SkyTrak 6036 Service Manual - Manual (Page 86)

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3.46 Model 6036 Legacy
Cracked Plates
Inspect the chains very carefully, front and back as
well as side to side, for any evidence of cracked
plates. If any one crack is discovered, the chain
should be replaced in its entirety. (Refer to Section
3.3.7, e. “Chain Replacement”.)
It is important, however, to determine the cause of the
crack before installing a new chain so the condition
does not repeat itself.
• Fatigue Cracking - Fatigue cracks (Fig. 3-99, 4)
are a result of repeated cyclic loading beyond the
chain’s endurance limit. The size of the load and
the frequency of its occurrence are factors which
determine when fatigue failure will occur. The
loading can be continuous or intermittent
(impulse load).
• Stress Corrosion Cracking - The outside link
plates are particularly susceptible to stress
corrosion cracking (Fig. 3-99, 5). Like fatigue
cracks, these initiate at the point of highest stress
but tend to extend in an arc-like path between
holes in the pin plate. More than one crack can
often appear on a link plate. In addition to rusting,
this condition can be caused by exposure to an
acidic or caustic medium or atmosphere.
Stress corrosion is an environmentally assisted
failure. Two conditions must be present: corrosive
agent and static stress. In the chain, static stress
is present at the aperture due to the press fit pin.
No cyclic motion is required, and the plates can
crack during idle periods.
• Corrosion Fatigue Cracking - Corrosion fatigue
cracks are very similar to fatigue cracks
(Fig. 3-99, 4) in appearance. They generally
begin at the aperture and grow perpendicular to
the chain pitch line. Corrosion fatigue is not the
same as stress corrosion. Corrosion fatigue is
the combined action of an aggressive
environment and cyclic stress, not a static stress
alone, as in stress corrosion.
Figure 3-99 Inspect Plates for Cracks
Other Modes of Failure
• Ultimate Strength Failure - These types of
failures are caused by overloads far in excess of
the design load. Either fractured plates
(Fig. 3-100, 6) or enlarged holes (7) can occur. If
either of these failures occurs, the chain should
be replaced immediately. (Refer to Section 3.3.7,
e. “Chain Replacement”.)
• Tight Joints - All joints in the chain should flex
freely. Tight joints (Fig. 3-100, 8) resist flexing
and increase internal friction, thus increasing
chain tension required to lift a given load.
Increased tension accelerates wear and fatigue
problems.
If the problem is caused by dirt or foreign
substance packed in the joints, clean and
lubricate thoroughly before re-installing the chain.
If the problem is caused by corrosion and rust or
bent pins, replace the chain. (Refer to Section
3.3.7, e. “Chain Replacement”.)
Figure 3-100 Other Chain Failure Modes
MM2080
4
5
MM2070
MM2100
MM2110
MM2090
8
6
7