Basic Instructions - Chain Wear Tables - Roller Chains - New Holland CR6090 Tier 4a Service Manual

Basic instructions - Chain Wear Tables - Roller Chains

Chain wear
The individual joints in a roller chain articulate as they en-
ter and leave the sprockets. This articulation results in
wear on the pins and bushings. Material that is worn away
from these surfaces will cause the chain to gradually elon-
gate. Chains do not stretch. Material is removed from pin
and bushing.
Critical dimensions of the chain are as follows:
• (1) 2X pitch
• (2) Wear plus 2X pitch
• (3) Elongation due to pin and bushing wear
Elongation is normal and may be minimized by proper
lubrication and drive maintenance. The rate of wear is
dependent upon: the relationship between the load and
the amount of bearing area between pin and bushing, the
material and surface condition of the bearing surfaces, the
adequacy of lubrication, and the frequency and degree
of articulation between pins and bushings. The latter is
determined by the quantity of sprockets in the drive, their
speeds, the number of teeth and the length of the chain
in pitches.
An accurate wear measurement (1) can be made by us-
ing the above illustration. Measure as closely as possible
from the center of one pin to the center of another. The
more pitches (pins) contained within the measurement in-
crease the accuracy. If the measured value exceeds the
nominal by more than the allowable percentage the chain
should be replaced. The maximum allowable wear elon-
gation is approximately 3 % for most industrial applica-
tions, based upon sprocket design. The allowable chain
wear in percent can be calculated using the relationship:
200/ (N), where (N) is the number of teeth in the large
sprocket. This relationship is often useful since the nor-
mal maximum allowable chain wear elongation of 3 % is
valid only up to 67 teeth in the large sprocket. In drives
having fixed center distances, chains running in parallel
or where smoother operation is required, wear should be
limited to approximately 1.5 %.
For example, if 12 pitches (12 pins) of a #80 chain were
measured and the result was 313.944 mm (12.360 in)
or greater (using 3 % as the maximum allowable wear),
the chain should be replaced.
313.944 mm (12.360 in) would still be acceptable by
most industrial standards.
INTRODUCTION
Anything less than
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96091478
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96091469