Page 252 - Improving Machinery Reliability

Machinery Reliability Audits arid Reviews 223

Two hand-operated, high-pressure rams are required for the mounting operation.
One of these applies a high axial force to the assembly sleeve, while the second one
forces its separate supply of hydraulic fluid into the shaft-coupling bore interface.
In the early 1970s, coupling hubs and shaft ends intended for hydraulic dilation
were often furnished with O-rings. More recently, it has been shown that accurately
machined mating tapers no longer require O-rings for satisfactory mounting and dis-
mounting of most commonly applied turbomachinery couplings.
For cylindrical shaft ends, which are still occasionally found on older equipment,
the reliability professional might consider Coupling Corporation of America’s
“Anderson Hub Clamp.” This patented device (Figure 3-98) is designed to accom-
modate most shafts, especially those with somewhat questionable surface smooth-
ness. On retrofits, users have had particular success on straight, tapered, keyed and
kzyless shafts.
The system is based on an asymmetrical profile thread into the outside diameter of
clamp hub flange (1) and the bore of clamp hub flange (2). When the installer
torques the loading screws (3), a predetermined uniform force pushes the sleeve
away from the flange. The special asymmetrical threads cause this axial force to
exert a clamping action radially inward on the split sleeve portion of the clamp hub
flange. It can be shown that the gripping action is sufficient to prevent slippage on
virtually any machine shaft.

Conclusion

The design approaches outlined here represent proven methods of reliable shaft-
hub connections. Although very tight fit is essential if the risk of potentially danger-
ous fretting action is to be avoided, it has been shown that this requirement does not
have to be incompatible with easy hub removal in case rapid access to turbomachin-
ery shaft seals should become necessary.

(1) Clamp hub
t . Coupling

FLE~OR
attaches
here
(2) Bore
Tighten bolts
“set” clamps
/to

sleeve
Figure 3-98. Anderson hub clamp for attaching coupling hubs to cylindrical shaft ends.