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Practical technologies mark Ductile Iron Society meeting.

A near-record turnout of about 120 members at the 1990 meeting of the Ductile Iron Society in Decatur, IL, is indicative of the expanding uses of ductile iron castings by design engineers, said John V. (Jack) Hall, incoming executive director of the DIS.

Ductile iron casting applications have risen steadily in response to their technical and economic advantages over competing materials. Ductile iron tonnage is expected to surpass gray iron production in the next decade.

DIS activities include sponsoring technical research, and promoting ductile iron's superior strength, castability and cost effectiveness as a replacement for steel, gray and malleable iron castings, forgings and weldments. Largely technical in nature, the October meeting was marked by a number of presentations dealing with ductile iron production. Technical Highlights

The transfer of sulfur to and the desulfurization of iron during cupola melting was addressed by William Henning, manager of technical services, Miller & Co. He said there was a definite progression of desulfurization practices starting in the '60s when cupola melting predominated. By 1968, the basic slag cupola used the continuous porous plug process.

Quality requirements in the mid- '70s led to closer control of carbon and silicon in the base metal. This was followed shortly by the BCIRA-REsearched fluorspar desulfurization treatment process, and more recently by a fluorspar/ lime process prompted by environmental concerns. Henning touched on a General Motors agglomeration research project to control porosity and use separate feeder lines for lime and fluorspar to control silicon.

Dynamic tear testing (DTT), developed by the U.S. Navy in the 60s, was discussed by Wagner Castings' Chuck McCauley as a useful tool to measure ductile iron under stress. DTT tests the loads necessary to force a sample to fail by gaging load resistance (plastic deformation), failure by gradual tearing and the force required for catastrophic failure.

Late stream inoculation was the point of Michael Barstow's presentation. A marketing development engineer for Elkem Metals Co, Barstow said one of the latest inoculant techniques was the use of a microseed dispenser. It is effective in controlling chill and rapid solidification while increasing nucleation sites with minimum undercooling.

He said eutectic solidification can be affected by three inoculant types: ferrosilicon/calcium, calcium/barium and strontium. He listed ladle, stream and mold inoculation sites as preferred, adding that stream inoculation was more effective than ladle inoculation.

In his presentation on ductile iron melting costs, James D. Mullins, senior technical specialist for QIT America, traced the cost of metal castings to the costs of scrap, heat treating, raw materials (additives) and processing in relation to ultimate furnace yield. Increasing yield by 1% can result in a savings in melt costs of $4-5/ton, he said.

Using least cost chemistry, reducing charge treatment and lowering process control costs are three ways to reduce melt costs and raise yield.

George Disylvestro, mold specialist for American Colloid Company and DIS education and technology transfer committee secretary, gave a progress report on a Dis-sponsored research project on the effect sulfur in molding sand has on producing flake graphite on the surface of ductile iron castings. The study, begun in 1988, involves 200 sulfur content tests by 11 DIS production members on 15 ductile iron molding sands. Sulfur levels fell in proportion to new sand additions and rose with increasing seacoal additions.

Fred Dudek, an Argonne National Laboratory scientist, reported that galvanized iron scrap is growing as the use of galvanized iron rises. He predicted 15 million tons of galvanized scrap would be available by 1995. For foundries this material is a potential resource that is largely untapped due to the expense of separating zinc from iron. Even with credits for zinc recovery, using galvanized scrap can be daunting. It can ruin furnace walls, add to dust collection problems, increase shop floor environmental hazards and cause zinc accretion on shafts and heat exchangers.

Suspended particles too small to incorporate into slag can sinter and constrict the throats of channel furnaces, Ronald Stark, refractory consultant, told the DIS conferees. Under carefully controlled situations, bridged furnace inductors can sometimes be cleared by pulsing furnaces at full-rated power every half hour, but he did not recommend the procedure.

The bridging problem begins when the oxygen balance is upset due to the moisture in a new refractory lining (as little as 2.5%) or in magnesium hydrate. This creates superheated steam driving off the hydrogen, leaving oxides to form at the channel. This creates the initial spike of clogging material in the furnace throat.

Calcium, aluminum and magnesium in scrap will lead to a buildup of spinel in the environment at the inductor and can damage the refractory causing superheating, wall penetration and eventually leakage. All clogging is not caused by oxides, Stark said, adding that carbides, nitrides and fluorides are also culprits.
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Author:Bex, Tom
Publication:Modern Casting
Date:Dec 1, 1990
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