However, an investment casting made it possible to provide mating parts having a clearance tolerance of .005" per side with no machining.


In fact, a key and keyway were cast in place on the respective parts to provide further stability to the assembly. Square cross passages were easily included as part of the casting, assuring the com- plete diffusion of air entering the mask.


The head, basically a segment of the mask's retain- ing ring, was required to hold the valve and its attached air hose securely to the rubber mask. A sheet stamping had been considered for both the head and the ring but as Hawley put it: "The head has got to be strong. I don't want to be responsible for an air hose ever pulling away from the mask."


Investment casting provided this strength. The cast head could later be welded to the remainder of the ring which would be of heavy gage.sheet. Two three- sided pockets were cast into the head, increasing the weld area to further maximize the strength. By investment casting this part it was also possible to form the head to the exact contour of the rubber mask and assure its mating accurately with the valve body itself.


During the design session, alloys were discussed thoroughly and it was decided to cast parts in both 421 Mn. Brass and in 300 series Stainless Steel. When chrome plated, the brass would be excellent for the average diver, but stainless steel would be preferable for certain types of professional usage.


Shortly after production began, Mr. Hawley found it necessary to design an alternate valve for use by divers having air tanks with pressures varying from those which had originally been considered. Com- plete new tooling would have made this costly ... but inexpensive inserts used with the basic tooling solved this additional problem.


This is just another impressive example_ 9f bow investment castings can solve any number of desigri·• ·"·-...... ~.. •.• , .. ,, ... . ~·, .. . . . ' - ~ ~ . .....


A


Photo (A) shows the scuba mask valve body; Photo (B) shows the valve head; photo (C) shows the head and ring assembled with alter- nate valve body (inset left) and standard valve body (inset right).


B


c


and production problems. However, the most im- portant point that should be remembered about this application is that designer Hawley was able to take full advantage of our process because he contacted us early in the design stage.


Intricate shaped parts with high strength, close tolerances and a variety of alloys are possible. How- ever, there was one simple reason for the success. The parts were designed for investment casting rather than being an adaptation of parts designed for another process.


The Investment Casting Institute and its member companies invite your inquiries at all times. How- ever, the earlier you contact them during the de- sign of a part or parts the greater assistance they can offer.


·" ...... ~·· .. ~ • " .. ~ ·- .... -,,. ... •"' ..... ...,..,'! ... · • ...,, '•'"" ............. .,... .... ~ .. ,.


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