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mechanical design an integrated approach Part 10

Tham khảo tài liệu 'mechanical design an integrated approach part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 520 PART H a Applications V-belt tensions. Note that if the sheave diameters are equal the contact angle is 180 and hence tight-side tension Fi is five times as great as the slack-side tension F . Practically the minimum contact angle is 90 for which F 2.24F2. Since V belts are usually made from reinforced rubber the required belt strength is governed mainly by the tension that is the effect of the additional force in the belt due to bending around the pulley may be neglected. However the tight-side tension should be multiplied by a service factor Ks. The maximum tension is then 13.22 Service factors are listed by the manufacturers in great detail usually based on the number of hours per day of overload variations in loading the driving and driven shafts starting overload and variations in environmental conditions. Examples of the driven equipment in V-belt drives are blowers pumps compressors fans light-duty conveyors dough mixers generators laundry machinery machine tools punches presses shears printing machinery bucket elevators textile machinery mil Is and hoists. Typical service factors relying on the characteristics of the driving and driven machinery are given in Table 13.5. The horsepower should be multiplied by a service factor when selecting belt sizes. The design of a V-belt drive should use the largest possible pulleys. As the sheave sizes become smaller the belt tension increases for a given horsepower output. Recommended pulley diameters for use with three electric motor sizes are given in Table 13.6. Table 13.5 Service factors K s for V-belt drives Driver motor or engine Normal torque High or nonuniform Driven machine characteristic torque Uniform 1.0 to 1.2 1.1 to 1.3 Light shock LI to 1.3 1.2 to L4 Medium shock 1 2 to 1.2 1.4 to 1.6 Heavy shock 1.3 to 1.5 1.5 to 1.8 Table 13.6 Recommended sheave pitch diameters in. for V-belt drives Motor hp Motor speed rpm 575 695 S70 U60 1750 1 2.5 2.5 2.5 .3 4 3.0 2.5 2.5 2 5 LOO 3.0 3.0 2.5 2.5 2.25 CHAPTER 13