PowerGrip ® GT ® , HTD ® and Timing <strong>Belt</strong> Drive Selection Procedure Step 1. Determine design load. Service factors between 1.5 and 2.0 are generally recommended when designing small pitch synchronous drives. Knowledge of drive loading characteristics should influence the actual value selected. A higher service factor should be selected for applications with high peak loads, high operating speeds, unusually severe operating conditions, etc. Lower service factors can be used when the loading is smooth, well defined, etc. and the reliability is less critical. Some designs may require service factors outside the 1.5 to 2.0 range, depending upon the nature of the application. Contact Gates Application Engineering for additional information. Stall torque of the driveR, or peak torque of the driveN unit, may be part of the nameplate data. If not, calculate Torque (Q) by using these formulas: Q (lb - in) = 63,025 times Shaft HP , Shaft RPM Q (lb - in) = 8.85 times Q (N - m) or Q (oz - in) = 16 times Q (lb - in) Peak Design Load = Load x Service Factor NOTE: When performing drive calculations based upon torque loads, drive input/output power is constant but drive input/output torque is not. Drive input/output torque is a function of the speed ratio. Drive designs should be based upon the smaller faster sprocket, at the torque load calculated for its operating speed. These critical drive parameters should be used for all engineering calculations. See engineering calculations on Page 88 for additional formulas and unit conversions. Step 2. Determine belt pitch and select sprockets. A. Select <strong>Belt</strong> Pitch by using the <strong>Belt</strong> Pitch Selection Guide on pages 17, 31 and 39. B. Determine the speed ratio by dividing the larger speed, Sprocket Pitch Diameter or Sprocket Groove Number by the lesser speed, Sprocket Pitch Diameter or Sprocket Groove Number. C. Refer to the appropriate Sprocket Diameter Tables on pages 22-24, pages 34-35 or page 41. Select sprockets based upon speed ratio and drive requirements. Use stock sprocket sizes, whenever possible. D. Check the <strong>Belt</strong> Speed, V, of the smaller sprocket selected, using the following formula: V (fpm) = 0.262 x Sprocket PD (in) x Sprocket RPM V (m/s) = 0.0000524 x Sprocket PD (mm) x Sprocket RPM and, m/s = 0.00508 x fpm NOTE: <strong>Belt</strong> speeds in excess of 6,500 fpm (33.02 m/s) require special sprocket materials and dynamic balancing. Step 3. Determine belt length and nominal center distance. A. Using the allowable range of center distances required by the drive design, calculate the belt Pitch Length (PL) using the following formula: (PD - pd)2 PL = 2CD + [1.57 x (PD + pd)] + over 4CD Where CD = Drive center distance (in) PD = Large pitch diameter (in) pd = Small pitch diameter (in) Using the calculated range of pitch lengths, select a belt of the proper length from the appropriate belt length table. Use a standard length as shown in the tables on pages 14-15, pages 29-30 or pages 37-38, if possible. B. The approximate nominal center distance for the drive can be calculated using the following formula: Center distance = K + K 2 - 32 (PD - pd) 2 16 K = 4PL - 6.28 (PD + pd) Where PD = Large pitch diameter (in) pd = Small pitch diameter (in) PL = <strong>Belt</strong> pitch length (in) If a more exact value is required (within 0.01"), use the Center Distance Calculation Table on page 91. See Engineering calculations on page 88 or contact Gates Application Engineering for accuracy within 0.001". Step 4. Determine belt width. <strong>Belt</strong> Width Selection Tables on pages 18-21, pages 32-33 and page 40 show the load ratings for the stock widths of each of the stock belt pitches. Using the smaller sprocket groove number and rpm as determined in Step 2, locate a torque or horsepower rating in the <strong>Belt</strong> Width Selection Tables of the proper belt pitch nearest to, but greater than, the peak design load from Step 1. Torque or horsepower ratings for various belt widths can be calculated by multiplying the table rating by the appropriate belt width multiplier. When designing with PowerGrip GT or HTD, use the belt length from Step 3 to find the proper belt length factor in the Length Factor Tables included with each <strong>Belt</strong> Width Selection table. Multiply the torque rating selected above by the belt length factor to obtain the corrected rating. For all designs, the torque or horsepower rating must be equal to, or greater than, the peak design load of Step 1. NOTE: The torque or horsepower ratings are based on 6 or more teeth in mesh for the smaller sprocket. Calculate the teeth in mesh for the selected drive design using the Teeth In Mesh Formula on Page 89. If the teeth in mesh is less than 6, the drive must be de-rated as indicated, which may require redesign for additional drive capacity. Step 5. Determine proper belt installation tension. Procedures to calculate proper belt installation tension for specific applications are included on Page 49. Step 6. Check and specify drive components. After the drive system components have been selected and checked against drive system requirements, contact Gates Application Engineering before going into production. 16 The World’s Most Trusted Name in <strong>Belt</strong>s, Hose & Hydraulics.
PowerGrip ® GT ® <strong>Belt</strong> <strong>Drives</strong> <strong>Belt</strong> Pitch Selection Guide The World’s Most Trusted Name in <strong>Belt</strong>s, Hose & Hydraulics. 17
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