KTR POLY-NORM Torsionally Flexible Shaft Coupling

Pump-drive jaw coupling with elastomer ring

The KTR POLY-NORM is a torsionally flexible, fail-safe shaft coupling in cast iron. The torque passes through elastomer elements between interlocking cams, and the same elements compensate shaft displacement and damp shocks and torsional vibration. KTR highlights its compact design and says it is used in almost every area of mechanical engineering, mainly in the pump industry, which makes it a common choice for a motor-to-pump drive.

The data below is taken from KTR operating and assembly instructions KTR-N 49510 EN (edition 17) for types AR, ADR, ADR-K, AVR, AZR, AR/AZR and AZVR, and for the AR version with taper clamping sleeve.

Technical specifications

Type selection: AR, ADR and AZR

Type AR is the basic two-part version: two hubs and one elastomer ring, covering sizes 28 to 280 and the full torque range. Type ADR is the three-part design with a flange hub in nodular iron EN-GJS-400-15, and ADR-K is the related variant listed in the same tables. Type AZR adds a steel spacer with a drop-out centre length of 100 mm or 140 mm. In general engineering practice a drop-out spacer of this kind lets a pump or motor be serviced or withdrawn without shifting the other machine, so it suits drives where a back-pull-out pump rotor has to be removed. AVR and AZVR are further variants with their own tables in the instruction.

KTR states that the torque data refer to the elastomer part only. The transmittable torque of the shaft-hub connection, set by bore, key and fit, must be checked by the customer. Selection follows DIN 740 part 2. For drives with torsional vibration, such as diesel engines or piston pumps, KTR asks for a torsional vibration calculation.

Assembly and alignment

The hubs can be warmed lightly, to about 80 °C, to ease fitting on the shaft. Setscrews to DIN EN ISO 4029 secure the hubs axially; for explosive atmospheres these screws and all fasteners need the locking measures described in the instruction. Taper clamping sleeves used without a feather key are not permitted in explosive atmospheres and carry no explosion-protection marking. Alignment must stay inside the displacement table, radial and angular values combined to no more than 100 percent, and in explosion group IIC only half of the table values may be used.

KTR also lists sleeve-and-hub combinations with attachments that can generate heat, sparks or static charge, such as brake drums, torque limiters or fan impellers, as not permitted in potentially explosive atmospheres without a separate analysis.

Documents and quotation

The attached PDF is the KTR operating and assembly instruction for POLY-NORM and holds the dimension tables for every type. For an enquiry send the pump and motor data, power and speed, shaft diameters with key sizes, the type (AR, ADR or AZR with drop-out length), ambient conditions and the explosion-protection requirement. See Pumps and Electric Motors and Gear Units for the machines it connects.