Belts & Chain Drives Flashcards by Mark Mathot

The grip of a belt depends on these 3 things

Area of contact, materials of belt and pulley, tension in belt

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The most common belt materials

Cotton, leather, rubber, nylon

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Most common pulley materials

Cast iron, pressed steel, die-cast alloys

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How is installed belt tension expressed

Percent elongation or percent tension

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The tension needed on the belt to transmit power without slipping

Effective tension

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What is the run in time of a new belt

12 to 24 hours before re-tension

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How can you check belt deflection

Halfway between the two shafts apply force so for 1/64” for each inch of distance.
Ex. Center distance = 32” = 32/64 = 1/2”

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Formula for belt length

((D+d) / 2) x π + (2C)

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How can you control belt slip

Use smaller pulley ratios

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What causes creep

The elasticity of the belt

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In this belt, the drive members (power plies) carry the forces to transmit power

Flat belts

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This belting contains a single row of cords

Compass

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Name the 3 types of ways to join a belt

Chemical - Use adhesives
Vulcanized - Use heat and pressure (strongest)
Mechanical - Hinges, lacing, plate

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V-belt efficiency

93%

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Velt construction (four sections)

Top section - extension section
Bottom section - compression section
Neutral section - give belt it’s tensile strength
Cover section - protect inner parts from wear, only part that touches the sheave

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Cord construction for long, heavy drives

Multi-layer

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Belt with two ropes that have high load capacity and great flexibility

Grommet

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How are conventional V-belts classified

A - 0.50"
B - 0.66"
C - 0.88"
D - 1.25"
E - 1.50"

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How are high-capacity V-belts classified

3V - 3/8”
5V - 5/8”
8V - 8/8” (1”)

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How much more horsepower can High capacity V belts transmit

3 times

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What does 3V250 and 8V500 mean

3V250 = 3/8 width and 25" pitch line 
8V500 = 5/8 width and 50" pitch line

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Light duty belts are also called this

Fractional horsepower belts

ex. 3L, 4L, 5L

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Type of V-belt where both halves absorb compression and tension

Double-angle V-belt

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Another name for positive drive belts

Timing or gear belts (have teeth)

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What does 390 L 100 mean

Pitch length = 39" (390 / 10) Pitch of drive = light Belt width = 1" (100 / 10)

Also referred to as multi-ribbed or V-ribbed belts

Poly V-belts (rib spacing of 3/32, 3/16, and 3/8) | Pitch line above the sheave

Operate at high ratios, retain contact under extreme conditions of misalignment and tension

Poly V-belts

Referred to as joined V-belts, group V-belts or grip-bands

Power band V-belts

Whats the most efficient rim speed

4000-6000 ft/min (3500 says Rob)

When are drives needed to be dynamically balanced

over 5000 ft/min

Surface speed formula

SS = .262 x RPM x D

Why are idler pulleys used

increase arc of contact | act as take up (cause a reverse bend in belt, shortens life)

How big should a outside idler be

One third larger than smallest drive pulley

How big should an inside idler be

As large or slightly smaller than the smallest drive pulley

How do you determine the width of a flat belt

Pulley face is one inch wider than the belt for pulleys up to 6 inches wide Two inches wider than the belt for pulleys over 6 inches wide

The higher the belt speed, the ______ the required crown

smaller

What is the groove angle of the sheave

Between 34 and 42 degrees

How should a proper belt fit on a sheave

Flush or slightly above outside diameter of the sheave

The two types of variable speed drives

Adjustable centres and Fixed centres (adjust while running)

Offset link designed for high speed or heavy service

Two-pitch

Chain roller dimensions

``` Pitch = 120 = 12/8 Width = 5/8 x pitch Roller diameter =5/8 x pitch Pin diameter = 5/16 x pitch Link plate thickness = 1/8 x pitch ```

Multi-strand chains are up to this many wide

What does 100-2H chain mean

1-1/4" pitch, regular, 2 strand, heavy series 0 = regular 1 = lightweight 5 = rollerless bushing

What does the letters C and A mean for chain

``` C = Rollerless A = Standard ```

Chain used for maximum power with the smallest pitch size

Multiple strand roller chain

Chain that consists of a series of toothed link-plates assembled on pin connectors. For high speed drives

Silent chain

What does a D 40 B 15 sprocket mean

``` D = Double - indicates number of strands in the chain 40 = chain number B = Hub type 15 = Number of teeth on sprocket ```

When can a sprocket be used with double pitch chain

With 36 teeth or more (less than 36 are cut specifically for double pitch chains)

Efficiency of roller chain drive assemblies

98% - 99%

How much centre distance of chain is adequate

30 to 50 pitches (20 for pulsating loads) | At least one third of teeth should engage chain (120 degree wrap)

The driven sprocket should not exceed this many teeth

120

Speed ratio formula

Speed ratio = N teeth on driven / n teeth on drive

Sprocket ratios that are allowed

12:1 for low speed (100 rpm max) Up to 7:1 for single chain Use a double reduction drive or countershaft for over 5:1

Recommended amount of slack for horizontal chain drives and vertical

2% (less for reversing or shock loaded) | Vertical chain one-quarter the chain pitch

On chain drives where should an outside idler go

towards the smaller sprocket

On chain drives where should an inside idler go

Middle, slightly towards the larger sprocket

When can chain guide rails be used

speeds less than 300 ft per minute

When should chain be replaced

When the extension is 1% to 2%

How much of a load can an open-ended belt carry compared to an endless belt

1/3 of the load

Maximum misalignment of the sheaves must not exceed this

1/16" per foot of distance

Should you use idlers on reverse drives

When transmitting power from a horizontal shaft to a vertical shaft use this

Quarter-turn drive (maximum speed ratio 2.5:1)

What temperatures are belts cured to operate at

60 C (Can use heat treated belts over that temp)

What is the minimum arc of contact for a synchronus belt

60 degrees (6 teeth must be engaged)

The strongest and most energy efficient belt tooth design

Rounded tooth

Double strand chain is approx this much stronger than single

1.7 times

The offset link of a silent chain is called

hunting link

Slip fit master links reduce the working capacity by this much

30%

The name of sprockets with an odd number of teeth

Hunting tooth