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Fig. 1. This plot shows the temperature along the increasing curve of the heat treat cycle.

Fig. 2. Shown is a modified heat treat cycle.

the outside before the second heating cycle. Some castings that McConway &

Torley produces in large quantities require a smooth contoured surface that will be gaged prior to being sent to a customer. Tese castings used to be made traditionally by incorporat- ing a cored surface which creates that smooth contour. In addition, there was a riser on the top of the core. Trials were performed to mold that contour in green sand with limited success. However, with the addition of a cus- tom made riser which fits that contour and the combination of good green sand, the plant was able to eliminate the core altogether. Tese changes resulted in an increase in general green sand quality, coupled with a decrease in time spent grinding the casting for gaging requirements. Figure 3 shows the difference between the cored surface, on the left, and the green sand surface, on the right. One of the dilemmas a

continuous improvement engineer must face when changing an already estab- lished process is to prove that the new process would be substantially more cost effec- tive than the old one. In the course of achieving this objec- tive, McConway & Torley set out to change a product which was the highest production piece at the company and had

remained unchanged for more than 20 years. It was a daunting task. Te problem that was most evident when McConway & Torley first took up this project was excess grinding. Te other driving force to change this part was improving the surface quality by at least twofold. In addition, the melt department was finding it difficult to pour these castings due to off-centered

Fig. 3. The casting before (left) versus after (right) the conversion from a core to a coreless surface is shown.

Fig. 4. The surface quality of the casting required extra grinding (left) and the castings were poured in a haphazard order prior to the change (right).

pouring cups. Figure 4 shows general surface quality that was achieved prior to making this improvement and the difficulty the melt department had to endure in pouring these castings. Traditionally, the melt department had to pour these castings in an alternat- ing technique. Tis created problems in positioning the crane above the cups. More superheat and thus more energy was needed to pour these molds. Tey turned to a new practice of pouring all straight lined pouring cups and came back and poured all the cross pouring cups. However, two molds are in a flask and all the gases that were generated when they poured the first pouring cup accumulated in the second half of the mold. Occasionally, metal would run over to the other side of the mold. In order to eliminate these problems, the gating design was taken back to the drawing board and the traditional way of gating the casting was changed. Research has been done in the past regarding the size of the riser’s breaker core in relation to the section size the riser would feed. On a particular casting that was using a 50% breaker, the operators had spongy shrink piping into the casting from the riser. Tis required extra welding on the casting surface and subsequent heat treatment due to the weld. Using a 70% breaker eliminated these problems by breaking clean and ensuring a solid casting (Figs 5-6).

October 2016 MODERN CASTING | 35

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