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PART- III: Advanced Agricultural Machinery Design - CHAIN DRIVES.pptx

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PART- III: Advanced Agricultural Machinery Design - CHAIN DRIVES.pptx

A chain is a power transmission element made as a series of pin-connected links. The design provides for flexibility while enabling the chain to transmit large tensile forces.
Today chain drives play an important part in many agricultural machines such as hay balers, corn pickers, combines, cotton pickers, and beet harvesters.

Another benefit is that chain drives are capable of transmitting a large amount of power at slower speeds.

However, chain drives require better shaft alignment and more maintenance than V-belt drives.

Method of Lubrication: The American Chain Association recommends three different types of lubrication depending on the speed of operation and the power being transmitted.

A chain is a power transmission element made as a series of pin-connected links. The design provides for flexibility while enabling the chain to transmit large tensile forces.
Today chain drives play an important part in many agricultural machines such as hay balers, corn pickers, combines, cotton pickers, and beet harvesters.

Another benefit is that chain drives are capable of transmitting a large amount of power at slower speeds.

However, chain drives require better shaft alignment and more maintenance than V-belt drives.

Method of Lubrication: The American Chain Association recommends three different types of lubrication depending on the speed of operation and the power being transmitted.

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PART- III: Advanced Agricultural Machinery Design - CHAIN DRIVES.pptx

  1. 1. Adama, Ethiopia Biniam Zewdie G/Kidan * •Haramaya Institute of University P.O.Box:138; Dire Dawa, Ethiopia •Mobile: +251910408218/+25191582832 •E-mail: nzg2001nzg@gmail.com/zewdienico@gmail.com
  2. 2. CHAIN DRIVES A chain is a power transmission element made as a series of pin-connected links. The design provides for flexibility while enabling the chain to transmit large tensile forces.
  3. 3. CHAIN DRIVES • Today chain drives play an important part in many agricultural machines such as hay balers, corn pickers, combines, cotton pickers, and beet harvesters. • Another benefit is that chain drives are capable of transmitting a large amount of power at slower speeds. • However, chain drives require better shaft alignment and more maintenance than V-belt
  4. 4. Chain Drives Cont.…
  5. 5. Chain Drives Cont.…
  6. 6. • The maximum permissible speed decreases as the pitch is increased. • Multiple-width chains of short pitch can be used for extremely compact drives at high speeds. • Roller chains are precision-built and under favorable conditions may have efficiencies as high as 98% to 99%. Chain Drives Cont.…
  7. 7. Chain Drives Cont.… • Sprockets may be driven from either the inside or the outside of a roller chain. • Although oil-bath lubrication is recommended for high-speed drives, this system often is not practical on agricultural machines. • Standard-pitch roller chain is several times as expensive as steel detachable-link chain. • Double-pitch chains are suitable for slow and moderate speed drives
  8. 8. • Method of Lubrication: The American Chain Association recommends three different types of lubrication depending on the speed of operation and the power being transmitted. Chain Drives Cont.… Type A. Manual or drip lubrication: oil is applied copiously with a brush or a spout can, at least once every 8 hours of operation. Type B. Bath or disc lubrication: The chain cover provides a sump of oil into which the chain dips continuously. Type C. Oil stream lubrication: An oil pump delivers a continuous stream of oil on the lower part of the chain.
  9. 9. • Recommended Lubricant for Chain Drives
  10. 10. Design Consideration Of Chain Roller Chain Construction • Roller chains are assembled using link plates, pins and rollers and connecting them in an endless chain using a connecting link.
  11. 11. Design Consideration Of Chain Cont.… Roller Chain Components
  12. 12. Design Consideration Of Chain Cont.… • Chain sections are made up from two separate assemblies called the Roller Link and the Pin Link. • Note: Smaller pitch chains (1/4 and less) do not have rollers. Chain Size (Pitch) • Chains are sized according to their pitch. The center-to-center distances of the link pins determine pitch.
  13. 13. • The pitch of chain drive components is specified by a 2 digit number. • The first digit specifies the center –to center distance of the chain link pins in 1/8ths of an inch, the second number specifies the chain style. • #25 chain means: Design Consideration Of Chain Cont.… • Chain pitch = 2 x 1/8 or ¼” pitch • Chain style =5 = roller less chain. Roller Chain Pitch
  14. 14. Roller Links and Pin Links • Chains are made up using two types of link assemblies; Roller links (Inside links) and pin links (outside links). • Roller links and pin links are assembled in a continuous loop using a connecting link. Roller Links and Pin Links Design Consideration Of Chain Cont.…
  15. 15. Pin Links Design Consideration Of Chain Cont.…
  16. 16. Standard Chain Dimensions
  17. 17. Designing Chain Drives • Chain Pitch is determined by the forces torque and RPM acting on the shafts and sprockets. • Larger pitch chain and sprockets are needed to handle higher torques and higher RPM. Drive Ratios • Drive ratios greater than 10:1 should not be used. • In order to achieve higher ratios it is good practice to create multiple drives using two drives in series. Design of Chain Cont.…
  18. 18. • The sprocket pitch diameter is an imaginary circle through which the chain pin centers move around the sprocket. • The pitch diameter is the fundamental design geometry that determines the size shape and form of the sprocket teeth dimensions. Design Consideration Of Chain Cont.…
  19. 19. • Pitch of chain. It is the distance between the hinge center of a link and the corresponding hinge center of the adjacent link. • Pitch circle diameter of chain sprocket. It is the diameter of the circle on which the hinge centers of the chain lie, when the chain is wrapped round a sprocket.
  20. 20. Chain Length Calculation • Chain length is a function of the number of teeth of the drive and driven sprockets as well as the center-to- center distance. • Chain length is customarily expressed in (even numbers) of pitch units since chains can only be shortened or lengthened by multiples of their pitch units. • If an odd number of pitches is required then a special link called an offset link is used. The chain length for a given drive is determined by: • The number of teeth in the drive sprocket • The number of teeth in the driven sprocket • The pitch diameter (PD) of the drive sprocket • The pitch diameter (PD) of the driven sprocket
  21. 21. Calculate the pitch circle radius for the drive sprocket • Calculate the pitch circle radius for the driven sprocket.
  22. 22. 3. Calculate the length of side DF a. Line AF is parallel to line BE and perpendicular to AB and DE b. Line BE is tangent to circles K and M c. Line DF = DE-AB 4. Calculate angle a. a. Triangle AFD is a right triangle b. Use the math. find the sine of angle a. Design of Chain Cont.…
  23. 23. 5. Calculate the length of the chain between the pitch circle tangent points, BE. BE = AF = AD cosine a 6. Find the pitch lengths of chain wrapped around each of the sprockets. Note: Each tooth on the sprocket represents a pitch unit. Therefore, if we calculate the arc lengths of chain wrapped around the sprocket in terms of teeth, we will have the arc lengths in pitch units and it will be unnecessary to convert inches to pitch units. Design of Chain Cont.…
  24. 24. Design of Chain Cont.…
  25. 25. Design Parts Cont.…Procedure • Half the chain wrapped around the large sprocket is represented by arc ME. Measured in pitch units (teeth) we find; • Half the chain wrapped around the small sprocket is computed in a similar way, except, the arc length of angle a is subtracted from the 90 degree arc KG.
  26. 26. 7. Using the information from the 6 preceding steps, we can find the chain length (In pitch units) for these 2 sprockets. • Calculating Center Distance From a Known Chain Length. Design of Chain Cont.…
  27. 27. 8. Factor of Safety for Chain Drives The factor of safety for chain drives is defined as the ratio of the breaking strength (WB ) of the chain to the total load on the driving side of the chain ( W ). Mathematically, • Factor of safety = Breaking strength(WB)/load(W) The breaking strength of the chain may be obtained by the following empirical relations, i.e. WB = 106p2 (in newton's) for roller chains = 106p (in newton's) per mm width of chain for silent chains. Design of Chain Cont.…
  28. 28. 9. The Total Load (or Total Tension): on the driving side of the chain is the sum of the tangential driving force (FT), centrifugal tension in the chain (FC) and the tension in the chain due to sagging (FS). W = FT + FC + FS 10. Tangential driving force acting on the chain, 11. Centrifugal tension in the chain, Design of Chain Cont.…
  29. 29. 12. Tension in the chain due to sagging Where, • m = Mass of the chain in kg per meter length, • x = Centre distance in meters, and • k = Constant which takes into account the arrangement of chain drive • = 2 to 6, when the center line of the chain is inclined to the horizontal at an angle less than 40º • = 1 to 1.5, when the center line of the chain is inclined to the horizontal at an angle greater than 40º. Design of Chain Cont.…
  30. 30. 13. Power Transmitted by Chains The power transmitted by the chain on the basis of breaking load is given by where WB = Breaking load in newton's, v = Velocity of chain in m/s n = Factor of safety, and KS = Service factor = K1.K2.K3 Design of Chain Cont.…
  31. 31. • The power transmitted by the chain on the basis of bearing stress is given by where b = Allowable bearing stress in MPa or N/mm2, A = Projected bearing area in mm2, v = Velocity of chain in m/s, and KS = Service factor Design of Chain Cont.…
  32. 32. 14. linear velocity d = Pitch circle diameter of the smaller or driving sprocket in meter N = constant speed of r.p.m. Design of Chain Cont.…
  33. 33. Minimum Center Distance • The arc of the chain engagement on the smallest sprocket should not be less than 120 degrees. • For drive ratios greater than 3:1, the center distance of the sprockets should be equal to or greater than the difference of the 2 sprocket diameters. • This will ensure 120 degrees of chain wrap around the smaller sprocket. Maximum Center Distances • The American Chain Association suggests that center distances between sprockets should not exceed 80 Pitch Units ( For unsupported chain drives). • Excessively long center distances create catenary tensions that act to increase chain wear and result in unnecessary chain vibration. • Consider supporting the chain on guides or rollers where long
  34. 34. Outside Sprocket Diameters (OD) • In order to accurately calculate the clearances for a given chain and sprocket drive, it is necessary to determine the outside diameters of the sprockets. • This dimension can be approximated using the following formula: Do = D + 0.8 d1 • where d1 = Diameter of the chain roller. Design of Chain Cont.…
  35. 35. Advantage Disadvantage 9. No slippage between chain and sprocket teeth. 10. Long operating life expectancy because flexure and friction contact occur between hardened bearing surfaces separated by an oil film. 11. Operates in hostile environments such as high temperatures, high moisture or oily areas, dusty, dirty, and corrosive atmospheres, etc. 12. Long shelf life because metal chain ordinarily doesn’t deteriorate with age and is unaffected by sun, reasonable ranges of heat, moisture, and oil. 13. Certain types can be replaced without disturbing other components mounted on the same shafts as sprockets.
  36. 36. 6. Noise is usually higher than with belts or gears, but silent chain drives are relatively quiet. 7. Chain flexibility is limited to a single plane whereas some belt drives are not. 8. Usually limited to somewhat lower-speed applications compared to belts or gears.
  37. 37. PARTIV:
  38. 38. Gears & Gear Trains…… Discussion Map o Gears are toothed, cylindrical wheels used for transmitting motion and power from one rotating shaft to another. o Most gear drives cause a change in the speed of the output gear relative to the input gear. o Some of the most common types of gears are spur gears, helical gears, bevel gears, and worm/worm gear sets.
  39. 39. • Gears are toothed members which transmit power/motion between two shafts by meshing without any slip. Hence, gear drives are also called positive drives. • In any pair of gears, the smaller one is called pinion and the larger one is called gear immaterial of which is driving the other. • When pinion is the driver, it results in step down drive in which the output speed decreases and the torque increases. Gears & Gear Trains……
  40. 40. • On the other hand, when the gear is the driver, it results in step up drive in which the output speed increases and the torque decreases. Gears & Gear Trains……
  41. 41. • The fundamental law of gearing states that the angular velocity ratio between the gears of a gear set must remain constant throughout the mesh. • The law of gearing states that the common normal at the point of contact between a pair of teeth must always pass through the pitch point. Pitch point is the common point of contact between two pitch circles of the gears Gears & Gear Trains…… Law of Gearing
  42. 42. Gears & Gear Trains……
  43. 43. • Spur gears have teeth that are straight and arranged parallel to the axis of the shaft that carries the gear. • The curved shapes of the faces of the spur gear teeth have a special geometry called an involute curve. • This shape makes it possible for two gears to operate together with smooth, positive transmission of power. • The teeth of helical gears are arranged so that they lie at an angle with respect to the axis of the shaft. • The angle, called the helix angle, can be virtually any angle. Typical helix angles range from approximately 10° to 30°, but angles up to 45° are practical. Gears & Gear Trains……
  44. 44. Details of two meshing spur gears showing several important geometric features
  45. 45. • The helical teeth operate more smoothly than equivalent spur gear teeth, and stresses are lower. Therefore, a smaller helical gear can be designed for a given power transmitting capacity as compared with spur gears. • One disadvantage of helical gears is that an axial force, called a thrust force, is generated in addition to the driving force that acts tangent to the basic cylinder on which the teeth are arranged. • The designer must consider the thrust force when Gears & Gear Trains……
  46. 46. Cycle of engagement of gear teeth
  47. 47. Figure : Identities of the three primary planes for helical gears
  48. 48. Pitches for Helical Gears To obtain a clear picture of the geometry of helical gears, you must understand the following five different pitches. ➭ Transverse Circular Pitch pt = πD/N = π/Pd ➭ Normal Circular Pitch pn = pt cosψ ➭ Axial Pitch px = pt/tanψ = π(Pd/tanψ) = πm > tanψ ➭ Diametral Pitch Pd = N/D ➭ Normal Diametral Pitch Pnd = Pd/cosψ Gears & Gear Trains……
  49. 49. Figure : Identities of the three primary planes and associated angles shown on a helical rack
  50. 50. Figure shows details of spur gear teeth with the many terms used to denote specific parts of the teeth and their relationship with the pitch diameter. Gears & Gear Trains……
  51. 51. Terminology and spur gear formula • Number of Teeth, (N): It is essential that there are an integer number of teeth in any gear. This seminar uses the symbol N for the number of teeth, with NP for the pinion and NG for the gear. • Pitch: The pitch of a gear is the arc distance from a point on a tooth at the pitch circle to the corresponding point on the next adjacent tooth, measured along the pitch circle. • Pitch Circle and Pitch Diameter. When two gears are in mesh, they behave as if two smooth rollers are rolling on each other without slipping. ➭ Circular Pitch p = πD/N ➭ Diametral Pitch Pd = NP/DP = NG/DG
  52. 52. Pitch radii: RP = DP/2 and RG = DG/2 • Center distance: C = RP + RG = DP/2 + DG/2 ➭ C = (DP + DG)/2 • Diametral pitch system: ➭ Center Distance in terms of NG, NP, and Pd • DP = NP/Pd and DG = NG/Pd • C = (DP + DG)/2 = (NP/Pd + NG/Pd)/2 ➭C = (NP + NG)/2Pd ➭ Center Distance in terms of NG, NP, and m DP = mNP and DG = mNG • C = (DP + DG)/2 = (mNP + mNG)/2 ➭ C = m (NP + NG)/2 Pressure Angle: The pressure angle is the angle between the tangent to the pitch circles and the line drawn normal (perpendicular) to the surface of the gear
  53. 53. Two spur gears in mesh showing the pressure angle, line of action, base circles, pitch diameters, and other ➭ Base Circle Diameter Db = D cosϕ
  54. 54. • Standard values of the pressure angle are established by gear manufacturers, and the pressure angles of two gears in mesh must be the same. Current standard pressure angles are14 1 2 ° , 20°, and 25° as illustrated in Figure. • Actually, the 14 1 2 ° tooth form is considered obsolete. Although it is still available, it should be avoided for new designs. The 20° tooth form is the most readily available at this time. • Figure : Illustration of how the shape of gear teeth change as the pressure angle, (phi), changes
  55. 55. Where, • ϕ = Pressure angle, RoP = Outside radius of the pinion = DoP/2 = (NP + 2)/ (2Pd) • RbP = Radius of the base circle for the pinion = DbP/2 = (DP/2) cosϕ = (NP/2Pd) cosϕ • RoG = Outside radius of the gear = DoG/2 = (NG + 2)/ (2Pd) • RbG = Radius of the base circle for the gear = DbG/2 = (DG/2) cosϕ = (NG/2Pd) cosϕ • C = Center distance = (NP + NG)/ (2Pd) • p = Circular pitch = (πDp/Np) = π/Pd The contact ratio is defined as the ratio of the length of the line-of-action to the base pitch for the gear.
  56. 56. TABLE : Formulas for Use When Implementing Gear Pair Contact Ratio Calculation in U.S. and SI Systems in Terms of Diametral Pitch and Module Gears & Gear Trains……
  57. 57. • Bevel gears are used to transfer motion between nonparallel shafts, usually at 90° to one another. • The four primary styles of bevel gears are straight bevel, spiral bevel, zero spiral bevel, and hypoid. Bevel Gear Geometry Gears & Gear Trains……
  58. 58. kinds of Bevel Gear
  59. 59. • Bevel gears have teeth that are arranged as elements on the surface of a cone. • The teeth of straight bevel gears appear to be similar to spur gear teeth, but they are tapered, being wider at the outside and narrower at the top of the cone. • Bevel gears typically operate on shafts that are 90° to each other. Indeed, this is often the reason for specifying bevel gears in a drive system. • Specially designed bevel gears can operate on shafts that are at some angle other than 90°. Gears & Gear Trains……
  60. 60. • When bevel gears are made with teeth that form a helix angle similar to that in helical gears, they are called spiral bevel gears. • The major difference between hypoid gears and the others just described is that the centerline of the pinion for a set of hypoid gears is offset either above or below the centerline of the gear.
  61. 61. Worm and Worm-Gearing • Worm-gearing is used to transmit motion and power between non-intersecting shafts, usually at 90° to each other. The drive consists of a worm on the high-speed shaft which has the general appearance of a power screw thread: a cylindrical, helical thread.
  62. 62. • A worm and its mating worm gear operate on shafts that are at 90° to each other. They typically accomplish a rather large speed reduction ratio compared with other types of gears. • The worm is the driver, and the worm gear is the driven gear. The teeth on the worm appear similar to screw threads, and, indeed, they are often called threads rather than teeth. Gears & Gear Trains……
  63. 63. • The teeth of the worm gear can be straight like spur gear teeth, or they can be helical. Often the shape of the tip of the worm gear teeth is enlarged to partially wrap around the threads of the worm to improve the power transmission capacity of the set. • One disadvantage of the worm/worm gear drive is that it has a somewhat lower mechanical efficiency than most other kinds of gears because there is extensive rubbing contact between the surfaces of the worm threads and the sides of the worm gear teeth. Gears & Gear Trains……
  64. 64. Gears & Gear Trains……
  65. 65. GENERAL GUIDELINES FOR WORM AND WORMGEAR DIMENSIONS • Typical Tooth Dimensions Table shows typical values used for the dimensions of worm threads and gear teeth.
  66. 66. Table: Summary and Evaluation of Gear Types Gears & Gear Trains……
  67. 67. Gears & Gear Trains……
  68. 68. Gear Train • A gear train is combination of gears that is used for transmitting motion from one shaft to another. • There are several types of gear trains. In some cases, the axes of rotation of the gears are fixed in space. In one case, gears revolve about axes which are not fixed in space. • Simple Gear Train In this gear train, there are series of gears which are capable of receiving and transmitting motion from one gear to another. • They may mesh externally or internally. Each gear rotates about separate axis fixed to the frame. Figure shows two gears in external meshing and internal meshing.
  69. 69. Let N1, N2 be speed in rpm for gears 1 and 2. The velocity of P, 𝑉 𝑝 = 2𝜋𝑁1𝑑1 60 = 2𝜋𝑁2𝑑2 60 𝑁1 𝑁2 = 𝑑2 𝑑1 = 𝑡2 𝑡1 t1, t2, t3, . . . be number of teeth of respective gears 1, 2, 3, . . .
  70. 70. Gear
  71. 71. SUMMARY • The power transmission devices are belt drive, chain drive and gear drive. The belt drive is used when distance between the shaft axes is large and there is no effect of slip on power transmission. Chain drive is used for intermediate distance. • Gear drive is used for short centre distance. The gear drive and chain drive are positive drives but they are comparatively costlier than belt drive. • Similarly, belt drive should satisfy law of belting otherwise it will slip to the side and drive cannot be performed. When belt drive transmits power, one side will become tight side and other side will become loose side.
  72. 72. RECOMMENDATION • Gear, Belt and chain drives can be used for transmission of mechanical power between two rotating shafts. Belt drives are often cheaper than the equivalent gears and useful for transmitting power between shafts that are widely separated or nonparallel drives. Chain drives are usually more compact than the equivalent belt drive and can be used in oily environments where the equivalent belt would be prone to slipping. There is a wide range of belt and chain drives and this seminar has served to reviews the technology and the selection and specification of wedge and flat belt and roller chain drives. The technology is constantly developing with new materials and surface treatments, improvements in understanding of kinematics, and wears and associated modeling procedures. As recommendation; Belts and chain drives thus represent an innovation opportunity area, particularly for new applications, extended life, and improved reliability, as well as miniaturization.
  73. 73. 99 END!! 10qvm 4u Attentions!!

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