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mod 6 > 6.9 transitions > Flashcards

6.9 transitions Flashcards

1
Q

What are gears used for?

A

Mechanical advantages or to change the direction of movement

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2
Q

Why are gears used in conjunction with shafts and bearings?

A

To transmit power and reduce or increase rotational speed

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3
Q

What is a spur gear?

A

They have straight teeth parallel to the shafts axis

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4
Q

What do spur gears connect?

A

Parallel shafts only

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5
Q

What is bad about spur gears?

A

They can be noisy

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6
Q

When two spur gears mesh together, what is the larger gear called?
What is the smaller gear called?

A

The wheel gear
The pinion

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7
Q

When are external spur gears used?

A

When a change of speed is required and the shafts are parallel to each other

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8
Q

When are internal spur gears used?

A

When a change of speed is required whilst maintaining an overall minimum diameter

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9
Q

What are helical cut spur gears?

A

They connect parallel shafts but have their teeth cut at an angle

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10
Q

What is an advantage of helical cut spur gears?

A

Smoother and carry heavier loads. Also quieter and smoothly

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11
Q

What load do single helical gears transmit?

A

Axial

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12
Q

What does single helical gears having more teeth in a mesh do?

A

Provide a larger contact area so transmit more power

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13
Q

What are double helical gears?

A

They are two identical gears joined on the same axis with opposite teeth

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14
Q

What force does double helical gears act in and what needs to be in the receiving end?

A

Axial

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15
Q

What should a double helical gear degree not be larger than?

A

20 degrees

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16
Q

In wheels with herringbone teeth, what happens to the axial forces?

A

They cancel each other out.

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17
Q

When are herringbone gears used?

A

For transmission of large forces.

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18
Q

What are bevel gears?

A

Used between intersecting shafts and can be designed for any angle of intersection

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19
Q

Why are bevel gears quieter, smoother and can take heavy loads better than a size equivalent spur gear?

A

They have curved teeth

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20
Q

What are hypoid gears a progression of?

A

Spiral bevel gears

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21
Q

How do hypoid gears differ to spiral bevel gears?

A

The shafts axis are not on the same plane so do not intersect

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22
Q

What do hypoid bears suffer from and how is this fixed?

A

Heavy sliding contact so require constant lubrication

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23
Q

Are hypoid bears quitter and smoother than spur gears?

A

Yes

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24
Q

What are worm gears?

A

Non intersection shafts not always at right angles

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25
Q

What do worm gears consist of?

A

A worm screw that drives a worm wheel (similar to a spar gears)

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26
Q

What do worm gears offer?

A

High reductions in simple steps.

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27
Q

Why are worm gears inefficient?

A

Large sliding movement of their teeth

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28
Q

What are worm gears good at?

A

Being driven in both directions

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29
Q

What is rack and pinion?

A

A gear system that is used to transmit motion between a rotating spur gear and linear toothed rack

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30
Q

What forces do rack and pinion gears transmit?

A

Rotational motion into linear motion

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31
Q

What are rack and pinion used for?

A

Leading edge flaps for extension and retraction

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32
Q

When is a mechanical advantage not gained?

A

If the drive and driven gear have the same number of teeth

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33
Q

What is the direction of the shaft and the rotation of the neighbouring gear?

A

Opposite

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34
Q

What is the gear ratio?

A

Number of teeth on A
Number of teeth on B

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35
Q

What are idler gears also known as?

A

Intermediate gears

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36
Q

What is one thing an idler gear is used forr?

A

To make the output gear move in the same direction as the input gear

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37
Q

What is another thing an idler gear can be used for

A

To link gears where there is a gap between them

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38
Q

Does the presence of an idler gear make a difference to the ratio of speed?

A

No

39
Q

For even numbers of gears from the input gear, what is the rotation?

For odd numbers of gears?

A

Opposite the first gear

The same

40
Q

How is the direction of rotation calculated?

A

By counting the number of gears because the driven gear and the gear

41
Q

What must engines operate at for high efficiency?

A

High speeds

42
Q

High speeds

A

An arrangement by which an input speed can be lowered to obtain a slower output speed with the same torque

43
Q

What does a reduction gear assembly consist of?

A

A set of rotating gears connected to a shaft

44
Q

What is the reduction gear assembly known as?

A

The reduction gear box

45
Q

What are epicyclic and planetary gears used for?

A

Reduction gearing in aircraft engines

46
Q

whatan does a epicyclic gear consist of?

A

Two mounted gears so that the centre of one gear revolves around the centre of the other (planets around the sun)

47
Q

What is the meshing and pattern of a gear determined by?

A

How the teeth mate

48
Q

What can happen if the gears are meshed too high?

A

The load is transmitted to the smallest portion of the tooth breaking the teeth

49
Q

Where is the ideal placement of teeth?

A

The middle

50
Q

What can happen if the teeth are too low?

A

They will not lubricate

51
Q

What can the pattern and meshing be?

A

Adjusted for direction

52
Q

What is gear backlash?

A

The gap between the gear teeth and the meshing point to allow for lubrication and prevent overheating

53
Q

What can gear backlash cause?

A

Lost motion (deviation) making it difficult to achieve accurate positioning

54
Q

What is an indication of worn gearing?

A

Excessive backlash

55
Q

What is a belt?

A

Used to link or drive two or more rotating shafts

56
Q

When are belts often used?

A

In parallel and offer high speed power transmission that is resistant to slipping and misalignment

57
Q

How can belts be used?

A

Can be driven in one direction
Can be crossed so that they work in reverse

58
Q

Why else can a belt be used?

A

To change the speed of rotation, either up or down

59
Q

What are two types of belts?

A

Friction and positive drive

60
Q

What are friction drive belts?

A

They rely on friction between belt and pulley to transmit power. They require tension

61
Q

What are positive drive belts?

A

Rely on the engagement of the teeth on the belt with grooves on the pulley. There is no slip apart from ratcheting or tooth jumping

62
Q

What are leaf chains?

A

A simple form of steel chain only consisting of a link plates and pins

63
Q

What is good about leaf chains? Compared to roller chains

A

They are strong and have high tensile strength compared to roller chains

64
Q

What do leaf chains not have and how does this affect their work?

A

Roller or bushes meaning they are only to be used for low speed applications and lubricated regularly

65
Q

What is an advantage of chain drives?

A

The chain cannot slip on the sprocket because of the teeth

66
Q

What is a disadvantage of chain drives?

A

They are heavy noisy and expensive

67
Q

Where are chain and sprocket gears used?

A

On areas were slipping must not occur

68
Q

On areas were slipping must not occur

A

Sheaves and is fitted with a clevis at each end

69
Q

What are roller chains comprised of?

A

Link plates and pins
Rollers and bushes

70
Q

What must the size of the chain link match?

A

The size and spacing of sprocket teeth

71
Q

What is a sprocket?

A

A toothed wheel that fits onto a shaft

72
Q

How is a sprocket stooped from rotating on the shaft?

A

By locking it with by a key way or grub screw

73
Q

How many sprockets do chains connect?

A

Two

74
Q

Why are sprockets called power transmission chains?

A

They can transmit motion and force

75
Q

Why are v belts used?

A

Low cost and ease of installation

76
Q

Low cost and ease of installation

A

Low cost and ease of installation

77
Q

What is the biggest advantage in the V belt?

A

The wedging action in the pulley groove

78
Q

What do v ribbed belts consist of?
What does the rib ensure?

A

Fist belts and V belts

The belt tracks properly making alignment less critical

79
Q

What is a positive (Synchronous) belt?

A

The tooth profile is a trapezia
design

80
Q

What properties does a synchronous belt have?

A

A flat belt with evenly spaced teeth perpendicular to the axis of the belt

81
Q

What do timing belts rely on?

A

Engagement with belt teeth on the sprocket, not friction

82
Q

Where are timing belts used?

A

Where exact synchronisation between driver and driven shaft is required

83
Q

What is a V belt pulley?

A

They have a geometry if the grooves located around the pulley to gain traction on a V belt

84
Q

What are V belt pulleys used for?

A

Transmit power between two parallel axels

85
Q

What do synchronous belt pulleys mate with?

A

The same pitch as synchronous belts

86
Q

What are the advantages of synchronous belts?

A

They’re quiet, are non slip and non lubricated operation. They have low maintenance requirementsv

87
Q

What is a stepped or cone pulley drive?

A

A system of pulleys made up from

88
Q

What does a step pulley consist of in terms of configuration?

A

2 to 4

89
Q

When can the same belt tension be achieved?

A

When the sum of both working stages are identical

90
Q

What is good about V ribbed belts?

A

They can run at high speeds

91
Q

Why is pulley alignment critical to flat belts?

A

Because there is no chance of belt slip off

92
Q

What is not advised with flat belts?

A

High outputs at high speeds

93
Q

What are modern belts made out of?

A

Aluminium and nylon with rubberised plastic

94
Q

What do timing belts not rely on?

A

Friction

mod 6 (12 decks)

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