Belt Selection for Horsepower and Torque

DESIGN FACTORS

SERVICE FACTORS

The selection of a synchronous belt drive for any application should be based on the nature of the load and the type of driving unit. Service factors for different kinds of driven machines combined with different types of driving units are shown in Table 14. The driven machines are representative samples only. Select a driven machine whose load characteristics most closely approximate those of the machine being considered.

DESIGN HORSEPOWER OR TORQUE

Select a service factor from Table 14. Careful consideration should be given to the nature of the drive and the conditions under which it will operate.

These may call for extra capacity in the belt beyond the nominal horsepower or torque rating of the prime mover. Nominal or basic horsepower or torque ratings assume a steady nonpulsating prime mover driving a load which is not subject to shocks, overloads, sudden starts and stops, or reversal of direction, and which operates 8 to 10 hours per day. Any variation from these conditions has the effect of increasing the peak load which the belt is called upon to handle.

To compensate for such variation, the nominal horsepower or torque of the drive should be multiplied by the sum of the service factors. The resulting figure is the horsepower or design torque.

Table 14 Suggested Service Factors For Synchronous Belt Drives
TYPES OF DRIVEN MACHINES TYPES OF DRIVING UNITS
AC Motors: Normal Torque, Squirrel Cage, Synchronous & Split Phase. DC Motors: Shunt Wound, Multiple Cylinder Internal Combustion Engines. AC Motors: High Torque, High Slip, Repulsion - Induction, Single Phase Series Wound & Slip Ring. DC Motors: Series Wound & Compound Wound. Single Cylinder Internal Combustion Engines. Line Shafts. Clutches.
Service (3-5 Hours Daily or Seasonal) Normal Service (8-10 Hours Daily) Continuous Service (16-24 Hours Daily) Intermittant Service (3-5 Hours Daily or Seasonal) Normal Service (8-10 Hours Daily) Continuous Service (16-24 Hours Daily)
Display Equipment Dispensing Equipment Instrumentation Projection Equipment Measuring Devices Medical Equipment 1.0 1.2 1.4 1.2 1.4 1.6
Appliances, Sweepers, Sewing Machines Office Equipment Wood Lathes, Band Saws 1.2 1.4 1.6 1.4 1.6 1.8
Conveyors: Belt, Light Package, Oven, Screws, Drums, Conical 1.3 1.5 1.7 1.5 1.7 1.9
Agitators for Liquids Dough Mixers Drill Press, Lathes, Screw Machines, Jointers, Circular Saws, Planers Laundry Machinery Paper Machinery (except pulpers) Printing Machinery 1.4 1.6 1.8 1.6 1.8 2.0
Agitators for semi - liquids Brick Machinery (except Pug Mills) Conveyor Belt: ore coal, sand Line Shafts Machine Tools: Grinder, Shaper, Boring Mill, Milling Machines Pumps: centrifugal, gear, rotary pipeline Screens: vibrating cam type Textile: warpers, reels Compressor: centrifugal 1.5 1.7 1.9 1.7 1.9 2.1
Conveyor: apron, pan, bucket, elevator Extractors, Washers Fans, Blowers: centrifugal, induced draft exhausters Generators & Exciters Hoists, Elevators Rubber Calender, Mills, Extruders Saw Mill Machinery Textile Machinery: looms, spinning frames, twisters 1.6 1.8 2.0 1.8 2.0 2.2
Centrifuges Conveyors: flight, screw Hammer Mills Paper Pulpers 1.7 1.9 2.1 1.9 2.1 2.3
Brick & Clay Pug Mills Fans, Blowers, Propeller Mine Fans Positive Blowers 1.8 2.0 2.2 2.0 2.2 2.4