TM 5-810-15
supporting. Bucket elevators are usually high
inclined and horizontal conveyors. The designer
maintenance items and should only be used where
may find it preferable to locate the drive internally
space restrictions apply. Manufacturers have to
or at the tail end of the conveyor if required by
take particular care when designing the track and
accessibility or maintenance, but should be avoided
load shoe.
if possible. The drive arrangement should be
b. Apron conveyors. Apron and pan conveyors
designed with the minimum amount of compact
consist of overlapped steel pans which are sup-
components as possible. Reducers, couplings and
ported between two strands of chain that pass
motors should be the same size as far as practical
around head and tail sprockets. This type of
for ease of maintenance and to reduce spare parts
conveyor is usually short, slow speed, and used for
inventories. On conveyor drives over 300 hp the
removing granular or lumpy material from under
designer should investigate the economical justifi-
the track hopper. An apron conveyor is a very high
cation of dual drives. This type of drive allows the
maintenance item and should be avoided when
conveyor to be operated at reduced capacity when
possible. Maximum conveyor incline is usually up
one of the drive units fails. V belts will not be used.
to 25 degrees or 45 degrees with pusher plates.
b. Reducers. The conveyor drive reducer will be
One distinct advantage of this type of conveyor is
American Gear Manufacturers Association
they can carry hot materials.
(AGMA) rated using a service factor of 1.5 of the
c. Screw conveyors. Screw conveyors are an eco-
input motor design hp. The thermal hp rating of the
nomical short, low tonnage type of conveyor which
reducer will not be less than the full load hp of the
can be used in areas with low headroom. Screw
conveyors are not usually used when their capaci-
Manufacturers Association (AFBMA) 100,000
ties exceed 50 tph. They are used to handle
hour L-10 minimum life. All conveyor drives will
pulverized, granular or noncorrosive materials
be capable of starting under full loaded conditions.
where product agitation or degradation can be
V belts will not be used.
tolerated. Where mixing or blending is required,
numerous conveyor screw configurations are avail-
speed shaft is transmitted to the conveyor head or
able. The conveyor is completely enclosed with
drive pulley by the use of a flexible coupling. The
only one moving part and can be fitted with
coupling will be capable of withstanding parallel,
multiple or single discharge openings. Extreme
axial and angular misalignment of the drive shafts.
caution must be taken when handling abrasive
The coupling will be incapable of transmitting axial
materials, as excessive wear will lead to premature
equipment failure. As the screw conveyor is
will not be permitted. Couplings will be rated using
inclined, the carrying capacity decreases. Trough
a minimum service factor of 2.0 for the input hp.
loading should not exceed 30 percent of the trough
d. Fluid couplings. Fluid coupling will be pro-
cross sectional area for coal, even though higher
vided between the drive motor and the reducer
loading is possible.
which allows a controlled amount of slip to occur
d. Flight conveyors. Flight conveyors are used to
without causing excessive tension and shock load-
move granular, lumpy or pulverized material along
ing to the drive components and conveyor belt. A
both horizontal and inclined paths. Inclines are
fluid coupling will allow the motor to run rapidly
limited to approximately 40 degrees, with capacity
up to full speed, but will allow the conveyor a
decreasing as incline increases. One percent of
smooth controlled acceleration start curve when
capacity should be deducted for each degree of
starting from rest when either empty or fully
incline over 30 degrees. Flight conveyor is a high
loaded. This type of coupling is also beneficial in
wear, very noisy and high maintenance item. With
extremely cold climates where a controlled acceler-
abrasive materials, the trough design should
ation start is required to prevent coal from back-
provide for renewal of the bottom plate without
sliding on inclined conveyors. Fluid couplings per-
disturbing or removing the side plates or flights. A
mit the use of standard motors with across-the-line
method of compensating for unequal chain wear or
stretching must be incorporated into the design.
starting capabilities which allows the use of less
Flight conveyors are well suited to conveying
expensive motors.
bottom ash from boilers and sludge from tanks and
ponds.
5-11.
Belt scales.
a. Scales. General Belt scales are used to con-
5-10.
Drive units and couplings.
stantly measure the rate at which a bulk material is
a. Conveyor drive units. The conveyor drive unit
being delivered to the plant on a moving conveyor
should be located at the discharge or head end of
belt, and to make a record of the delivered amount
5-8
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