Product category: Gears, brakes, couplings and engines
News Release from: R+W Coupling Technology | Subject: Thermoplastic shaft couplings
Edited by the Engineeringtalk Editorial Team on 28 September 2005
Thermoplastic coupling offers
quality at low price
R + W Coupling Technology's thermoplastic shaft couplings can be used in over 90% of areas where traditional insert couplings have been used in the past
Engineered plastics are receiving more and more attention in the fields of mechanical and plant engineering every day. Compared to conventional metals, the mechanical parameters and material properties of thermoplastics can be manipulated for optimal performance, or be used to mimic the properties of metals at dramatically reduced cost.
This article was originally published on Engineeringtalk on 28 September 2005 at 8.00am (UK)
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Designers and builders, recognising the important advantages of thermoplastics, are increasingly integrating them into new and existing applications, and plastic components can now be found in a multitude of areas where metals would have been used exclusively a decade ago.
In the field of mechanical design, the most significant technical advantage for thermoplastics is a dramatically reduced mass and moment of inertia, accompanied by a high level of chemical compatibility and tolerance for heat.
Of course it is also difficult to ignore the fact that plastics can provide a tremendous cost reduction compared to metals, as the result of decreased production times and relatively low material cost.
Unifying the goals of enhancing technical performance and durability with cost savings, engineered plastics are revolutionising mechanical engineering across a whole spectrum of industries.
The latest breakthrough in this area is the release of the all new TX series of thermoplastic shaft couplings from R+W.
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The coupling can be used in over 90% of areas where traditional insert couplings have been used in the past.
This invention is the first thermoplastic coupling capable of a full range of torque ratings.
To manufacturers of low-cost machinery and systems who found the price of backlash-free and torsionally rigid shaft couplings prohibitive, the TX coupling is the answer at half the cost or less.
To manufacturers of high-performance machinery, interested in optimising acceleration and control, the TX is the solution, with 65% reduced mass over aluminium and 89% reduced mass over steel, and a nearly proportionate advantage in terms of moment of inertia.
While many plastic components must be produced to larger dimensions than their metallic predecessors, R+W has been able to maintain identical dimensions to existing metal coupling designs.
The basic structure of the material allows for the same manufacturing tolerances of +/- 0.01mm or better.
The couplings also exhibit the same load tolerance and torsional stiffness properties, making them appropriate for positioning systems.
The result is that time consuming evaluations necessary for engineering changes will not be necessary, as a 1:1 replacement for existing designs is available in the TX.
The material itself is a specially engineered thermoplastic polymer with glass fiber reinforcement.
The plastic has a temperature range of -20 to 100C.
The fluid absorption rate in liquid media is less than 1% with virtually zero change to the dimensioning, as tested in the TX couplings.
The high chemical resistance and low absorption rate make these couplings ideal for corrosive environments as an alternative to costly stainless steel designs.
Beyond the typical applications for servo couplings, such as packaging machinery, machine tool automation and material handling, the TX offers superior performance and equivalent cost in centrifugal, radial piston and vacuum pumps.
Since in almost any case motor and pump connections are effected via shaft keys, for ease of installation and safe holding torque, the first series of TX couplings will mount in the same way.
The high-strength material and construction allow for high startup and impact torques.
The real advantage for pump manufacturers is the light weight and high torsional stiffness in comparison to the sintered metal couplings typically used, serving to optimise acceleration times during startup.
This difference can be taken into account during motor sizing, noticeably improving efficiency in any drive system.
While the first model, TX1, involves a keyway and set screw interface, it will be followed shortly by clamp collars and tapered bushing designs, which are in the final testing stages.
Torque ranges of 2 to 660Nm and bore diameters of 8 to 45mm and .375 to 1.75 inches are already available for OEM applications.
Optimisation of specific material properties, such as rheology, stiffness and resilience, have allowed for extended testing involving 40 million plus load reversals to be carried out with no recognisable wear or fatigue.
In addition to the accelerated life testing, static fracture testing was used to reveal a three to four times safety factor in the torque ratings.
Even at a four-fold torque overload, the units survived testing, with the limiting factor being the keyed shaft connection.
Hardened steel key stock became deformed before any signs of cracking were evident in the coupling hubs.
Climate chamber testing was also conducted in order to more accurately simulate the coupling life cycle.
Exposure to high levels of humidity and UV radiation yielded no change to stiffness or durability.
The combination of both performance and cost advantages are rarely achieved in machine component design, except in the case of engineered plastic components.
It is no understatement therefore, that the TX series represents a significant evolution in coupling design.
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