Belt and Chain Drives (Flexible Drive...

Belt and Chain Drives

(Flexible Drive Elements)

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Why Flexible Drives?

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+ • Long Distances Between Shafts

• Less Expensive

• Adjustable Centers

• Tolerates some mis alignment better than gears

- • Not as compact as gears

• Some speed limits

• Power and torque limits

Common Belt Types

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Type Pulley

1. Flat Crowned pulley

(conveyor belts)

2. Round (O-ring) Grooved pulley

3. V-belt Flanged pulleys

4. Timing (toothed) Cogged pulley

(no stretch or slip)

5. Proprietary belt designs

Characteristics of Some Common Belt Types

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Table 17–1

Flat-Belt Geometry – Open Belt

Shigley’s Mechanical Engineering Design Fig.17–1a

Reversing Belts

Shigley’s Mechanical Engineering Design Fig.17–2

Typically

O-Ring

Drives

Flat-belt with Out-of-plane Pulleys

Shigley’s Mechanical Engineering Design Fig.17–3

Variable-Speed Belt Drives

Shigley’s Mechanical Engineering Design Fig.17–5

Free Body of Infinitesimal Element of Flat Belt

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Fig.17–6

m is the mass/length

Free Body of Infinitesimal Element of Flat Belt

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Fig.17–6

Analysis of Flat Belt

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Fc = Hoop Tension Due to Centrifugal Force

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Forces and Torques on a Pulley

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Fig.17–7

Initial Tension

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Flat Belt Tensions

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Transmitted Horsepower

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Correction Factors for Belts, Based on Manufacturer Data

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Velocity Correction Factor Cv for Leather Belts

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Fig.17–9

Pulley Correction Factor CP for Flat Belts

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Belt-Tensioning Schemes

Shigley’s Mechanical Engineering Design Fig.17–11

Standard V-Belt Sections

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Table 17–9

Inside Circumferences of Standard V-Belts

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Table 17–10

Length Conversion Dimensions

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V-Belt Pitch Length and Center-to-Center Distance

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Horsepower Ratings of Standard V-Belts

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Table 17–12

Adjusted Power

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Angle of Wrap Correction Factor

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Table 17–13

Belt-Length Correction Factor

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Table 17–14

Belting Equation for V-Belt

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Design Power for V-Belt

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Number of belts:

V-Belt Tensions

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Roller Chain

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Roller Chain

Shigley’s Mechanical Engineering Design Fig.17–16

ANSI numbers

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ANSI Chain No. XY

X: pitch in 1/8-inches

Y: 0=standard, 1=light duty,

5 for bushed chain with no rollers

Most roller chain is made from plain

carbon or alloy steel, but stainless steel is

used in food processing.

Dimensions of American Standard Roller Chains

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Table 17–19

Engagement of Chain and Sprocket

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Fig.17–17

Chain Velocity

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Chordal Speed Variation

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Fig.17–18

Roller Chain Rated Horsepower Capacity

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Roller Chain Rated Horsepower Capacity

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Available Sprocket Tooth Counts

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Example 17–5

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Example 17–5

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Example 17–5

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Wire Rope

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Fig.17–19

Berg cable timing belts

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Stress in Wire Rope

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Wire-Rope Data

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Table 17–24

Equivalent Bending Load

Wire rope tension giving same tensile stress as sheave bending is

called equivalent bending load Fb

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Percent Strength Loss

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Fig.17–20

Minimum Factors of Safety for Wire Rope

Shigley’s Mechanical Engineering Design Table 17–25

Bearing Pressure of Wire Rope in Sheave Groove

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Maximum Allowable Bearing Pressures (in psi)

Shigley’s Mechanical Engineering Design Table 17–26

Relation Between Fatigue Life of Wire Rope and Sheave Pressure

Shigley’s Mechanical Engineering Design Fig.17–21

Fatigue of Wire Rope

Fig. 17–21does not preclude failure by fatigue or wear

It does show long life if p/Su is less than 0.001.

Substituting this ratio in Eq. (17–42),

Dividing both sides of Eq. (17–42) by Su and solving for F, gives

allowable fatigue tension,

Factor of safety for fatigue is

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Factor of Safety for Static Loading

The factor of safety for static loading is

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Typical Strength of Individual Wires

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Service-Life Curve Based on Bending and Tensile Stresses

Shigley’s Mechanical Engineering Design Fig.17–22

Some Wire-Rope Properties

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Working Equations for Mine-Hoist Problem

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Working Equations for Mine-Hoist Problem

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Working Equations for Mine-Hoist Problem

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Example 17–6

Shigley’s Mechanical Engineering Design Fig.17–23

Example 17–6

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Example 17–6

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Example 17–6

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Flexible Shaft Configurations

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Fig.17–24b

Flexible Shaft Construction Details

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Fig.17–24a