Efficient Plant April 2018 - 31
Make sure your drive roller chains are neither too loose nor too tight.
Information in this chart courtesy of Diamond Chain
Recommended Possible Mid-Span Movement AC
Tangent length between sockets
to 45 deg.
AC = total possible mid-span movement
Depth of free sag = 0.866 AB approximately
Chain A 'Hand'
WHILE DRIVE ROLLER chain may be a mature form of mechanical-power transmission, it's still well-suited to many applications. Among
other things, roller chain is economical; resistant to shock loads; easy to
install; relatively efficient; available in a variety of shapes, forms, and materials; and capable of operating successfully in hostile environments. It also
can be used for conveyance.
A drive-chain system consists of the chain, sprockets (at least one pair),
guards, and some form of lubrication. According to Richard Knotek of
Motion Industries, Birmingham, AL (motionindustries.com), it's imperative that these systems be installed and maintained properly to deliver safe
operation and maximum service life. Using the five fingers of the human
hand as a mnemonic, he offered the following reminders.
- Jane Alexander, Managing Editor
Richard R. Knotek is a technical-training specialist with the Motion Institute,
a division of Motion Industries (MotionIndustries.com). Learn more about
extending roller-chain life through the company's "MiHow2" videos at
Drive roller chain has a recommended total mid-span movement of
0.5 in./10 in. of shaft-center-line distance, for horizontal applications, and half of that for vertical orientation (see chart). If a chain
is too loose, it will jump. If it's too tight, bearing loads increase
dramatically, leading to failure
First and foremost, the system must be electrically locked-out,
tagged-out, verified, and mechanically load-leveled prior to performing work on it. Avoid pinch points. Use proper guards.
MIDDLE FINGER: CHAIN AND
"Stretch" is actually caused by the wearing away of chain components. Maximum recommended stretch should not exceed 3% of
original installed length. Half links are weak links. Worn chain will
jump, whip about, and accelerate sprocket wear. Sprocket teeth
should not look like shark fins or be worn to the nub. These conditions contribute to system vibration, leading to rapid failure. Clean
chain and sprockets last longer.
RING FINGER: LUBRICATION
Since drive roller chain is essentially a series of interconnected
bearings revolving around an axis, it requires lubrication. (Note:
polymer types do not.) Featuring additives for sliding friction,
roller-chain lubricants are formulated to prevent centrifugal forces
from flinging the lubricant off the chain. There are three major
Manual or drip: Oil is applied periodically with a brush, spout, or
dripped on chain.
Bath: Oil covers the lowest portion of a chain enclosed in a leakproof guard.
Circulating stream: In this type of closed system (similar to the bath
system above), oil is sprayed on to chain, circulated, and filtered.
LITTLE FINGER: ALIGNMENT
Sprocket shafts should be parallel. The offset of sprocket faces
should be < 0.0625 in./ft. of shaft-center-line distance. Angularity
should be < 0.5 deg. Axial run-out (wobble) of sprockets should be
< 0.001 in./in. of sprocket diameter (see chart). EP