Chapter 7:. Belt Drives and Chain Drives. CVT. 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 .
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Belt Drives and Chain Drives
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.
Belt: high speed/low torque
Chain: Low speed/high torque
ChainsBelts vs. Chains
High Speed, Low T
High T, Low 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
Quiet, flexible, cost
Strength, length flexibility
Belt speed (no slipping) =
Speed ratio =
Pitch dia’s of sheaves
Pitch dia in inches
Belt speed ft/min
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
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).
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
2.) Select belt type, Use table 7-9
Speed = 1800 rpm
Design Power = 88 hp
3.) Calculate speed ratio
SR = w1/w2
= 1800 rpm/1200 rpm
4.) Determine sheave sizes
Choose belt speed of 4000 ft/min
(Recall 2500ft./min. < vb < 7000 ft./min)
D1 = 8.488in
D2 = SR * D1 = 1.5 * 8.488
D2 = 12.732in
5.) Find sheave size (Figure 7-11)
Must find acceptable standard sheave 1, then corresponding acceptable sheave 2
**All look OK, we will try the first one
6.) Find rated power (use figure 7-11 again)
Rated Power = 21 hp
Total power = 21hp +1.55hp = 21.55hp
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 + 8.4)
12.4 < C < 62.4
To provide service access will try towards long end, try C = 40”
8.) Find belt length
9.) Select standard belt length
Lcalc = 112.765
10.) Calculate actual center distance
12.) Determine correction factors
13.) Calculate corrected power
14.) Belts needed
Use 4 belts!
Belt Length = 112”
Center Distance = 39.62”
4 Belts Needed
DP = SF x HP
DP = 1.4 ( Table 7-8) x 100 hp
DP = 140 hp
n = speed
N = teeth
VR = 2.78
Required HP/chain = 140hp/3.3
= 42.42 hp/chain
No = 69.5 use 70 teeth
Guess center distance: 40 Pitches
L = 128.8 pitches use 130 pitches
Actual Center Distance, C
C = 40.6 use 40 Pitches