UNIVERSAL COUPLING

 UNIVERSAL COUPLING

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Designing Flat Belt Drives:

Machine Design

 By Jindal, U. C.

Method wrong used in diploma 
 http://mechteacher.com/flat-belt-design

Steps involved in Designing Flat Belt Drives:

Step 1 – Finding Pulley Diameters (D and d):

This step involves finding the diameters of the driving and driven pulleys of the belt drive. 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

Note: Here, we have assumed that the driven pulley is larger in diameter than the driving pulley.

After finding the pulley diameters, you must change it to the nearest standard value (greater than the one determined) and fix it as the permanent value.

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

Note: If you are using PSG design data book, refer page no. 7.54 (May 2012 reprint) for finding the standard pulley diameter.

Step 2 – Finding the Speeds of Driving and 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 above 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.

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.

Determination of Correction Factors:

a. Load Correction Factor:

Load correction factor can be determined from the following table.

Table (i) – Load Correction Factor

Type of Load	Applications	Load Correction Factor
Normal Load	(When maximum load is known)	1.0
Steady Load	Light duty fans, centrifugal pumps, printing machinery, textile machinery, screens, agitators, evaporators and light machinery	1.2
Intermittent Loads	Heavy machine tools, heavy duty fans and blowers, air compressor, reciprocating pumps, elevators, mill machinery, line shafts, paper mill and saw mill machinery	1.3
Shock Loads	Hammers, grinders, crushing machines, disintegrators, vacuum pumps, rolling mills, tube mills, ball mills, automated machinery and stamp presses	1.5

Note: If you are using PSG design data book, refer page no. 7.53 (May 2012 reprint) for this table.

b. Arc of contact factor:

In order to determine arc of contact factor, you must first find the arc of contact. Arc of contact can be determined using the following equation:

where,

D → Diameter of the larger (driven) pulley

d → Diameter of the smaller (driving) pulley

C → Centre distance between the two pulleys

Note: If you are using PSG design data book, refer page no. 7.54 (May 2012 reprint) for this equation.

After finding the arc of contact, you must change it to the nearest standard value (greater than the one determined) and find its corresponding correction factor. The following table will help you do this.

Table (ii) – Arc of contact factor

Arc of Contact	Arc of Contact Factor
90°	1.68
120°	1.33
130°	1.26
140°	1.19
150°	1.13
160°	1.08
170°	1.04
180°	1.00
190°	0.97
200°	0.94
210°	0.91
220°	0.88
230°	0.86
240°	0.84
250°	0.82

Note: If you are using, PSG design data book, refer page no. 7.54 (May 2012 reprint) for this table.

c. Smaller Pulley Diameter Factor:

Smaller pulley diameter factor can be found using the table below:

Table (iii) – 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

Step 5 – Selection of Belt:

There are two types of belts from which you can select from. They are:

1. Dunlop “HI – SPEED” 878 g duck belting – Used in light and medium duty applications with high belt velocity.
2. Dunlop “FORT” 949 g duck belting – Used in heavy duty applications with medium belt speeds.

For design power < 20 kW and belt velocity > 16 m/s, select Dunlop “HI – SPEED” 878 g duck belting.

For design power > 20 kW and belt velocity < 16 m/s, select Dunlop “FORT” 949 g duck belting.

Note: If you are using PSG design data book, refer page no. 7.52 (May 2012 reprint) for selecting the right flat belt.

Step 6 – Determination of number of plies:

The number of plies can be determined using the maximum belt velocity and the minimum pulley diameter from the following table.

Table (iv) – Determination of number of plies using maximum belt velocity and minimum pulley diameter

No. of plies	Maximum belt velocity in m/s
	10	15	20	25	30
3	90	100	112	140	180
4	140	160	180	200	250
5	200	224	250	315	355
6	250	315	355	400	450
8	450	500	560	630	710

In the above table, the values given in italics are the values of minimum pulley diameter in mm.

Note: If you are using PSG design data book, refer page no. 7.52 (May 2012 reprint) for the above table.

Step 7 – Finding Load Rating at V m/s:

For “HI – SPEED” 878 g duck belting, load rating at 10 m/s is 0.023 kW per mm per ply.

For “FORT” 949 g duck belting, load rating at 10m/s is 0.0289 kW per mm per ply.

Load rating at V m/s = Load rating at 10 m/s × (V/10) kW per mm per ply

Note: If you are using PSG design data book, refer page no. 7.54 (May 2012 reprint) for finding the load rating.

Step 8 – Finding Belt Width (b):

Width of belt (b) can be found using the following equation:

In the above equation, load rating implies load rating at V m/s that you have found in the previous step.

After finding the belt width, you must change it to the nearest standard value (greater than the one determined) and fix it as the permanent value. Refer the following table to choose a standard belt width according to the number of plies and the type of belt used.

Table (v) – Standard Flat Belt Widths in mm

3 Plies	4 Plies	5 Plies	6 Plies	8 Plies
25◊	25•	76◊	100•	200¤
32•	32•	90•	112◊	250¤
40◊	40◊	100◊	125◊	305¤
44•	44◊	112◊	152◊	355¤
50◊	50◊	125◊	180◊	400¤
63◊	63◊	152◊	200◊
76◊	76◊	180¤	250¤
90•	90◊	200•
100•	100◊	224•
	112◊	250¤
	125◊
	140•
	152◊
	200•

In the above table,

◊ → Sizes available in both “HI-SPEED” and “FORT” duck belting

• → Sizes available only in “HI-SPEED” duck belting

¤ → Sizes available only in “FORT” duck belting

Note: If you are using PSG design data book, refer page no. 7.52 (May 2012 reprint) for the above table.

Step 9 – Determining Pulley width:

Pulley width can be obtained using the following equation:

Pulley width = Belt width (chosen standard) + Additional width

Additional width has to be chosen according to the belt width. The following table helps you do that.

Table (vi) – Determination of Additional Width from Belt Width

Belt Width	Additional width
Upto and including 125 mm	13 mm
Above 125 mm upto and including 250 mm	25 mm
Above 250 mm upto and including 375 mm	38 mm
Above 375 mm upto and including 500 mm	50 mm

Note: If you are using PSG design data book, refer page no. 7.54 (May 2012 reprint) for this table.

Once the pulley width is found, you must change it to the nearest standard value (greater than the one determined) and fix it as the permanent value.

A list of standard pulley widths (in mm) is given below:

20, 25, 32, 40, 50, 63, 71, 80, 90, 100, 112, 125, 140, 160, 180, 200, 224, 250, 280, 315, 355, 400, 450, 500, 560, 630

Note: If you are using PSG design data book, refer page no. 7.55 (May 2012 reprint) for finding the standard pulley width.

Step 10 – Determining the length of flat belt (L):

This is the last step. Length of belt varies according to the type of flat belt drive.

For open flat belt drive, length of belt is given by:

For crossed flat belt drive, length of belt is given by:

For quarter turn flat belt drive, length of belt is given by:

where,

D → Diameter of the larger pulley

d → Diameter of the smaller pulley

C → Centre distance between the two pulleys

Note: If you are using PSG design data book, refer page no. 7.53 (May 2012 reprint) for these length formulae.

That’s it. You have successfully designed a flat belt drive using manufacturer’s data 

Read more: http://mechteacher.com/flat-belt-design/#ixzz3eJq6ncwH