Mechanical Drives: Belt and Chain Systems
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Questions and Answers

What happens when the center distance between the two sheaves is reduced while placing the belt around them?

  • The belt breaks
  • The belt does not grip the driving sheave
  • The belt tension increases on both sides
  • Friction causes the belt to grip the driving sheave, increasing the tension in one side (correct)

    • What is the typical range of the coefficient of friction between the belt material and the pulley surface?

  • μ = 1.0 – 2.0
  • μ = 0.5 – 1.0
  • μ = 0.05 – 0.1
  • μ = 0.15 – 0.5 (correct)

    • What is the formula for the initial tension in the belt?

  • fi = f1 + f2 (correct)
  • fi = f1 * f2
  • fi = f1 - f2
  • fi = f1 / f2

    • What is the formula for the stress due to bending of the belt over the pulley?

    <p>fb = E(t/D)</p> Signup and view all the answers

    What is the typical range of the recommended velocity for the belt drive?

    <p>V = 15-20 m/s</p> Signup and view all the answers

    What type of belt drive is used for the transmission of small powers at belt speeds up to 12m/s?

    <p>Light drives</p> Signup and view all the answers

    What is the formula for the tension in the belt material?

    <p>f = 0.27 – 1.7 N/mm2</p> Signup and view all the answers

    What is the formula for the stress due to the effect of centrifugal force?

    <p>fc = Fc/bt = ρV2</p> Signup and view all the answers

    What is the maximum stress in a belt drive composed of?

    <p>fi, fb, and fc</p> Signup and view all the answers

    What is the ratio of driving and driven forces in a belt drive?

    <p>F1/F2 = eμθ</p> Signup and view all the answers

    What is the design power of a belt drive dependent on?

    <p>Difference in belt tension, coefficient of friction, and center distance</p> Signup and view all the answers

    What is the expression for the belt section for V > 10 m/s?

    <p>bt = F1/(ft – ρV2)C1</p> Signup and view all the answers

    What is the corrector factor C1 dependent on?

    <p>The angle of the center line of drive with horizontal and type of drives</p> Signup and view all the answers

    What is the typical service factor for oily, jerky loads, shock, and reversed loads?

    <p>1.2 - 1.4</p> Signup and view all the answers

    What is the typical feature of a V-belt drive?

    <p>The V-shape causes the belt to wedge tightly into the groove</p> Signup and view all the answers

    What is an advantage of V-belt drives?

    <p>Higher velocity ratio up to 7-10</p> Signup and view all the answers

    What is the primary reason for the application of belt drives in a system?

    <p>Relatively high rotational speeds</p> Signup and view all the answers

    What is the typical range of linear speed of a belt in m/min?

    <p>762-1981 m/min</p> Signup and view all the answers

    What is the primary advantage of belt drives in terms of machinery life?

    <p>Load fluctuations are cushioned</p> Signup and view all the answers

    What is the primary disadvantage of belt drives at lower speeds?

    <p>Slipping of up to 3% may occur between the belt and pulley</p> Signup and view all the answers

    What is the purpose of cogged design in some belt drives?

    <p>To enhance the ability to transmit high forces at low speeds</p> Signup and view all the answers

    What is the typical efficiency of belt drives?

    <p>90-98%</p> Signup and view all the answers

    Why are belt drives suitable for applications with large distances between shafts?

    <p>Because they are very economical when shafts are separated by large distances</p> Signup and view all the answers

    What is the primary difference between belt drives and chain drives?

    <p>Belts operate on sheaves or pulleys, whereas chains operate on toothed wheels called sprockets</p> Signup and view all the answers

    What is the primary advantage of chain drives over belt drives?

    <p>Positive engagement feature</p> Signup and view all the answers

    What is the typical application of chain drives in terms of distance and speed?

    <p>Large distances and slow speed</p> Signup and view all the answers

    What is the primary advantage of multiple-strand roller chains?

    <p>Increased power transmission capacity</p> Signup and view all the answers

    What is the formula to calculate the power transmitted through each chain in a multi-strand chain drive?

    <p>Power per chain = total power transmitted / multi-strand factor</p> Signup and view all the answers

    What is the typical range of pitch (p) for standard bush-roller chains?

    <p>6.35 – 76.0 mm</p> Signup and view all the answers

    What is the primary advantage of offset sidebar roller chains?

    <p>Lower cost</p> Signup and view all the answers

    What is the typical application of silent chains?

    <p>High-speed, smooth, and quiet power transmission</p> Signup and view all the answers

    What is required to maintain the reliable operation of silent chains?

    <p>Lubrication</p> Signup and view all the answers

    What is the relationship between the speed ratio and the ratio of the sheave pitch diameters in a V-belt drive?

    <p>Inversely proportional</p> Signup and view all the answers

    What is the design value of the ratio of the tight side tension to the slack side tension in V-belt drives?

    <p>5.0</p> Signup and view all the answers

    What is the purpose of the cogs on synchronous belts?

    <p>To provide a positive drive without slippage</p> Signup and view all the answers

    What is the characteristic of synchronous belts that allows for no slippage?

    <p>Their teeth on the underside of the belt</p> Signup and view all the answers

    What is the main advantage of chain drives over V-belt drives?

    <p>They are smoother and quieter</p> Signup and view all the answers

    What is the formula for the length of the pitch line of both sheaves in a V-belt drive?

    <p>L = 2C + 1.57(D2 + D1) + (D2 - D1)2/4C</p> Signup and view all the answers

    What is the reason for the limitation of V-belt drives at high speeds?

    <p>Centrifugal force prevents the use of V-belt drives at speeds above 50m/s</p> Signup and view all the answers

    What is the typical location of the maximum total stress in a V-belt drive?

    <p>Where the belt enters the smaller sheave</p> Signup and view all the answers

    Study Notes

    Belt and Chain Drives

    Objectives

    • Describe the basic features of a belt drive system
    • Describe several types of belt drives
    • Specify suitable types and sizes of belts and sheaves
    • Specify the primary installation variables for belt drives
    • Describe the basic features of a chain drive system
    • Describe several types of chain drives

    Areas of Application of Belt Drives

    • Belt drives are applied where the rotational speeds are relatively high
    • Linear speed of a belt: 762-1981 m/min
    • Result: relatively low tensile forces in the belt
    • High speed of the electromotor makes belt drives suitable for the first stage of reduction

    Advantages of Belt Drives

    • Simple
    • Economical
    • Overload and jam protection are provided
    • Noise and vibration are damped out
    • Machinery life is prolonged because load fluctuations are cushioned (shock-absorbed)
    • Lubrication-free
    • Require only low maintenance
    • Highly efficient (90–98%, usually 95%)
    • Some misalignment is tolerable
    • Very economical when shafts are separated by large distances

    Disadvantages of Belt Drives

    • At lower speeds, the tension in the belt becomes too large for typical belt cross sections, and slipping of up to 3% may occur between the sides of the belt and the pulley that carries it
    • At higher speeds, dynamic effects such as centrifugal forces, belt whip, catch of air, and vibration reduce the effectiveness of the drive and its life

    Types of Belt Drives

    • Flat belts
    • Grooved or cogged belts
    • Standard V-belt
    • Double-angle V-belts
    • Wrapped Die cut, cog type Synchronous belt construction
    • Poly-rib belt
    • Vee – band
    • Double angle V-belt

    Classification of Belt Drives

    • Based on peripheral speed
      • Light drives: transmission of small powers at belt speeds up to 12m/s (agriculture machines, small machine tools, etc)
      • Medium drives: for medium powers at 12 – 24 m/s (machine tools, cars, etc)
      • Heavy drives: for large powers and speed > 24m/s (generators, compressors, main drives)

    Design of Belt Drives

    • Depends on:
      • Difference in belt tension
      • Coefficient of friction
      • Area of contact
      • Center distance

    Belt Section

    • bt = F1/ftC1 for V < 10 m/s
    • bt =F1/(ft – ρV2)C1 for V > 10 m/s
    • ft – allowable stress in a belt (N/mm2)
    • C1 – 0.6 – 1.0 - a corrector factor depending upon the angle of center line of drive with horizontal, type of drives

    Pulley Size

    • D > 50t
    • D = 1.2(P/nmax)1/3
    • B = 1.2b
    • d = 0.005D + 3

    V-Belt Drives

    • Advantages:
      • Higher velocity ratio up to 7 – 10
      • Provide long life, 3 –5 years
      • Possibility of using small center distance
      • Transmit higher torsional moment at less width and tensions
    • Disadvantages:
      • Cannot be used with large center distances
      • Subjected to a certain amount of creep
      • More complex design
      • Belt life above 82oC and below – 15o is shortened
      • Centrifugal force prevents the use at speed above 50m/s and at speed below 5m/s are not economical

    Synchronous Belts

    • Ride on sprockets having mating grooves into which the teeth on the belt seat
    • Cog belts are applied to standard sheaves
    • The cogs give the belt greater flexibility and higher efficiency compared with standard belts

    Chain Drives

    • Used to transmit rotational motion and torque from one shaft to another, smoothly, quietly, and inexpensively
    • Provide the flexibility of a belt drive with the positive engagement feature of a gear drive
    • Suited for applications with large distances (8m) between the respective shafts, slow speed, and high torque

    Types of Chains

    • Roller chain
    • Multiple-strand roller chain
    • Construction of bush-roller chain
    • Offset sidebar roller chain
    • Silent chain

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    6. BELTS AND CHAINS.pptx

    Description

    Quiz about the basics of belt and chain drives, their features, types, and applications. Learn about the installation variables, suitable belt sizes, and rotational speeds.

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