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C-30HD — PARTS & OPERATION MANUAL — REV. #4 (03/06/01) — PAGE 91
Roller chain properly selected, installed and maintained is an
extremely versatile means of power transmission. It is possible,
however, to greatly reduce a chain’s life and even induce failure if
the chain is abused through improper installation, operating or
maintenance procedures. In certain applications, failure can lead to
personal injury or property damage.
Recommendations and comments on how to get the most from
your roller chain drive are given on the following pages.
WORKING LOADS
UTS-Ultimate Tensile Strength-is the one time pull required to break
the chain. The Tensile Strength figures given in the Diamond catalog
are not allowed working loads. For single strand chain, the load
(pull) applied to the chain in service should never exceed 1/6th of
the UTS for the chain being used except as noted below.
It is possible to exceed the allowable working loads for a limited
number of cycles, but you should contact Diamond Chain Company
before this is considered. A roller chain should never be loaded
above 50% of UTS for even one cycle. To do so will damage
the chain structure and reduce its capacity.
The UTS or one time breaking load of multiple strand chain is the
UTS of a single strand chain times the number of strands; i.e., two
strand chain is twice as strong as single.
When allowable working loads are considered, however, the
capacity of each strand in a multiple strand chain is only 65% of the
single strand rating; thus, three-strand chain would rate not three
times single but only 1.95 times. This is because the chain load
cannot be exactly distributed across all three strands of the three-
strand chain.
INSTALLATION AND DRIVE ALIGNMENT
Chain and sprockets must be installed correctly. Sprockets must be
properly aligned and sprocket shafts must be parallel so the drive
will run in a plane perpendicular to them. Axial alignment should be
checked with a straight edge which will extend across the finished
sides of the sprockets. They should be true-running with minimum
wobble and eccentricity. The higher the drive speed, the more
important these details become.
ROLLER CHAIN — APPLICATION INFORMATION
The chain should be installed so the slack span is properly tensioned.
To check chain tension, turn one sprocket to tighten the upper span
of the chain while holding the other sprocket fixed. The lack span
should have 4-6% of span length in the mid-span movement for
horizontal drives and 2-3% for vertical drives.
A roller chain’s capacity can be significantly reduced if it is twisted
or bent sideways in the direction of the pin axis. Exercise particular
care in alignment of hoist or other applications where loads are
suspended near personnel.
LUBRICATION
As a chain articulates in entering and leaving a sprocket,
there is
relative movement between pin and bushing surfaces. These
surfaces wear causing chain elongation. If a lubricant film can
be maintained between the pin and bushing, the wear rate is
very slow and the chain wear life very long. Maintaining the oil
film is relatively simple at low speeds but becomes increasingly
difficult as the speed increases.
It is recognized that good lubrication is not possible in many
applications, so shorter wear life must be accepted in these
situations.
In general, chain wear leads to rough or unsatisfactory service
prior to actual chain breakage. Good lube can help to prevent
chain failure by providing protection against rust or corrosion.
Rusting can allow pits to form in the surfaces of the chain parts
causing stress concentration points. This can lead to chain
failure at relatively low
loads.
The clearance between
pin and bushings is very
small, on the order of
.003 to .005 inches. A
lubricant must be thin
enough to flow into the
chain. SAE 30 weight oil
is about right for room
temperature. Lighter oil
should be used for lower
ambients and heavier
for higher operating temperatures. Grease should not be used
as it cannot penetrate chain clearances.