V-Belt

Motor nd Drive. The preferred prime mover for a fan is usually an electric motor. Eor fans of low to moderate power, V-belt drives are frequently employed. This permits selection of fans that can be operated over a wide range of speeds rather than being limited to motor synchronous speeds. Furthermore, change of speed is less expensive with V-belt drives. However, fans requiring powerful motors, 37—75 kW (50—100 hp) and higher, are generally directly connected to the motor and driven at synchronous speed. 

Chloroprene Elastomers. Polychloroprene is a polymer of 2-chloro-l,3-butadiene. The elastomer is largely composed of the trans isomer. There are two basic polymer types the W-type and the G-type. G-types are made by using a sulfur-modified process W-types use no sulfur modification. As a result, G-types possess excellent processing and dynamic properties, and tend to be used in V-belts. However, they have poorer aging properties than W-types. The W-types tend to be used in appHcations requiring better aging, such as roUs and mechanical goods (see Elastomers, SYNTHETIC-POLYCm.OROPRENE). 

Principal uses include automotive V-belts, industrial and hydraulic hose, specialty roofing, heels and soles in footwear, wine coveting, and a wide variety of coated fabric uses, eg, rafts. Chloroprene elastomers are also used extensively in adhesives (qv). It is estimated that about 77,000 t of chloroprene are used each year in the United States. The two main suppHers of chloroprene elastomers in the United States are DuPont and Bayer. In addition, Distiguil (France) sells polymers through the A. Schulman Company. 

Air-cooled heat exchangers include a tube bundle, which generally has spiral-wound fins upon the tubes, and a fan, which moves air across the tubes and is provided with a driver. Electric motors are the most commonly usea drivers typical drive arrangements require a V belt or a direc t right-angle gear. A plenum and structural supports are basic components. Louvers are often used ... 

The forced-draft design offers better accessibility to the fan for onstream maintenance and fan-blade adjustment. The design also provides a fan and V-belt assembly, which are not exposed to the hot-air stream that exits from the unit. Structural costs are less, and mechanical life is longer. 

V-belt drive assemblies are generally used with fans 3 m (10 ft) and less in diameter and motors of 22.4 kW (30 hp) and less. 

Roll presses are now manufactured by most cement-equipment manufacturers, for example Krupp-Polysius AG. For drives up to 1200 kW they are equipped with V-belt drives, allowing speed to be changed. Rolls in one particular crusher are 48 inches (1200 mm) in diameter and 30 inches (700-mm) wide and each weighs 90 tons. Machines with up to 2500 kW installed power and 1000 ton/h (900... 

The number of speed reduetions is another way to classify conveyor drives. Most common of the speed-reduction methods is the two-step system, in which the motor is coupled to a speed reducer and the slow-speed shaft of the reducer is connected to the conveyor-drive shaft by a V belt or a roller chain. The second reduction not only permits the use of a simpler speed reducer but also allows a more flexible layout of the motor and reducer mounting plate. On many installations this eliminates the need for a specially designed drive mount. 

Since it is good practice to maintain a selected inventory of spare parts for drives, economy can be achieved by standardizing conveyor drives throughout the plant. For example, intermediate speed reduction by means of V belts, sheaves or chains, and sprockets can frequently permit using the same speed-reducer size for several drives. Thus, it may be necessary to keep only one repair-stock speed reducer for a number of conveyors. 

Roller conveyors are quite frequently powered, the simplest method being use of a pressure belt in contact with the lower surface of the rolls. A special ripple belt with raised pads is capable of starting up the load but does not build up excessive blocked pressure if the line fills up. Other similar drives are available, with varying degrees of control over the applied power. Most expensive of the powered roller units are those in which each roll is equipped with V-belt or chain drives. Pusher bars suspended from overhead chain conveyors may also be used to move containers along a roller hne. 

Pipe-hne and marine installations are frequently arranged so that the engine drives all its auxiharies from the crankshaft by means of chains and V belts. But process-plant practice is to have all the auxiliaries independently driven, using standby pumps to minimize engine downtime. 

A centrifugal compressor driven through V-belts at a speed of 4500 r.p.m. having the torque curve as shown in Figure 2.18 and a moment of inertia /WK of 2.50 kgm employs a squirrel cage motor with the following parameters ... 

The flat belt is a friction drive transmitting load through the friction between the belt and the pulley while the V-belt is a positive drive which is flat on one side and has a projection like a geartooth on the other. These... 

The selection of flat belts is made along similar lines to that for V-belts (discussed later in more detail). The load-transmission capacity of a flat belt can be defined by... 

These are short centre drives unlike flat belt drives. The belt slip in such drives is negligible. The recommended maximum power that can be transmitted through such belts of different cross-sectional areas is provided by the belt manufacturer. The normal cross-sections of V belts in practice are given in Table 8.3. The cross-section of a belt depends upon the power to be transmitted and its speed. To select the appropriate section of the belt for the required transfer of load refer to Figure 8.11 also provided by the manufacturer. It is recommended that... 

Table 8.3 Nominal cross-sections of V-belts and their code numbers...

The load-transmitting capacities of a single V-belt, at 180° arc of contact, are provided by the belt manufacturer as standard selection data for the user for different areas of belt cross-sections and speed of the faster shaft. We have provided this data for a leading manufacturer, for belts of section D, in Table 8.4, to illustrate the selection of V-belts for the drive of Example 8.2. 

Consider a reciprocating compressor operating in a process plant and using a motor of 110 kW, 980 r.p.m. The compressor is required to operate at 825 r.p.m. through V-belts. The approximate centre distance between the motor and the compressor may be considered as 1 m. 

Table 8.4 Power ratings for section D V-belts, with 180° arc of contact with the smaller pulley...

Figure 8.12 Determining the belt details in a V-belt drive...

Indusirial Power Engineering and Applications Handbook Table 8.5 Service Factors for flat and V-belts... 

K = belt factor, 2 to 2.5 for V-belts and 2.5 to 2 for flat belts. Sometimes it may be higher (up to 4 to 5). (The higher values must be considered when the distance between shafts is short or belt tension is high). 

Transmission of load and suitability of bearings 8/213 Table 8.9 Nominal inside lengths, pitch lengths L for all standard sizes of multiple V-belts... 

Endless V-belts for industrial purposes - Industrial V-belt drives - calculation of power ratings Pulley and V ribbed belts for industrial applications-PH, PJ, PK. PL and PM profiles 2494-1/1994 3790/1995 4184 5292/1980 9982/1998... 

The mechanical seal on the radiator water pump of your car has to work under severe conditions. This seal must resist the pressures and temperatures, corresponding to the velocities of the motor, and the variable operating times. This seal is not a precision seal (it has stamped parts rather than machined components) and the pump is a portable pump. The pump doesn t use a direct coupling but a v-belt pulley with radial loading. The seal must resist many vibrations commencing with the v-belt slapping and whipping. 

Effluent air temperature should be limited to 200°F, to prevent potential damage to fan blades, bearings, V-belts, or other mechanical components in the hot air stream. 

Most of the drivers used with the sliding vane compressor are electric motors. Variable speed operation is possible within the limits of vane speed requirements. The vanes must travel fast enough to seal against the cylinder wall but not so fast that they cause excessive wear. For the smaller units, under 100 hp, V-belts are widely used. Direct connection to a motor, however, is possible for most compressors and is used through out the size range. 

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