Technical paper by Jochen Pelzer
The coupling of drives with work machines like pumps, fans and compressors is simple – at least at first glance. Because, while for selection of the right coupling knowledge of torque and speed are theoretically sufficient, practice shows that plenty of experience and high-quality products increase availability and reduce service costs.
Pumps, fans and compressors are not infrequently heavily loaded appliances that have one thing in common: they must be highly reliable and so need a simple, inexpensive and reliable interface to the drive – the coupling. Basically, a C-class part that still materially influences the faultfree operation of the appliances. Add to this adverse operating and environmental conditions and what are supposedly simple machine elements become decisive key points for smooth continuous operation.
For example, Flender in Bocholt launched with its Eupex coupling its first elastic couplings on the market in 1927. The name at that time already said it all, because the first syllable “eu” standing for “well” and the syllable “pex” for “fastening” or “gripping” show what matters most about the coupling: the claws of cast material and the intermediate elements of elastomer material must go together perfectly. Then in 1967 the N-Eupex flexible claw coupling appeared on the market, becoming what is today the most successful connection technology by the Flender company. And not without reason!
Universal solutions from the standard modular construction kit
Its decisive advantage is that it has universal application and is used as a shock-absorbing shaft coupling, to compensate shaft displacements. 23 standard sizes transmit rated torques of between 19 Nm and 62,000 Nm. At the same time the machine elements cover a temperature range of between -50 °C and +100 °C. The reason for this wide range of applications is, on the one hand the engineering design and on the other hand, the precise choice of materials: high-grade EN-GJL-250 cast iron for the claws and NBR synthetic rubber for the elastomeric buffers between.
The result is the long service life as expected in many branches of industry for pumps, fans and compressors. The elastomer elements are subjected to pressure, so materials have to be carefully selected to be able to transmit the occurring displacements through flexing in the rubber under corresponding loads. As part of a competitor analysis, Flender scrutinized relevant products in the market in a continuous test. Result: The N-Eupex more than lived up to its reputation as a robust and lastingly stable coupling for most applications.
To this extent perfect coordination with the application is one of the most important requirements for selecting a coupling. If problems occur, external specialists mostly restrict themselves to the diagnosis and determine the cause of the damage or failure. Flender, however, brings its decades of know-how to bear. Thus, for example, torsional vibration analyses enable the optimum coupling solution for the specific drive case to be determined.
Particularly also on piston machines with their periodic excitation torsion-resistant, high-quality coupling solutions result in prolonged useful lives and so in long-term durability of the connecting element. Feedback from users shows that, with couplings made in Bocholt used correctly, no failures are to be expected.
The right coupling for every application
For peripheral speeds of up to 36 m/s the N-Eupex delivers the right response to the mostly very individual demand for the optimum coupling solution. In addition the Flender portfolio offers large number of coupling systems for different requirements – some torsionally rigid, some semi-flexible or even highly flexible – such as, for example, the N-Bipex for lower torques or the Rupex for torques higher than 1 million Nm. Even for torques up to 10 million Nm and peripheral speeds of up to 200 m/s Flender has torsionally rigid couplings in its portfolio.
The flexible N-Eupex couplings are fail-safe (load-holding), so ensuring the highest possible operational reliability. In the N-Eupex H variant the load-holding elastomer coupling also comes with a separate spacer that enables the pump seals on the shaft side to be replaced as required without having to detach the whole appliance from its foundation and then to go to the trouble of re-aligning it. That saves time and makes the whole job of servicing pumps, compressors and motors easier.
For those, however, who want a load-shedding variant to separate the drive and output if the flexible elements fail Flender can offer the N-Eupex DS variant. Here too there are 19 standard sizes for torques of between 60 Nm and 21,200 Nm. Because of their design configuration both are plug-type claw couplings.
Engineering design for high reliability and availability
As well as the choice of material the engineering design is also a vital factor. Thus by optimisation of the casting process over decades the geometry of the coupling parts became perfected. The combined action of coupling claw and elastomer enables the most efficient power transmission possible. The result is elastomer service lives like nothing found anywhere else. Typical of the flexible coupling is the universal range of applications, this results in a wide variety among manufacturers and so making choice very complicated. Flender, however, with its 23 N-Eupex standard sizes covers most applications with its modular construction kit. Couplings are then normally available within five working days. If the requirement is more urgent, there is a hotline number on the Website for direct contact that enables requirements to be met even faster.
Readiness for delivery within 24 hours is the target that the traditionally minded manufacturer has set himself. This is possible, because couplings are manufactured to a very great extent with the manufacturer’s own production resources. At the plant in Bocholt a lot of finished parts are kept readinesses that, if required, are adapted on a special machining line to meet any fast-lane requirement.
Standard modular components plus experience for perfect solutions
Several dozen coupling variants used for the most varied applications could be replaced by Flender’s N-Eupex alone, Flender experts estimate. Manufacturers of machines and equipment and operators can thus sustain their standardisation strategy over the long term. These machine elements are even suitable for use in potentially explosive environments because of their certification under Atex Directive 2014/34/EU.
In short, because of the modular principle, particularly for typical applications like pumps, fans and compressors and even with brake disks and brake drums flexible couplings can be assembled from just a few standard parts. For individual configurations Flender’s know-how can be incorporated at any time, so making an optimum coupling solution very quickly available, even in borderline cases. The decisive thing every time is the good understanding of applications as brought to bear by the experts in Bocholt for decades. That makes the choice of coupling much, much easier.