. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . inDustry neWs
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . letterBox
Add In-Process Metal Loss to the Discussion of Surcharges (continued from page 13)
3. Skulls and Heels—Alloys adhere to the refractory walls of furnaces and ladles.
4. Spills and Splatters. 5. Run-Outs and Overfills. Because the loss is based on the pour
weight rather than the casting weight, yield is a major factor. If the melt loss is 8%, a yield of 50% means a total loss of 16% when compared to the shipping
weight of the casting. Lower yield means greater IML. At 33% yield, the total loss becomes 24% of the casting weight. Metal also is lost cutting off gates,
riser heads, bases and padding. The loss is influenced by the complexity of the rigging. The IML for cut-off varies from job to job and depends on the method of cut off. In arc-air cutoff, metal at the riser contact area is melted with an electric carbon arc and blown
off with a compressed air nozzle. Straight saw cuts can be made with a 24-in. swing-frame friction saw and consume less metal than arc-air. Torch cut-off, or gas cut-off, has restricted use in a high alloy metalcasting facility. The amount of metal lost in the
grinding and finishing of castings is dependent on how close the cut-off comes to the finished shape. If the castings are sold in the rough machined or finished part condition, the metal removed by machining also must be taken into account. The most important factors deter-
mining IML are the complexity of the rigging required by the casting design and the resulting yield. Casting weight also is a major item. Remember these rules of thumb: • The more complex the rigging, the higher the IML.
• Larger riser necks and bases pro- duce higher IML.
• Contoured riser contacts result in higher IML.
• Padding that has to be removed equals higher IML.
• Over-finishing (i.e. doing more than the specification requires) results in higher IML.
• Smaller castings generally have higher IML.
• Similar types of castings often fall into the same IML percentage range.
• Higher alloy content can result in higher IML.
RAYMOND MONROE
STEEL FOUNDERS’ SOCIETY OF AMERICA EXECUTIVE VICE PRESIDENT
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . cAlenDAr
August
• CMI Analysis & Reduction of Investment Casting Defects, August 17-18, AFS Headquarters, Schaumburg, Ill.
September
• CMI Casting Cost Estimating Workshop, September 15- 16, AFS Headquarters, Schaumburg, Ill.
16 MetAl cAsting Design & PurchAsing July/August 2010
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