Torsion/torsional driving

Belts should not be tightened more than necessary, otherwise the drive and the driven shafts will come under torsion and excessive bending moment. The bearings would also be subjected to excessive stresses. 

Wright, J., A Practical Solution to Transient Torsional Vibration in Synchronous Motor Drive Systems, American Society of Mechanical Engineers, Pub. 75-DE-15. 

Besides the inherent lateral natural frequency characteristic, compressors are also influenced by torsional natural frequencies. All torsionally flexible drive trains are subject to non-steady or oscillatory excitation torques during normal operation of the system. These excitation torques can be an inherent function of either the driver or the driven equipment and, when superimposed on the normal operating torque, may appear to be of negligible concern. However, when combined with the high inertia loads of many turbomachinery trains and a torsional resonant frequency of the system, these diminutive ripples can result in a tidal wave of problems. 

Minimum drive-end peak torques, reducing drive train torsional stresses. 

Jackshafts Some machine-trains use an extended or spacer shaft, called a jackshaft, to connect the driver and a driven unit. This type of shaft may use any combination of flexible coupling, universal joint, or splined coupling to provide the flexibility required making the connection. Typically, this type of intermediate drive is used either to absorb torsional variations during speed changes or to accommodate misalignment between the two machine-train components. 

Universal joints There are a variety of universal joints used to transmit torsional power. In most cases, this type of intermediate drive is used where some misalignment between the drive and driven unit is necessary. Because of the misalignment, the universal s pivot points generate a unique forcing function that influences both the dynamics and vibration profile generated by a machine-train. 

Spindles and jackshafts are designed to transmit torsional power between a driver and driven unit that are not in the same plane or that have a radical variation in torsional power. Typically, both conditions are present when these flexible drives are used. 

Repeated twisting of the spindle s tube or the solid shaft used in jackshafts results in a reduction in the flexible drive s stiffness. When this occurs, the drive loses some of its ability to absorb torsional transients. As a result, damage may result to the driven unit. Unfortunately, the limits of single-channel, frequency-domain data acquisition prevents accurate measurement of this failure mode. Most of the abnormal vibration that results from fatigue occurs in the relatively brief time interval associated with startup, when radical speed changes occur, or during shutdown of the machine-train. As a result, this type of data acquisition and analysis cannot adequately capture these... 

There are two types of flexible intermediate drives used to transmit torsional power belt drives and chain drives. Flexible belts are used in industrial power transmission applications primarily when the speeds of the driver and driven shafts must be different or when the shafts must be widely separated. The trend toward higher speed primary drivers and the need to achieve a slower, useful driven speed are additional factors favoring the use of belts. In addition to V-belts, there are round belts and flat belts. Chain drives are typically used in applications where space is limited or obstructions prevent direct coupling of machine-train components. 

This module discusses two important drive-train components couplings and clutches. Each of these components is used to connect a driver (i.e., power source) shaft to the shaft of the driven unit. Such a connection allows torsional force to be converted into work in the driven unit. Keys and keyways, which are required to prevent slippage and to guarantee positive power with such connections, are also discussed. 

The primary advantage of this type of clutch is its ability to transmit full torsional force without any possibility of slip. Its major disadvantage is that the two shafts are instantaneously coupled when the clutch engages. This results in abrupt starts, which may cause excessive torsional shock loads that damage drive-train components. Figure 59.21 shows a positive clutch. 

Such a distribution has a plausible physical basis, since the driving force for phenyl rotation into the porphyrin plane provided by the electronic excitation (the eg orbital has particularly large coefficients at the meso carbon atoms ( )) encounters steric resistance from the non-bonded interactions between the protons at the ortho positions of the phenyl groups and those on the outer pyrrole carbon atoms (20). Consequently the phenyl torsion potential in the excited states may be relatively flat. Nevertheless, the vibrational frequencies are expected to be sensitive to the torsion angle for orientation close to co-planar because of the effect of conjugation. 

Molecules may be strained by a variety of modes of distortion that include angle bending, torsional strain, and steric interactions. In some cases, strain can provide an important driving force for reaction. However, it is not the strain in the molecule that is important, but rather the change in strain in a reaction. Even this is not sufficient because there must also be a mechanism for the conversion of a compound to a lower energy product that leads to a relatively low barrier for reaction. 

Baz, A., and T. Chen, Torsional stiffness of nitinol-reinforced composite drive shafts. Composites Eng., 3, 1119 (1993). 

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