TM 55-203
CHAPTER 6
DRAFT GEAR
to compression of the springs will be at its lowest. As
6-1. General
compression steadily increases, thrust on the friction
devices increases. As a result, resistance to the complete
As noted in paragraph 3-6, the draft gears in a car are
closing of the springs increases progressively as the pull
mechanisms which connect the couplers to the
on the coupler increases. Upon release of the gear, the
underframe. Their purpose is to absorb the shocks of
friction elements cause the springs to expand gradually,
coupling and train movement. Various kinds of draft
thus preventing strong recoil. Regulations include test
gears have been developed, but Army-owned rolling stock
requirements for friction-type gears, covering minimum
generally is equipped with the friction type illustrated in
exterior dimensions, restrictions of the travel of gear, and
limits on the minimum closed length of the gear under
(Defense Freight Railway Interchange Fleet) cars (in
specific load conditions.
CONUS) are usually Cardwell, Miner, National, or
b. Components. All approved friction draft gears
Westinghouse spring and/or friction types. However,
consist of two major components-a coilspring unit and a
some of the newer DFRIF cars may be equipped with the
friction unit assembled within a single housing. The coil-
shock-resistant rubber cushioned draft gears made by one
spring unit usually is composed of a nest of coil springs
of the various commercial manufacturers. These draft
fitted within the housing, with frictional elliptical springs or
gears are discussed in paragraph 6-3. Yokes, followers,
friction segments of steel blocks or plates seated in a
arms, and other attachments make up a complete draft
grooved wedge Whatever form the friction unit may have,
gear installation Some cars, particularly oversea types,
the action will be similar. As the coil springs begin to
may be equipped with either spring or friction-type buffers
compress, they meet the resistance of the fixed friction
to provide more cushioning against shock The travel must
unit.
As the force on the springs increases, they
be not less than 2 1/2 inches, nor more than 2 3/4 inches,
compress further and the friction unit offers further
and the draft gear followers must be at least 2 1/4 inches
resistance. This combined action of the units contributes
to the smooth starting of the car. The recoil of the springs
only elements subject to wear. A disassembled draft gear
is diminished when the pull is relieved and any slight
and yoke are shown in figure 6-2.
vibration that may follow a recoil is prevented from being
transmitted to the car. The performance of the friction
6-2. Friction Type
and coil-spring units is similar when the gear is suddenly
pushed rather than pulled. Briefly, the friction-type draft
a. General Any draft gear must create as low an
gear, by eliminating spring recoil, insures smoother
initial resistance to the compression of the draft gear
starting of a car. When the force of the coupling, whether
springs as possible to permit the slack to be taken up and
it be by pull or buff, is removed, there is no violent action
the train to be started smoothly, one car at a time. From
of recoil as there would be from a simple coil-spring draft
this point on, an increasingly high resistance must be
gear
created to prevent the closure from coming too soon.
Also, when the coupler pull is decreased, a rapid and
6-3. Cushioned Rubber-Type Gear
powerful recoil must not accompany the release of the
gear. Low initial resistance, followed by an increasing
A multipad, twin-cushioned, two-way rubber draft gear has
resistance, is attained by arranging each spring so that
been developed and accepted as standard for use on both
one of the ends butts against the friction member of the
freight and passenger
gear. When springs begin to compress, pressures of the
friction elements will be relatively low and the resistance
6-1
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