Torsion shaft

Before a torsion shaft with strain gauges was employed to determine the torque on a rotating stirrer shaft, a swiveling motor had to be used and the torque measured by weighing. 

Power measurements require the measurement of the torque and the rotational speed. The torque can be measured using a torsion shaft with strain gauges, electrically with eddy-current torque transducers, or mechanically with a swiveling motor. The speed of rotation can be measured using mechanical, electrical (photocell), or optical (stroboscope) instruments. 

It will be necessary to describe the definition and measurement of the parameters used to quantify viscoelastic effects, in the sense that elastic moduli allow one to quantify elastic effects. For example how do you design the size of a torsional shaft when the pofymer creeps for a plastic bolt after it is tightened, how do you conqwte the rate of stress deca or, for the damping of mechankal vibrations what parameters would you require to design the pofyurethane foam used to control and dampen vibrations and resonances in a hi-fi tone arm ... 

A splined torsion-shaft, Fig. 5.52, 2" diameter is subjected to a constant torque M,= 180 KN. The material is high strength carbon steel heat treated to 1,200 MPa ultimate strength and 313 MPa fatigue limit xyin completely reversed torsion. Service experience indicates continuous untimely failures along section A-A in correspondence of a shoulder fillet of radius p — 2 mm. 

Fig. 5.52 Splined torsion shaft failed along section A-A at a shoulder fillet...

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. 

Note The shaft deflection should not be more lhan 11% of the air gap between the stator and the rotor. For loads that exert more force and torsional stress on the motor shaft and bearings than is permissible, due to the larger width of pulleys which may shift the... 

Expander-compressor shafts are preferably designed to operate below the first lateral critical speed and torsional resonance. A flame-plated band of aluminum alloy or similarly suitable material is generally applied to the shaft in the area sensed by the vibration probes to preclude erroneous electrical runout readings. This technique has been used on hundreds of expanders, steam turbines, and other turbomachines with complete success. Unless integral with the shaft, expander wheels (disks) are often attached to the shaft on a special tapered profile, with dowel-type keys and keyways. The latter design attempts to avoid the stress concentrations occasionally associated with splines and conventional keyways. It also reduces the cost of manufacture. When used, wheels are sometimes secured to the tapered ends of the shaft by a common center stretch rod which is pre-stressed during assembly. This results in a constant preload on each wheel to ensure proper contact between wheels and shaft at the anticipated extremes of temperature and speed. 

It is required to find the torque without slippage that can be transmitted by a hub that is assembled by an interference fit to a powered shaft. The hub outside diameter D = 070 mm, and the shaft diameter d = 050 mm, as shown in Figure 4.55. The length of the hub is 100 mm. Both hub and shaft are machined from hot rolled steel SAE 1035 with a yield strength Sy A(342,26) MPa (see Table 4.6). Given that the hub is stopped suddenly in service due to a malfunction, and considering only the torsional stresses, what is the probability that the shaft will yield ... 

The stress eoneentration faetor kf results from the keyway and must be used in torsional stress ealeulations. Faetor /c takes into aeeount the shaft step it must be used in the bending stress ealeulation. 

Load—during the back flow the shaft torque is reduced, then restored with feed forward giving a torsional pulse with each cycle. 

The torsionally soft or resilient coupling such as the quill shaft and the metal-metal resilient transmit torque can handle misalignment through springs, metal strips, coils, disks and diaphragms, They will tune the system by changing the spring constant K. 

Hafner, K. E., Torsional Stresses of Shafts Caused by Reciprocating Engines Running through Resonance Speeds, ASME 74-DGPl, New York American Society of Mechanical Engineers, 1974. 

Hi/ume, A., Transient Torsional Vibration of Steam Turbine and Generators Shafts due to High Speed Reclosing of Electric Power Lines, ASME... 

Most materials scientists at an early stage in their university courses learn some elementary aspects of what is still miscalled strength of materials . This field incorporates elementary treatments of problems such as the elastic response of beams to continuous or localised loading, the distribution of torque across a shaft under torsion, or the elastic stresses in the components of a simple girder. Materials come into it only insofar as the specific elastic properties of a particular metal or timber determine the numerical values for some of the symbols in the algebraic treatment. This kind of simple theory is an example of continuum mechanics, and its derivation does not require any knowledge of the crystal structure or crystal properties of simple materials or of the microstructure of more complex materials. The specific aim is to design simple structures that will not exceed their elastic limit under load. 

Rad, n. wheel, -achse, /. axle or shaft of a wheel, -arm, m. spoke (of a wheel), -be-wegung, /. rotary motion, rotation, -dre-hnng, /. rotation torsion. 

The calculation for torque is a primary example of a single degree of freedom in a mechanical system. Figure 43.15 represents a disk with a moment of inertia, /, that is attached to a shaft of torsional stiffness, k. 

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. 

Because of the length of these shafts and the flexible couplings or joints used to transmit torsional power, jackshafts tend to flex during normal operation. Flexing results in a unique vibration profile that defines its operating mode shape. 

Both the jackshaft and spindle are designed to absorb transient increases or decreases in torsional power caused by twisting. In effect, the shaft or tube used in these designs winds, much like a spring, as the torsional power increases. Normally, this torque and the resultant twist of the spindle are maintained until the torsional load is... 

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... 

The conjoint action of a tensile stress and a specific corrodent on a material results in stress corrosion cracking (SCC) if the conditions are sufficiently severe. The tensile stress can be the residual stress in a fabricated structure, the hoop stress in a pipe containing fluid at pressures above ambient or in a vessel by virtue of the internal hydraulic pressure created by the weight of its contents. Stresses result from thermal expansion effects, the torsional stresses on a pump or agitator shaft and many more causes. 

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. 

There is a wide variety of commercially available sprockets. While they may vary in design, methods of manufacture, and materials of constmction, they all have some common features. They will all have hardened teeth designed to mate with a specific type of chain, sufficient web strength to effectively transmit their rated horsepower or torsional forces, and a boss or hub that can be bored to the mating shaft s diameter. 

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. 

Figure 59.15 is an example of a keyed shaft that shows the key size versus the shaft diameter. Because of standardization and interchangeability, keys are generally proportioned with relation to shaft diameter instead of torsional load. 

Torsional stresses are developed when power is transmitted through shafts. In addition, the tooth loads of gears mounted on shafts create bending stresses. Shaft design, therefore, is based on safe limits of torsion and bending. 

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. 

A torsional beam spring absorbs energy by twisting through an angle 0 (Fig. 3-14) and may thus be treated as a shaft in torsion. 

A shaft subject to torque is generally considered to have failed when the strength of the material in shear is exceeded. For a torsional load the shear strength used in design should be the published value or one half the tensile strength, whichever is less. The maximum shear stress on a shaft in torsion is given by the following equation ... 

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