Installation and disassembly
To maintain maximum operational reliability and to simplify assembly and service it is important that the machines connected are securely mounted, preferably on a common foundation and baseplate. Guards must be fitted to rotating parts according to safety requirements, see Section 12.13.
Alignment of couplings or, more correctly, alignment of the shafts which the coupling is to connect, should be carried out as accurately as possible. For fans packaged on baseplates with their driver and other equipment, provisional alignment should be achieved by “chocking” the baseplate during levelling. After grouting, the alignment should be set correctly by adjusting the shims. A perfect alignment should be considered as an economic possibility, since alignment can considerably affect both service life and maintenance costs. See Section 12.11 with regard to methods of shaft alignment.
It is normal practice to bolt the fan directly to the baseplate. Other drive train equipment is shimmed to achieve correct alignment. In the case of cardan shafts the angular deviation should be equally distributed between the two joints to avoid unequal rotational velocities. Furthermore, a universal coupling should always rotate with a slight amount of angular misalignment to promote lubrication.
The attachment of a coupling half to a shaft usually presents a dilemma. The hub should be securely attached and preferably absorb part of the torque, to reduce the load on the key, as well as being easy to detach. The practice of hub attachment is similar to that for motor shafts where the fit is usually H7/k6, light push fit up to 48 mm diameter. A push fit H7/m6 is preferred for diameters above 55 mm. Some fan manufacturers prefer a positive interference fit, typically 0.001 mm per mm of shaft diameter. These couplings are heated for mounting and dismounting. Large couplings become unwieldy. Oil injection on shallow taper shafts, without keys, can be very successful.
The tighter fit is brought about by the fact that the height of the key is reduced from 12.5% of the diameter at 24 mm diameter to only 6% at 100 mm shaft diameter. This reduction should also be compensated for by increasing the length of the hub. In the case of electric motors the key does not normally extend right to the end of the shaft, which also increases the strain on the key. This must also be compensated for by increased hub length.
Assembly and disassembly of the coupling halves must be carried out carefully to avoid damage to the shaft ends and bearings. This operation could be simplified considerably if motor, fan and coupling suppliers fitted their equipment with suitable lugs, etc., to assist the attachment of pullers. For electric mo-
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Figure 12.10 Tapped assembly hole in electric motor shaft
Tors a tapped hole in the end of the shaft, as shown in Figure
12.6 can be supplied at extra cost, and ought to be standardised on all equipment.
Other methods of attaching the coupling halves are shrink fits, bolted joints or some form of clamping sleeve, Figure 12.11. Taper bushes are used primarily for vee belt pulleys, but can be a useful alternative for couplings where space permits. Some manufacturers offer taper bushes as an alternative to parallel bores. The hydraulically loaded clamping sleeve shown is a relatively new innovation and is not used extensively in fans.
The resilient elements in the shaft coupling must be easy to purchase, replace or repair. That it must be possible to replace without disturbing the machines or coupling hubs, goes without saying.
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Figure 12.11 Examples of clamping sleeves
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