1

Belt Drives

Section VIII

2

Belts? & Types of Belts Belt Design V-Belt Angle of Wrap

Talking Points

3

Belts are used to transmit power from one shaft to another where it is not necessary to maintain an exact speed ratio between the two shafts.

Two famous types of belts are: Flat Belts. V-Belts.

Power losses due to slip and creep amount to from 3.0 to 5.0 percent for most belt drives.

In this course, it will be assumed that the shafts are parallel.

Belts? & Types of Belts

4

Belt Design It involves either the proper belt

selection to transmit a required power or the determination of the power that may be transmitted by a given flat belt or by one V-belt. In the first case, the width of the belt is unknown, while in the second case, the width is known. The belt thickness is assumed for both cases.

The power transmitted by a belt drive is a function of the belt tension and belt speed.

hp ,

550

VTTPower or W V,TTPower 21

21

Where:

m/s speed,belt V

N side, loosein ion belt tens T

N side, in tight ion belt tens T

2

1

The following formula is for determining the stress, 2, for the flat belts applies when the thickness of the belt is given but the width is unknown.

fe

22

21

Vm

Vm

rad. pulley,on belt of wrapof angle

pulley &belt between friction oft coefficien

kg/m section,-crossin m 1.0belt of m 1.0 of mass m

Pa belt, theof sideslack in the stress Pa; stress, allowable maximum 32

21

f

Where:

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Belt Design – Con.

Where:

The required cross-sectional area of the flat belt for the case of the width unknown may be determined by: 21

21

σσ

TT Area Required

beltflat afor 180 Belt -V for the angle groove

kg/m density,belt p m; kness,belt thic tm; h,belt widt b

kg/m belt, of m 1.0 of massptb m3

2sin2

2

21

VmT

VmT f

e

The required flat belt width b is therefore:Thickness

Area b

The value of may be determined from the power requirement, WV,TTPower 21 21 TT

The maximum tension in the tight side of the belt depends on the allowable stress of the belt material. The allowable tensile stress for leather belting is usually 2.0 to 3.45 MPa, and the allowable stress for rubber belting will run from 1.0 to 1.7 MPa, depending on the quality of the material. Leather belting can be obtained in various single ply thicknesses. Double and triple ply belts are also available.

The following formula is for determining the value of 2, for both flat & V-belts applies when the width & thickness of the belt are known.

The quantity mV2 is due to centrifugal force, which tends to cause the belt to leave the pulley and reduce the power that may be transmitted.

V-Belt

6

Multiple V-Belts

V-Belt Configurations

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Angle of Wrap The angles of wrap for an open belt may be

determined by:

The angles of wrap for a crossed belt drive may be determined by:

c

rR

c

rRc

rR

12

11

sin21802180

sin21802180

sin

c

rRc

rR

121 sin21802180

sin