Belt Drives and Chain Drives

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Chapter 7

• Belt Drives and Chain Drives

CVT
2
Overview why used

• 1.) Transfer power (torque) from one location to
  another. From driver motorpeddles
  enginewindmillturbine to driven conveyor belt
  back wheels/bikegenerator rock crusherdryer.
• 2.) Used to span large distances or need flexible
  x-mission elements. Gear drives have a higher
  torque capability but not flexible or cheap.
• 3.) Often used as torque increaser (speed
  reducer) max speed ratio 3.51. Gear drives
  Virtually unlimited!
• Applications Show rust abrader glove factory
  draw sample drive of rust abrader shows
  from mechanism book.

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Sometimes desirable to have both chain and belt
drive (Fig 7.1) Belt high speed/low
torque Chain Low speed/high torque
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Belts vs. Chains

• Belts

• Chains

Use When
High Speed Low T
High T Low Speed
Speed
2500 lt Vt lt 7000 ft./min.
V lt 1500 ft./min.
Must design with standard lengths wear creep
corrosive environment slip temp. when must
have tension need idler
Must be lubricated wear noise weight vibration
Dis
Advs
Quiet flexible cost
Strength length flexibility
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Types of Belts

• a)V-belt most common for machine design several
  types (Fig. 7.5 7.8)
• Timing belt (c d) have mating pulleys to
  minimize slippage
• c) Pos retention due to mating pulleys
• d) Pos retention due to increased contact area
• Flat belt (rubber/leather) not shown run on
  tapered pulleys

Add notes
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Types of V-Belts
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V-belt Drive Design Process

• Need rated power of the driving motor/prime
  mover. BASE sizing on this.
• Service factor based on type of driver and driven
  load.
• Center distance (adjustment for center distance
  must be provided or use idler pulley) nominal
  range D2 lt C lt 3(D2 D1)
• Power rating for one belt as a function of size
  and speed of the smaller sheave
• Belt length (then choose standard size)
• Sizing of sheaves (use standard size). Most
  commercially available sheaves should be limited
  to 6500 ft/min belt speed.
• Belt length correction factor
• Angle of wrap correction factor. Angle of wrap
  on smaller sheave should be greater than 120 deg.
• Number of belts
• Initial tension in belts

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Key Equations
Belt speed (no slipping)
Speed ratio
Pitch dias of sheaves
Pitch dia in inches
rpm
Belt speed ft/min
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Key Equations

• Belt length
• Center Distance
• Where

Recommended D2 lt C lt 3(D2D1)
Note usually belt length standard (use standard
belt length table 7-2) then calculate C based on
fixed L
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Key Equations cont

• Angle of contact of belt on each sheave

Note Select Ds and Cs so maximum contact (1
2 180º). If less then smaller sheave could
slip and will need reduction factor (Table 7-14).
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V-Belt Design Example

• Given 4 cylinder Diesel runs _at_ 80hp 1800 rpm to
  drive a water pump (1200 rpm) for less than 6
  hr./day
• Find Design V-belt drive

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V-belt Design Example Cont

• 1.) Calculate design power
• Use table 7-1(lt6h/day pump 4 cyl. Engine)

Design Power input power x service factor
80 hp x 1.1
88 hp
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V-belt Design Example Cont

• 2.) Select belt type Use table 7-9

Choose 5V
Speed 1800 rpm
Design Power 88 hp
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V-belt Design Example Cont

• 3.) Calculate speed ratio
• SR w1/w2
• 1800 rpm/1200 rpm
• 1.5

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V-belt Design Example Cont

• 4.) Determine sheave sizes
• Choose belt speed of 4000 ft/min

• (Recall 2500ft./min. lt vb lt 7000 ft./min)

So D1 8.488in D2 SR D1 1.5
8.488 D2 12.732in
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V-belt Design Example Cont

• 5.) Find sheave size (Figure 7-11)

Must find acceptable standard sheave 1 then
corresponding acceptable sheave 2
Engine (D1) 8.4 8.4 8.9
X 1.5 12.6 12.6 13.35
Standard D2 12.4 13.1 13.1
Actual n2 1219 1154 1223
All look OK we will try the first one
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V-belt Design Example Cont

• 6.) Find rated power (use figure 7-11 again)

Rated Power 21 hp
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V-belt Design Example Cont

• Adjust for speed ratio to get total power/belt

Total power 21hp 1.55hp 21.55hp
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V-belt Design Example Cont

• 7.) Find estimated center distance

Notice using standard sheave sizes found
earlier not calculated diameters
D2 lt C lt 3(D2D1)
12.4 lt C lt 3 (12.4 8.4)
12.4 lt C lt 62.4
To provide service access will try towards long
end try C 40
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V-belt Design Example Cont

• 8.) Find belt length

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V-belt Design Example Cont

• 9.) Select standard belt length
• Lcalc 112.765

Choose 112
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V-belt Design Example Cont

• 10.) Calculate actual center distance

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V-belt Design Example Cont

• 11.) Find wrap angle small sheave

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V-belt Design Example Cont

• 12.) Determine correction factors

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V-belt Design Example Cont

• 13.) Calculate corrected power

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V-belt Design Example Cont

• 14.) Belts needed

Use 4 belts!
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V-belt Design Example Cont

• 15.) Summary

D18.4 D212.4 Belt Length 112 Center
Distance 39.62 4 Belts Needed
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Chain Drives
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Chain Drives

• Types of Chains

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Chain Drives

• Roller Chain Construction (Most common Type)

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Chain Design Process

• 1.) of sprocket teeth N1 (smaller sprocket) gt
  17 (unless low speed lt 100 rpm.)
• 2.) Speed ratio n1/n2 7
• 3.) 30 x Pitch Length lt Center Distance lt 50 x
  Pitch Length
• 4.) Angle of contact of chain on smaller sprocket
  gt 120
• 5.) sprocket teeth N2 (longer sprocket) lt 120

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Chain Drives
33
Chain Drives Design Example

• Given
• Driver Hydraulic Motor
• Driven Rock Crusher
• ni 625 rpm 100 hp
• no 225 rpm
• Find
• Design belt drive

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Chain Drives Design Example

• 1.) Design Power
• DP SF x HP
• DP 1.4 ( Table 7-8) x 100 hp
• DP 140 hp

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Chain Drives Design Example

• 2.) Calculate Velocity Ratio

n speed N teeth
VR 2.78
Heavy Requirement!!
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Chain Drives Design Example

• 3.) Choose
• Size - (40 60 80) 80 (1in)
• Strands use 4
• Required HP/chain 140hp/3.3
• 42.42 hp/chain

No 69.5 use 70 teeth
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Chain Drives Design Example

• Conclusion
• 4 Strands
• No. 80 Chain
• Ni 25 Teeth
• No 70 Teeth

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Chain Drive Design Example

• Guess center distance 40 Pitches

L 128.8 pitches use 130 pitches
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Chain Drives Design Example

• Actual Center Distance C

C 40.6 use 40 Pitches