DESIGN OF FLAT BELT DRIVE
Solving Design Problems Based on Flat Belts There are two ways by which you can design a flat belt drive. They are: • Designing flat belt drive using manufacturer’s data • Designing flat belt drive using basic equations
STEPS INVOLVED IN DESIGNING FLAT BELT DRIVES • • • • • • • • • •
Finding Pulley Diameters (D and d): Finding the Speeds of Driving & Driven Pulleys (N1 & N2) Finding Design Power in kW Finding the Belt Velocity (V m/s) Selection of belt Determination of number of plies Finding Load Rating at V m/s Finding Belt Width (b) Determining Pulley width Determining the length of flat belt (L)
Step 1 – Finding Pulley Diameters (D and d) • In some problems, diameters of the driving and driven pulleys may be given. If any one of them is not given, use the following equation to find it:
• • • • •
where, N1 → Speed of the driving pulley in rpm N2 → Speed of the driven pulley in rpm D → Diameter of the larger (driven) pulley in m d → Diameter of the smaller (driving) pulley in m
Find the std. pulley diameter PSG design data book, page no. 7.54 • A list of standard pulley diameters (in mm) is given below: 40, 45, 50, 56, 63, 71, 80, 90, 100, 112, 125, 140, 160, 180, 200, 224, 250, 280, 315, 355, 400, 450, 500, 560, 630, 710, 800, 900, 1000, 1120, 1250, 1400,1600, 1800, 2000
Step 2 – Finding the Speeds of Driving & Driven Pulleys (N1 and N2) • In many problems, the speeds of the driving and the driven pulleys will be given. If any one speed is not given, either the velocity ratio or the pulley diameters will be given. Use the same equation from the above step to find the unknown pulley speed. Note: • The Previous formula can be used in any problem where percentage slip is zero (or not given). If percentage slip is given for each pulley, use the following equation to find the unknown pulley speed or diameter.
(Contd….)
where, • S1 → Percentage slip between the driving pulley and the belt • S2 → Percentage slip between belt and the driven pulley
• If thickness of belt (t) is considered, use the following equation
Step 3 – Finding Design Power in kW • Design power in kW can be found out using the following equation:
• Rated power in KW will be provided in the problem itself
• To find the correction factors in the above equation, see the section below. • Load Correction Factor: • Arc of contact factor: • Smaller Pulley Diameter Factor:
THANK YOU
Load Correction Factor (PSG DB Pg. 7.53) Load Type of Load
Applications
Correction Factor
Normal Load
Steady Load
Intermittent Loads
Shock Loads
(When maximum load is known)
1.0
Light duty fans, centrifugal pumps, printing machinery, textile machinery,
1.2
screens, agitators, evaporators and light machinery
Heavy machine tools, heavy duty fans and blowers, air compressor, reciprocating pumps, elevators, mill machinery, line shafts, paper mill and saw
1.3
mill machinery
Hammers, grinders, crushing machines, disintegrators, vacuum pumps, rolling mills, tube mills, ball mills, automated machinery and stamp presses
1.5
Continue…
Arc of contact factor (PSG DB Pg. 7.54)
where, • D → Diameter of the larger (driven) pulley • d → Diameter of the smaller (driving) pulley • C → Centre distance between the two pulleys After finding the arc of contact, you must change it to the nearest standard value and find its corresponding correction factor
Arc of contact factor (PSG DB Pg. 7.54) Arc of Contact
Arc of Contact
Factor
Arc of Contact
Arc of Contact
Factor
90°
1.68
190°
0.97
120°
1.33
200°
0.94
130°
1.26
210°
0.91
140°
1.19
220°
0.88
150°
1.13
230°
0.86
160°
1.08
240°
0.84
170°
1.04
250°
0.82
180°
1.00 Continue…
Smaller Pulley Diameter Factor Smaller Pulley Diameter (in mm)
Smaller Pulley Diameter Factor
Upto 100
0.5
100-200
0.6
200-300
0.7
300-400
0.8
400-750
0.9
Above 750
1.0
Step 4 – Finding the Belt Velocity (V m/s) • Maximum velocity of belt (V) can be found out using the following equation:
• where, • d → Diameter of the smaller (driving) pulley in m • N1 → Speed of the driving pulley in rpm
