N2 Fitting Machining Theory V Belts

N2 FITTING & MACHINING THEORY MALUTI TVET COLLEGE LECTURER : MT MPHAGO Downloaded from hlayiso.com ITEMOHELENG CAMPUS

MODULE 11 V-BELT DRIVES LO : Describe the safety precautions to be observed when working on or near the V-belt drives, advantages and disadvantages of V-belts drives compared to chain or gear drives as well as naming most common V-belts and their uses. Downloaded from hlayiso.com ITEMOHELENG CAMPUS

SAFETY PRECAUTIONS TO BE OBSERVED WHEN WORKING ON OR NEAR V-BELT DRIVES • Never work on or near moving V-belt drive. Always switch off the drive source before approaching. • Make sure that all portions of any belt are totally covered by enclosed sturdy guards. • Never adjust a V-belt while it is in operation. • Select the right belt for the job required, section and length. • Where necessary make use of a tensioning pulley to achieve maximum contact angle. • Keep the belt clean and dry. Downloaded from hlayiso.com ITEMOHELENG CAMPUS

APPLICATION OF V-BELTS • V-belts are used to connect shafts that must be driven but are too far apart to use gears. • Torque and power are easily transferred from the driving pulley to the driven one without changing the direction of the rotation by connecting with a belt. • V-belt s are mostly used in motor industry and also to connect machines like lathes, milling and drilling machines to the electric motors that drives them. • Most industries are using multi-groove type belts for water pumps and alternators instead of a single V-belt type. Downloaded from hlayiso.com ITEMOHELENG CAMPUS

ADVANTAGES AND DISADVANTAGESOF V-BELTS OVER CHAIN AND GEAR DRIVES Advantages • V-belts drives run for long time without requiring any maintenance. • Gear drives works when two shafts are right next to each other. • Chain drives needs regular maintenance and lubrication . Disadvantage • Belts wear out and have to be replaced before they break. Downloaded from hlayiso.com ITEMOHELENG CAMPUS

IDENTIFY AND EXPLAIN THE BELT DRIVES TERMS Driver pulley • Is the pulley on the motor. • It transmit the torque to turn the driven pulley on the pump or other device via a belt. Driven pulley • Is the one the torque is transferred to via the belt. • Is mounted to the device to be driven. Idler pulley • It is often small in diameter than the other two. • It has no influence on the ratio of the driver and the driven pulleys. • Its main function is to take up the slack in the belt between the two pulleys. • It increases the angle of contact on the smaller pulley and prevent jumping and slippage. Pulley pitch diameter • Downloaded from hlayiso.com It is the effective diameter pulley that includes one thickness of the belt in flat belts . • In V-belts it is measured at the Centre, half way down the groove where the belt work the hardest. ITEMOHELENG CAMPUS

BELT DRIVE TERM • Average belt used today is single and has an angle of 40 degrees • It is available in standard lengths and in sections between A and E. • A is the narrowest belt and E is the widest Downloaded from hlayiso.com ITEMOHELENG CAMPUS

V-BELT SECTIONS • Modern V-belt is made is made up of a number of sections such as the outer layer which is usually synthetic rubber compound . • This rubber compound is hard wearing and has a high coefficient of friction to limit the slippage on the pulley. • The outer cover prevents the liquids from penetrating the belt. • In the upper half are a row of Kevlar cords that have high tensile strength to prevent the belt from stretching under tension. • The top section of the belt is under tension while the lower area is subject to compression forces. Five groups of belts: . . Downloaded from hlayiso.com ITEMOHELENG CAMPUS

THE DIFFERENCE BETWEEN A SINGLE AND MULTIPLE BELT DRIVE • In the drawings shown below , the multi V-belt is the drawing on the right. It is ultimate, latest belt to drive high KW transmission, from the driving pulley to the driven pulley. • A single V-belt drive is shown by the drawing on the left. Downloaded from hlayiso.com ITEMOHELENG CAMPUS

CHECKING V-BELT SIZES AND LENGHTS Measuring: • The first step is to measure the groove width to determine whether the belt is an “ A or B” etc. section belt. • Length is next to be measured using a metal tape measure. • Run the tape measure along the same route as the belt will run until you get back where you started, then add on one belt thickness and you have the required length to within a few mm. • Keep the arc of contact more than 180 degrees on both pulleys. Maintenance: • Must be done properly at regular intervals. • Stop the belt . Remove guards, clean and inspect for wear, cracks, blistering and signs of any other damage. • Guards must be cleaned and inspected for safety reasons to ensure free air flow or over heating does not take place. Downloaded from hlayiso.com ITEMOHELENG CAMPUS

• The belt must be replace before it breaks because broken belts can lead to expensive damages in engines and down time in production machines. • Apply belt dressing to improve belt traction on slight worn belts to extend their life span. Alignment • When alignment is out belt life will be reduced. • Belt alignment is illustrated in the below drawing using a straight edge. • Tension be right if it is too slack belt will jump or slip and if it too tight it will place overload on bearings. Downloaded from hlayiso.com ITEMOHELENG CAMPUS

INSTALLING V-BELT • When fitting the or replacing V-belt always slack off the bolts securing the motor. The motor has slots for bolts holding it down. • Move the motor towards the driven pulley to reduces the distance between the pulleys. • The new belt will fit easy without being forced or damaged. • Belt alignment is illustrated in the below drawing using a straight edge. • Tension be right if it is to slack belt will jump or slip and if it too tight it will place overload on bearings Downloaded from hlayiso.com ITEMOHELENG CAMPUS

SUMMARY • Safety precautions to be observed when working on or next to V-belt drives. • Application of V-belts. • Advantages and disadvantage of V- belts drives over chain and gear drives. • Identify and explain the belt drive terms. • Belt drive term. • V-belt sections. • The difference between a single and a multiple belt drive. • Checking V-belt sizes and lengths. • Installing V-belts. Downloaded from hlayiso.com ITEMOHELENG CAMPUS

ASSESSMENT Exercise 11.1 page 136 of the textbook supplied by the college. “N2 fitting & machining theory by D Meyer & AG Murdcoch.” 1 to 7. . PLEASE FEEL FREE TO CONTACT ME ON WHATTSHAP FOR ANY QUESTIONS THAT YOU MAY HAVE. Downloaded from hlayiso.com MY WHATTSHAP NUMBER IS 073 215 7689 ITEMOHELENG CAMPUS