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Millwright Manual > Chapter 10 - Belt Drives > Flashcards

Chapter 10 - Belt Drives Flashcards

1
Q

What are the merits of belt drives?

A
  • offer a good wide range of shaft centres (the distance between the axes of two parallel shafts) with versatility of sheave or pulley diameters
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2
Q

How is power transmitted from pulley to belt?

A
  • friction drives
  • transmit power by means of a belt pressed tightly onto a pulley
  • the power of the prime mover is transmitted to the pulley by the belt
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3
Q

How is area of contact determined on a belt?

A
  • depends on:
    — pulley diameter
    — centre-to-centre distance
    — take-up devices used
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4
Q

What types of materials are required for belts?

A
  • cotton
  • leather
  • rubber
  • nylon or other synthetics
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5
Q

How is the coefficient of friction determined between belt and pulley?

A
  • the frictional grip varies with the coefficient of friction between the belt and pulley
  • it is determined by the belt and pulley materials and their surface structures
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6
Q

Define installed tension and effective tension

A
  • installed tension
    — the tension on the belt when the drive is not running
    — for flat and v-belts, this is expressed as percent elongation or percent tension
  • effective tension
    — the tension needed on the belt to transmit power without slipping
    — when the drive is running, the pull on the belt increases the tension and stretch on the tight side as it overcomes the resistance of the load
    — the slack side had no tension increase because it simply returns the belt to the driven pulley
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7
Q

How much force is required to deflect the following new belt:

D size V-belt correctly installed on sheaves, 40” centre-to-centre?

A
  • 26 pounds for new belt

- 22 pounds after run-in

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8
Q

How much deflection should the mentioned belt have?

D size V-belt correctly installed on sheaves, 40” centre-to-centre?

A
  • 40/64 = 0.625” = 1-1/8”
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9
Q

What is the approximate length of belt required for the following drive:

1 sheave 16”
1 sheave 8”
Centre-to-centre distance is 50”

A
  • belt length = (D+d/2)Pi + 2C
D = large diameter pulley
d = small diameter pulley
C = shaft centres
Pi = 3.1416
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10
Q

What are the causes of slip and how is slip controlled?

A
  • slip is caused by the surface characteristics of the belt and pulley
  • severe slippage burns the belt
  • it also polished the belt and pulley surfaces, reducing friction grip between the belt and pulley (pulley should look smooth and rather dull, NOT shiny)
- Causes:
— the driving pulley is too small
— the load is too great
— the belt is running too loose
— the belt is not being properly cleaned and tensioned
  • Controls:
    — using smaller pulley ratios (3:1 or 4:1)
    — aligning the pulleys correctly
  • ensuring adequate take-up
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11
Q

Describe creep

A
  • a physical characteristic of a belt affecting power transmission
  • caused by the elasticity of the belt

1 - belt on the slack side is delivered to the pulley slower than the rate at which it comes off the tight side
2 - the belt creeps ahead on the pulley and he belt surface runs slower than the belt as a whole

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12
Q

What are the purposes of flat belts?

A
  • used in conveyors and drip belts, where the belt itself carries the load
  • in a flat belt, the drive members (power plies) carry the forces to transmit power
  • they may be embedded in substances such as rubber and encased in covers to provide protection and traction
  • if the top side is unrecognizable, it will be marked
  • if the drive direction is important, it will be marked
  • flat belts may be manufactured as:
    — endless (continuous loop)
    — reel-stock (open-ended), must be fastened together
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13
Q

Briefly describe the following belt materials:

- leather

A
  • have single or multiple layers
  • May be combined with other materials such as cords and polymers
  • leather belts are being replaced by rubber or synthetic belts
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14
Q

Briefly describe the following belt materials:

- rubber

A
  • made from fabric or cord impregnated with natural or synthetic rubber compounds
  • provide various degrees of:
    — strength
    — stretch
    — pulley grip
    — protection against abrasion, oil, or moisture
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15
Q

Briefly describe the following belt materials:

- fabric

A
  • made from cotton or synthetic fabrics, with or without rubber impregnation
  • made in layers and are 3-12 ply, depending on their width
  • direction of the weave varies, but alternate layers have their fibres running in different directions for added strength
  • used for moderate loads and speeds
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16
Q

Briefly describe the following belt materials:

- cord

A
  • have drive members made from twisted cotton or synthetic cords embedded in rubber
  • the rubber has a fabric cover to protect against wear
  • heavy-duty belts, used for high-speed, small-pulley, shock-load applications
  • compass belting (folded or rolled edges) contains a single row of cords
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17
Q

Briefly describe the following belt materials:

- steel-cable

A
  • similar in construction to cord belts

- high-capacity and lower stretch than cord flat belts

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18
Q

Briefly describe the following belt materials:

- nylon and other synthetics

A
  • flexible to permit use on small-diameter pulleys

- nylon member is sandwiched between the outside cover and the pulley-side cover

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19
Q

Briefly describe the following methods of joining belts:

- vulcanized splices

A
  • use heat and pressure to create a bond

- these splices are the strongest and most efficient belt joints

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20
Q

Briefly describe the following methods of joining belts:

- chemical splices or synthetic ply belts

A
  • use adhesives
  • the type of belt determines the adhesive to be used
  • old and new belts may be chemically spliced together
  • a belt containing more than one synthetic may need two different chemicals
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21
Q

Briefly describe the following methods of joining belts:

- mechanical flat-belt fasteners

A
  • it is important to cut the ends properly so that the ends align properly before being fastened
  • various types of fasteners are used:
    — wire lacing
    — steel hinges
    — plate fasteners
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22
Q

What are the advantages of v-belts

A
  • wedging action permits lower arc of contact on small pulley and large speed ratio
  • shorter centre distances can be used to achieve a compact drive
  • they absorb shocks to cushion motors and bearings against load fluctuations
  • vibration and noise levels are low
  • maintenance and replacements are quick and easy
  • power transmission efficiency can be as high as 93% after run-in
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23
Q

Describe the construction of V-belts

A
  • v-belts can have a variety of sizes and cross sections, each with its own particular function
  • each has four sections:
    — the top section of the belt is the extension section. It is rubber and stretches as the belt wraps around the sheave

— the bottom section is the compression section. It compresses when wedged into, and shaped around, the sheave

— the neutral section of the belt neither compresses nor stretches. The driving members in this area give the belt it’s tensile strength

— the cover section protects the inner parts of the belt from wear. The cover is the only part in direct contact with the sheave.

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24
Q

What are the applications of the following V-belts:

- single-layer compass construction

A
  • used mainly on short-centre drives with small diameter pulleys
  • each strand is separated by, and bonded in, rubber.
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25
Q

What are the applications of the following V-belts:

- multi-layered cord construction

A
  • used for long, heavy drives
  • each strand is separated by, and bonded in, rubber
  • this type has two main bands of blocks or cords
  • these v-belts are designed to flex in only one direction and should not be used with reverse bending
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26
Q

What are the applications of the following V-belts:

- grommet-style construction

A
  • the layer or layers of small cords can be replaced by two grommets or ropes to carry the load
  • this style has both high load capacity and great flexibility
27
Q

How are fabric ply belts constructed?

A
  • several plies of fabric can be bonded together to make a driving section
  • like cord belts, they can be supplied with one of the following:
    — a single band on the pitch line
    — one band on the pitch line and another near the bottom of the belt
28
Q

What are the reasons for concave side-wall V-belts, notched V-belts, and joined V-belts?

A
  • concave side walls have more contact on sheaves when loaded
  • notches give belts increased flexibility and heat-dissipation capabilities
  • they are normally used in small-sheave, short-centre, and high-speed drives
29
Q

Are V-belts made to close tolerances when compared to roller chains?

A
  • v-belts are not manufactured with the same close tolerances as gears or roller chains
  • v-belts are made to an industry standard of section sizes and angles so that belts from different companies can be used on the same sheaves
30
Q

What are the five sizes of standard V-belts?

A
  • A, B, C, D, E
  • also called standard cross section
  • May have either straight or concave side walls
31
Q

What is the purpose of high-capacity V-belts?

A
  • also called wedge, hi-torque or narrow v-belts
  • sizes designated as: 3V, 5V and 8V
  • they can transmit up to three times the horsepower of standard v-belts in the same drive space, due to sheave groove design and increased contact area
32
Q

What size belt is a high-capacity 5V300?

A

— 5/8” width and 30” pitch-line length

33
Q

How are light-duty V-belts codes?

A
  • they have cross sections the same as conventional v-belts but coded 2L, 3L, 4L and 5L
  • these codes indicate width increments of 1/8”
34
Q

What are the purposes of double-angle and wide V-belts?

A

-

35
Q

What are the advantages and disadvantages of positive-drive belts compared to gears and chains?

A

-

36
Q

How are the pitch circle and the pitch line related in a positive-drive belt?

A

-

37
Q

What is the meaning of the code 400 H 100 with regard to a positive-drive belt?

A

-

38
Q

Why are positive drive-pulleys usually flanged?

A

-

39
Q

What are the purposes of double positive-drive belts and linked V-belts?

A

-

40
Q

Briefly describe poly V-belts

A

-

41
Q

What is the length of the following belt?

700L6

A

Briefly describe power band

V-belts

42
Q

How does a millwright ensure that matched belts are the same length?

A

-

43
Q

Calculate the rim and belt speed of the following:

Diameter= 11”
RPM = 1750
A

-

44
Q

What is the preferred location of an outside idler and what size is recommended?

A

-

45
Q

What is the preferred location of an inside idler and what size is recommended?

A

-

46
Q

What is used to install and disassemble tapered bushings?

A

-

47
Q

How are the size (diameter) and width of pulleys for a flat belt determined?

A

-

48
Q

What are the purposes of crowned pulleys?

A

-

49
Q

What are the applications for flanged flat belt pulleys?

A

-

50
Q

Where is the pitch line located on a V-belt?

A

-

51
Q

How should a belt fit the sheave?

A

-

52
Q

What is the advantage of combination-groove sheaves compared to regular sheaves?

A

-

53
Q

Briefly describe a V-flat belt drive

A

-

54
Q

Describe the two general types of variable-speed belt drives

A

-

55
Q

When should speed adjustments be made?

A

-

56
Q

What problems may be encountered when adjusting variable-speed drives?

A

-

57
Q

What factors ensure maximum belt life?

A

-

58
Q

How is alignment achieved?

A

-

59
Q

How are rubber belts stored?

A

-

60
Q

How and when should belts be inspected?

A

-

61
Q

What causes the following problems:

- slips and squeals?

A

-

62
Q

What causes the following problems:

- runs crooked?

A

-

63
Q

What causes the following problems:

- cracked outside ply?

A

-

64
Q

What causes the following problems:

- cracked inside ply?

A

-

Millwright Manual (24 decks)

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