thereby compromising the seal and allowing corrosive fluid to
reach the SS impeller core.
The gap was determined to result from PFA solidification
shrinkage, or drawback, following injection molding of the
impellers. See Figure 6 for a close up of the gap.
Another meeting was held with purchasing, the OEM
engineer, and the OEM product line manager to review the
O-ring groove defect. They stated that the primary mechanical
seal joint was intended to be between the non-metallic shaft
sleeve and the PFA lining on the back of the impeller – even
Figure 7. New O-ring groove design.
though this was not a proven design. Albemarle did not accept
this response due to the lack of flatness and typical mold surface irregularities present, and began rejecting any impeller that
did not pass a thorough visual inspection. After several more
discussions, the OEM agreed that an improved impeller design
was needed to allow the O-ring to function as intended.
Molding modifications were made that eliminated the
gap between the PFA lining and the shaft, so that a positive
seal could be made between the O-ring and its mating surfaces. See Figure 7 for the improved design, which yields a zero
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