JLG G12-55A AccuPlace Service Manual - Manual (Page 31)

3.9 G10-55A & G12-55A AccuPlace
Boom
3.4 BOOM EXTEND AND RETRACT
CHAINS
3.4.1 Boom Chain Inspection
Under normal operating conditions the boom chains will
need to be inspected every
250 hours of operation. The
retract chains 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
temperature 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%. As the chain flexes back and forth over the
sheave, the bearing joints (pins and inside link plates)
gradually incur wear due to articulation.
3.4.2 Inspection Guidelines
1. Park the machine on a firm, level surface, raise the
boom to a horizontal (level) position, place the
transmission control lever in (N) NEUTRAL, engage
the park brake switch.
2. Fully extend the boom until the extend chain is taut.
Shut the engine off.
3. The extend chains will be visible for inspection with
the vehicle in this state.
4. While doing the chain inspection, check all chain
clevis ends for distortion or cracking and sheaves for
bearing wear or grooving from the chain.
5. Inspect the retract chains every 1000 hours of
operation.
6. Inspect the chains for the following conditions:
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 machine instability, and could cause death or
serious injury and/or property damage.