Cope and drag shifting. not conform to the pattern. A seam is a visual indented line on the casting • Low molding sand permeability. surface. A plate is a layer of metal partially separated from the main body of • Plugged mold vents. the casting section. These defects usually occur on flat surfaces. • Gassy cores and molds. • Turbulent flow of molten metal. • Slow pouring. Shifts • Misalignment of patterns. A shift is a mismatch of the casting at the parting line. • Worn out flasks. They may occur in cores or core assemblies. • Weak molds. • Green (uncured) core distortion. • Rough mold handling. • Excessive rapping of mold. Shot metal • Flask wall is too close to mold cavity. Shot metal are small globules of metal embedded in, • Violent metal boil. but not entirely fused with, the casting. • Careless pouring of mold. • Plugged mold vents. Shrinkage cavities, Depressions • Too abrupt change in section size. A shrinkage cavity is a jagged hole or spongy area lined with fernlike structure • Fillets are too small. called dendrites. A shrink age depression on the surface of the casting is a • Worn out patterns. recession from the true plane of the mold surface. • Risers are too small. • Insufficient gates. • Careless furnace charging. Stickers • Wet sand. A sticker is excess metal on the surface of the casting caused by • Stickiness of pattern. a portion of the mold face remaining in the pattern. • Insufficient pattern draft. • Hot molding sand. • Oversized ram-up core. • Rough mold handling. • Over-jolting in machine molding. • Rough pattern. Swells, Strains, Sags, Core fins • Mold-wall movement. A swell is an enlarged metal section related to mold-wall movement. • Inadequate relief vents. A strain is a swell with a fin on it. • Weak cores. A sag is an increase or decrease in a metal section due to the • Too soft ramming of mold. sagging of the cope or core. • Excessive metal pressure or temperature. A core fin is a depression in the casting caused by • Too light mold weights. a fin on the core which was not removed when the core was set. Warped castings Warpage is deformation that occurs during or after solidification, mostly in gray or • Incorrect rib design. white cast iron (non-ductile). The problems are similar to those of "hot tears," • Too high combined carbon in metal. namely, differential stresses set up during cool-ing. The difference between the • Too cold tapping and pouring temperature. two defects (aside from appearance) is either in the degree of stress or in the • Poor molding sand collapsibility. tearing tendency of various metals. A stress situation which would tear a steel or • Restricted contraction of casting during malleable iron casting might only warp a gray or ductile iron casting. solidification.