1. Belt and chain drive Prepared by, ME 1 Batch D

2. INTRODUCTION INTRODUCTION 1.A belt is a looped strip of flexible material, used to mechanically link two or more rotating shafts. 2.They may be used as a source of motion, to efficiently transmit power, or to track relative movement. Belts are looped over pulleys. 3.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.

3. 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.

4. The angular-velocity ratio is not necessarily constant or equal to the ratio of pulley diameters, because of belt slip and stretch. 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). 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). 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. 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. A means of disassembly must be provided to install endless belts. Disadvantages of belt drive

5. FLAT BELT TYPES OF BELTS:

6. VEE BELT

7. TIMING BELT

8. ROUND BELT

9. Open belt drive

10. Cross belt drive.

11. OPEN BELT DRIVE WITH IDLER PULLEY:

12. MULTIPLE BELT DRIVE:

13. QUARTER TURN BELT DRIVE:

14. COMPOUND BELT DRIVE:

15. STEPPED OR CONE PULLEY DRIVE:

16. FAST AND LOOSE PULLEY DRIVE:

17. Desirable properties of materials used for belt High coefficient of friction High flexibility Durability High strength

18. Materials Leather Fabric Rubber Polyster or polyamide Balata

20. Velocity ratio of belt it is the ratio between the velocities of the driver and the follower or driven. d1 = Diameter of the driver, d2 = Diameter of the follower N1 = Speed of the driver in r.p.m., and N2 = Speed of the follower in r.p.m.

21. Length of the belt that passes over the driver and the follower in one minute will be l 1 = πd 1 N 1 and l 2 = π d 2 n 2, respectively. Since, the lengths are equal πd 1 N 1 = π d 2 N 2 Where, N 2 /N 1 is the velocity ratio. If we take the thickness of belt into account then above expression can be written as N 2 / N 1 = d 1 + t / d 2 + t

22. Velocity of belt drive considring slip the motion of belts and shafts assuming a firm frictional grip between thebelts and the shafts. But sometimes, the frictional grip becomes insufficient. This may cause some forward motion of the driver without carrying the belt with it. This may also cause some forward motion of the belt without carrying the driven pulley with it. This is called slip of the belt and is generally expressed as a percentage. The result of the belt slipping is to reduce the velocity ratio of the system. As the slipping of the belt is a common phenomenon, thus the belt should never be used where a definite velocity ratio is of importance (as in the case of hour, minute and second arms in a watch). Let s1 % = Slip between the driver and the belt, and s2 % = Slip between the belt and the follower. If thickness of belt is considred N2/N1= d1+t/d2+t(1-s/100)

23. GEOMETRICAL RELATIONSHIPS FOR BELT DRIVES Flat belts are used in open and crossed configurations. The figures below show the geometry of open flat belt and crossed flat belt drives. The open belt drive is used with shafts arranged parallel and rotating in the same direction. The driver pulls the belt from one side and delivers it to the other side. Thus the tension in the upper side will be more and on the lower side will be less. The crossed belt drive is used with shafts arranged parallel and rotating in the opposite direction. The driver pulls the belt from one side and delivers it to the other side. Thus the tension in the upper side will be less and on the lower side will be more.

24. LENGTH OF AN OPEN BELT DRIVE Let r 1 and r 2 = Radii of the larger and smaller pulleys, x= Distance between the centres of two pulleys (i.e. O 1 O 2 ), and L= Total length of the belt. Let the belt leaves the larger pulley at E and G and the smaller pulley at F and H as shown in figure. Through O 2 draw O 2 M parallel to FE. From the geometry of the figure, we find that O 2 M will be perpendicular to O 1 E. Let the angle MO 2 O 1 = α radians.

25. Let the belt leaves the larger pulley at E and G and the smaller pulley at F and H as shown in Fig. 18.13. Through O2 draw O2M parallel to FE. From the geometry of the figure, we find that O2M will be perpendicular to O1E. Let the angle MO2O1 = α radians. We know that the length of the belt, L = Arc GJE + EF + Arc FKH + HG= 2 (Arc JE + EF + Arc FK) From the geometry of the figure, we also find that sin α = O1M/O1O2 = O1E – EM / O1O2 = r1 – r2 / x Since the angle α is very small, therefore putting sin α = α (in radians) = r1 – r2 / x …………………….(ii) ∴ Arc JE = r1 (π/2 + α) ………………………….(iii) Similarly, arc FK = r2 (π/2 – α) ……………………..(iv) and EF = MO2 = [(O1O2)^2 – (O1M)^2]^0.5 = [x^2 – (r1 – r2)^2]^0.5 = x [1 – {(r1-r2)/x}^2]^0.5 Expanding this equation by binomial theorem, we have EF = x [1 – {0.5 {(r1 – r2)/x} + … ] = x – (r1 – r2)^2/2x …………………..(v)

26. Substituting the values of arc JE from equation (iii), arc FK from equation (iv) and EF from equation (v) in equation (i), we get

27. LENGTH OF CROSSED BELT DRIVE Let r1 and r2 = Radii of the larger and smaller pulleys, x = Distance between the centres of two pulleys (i.e. O1O2 ), and L = Total length of the belt.

28. Let the belt leaves the larger pulley at E and G and the smaller pulley at F and H as shown in Fig. 1. Through O2 draw O2M parallel to FE. From the geometry of the figure, we find that O2M will be perpendicular to O1E. Let the angle MO2O1 = α radians. We know that the length of the belt, L = Arc GJE + EF + Arc FKH + HG = 2 (Arc JE + FE + Arc FK) …………………(i) Fig. 1 Crossed belt drive From the geometry of the figure, we find that sin α = O1M/O1O2 = (O1E + EM)/O1O2 = r1+r2 / x Since the angle α is very small, therefore putting sin α = α (in radians) = r1+r2 / x ………………(ii).’. Arc JE = r1 (π/2 + α) …………………(iii) Similarly, arc FK = r2 (π/2 + α) …………………(iv) and EF = MO2 = [(O1O2 )^2 – (O1M)^2]^0.5 = [x^2 – (r1 + r2 )^2]^o.5 = x [1- (r1+r2 /x)^2]^0.5

29. Expanding this equation by binomial theorem, we have EF = x [1- 1/2(r1+r2 /x)^2 + …] = x [(r1+r2)^2/2x] ……………………(v) Substituting the values of arc JE from equation (iii), arc FK from equation (iv) and EF from equation (v) in equation (i), we get, L = 2 [r1(π/2 +α) + x – {(r1+r2)^2/2x} + r2(π/2 +α)] = 2 [{r1 × π/2} + {r1×α} + x – {(r1+r2)^2/2x} + {r2 × π/2} + {r1×α}] = 2 [π/2(r1+r2) + α(r1+r2) +x – {(r1+r2)^2/2x}] = π(r1+r2) + 2α(r1+r2) +2x – {(r1+r2)^2/x} Substituting the value of α = (r1+r2)/x from equation (ii), we get L = π(r1+r2) + 2{(r1+r2)/x}{(r1+r2)} +2x – {(r1+r2)^2/x} = π(r1+r2) + 2{(r1+r2)^2/x} + 2x – {(r1+r2)^2/x} = π(r1+r2) + 2x + {(r1+r2)^2/x} ……………….. (in terms of pulley radii) = π(r1+r2) + 2x + {(r1+r2)^2/x} ……………….. (in terms of pulley diameters) It may be noted that the above expression is a function of (r1 + r2). It is thus obvious, that if sum of the radii of the two pulleys be constant, length of the belt required will also remain constant, provided the distance between centres of the pulleys remain unchanged.

30. In a flat belt pulley, the rim surface is given a convex shape by increasing the thickness of a rim at the center. This increased thickness is called crown and the process is known as crowning of pulley. OBJECTIVES OF CROWNING OF PULLEY i)In flat belt drive, if the two shaft are not exactly parallel, there is tendency of belt to come off from the pulley in running condition. The crowning prevents the coming off of the belt from the pulley. ii)The crowning helps to keep the belt near the mid plane of the pulley in running conditions. CROWNING OF PULLEY

31. Power Transmitted by Belt drive Power transmitted by the belt is given by,

32. To calculate the limiting values T and [T] can be equated. Therefore, for maximum transmission of power, centrifugal tension in the belt should be 1/3 rd of the maximum permissible tension in the belt or velocity of the belt should be

33. STREESES IN BELT OTHER STRESSES ARE DIRECT STRESS AND BENDING STRESS

34. The angle of contact The wedge angle of the belt (and groove). Because you will be selecting a standard belt you are not able to change this angle which is usually 34° or 38° depending upon the size of the belt and the size of the pulleys. The coefficient of friction. You have little control over this because it is determined by the belt material and the pulley material (and finish). The pulley diameters. The larger the diameters, the greater the torque and power. This is simply because for a given belt tension force, the larger the pulley, the larger the torque (torque = force x radius) and hence the greater the power for a given speed. Initial belt tensions. The higher the initial tension in the belts, the greater the torque and power that can be transmitted. At rest, when no power is being transmitted, the belt tensions are equal on both sides of the pulleys. SELECTION OF FLAT BELTS FROM MANUFACTURING CATALOUGE

35. The size of the belt. The larger the belt section, the greater the tension that can be carried by the belt and the greater the torque and power. The number of belts. Belt drives with a single belt are the most common but belt drives are often used with 2 to 6 belts in parallel on multi-grooved pulleys.

36. Selection of v-belt from manufacturer catalogue 1.The data is available :- a.power to be transmitted b.Input and output speed 2. Select the service factor or load correction factor for the given application 3.Select type of v-belt cross section 4. calculate the design power 5. select the standard pulley 6. calculate pitch length of the belt 7.Select nearest standard pitch length of the belt from manufacturer catalogue and calculate the exact centre distance

37. Selection of v-belt from manufacturer catalogue 8. Find the power rating of the selected v- belt from manufacturer catalogue 9.Calculate arc of contact for the smaller pulley and find arc of contact correction factor 10.Find belt length correction factor 11.Calculate the modified power rating of the v-belt 12.Find the number of belt required

38. Creep In Belt When the belt moves over the pulleys to transmit the power, the tension Ft1 in the right side is more than the tension Ft2 in the slack side. As the belt material is elastic, it elongates more on the tight side than on the slack side, resulting in unequal stretching on two sides of the drive. Therefore the length of the belt received by the driving pulley is more than the length of the belt that moves off the driving pulley. On the other hand length of the belt received by the driven pulley is less than the length of the belt that moves off the driven pulley. Hence, the belt must creep forward slightly relative to the driven pulley rim.

39. Creep In Belt

40. This motion of the belt relative to drive and driven pulley due to unequal stretching of two sides of the drive is known as creep. The effect of creep back on the driving pulley is to slow down the speed of the belt with respect to driving pulley and the effect of creep forward on the driven pulley is to slow down the speed of the driven pulley with respect to the belt. It is important to note that, the creep which is due to the elastic property of the belt is totally different than the conventional slip, which is due to insufficient frictional grip between the belt and pulley.

41. Method of belt tensioning In order to transmit the power, the belt must be provided with the sufficient initial tension. The power transmitting capacity of the belt drive also depends upon the initial tension. Some of the method use to adjust the belt tensions are as follows:- 1.Manual adjustment 2.Pivoted overhung motor 3.Weighted idler pulley

42. Manual adjustment The position of motor and hence the initial tension can be adjusted manually with the help of the screw and nut adjustment.

43. Pivoted overhung motor The belt tension is due to the product of the weight of the motor and the moment arm.

44. Weighted Idler Pulley The idler pulley is held against the belt by its own weight and the adjustable weight. By changing the position of the adjustable weight, the required belt tension can be achieved.

45. Inroduction to chain drive Chain drive is a way of transmitting mechanical power from one place to another. It is often used to convey power to the wheels of a vehicle, particularly bicycles and motorcycles. It is also used in a wide variety of machines besides vehicles. Most often, the power is conveyed by a roller chain known as the drive chain or transmission chain, passing over a sprocket gear, with the teeth of the gear meshing with the holes in the links of the chain.

46. Advantages of chain drive As no slip takes place during chain drive, hence perfect velocity ratio is obtained. Since the chains are made of metal, therefore they occupy less space in width than a belt or rope drive. It may be used for both long as well as short distances. It gives a high transmission efficiency (upto 98 percent). It gives less load on the shafts. It has the ability to transmit motion to several shafts by one chain only. It transmits more power than belts. It permits high speed ratio of 8 to 10 in one step. It can be operated under adverse temperature and atmospheric conditions.

47. Limitations of chain drive The production cost of chains is relatively high. The chain drive needs accurate mounting and careful maintenance, particularly lubrication and slack adjustment. The chain drive has velocity fluctuations especially when unduly stretched.

48. Types of power transmission chain Roller chain – Large reduction ratio (usually up to 1:7) – Chains can be used with long shaft center distances (normally up to 4m). By changing the number of links it is possible to freely adjust the shaft center distance. – The chain can be used on both sides and drive multiple shafts at the same time. – Easy installation and replacement (easy to cut and connect chains). – If the distance between shafts is short, it can be used vertically. – The sprocket diameter of a chain drive could be smaller than a belt pulley while transmitting the same torque. – Transmitting power by meshing many teeth results in less wear of sprocket teeth than gears. – Chain drives have greater shock absorption than gear drives.

49. Roller chain drive

50. Inverted tooth drive chains – Inverted tooth drive chain are the optimal solution for requirements exceeding those met by other chains (e. g. roller chains). They allow for low- backlash drives with exact positioning. They are also highly effective, inured to vibration and have minimal noise emission.roller chains

51. Inverted tooth chain drive

52. Lubrication of chain It is very important for the effective and durable functioning of chains. The chains are lubricated by light or medium mineral oils like SAE30.SAE40,SAE50 Methods of lubrication 1.Manual 2.Drip 3.Oil bath 4.Oil stream

53. THANK YOU..