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Lead standard, grain refinement top list of division presentations.

OSHA's Lead Standard, its compliance measures and enforcement dates, was a major topic of conversation in the Brass & Bronze sessions. G. Mosher, American Foundrymen's Society, presented an update of what is going on in court and what the outcome will mean to brass and bronze foundries.

What it boils down to, according to Mosher, is that OSHA considers feasible a 50 [micro]g/m[.sup.]3 engineering control level for airborne lead for foundries employing more than 2O people ; 75 [micro]g/ m[.sup.]3 for less than 20. These feasibility levels are now before the court, with all briefs and oral arguments expected to be filed by June and a decision by Fall. If the court says OSHA is correct, foundries will have up to five years to comply.

Other presentations included a report on the work (90-97) of M. Sahoo and M. Wirth, Canmet/MTL, on attempts to refine the grain size of Cu-lONi-8Sn alloys by adding small amounts of Nb, Zr, V, Ti, Cr, Mo or B. Results show that trace amounts of Nb, Zr, Ti, Cr, V, Nb + Zr and Nb + Mn produce a fine grain structure. The alloys develop high hardness and mechanical properties following solution treatment and aging, but the expected benefits of increased ductility and good fracture toughness associated with a fine grained material were not obtained.

"The most common casting defect that occurs in permanent molding of copper alloys, and namely yellow brass alloys, is the crack occurrence," said R.H. Haupt, Miller & Engelhardt, Ltd. Results of investigations into the Development of Copper Alloy Composition for Gravity, Low Pressure and High Pressure Die Casting" (90-55), have shown that use of a grain refined B2 alloy, now available in the U.S., virtually eliminates these defects. Shrinkage and sink problems have been solved for the most part by the lower pouring temperatures now possible and the avoidance of heavy core insulated cast sections. The fine grain structure increases the strength and corrosion resistance as well.

According to K.G. Davis and J.G. Magny, Canmet/PMRL, "Thin section castings of Al bronze, Mn brass and Si brass, of the order of 5 mm wall thickness, can be poured in permanent molds at high yields, with small section gates and runners similar to those used for cast iron. No risers are needed to get satisfactory structures."

This was the main conclusion reached as a result of their observations made on two thin walled castings, a simple plate and a sand cored plumbing fitting (90-69). "In contrast they said, "leaded Sn bronze and high strength yellow brass both needed higher superheat to fill the molds, and for these, 'cast iron' mold design is not satisfactory."

E.P. Bloomfield, Milwaukee Valve Co, Inc, reported on results of tests done at a brass and bonze foundry to determine the suitability of the LTB-l bar for determining melt quality.This test bar, which requires no machining prior to testing, offers a solution to the problem of timely results.

The goal of the investigation was to gain the ability to evaluate furnace heats causing scrap castings the same day as production occurred, reduce the cost of mechanical testing and eliminate the backlog of test bars.

Among the findings reported, said Bloomfield, are that "use of the LTB-L bar will allow bronze foundrymen to better control melt practice through reduced turnaround time of the results of a heat's mechanical properties."
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Publication:Modern Casting
Date:Jun 1, 1990
Words:570
Previous Article:Reduced costs, repeatability benefits of automated tooling.
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