The clamp casting is designed with two varying angles so the fi eld harrow can be pulled from either side for a more or less aggressive go at the soil.
The metalcasting facility suggested
65-45-12 ductile iron, which exhibits 65,000 psi tensile strength, 45,000 psi yield strength and 12% elongation. “There wasn’t a real high strength
requirement, but they wanted high ductility, which is why we went with that grade,” Pint said. With material selected, Hammond
sent over his fi rst drawing of the re- designed component. Smith Foundry responded with a redesign of its own that would make it easier (and less
costly) to cast. But Smith Foundry’s version inhibited key features of the tube clamp. The main culprit to a quick and easy design: the casting’s parting line location. The parting line is the line on a
casting corresponding to the separa- tion between the cope (top) and drag (bottom) parts of the mold. For ease of setting the core into the mold, Smith Foundry initially wanted to position the casting so the parting line would run through the center of the Besler Industries name on one of the fl at ends and across the top hole (Fig. 1). “Since I had never designed for
casting, I would send them a picture,” Hammond said. “They would draw
on that picture showing where the parting line would be, spelling it out pretty easily.” The parting line in a mold is typi-
cally located at the largest cross sec- tion, and the patternmaker develops the pattern and corebox around it. Often, gates and risers are located on the parting line and will require removal via grinding, which may confl ict with the customer’s require- ments for the part. Hammond determined the initial
parting line location would not allow the redesigned component to include an important design element—a recessed diameter surrounding the top hole. Each clamp is bolted onto the tube through the top hole. Sometimes the clamp is positioned onto the tube so that a spike, which drags through the farm soil, must go through the hole instead of just a bolt. Besler found that the fabricated clamp often required modifi cation to allow the spike to fi t, adding expense and time. “In some places, the threads on the
Fig.1. Smith Foundry’s initial parting line location would have run across the top of the casting for ease of core placement, but it would have affected the top hole and recessed diameter.
34 METAL CASTING DESIGN AND PURCHASING
spike would be a hair short,” Ham- mond said. “We decided to dish the hole down and put a recess there so we wouldn’t have to modify the spike every time.” With the recess at the hole, the part- ing line location had to change.
MAY/JUNE 2011
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