Changes Bring Changes
Development of the new four-cylinder auto compressor, however, led to a review of the deburring and finishing techniques. Among the processes evaluated were thermal deburring, high-pressure-water deburring, ball burnishing, extrusion deburring, photochemical etching, and chemical deburring.
Some compressor components posed special problems, and the valve reeds were in this "problem" category. To be certain that the new, lightweight compressor (17.3 lb compared with up to 35 lb for some six-cylinder models) would meet high-performance specs, it was built to operate at speeds up to 7000 rpm. This, in turn, called for a redesign of the reeds.
A thorough testing program in Delco's product engineering department resulted in the evolution of this reed from a four-spoke, 0.013" thick disk to the present two-spoke, 0.015" thick reed, which is known as the R-4 reed. During these tests, it became obvious that a full radius was needed on the edges of the 0.191" to 0.195" diameter center hole; it also became obvious that this wasn't going to be easy to do.
The combination of the small central hole and the high material hardness (Re 51-53 at this stage) resulted in 90- to 96-hour cycles in conventional vibratory finishing machines. Because of these excessively long cycles, Delco investigated several alternative finishing methods, settling finally on centrifugal barrel finishing and deburring.
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