1. Belt Drives and Chain Drives
Chapter 7:
Belt Drives and Chain Drives
CVT

2. Overview – why used?
1.) Transfer power (torque) from one location to another. From driver: motor,peddles, engine,windmill,turbine to driven: conveyor belt, back wheels/bike,generator rock crusher,dryer.
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: 3.5:1. Gear drives?? Virtually unlimited!
Applications? Show rust abrader, glove factory, draw sample drive of rust abrader, show slides from mechanism book.

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

4. Belts vs. Chains Belts Chains Use When: Speed: Dis: Advs:
High Speed, Low T
High T, Low Speed
Speed:
2500 < Vt < 7000 ft./min.
V < 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

5. 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

6. Types of V-Belts

7. 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 < C < 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

8. Key Equations Belt speed (no slipping) = Speed ratio =
Pitch dia’s of sheaves
Pitch dia in inches
rpm
Belt speed ft/min

9. Key Equations Belt length: Center Distance: Where,
Recommended D2 < C < 3(D2+D1)
Note: usually belt length standard (use standard belt length table 7-2), then calculate C based on fixed L

10. Key Equations cont… Angle of contact of belt on each sheave
Note: Select D’s and C’s so maximum contact (Ѳ1 + Ѳ2 = 180º). If less then smaller sheave could slip and will need reduction factor (Table 7-14).

11. V-Belt Design Example
Given: 4 cylinder Diesel 80hp, 1800 rpm to drive a water pump (1200 rpm) for less than 6 hr./day
Find: Design V-belt drive

12. V-belt Design Example Cont…
1.) Calculate design power:
Use table 7-1(<6h/day, pump, 4 cyl. Engine)
Design Power = input power x service factor
= 80 hp x 1.1
= 88 hp

13. V-belt Design Example Cont…
2.) Select belt type, Use table 7-9
Choose 5V
Speed = 1800 rpm
Design Power = 88 hp

14. V-belt Design Example Cont…
3.) Calculate speed ratio
SR = w1/w2
= 1800 rpm/1200 rpm
= 1.5

15. V-belt Design Example Cont…
4.) Determine sheave sizes
Choose belt speed of 4000 ft/min
(Recall 2500ft./min. < vb < 7000 ft./min)
So…
D1 = 8.488in
D2 = SR * D1 = 1.5 * 8.488
D2 = in

16. 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
8.9
X 1.5
12.6
13.35
Standard D2
12.4
13.1
Actual n2
1219
1154
1223
**All look OK, we will try the first one

17. V-belt Design Example Cont…
6.) Find rated power (use figure 7-11 again)
Rated Power = 21 hp

18. V-belt Design Example Cont…
Adjust for speed ratio to get total power/belt
Total power = 21hp +1.55hp = 21.55hp

19. V-belt Design Example Cont…
7.) Find estimated center distance
Notice – using standard sheave sizes found earlier, not calculated diameters
D2 < C < 3(D2+D1)
12.4 < C < 3 ( )
12.4 < C < 62.4
To provide service access will try towards long end, try C = 40”

20. V-belt Design Example Cont…
8.) Find belt length

21. V-belt Design Example Cont…
9.) Select standard belt length
Lcalc =
Choose 112”

22. V-belt Design Example Cont…
10.) Calculate actual center distance

23. V-belt Design Example Cont…
11.) Find wrap angle, small sheave

24. V-belt Design Example Cont…
12.) Determine correction factors

25. V-belt Design Example Cont…
13.) Calculate corrected power

26. V-belt Design Example Cont…
14.) Belts needed
Use 4 belts!

27. V-belt Design Example Cont…
15.) Summary
D1=8.4”
D2=12.4”
Belt Length = 112”
Center Distance = 39.62”
4 Belts Needed

28. Chain Drives

29. Chain Drives
Types of Chains

30. Chain Drives
Roller Chain Construction (Most common Type)

31. Chain Design Process
1.) # of sprocket teeth, N1 (smaller sprocket) > 17 (unless low speed < 100 rpm.)
2.) Speed ratio = n1/n
3.) 30 x Pitch Length < Center Distance < 50 x Pitch Length
4.) Angle of contact of chain on smaller sprocket > 120°
5.) # sprocket teeth, N2 (longer sprocket) < 120

32. 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

34. Chain Drives Design Example
1.) Design Power
DP = SF x HP
DP = 1.4 ( Table 7-8) x 100 hp
DP = 140 hp

35. Chain Drives Design Example
2.) Calculate Velocity Ratio
n = speed
N = teeth
VR = 2.78
Heavy Requirement!!

36. Chain Drives Design Example
3.) Choose:
Size - (40, 60, 80) (1in)
# Strands – use 4
Required HP/chain = 140hp/3.3
= hp/chain
Number of Roller Chain Strands
Multiple Strand Factor 2
1.7 3
2.5 4
3.3 5
3.9 6
4.6
No = 69.5  use 70 teeth

37. Chain Drives Design Example
Conclusion:
4 Strands
No. 80 Chain
Ni = 25 Teeth
No= 70 Teeth

38. Chain Drive Design Example
Guess center distance: 40 Pitches
L = pitches  use 130 pitches

39. Chain Drives Design Example
Actual Center Distance, C
C = 40.6  use 40 Pitches