Standard and customised shaft couplings to match applications

Shaft couplings are used in many different applications. As it is important that the coupling optimally matches the application, different coupling types with varying characteristics are required. Mayr Transmissions not only provides products for the increasingly popular high-performance couplings with high speeds, but also provides the prerequisites for intelligent, networked machines with the ROBA-DSM torque measurement shaft coupling.

In machines and systems, shaft couplings transfer energy from one shaft to another in the form of torque and speed, and in the process compensate for any occurring shaft misalignment. Each drive has its own special characteristics and places different requirements on the couplings. As a result, depending on the application, the main focus is either placed on high torsional rigidity, large misalignment capability, low mass inertia, excellent damping capacity or even a combination of these characteristics. Mayr Transmissions has developed and manufactured backlash-free shaft couplings for over 30 years, and provides a wide and sophisticated product range for different drive constellations featuring various steel bellows, elastomer and disk pack couplings.

Mayr's smartflex steel bellows coupling is designed with a multiple-layer steel bellows which gives the coupling high torsional rigidity. This ensures very high positioning accuracy and shaft run-out accuracy in servo axes even under difficult conditions, and guarantees a backlash-free, and therefore flawless, torque transmission between the two shafts. Furthermore, the multi-layer bellows design provides a much higher misalignment capacity in comparison with single-layer bellows.

Higher misalignment capability also means greater reliability, operational safety and service lifetime. In addition, the smartflex couplings distinguish themselves through a clamping connection between the shaft, hub and steel bellows which is described as unique on the market. As a result, the couplings can be easily and flexibly assembled according to modular principles.

The hubs of the coupling consist of a clamping ring with latched reducing bushings. In operation, this clamping ring connects the steel bellows, bushings and shaft through force locking. Therefore, by changing the only reducing bushing, the smartflex coupling can be easily and quickly adjusted to changed shaft diameters. In addition, the direct clamping of the steel bellows guarantees the optimum centring of the bellows to the shafts and also ensures high running quality and torsional rigidity. One single, radial, easily-accessible screw per hub ensures the necessary pre-tension force for the torque transmission and permits quick installation.

Thanks to the consistent use of high-strength aluminium, the coupling has a high performance density with a low mass and mass inertia. Besides the smartflex, Mayr Transmissions provides a cost-effective, plug-in option for simple installation or removal with the primeflex steel bellows coupling. Even after longer operating times, the primeflex can be safely removed without damage to the steel bellows.

Flexible and vibration-damping

In servo axes, in which critical vibrations occur and torsionally rigid shaft couplings reach their limits, the flexible ROBA-ES claw couplings come into operation. These couplings transmit the torque backlash-free and compensate for shaft misalignments. The damping compensation element protects the drive system against critical vibrations. Nevertheless, the couplings are torsionally rigid enough that, even on highly dynamic servo drives, no compromises have to be made regarding accuracy.

With the ROBA-ES coupling, claws engage alternately on the input and output side of the hub into a star-shaped intermediate ring made from elastomer. Under slight pre-tension, the transmission elastomer, made from polyurethane, fills the space between the claw profiles and absorbs vibrations. The damping properties and rigidity of the coupling can be varied by using different plastic Shore hardnesses. The clamping hubs made from aluminium guarantee low mass inertia and ensure quick and reliable installation. In addition, the coupling is maintenance free, resistant to media and temperature resistant, and therefore guarantees operational reliability.

Disk pack couplings such as the ROBA-DS have the highest torsional rigidity in comparison with steel bellows and elastomer couplings. The ROBA-DS servo couplings have small dimensions, reduced weight, low moments of inertia and high performance density. They can transmit high torques even using a comparatively small diameter, and are therefore shaft couplings well suited for dynamic drive systems with high speeds. The basis for this compact construction is the steel and high-strength aluminium alloy materials used in the manufacture of these products. Thanks to the flexible disk packs, the couplings compensate for radial, axial and angular shaft misalignments. As a result, they safeguard the bearing against undesired loads and prevent unnecessary downtimes and costs.

The ROBA-DS all-steel couplings with large construction sizes also simultaneously combine high performance density with absolute backlash-free operation. Design details, such as the blasting of the disks and the use of specially shaped collar bushings, ensure a backlash-free flow of force with outstanding force flow density between the input and output. The ROBA-DS disk pack couplings transmit torques backlash-free up to their nominal torque and with a consistently high torsional rigidity. The shaft misalignments stated in the catalogue can be exploited to 100 per cent, without influencing the transmittable torque.

These couplings are robust and reliable. Furthermore, they are temperature resistant and wear and maintenance free, and are therefore suitable for applications in extreme ambient conditions. Mayr Transmissions provides a large spectrum of disk pack couplings and therefore covers a wide range from very small to very large torques. A wide selection of standard modules with a multitude of hub designs ensures adaptability as well as flexibility in diverse drive constellations. With appropriately selected hubs, the couplings can be easily and quickly installed and removed, even in difficult ambient conditions.

High flexibility through variant diversity

Mayr provides variant diversity even in special designs which supplement the standard modules. For example, if shafts are to be connected over greater distances in high-speed drive constellations, then it is often necessary to position a length-adapted sleeve between the coupling hubs. In doing so, the bend-critical speed of the sleeve may not lie within the range of the operating speed. Intermediate sleeves made from carbon fibre-reinforced plastics (CFRP) permit high speeds even with long couplings. In comparison with steel, the CFRP variants have a significantly higher bend-critical speed. Furthermore, CFRP sleeves are up to 80 per cent lighter, which plays an important role particularly for large construction sizes and long sleeves.

A further advantage of the plastic composite is its high corrosive resistance. If additional leakage current resistance, i.e. electrical insulation, is required in an application, then glass fibre-reinforced plastics are used. In addition, an innovative ROBA-DS spindle coupling with integrated cooling lubricant feed through enables cooling lubricant to be guided across long distances directly to the spindle and therefore into the tool. As a result, the downtime, cutting speed and machining performance of the machining centres is significantly improved.

In the case of difficult applications, Mayr can call on appropriate know-how and experience. As a result, high-performance couplings with very high torques or speeds function accurately and reliably, even under extreme loads. The company has the appropriate test facilities, and tests all couplings comprehensively under the conditions which also will prevail in actual operation. Mayr also provides couplings of a high and reproducible balancing quality, so that the required manufacturing accuracy and machining performances are achieved in machining centres with very high spindle speeds, for example.

Mayr has equipped the large ROBA-DS disk pack couplings for high torques, i.e. with a nominal torque range from 22,000 to 110,000Nm, with an installation-friendly, positive locking cone connection. This cone connection acts as a torque multiplier and reduces the screw tightening torques to a fraction of the torques required on conventional frictionally locking designs. This significantly simplifies installation and removal. Furthermore, drive units such as the motor and transmission need not be displaced for the installation and removal of the coupling.

The measuring machine element

With the ROBA-DSM torque measurement shaft coupling, based on the proven disk pack coupling ROBA-DS, Mayr creates the decisive prerequisites for the intelligent, networked machine. The innovative coupling enables simple monitoring of the condition of the machine and systems. Furthermore, machines can be optimally utilised to capacity using the data from the coupling. The application range of this torque measurement coupling extends from classic test stands to series-manufactured machines, right up to condition monitoring.

For more information about the range of shaft couplings available from Mayr Transmissions, please go to www.mayr.com.