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Identification | Operation
| Installation | Preventive
Maintenance | Safety | Theory
| Terms | Specifications
WORM GEAR WINCH THEORY OF OPERATION
The illustration shown above points out the basic components of
a typical upright worm gear winch. Torque is applied to the input
end of the worm shaft by a PTO driven sprocket and chain or a hydraulic
or electric motor. The steel worm and worm shaft are supported by
anti-friction roller bearings. Tapered bearings are shown in this
illustration while ball bearings and needle roller bearings may
be used on other models. As the steel worm turns, the "threads"
push or pull the aluminum-bronze alloy worm gear. The worm gear
is keyed to the drum shaft which is supported on bronze bushings
in the worm gear housing and bearing leg. A sliding dog-type clutch
is splined or keyed to the cable drum shaft. The drum clutch transmits
the torque of the worm gear to the cable drum.
An oil cooled automatic safety brake is installed on the end of
the worm shaft on most winches with a 12,000 pound (5,444 Kg) or
greater rated capacity. The majority of the worm gear winch's load
holding ability is achieved by the inability to back-drive the worm
gear set. The safety brake provides additional resistance to rotation
of the worm shaft and absorbs the inertia of the PTO gear train
if so equipped. A band-type brake or small shoe-type brake is installed
on most worm gear winches to reduce wire rope "birdnesting" when
the drum clutch is disengaged to pull wire rope out by hand. These
drum brakes are NOT designed for load holding.
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