Prof. H. D. Mhatre BELT DRIVE Prof. H. D. Mhatre Prof. H. D. Mhatre

Content Belt Drive Types of Belt Drives Advantages and Disadvantages Application Selection Method from Manufacturing Catalogue Prof. H. D. Mhatre

BELT DRIVE A Belt is a looped strip of flexible material, used to mechanically link two or more rotating shafts. In flexible drives, the rotary motion of driving shaft is first converted into translatory motion of belt and then converted into rotary motion of driven shaft. 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. Prof. H. D. Mhatre

TYPES OF BELT DRIVES Length of the belt is smaller Two pulley rotate in the same direction Length of the belt is smaller Angle of lap is different for driver and driven pulley Pulleys rotate in the opposite directions length of the belt is larger Angle of lap is same for driver and driven pulley Prof. H. D. Mhatre

Rope belt Drive Timing Belt Drive A rope drive is a form of belt drive, used for mechanical power transmission. Rope drive used in hydroelectric power plant A timing belt, is a part of an internal combustion engine that synchronizes the rotation of the Crankshaft and the Camshaft. Prof. H. D. Mhatre

V belt Drive V belts are popularly used where an electric motor is used as the prime mover to drive compressor, pump , fans. Etc  Belts are anti-static, oil and heat resistant and can be used in applications where belt linear speeds do not exceed 30 meters/sec.  Prof. H. D. Mhatre

ADVANTAGES OF BELT DRIVE- Belt drives are simple are economical. They don’t need parallel shafts. Belts drives are provided with overload and jam protection. Noise and vibration are damped out. Machinery life is increased because load fluctuations are shock-absorbed. They are lubrication-free. They require less maintenance cost. Belt drives are highly efficient in use (up to 98%, usually 95%). They are very economical when the distance between shafts is very large. Prof. H. D. Mhatre

DISADVANTAGES OF BELT DRIVE- In Belt drives, angular velocity ratio is not necessarily constant or equal to the ratio of pulley diameters, because of slipping and stretching. Heat buildup occurs. Speed is limited to usually 35 meters per second. Power transmission is limited to 370 kilowatts. Operating temperatures are usually restricted to –35 to 85°C. Some adjustment of center distance or use of an idler pulley is necessary for wearing and stretching of belt drive compensation. Prof. H. D. Mhatre

A Planar Machine with Guide Pulleys APPLICATIONS Skiving Machine A Planar Machine with Guide Pulleys Prof. H. D. Mhatre

A Timing Belt in Lathe Machine A Guide Pulleys Belt Drive in Spindle Mould Machine A Flat Belt in Circular Saw Machine A Timing Belt in Lathe Machine Prof. H. D. Mhatre

Selection of a Belt Drive Following are the various important factors upon which the selection of a belt drive depends: Speed of the driving and driven shafts Speed reduction ratio Power to be transmitted Centre distance between the shafts Positive drive requirements Shaft layout Space available Service conditions Prof. H. D. Mhatre

Selection of Flat belt from manufacturer catalogue: How much power to be transmitted What may be the power transmitting capacity From the given conditions like power, type of working conditions, diameters of pulleys, speed ratio etc, determine maximum power Then calculate the belt rating Find the required width by design power by belt capacity and adopt the standard available Determine the length of belt based on type of drive and reduce certain amount length Find out the pulley dimension and draw the arrangement of belt drive. Prof. H. D. Mhatre

Selection of v-belt from manufacturer catalogue: The data is available : a. power to be transmitted b. input and output speed Selection the service factor or load correction factor for the given application Select type of v-belt cross section Calculate the power Select the standard pulley Calculate pitch length of the belt Select nearest standard pitch length of the belt from manufacturer catalogue and calculate the exact centre distance Prof. H. D. Mhatre

Step I Diameter of smaller and bigger pulleys (Refer Fig.) Example. It is required to select a flat belt drive for a compressor running at 720 rpm, which is driven by a 25 kW, 1440 rpm motor. Space is available for a centre distance of 3 m. The belt is open-type. Solution Given kW = 25 n1 = 1440 rpm n2 = 720 rpm C = 3 m Step I Diameter of smaller and bigger pulleys (Refer Fig.) Prof. H. D. Mhatre

Using a belt velocity of 18 m/s, Selecting the preferred pulley diameter of 250 mm, d = 250 mm and D = 2 \ 250 = 500 mm The belt velocity for these dimensions is given by, Step II Maximum power for selection From Table 13.1, the load correction factor for the compressor is 1.3. Therefore, Maximum power = 1.3(25) = 32.5 kW Prof. H. D. Mhatre

Step III Arc of contact factor (Fd) From Eq. (13.1), Assuming linear interpolation, the arc of contact factor is given by, Step IV Corrected power Corrected power = 1.019(32.5) = 33.12 kW Step V Corrected power rating of belt Selecting a HI-SPEED belt, the corrected rating at a belt speed of 18.85 m/s is given by, Prof. H. D. Mhatre

Step VI Selection of belt We shall select a HI-SPEED belt of 152 mm preferred width and 5 plies. Prof. H. D. Mhatre

The belt length is given by Step VII Belt length The belt length is given by Belt Specification 7.2 m length of 152 mm width and 5 plies HI-SPEED belting. Prof. H. D. Mhatre

Prof. H. D. Mhatre

Difference between Flat Belt Drive & V-Belt Drive Flat belt has a rectangular cross section. V-belts are characterized by their trapezium shaped cross section. Two or more straps can be used on pulleys with multiple grooves. Simple design, inexpensive and require littlemaintenance. Construction of V-belt and V-groove pulleys is complicated and expensive compared to the flat belt. Precise alignments of shafts and pulleys are not as critical with flat belts. Require precise alignment for uniform tension across the section. Friction engagement at the outer pulley surface. Frictional engagement between lateral wedge surfaces of the belt. The Slip may occur. Slip is negligible due to wedging action between the belt and V-groove pulley. Compared to v-belts, flat belts require significantly greater pretension to transmit a particular torque. Require little pretension. Prof. H. D. Mhatre

Flat Belt Drive V-Belt Drive Flat belts can be used for long distances, up to 15 m. V-belt cannot use for long distance because weight per unit length of the belt is greater than that of the flat belt. It used where pulleys were very near to each other. V-belt provides compactness due to the small distance between the centers of the pulleys. Low-velocity ratio. High-velocity ratio. It can deliver power at high speeds. The centrifugal tension limits the speed of V-belt between 5m/s to 50m/s. Power transmission capacity is low. V-belt can transmit more power for the same coefficient of friction. Efficiency is higher than V-belt drive. Its efficiency is comparatively lower than the flat belt. It can be used in a filthy atmosphere. It cannot use in a nasty environment; it requires a casing. Not used in the vertical direction. V-belt can run even the belt is vertical. Prof. H. D. Mhatre

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