TM 5-810-15
b. Stationary type. Stationary trippers are used to
limiting gate will be provided to control the depth
discharge material at a specific fixed location into
of material on the feeder pan.
a bin or silo, or direct the material back onto the
(3) Maximum recommended feeder angle of
conveyor belt to the next point of discharge.
slope is 10 degrees down from the horizontal.
c. Motor driven. Motor driven movable trippers
Larger slopes are possible, but care must be taken
have the tripper frame mounted on wheels, which
to prevent the material from "flushing" (self emp-
engage parallel rails supported on either side of the
tying), when the feeder is shut down.
belt. This type of tripper can remain in a specific
(4) The more common type of primary
location for a short time or locked in position for
feeder supports consist of steel cable or bar hangers
longer periods. Provide a cable reel or festoon
supported from the hopper or roof support steel
cable system to provide power to controls and
above, with spring type shock absorbers in each
motor drives. The designer must provide safety
hanger. A support frame can be used to support the
devices at each end of the tripper travel to reverse
feeder from below if the feeder cannot be
or stop the tripper car. Dust seals will be provided
supported from the hopper or overhead support
near the lower end of the discharge chutes to
steel. The feeder will be provided with at least two
prevent the escape of dust from the covered bins or
safety slings to prevent the feeder from falling in
hoppers. For a clean operation hoppers or bins
the event of a primary support failure. Application
must be vented to release air displaced by incoming
of suspended feeders will take into account "back
coal. Belt propelled tripper cars will be avoided.
out" action of the feeder.
Traveling trippers are installed in stream plants
c. Feeder construction. Feeder pan will be con-
where material is discharged into multiple bins,
structed from a minimum of 3/8-inch thick, type
hoppers or silos.
304 solid stainless steel plate. Replaceable stainless
d. Winch type. Winch trippers have positive
steel liner plates can be used, but are far more
drives using cable connected to both ends of the
expensive to install. Plastic type liner plates should
conveyor, and looped up through winch. No power
be investigated when a sticky material is being
is required on the tripper. Winch trippers should be
handled.
used when conveyor would be exposed to weather.
d. Controls. There are two common types of
Wind can fold the belt which could cause a self-
control systems which are used to control the
propelled tripper to come off the tracks. Rain or
vibrating feed rate; Silicon Controlled Rectifier and
handling material that absorbs moisture could make
Variable Auto-Transformer. The control system
the rails slippery, which would not adversely affect
will be capable of adjusting the feed rate from 0 to
a positive drive unit such as a winch tripper.
100-percent of the vibrating feeder capacity.
(1) Silicon Controlled Rectifier (SCR). This
5-17.
Conveyor chutework.
is the more commonly preferred method of
vibrating feeder control. The SCR is a solid state,
a. Chutework design. Design of conveyor trans-
variable voltage, soft start control device that can
fer and headchutes depends upon the accurate
be used for both local and remote operation where
prediction of the material trajectory path as it
a manual or electronic process control signal input
discharges over the end of the pulley. The curva-
is used. A full voltage start circuit is recommended
ture of the material trajectory is dependent on the
to protect against full inrush starting current.
material depth on the conveyor belt, the belt speed,
(2) Variable auto transformer. This is a
the angle of the conveyor, pulley size and the force
variable voltage device that is used for local,
of gravity on the material. All the above factors
manual control of the feeder feedrate. The auto
should be considered during the design stage to
transformer requires that a servo device be used for
prevent the material from choking or plugging the
dial adjustment. This type of control is being
chutework and causing material spillage.
replaced by the solid state circuitry of the SCR,
b. Chute slope. For good coal flow all chutework
which is capable of both local and remote control.
side plates will be as steep as possible but will have
a slope no less than 55 degrees off horizontal. For
5-16.
Trippers.
western coal slope will be minimum 60 degrees,
preferably 70 degrees. The designer must eliminate
a. General. Tippers are used in conjunction with
offsets, turns or changes in direction of chutework
a horizontal belt conveyor to discharge material
as much as possible.
from the belt at points along its length. Trippers
c. Chute liners. Stainless steel or Ultra High
can be stationary or fixed position, arranged with
Molecular Weight (UHMW) liner plates will be
suitable chutework to discharge material to either
installed on all surface subject to wear or slide,
side of the conveyor or back onto the conveyor
such as "dribble" from belt scrapers landing on
belt.
5-11
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