Reducing Copper Alloy Problems.
In a panel presentation on reaching maximum life for crucibles and furnace linings, G. Weis, Morganite Crucible, Inc., explained the "basic rules" to extending the work life of a crucible for copper melting. First, foundries must avoid any abrasions to the crucible's surface. Also, crucibles should never be rolled and they should be stored on a pallet in a dry area at 65F (18C) or higher. Base blocks also are beneficial in allowing crucibles to offer uniform heating, he added.
Focussing on careless and channel induction furnaces, D.C. Williams, Allied Mineral Products, Inc., stated that metal finning and buildup are problems related to furnace linings. To alleviate the metal finning in coreless furnaces, increase the gas heat to 2000F (1093C) and maintain it for 1-3 hr, Williams said. It's important to do it from a cold start-up, he added. Also, increasing the silicon carbide content to improve thermal conductivity, increasing the buffer agent to boost reversible expansion, or decreasing the amount of low temperature binder are other ways to alleviate metal finning. For channel furnaces, Williams recommended more insulation to reduce buildup.
In their presentation on comparative corrosion resistance of copper base alloys (01-127), F.A. Fasoyinu, M. Sahoo and M. Elboujdaini, CANMET/MTL, concluded that the corrosion resistance of the Cu-based alloys in the permanent mold cast condition is better than in the sand cast condition. Also based on electrochemical polarization and salt fog tests, high-manganese brass (C99700) is the most corrosion resistant alloy. The yellow brass (C86300) and aluminum-bronze (C95400) are the least resistant to corrosion in all the test environments.
In another CANMET/MTL paper on weld cracking in the heat affected zone of aluminum bronze (C95800) (01-108), Sahoo, M. Letts, R. Zavadil and M. Sadayappan determined that high levels of impurity elements, such as lead (0.15%) and bismuth (0.08%), promote macroscopic cracking when added individually to the metal. Results to prevent heat-affected zone cracking in C95800 can be specified as: lead-0.05%; zinc-l.2%; tin-0.3%; bismuth-0.03%; selenium-0.035%; silicon-0.25%; chromium-0.1%; and beryllium-0.1%.
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|Date:||Jun 1, 2001|
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