User Manual

37
CRITERIA FOR REPLACEMENT OF WIRE ROPE – TEREX-AMIDA LIGHT TOWERS
The wire ropes used to raise and lower the masts on a TEREX Light Tower are probably some of the most impor-
tant mechanical parts used in day-to-day operation of the machinery. It is therefore very important that the cables
be inspected on a frequent basis (once a month) for wear and tear, and immediately in the event of possible dam-
age due to operator error in using the winch, or possible damage from other equipment.
NORMAL WEAR AND TEAR
When used properly, the wire ropes should give years of trouble-free service, depending on how often the masts
are raised and lowered. The rule of thumb at TEREX is that if the tower is raised and lowered an average of once
per day, that the cables should be replaced every two years of service.
NORMAL INSPECTION
The wire ropes are constructed of 7 strands of 19 plow steel wires each twisted together, and then the assembly
galvanized to resist corrosion. Using a wadded-up cloth or heavy leather gloves (to avoid being pricked by a
broken wire), run a hand up and down a length of the cable. If any exterior wires are broken, they will lift up
from main body of the cable and become visible. For any given 1 foot of cable length; if there are 4 or more wires
each, on any 2 or more strands broken, the suspect rope should be replaced immediately.
OPERATOR ERROR – OTHER MACHINERY DAMAGE
One of the most common reasons for failure of a Light Tower wire rope is due to operator error in using the
winch, or damage to the cable by tools or other machinery. The most common operator error happens when the
mast is telescoping down. When the upper telescoping lock engages, the operator does not pull the lower pivot lock
out (located on the tower base) and keeps on cranking the winch. This results in the cable becoming loose around
the drum due to the tower not pivoting down. This can result in three problems: the loose cable can get trapped
underneath itself, resulting in a sudden or partial “drop” of the mast when the loose section releases at a later time,
thus damaging the cable; or the cable can jump off the winch drum and be damaged by the gears of the winch. The
loose cable can also cause the drum to spin to take up the slack cable. If there is enough friction in the threaded
parts of the winch, the drum can cause the crank handle to start spinning. This can cause the tower to “freefall”
and the results can be catastrophic for anyone standing underneath the tower. A spinning crank handle can also
break bones. Other reasons damage can occur are due to some outside force such as forklift blade nicking or
crushing a cable when moving a unit, or an accidental blow or damage by a hand tool, etc.
DAMAGE INSPECTION
If any nicks (partial strand cut through), kinks (permanent bends), or weld spatter on the cable (from field
service) are observed, the suspect wire rope should be changed immediately. If there is a crushed spot somewhere
on the wire rope, it should be replaced only if the width of the crushed spot exceeds 1-1/4 times the nominal diam-
eter of the cable (5/16” on a 1/4” cable, and 7/32” on a 3/16” cable), or if there are broken wires at the point of
damage.