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Belt Drive

Dr. Mostafa Rostom A. AtiaAssociate Prof.

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Belt Drive

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Belt types

Crowned pulleys are used for flat beltsGrooved pulleys, or sheaves are used for round and V belts. Timing belts require toothed wheels, or sprockets.

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Flat Belt

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Belt Geometry

Open Belt

Crossed Belt

θ : Angle of Wrap

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Special belt geometry

Quarter-twist belt drive

Clutch-like belt drive

Variable speed belt driveReversed

belt drive

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Force analysis

Tight side

Loose side

F1 > F2

𝐹𝐹𝑖𝑖 = 𝑇𝑇𝐷𝐷

𝑒𝑒𝑓𝑓𝜃𝜃 + 1𝑒𝑒𝑓𝑓𝜃𝜃 − 1

Centrifugal force

Initial force

𝐹𝐹1 = 𝐹𝐹𝑐𝑐 + 𝐹𝐹𝑖𝑖 2 𝑒𝑒𝑓𝑓𝜃𝜃

𝑒𝑒𝑓𝑓𝜃𝜃 + 1

𝐹𝐹2 = 𝐹𝐹𝑐𝑐 + 𝐹𝐹𝑖𝑖 2

𝑒𝑒𝑓𝑓𝜃𝜃 + 1

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Allowable tension force

(For leather belt only)

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Useful data

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Crown effect

The higher section of the crowned pulley puts more tension on the rubber band on that side. As a result, the rubber band flexes into a slight arch towards the right. As the rubber band winds onto the pulley, this arch causes the band to always wind further up on the conical section than what was previously wound on. The higher point on the pulley always creates more tension in the belt and causes it to arch in that direction.

With this exaggerated crowned pulley, it takes just a few turns for the rubber band to wander from the edge of the pulley all the way to up the hump. Once the rubber band is on top of the crowned pulley, the maximum tension will be in the middle of it, and it no longer has any reason to arch in either direction.

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Factors influence reliability and Durability

Pulley condition The pulley surface must be smooth (No excessive wear, scuffing or

peeing) No sharp edges on the flanges ( No frayed edges)

Pulley alignment Misalignment causes belt running in extreme position, rubbing on

flanges and worn or frayed edges of belt

Belt tension Too low tension will lead to slipping of the belt an excessive wear and

over heating Very high tension will leads to excessive wear and possible or joint

fraction. There may be a problem, such as over heat, with bearings dueto excessive load

Shift fork Sharp edges causes frayed or worn edges of belts

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V belt

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V belt sections

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V belt metric section

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V Belt and bully sizes

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Belt geometry

Add the Listed Quantity to the Inside Circumference to Obtain the Pitch Length in

The pitch length Lpthe center-to-center distance C

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Power calculations

The design power

Hnom is the nominal power, Ks is the service factor, nd is the design factor. The number of belts, Nb, is the next higher integer to Hd/Ha.

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Power Ratings of Standard V Belts, KW

Belt-Length Correction Factor K2

Angle of Contact Correction Factor K1 for V Drives

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Force calculations

Some V-Belt Parameters

Service Factors KS for V-Belt DrivesThe number of belts, Nb, is the next higher integer to Hd/Ha.

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Life time calculationsT1, T2 : Equivalent tensions due to bending

Durability Parameters for V-Belt Sections

Lp: The pitch length in m

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V Belt power chart, Commercial

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V Belt tension force

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V Belt assembly faults

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Timing belt

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