SkyTrak 8042 Service Manual - Manual (Page 183)

Boom
3.122 Model 8042, 10042, 10054 Legacy Rev. 03/04
Environments in which material handling vehicles
operate can vary widely, from outdoor moisture to mildly
corrosive or highly corrosive industrial atmospheres, in
addition to abrasive exposures such as sand and grit.
Some effects can be as follows:
• Moisture - Corrosive rusting reduces chain strength
by pitting and cracking.
• Temperature - Low temperature reduces chain
strength by embrittlement. Going in and out of cold
storage results in moisture from condensation.
• Chemical Solutions or Vapors - Corrosive attack on
the chain components and/or the mechanical
connections between the chain components.
Cracking can be (and often is) microscopic. Going
from microscopic cracking to complete failure can be
either abrupt or may require an extended period of
time.
• Abrasives - Accelerated wearing and scoring of the
articulating members of the chain (pins and plates),
with a corresponding reduction in chain strength.
Due to the inaccessibility of the bearing surfaces (pin
surfaces and plate apertures), wear and scoring are
not readily noticeable to the naked eye.
Following are some examples of dynamic shock loading
which can impose abnormal loads above the endurance
limit of a leaf chain:
• High velocity movement of load, followed by sudden,
abrupt stops.
• Carrying loads in suspension over irregular surfaces
such as railroad tracks, potholes and rough terrain.
• Attempting to “inch” loads which are beyond the
rated capacity of the vehicle.
The above load cycles and environmental conditions
make it impossible to predict chain life. It is therefore
necessary to conduct frequent inspections until
replacement life can be predicted.
The boom chain’s normal life expectancy can be expressed
as a maximum percent of elongation. This is generally
3% of pitch. As the chain flexes back and forth over the
sheave, the bearing joints (pins and inside link plates)
gradually incur wear due to articulation.
a. Inspection Guidelines
Expose the extend and retract chains (refer to Section
3.7.1, b. “Expose Extend Chains for Inspection,” Section
3.7.1, c. “Expose Intermediate Boom Retract Chain for
Inspection,” or Section 3.7.1, d. “Expose Inner Boom
Retract Chain for Inspection.”) and inspect the chains for
the following conditions:
Elongation
When the original length (1) of 12" (305 mm) per foot of
new chain has elongated from wear to a length (2) of
12.36" (313 mm), the chain must be discarded and
replaced. (Refer to Section 3.7.6, “Boom Extend and
Retract Chains Removal and Replacement.”)
It is important to measure the chain in the section that
moves over the sheaves because it receives the most
frequent articulation. Measuring the chain near its clevis
terminals could give an inaccurate reading.
Intermediate Extend Chains and Retract Chains
Measure across a span of 17 pins at the center of the
chain. Measure from pin center to pin center.
Inner Extend Chain
Measure across a span of 13 pins at the center of the
extend chain. Measure from pin center to pin center.
All Chains
The maximum measurement allowed is 12.36" (313 mm).
If the measurement is more than 12.36" (313 mm), the
chain must be replaced. (Refer to Section 3.7.6, “Boom
Extend and Retract Chains Removal and Replacement.”)
MM2120
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