1. C.K. PITHAWALA COLLEGE OF ENGINEERING & TECHNOLOGY
SUB: DESIGN OF MACHINE ELEMENTS

2. - SELECTION OF BELTS FROM CATALOGUES
Topic ::
Div : A (Mechanical – 3rd Year)
5th sem
Name
Roll No.
Enrollment No.
VISHAL PATEL
131992
VARDHAN KHANDELWAL
131944
RAVI DESAI
131921
KRUNAL

3. TYPES OF BELTS 2. V – belt 3. Circular belt 4. Timing belt
1. Flat belt
2. V – belt
3. Circular belt
4. Timing belt

4. Selection of Flat Belt
In most of the applications, belts are generally selected by the designer from the manufacturer’s catalogue. This helps in the use of standard available sizes. Following input data is required for the selection of belt:
1.Power to be transmitted
2.Transmission ratio
3.Centre distance

5. 1. Select suitable belt material
Following is the procedure for selection of a flat belt:
1.      Select suitable belt material
Two types of belts are generally available – HI-SPEED duck belting and FORT duck belting. Specified transmission capacities of these two types, for an angle of contact of 180°and belt velocity of 5.08 m/s, is as follows:
Type of Belt                                         Transmission Capacity/ Power Rating (R)
HI-SPEED                                                             kW /
mm width / ply
FORT                                                                     kW / mm width / ply

6. 2. Assume belt velocity and calculate diameters of pulleys
Optimum value of belt velocity lies between 15 m/s to 25 m/s. Assume any value for belt velocity, within this range and calculate diameter of the smaller (driving) pulley using the following relationship:
where,       v = velocity of belt
            N1 = input speed (rpm) of smaller pulley
Diameter of larger pulley (D) can be calculated, for required velocity ratio i.e. for required output speed (N2), using the following relationship:
N1d = N2D

7. 3. Calculate design power
For design purpose, maximum power transmitted by the belt is obtained by multiplying the required power (P) by a load correction factor (K load). Value of K load can be taken from Table (A). Also, Power transmission capacity of belts (Step 1) is based on angle of contact of 180°. But in actual conditions, angle of contact varies depending upon diameters of pulleys and centre distance. If angle of contact is less than 180°, there is additional tension in the belt. This is taken care of, by multiplying the required power to be transmitted by angle of contact factor, Ka.. Value of Ka can be taken from Table (B). Design power of the belt is thus given by,

8. Table (A). Load Correction Factor, K load
Type of Load
Kload
Normal Load
1.0
Steady Load
(light machine tools, fans, centrifugal pumps, conveyors etc.)
1.2
Intermittent Load
(compressors, blowers, heavy-duty fans, line shafts, reciprocating pumps, heavy-duty machines etc.)
1.3
Shock Load
(hammers, grinders, rolling mills, vacuum pumps etc.)
1.5
Table 20.2 Angle of Contact Factor, Ka
Angle of Contact (as)
120°
130°
140°
150°
160°
170°
180°
190°
200°
210°
Angle of Contact Factor, Ka
1.33
1.26
1.19
1.13
1.08
1.04
1.00
0.97
0.94
0.91

9. 4. Determine corrected power rating
Power transmission capacity of belts (Step 1) is based on belt velocity of 5.08 m/s. But in actual conditions, belts run at different speeds. For different velocity, corrected power rating is obtained as follows:
where, R is Power Transmission Capacity or Rating of belt and v is actual belt velocity
5.      Calculate the product of width and number of plies by dividing maximum power to be transmitted by corrected power rating.

10. 6. Select suitable width and number of plies
Suitable width and number of plies can now be selected from the catalogue so that the desired product is obtained. Table (C) gives standard width thickness and number of plies for rubber belts.
Table (C) Rubber Belt Data
No. of Plies
Thickness (mm)
Belt Width (mm) 3
3.9
25, 32, 40, 50, 63, 71 4
5.2
40, 50, 63, 71, 80, 90, 100, 112, 125, 140 5
6.5
71, 80, 90, 100, 112, 125, 140, 160 6
7.8
112, 125, 140, 160, 180, 200, 224, 250 7
9.1
160, 180, 200, 224, 250, 280, 315 8
10.4
224, 250, 280, 315, 355, 400, 450, 500
7.         Calculate desired length of belt and specify all the dimensions.

11. Selection of V-Belts 1. Select suitable V-belt section
V-belts are also selected from the manufacturer’s catalogue. Following is the procedure for selection of a flat belt:
1.      Select suitable V-belt section
Five types of standard V-belt sections are available. Dimensions of these are given in Table(D) . Refer figure (1) for basic dimensions of the trapezoidal section of V-belt.

12. Table (D). Dimensions of V-belt Sections
Pitch Width, (mm) 11 14 19 27 32
Nominal Top Width, w (mm) 13 17 22 38
Nominal Thickness, t (mm) 8 23
Recommended Velocity (m/s) 25 30
Recommended Power Range (kW)
70 – 260
Recommended Minimum
Pitch Diameter of Pulley (mm)
125
200
315
500
630

13. 2. Determine diameters of pulleys
Recommended diameter of smaller pulley (d) can be taken from table 20.4 for selected cross-section. Diameter of larger pulley (D) can be calculated, for required velocity ratio i.e. for given input speed (N1) and required output speed (N2), using the following relationship:
N1d = N2D
3.      Calculate design power
For design purpose, maximum power transmitted by the belt is obtained by multiplying the required power (P) by service factor (Ks). Value of Ks can be taken between 1 and 2, depending upon the service conditions i.e. light, medium, heavy or extra-heavy duty, type of driver and driven machinery and operational hours.

14. Pdesign = Ks X P 4. Determine Pitch Length and Centre Distance
Calculate length of the belt from its relation with d, D and C. Select the nearest standard value of belt pitch length from table (E). Calculate exact centre distance, C from the relation again.

15. Angle of Contact Factor, Ka
Table (E). Angle of Contact Factor, Ka
Angle of Contact
on Smaller Pulley, as
Angle of Contact Factor, Ka
0.00
180
1.00
0.05
177
0.99
0.10
174
0.15
171
0.98
0.20
169
0.97
0.25
166
0.30
163
0.96
0.35
160
0.95
0.40
157
0.94
0.45
154
0.93
0.50
151
0.55
148
0.92
0.60
145
0.91
0.65
142
0.90
0.70
139
0.89
0.75
136
0.88
0.80
133
0.87
0.85
130
0.86
127
123
0.83
120
0.82

16. 5. Determine corrected power rating
Power transmission capacity / rating (R) for a single V-belt, for different types of cross-sections, can be taken from manufacturer’s catalogue. Corrected power rating is obtained by multiplying the power rating by Pitch Length Correction Factor (K length) and Angle of Contact Factor, Ka as follows:
Values of Ka can be taken from table (E).
6.      Determine the number of belts required
Required number of belts is determined by dividing the design power with corrected power rating for one belt.

17. THANK YOU