KTR TOOLFLEX Metal Bellows Coupling

All-metal bellows coupling for precise motion control

The KTR TOOLFLEX is a torsionally stiff, backlash-free bellows coupling for servo drives, encoders, spindles and measuring equipment. A stainless steel bellows carries the torque and absorbs axial, radial and angular shaft displacement, while the hubs are normally aluminium, with steel hubs on the largest sizes. Because the coupling is all metal it has no wearing elastomer part, so it needs no maintenance and does not change its characteristics with age. It suits applications where the angle of rotation of the drive must be reproduced exactly at the driven shaft, such as machine tool axes, handling systems, printing and packaging machines.

The values below are taken from KTR operating and assembly instructions KTR-N 45810 EN for TOOLFLEX bellows couplings.

Technical specifications

Choosing between 4-layer and 6-layer bellows

The four-layer bellows (type S) is the stiffer version and is chosen when torsional rigidity and positioning accuracy matter most. The six-layer bellows (type M) is softer in bending and so tolerates larger displacements, at the cost of a lower torsional stiffness. In both versions the displacement figures given by KTR are maximum values that must not occur at the same time; if radial and angular misalignment arise together, only a proportion of each may be used. Keeping the alignment as good as possible extends the life of the bellows, which is a fatigue part and is stressed by every cycle of displacement.

The setscrew version suits small shafts and moderate loads. Clamping hubs avoid a keyway, distribute the clamping force around the shaft and are usually preferred on servo motors with smooth shafts. The pluggable PI type allows the coupling to be disconnected axially, which is helpful where the motor must be removed often.

Assembly and operating notes

The bellows must not be twisted, bent or compressed during assembly, and the shafts should be inserted without force so that the bellows is not stressed axially. Clamping screws are tightened to the torque listed for each size in the instruction. A bellows coupling does not tolerate shock loads or operation outside its torque rating, so the selection should include a service factor and, for drives with high acceleration, a check of the peak torque. The maximum circumferential speed is 25 m/s for the whole range.

Documents and quotation

The attached PDF is the KTR operating and assembly instruction with the dimension and technical data tables. For a quotation send the shaft diameters and tolerances, nominal and peak torque, speed, expected misalignment and the hub version required. Compatible drives are listed under Servo Drives, and other coupling ranges under Electric Motors.