Simple Solutions That Work! Issue 9

Most foundries will attest that over the past 25 years, scrap quality has steadily deteriorated. Consequently, insoluble buildup and slag related problems have increased, resulting in instances of slower melting rates and inefficient furnace utilization. The coreless induction furnace is essentially a refractory-lined vessel surrounded by an electrically energized, current- carrying, water-cooled copper coil. Electrical current in the coil induces an electromagnetic field, which magnetically "couples" with the magnetic charge, producing electrical current within the charge itself. Each piece of charge has its own internal resistance which, when energized by these internal currents, will heat up and eventually melt. The resulting magnetic field in the molten metal causes a stirring action, thus ensuring a homogenous liquid mass. In all coreless induction furnaces, there is an “ideal” refractory wall thickness, carefully calculated by the furnace manufacturers to offer the optimum melting performance. Designed into this calculation are safety considerations, electrical characteristics of the coil, metallic charge resistance / electrical conductivity, structural and refractory considerations, operational constraints and production needs. When the furnace melt diameter is reduced by buildup, the melting process efficiency becomes compromised. The result is a reduction in the percent power utilization that causes the energy consumption to increase, which is graphically illustrated in Figure 1. Traditionally, to remove the buildup, furnace operators are forced to mechanically scrape the lining which may also damage the refractory face. During this scraping process, the power is turned off for safety reasons. The formation of slag during the melting of metal is an inevitable process. In a coreless induction furnace, slag residuals normally deposit along the refractory walls within or slightly above the active power coil. The composition of slag varies with the type of metal being melted. The cleanliness of the metallic charge, (often consisting of sand- encrusted gates and risers, or rust- and dirt-encrusted scrap) significantly affects the type of DR. R.L. NARO, D.C. WILLIAMS & P. SATRE ASI INTERNATIONAL, Inc. ARTICLE TAKEAWAYS: • Improve Coreless Induction Melting Efficiency • Reduce Melting Electrical Costs • Eliminate Refractory Wall Slag Buildup ECONOMIC CONSEQUENCES OF INSOLUBLE BUILDUP ON CORELESS MELTING EFFICIENCY 52 Figure 1. Generalized Relationship between Energy Consumption (kWH/ton) and Power Utilization (1).