Trip speed coupling

The rotational speed of the coupling corresponding to the speed at which the independent emergency overspend device operates to shut down a variable-speed prime mover. Where the term is used in relation to a machine train driven by a fixed-speed electric motor, the trip speed shall be assumed to be the coupling speed that corresponds to the synchronous speed at the maximum supply frequency.

Torque (Moment of a force)

A measure of the tendency of a force to rotate the body upon which it acts about an axis. The magnitude of the moment due to a force acting in a plane perpendicular to some axis is obtained by multiplying the force by the perpendicular distance from the axis to the line action to the force. Torque is commonly expressed in pound-feet or pound-inches.

Torsional tuning

The shifting of one or more torsional natural frequencies of a coupled system to avoid system resonance at a known excitation frequency. Torsional tuning is normally accomplished by varying the torsional stiffness of the coupling.

Total indicator reading (TIR)

The difference between the maximum and minimum readings of a dial indicator, or similar device, monitoring a face or cylindrical surface during one complete revolution of the monitored surface. Note: For a perfectly cylindrical surface, the indicator reading implies an eccentricity equal to half the reading. For a perfectly flat face, the indicator reading implies an out-of-squareness equal to the reading. If the surface in question is not perfectly cylindrical or flat, the interpretation of the meaning of TIR is more complex and may represent an out-of-round condition.

Transient torque

The torque that the coupling is to transmit during unusual or short-term operation. The coupling should be designed to transmit the transient

Transmitted axial force

The axial force transmitted through the coupling from one shaft to the other. It is a function of the resistance to deflection of the flexible element or the sliding of the gear teeth.

Tapered bore

A concentric axial conical hole finished to tolerances appropriate for mounting.

Torsional critical speed

The critical speed of a whole system rather than of a coupling alone. A torsional critical speed exists when the rotating bodies vibrate back and forth relative to each other in the torsional (twisting) direction. The coupling is just the “middleman” in this situation.

Torsional damping

The absorption or dissipation of oscillatory rotational energy. Torsional damping may be necessary to limit the buildup of transient or steady-state torsional resonant oscillations in a system.

Torsional natural frequency

Any natural cyclic rotational oscillatory rate of a system composed of rotating mass inertias acting in combination with the restraining torsional rigidities of the connected shafts and couplings.