I-trans - Power and Gear & Transmission Manufacturers

Technical Selection of Flexible Shaft Couplings

Temperature Allowances

Classification
Correct Installation
Elastomeric Element Failure
Selection based on kW rating
Selection based on torque
Temperature Allowances

The allowance for an extra temperature service factor for flexible couplings (guidelines only):

As the coupling element and hub material are subjected to higher temperatures they will progressively lose their strength particularly the elastomeric element. This means an additional service factor is required in the coupling calculation. Also for colder temperatures particularly extremes an extra factor will also need be added. Listed below are some service factor guidelines and generally a flexible couplings temperature range is controlled by its elastomeric element rather than the hub material properties. Listed below are some service factor guidelines for the elements.

Element Material	Temperature Range	Additional Service factor
Polyurethane - Offers 1.5 times more torque capacity than NBR but less of a dampening effect. Excellent oil and chemical resistance. Not good for high cyclic, stop/start situations.	-30 °C thru to +70°C additional spikes up to +100°C	Normal ambient temps 30°C to 35°C above this range add +.5 to +1 0°C thru to –30°C add +1
NBR Rubber - Highly flexible material and resilient. Oil resistant good industry standard.	-40°C thru to +100°C additional spikes up to 120°C	Normal ambient temps & service factors as above 0° thru to -40° add +1
Hytrel designed for high torque & temperature. Not good for cyclic or stop/start situations	-51°C thru to +121°C	Service factors as above -0°C thru to -51°C add + 1
Sintered Bronze rigid, porous oil impregnated, high torque.	-40°C thru to +232°C Not affected by temp extremes	Low speed applications (max 120 RPM) add hub factor +1

Selection based on torque