CECOS University of IT and Emerging Sciences

Assignment # 4

Department: Mechanical Engineering

Class, Class Code and Section: ME-2017A

Subject: Maintenance Engineering

Name of Student: Hamza Nawaz

Student’s ID: CU-369-2017A

Submitted to: Engr. Umair Ali
Date of submission: 19-07-2021
What are couplings? Write the types of couplings.

Hint: (Read chapter 10 from the book)

Couplings

Couplings are an important part of power machines where they perform the following two
important functions,

1. transmit torsional power between a power source and drive unit

2. absorb torsional variations in the drive train

Some couplings also provide some correction for slight misalignment, but these devices are
not designed to align two misaligned shafts. Therefore, they should not be relied upon to
obtain alignment for two shafts.

Types

Rigid Couplings

It is primarily used for vertical applications for example vertical pump. It does not permit
relative motion in both radial and axial direction between driver and driven shafts. It connects
two shafts properly and solidly making them a single shaft.

It is divided further into three types,

i. Flanged Coupling

A flanged rigid coupling is composed of two halves, one located on the end of the driver shaft
and the other on the end of the driven shaft. These halves are bolted together to form a solid
connection. To positively transmit torque, the coupling incorporates axially fitted keys and
split circular key rings or dowels, which eliminate frictional dependency for transmission.
The use of flanged couplings is restricted primarily to vertical pump shafts.
 Figure 1) Typical flanged rigid coupling

ii. Split Coupling

A split rigid coupling, also referred to as a clamp coupling, is basically a sleeve that is split
horizontally along the shaft and held together with bolts. It is clamped over the adjoining
ends of the driver and driven shafts, forming a solid connection. Clamp couplings are used
primarily on vertical pump shafting. Just like the flanged coupling, the split rigid coupling
also incorporates axially fitted keys and split circular key rings to eliminate frictional
dependency in the transmission of torque.

Figure 2) Typical Split rigid coupling

iii. Compression Coupling

A rigid compression coupling is composed of three pieces:

 a compressible core and

 two encompassing coupling halves that apply force to the core

The core is composed of a slotted bushing that has been machine-bored to fit both ends of the
shafts. It also has been machined with a taper on its external diameter from the center
outward to both ends. The coupling halves are finish-bored to fit this taper. When the
coupling halves are bolted together, the core is compressed down on the shaft by the two
halves, and the resulting frictional grip transmits the torque without the use of keys.

Figure 3) Typical compression rigid coupling

Flexible Couplings

These couplings allow the coupled shafts to slide or move relative to each other. Although
clearances are provided to permit movement within specified tolerance limits, flexible
couplings are not designed to compensate for major misalignments. (Shafts must be aligned
to less than 0.002 in. for proper operation.) Significant misalignment creates a whipping
movement of the shaft, adds thrust to the shaft and bearings, causes axial vibrations, and
leads to premature wear or failure of equipment.

i. Mechanical Flexing Coupling

These couplings provide a flexible connection by permitting the coupling components to

move or slide relative to each other. To permit such movement, clearance must be provided
within specified limits. It is important to keep cross loading on the connected shafts at a
minimum. This is accomplished by providing adequate lubrication to reduce wear on the
coupling components. The most popular of the mechanical-flexing type are the chain and
gear couplings.

a. Chain Coupling

The design consists of two hubs with sprocket teeth connected by a chain of the single-roller,
double-roller, or silent type. Chain couplings provide a good means of transmitting
proportionately high torque at low speeds. Minor shaft misalignment is compensated by
means of clearances between the chain and sprocket teeth and the clearance that exists within
the chain itself.

Figure 4) A roller chain coupling

Special-purpose components may be specified when enhanced flexibility and reduced wear
are required. Hardened sprocket teeth, special tooth design, and barrel-shaped rollers are
available for special needs. Light-duty drives are sometimes supplied with non-metallic
chains on which no lubrication should be used.

b. Gear Coupling

Gear couplings are capable of transmitting proportionately high torque at both high and low
speeds. The most common type of gear coupling consists of two identical hubs with external
gear teeth and a sleeve, or cover, with matching internal gear teeth. Torque is transmitted
through the gear teeth, whereas the necessary sliding action and ability for slight adjustments
in position comes from a certain freedom of action provided between the two sets of teeth.

Figure 5) Typical gear tooth coupling

Slight shaft misalignment is compensated by the clearance between the matching gear teeth.
However, any degree of misalignment decreases the useful life of the coupling and may cause
damage to other machine-train components such as bearings.

ii. Material Flexing Coupling

Material-flexing couplings incorporate elements that accommodate a certain amount of

bending or flexing. The material-flexing group includes laminated disk-ring, bellows, flexible
shaft, diaphragm, and elastomeric couplings.

Various materials such as metal, plastic, or rubber are used to make the flexing elements in
these couplings. The use of the couplings is governed by the operational fatigue limits of
these materials. Practically all metals have fatigue limits that are predictable; therefore, they
permit definite boundaries of operation to be established. Elastomers such as plastic or
rubber, however, usually do not have a well-defined fatigue limit. Their service life is
determined primarily by conditions of installation and operation.

iii. Combination (Metallic-Grid) coupling

The metallic-grid coupling is an example of a combination of mechanical-flexing and

material-flexing type couplings.

Figure 6) Typical metallic grid couplings

The metallic-grid coupling is a compact unit capable of transmitting high torque at moderate
speeds. The construction of the coupling consists of two flanged hubs, each with specially
grooved slots cut axially on the outer edges of the hub flanges. The flanges are connected by
means of a serpentine-shaped spring grid that fits into the grooved slots. The flexibility of this
grid provides torsional resilience.
 iv. Laminated Disk-Ring Coupling

The laminated disk-ring coupling consists of shaft hubs connected to a single flexible disk, or
a series of disks, that allows axial movement. The laminated disk-ring coupling also reduces
heat and axial vibration that can transmit between the driver and driven unit.

Figure 7) Typical laminated disk-ring couplings

v. Bellows Coupling

Bellows couplings consist of two shaft hubs connected to a flexible bellows. This design,
which compensates for minor misalignment, is used at moderate rotational torque and shaft
speed. This type of coupling provides flexibility to compensate for axial movement and
misalignment caused by thermal expansion of the equipment components.
 Figure 8) Typical bellows coupling
vi. Flexible Shaft or Spring Couplings

Flexible shaft or spring couplings are generally used in small equipment applications that do
not experience high torque loads.

Figure 9) Typical flexible shaft coupling

vii. Diaphragm Coupling

Diaphragm couplings provide torsional stiffness while allowing flexibility in axial

movement.

Typical construction consists of shaft hub flanges and a diaphragm spool, which provides the
connection between the driver and driven unit. The diaphragm spool normally consists of a
center shaft fastened to the inner diameter of a diaphragm on each end of the spool shaft. The
shaft hub flanges are fastened to the outer diameter of the diaphragms to complete the
mechanical connection.
 Figure 10) Typical diaphragm coupling
viii. Elastomeric Coupling

Elastomeric couplings consist of two hubs connected by an elastomeric element. The

couplings fall into two basic categories,

 One with the element placed in shear and the other with its element placed in
compression. The coupling compensates for minor misalignments because of the
flexing capability of the elastomer. These couplings are usually applied in light- or
medium-duty applications running at moderate speeds.
 With the shear-type coupling, the elastomeric element may be clamped or bonded in
place, or fitted securely to the hubs.

The compression-type couplings may be fitted with projecting pins, bolts, or lugs to connect
the components. Polyurethane, rubber, neoprene, or cloth and fiber materials are used in the
manufacture of these elements.

Although elastomeric couplings are practically maintenance free, it is good practice to

periodically inspect the condition of the elastomer and the alignment of the equipment. If the
element shows signs of defects or wear, it should be replaced and the equipment realigned to
the manufacturer’s specifications.
 Figure 11) Typical elastomeric couplings

Special Application Couplings

Two special application couplings are discussed below,

i. Floating-Shaft or Spacer Coupling

Regular flexible couplings connect the driver and driven shafts with relatively close ends and
are suitable for limited misalignment. However, allowances sometimes have to be made to
accommodate greater misalignment or when the ends of the driver and driven shafts have to
be separated by a considerable distance.

Such is the case, for example, with end-suction pump designs in which the power unit of the
pump assembly is removed for maintenance by being axially moved toward the driver. If
neither the pump nor the driver can be readily removed, they should be separated sufficiently
to permit withdrawal of the pump’s power unit. An easily removable flexible coupling of
sufficient length (i.e., floating-shaft or spacer coupling) is required for this type of
maintenance.
 Figure 12) Typical floating-shaft or spacer couplings
In addition to the maintenance application described above, this coupling (also referred to as
extension or spacer sleeve coupling) is commonly used where equipment is subject to thermal
expansion and possible misalignment because of high process temperatures. The purpose of
this type of coupling is to prevent harmful misalignment with minimum separation of the
driver and driven shaft ends.

Figure 13) Typical floating-shaft or spacer couplings for high-temperature applications

The floating-shaft coupling consists of two support elements connected by a shaft.
Manufacturers use various approaches in their designs for these couplings. For example, each
of the two support elements may be of the single-engagement type, may consist of a flexible
half-coupling on one end and a rigid half-coupling on the other end, or may be completely
flexible with some piloting or guiding supports.
Floating-shaft gear couplings usually consist of a standard coupling with a two-piece sleeve.
The sleeve halves are bolted to rigid flanges to form two single-flex lings. An intermediate
shaft, which permits the transmission of power between widely separated drive components,
connects these.

ii. Hydraulic or Fluid coupling

Hydraulic couplings provide a soft start with gradual acceleration and limited maximum
torque for fixed operating speeds. Hydraulic couplings are typically used in applications that
undergo torsional shock from sudden changes in equipment loads (e.g., compressors).

Figure 14) Typical hydraulic coupling