Page 188 - Improving Machinery Reliability

Machinery Reliability Audits and Reviews 159

Table 3-13
Machinery Component Specification

Radial and Angular Contact Ball Bearings
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1.0 Scope
1.1 This specification covers the mandatory requirements for radial and angular contact ball bear-
ings used in general purpose process machinery.
1.2 Bearings shall comply with the specification requirements of the AFBMA for ball bearings.
Bearing dimensional tolerances shall meet or surpass the tolerances defined by ABEC Class 1.
1.3 All bearings supplied per this specification shall be obtained directly from the identified bear-
ing manufacturer or authorized distributor.
1.4 The bearings shall be packaged per AFBMA Standards, Section 6. The bearing box shall be
marked to identify the original bearing manufacturer and the alphanumeric bearing identifica-
tion code or designation system.
2.0 Ball bearing design
2.1 Radial and angular ball bearings shall have the following design and features:
Bearing ABEC Ball Other Acceptable
- type clearances retainer features manufacturers
Single row, c-3 Riveted Conrad type, SKF/MRC, FAG
deep groove steel no filling Torringtonl
ball bearings slot allowed Fafnir, NSK,
NTN, KOYO
Double row, c-3 Stamped No filling SKF/MRC, NTN,
deep groove steel slot allowed Torrington/
ball bearing Fafnir, KOYO
40" angular Standard Machined Land riding, SKF/MRC,FAG,
contact ball bronze if available; Torringtod
bearing duplex mount- Fafnir, KOYO,
able, nil prel. Rollway
2.2 Bearing shields, seals, snap rings, etc., shall have the configuration specified by purchaser's
applicable spare parts symbol number or specified description for the stipulated application.
2.3 No substitutions are allowed for the bearing manufacturers or the bearing features shown with-
out the auuroval of the uurchaser's rotating equipment reliability engineer.

Regreasable vs. Non-Regreasable Rolling Element Bearings
At the inception of a project, the specifying engineeer will often be confronted with
the question of when sealed, non-regreasable bearings present advantages over the tra-
ditional, regreasable variety. It is intuitively evident that fully sealed rolling element
bearings would be the right choice for a wide range of appliances, such as a vacuum
cleaner or household cooling fan. Conversely, experienced engineers have known for
years that regreasable bearings are the correct choice for larger size or higher speed
bearings. There was, however, no clear-cut guideline as to when to request one or the
other, or which of the two modes-regreasable or non-regreasable-would make more
economic sense when the labor cost of regreasing and the cost of rectifying greasing-
related errors were considered.
Some time ago, a large international bearing manufacturer provided a rule of
thumb that can be used under typical circumstances, The rule requires calculating the