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Metal Casting Technologies : March 2010
48 www.metals.rala.com.au Back to the in the United States (I chose the University of Wisconsin in Madison, a great university for Mineral and Metal Engineering located in the heart of the American foundry industry). I supplemented this formal education with a three-week "on-the-job training" in a steel foundry in Milwaukee, Wisconsin (in plain carbon steels) and one month in another steel foundry in Aarau, Switzerland (in low-alloy steels). When I got back home, I developed the reputation for making very good castings of steel (from plain carbon steels to low- alloy steels) for replacement parts of heavy equipment and mills - mining, sugar, cement, and steel rolling mills. I supplied the most prestigious dealers of these items in the country. I was even tagged as the "best foundryman" in the Philippines; probably because there was no other steel foundry available. I would like to share how I managed to make good steel castings at a time when spectrometers were not yet available in the market. I had to use some other means to ensure my compositions, especially of the low-alloy steels. The acid-electric steel melting process I used this acid-electric process because this was what my furnace was adapted to. We used silica bricks in the lining. Our Size R, 'Lectromelt Furnace was rated at 1,000 kva, at a two- tonne charge; but our power supply (the furnace transformer available) was only 600 kva, so we reduced the diameter of the hearth and made the furnace a one-tonne charge furnace while still using its 5-inch diameter electrodes. Being relatively over- sized, these electrodes made the melting time improve to less than one hour per charge. And this was how we did it. We carefully selected our scrap, taking note of possible resident alloying elements, and computed probable resultant compositions at melt down. Then we used the complete- oxidation process, reducing all oxidative elements (especially carbon, silicon, manganese and chromium), to almost nil and reintroducing the amounts needed to meet specified composition. We used an oxygen lance to start oxidation and maintain the "boiling" of the melt until we got about 0.200C in the melt (as checked by the spark test done on a sample from the melt using a grinding wheel). Then we "killed" the melt (stopped the boiling) with a 50% ferro-silicon batch thrown in. The other alloying elements that were oxidized would then be replenished to desired levels. After getting a sample from the melt that shrinks when it solidified, the metal was ready for tapping. We raised the temperature to tapping temperature by checking how fast a sample "filmed over," using seven seconds as the norm. During tapping, we throw in pure aluminium as a final deoxidizer to ensure gas-free metal. We used a tea-pot ladle to pour our molds, and placed a 50-50 mixture of iron oxide and aluminium powder contained in paper bags inside the mold risers to effect delayed solidification of the risers and ensure effective feeding into the castings. Needless to say, I designed the castings' gating, risering and feeding systems. Our molds were made of white silica sand bonded with western bentonite and, because melting and pouring was not done everyday, we skin-dried our molds before closing them on casting-day. Suffice it to say that our resultant casting surface-finish was extremely good and our cast parts exceeded specifications all the time. This was excusable at the time because we had no spectrometer to check and control metal compositions; it was better to exceed than to fall short of specifications. Today, the spectrometer could guarantee closer metal compositions to specifications. There was a time that we made a tractor drive-hub for a customer who sold it as a replacement part. The original was a plain carbon steel forging. Since there was no steel forging company at the time, we cast it as a manganese- molybdenum alloy. The surface finish was so fine; it passed off as a forging. After more than five years of use, the tractor was sold by the owner to our customer as surplus- junk. When our customer dismantled it to retrieve any useful parts, he came to the drive-hub that we supplied to him then and he cleaned it up and checked its dimensions. He found practically no wear, so he repackaged it in waxed paper and resold it as a new part again. In a sequel to this article, I shall discuss how to "make" steel using the complete-oxidation method of melting in an arc furnace in more detail. The arc furnace actually "makes steel" as it is a refining furnace, the induction furnace, on the other hand, is merely a remelting furnace. The difference is that one can subtract or add elements in a refining furnace, except the undesirable elements of sulphur and phosphorus; while he can only add in a remelting furnace. A difference with great significance. The time frame in this article is in the decade of the 1950s. Those were the days, when still recovering from the Pacific War, replacement parts were difficult to come by, especially for heavy equipment and mill parts and the best alternative was to produce them. I'd like to think that the shipyard's foundry found its niche in the country's industrial economy and it was a thriving business when I left later for "greener" pastures; that is, to mass producing cast iron round head sewing machines and refrigeration and air-conditioning compressors. The foundry I set up this time was a model for the industry in the Philippine context during the 1960s. ■
Media Kit 2010