Page 389 - Analysis and Design of Machine Elements

Couplings and Clutches
connected by a rigid coupling and are forced into alignment, the coupling, shafts and 367
bearings may subject to severe variable stresses, which may lead to rapid fatigue failure.
Ideally, a flexible coupling is a better choice as they can produce the greatest flexibility
without significant stresses induced in the connected shafts.
13.1.3 Types of Couplings

Mechanical couplings are typically divided into two broad categories: rigid couplings
and flexible couplings. Rigid couplings are only for accurate shaft alignment that
presents at initial installation and maintains during operation. If significant misalign-
ments occur, flexible couplings are preferred, as they can accommodate misalignments
and reduce stresses induced in the connected shafts, which may lead to early fatigue
failure. Table 13.1 shows typical types of rigid couplings.
Flanged couplings are probably the most common type of rigid connection. The cou-
pling flanges are mounted on the ends of the driving and driven shaft with keys and
are joined together by a group of precision bolted joints or ordinary bolted joints on
the bolt circle. A piloted boss is used for precise alignment if ordinary bolted joints are
used. An outer protective rim is often added to the flanges to provide a safety shield
for the bolt heads and nuts. While transmitting torque, the load is transmitted from the
driving shaft to its flange, through the bolts, into the mating flange and out to the driven

Table 13.1 Types of rigid couplings [8].

Types of couplings Figures Features and applications

Flanged Simple structure, low cost;
couplings
Suitable for heavy-duty, slow
speed, stable load applications.

Sleeve couplings Simple structure, small radial
dimension;
Suitable for light duty
applications.

Ribbed Convenient for assembly and
couplings disassembly;

Suitable for small to medium
torque, slow speed and stable
load transmission, such as in
vertical pumps, agitators, and
many other types of applications.