Possible Cause Pouring temperature is too low.
Suggested Action Determine and use the best temperature. Metal
temperature checked with a pyrometer should not vary more than 20 degrees with the furnace readout. If the level of metal in the furnace is more than 4 in. below the “full” level, then an inaccurate reading may be expected. If it is a full furnace, the thermocouple may need to be replaced. Degas if necessary.
Possible Cause Excessive heat is
carried to the support- ing frame through a large contact area.
Suggested Action Decrease the
contact area to the frame or interpose light thermal insulation.
Possible Cause
Mold coating is improp- erly applied or trimmed.
Suggested Action Inspect for areas of mold coating that have worn thin from normal production. If feasible, increase coating in the misrun area.
Defect: Misruns completely before solidifying.
Suggested Action 1. Avoid fast pouring rates to decrease metal agitation. Flux to remove dross. 2. Skim metal frequently. Push back the surface when dipping the ladle. Avoid splashing or pushing dross under the surface. Ladle only enough metal to fill the mold.
3. Improve your gating practices to decrease metal agitation. In vertical castings, increase the width of the web feeding cavity from the side riser.
Possible Cause Mold tilting rate is too slow.
Suggested Action
Check the pouring rate. If necessary, open gates or provide more gates to fi ll faster without turbulence. Inform the appropriate supervisor of adjustments to tilt speed and timer settings. Provide more venting for core gas to escape in semi-permanent molds.
Possible Cause Dirt in the metal is making it sluggish, preventing it from fi lling the mold
Possible Cause Dirt in metal increases viscosity, so trapped
air or gas does not escape as it should.
Suggested Action 1. Avoid fast pouring rates. Pour at a steady rate with minimum fall of metal. Flux to remove suspended dross.
2. Skim metal frequently. Push back the surface when dipping the ladle. Avoid splashing or pushing dross under the surface. Ladle only enough metal to fill the mold.
Defect: Trapped Gas
Possible Cause Defi ciency in venting prevents air from
escaping as metal enters the mold cavity.
Suggested Action Check venting at specifi c areas where gas holes occur and increase where possible.
42 | MODERN CASTING February 2012
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68