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Production, steel quality stressed.

Steel founders, like others in the foundry industry, may be suffering through a difficult period of weak demand for castings, but there certainly is no lack of enthusiasm for the work they do or a keener interest in ways to do it better.

That spirit was evident at the recent gathering of 180 technical and operating personnel from steel foundries across the U.S. and Canada. They were attending the Steel Founders' Society's 46th Technical and Operating Conference on November 4-7 in Chicago to hear experts tell of advances in nearly every facet of steel casting technology.

The range of topics presented and the positive response by conferees were indicative of the drive and motivation of the steel foundry industry to maintain its competitive position, said Malcolm Blair, SFSA technical and research director and conference chairman.

He noted that steel foundries, through the SFSA, are committed to research in two major areas--clean steel processes to reduce or eliminate casting defects and the rapid integration of advanced computer technologies into operations.

"One of those technologies is stereolithography, the computerized modeling process that promises to reduce significantly the time and cost incurred between an engineering concept and a finished part," Blair said. "Another is solidification modeling, a defect-limiting computer technique that allows casting engineers to simulate the liquid-to-solid transition that takes place within the mold of a cooling casting.

"These and other examples of applied research are at the center of our efforts to gain in our traditional markets and secure a place in new ones."

Clean Steel Technology

Charles Bates, head metallurgist, Southern Research Institute, Birmingham, Alabama, updated progress on the SFSA clean steel research project. The project is investigating the physical pouring events leading to air entrainment, a source of serious casting defects.

Air entrainment and subsequent metal reoxidation are caused by a molten metal stream flaring as it leaves a ladle, exposing larger metal surface areas to oxidizing air. The falling metal forms a vortex in the sprue, entraining still more air. Turbulent metal and trapped air flow down the sprue through the runners and into the mold cavity.

Bates said entrained air bubbles multiply the surface area across where oxidizing reactions can occur. He explained that bottom-pour ladles result in more air entrainment than lip-poured streams, but liquid flow characteristics in all pouring systems affect the amount of air entrained.

As the result of extensive water modeling trials, several new technologies have been identified as having the potential for eliminating reoxidation defects and improving metal cleanliness, Bates said. These technologies include plasma arc refining, argon stirring and rinsing, calcium wire treating, filtration, inert gas or mechanical shrouding of the pouring stream and vacuum-lift pouring.

Water Modeling

Christoph Beckermann, University of Iowa's Mechanical Engineering Dept., reported on the usefulness of water modeling to simulate the removal of reoxidation inclusions from molten steel.

He said the flow of liquid steel and the transport of inclusions through the casting system can be simulated by using a full-scale water model. The aim of his work is to model air entrainment by studying the transport capacity of the flow, which is governed by downstream flow velocity and turbulence.

Ductile Iron

Ductile iron castings are a direct competitor of steel castings and Blair discussed the attributes of each. He said the decision to use ductile iron or steel depends on the properties required for the cast part.

Steel has significant technical advantages over ductile and austempered ductile iron (ADI) castings when modulus of elasticity (stiffness), tensile yield compared to elongation, impact resistance and weldability are factors, Blair said. Ductile iron's advantages are machinability, fewer inclusions and dimensional tolerance on short production runs.

Considering the trends towards thin-wall castings, steel has an advantage over any of the irons. The nodule size in ductile iron and ADI is such that fatigue properties are reduced, making them unsuitable for such components as exhaust manifolds with a wall thickness of 0.080 in.

Recycling, Safety

The reuse of foundry waste sands (ranging from 500-5000 lb/ton of produced metal casting) was addressed by Viral Patel, University of Wisconsin-Milwaukee, who reported on a successful project to fabricate masonry blocks using up to 35% foundry sand.

With landfills a finite alternative and disposal costs skyrocketing, Patel contends that finding uses for waste sands for building materials and road ballast could be a viable solution for byproducts.

Thomas Stevens, American Magotteaux, Pulaski, Tennessee, presented his foundry's cost-effective sand reclamation system. He said it operates with 22% thermally reclaimed sand, 4% new sand and 76% mechanically reclaimed sand. The system returns a net monthly saving of $16,000 and has extended by a full decade the useful life of the company's on-site dump.
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Title Annotation:46th Steel Founders' Society of America conference
Author:Bex, Tom
Publication:Modern Casting
Date:Jan 1, 1993
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