Torque Requirements

Figure 5,16. It is assumed that by using an exactly symmetric cone a shear rate distribution, which is very nearly uniform, within the equilibrium (i.e. steady state) flow held can be generated (Tanner, 1985). Therefore in this type of viscometry the applied torque required for the steady rotation of the cone is related to the uniform shearing stress on its surface by a simplihed theoretical equation given as...

Color Coding. New machinery and equipment must conform to OSHA standards and OEM specifications for color coding. Color coding can also help to speed up maintenance procedures. Examples include lubrication information, orientation, timing marks, torque requirements, etc. 

Fig. 29. Measurements of yield stress with a vane device and Rheometrics controlled stress rheometer. The torque required to cause yielding is between 1.88...

Fluid-pressure distribution tends to close the valve. For this reason, the smaller manually operated valves have a latching device on the handle, and the larger manually operated valves use worm gearing on the stem. This hydraulic unb ance is proportional to the pressure drop and, with line velocities exceeding 7.6 m/s (25 ft/s), is the principal component in the torque required to operate the valves. Compared with other valves for low-pressure drops, these valves can be operated by smaller hydrauhc cylinders. In this service butterfly valves with insert bodies for bolting between existing flanges with bolts that... 

A double helix shortens mixing time but requires more power. The disadvantages of the higher torque requirement are freqiientlv offset bv the better mixing and heat transfer,... 

During a run, if the supply voltage to a motor terminal drops to 85% of its rated value, then the full load torque of the motor will decrease to 72.25%. Since the load and its torque requirement will remain the same, the motor will star to drop speed until the torque available on its speed-torque curve has a value as high as 100/0.7225 or 138.4% of T to sustain this situation. The motor will now operate at a higher slip, increasing the rotor slip losses also in the same proportion. See equation (1.9) and Figure 1.7. 

When the running torque requirement is high but the starting torque requirement not as high then a... 

The size of capacitors C, C l or C will depend upon the horsepower of the motor and the torque requirement of the load. For starting duty capacitors generally in the range of 30-100 pF and for a run of 2-20 //F will be adequate. 

Instead, if the load values represent the torque requirement, then... 

The nearest standard rating to this is 7.5 kW, and a motor of this rating will suit the duty cycle. To ensure that it can also meet the torque requirement of 10.5 kW, it should have a minimum pull-out torque of 10.5/7.5 or 140% with the slip at this point as low as possible so that when operating at 140%... 

There are several methods of braking, external or internal, and they are briefly diseussed below. Any of them can be employed, depending upon the torque requirement, i.e. size of motor, its speed, the type of load, etc. 

Since card and ring frame motors are normally mounted inside the machine frame, there is an obvious obstruction in the cooling. With this in mind and to meet the torque requirements, the common practice is to choose the next... 

This will depend upon the type of drive, the torque requirement and operations in hour per day etc. The subsequent deratings are the same for all manufacturers and we provide these in Table 8.5. 

The torque required to drive the rolls increases with yield strength so hot-rolling (when CTy is low - see Chapter 17) takes less power than cold-rolling. It obviously increases with the reduction in section (t - t2). And it increases with roll diameter 2r this is one of the reasons why small-diameter rolls, often backed by two or more rolls of larger diameter (simply to stop them bending), are used. 

Induction motor mechanical considerations. If the motor is plaeed between the eompressor and the expander its shaft ends must be eapable of full torque transmission. Unit torque requirements are generally well above those required by the motor rating. The result is speeially designed motors. 

Induction motor electrical considerations. When motor starting is desired, the startup torque requirements generally dietate the motor design. The eleetrie eunent inrush at startup is signifieant. The plant eleetrieal grid must be analyzed for eompatibility. 

It might appear that the most economical mixer w ould have a lai ge impeller and low mixer horsepower. How ever, the torque required to turn large impellers is often greater than for smaller impellers, even though the power required for larger impellers is less. In other words, the mixer cost is governed largely by the torque required to drive the mixer. 

In this apparatus the polymer melt is sheared between concentric cylinders. The torque required to rotate the inner cylinder over a range of speeds is recorded so that viscosity and strain rates may be calculated. 

Typical Torque Requirements for Synchronous Motor Applicationsc )... 

For applications having higher inertia, the Wk of the load may require a motor design that cannot be determined from the torque requirements alone. For such applications, the motor manufacturer should always be provided with the actual value of the Wk of the load. 

For horizontal shaft pumps and vertical shaft pumps having no thrust bearing (entire thrust load carried by the motor), the locked-rotor torque required is usually between 5 and 20%, and for vertical shaft machines having their own thrust bearing a locked-rotor torque as high as 40% is sometimes required. 

The torque requirements of the driven equipment determine the torque specifications of the motor from initial start to shutdown. NEMA definitions are adapted as follows ... 

The torque after breakaway for acceleration to full speed must be considerably greater than the torque required by the driven machine. The greater the margin, the shorter will be the time to accelerate the inertia (Wk ) of the driven equipment and of the motor rotor to full speed. The Wk of the driven equipment must be obtained from the equipment manufacturer and given to the motor manufacturer. 

The pull-out or breakdown torque must be greater than the maximum torque required by the driven equipment to prevent stalling, usually 150% of full load torque for unity-power fector motors and 220-225% for 0.8 leading power factor motors. ... 

Type and make of any direct-connected (to shaft) gears, blowers, etc. Give torque requirements. 

Byberg, G. and Eredrick, E. H., Torque Requirements of Large Motor Driven Loads, Product Engineering, p. 81, Jan. (1950). 

Torque requirements are a primary concern during the selection process. In all applications where variable or high torque is transmitted from the driver to the driven unit, a flexible coupling rated for the maximum torque requirement must be used. Rigid couplings are not designed to absorb variations in torque and should not be used. 

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