Chapter 2 BELTING SYSTEM

NAS, msy-rev1 01/07/2019 Conveying system 1-Rope 2-Chain 3-Belt

NAS, msy-rev1 01/07/2019 Belting

NAS, msy-rev1 01/07/2019 If not belt????

Timing belt vs Timing chain NAS, msy-rev1 01/07/2019 Timing belt vs Timing chain

NAS, msy-rev1 01/07/2019 Type of belts

Selection of Belt Drive NAS, msy-rev1 01/07/2019 Selection of Belt Drive Speed of the driving and driven shafts, Positive drive requirements, Speed reduction ratio, Shaft layout, Power to be transmitted, Centre distance between the shafts, Space available, Service conditions.

factors that affect the amount Of power transmitted: NAS, msy-rev1 01/07/2019 factors that affect the amount Of power transmitted: The velocity of the belt. The tension under which the belt is placed on the pulleys. The arc of contact between the belt and the smaller pulley. The conditions under which the belt is used.

NAS, msy-rev1 01/07/2019 Types of Belt Drives Open belt drive

Crossed or twisted belt drive NAS, msy-rev1 01/07/2019 Crossed or twisted belt drive

D – large pulley diameter d – small pulley diameter NAS, msy-rev1 01/07/2019 D – large pulley diameter d – small pulley diameter  - angle of contact C – center distance

NAS, msy-rev1 01/07/2019 Belt length Angle of contact, ANGLE IN RADIAN

D – large pulley diameter d – small pulley diameter NAS, msy-rev1 01/07/2019 D – large pulley diameter d – small pulley diameter  - angle of contact C – center distance

NAS, msy-rev1 01/07/2019 Belt length Angle of contact, ANGLE IN RADIAN

Velocity Ratio, Ratio of tensions and power transmission NAS, msy-rev1 01/07/2019 Velocity Ratio, Ratio of tensions and power transmission D1 = diameter of the driver D2 = diameter of the driven/follower N1 = speed of the driver in rpm and N2 = speed of the driven/follower in rpm and

Velocity of the belt on the driving pulley, NAS, msy-rev1 01/07/2019 Velocity of the belt on the driving pulley, Velocity of the belt on the driven or follower pulley when there is no slip, then V1 = V2,

Ratio of Tensions T1 = Tension in the belt on the tight side NAS, msy-rev1 01/07/2019 Ratio of Tensions T1 = Tension in the belt on the tight side T2 = Tension in the belt on the slack side  = coefficient of friction θ = wrap/contact angle (usually at smaller diameter pulley, θd)

NAS, msy-rev1 01/07/2019 Open belt Crossed

Power Transmitted P = (T1 –T2).v Note that, T1 >T2 NAS, msy-rev1 01/07/2019 Power Transmitted P = (T1 –T2).v Note that, T1 >T2

NAS, msy-rev1 01/07/2019 Example 1 A flat belt drive system consists of a two parallel pulleys of diameter 200 mm and 300 mm, which have a distance between centres of 500 mm. Given that the maximum belt tension is not to exceed 1.2 kN, the coefficient of friction between the belt and the pulley is 0.4 and the larger pulley rotates at 300 r.p.m. Find : angle of contact between the belt and each pulley, the length of the belt required, the power transmitted by the belt system.

Centrifugal Effect on belts NAS, msy-rev1 01/07/2019 Centrifugal Effect on belts Centrifugal Tension, Tc is given by Total tension at the tight side, Total tension at the slack side,

NAS, msy-rev1 01/07/2019 Strength of belt Maximum tension in the belt is equal to the total tension in the tight side(Tt= Tmax) of the belt Velocity of belt for maximum power,

NAS, msy-rev1 01/07/2019 Torque on THE shafts Shaft

NAS, msy-rev1 01/07/2019 For big pulley, For small pulley, T2 T2 T1 T1

efficiency Efficiency is given by Power input, Power Output, NAS, msy-rev1 01/07/2019 efficiency Efficiency is given by Power input, Power Output,

NAS, msy-rev1 01/07/2019 EXAMPLE 2 An open belt drive connects two pulleys 1.2 m and 0.6 m diameter on parallel shafts 3.6 m apart. The belt has a mass of 1 kg/m length and the maximum tension in it is not to exceed 2 kN. The 1.2 m pulley, which is the driver, runs at 250 r.p.m. Due to the slip on one of the pulleys, the velocity of the driven shaft is only 450 r.p.m. If the coefficient of friction between the belt and the pulley is 0.3, find Torque on each of the two shafts Power transmitted Power lost in friction, and Efficiency of the drive