Page 170 - The Tribology Handbook

B2 Roller chain drives

INSTALLATION AND MAINTENANCE

Wheel alignment Chain adjustment

Make sure that the shafts are properly supported in The chain should be adjusted regularly so that, with one
bearings. Shaft, bearings and foundations should be suit- strand tight, the slack strand can be moved a distance ‘A’
able to maintain the initial static alignment. at mid point (see diagram below). To cater for any
Sprockets should be arranged close to the bearings. eccentricities of mounting, the adjustment of the chain
Accurate alignment of shafts and sprocket tooth faces should be tried through a complete revolution of the large
provides uniform distribution of the load across the entire sprocket.
chain width and contributes substantially to maximum
drive life.
A

.c--
I-
C
A = ST Where K = 25 for smooth drives
= 50 for impulsive drives
\, ”
To measure wheel wear To measure chain wear

Examination of the tooth flanks will give an indication of Measure length M in millimetres (see diagram). The
the amount of wear which has occurred. Under normal percentage extension can then be calculated using the
circumstances this will be evident as a polished worn strip following formula:
about the pitch circle diameter of the sprocket tooth. If the M- (XX P)
depth of this wear has reached an amount equal to 10% of Percentage extension = x 100
the ‘Y’-dimension (see diagram) then steps should be XXP
taken to replace the sprocket. Running new chain on
sprockets having this amount of tooth wear will cause where X = number of pitches measured.
rapid chain wear. It should be noted that in normal P = Pitch in mm
operating conditions with correct lubrication, the amount As a general rule, the useful life of the chain is terrni-
of wear at ‘X’ will not occur until several chains have been nated, and the chain replaced, when the percentage
used. extension reaches 2% (1 ‘/o in the case of extended pitch
I Y i chains). For drives with no provision for adjustment, the
rejection limit is lower, dependent upon speed and layout.
A useful figure is between 0.7% and 1% extension.

!Mi--

Health and safety
CAUTION 5. Always ensure that directions for the correct use of
The following precautions must be taken before discon- any tools are followed.
necting and removing a chain from a drive prior to 6. Always loosen tensioning devices.
replacement, repair or length alteration: 7. Always support the chain to avoid sudden unexpected
1. Always isolate the power source from the drive or movement of chain or components.
equipment. 8. Never attempt to disconnect or re-connect a chain
2. Always wear safety glasses. unless the chain construction is fully understood.
3. Always wear appropriate protective clothing, e.g. 9. Never re-use individual components.
hats, gloves and safety shoes etc. as warranted by 10. Never re-use a damaged chain or chain part.
circumstances. 11. On light duty drives where a spring clip joint (No. 26)
4. Always ensure tools are in good working condition is used always ensure that the clip is fitted correctly in
and use in the proper manner. relation to direction of travel, with open end trailing.
B2.6