BELT DRIVE

BY• IMMANUEL

ALEXANDER(9203)

INTRODUCTION A belt is a looped strip of flexible

material, used to mechanically link two or more rotating shafts.

They may be used as a source of motion, to efficiently transmit power, or to track relative movement. Belts are looped over pulleys.

In a two pulley system, the belt can either drive the pulleys in the same direction, or the belt may be crossed, so that the direction of the shafts is opposite.

OVERVIEW WHY USED? Transfer power (torque) from one location to

another. From driver: motor,peddles, engine,windmill,turbine to driven: conveyor belt, back wheels/bike,generator rock crusher,dryer.

Used to span large distances or need flexible x-mission elements. Gear drives have a higher torque capability but not flexible or cheap.

Often used as torque increaser (speed reducer), max speed ratio: 3.5:1. Gear drives?? Virtually unlimited!

BELT DRIVE ARRANGEMENTS

Machines operated by belt drives must have an idler, an adjustable base, or both

Idler is use to help maintain constant tension on the belt

Slack side: top side of belt in horizontal arrangement

Tight side: bottom side of belt in horizontal arrangement

Inside idler pulley is placed near the driver on the slack side or on the tight side near the driven pulley

Idler pulley should be same diameter or larger than the driver

Outside idler pulley is placed near the driver on the outside of the belt on the slack side or on the tight side near the driven pulley

Idler pulley should be slightly larger than the driver pulley

TYPES FLAT BELT ROUND BELT VEE BELT MULTI-GROOVE BELT TIMING BELT

FLAT BELT DRIVE Flat belts for power transmission Flat belts: Advantages-Simple construction Low cost High

flexibility High tolerance to overload Good resistance in abrasive environments

Disadvantages-Noisy Sliding is possible Low efficiency at low speeds Tensioning is required

But these drives are bulky, requiring high tension leading to high loads, and are poorly suited to close-centers applications.

Flat belts were traditionally made of leather or fabric. Today some are made of rubber or polymers. Grip of leather belts is often better if they are assembled with the hair side (outer side) of the leather against the pulley

USES/ADVANTAGES where high-speed applications (up to

140,000 rpm) are more important than power transmission

long center distances are necessary where drives with non-parallel shafts are

required (belt can be twisted) applications requiring small pulley

diameters (as small as 3/8")

DISADVANTAGE tend to slip under load lower efficiency at moderate speeds must be kept under tension to function

(require tensioning devices); causes high bearing loads

require friction for proper functioning (therefore, cannot be used when absolute synchronization between pulleys must be maintained)

stretch over time

FLAT BELT

ROUND BELT DRIVE

Round belts are a circular cross section belt designed to run in a pulley with a 60 degree V-groove.

Round grooves are only suitable for idler pulleys that guide the belt, or when (soft) O-ring type belts are used.

 Early sewing machine utilized a leather belt, joined either by a metal staple or glued, to great effect.

ROUND BELTS

VEE BELT DRIVE They provide the best combination of traction,

speed of movement, load of the bearings, and long service life.

. The "V" shape of the belt tracks in a mating groove in the Pulley (or sheave), with the result that the belt cannot slip off. The belt also tends to wedge into the groove as the load increases—the greater the load, the greater the wedging action improving torque transmission and making the V-belt an effective solution, needing less width and tension than flat belts. V-belts trump flat belts with their small center distances and high reduction ratios.

USES/ADVANTAGES Useful in automotive, household, industrial, and

agricultural applications easy to install and replace low maintenance provide shock absorption between driver and driven

shafts best at speeds between 1500 to 6500 feet per minute

(with 4500 fpm peak capacity, or ideal speed) useful with temperature range of –30 F to 180 F are 90-98% efficient maximum satisfactory speed ratio is approximately 6:1

DISADVANTAGE improper belt tension can reduce service

life belt life at increased temperatures

(above 180 F) is significantly shorted require friction for proper functioning

VEE BELT

MULTI GROOVE BELT DRIVE

A multi-groove or polygroove belt is made up of usually 5 or 6 "V" shapes alongside each other.

This gives a thinner belt for the same drive surface

offers an improved efficiency, as less energy is wasted in the internal friction of continually bending the belt.

this gain of efficiency causes a reduced heating effect on the belt and a cooler-running belt lasts longer in service.

MULTIGROOVE BELT

TIMING BELT DRIVE

Timing belt are a positive transfer belt and can track relative movement.

These belts have teeth that fit into a matching toothed pulley. When correctly tensioned, they have no slippage, run at constant speed, and are often used to transfer direct motion for indexing or timing purposes.

Timing belts need the least tension of all belts, and are among the most efficient.  

USES/ADVANTAGES useful in operations requiring high

efficiency, timing or constant velocity no slippage (more positive power

transmission) will not stretch required belt tension is very low speed is transmitted uniformly

DISADVANTAGE shorter center distance required than flat

belts used on parallel shafts only cost

TIMMING

BELT

ADVANTAGES OF BELT DRIVE They are simple. They are economical. Parallel shafts are not required. Overload and jam protection are provided. Noise and vibration are damped out. Machinery

life is prolonged because load fluctuations are cushioned (shock-absorbed).

They are lubrication-free. They require only low maintenance.

They are highly efficient (90–98%, usually 95%). Some misalignment is tolerable.

They are very economical when shafts are separated by large distances.

Up to 95% efficient Designed to slip when an overload occurs Resist abrasion Require no lubrication (no metal to metal

contact) Smooth running Quiet Can transmit motion and power over long

distances

Operate effectively at high speeds Flexible shaft center distances Inexpensive (when compared to other

drive systems such as chain or gear drives)

Easy to assemble and install Have flexible tolerances Absorb shock well Easy and inexpensive to maintain

DISADVANTAGES OF BELT DRIVE The angular-velocity ratio is not necessarily

constant or equal to the ratio of pulley diameters, because of belt slip and stretch.

Heat buildup occurs. Speed is limited to usually 7000 feet per minute (35 meters per second). Power transmission is limited to 370 kilowatts (500 horsepower).

Operating temperatures are usually restricted to –31 to 185°F (–35 to 85°C).

Some adjustment of center distance or use of an idler pulley is necessary for wear and stretch compensation.

A means of disassembly must be provided to install endless belts.