Handbook Of Shaft Alignment Episode 1 Part 7 doc

Disadvantages:

. Requires lubrication

. Temperature limitation due to lubricant

. Difficult to calculate reaction forces and moments of turbomachinery rotors when using

these couplings since the values for the coefficient of friction between the gear teeth vary

considerably

Coupling hubs and sleeves on shafts

Coupling hubs and sleeves on spool

FIGURE 4.8 Two different variations of gear couplings employing a spool piece.

Sleeve

Gear tooth in

“pivoted” position

Gear tooth in

“tilted” position

Centerline of

sleeve

Centerline of coupling

hub (with gear teeth)

FIGURE 4.9 Tilted and pivoted positions of the gear teeth in its sleeve.

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150 Shaft Alignment Handbook, Third Edition

4.4.1.3 Metal Ribbon Couplings

The metal ribbon coupling was introduced around 1919 by Bibby Co. Metal ribbon couplings

consist of two hubs with axial ‘‘grooves’’ on the outer diameter of the hub where a continuous

S-shaped grid meshes into the grooves. Misalignment and axial movement is achieved by

flexing and sliding of the grid member in specially tapered hub ‘‘teeth.’’

. Capacity: up to 70,000 hp=100 rpm

. Maximum recommended speed: to 6000 rpm

. Shaft bores: to 20 in.

. Shaft spacing: to 12 in.

Tilted position

Pivoted position

Pivoted position

Tilted position

Pivoted position

FIGURE 4.10 Gear tooth tracking pattern when subjected to misalignment conditions.

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Flexible and Rigid Couplings 151

. Special designs and considerations: Grid fabricated from hardened, high-strength steel.

Close coupled hubs with removable spacer available.

Advantages:

. Easy to assemble and disassemble

. Long history of successful applications

. Torsionally soft

Disadvantages:

. Requires lubrication

. Temperature limited

. Speed limited

4.4.1.4 Universal Joint Couplings

Perhaps the oldest flexible coupling in existence is the universal joint coupling. This coupling

is also known as the Cardan or Hooke joint. The basic design consists of U-shaped shaft ends

with a hole drilled through each ‘‘U’’ to accept a ‘‘þ’’ shaped cross.

If one universal joint is used to connect two shafts together, then only pure angular

misalignment can exist where the centerlines of rotation intersect at the center of the ‘‘þ’’

shaped cross. For a flexible coupling to accept both parallel and angular misalignment, there

FIGURE 4.11 Metal ribbon type coupling. (Courtesy of Falk Corporation, Milwaukee, WI. With

permission.)

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152 Shaft Alignment Handbook, Third Edition