Page 396 - Analysis and Design of Machine Elements

Analysis and Design of Machine Elements
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Pin and bushing couplings are similar to flanged couplings, except that they join two
half coupling flanges 1, and 4 by pins 2 with rubber-cushioned bushings 3 instead of
bolts. Since they transmit motion and torque through nonmetallic elastomeric bush-
ings, pin and bushing couplings can compensate for misalignments and absorb torsional
shock and vibration.
Elastomeric pin couplings use elastomeric material, usually nylon, as pins 2, to con-
nect two halves of coupling flanges 1 and 3. Compared with pin and bushing couplings,
elastomeric pin couplings have greater torque transmission capability. Elastomeric pin
couplings can absorb shock and vibration, and accommodate axial and minor radial and
angular misalignments, so they are usually used on large vehicles or modern industrial
machinery. However, because nylon studs are sensitive to temperature, the operating
∘
temperature is limited to a range of −20–+70 C.
A resilient coupling with spider has an elastomeric element 2 and a pair of axially
overlapping rigid jaws 1 and 3. The elastomeric element can be in the form of a star or a
plum, with different hardnesses to suit load carrying capacities. The elastomeric spider
is placed between the crowning teeth of the two jaws to transmit power through com-
pression and to achieve shaft coupling. Elastomers are generally made from plastic or
rubber, which combines resiliency with high damping capacity. Therefore, resilient cou-
pling with spider can cushion and dampen impact and shock, and are usually used in
strong vibration occasions. They can compensate for radial, axial and angular misalign-
ments. The flexibility is derived from clearances in mating parts, or from deflection of
elastomeric members [2]. However, the operating temperature is limited by the elas-
∘
tomer material, usually from −35–+80 C.
A tyre coupling has a moulded, reinforced rubber tyre 2 assembled to the two metal
hubs 3 and steel frames by a group of bolts 1. The reinforced rubber tyre is composed
of two radially split halves, which facilitates installation and maintenance without the
need for moving driving and driven shafts. Tyre couplings have superior misalignment
compensation performance. The elastomeric tyre can flex in any direction to accommo-
date single or combined end float, parallel offset and angular misalignments. It cushions
shocks and damps torsional vibrations, providing a resilient shaft connection.
Metallic element couplings refer to the couplings that contains metallic elastic ele-
ments, including metallic grid couplings and diaphragm couplings. These couplings
compensate for misalignments by the flexure of flexible metallic elements.
A metallic grid coupling consists of a spring steel alloy grid, and two hubs with tapered
or contoured parallel slots cut into the peripheries. The two hubs are connected by the
serpentlike spring steel alloy grid fitted in the slots. Torque is transmitted through the
flexible spring steel alloy grid. Under a light or normal load, the serpentlike springs have
a relative long span. As the load increases, the springs deflect and the span is reduced.
Greater support is afforded to the springs by the walls of flared slots [5, 6]. The flexi-
ble span provides flexible accommodation to varying loads, which is most desirable for
damping torsional vibration and reducing shock loads. Metallic grid couplings accom-
modate end float, parallel offset and angular misalignments by the movement of steel
grid in the lubricated slots [7]. The couplings are usually enclosed in oil-tight, dust-proof
covers. They are adaptable to nearly all types of industrial equipment.
A typical diaphragm coupling consists of two half couplings 1 and 6, one or more thin
diaphragms 2 and 4 and spacer tubes 3. The diaphragms are crisscrossed with the two