PRODUCT INNOVATIONS Mexican Foundry Reduces Chip Melt Loss With In-House Melting
At full capacity, Pistones Moresa, Mexico City, Mexico, an aluminum casting facility producing pistons for the Mexican automotive market, generates 65 tons of machining chips per month. Its melt loss for the chips sent to a smelter is more than 20%. Trough the years, it became the norm for the metalcasting facility to sign the yearly contract with the smelter under the premise that the weight of metal return would be no less than 76% of the weight of the smelted material, with losses of 7% to moisture, 17% to dross and negligible amounts to iron and other contaminants. Pistones Moresa wanted to increase the amount of chips recovered, reduce the cost of recovering the machining chips and save on gas consumption by eliminating the double melting of machining chips. After a cost-benefit analysis, the casting business decided to invest in an in-house chip melting system. Doing so led to a total melt loss reduction from 17 to 3% for a par- tial monthly savings of $31,000, before subtracting the cost of low chip melt- ing. Te savings also included the costs due to reductions for ingot purchased, as well as reductions in freight costs as- sociated with smelting chips and haul- ing recycled metal back to the foundry. Te investment in the in-house system was paid back in 1.5 years. Pistones Moresa implemented the in-house chip melting process in a joint effort with SIA Automation, Aguascalientes, Mexico, and Molten Metal Equipment Innovations,
Middlefield, Ohio. Te project in- tegrated various individual pieces of equipment grouped into four clusters: 1. chip pre-treatment; 2. chip submergence system; 3. melting furnace; 4. alloying furnace. Te system was designed to melt
chips at a rate of 1,102 lbs./hour (500 kg/hour). Te chip pre-treatment system consists of seven basic com- ponents: collection hopper, three conveyors, solids separator, centrifugal dryer, magnetic separator, drying oven and charging scale. Te chip submer- gence system consists of a mixer and a recirculation pump. Te pump draws hot metal from the furnace’s holding chamber directly into the mixer well to increase the melt rate of the chips be- ing submerged in the mixer. A launder system transfers metal from the chip- melting furnace to the central alloying tilting-furnace. Detailed evaluation of the chip melting process showed the chips coming from the machining operation contain between 12 and 15% moisture;
the drain system in the collection hop- per removes about 8% of the moisture, leaving chips with 4 to 7% moisture. Te centrifugal unit then may subtract up to 5% of moisture for a total mois- ture percentage less than 2. Te drying oven further reduces moisture content to less than 0.3%. During the optimization of the melting practices and process param- eters to configure the in-house chip melting system, Pistones Moresa established and documented that for every 8,800 lbs. (4,000 kg) of dry chips that were charged, between 176 and 264 lbs. of dross was generated. Using a mass balance formula where metal input (dry chips) equals metal output (aluminum transferred to alloying furnaces) plus oxidized metal output (dross), the metalcaster determined its recovery rate was between 97 and 98%, for a 2 to 3% metal loss. Tis article was adapted from the AFS Proceedings paper (11-098) “Improving Competitiveness Trough In-House Alu-
minum Chip Melting: A Case Study.” Visit
www.mmei-inc.com for more information.
The side view of the furnace wells at Pistones Moresa shows the position of the cleaning well (A), mixer (B), recirculation pump (C) and submerged openings (D).
54 | MODERN CASTING September 2011
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