Simple Solutions That Work! Issue 5

48 CRUCIBLES Crucibles have been around for thousandsof yearsandarestillwidely used. They are subject to leaks and catastrophic failure that candamage the heating system and build-up in the bottom of the furnace. This can be dangerous and is difficult and messy toclean-up. Production is lost for some time after such a failure. Formaximumenergy efficiency, the metal level inacrucible furnacemust be nearly the full height of the cruci- ble. Thismeans that when themetal level is less than full, the exposed wall inside the crucible is being super-heated causing hard oxides and corundum to form. Energy is wastedwhen heating a less than full crucible. The build-up on the crucible wall is timeconsumingtoremoveandcon- tributes toearly crucible failure. Time spent cleaning the crucible, and or, the operator adding a small amount of metal at a time to maintain a full crucible reduces castingproduction. GAS FIREDHEAT ABOVE THE MELT Natural gas fired furnaces are very common. Unfortunately, much of the products of combustion are oxygen and hydrogen. Aluminum loves them both. Natural gasfired furnaces super-heat the surface of the melt and gener- ate a large amount of oxides on the surface of the melt. As these oxides grow, it becomes ever harder to heat themelt beneath themthereby wasting energy. Many of the oxides sinkwhile others become suspended in the melt and end up contributing to casting defects. Oxides contribute signifi- cantly tomelt losswasting both alu- minum and energy. These furnaces are shallow with a large surface area, They frequently require time consuming oxide removal. Metal temperature is lost when the furnace is open for oxide removal and the dip-well tempera- tureoftendrops belowcasting tem- perature. Production is often lost for several hours while waiting for the furnace to regain casting tempera- ture in the dip-well. OXIDE REDUCTION WITH IMMERSIONHEAT Dean Vander Jagt President New Century Heaters Ltd. www.newcenturyheaters.com Article Takeaways: 1. Understanding costly oxide build-up 2. Immersion furnaces vs reverb and crucible 3. Reducing melt loss and saving energy SIMPLE SOLUTIONS THAT WORK!