Disc coupling — Unlike claw couplings — which contain rubber — rigid,
all-metal disc couplings require no lubrication and will operate reliably with
little to no wear or maintenance.
Gear couplings:
Although the style and function of cranes and hoists vary, these machines
maintain many of the same basic design principles — including the need to
connect shafts, drums and brakes to the prime and auxiliary movers that
power the drive, travel, and hoist functions. With their high-power density
and ability to accommodate various design and misalignment variations,
gear couplings have become an industry standard.
Gear couplings are designed to transmit torque between two shafts that
are not collinear. They typically consist of two flexible joints — one fixed
to each shaft — which are connected by a spindle, or third shaft. The gear
coupling connects the drive motor to the gearbox in hoist mechanisms, but
it can also connect the gearbox directly to smaller wire rope drums using
a flanged half. In terms of their design, gear couplings transmit torque
via hubs with crowned gear teeth that are in permanent mesh with the
straight gear teeth of the sleeves — a design that provides the highest torque
transmission for the smallest size. They also run at high speeds, conform
to the AGMA bolting pattern and compensate for angular, radial, and axial
shaft misalignment.
Sizing a barrel coupling
Sizing a barrel coupling comes down to three things: transmission torque
(T), the applied radial load, (F) and shaft diameter of the gearbox unit.
What follows is a simplified version of the process, including some of the
calculations involved at various steps:
1 Calculate the nominal transmission torque (T) based on
maximum installed motor power or consumed power. This value must
be less than the transmission torque (TKmax) of your selected coupling
according to the datasheet.
Calculating T in terms of installed motor power:
Where:
Pi = maximum installed motor power
n = rotary speed of the rope drum
K1 = service factor (see table)
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122 August 2019 http://www.designworldonline.com DESIGN WORLD
Calculating T in terms of consumed motor power:
Where:
Pc = maximum consumed motor power
FP = drum static pull, including cable and pulley efficiency
Vr = drum cable lifting rate
n = rotary speed of the rope drum
D = drum pitch diameter
K1 = service factor
2 Calculate the applied radial load (F). The next step
in the process requires you to evaluate the radial load that
will act on your coupling. Radial load refers to the fraction of
the load that your coupling must withstand due to the pull
of the load and hoisting tackle. This calculated value must be
lower than the admissible radial load (Frad) indicated in the
datasheet.
For systems with double line to drum. Where:
FP = static pull of drum, including cable and pulley efficiency
w = weight of the drum, including the rope and connected
parts of the coupling
3 Verification of the geometric dimensions. Finally,
make sure the diameter of your gearbox shaft is smaller than
the coupling’s maximum admissible diameter (d1kmax) as
indicated in the datasheet. These values are valid for shafts
with keyways according to DIN 6885/1. Please contact our
technical team for other types of fixing. DW
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