Simple Solutions That Work! Issue 8

The refractory systems used in the inductors of channel induction furnaces are often the limiting factor in campaign life. The refractory portion of the lower part of the furnace must be rammed or cast over a form that creates the channel inductor. These forms, with current technology, are of necessity consumable. They may be a combustible, such as wood, which burns out as the lining is cured, but in doing so cannot keep the refractory in compression to create a strong, dense surface. Thus, the refractory channel surface is readily susceptible to erosion and metal penetration, shortening the useful life of the furnace campaign. A better, but far more costly technique, involves the use of metal melt-out channel loop forms. This system allows a denser surface to be produced, but it is still subject to metal penetration, especially at higher power or temperature. A new technique has been developed, using permanent CeraLoop™ ceramic loop forms produced by the proprietary Blasch Precision Ceramics process, and backed by Allied Mineral dry vibratory backing material which offers many benefits to the older refractory systems. The smooth pre-fired surface greatly reduces erosion, and the miniscule average 5-micron pore size greatly limits metal penetration. This pre-fired hot face reduces saturation during start up and sintering. The chemistry of the ceramic channel loop forms can be adjusted to suit the requirements of the metal being melted. The result is vastly improved furnace lining campaign life, and at reduced material cost compared to metal melt-out loop form technology. CHANNEL FURNACE FUNDAMENTALS Channel induction furnaces have long been an effective method of melting and holding many metals including iron and non-ferrous alloys of copper, aluminum and zinc. The furnace itself consists of two sections; the upper case where the metal is held, and the inductor beneath it, where the heating or melting occurs. The inductor is essentially a channel or tube, which surrounds an induction coil, similar to the primary winding of a transformer. Metal flows through the channel, and becomes, essentially, the secondary winding that produces low voltage and high current. This produces the heat required to keep molten, or superheat, the metal bath. PHILIP GEERS Molten Metal Market Manager BLASCH PRECISION CERAMICS ARTICLE TAKEAWAYS: 1. A new approach to lining channel furnace inductors 2. Shorten downtime and increase campaign life 3. Ceramic leads to lower potential for erosion IMPROVEDMETHOD FOR LINING CHANNEL FURNACE INDUCTORS 28 Figure 1. Channel Induction Furnace There are a variety of inductor channel designs, but all are basically tubes forming one or two roughly circular shapes. Metal is drawn from the upper case, through the channel tube where it is inductively heated, and returned to the upper case. The tubes vary in cross section, depending on OEM design. While many are rectangular, others require special and critical geometry. Figure 2. Channel Loop Designs Single Loop Double Loop