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Post-Pour: Diagnosing. See our text for pictures

September 26, 2016

POST POUR:

 

DIAGNOSING: (see pgs. 146 – 154)

Misrun = incomplete casting; poured too cool, metal froze before mold was filled; kiln didn’t preheat shell; waited too long between kiln removal and pouring; needs better gas venting; bad job handling shell

 

Gas defects = nonfill, porosity, bubbles, pits in metal surface

carbon not completely removed in dewax and preheat; could have been contaminated wax; be sure burnout and preheat atmosphere is an oxidizing one.

fix: more time for burnout and preheat 1-3 hrs;

 

Shrinkage or Drawing in: inadequate spruing to a heavy or thin section; you should: pour metal at cooler temp

 

Flashing: be more careful during dewaxing to minimize shell expansion; reinforce mold w/ fiberglass or stainless wire; improve wax sprue design

 

Porosity: gases accumulated during melting of metal; furnace must have oxidizing flame; use de-gassing agent; avoid turbulence in pour

 

Pin Holes: due to gases that molten metal absorbs during the melt and pour; try bigger sprues, more vents, oxidizing atmosphere

 

Wormy Tracks: inadequate spruing; excessive pouring temp

 

Inclusions of shell in wrong places: poor dipping practices; improper melt of metal; failure to skim slag during poor, poor shell bonding

 

Hot tears and Cold cracks: caused as metal shrinks in the cooling due to poor wax sprue design, metal too hot; using same metal too many times; when using a core: bottom and sprues cool before piece

 

Warping: uneven cooling of metal, irregular thickness in wall of wax. Cool metal more slowly; improve sprue design; build shell thickness as evely as possible over entire piece; reinforce shell w/ fiberglass or stainless steel wire.

 

Cold Shot: metal escaped during pour

 

Cold Shut: hairline crack on surface of casting; metal fed into mold from two or more streams and the flows don’t bond; metal too cold, mold too cold, poor wax sprue design

 

Blow Holes: trapped gases; poor sprue design of vents; shell or core not de-gassing

 

Holes in surface: metal contamination (clean the crucible); gas from furnace — reduce gas to air ratio

 

Cold Chill Lines: inadequate # of sprues; not enough head pressure during pour; metal sluggish coz contaminated; too much gas; metal too cold; sprue design

 

REMOVING THE SHELL

Wear gloves and eye and ear protection!

Sandbag; tap the cup; use blunt chisels; sand blasting, saws, abrasives, sandblaster, grinder: cutting wheel, air arc, bolt cutters

 

WELDING, CHASING, CLEANING

Welding: Oxy-acetylene, TIG (heliarc) welder: use 10/10 Everdur rod for welding bronze; burnish the welded area w/ wire brush to check weld; surfaces must be clean before being joined

 

Chasing: (cover jaws of vise with leather, wood or soft lead) remove bronze sprues and leave enough for good access to holding piece in vice.

Chisels, ballpein hammer, nail set,

 

Types of files (coarse, med, fine) flat, round, rat tail, ½ round, cross-cut. (Swedish steel files are best), stamping or matting tools

Taps, fillers use: 10/10 Everdur rod

 

Tools to have at the ready: pliers for flashing removal; small grinder like flex shaft, dremel, die grinder; electric drill

Tungsten carbide cutters for dremel

Swivel-point sanding pad from 80 up to 600 grit

 

Chasing Techniques:

  1. When removing sprues and flash: leave a little excess so that it can be worked carefully down to the original plane of the surface
  2. Work from coarse to fine when filing or sandpapering
  3. Burnish with steel brush or steel wool, area to be chased use chisel to eliminate rough areas
  4. Work the excess metal over into a hole using ballpein hammer or flat punch.
  5. Matting: heat up a high carbon steel piece of metal4-6 inches long to cherry red (1400 degrees) put other end of steel in vise and use old hacksaw blades, chisels, files to roughen one end till it resembles texture of sculpture. Round the edge of the matting tool harden it by quickly quenching in water or oil
  6. Medium-fine emery cloth can work as matting
  7. If smooth final surface is desired: use belt sander or wet/dry sandpaper; buffing is even smoother
  8. After chasing, spray w/ liver of sulphur to blacken it and rub w/ steel wool. This will show up uneven texture
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