Simple Solutions That Work! Issue 7

In this article we will give you some basic facts about melting and holding aluminum in everyday furnaces as well as a ranking of ROI on improvements you can make to those furnaces to increase efficiency and energy usage is a number of different types of furnaces. Ranking of ROI Expenditures The ‘Ranking of ROI’ expenditures for aluminum furnaces, in other words, how to get the biggest bang for your bucks from quickest-to-slowest investment recovery. 1. Buying the best furnace designs and most cost effective materials. a. Central melt furnaces are large – it is difficult to clean furnaces manually that are larger than 50-to-60,000 pounds hold capacity. Mechanized cleaning (fork truck and hoe) does the best job on larger high headroom furnaces. Most large furnaces have single end clean-out doors that are narrower than the interior furnace width. This makes for hidden, right-angled corners that are difficult to clean. Unacceptable oxide build-up leads to premature relines and impaired efficiencies. 1) The solution is having better access to the furnace interior with full width double-end doors. The floors should have gentle transition slopes from door opening hearths-to-the flat portion of the floor (no greater than 35”) so that the furnace can be easily cleaned for “sludge” on the floor. 2) It pays to not go cheap on the hot face furnace linings. Modern central melt furnaces have 80-to-90% alumina non-wetting hot face linings. They are easily cleaned (build- up is easily removed), rugged and will not penetrate at the all important belly-band area (molten metal contact area). a) Premium hot face linings pay. We recommend higher alumina products containing a phos bonding agent. If you do use the cheaper hot face linings, a product like 70-to-85% alumina phos- bonded plastic refractory will hold up better in a melter than the same alumina content non-wetting low cement castables. 2. Spend the money to super insulate the furnace linings. New products, such as micro porous silica insulating materials will save a huge amount of “fixed heat loss” energy. If the lining is properly engineered, the all- important “freeze plane” will still occur in non-wetting lining materials. This is a case of your being able to “have your cake and eat it too.” These super insulating products normally add about $18.00/sq. ft. to the cost of the furnace lining, but they normally provide about a 16-to-20 month ROI. 3. Sow pre-heat hearths are a wise investment. If 50% of the aluminum you melt is new metal (typical of a foundry with a 50/50 yield), and 50% is scrap and returns melted in the charge well, the metal pre- heated for about 30 minutes on the hearth and then pushed into the bath will save 12-15% of the normal energy required to melt the metal if it were all cold charged into the bath. DAVID WHITE National Sales Manager THE SCHAEFER GROUP ARTICLE TAKEAWAYS: 1. Super insulate your furnace linings to reduce energy costs 2. Why Sow pre-heat hearths are a wise investment 3. Understanding “hard energy” use numbers for Gas-fired, Electric Radient-roof, Crucible and Tower Melters 6 FURNACE FACTS, ROI’S & ENERGY USE NUMBERS