|
 WH78 |
| WR82 |
| WHX124 |
| WHX132 |
| WHX150 |
| WHX155 |
| WHX157 |
| WHX159 |
| SS-2184 |
| SS-800 |
| 81X,81XH |
| M315 |
| M450 |
| M630 |
| M900 |
| 9835M |
| 110M |
| 111M |
| 150M |
| 5907D |
|
 |
| BACK |
|
|
BELT AND CHAIN DRIVES |
|
Belt and chain drives are used to transmit powerfrom one rotational drive to another. A belt is aflexible power transmission element that runstightly on a set of pulleys. A chain drive consistsof a series of pin-connected links that run on aset of sprockets. The aims of this chapter are tointroduce various types of belt and chain drivesand to develop selection procedures for wedgeand fiat belts and for roller chains.
LEARNING OBJECTIVESAt the end of this chapter you should:
be able to differentiate whether to use a chain,belt or gear drive for a given application; 9 be able to select a particular wedge belt for agiven speed and power requirement; be able to determine the width of fiat belt fora given speed and power requirement; be able to determine an appropriate chainratio using standard components; be able to select an appropriate chain typeand pitch for a given application; be able to specify an appropriate chain drivefor a given speed and power requirement.
IntroductionBelt and chain drives consist of flexible element srunning on either pulleys or sprockets as illustratedin Figure 8.1.The purpose of a belt or chain driveis to transmit power from one rotating shaft toanother.
A belt drive transmits power between shafts byusing a belt to connect pulleys on the shafts bymeans of frictional contact or mechanical interference.
A chain consists of a series of links connectedby pins. The chain is designed to mesh with correspondingteeth on sprockets located on boththe driving and the driven shafts.
Power transmission between shafts can beachieved by a variety of means including belt, chainand gear drives and their use should be comparedfor suitability and optimization for any given application.
In addition to power transmission, constantspeed ratio or synchronization of the angularposition of the driving and driven shaft may becritical to operation. This can be achieved bymeans of gears, chains or special toothed belts,called synchronous or timing belts.
Both belt and chain drives can transmit powerbetween shafts that are widely separated givingdesigners greater scope for control over machinelayout. In comparison to gears they do not requiresuch precision in the location of centre distances.
Both belt and chain drives are often cheaper thanthe equivalent gear drive. Belts and chains aregenerally complementary covering a range ofoperational requirements.
In general, belt drives are used when rotationalspeeds are of the order of 10 to 60 m/s. At lowerspeeds the tension in the belt becomes too highfor typical belt sections. At higher speeds centrifugalforces throw the belts off the pulleys reducingthe torque capacity and dynamic phenomenareduce the effectiveness and life of the belt drive.
Transmission Chain drives are typically used at lower speeds andconsequently higher torques than belts. Recallthat for a rotating machine torque is proportional topower/re. As the angular velocity reduces, fora given power, the torque increases.
Belt drives have numerous advantages overgear and chain drives including easy installation,low maintenance, high reliability, adaptability tonon-parallel drive and high transmission speeds.
The principle disadvantages of belt drives aretheir limited power transmission capacity andlimited speed ratio capability. Belt drives are lesscompact than either gear or chain drives and aresusceptible to changes in environmental conditions,such as contamination with lubricants. Inaddition, vibration and shock loading can damagebelts.
Chains are usually more compact than belt drivesfor a given speed ratio and power capacity. Chaindrives are generally more economical than theequivalent gear drive and are usually competitivewith belt drives. Chains are inherently stronger thanbelt drives due to the use of steels in their manufactureand can therefore support higher tensionand transmit greater power. The disadvantages ofchain drives are limited speed ratios and power transmission capability and also safety issues. Chaindrives can break and get thrown off the sprocketswith large forces and high speeds. Guards shouldbe provided for chain drives and some belt drives toprevent damage caused by a broken chain or beltand also to prevent careless access to the transmission chain drive.
|
|
|
