Starter rings

Starter rings can be used as a substitute for starter blocks. The outer diameter is approx. 100 mm less than the crucible diameter, and the inner diameter of the rings is approx. 200 mm less than the outer diameter. The use of such rings was recommended in the 1970’s for mains frequency furnaces with crucible diameters > 1,000 mm for sinter charging. The first ring was placed on the crucible cone; distance pieces 50 mm thick and about 100 mm long and wide were then placed at three places around the circumference of the ring. The next ring was then placed on top of these parts. This procedure was repeated up to the upper edge of the induction coil. Compact scrap can also be filled in inside the rings right up to the top. Due to the good coupling, this ensures very even heating of the rings, and thus also of the ramming template and ramming mix. Dry mixes were heated at approx. 100 °K/h. When semi-plastic mixes with up to 4% moisture were used, the temperature increase was reduced to 50 °K/h. This allowed even drying by means of the ramming template on the crucible wall. This process was however discontinued at the end of the 1970’s for cost reasons. The starter rings were made from approx. 80/100 mm thick steel plates. One customer in Finland cast the rings from scrap iron.