Polyflex JB and Micro-V Belt Drive Selection Procedures

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1 Polyflex JB and Micro-V Belt Drive Selection Procedures How to Design Polyflex JB and Micro-V Belt Drives Note: The upcoming drive selection and engineering sections provide information for Polyflex JB and Micro-V belts and sheaves (or pulleys). Where we refer to sheaves (for Polyflex JB belts), you can substitute pulleys for Micro-V belts. If you need additional information, contact Gates Product Application Engineering, Denver. This section describes how to design standard two-sheave Polyflex JB and Micro-V drives. To select either a Gates Polyflex JB and Micro-V Belt drive, you need to know these five facts: 1. Horsepower or kilowatt rating of the driver machine 2. rpm of the driver machine 3. rpm of the driven machine 4. Approximate center distance required 5. Hours per day operation. Follow these seven steps to design a drive: Step 1 Find the Design Horsepower (Design kw) Design Horsepower = (Service Factor) x (Horsepower Requirement) A. Select the proper service factor from Table 37 on Page 87. If your driven machine is not listed, find a machine with comparable starting, running and shock load characteristics. B. The horsepower requirement of the drive usually is taken as the nameplate rating of the driver. The actual requirement of the driven machine may be used as the horsepower requirement, if it is known. This type of load approximation is used in those applications where a small auxiliary machine is being driven from a large motor or engine. Step 2 Find the Speed Ratio Use Formula 7 on this page to calculate the desired speed ratio for your drive. The speed ratio can be determined from either the shaft speeds or the sheave pitch diameters. To determine the pitch diameter of a sheave, measure the outside diameter and add the appropriate add-on factor from Table 33. Speed = Ratio Formula 7 RPM of Faster Shaft RPM of Slower Shaft Pitch Dia. of Larger Sheave = Pitch Dia. of Smaller Sheave Step 3 Choose the Sheave Diameters A. The drive can be designed around a known sheave diameter. For example, if you have one sheave available, or if a minimum or maximum sheave diameter is known, use Formula 7 to determine the other sheave diameter. To calculate the pitch diameter of the larger sheave, multiply the pitch diameter of the smaller sheave by the speed ratio, or divide the pitch diameter of the smaller sheave. To convert the pitch diameter to outside diameters, subtract the values in Table 33 from the pitch diameters. Table 33 Factors to Calculate Polyflex JB and Micro-V Pitch Diameters O.D. to P.D. Value Cross Section (in) (mm) 3M Polyflex JB M Polyflex JB J Micro-V NOTE: Pitch diameters are always used in speed ratio calculations. If your drive uses an electric motor, the minimum selected sheave O.D. should be at least as large as the sheave outside diameters specified in Table 38 on Page 87. B. Calculate the sheave rim speed for your drive using Formula 8 below: Formula 8 Sheave Rim (O.D. of either sheave) x (rpm of same sheave) = Speed (ft/min) 3.82* *This constant is derived from 12/π. Polyflex JB and Micro-V sheaves made with standard materials should not exceed 6,500 feet per minute. If the rim speeds exceed this figure, special sheave materials and dynamic balancing are usually required. If possible, redesign the drive using smaller diameter sheaves so that the rim speed is between 4,000 and 6,000 fpm. C. When designing a drive with larger diameter sheaves consider these factors: Cost Considerations: Since sheave diameter and rated horsepower per belt or rib are proportional, larger diameter drives will usually require fewer belts or ribs to transmit a specific load. This generally results in a more cost effective drive. Space Limitations: In addition to being more cost effective, large diameter sheaves will result in a narrower drive. Therefore, to minimize the sheave face width, select the largest diameter drive from the group of drives being considered. However, if there are space restrictions and larger diameter sheaves cannot be used, consider using a smaller diameter drive from the group of drives being considered. If the driver is an electric motor, the smallest sheave must be at least as large as the Minimum Recommended Sheave O.D. specified in Table 38 on Page 87. Component Life: As sheave diameters are increased, the required drive tensions and shaft pulls are decreased. By lowering the forces on the bearings, belts and sheaves, component wear is reduced and component service life is extended. NOTE: On some lightly-loaded drives, the cost of the larger sheave (to obtain belt speed between 4,000 and 6,000 feet per minute) may result in a less economical drive. For high horsepower drives, it is usually best to check several designs for economics before making a final choice. D. If the drive requires an idler, refer to Table 43 on Page 96 for recommended idler diameters. 85

2 Polyflex JB and Micro-V Belt Drive Selection Procedures How to Design Polyflex JB and Micro-V Belt Drives Continued Step 4 Determine the Belt Length Designation and Actual Center Distance A. For a two-sheave drive, calculate the belt effective length from Formula 9. If your drive requires an idler, determine the belt effective length from Engineering Section VII. Design of Drives With Idlers on Page 97. Formula 9 Belt Effective Length (in) = 2CD (D + d) + (D d)2 4CD Where: d = Small sheave outside diameter, inches D = Large sheave outside diameter, inches CD = Desired center distance, inches. Compare the calculated belt effective length from Formula 9 to the standard belt effective lengths given in Table 25 or Table 31 on Pages 82 or 84. Find the closest standard belt effective length in Table 25 or Table 31 and calculate the actual center distance using Formula 10 below. B. The approximate nominal center distance for the drive can be calculated using the following formula: Formula 10 Center Distance = K + K2 32 (D d) 2 K = 4EL 6.28 (D + d) 16 Where: d = Small sheave outside diameter, inches D = Large sheave outside diameter, inches EL = Belt effective length, inches Step 5 Calculate the Number of Strands/Ribs Required A. From the tables on Page 88, 89, or 90 find the basic horsepower rating based on the small sheave diameter and rpm of the faster shaft. Add the additional horsepower per strand or rib for speed ratio from the right of the table to find the rated horsepower per strand or rib. Interpolate if necessary. B. From Table 34, find the Arc of Contact Correction Factor (G) based on the quantity (D - d)/c. (D and d are large and small sheave outside diameters and C is the actual center distance. All values are in inches.) C. Based on the belt length and cross section that you selected, determine the Belt Length Correction Factor from Table 35 or Table 36 on this page. D. From Steps B and C, multiply the Arc of Contact Correction Factor (G) and the Belt Length Correction Factor (K L ) to get the Horsepower Correction Factor. E. Multiply the rated horsepower per strand or rib by the Horsepower Correction Factor to obtain the Horsepower Per Strand or Rib. F. Divide the design horsepower from Step 1 by the horsepower per strand or rib to find the number of strands or ribs required. The answer may be a fraction, so always round to the next larger whole number. 3M Belt Length 3M Belt Length Designation Correction Factor Belt Length Length Correction Designation Factor Table 34 Arc of Contact Correction D-d c Factor Arc of Contact On Small Sheave (degrees) Table 35 Polyflex JB Length Correction Factors (K L ) 3M Belt Length 3M Belt Length Designation Correction Factor Table 36 Micro-V Length Correction Factors (K L ) Belt Length Length Correction Designation Factor Arc Correction Factor (G) Polyflex JB Micro-V 5M Belt Length 5M Belt Length 5M Belt Length 5M Belt Length Designation Correction Factor Designation Correction Factor Belt Length Length Correction Designation Factor

3 Polyflex JB and Micro-V Belt Drive Selection Procedures How to Design Polyflex JB and Micro-V Belt Drives Continued Step 6 Determine the Minimum Installation and Takeup Allowances A. Find the recommended installation and takeup allowance in Engineering, Section V. Installation and Takeup Table 41 or Table 42 on Page 95. B. For optimum belt performance, the drive must have sufficient belt installation and takeup allowance. Tables 41 and 42 on Page 95 show the required center distance movement to provide proper installation and takeup. However, if you have a fixed center drive, it also must have provisions for belt length adjustment. Use of idlers is the most common method to provide belt length adjustment with fixed center drives. See Engineering Section VI: Idler Usage on Page 95 and Section VII. Design of Drives With Idlers on Page 97. DriveN Machine The machines listed below are representative samples only. Select the group listed below whose load characteristics most closely approximate those of the machine being considered. Agitators for Liquids Blowers and Exhausters Centrifugal Pumps & Compressors Display Equipment Dispensing Equipment Fans up to 10 Horsepower Instrumentation Light Duty conveyors Office Equipment Belt conveyors for Sand, Grain, Etc. Dough Mixers Fans - Over 10 Horsepower Generators Line Shafts Laundry Machinery Machine Tools Punches - Presses - Shears Printing Machinery Positive Displacement Rotary Pumps Brick Machinery Bucket Elevators Exciters Piston Compressors Conveyors (Drag-Pan-Screw) Piston Pumps Positive Displacement Blowers Textile Machinery Hoists Rubber Calendars - Extruders Mills Table 37 Gates Polyflex JB and Micro-V Service Factors DriveR AC Motors: Normal Torque, Squirrel Cage, Synchronous Split Phase DC Motors: Shunt Wound Engines: Multiple Cylinder Internal Combustion Intermittent Continuous Service Normal Service Service 3-5 Hours Daily 8-10 Hours Hours or Seasonal Daily Daily AC Motors: High Torque, High Slip, Repulsion-Induction, Single Phase, Series Wound, Slip Ring DC Motors: Series Wound, Compound Wound Engines: Single Cylinder Internal Combustion Line Shafts Clutches Intermittent Continuous Service Normal Service Service 3-5 Hours Daily 8-10 Hours Hours or Seasonal Daily Daily Motor rpm (60 Cycle and 50 Cycle Electric Motors) Motor Horsepower 485* 575* 725* 950* 1425* 2850* 1/ / / *These speed values are for 50 Cycle electric motors. Table 38 Minimum Recommended Sheave Outside Diameters for General Purpose Electric Motors Motor rpm (60 Cycle and 50 Cycle Electric Motors) Motor Horsepower 485* 575* 725* 950* 1425* 2850* /

4 rpm of Faster Shaft Polyflex JB Power Ratings Polyflex JB and Micro-V Belt Drive Selection Procedures 3M Polyflex JB Power Ratings Basic Horsepower per Strand for Small Outside Diameter Additional Horsepower per Strand for Speed Ratio (in) to to to to to to to to to and (mm) over Basic Kilowatt per Belt for Small Sheave Outside Diameter Additional Kilowatt per Belt for Speed Ratio

5 Polyflex JB and Micro-V Belt Drive Selection Procedures Polyflex JB Power Ratings rpm of Faster Shaft 5M Polyflex JB Power Ratings Basic Horsepower per Strand for Small Outside Diameter Additional Horsepower per Strand for Speed Ratio (in) to to to to to to to to to and mm over Basic Kilowatt per Strand for Small Outside Diameter Additional Kilowatt per Strand for Speed Ratio

6 Micro-V Power Ratings rpm of Faster Shaft Polyflex JB and Micro-V Belt Drive Selection Procedures J Section Micro-V Power Ratings Basic Horsepower per Rib for Small Outside Diameter Additional Horsepower per Rib for Speed Ratio (in) to to to to to to to to to and mm over Basic Kilowatt per Rib for Small Outside Diameter Additional Kilowatt per Rib for Speed Ratio

TIMING PULLEYS & BELTS Timing Belts and Pulleys

TIMING PULLEYS & BELTS Timing Belts and Pulleys Timing Belts and Pulleys Z e d o1 F U1 v n1 d k1 z 1 a = Centre distance (mm) M B = Acceleration torque (Nm) t B = Acceleration time (s) d = Bore (mm) r = Density (kg/dm 3 ) M = Torque (Nm) n = RPM d k