Skytrak 6042 Service Manual User Manual download pdf (Page 92)

Boom

3.46

Model 6042 Legacy Origin 7/02

3.4 BOOM CHAINS

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

Figure 3-99 Every 250 Hours of Engine Operation,

Inspect Boom Extend Chain Condition

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 nor-

mal operating conditions and require more frequent in-

spection 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.

MM2130

250

MS21702

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