TECHNICAL TOOLBOX ISSUE 61 Contact: DAVID WHITE [email protected] ELECTRIC LAUNDERS For those that have a die cast machine row all on the same level and all the same alloy, electric launders provide some real benefits and are clean energy. They can hold metal for less than 1 kW per foot of launder. They provide a quiet transfer of the aluminum which helps the quality and metal melt loss. You can lose up to ½ of 1% of metal in the dross from pouring metal into holding furnaces. Remember the aluminum must go through three transfers if you do not use a launder: • Transferring the metal from the melter to the transfer ladle either by tap out or pump both are turbulent transfers. • Pouring the metal into the holding furnace is another turbulent transfer. • When the ladle scoops up the metal to put into the shot sleeve is the third. • This causes oxides and inclusions in the metal that can affect scrap rates considerably. ELECTRIC IMMERSION MELTING & HOLDING FURNACES The latest in electric furnaces are the immersion element furnaces. They originated in Japan over 15 years ago but became popular in the US about 9 years ago. There have been numerous improvements to the original design. By using a dense castable hot face and a micro porous silica back up super insulated lining you can get excellent energy numbers from these furnaces. Casing temperatures with 1250° F metal temperatures are as low as 105° F. The newer electric immersion element holding furnace uses electric elements inside sialon tubes in the middle of the aluminum bath. This produces no thermal head temperatures which means less metal loss, less oxide growth, less dross, excellent bath temperature uniformity and a casing temperature of less than 118° F. WOW! What more could you ask a holding furnace to do? Oh yeah, how about holding aluminum at temperature (1250° F) for less than 15 BTUs/# with well covers on and less than 22 BTUs/# in production. This is compared to 35-40 BTUs/# in a conventional radiant roof electric holding furnace. They average 2 years life on the elements and over 5 years life on the tubes. You can change the elements on the fly and can stay hot with one element till the other one gets changed. The 2,000# units have 25 kW connected, 4400# units have 35 and the 9,000# units have 90 kW connected. Some immersion element furnaces have additional power connected in case you need a passing gear. Since these units have full proportional controls you only use what you need to maintain temperature saving you more energy vs the on-off designs. In conclusion, when reviewing ‘green technologies’ for your plant and community, remember to look at electric melters and holders for reducing carbon footprint, emissions, and number of EPA permits required. Additionally, you will have a cooler plant and the cleanest metal in the business. * Gas fired melters work at 1.5 cubic feet/# of metal melted. With pre-heating and recirculation, you can achieve 1250 BTUs/# (or 1.25 cubic feet/#0. ** Gas pricing based on $6.50/1,000 cubic feet: electricity based on $ .065 per kWh. Photos courtesy of: The Schaefer Group, Inc. Radiant tubes in immersion furnace 2,000KG immersion holding furnace
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