SkyTrak 8042 Service Manual - Manual (Page 107)

Boom
3.46 Model 8042, 10042, 10054 Legacy Rev. 03/04
3.4 BOOM CHAINS - THREE SECTION
BOOM (8042 AND 10042)
This vehicle uses double extend chains to extend the
boom and a single retract chain to retract the boom. The
extend and retract chains are constructed of 3/4" pitch
links with 6 x 6 leaf lacing.
Note: DO NOT attempt to repair a chain. Replace a
stretched or damaged chain with a new part. Always
replace both the chain and the clevis. It is recommended
that when any chain is replaced, that all the chains and
clevis’ be replaced at the same time.
3.4.1 Boom Chain Inspection
Under normal operating conditions the extend chains will
need to be inspected every 250 hours of operation. The
retract chain will need to be exposed and inspected every
1000 hours of operation. Environmental conditions and
dynamic impulse/shock loads can drastically affect
normal operating conditions and require more frequent
inspection intervals.
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.
WARNING:
Worn pins, stretched or
cracked links or corrosive environments can
cause chain failure. A chain failure could result
in uncontrolled boom movement, loss of load
or vehicle instability, and could cause death or
serious injury and/or property damage.
250
OH23902
MS21702