The German couplings specialist, KTR, has come up with a novel way to use jaw couplings in temperatures too high for the elastomer materials conventionally used for coupling spiders. It has developed a spider made from “knitted” steel wire, similar to the steel wool used to clean pots and pans.
Standard spiders are made from thermoplastic polyurethane materials that can be used in temperatures from –30° to +90°C. The materials are produced in various hardness ratings, depending on the damping capacity and the torsional stiffness required. Both of these parameters are linked closely to the operating temperature.
KTR’s knitted-wire spider (above) allows vibration-damping couplings to operate in temperatures from –40°C to +180°C without affecting their torque capacities, torsional stiffness or damping. For an ambient temperature of 30°C, the characteristic curves of the knitted-wire spider are similar to those of standard elastomer spiders.
KTR expects the benefits of the knitted spiders to be most significant for applications with operating temperatures above 120°C. The stainless-steel spiders are also suitable for use in corrosive environments.
The knitted-wire spiders can be used with steel, cast-iron or hard-coated aluminium hubs. Initially, KTR is producing the spiders for its Rotex couplings. Damping figures are the same as for elastomer versions, while torque capacities and torsional stiffness are said to remain almost constant, even under permanent loads. The steel spiders are available in sizes from 14 to 90, corresponding to rated torques from 12.5–3,600kN (with peak torque ratings twice as high).
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