A new model of metal disc shaft couplings has been added to the range manufactured by the German specialist supplier Mönninghoff. Their Arcoflex range that starts at 800Nm now extends to 23000Nm with the new size 120. There are now eight sizes in the range, all torsionally rigid and backlash free, suiting angular misalignments up to 1 degree. Compared with the alternatives of carden shaft universal joints and gear couplings, these metal disc designs give the advantages of being both maintenance and backlash free.
Metal disc couplings are available with one or two disc packs. Each disc pack is constructed with laminations of stainless spring steel, typically 12, bushed together at six points for the Arcoflex range. The coupling is assembled with the disc packs connected alternatively left and right with fitted bolts to the hubs and a central spacer. In operation the disc packs flex to take up angular misalignment and also any axial movement, typically a result of thermal expansion. Usually there is also an element of radial misalignment, also known as shaft offset. However if one shaft is self-aligning in a single bearing, then couplings with a single disc pack are suitable.
Metal disc couplings are torsionally rigid although they do exhibit a tiny amount of wind-up under load. For the Arcoflex stiffness values are from 6000 to 100,000Nm/degree, and this makes them suitable for line shafts and machines where precise registration is needed, such as printing. A common option is to add a central spacer tube which can be up to 6m long. Generally the tube is constructed in steel for machinery applications, but glass or carbon fibre are also available. Although the couplings are backlash free due to their construction with fitted bolts, the shaft-to-hub connection may exhibit backlash due to keyways. Here another standard option is to use locking bushes to connect from the shafts to the hubs without backlash, and giving the added benefit of the ability to radially adjust timing.
The new Arcoflex size 120 adds to the top of the Mönninghoff range which comprises three series and now runs from 1 to 23000Nm. Availability and technical support is available in the UK from Techdrives at www.techdrives.co.uk/.