Chain Stretch Tolerance - JLG AM-19 Operators And Safety Manual Service & Maintenance Manual Illustrated Parts Manual

JLG
Lift SECTION 8 - SERVICE PROCEDURES
JLG
Lift
lubrication at the factory is applied in a hot dip
tank to assure full penetration into the joint. Do
not steam clean or degrease chains. At time of
chain installation, factory lube must be supple-
mented by a maintenance program to provide
a film of oil on the chains at all times. If chains
are corroded, they must be inspected, espe-
cially the outside plates, for cracks in-line with
the pins. If cracks are found, replace the chain;
if no cracks are discovered, lubricate the chains
by dipping in heated oil, and reinstall on the
machine. Keep chains lubricated.
Table 8-1.
Chain Stretch Tolerance
Chain Size
I
Pin to Pin
I
Allowable Stretch
Measurement 12" Span
. 50" Pitch 12" or 24 pitches .36 in.
3. Fatigue Cracks: Fatigue is a phenomenon that
affects most metals, and is the most common
cause of chain plate failures. Fatigue cracks
are found through the link holes, perpendicular
(90 degrees) from the pin in-line position. In-
spect chains carefully after long time use and
heavy loading for this type of crack. If any
cracks are discovered, replace all chains, as
seemingly sound plates are on the verge of
cracking. Fatigue and ultimate strength failures
on JLG Lifts are incurred as a result of severe
abuse as design specs are well within the rated
lifting capacity of these chains.
4.
Tight Joints: All joints in the roller chain should
flex freely. On roller chain, tight joints are usu-
ally caused by rust/corrosion, or the inside
plates "walking" off the bushing. Limber up
rusty/corroded chains (after inspecting care
fully) with a heavy application of oil (preferably
a hot oil dip). Tap inside "walking" plates in-
ward; if "walking" persists, replace the chain.
This type of problem is accelerated by poor
lubrication maintenance practice, and most
tight joint chains have been operated with little
or no lubrication. Tight joints on leaf chain are
generally caused by:
a. Bent pins or plates.
b. Rusty joints.
c. Peened plate edges.
Oil rusty chains, and replace chains with bent
or peened chain components. Keep chains
lubricated.
5. Protruding or Turned Pins: Chains operating
with inadequate lube generate tremendous
friction between the pin and plates (pin and
bushing on roller chain). In extreme cases, this
frictional torque can actually turn the pins in the
outside press-fit plates. Inspect for turned pins,
which can be easily spotted as the "V" flats on
the pin heads are no longer in line. Replace all
chains showing evidence of turned or protrud-
ing pins. Keep chains lubricated.
6. Chain Anchors and Sheaves: An inspection of
the chain must include a close examination of
chain anchors and sheaves. Check chain an-
chors for wear breakage and misalignment.
Anchors with worn or broken fingers should be
replaced. They should also be adjusted to
eliminate twisting the chain for an even load
distribution .
Sheaves should be inspected for worn flanges,
which would indicate misalignment, and wear
on the outside diameter of the sheave. A worn
sheave can mean several problems, as fol-
lows:
a. Chains too tight.
b. Sheave bearings/pin bad.
c. Bent/misaligned chains.
• Mast Cable Inspection Procedure
A
IMPORTANT
MAST CABLES ARE TO BE INSPECTED EVERY
THREE MONTHS.
A
CAUTION
WEAR PROTECTIVE GLOVES TO PROTECT HANDS
WHEN HANDLING CABLE.
The periodic inspection shall cover the entire length
of the cable. The inspection frequency shall be based
on such factors as expected cable life as determined
by experience on the particular application or similar
installations, severity of environment, percentage of
capacity lifts, frequency rates of operation, and expo-
sure to shock loads. Inspection should be more fre-
quent as cables approach the end of their useful
lives.
Only the surface wires of the cable require inspec-
tion, do not attempt to open the cable. Any deteriora-
tion resulting in a appreciable loss of original
strength, such as described below, shall be noted,
and then a determination made if further use would
-JLG
Lift- 8-3