sions between both Albemarle and the OEM, the rubbing contact
was resolved by simply adjusting the impeller setting procedure in
the field, and by the OEM slightly modifying the dimensions and
manufacturing tolerances to ensure proper internal clearance of the
pump impeller. A corrective action list was created to keep the team
on track with the remaining issues around the recesses in the impel- Figure 5. Impeller
ler balance holes. section close-up.
The issue of the recesses in the PFA
in the balance holes was not adequately
appreciated by the OEM since there was
not a perceived problem with the PFA
molding process. In order to ensure
quality parts were sent to Albemarle,
visual quality checks and spark testing
of the lining for pinholes was required
for all new impellers.
Over the course of several months,
as new pump installations were brought
into service, more impellers were caught
at the local OEM supplier that did not
pass the QC inspection. The matter
reached the point where the supplier
stock did not have any acceptable impellers, and an unexpected failure requiring
an impeller replacement could have shut
the plant down while the plant waited
for an acceptable part.
Another meeting was held with the
OEM lead engineer to express the need
to address the root causes of the defects
found in the balance holes. Following
many other lengthy discussions and
emails, a new manufacturing design was
proposed to address the causes of the
recesses. After agreeing to the changes,
the OEM and their part supplier took
several more months to make the first
test impellers. Samples were sent to
Albemarle for inspection, and one
sample was sectioned by the OEM to
ensure that no voids or recesses were
present.
The new impeller design proved
successful after further testing in the
plant at Albemarle. The corrective
action list was updated with all of the
information learned up to that point
resulting in a successful impeller design.
We requested that the same modifications be made to the other pump impeller sizes so they would not experience
the same phenomenon. The OEM did
not quickly respond in agreeing to make
the changes.
