DIS conference looks at shrinkage, hardness.
Focusing on factors leading to shrinkage in ductile iron castings and the role of hardness in overall casting quality, the Ductile Iron Society held its annual meeting June 13-15 in Dearborn, MI.
Arthur F. Spengler, American Alloys, Inc, began the Technical and Operating Session with a discussion of "Ferroalloys for the Ductile Iron Process." He noted that the higher percent Ca used outside the U.S. has a twofold effect: It lessens the violence of the reaction and increases Mg recovery.
"But it does something else: It slows the reaction down, helps the customer get more for his money--less dross, less slag," Spengler added.
He said the best inoculant is a ferrosilicon alloy that contains enough silicon to make it exothermic. It should go into solution within 12 seconds--depending on the alloy size and iron temperature.
"But in order to get the best results, use a ferrosilicon inoculant with Ca, 1% Al, and that's all," Spengler said.
William J. Meinhard, Don Day and Mike Flaugher, Teledyne Casting Service, reported on "Recent Observations of Heavy Section DI Castings." The test procedures involved two molding methods (an exothermic riser and full-mold polystyrene patterns) and two processing methods (Flotret and sandwich).
Efforts to reduce the amount of heat given off and amount of particulates during pouring led Teledyne to experiment with the Flotret process.
"We found that a 3% magferrosilicon, high calcium content sandwich cover, eliminated all our smoke and fire problems," Meinhard said. "We feel that the reduction of activity in the sandwich using the 3% Mg-Fe-Si and 1% Ca eliminated about 99% of the smoke and fire in the sandwich."
The Global Effect
Kenneth H. Kirgin, International Metalcasters Council, Inc, discussed "The Effect of Global Conditions on the Ductile Iron Forecast." The continued rebound of the U.S. iron industry strongly depends on the exchange rate, Kirgin noted.
"We're saying that if the currency exchange rates stay the same, as the macroforecasters say they will, we're looking at continued strong demand," he said. "We can be competitive in their ballpark. But its not just the currency exchange rate; we have improved our productivity. As a consequence we are the low-cost producers of rotors, drums, blocks, exhaust manifolds, and calipers.
"'Europe 1992' is not 'Fortress Europe.' It will be a new and one of the biggest economies in the world, and our feeling is that we must take advantage of it."
Mark Charlton, GM of Canada, Ltd, discussed, "A Designed Experiment on Casting Hardness." The hardness variation on one line at GM's St. Catharines (Ontario) foundry was threefold: mold to mold, within the same mold and in the same casting (end to end). The line produces crankshafts, calipers, steering knuckles, suspension parts and some exhausts.
The project also had two other objectives: meeting new hardness ranges and increasing productivity. Hardness was targeted at 3.8-4.2, with a minimum of 70% pearlite.
Charlton said a surprising result of the study was that line speed (and shakeout) were shown to have no effect on variation in hardness. As a result, the line was increased from 200-240 molds an hour. Cu, Si and Mg were shown to be the principal contributing factors to hardness variation.
Changes in metal chemistry resulted in the new Brinell spec being met, using 100% of the tolerance (versus 240% to meet the old spec). Further experimentation will be required to meet the pearlite specification, according to Charlton.
Noting the value of the designed experiment, Charlton said: "We would never have found the three-factor answer: Cu, Si and Mg using the only one-step-at-a-time approach. Total savings in scrap were $220,000/yr on one job. Heat treat savings were over $60,000 and an increase of 20% in productivity."
DIS-sponsored research, Research Project No. 10: "Review of Ductile Iron Society Shrinkage Research" was reviewed by Sam F. Carter. The study, conducted by Professor Jack Wallace, Case Western Reserve Univ, was presented to DIS members in 1980.
Shrinkage was generally believed to be greater and more confusing in DI than in gray iron. Yet some producers of fairly heavy castings using what they call rigid molds said they didn't have shrinkage problems.
The study involved green sand and alkyd nobake molds and variations in C, si and carbon equivalents. Mold wall movement was shown to be the leading cause of shrinkage.
"Mold inoculation didn't really show anything because we had such a short holding time of two to three minutes," Carter said. "We know that if we had held it longer, we would have seen some effect of mold inoculation. That's a deficiency in the experimental approach, I think.
"Nodule counts showed a very strong effect on the volume of shrinkage. Now, that wasn't bad news because you know that if you have high nodule count, it's good for a lot of other things, but it gives you more shrinkage. Magnesium level really showed very little effect. We think it was overpowered by these other variables."
Pouring temperature showed a minor effect. However, Carter said, "There is just too much production experience to indicate that if we can control all of these variables, that pouring temperature would have more effect than what we showed."
Making separate presentations before participating in a panel discussion were: Gary Gigante, Waupaca Foundry Co; David J. Herron, University Gating Design; Dr. Wolfgang Knothe and Walter Hundhausen, GmbH & Co; and George DiSylvestro, American Colloid Co.
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|Title Annotation:||Ductile Iron Society|
|Author:||Burditt, Michael F.|
|Date:||Nov 1, 1989|
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