8-18
Rust and corrosion
Chains used on lift trucks are highly stressed precision components. It is very important that the
“as-manufactured” ultimate strength and fatigue strength be maintained throughout the chain
service life. Corrosion will cause a major reduction in the load-carrying capacity of lift chain or
roller chain because corrosion causes side plate cracking.
Cracked plate
The most common cause of plate cracking is fatigue failure. Fatigue is a phenomenon that
affects most metals and many plastics. After many repeated heavy loads, the plates may crack
and the chains will eventually break. Fatigue cracks are almost always found through the pitch
holes perpendicular to the pitch line. Contrast this failure mode to the random failures caused by
stress-corrosion cracking. If cracks are present, replace all the chain on the truck. Noise in the
chain indicates that the plate is on the verge of cracking and will be failed before long.
Tight joints
All joints in lift chain should flex freely. Tight joints resist flexure, increase internal friction, thus
increasing chain tension required to lift a given load. Increased tension accelerates wear and
fatigue problems.
Tight joints in lift chains can be caused by :
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Bent pins or plates.
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Rusty joints.
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Peened plate edges.
Oil rusty chains and replace chains with bent or peened components.
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rotruding or turned pins
Heavily loaded chains operating with lube generate tremendous friction between pins and plates.
In extreme cases, the frictional torque in the joint can actually turn pins in the press-fit outside
plates. If chain is allowed to operate in this condition, the pins slowly work out of the chain
causing chain failure. Turned pins can be quickly spotted because the flats on the V heads are
no longer in line. Chains with turned or protruding pins should be replaced immediately. Do not
attempt to repair the chain by driving pins back into the chain.
Chain side wear
A wear pattern on pin heads and outside plates indicates misalignment. This condition damages
chain and sheaves as well as increasing internal friction in the chain system.
Chain anchors and chain wheel bearings
An inspection of the chain system includes a close examination of chain anchors and chain
wheel bearings. Check chain anchors for wear, breakage and misalignment.
Anchors with worn or broken fingers should be replaced. Anchors should be adjusted to
eliminate twisting or other misalignment in the chain. When chain is misaligned, load is not
distributed uniformly between the plates. Prolonged operation will result in premature fatigue
failure. Chain wheel bearings with badly worn flanges and outside diameter should be replaced.
Heavy flange wear indicates chain misalignment.
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