Basic Belt Drive Design

Size Shaft Size Belt Drive Basics Motor Nameplate Rated HP Speed Efficiency Center Distance (center shaft to center shaft) Take-up/Installation Allowance Size DRIVER (R)DRIVEN (N)

Belt Drive Basics R N R N Speed-Up Speed-Down10” 1750 rpm 10” 4” 4” 1750/2.5 = 700 rpm 1750 x 2.5 = 4375 rpm NOTE: Ratio is always specified as a number greater than 1 Speed Ratio = 2.5

Belt Drive Terms Pitch Length -Total length in mm as measured along the pitch line Tooth Pitch-Distance in mm between two adjacent tooth centers as measured along pitch line of belt Pitch line-Section of belt between teeth and backing Pitch Diameter-Imaginary line on sprocket just above the teeth, where pitch line of belt rides Bore-Size of hole in bushing Bushing-Sprockets come with pilot holes, bushings connect sprocket to shaft through pilot hole. Minimum Plain Bore-No bushing needed, bored to size, or bore yourself Bushing styles-TaperLock, narrow like roller chain, QD has shoulder

Effect of Variable Drive Loading Mathematics and Testing Confirm That -- l Belt Drives Exert Belt Pull Equivalent to Belt Installation Tension --- Continuously l Roller Chain Drives Exert Belt Pull Proportional to Torque Loads --- Effective Pull l Belt Pull Remains Constant Under Variable Loads – Until Belt Lift Occurs

Drive Designed for Reduced Belt Pull l D rives Designed & Tensioned for Peak Loads Exert Peak Belt Pull Continuously l Apply Reduced Design Service Factor to Peak Load for Reduced Belt Pull l Drive Design Load Should Meet or Exceed Intermittent Peak Load -- At Least 1.0 Service Factor l Belt Pull From Reduced Design Loads Will Still Remain Constant

Drive Design Example CA S H enter distance pplication data peed / size / ratio orsepower rpm 2.5 : 1 28 in. Fan, 24 hr/day

Drive Design Steps l Determine service factor, design HP l Estimate pitch required / select belt type l Find ratio(s) in table l Select appropriate combo (c.d., belt length.) l Select width (check HP ratings, apply factors) l Check dimensional restrictions l Re-iterate if necessary

We see, For a 10 HP motor, running a fan 24 hours a day, SERVICE FACTOR = 1.7 Thus the DESIGN HORSEPOWER = 10 x 1.7 = 17 H.P.

Drive Design Steps l Determine service factor, design HP l Estimate pitch required / select belt type l Find ratio(s) in table l Select appropriate combo (c.d., belt lgth.) l Select width (check HP ratings, apply factors) l Check dimensional restrictions l Re-iterate if necessary

We see, For a DESIGN HORSEPOWER HP running a fan at 1750 RPM, the Belt Pitch falls in the 8mm region. So we select a 8mm pitch Belt.

Drive Design Steps l Determine service factor, design HP l Estimate pitch required / select belt type l Find ratio(s) in table l Select appropriate combo (c.d., belt lgth.) l Select width (check HP ratings, apply factors) l Check dimensional restrictions l Re-iterate if necessary

R = 8M ?? N = 8M ?? Belt = 8M ??

Drive Design Steps l Determine service factor, design HP l Estimate pitch required / select belt type l Find ratio(s) in table l Select appropriate combo (c.d., belt length.) l Select width (check HP ratings, apply factors) l Check dimensional restrictions l Re-iterate if necessary

= 15.98

15.98 x 1.26 = 20.1 HP 8M - 56S - 12 driveR 8M - 140S - 12 driveN 8M Belt