Elastic Couplings to Improve Drive System

September 10, 2012 8:59 am

For all those traditional applications operating with either rigid connections or belt driven machines, sources of failures should be excluded as far as possible or as long as they are acceptable from an economic point of view. Failures always cause incredible expenses for repair and loss of productivity. In addition to preventing dangers, superfluous noise should also be avoided.
Things can often be put right by the use of a flexible coupling originating from KTR’s extensive programme. KTR’s product portfolio is based on 50 years of experience in the development and production of innovative couplings transmitting torques up to 750 kNm setting trends in the market.
Rigid Connections or CouplingsConnections realised by a rigid sleeve are mainly used in the low cost segment. In such cases only low operating performances of partly less than 50 hours are assumed. The reason is often benefit in price or compactness only, however with this, considerable disadvantages may arise. If two shafts are combined by means of a rigid sleeve, torque peaks are transmitted without any damping and peak loads are transmitted directly to the adjacent components. The production of constraint forces has to be considered, too, since this type of connection is not in a position of compensating for displacement which may be caused. Such constraint forces reduce the service life of all components, the bearing and the shaft-hub-connection are loaded heavier and the feather keys break. This is also the case with agricultural engineering where the status of technology often is to combine two shafts by a rigid sleeve.
Instead, If KTR couplings are used to combine the shafts (Image 2), the amount of wear would considerably reduced. A high amount of wear was realised in the gearbox of an agricultural machine. Tests on a test bench have shown that the high amount of wear was caused by the combination of the shafts by means of a rigid sleeve. Having installed a ROTEX 38 with a PA6 spider by KTR, the service life of all components has considerably increased. ROTEX couplings (Image 1) are characterised by small dimensions, low weight and low flywheel effects while transmitting high torques. The accurate, all over machining has a positive influence on the running properties while increasing the service life of the couplings considerably. They assure power transmission while damping Torsional vibrations and compensate for shocks produced by engines with irregular operation.
The direct connection of driving and load side by means of hollow shaft gears which is often used by the industry is part of the rigid connections. Here a flexible separation does not take place. This means that the structure-borne noise is transmitted without any damping. The noise produced in this way may be unwanted in certain applications: In a theatre the windlasses have been connected directly to the hollow shaft gear up to now. This kind of connection has caused noise which disturbed the smooth running of the theatre. To solve this problem a flexible pin & bush coupling type REVOLEX KX 85 spec by KTR was installed between worm gear pair and windlass (Image 3). The flexible separation makes the drives run at very low noise now so that the visitor of the theatre can enjoy the play without any disturbances. The torsionally flexible, fail-safe pin & bush couplings type REVOLEX KX can be plugged in axially and are characterised in particular by short dimensions (Image 4). Moreover, they assure a disassembly of the elastomer rings including the pins while being assembled without any problems. In addition the couplings compensate for all kind of shaft misalignment.
Unusual operating conditions such as a crash can be better controlled with the use of couplings. Often the coupling is the weakest link in a chain. By equipping the coupling with overload elements all other components are protected so that they only have to be replaced in case of a major failure. Designs without a coupling are often more difficult to dismantle or assemble. If vibrations arise, couplings are also most beneficial, because various damping properties can be realised with the same coupling by using different kinds of elastomer hardness. The majority of KTR couplings can be plugged in axially (plug and play). The easy assembly cannot be compared to a shaft-hub-connection which needs to be shrinked on.
Belt Drives or CouplingsThe comparison of coupling and belt drive as a transmission element also indicates considerable advantages for the use of couplings. The drive of compressors via a KTR coupling has a higher efficiency than the solution of motor – V-belt – compressor. The user saves money in this way. The wear on the belt drive and the frequent need of resetting, causes high radial forces on the bearings of the drive which do not arise if a coupling is used. Other advantages supporting the use of couplings instead of belts are the low volume, the low mass and the compact design. KTR couplings are beneficial with assembly and disassembly as well. Many belts often cannot be opened and therefore are difficult to replace. Moreover, the application range of belt drives is limited by high temperature ranges and environmental influences like oils, fuel, water or dust. If a synchronism of several shafts is to be realised, the use of non-positive belt drives has to be excluded because of the elongation, too. 
ConclusionFor many applications, it makes sense to use a coupling instead of the direct connection via hollow shaft gears or using sleeves or belts, respectively. KTR, a leading manufacturer of couplings for more than 50 years, offer an extensive coupling programme for torques up to 750 kNm. Numerous applications can be equipped with standard couplings. Couplings which are available from stock only cover 45 per cent of KTR’s business. Now the majority of customers require the optimum integration of a coupling into the drive concerned. As a consequence, customised coupling solutions are required which are realised by more than 100 KTR engineers and experts worldwide for numerous industries.
Author:Kumar Karandikar, Sales ManagerKTR IndiaTel: +91-7798984101k.karandikar@ktr.com