The elastomeric spider or the drive insert in a flexible coupling is the flexible medium principally employed to dampen harmful torsional vibrations and accommodate for the misalignment forces - angular, parallel and axial, which invariably exist between two on-line rotating shafts. The spider or the drive inset is therefore subjected to a number of forces, which are fluctuating in nature. The spider is continuously therefore in a dynamic state and gets deformed in proportion to the torque that is being transmitted. In addition to the simple function of torque transmission, the spider has to accept several fluctuating and unpredictable forces due to a combination of different kinds of misalignments, temperature, environmental conditions, etc., which causes fatigue failure of the material either by way of development of a crack or compression set which results into its premature failure.

In a cyclic or dynamic situation, the fact that rubber and elastomers are visco-elastic materials and therefore contain both elastic and viscous elements is very important to understand. The energy required to deform a perfectly elastic spider is completely recovered when the force is removed, but the viscous element, which is caused by internal molecular friction, retards elastic deformation and energy is lost. This lost energy is dissipated in the form of heat and the consequent temperature rise in the spider caused "hysteresis" failure of the spider and the subsequent failure of the coupling.

The new generation of NENFLEX spiders-the star shaped, the wrap around and the individual free floating drive insets are the subject matter of a patent and a result of thorough CAD analysis and practical dynamic tests.

Our R & D has now developed the polyurethane technology to offer a variety of high performance insert materials, which are tested on our unique dynamic test bed "DynaTest" which simulates real life like conditions that prevail on a spider while the coupling is rotating.