Mechanical drives

Acetal resins are also used extensively in transportation, especially automotive. Handles and internal components (gears, gear racks, cables) for window lifts and other similar devices are examples. Most of the appHcations which do not involve painting or plating are below the window line. Many common consumer items are manufactured essentially entirely from acetal resin (eg, disposable lighters) or have critical components molded from acetal resin (eg, hubs and platforms for videocassettes). The properties that make acetal resins useful in industrial appHcations make them useful for internal components, especially mechanical drive systems, of many household appHances. 

Variable Flow Rate Conventional variable clearance volume and valve lifting devices are impracticable at high pressures and, should it be necessary to vary the flow rate, use has to be made of variable speed electric drives or magnetic clutches. Integral steam and gas engines have been used and Burckhardt (168) developed an hydrauhc drive to provide an integrated variable capacity machine, but its efficiency is less than that of a straight mechanical drive. 

E. R. Booser, Handbook ofl ubrication Vol. 2, CRC Press, Boca Raton, Fla., 1984. Machine Design, Mechanical Drives Reference Issue, pubHslied annually. 

Backstops. A backstop is a device that permits rotation of the pulley in the forward direction but automatically prevents rotation in the opposite direction. A backstop should be installed at the headshaft of an inclined belt to prevent the belt from moving in reverse if the power to the motor is intermpted or if there is a failure in the mechanical drive system. 

The distinguishing feature of this dryer is the bottom-screw drive, as opposed to a top-drive unit, thus ehminating any mechanical drive components inside the vessel. The bottom-driven screw rotates about its own axis (speeds up to 100 rpm) and around the interior of the vessel (speeds up to 0.4 rpm). The screw is cantilevered in the vessel and requires no additional support (even in vessel sizes up to 20 m operating volume). The dryer is available in a variety of materials of construction, including SS 304 and 316, as well as Hastelloy. 

Steam turbines are divided into two broad categories those used for generating electric power and general-purpose units used for driving pumps, compressors, etc., and frequently called mechanical-drive turbines. 

Figure 29-11 illustrates in general the relationship of capability versus speed. At 1800 and 3600 r/min are the turboelectric generator drives with capability hmits above the top of the chart. The majority of mechanical-drive applications are within the shaded area capabilities above the solid hue are special and unusual. 

As the stress is reduced, the rate of power-law creep (eqn. (19.1)) falls quickly (remember n is between 3 and 8). But creep does not stop instead, an alternative mechanism takes over. As Fig. 19.4 shows, a polycrystal can extend in response to the applied stress, ct, by grain elongation here, cr acts again as a mechanical driving force but, this time atoms diffuse from one set of the grain faces to the other, and dislocations are not involved. At high T/Tm, this diffusion takes place through the crystal itself, that... 

Both the Power Industry and the petrochemical industries use the aircraft-type turbine. The Power Industry uses these units in a combined cycle mode for power generation especially in remote areas where the power requirements are less than 100 MW. The petrochemical industry uses these types of turbines on offshore platforms especially for gas re-injection, and as power plants for these offshore platforms, mostly due to their compactness and the ability to be easily replaced and then sent out to be repaired. The aeroderivative gas turbine also is used widely by gas transmission companies and petrochemical plants, especially for many variable speed mechanical drives. These turbines are also used as main drives for Destroyers and Cruise Ships. The benefits of the aeroderivative gas turbines are ... 

Water injection, or steam injection systems, are being used extensively to augment power. Corrosion problems in the compressor diffuser and combustor have not been found to be major problems. The increase in work and efficiency with a reduction in NO makes the process very attractive. Split-shaft cycles are attractive for use in variable-speed mechanical drives. The off-design characteristics of such an engine are high efficiency and high torque at low speeds. 

Mechanical Drives. Mechanical drive gas turbines are widely used to drive pumps and compressors. Their application is widely used by offshore and petrochemical industrial complexes. These turbines must be operated at various speeds and thus usually have a gasifier section and a power section. These units in most cases are aero-derivative turbines, turbines, which were originally designed for aircraft application. There are some smaller frame type units, which have been converted to mechanical drive units with a gasifier and power turbine. 

An examination of the above standards as they apply to the gas turbine and its auxiliaries are further examined in this section. The ASME B 133.2 basic gas turbines and the API standard 616, gas turbines for the petroleum, chemical, and gas industry services are intended to cover the minimum specifications necessary to maintain a high degree of reliability in an open-cycle gas turbine for mechanical drive, generator drive, or hot-gas generation. The standard also covers the necessary auxiliary requirements directly or indirectly by referring to other listed standards. 

Figure 1. Typical efficiencies for mechanical drive turbines.

Forces and moments which the compressor can accept without causing misalignment to the machine are to be specified by the vendor. Many factors go into this determination, and as one may guess, the limits arc determined quite arbitrarily in most cases. With all the many configurations a compressor can take, a single set of rules cannot fit all. Despite this. NEMA SM-23[13] for mechanical drive steam turbines is used as a... 

NEMA Standards Publication No. SM 23-1979, Steam Turbines for Mechanical Drive Service, National Electrical Manufacturers Associatioi., Washington, DC, 1979. 

Most gas turbine manufacturers manufacture a mechanical drive turbine. This unit generally includes the auxiliary and control equipment... 

Figure 8-22. Cutaway of a multiple diaphragm flexible element coupling. Courtesy of Zum Industries, Inc., Mechanical Drives Division)...

Rgure 8-31. Multiple diaphragm flexible element coupling with a strain gauge type torque meter. Courted ofZum Industrie Inc., Mechanical Drives DMsforii... 

The basic assumptions of fracture mechanics are (1) that the material behaves as a linear elastic isotropic continuum and (2) the crack tip inelastic zone size is small with respect to all other dimensions. Here we will consider the limitations of using the term K = YOpos Ttato describe the mechanical driving force for crack extension of small cracks at values of stress that are high with respect to the elastic limit. 

The utility of K or any elastic plastic fracture mechanics (EPFM) parameter to describe the mechanical driving force for crack growth is based on the ability of that parameter to characterize the stress-strain conditions at the crack tip in a maimer which accounts for a variety of crack lengths, component geometries and loading conditions. Equal values of K should correspond to equal crack tip stress-strain conditions and, consequently, to equivalent crack growth behavior. In such a case we have mechanical similitude. Mechanical similitude implies equivalent crack tip inelastic zones and equivalent elastic stress fields. Fracture mechanics is... 

The bearing of top and bottom driven filters, that supports the rotating plate stack and its sealing, is complex since it has to withstand the internal pressure and the side forces imposed by the mechanical drive. However, side loads on some machines are eliminated by the use of hydraulic motors. 

Figure 11-49D. Mechanical drive steam turbine specifications.

This chapter gives primary attention to the commonly used general-purpose alternating current motors, although others are noted to acquaint the engineer with the variety of motors, motor enclosures, and mechanical drive turbines available and sometimes used in the chemical and petrochemical industries. Because direct-current motors are not frequently used in the process industries (other than in heavy-duty processes), they are not examined further in this chapter. 

The mechanical drive steam turbine uses expanding steam to drive a rotating wheel with a power shaft. See Figures 16-16A-H. 

Mechanical drive turbines, although designed for steam, can be adapted and modified to operate with high pressure gas as the motive power. This is particularly profitable where the gas is needed at reduced pressure. The driven applications can be the same as for the turbine when steam is the motive medium. 

TEST FDR A CONTROLLED EXTRACTION CONDENSING TURBINE mechanical drive (SUPERHEATED INLET AND EXTRACTION STEAM)... 

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