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Red Seal Study Prep > Gearing > Flashcards

Gearing Flashcards

1
Q

For gears to mesh properly they need:
Same diametral pitch
Same pressure angle
Correct hand of gear (unless straight)
Shafts in the correct position
And?

A

Same helix angle

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2
Q

Two types of gear profiles?

A

Involute and straight

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3
Q

Describe involute tooth profile?

A

Most gears use involute, provides the smoothest tooth profile

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4
Q

Straight cut teeth are:

A

Noisy
Not suitable for high speed or power applications

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5
Q

What are some main causes of gear wear?

A

Lack of lubrication
Abrasives in the gear train
Incorrect tooth contact
Extended heavy loads

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6
Q

What can be a sign of excessive wear in gears?

A

Excessive backlash

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7
Q

What is floating gear or shaft?

A

When one gear or shaft is allowed to move axially to its best position. Common with double helical and herringbone gears

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8
Q

Why is most of the wear in gearboxes on the drive side of the tooth?

A

Typically most gearboxes run in one direction

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9
Q

On large large hypoid gears you can flip the gears to extend ________ ?

A

Service life of the system by flipping the gear you can transmit force onto the coast side

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10
Q

Simply speaking addendum is?

A

Top half of the tooth

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11
Q

Simply speaking dedendum is?

A

Bottom half of the tooth including clearance

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12
Q

Whole depth on a gear?

A

Addendum + dedendum

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13
Q

Working depth

A

Addendum + dedendum - clearance

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14
Q

Why is clearance important?

A

Lack of clearance will cause binding, increased friction and loss of power.

Clearance allows room for lubricant and thermal expansion

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15
Q

Steeper helix angles lead to smoother tooth action, but?

A

Have more sliding friction and greater axial thrust

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16
Q

What is a start on worm and wheel?

A

Number of thread starts on the worm.

The more the worm has the faster the worm wheel advances in one turn.

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17
Q

What way could you check for contact pattern?

A

Red lead or pursian blue with oil

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18
Q

What is backlash?

A

Clearance between gear teeth at the pitch line.

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19
Q

If the diameteral pitch number is small, gear teeth are physically ______?

A

Large

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20
Q

Binding can be checked by rotating gears without load.what can cause binding?

A

Lack of backlash or clearance between mating teeth
- incorrect centre distance between gears
- gear centre out of tolerance
- bent shaft or shaft deflection under load
- thermal expansion of the gears and the housing

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21
Q

Meshing teeth must have the same _______?

A

Pressure angle

20 degree pressure angle is stronger because it is wider at the base

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22
Q

For gears to mesh properly they must have:

A
  • same diametral pitch
  • same pressure angle
  • correct hand of gear
  • shaft in the correct position
  • same helix angles
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23
Q

What tooth profile is smoother, involute or straight?

A

Involute

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24
Q

When even number of gears are used the last gear rotates in what direction?

A

Opposite of the first one

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25
Q

If an odd number of gears are used the last gear rotates in the _______ as the first gear

A

Same direction

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26
Q

Which direction do internal gears rotate in?

A

Same direction

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27
Q

Do idler gears count in gear ratios?

A

No but they change the direction of gear rotation in a gear system

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28
Q

Why do you need an idler gear in a gear setup?

A

To keep the same direction of travel

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29
Q

Gears that transfer power with no change in speed?

A

Driven sprocket has same teeth as drive sprocket. Expressed as 1:1 ratio

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30
Q

If the gear box is a speed reducer it is expressed as a ratio 2:1. What does that mean?

A

For every 2 revolutions of the input shaft there is 1 rotation of the output shaft.

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31
Q

How do you figure out reduction ratio?

A

Divide driven teeth by drive teeth.

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32
Q

How can you tell if it is a speed increaser or reducer? Often called overdrives

A

If the ratio is not a whole number

.50:1

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33
Q

If you increase torque you decrease _______?

A

Speed

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34
Q
A

1: shafts parallel to each other
2: centrelines intersecting at right angles
3: centrelines crossing at right angles
4: special cases where intersecting or crossing not at 90degrees

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35
Q

External spur gear

A

Direction of gear and pinion is different. If they need to be the same an idler must be used

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36
Q
A

Internal spur gear:
- rotate same direction
- compact
- carry same loads/speeds as external
- more teeth engagement
- quieter

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37
Q
A

Rack and pinion gear:
-Convert rotary motion to a linear motion
- rack is the flat part

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38
Q
A

Helical gears:
- similar to spur gears but except gear teeth are on an angle to the bore of the gear.
- helix angle varies from a few degrees to the standard 45 degrees
- creates a smooth quite drive

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39
Q

When parallel shafts are connected by a single set of helical gears the shafts develop axial thrust. The direction of the thrust depends on:

A
  • Weather the shaft is a drive or driven
  • direction of rotation
  • the hand of the gear on the drive shaft
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40
Q

Axial thrust is compensated by?

A

Axial thrust bearings
Thrust of the driven shaft is always opposite to the direction of thrust of the drive shaft

41
Q
A

Double helical gears:
- two helical gear pairs of opposite hands
- thrust generated in one of the gears is counteracted by the thrust in the other hand

42
Q
A

Herringbone gears:
- slow turning heavy loads
- thrust is counteracted

43
Q
A

Straight bevel gears:
- connect shafts that intersect at right angle
- smaller gear is the pinion
- larger gear is the ring gear
- straddle mount or overhung
- produce axial and radial thrust

44
Q

Straight bevel gears have _____ teeth
Spiral bevel gears have ______ teeth
Zerol bevel gears have _______ teeth

A

Straight - run noisily create thrust
Spiral - curved create axial thrust
Curved - run smooth and quite

45
Q
A

Mitre gears: brush saw head
- used to change shaft direction without altering the drive ratio
- need thrust bearings

46
Q
A

Hypoid gears (rear differential)
- transmit power between shafts that cross but do not intersect
- extremely smooth running

  • disadvantage is the sliding action requires EP lubricant to reduce excess friction
47
Q
A

Worm and wheel:
- connects shafts that cross
- helical teeth around the worm shaft are called threads.
- gear ratio is obtained by dividing # of teeth on the worm gear by # of starts on the worm

48
Q

What are the contact patterns in worm and wheel gears

A

Non throated contact - linear pitch

Throated contact - circular pitch. Forms to the worm gear

49
Q
A
50
Q

What is PIV (like variable speed belt drive)

A
51
Q

When preloading worm and wheel bearings the shims usually go where?

A

Between the retaining cap and the housing

52
Q

When applying shims to worm and wheel you split the required shims in half and place them under each cap. Then what?

A

Wipe coating of bluing onto the worm
- rotate the worm in desired direction
- check the gear to see where the worm contacts the teeth
- adjust worm by transferring shim gaskets from one cap to another
- refer to owners manual for proper specs

53
Q

What hand are most worm and wheels?

A

Clockwise (right hand)

54
Q

Single reduction worm and wheel gear boxes come in speeds of 5:1 to ______

A

70:1

55
Q

Multiple reduction worm and wheel have two or more reductions, and may have different reduction _______?

A

Methods

56
Q
A

Planetary gear reduction:
- shafts can be inline
- may be reduction, overdrive, reversing, or direct drive.
- available in 1.1:1 to 50 000:1
- made up of sun gear, ring gear, carrier which holds the pinion gears

57
Q

Sun gear is the _______?

A

Centre

58
Q

Planet (pinions) travel where?

A

Surround and mesh with the sun gear

59
Q

Ring gear meshes with the ?

A

Pinion gear

60
Q

What is the reaction member in a planetary system

A

Part that is held

61
Q

If two members are locked in a planetary system what happens?

A

Produces direct drive

62
Q
A
63
Q

What are two ways reduction units can be mounted?

A

Indirect drive - V belt or chain drive

Direct mount - couple with a coupling both units bolted to a strong rigid base

64
Q

When using a v belt drive with a reducer can you have extra variations in the speed?

A

Yes by changing the v belt sheave sizes

65
Q

Reduction units are often lubricated with which method?

A

Splash

66
Q

Excessive noise and vibration?

A
67
Q

Unit runs hot?

A
68
Q

Oil seals leak

A
69
Q

Oil level drops but oil is clean

A
70
Q

Oil is dirty with even discolouration

A
71
Q

Oil is dirty with colour streaks or rings

A
72
Q

Bearing failure

A
73
Q

What are the four methods of checking mesh patterns?

A

-Prussian blue (not layout bluing)
- Venetian red
- black light
- pencil lead

74
Q

How much bluing should be applied when checking gear mesh?

A

Thin film only

75
Q

When checking mesh after applying bluing you drive then worm either by hand or drill while applying ______ to output shaft?

A

Resistance

76
Q
A

Good mesh pattern

77
Q
A
78
Q

Lack of backlash can cause?

A

Noise
Overloading
Overheating of gears and bearings
Seizure and failure

79
Q

Backlash is measured by restricting the rotation of one gear member, usually the pinion. And measuring the rotational movement of the worm wheel on its______

A

Pitch circle (halfway up the tooth)

80
Q

If space is permitted a ______ should be used to check backlash. Other methods would be?

A

Dial indicator
Lead wire deformed between teeth
Using feeler gauges manually fitted between teeth

81
Q

Checking backlash on helical gears is checked by?

A

Attaching lead wire to one of the gears and feeding it through the gear teeth. As the wire travels between the teeth it is squeezed into the thickness that represents the backlash.

82
Q

If lead wire readings are not uniform you would check the _______ and _______

A

Shaft for straightness and gear bore for eccentricity

83
Q

Excess backlash is an indication of?

A

Teeth are wearing

84
Q

What is the primary cause of of gear teeth wearing?

A

Not fully film lubricated

85
Q

How can bearing positions on the shafts and within the housings be adjusted?

A

Machining or shimming. The thickness and positioning of the shims adjusts the axial float of the shafts to the desired position

86
Q

How is end float measured in a gear box?

A

Dial indicator Either can be mounted inside or outside the gearbox.

87
Q

When installing new gear box you should instal with ______ “ shims under all feet to allow for downward movement when aligning.

A

1/8 shims

88
Q

Soft foot when mounting a gear box results in?

A
  • distortion of internal parts leads to binding heating and eventual lubrication and bearing failure
89
Q

To ensure longevity of a shaft mounted gear box where should it be located?

A

Reducer should be mounted as close to the support bearing as possible.

90
Q

What is the best method of installing a shaft mounted gear box on a shaft?

A

Heat in oven to about 65degrees C (150F) expansion of the hollow shaft will allows you to slide it onto the driven shaft.

91
Q

What is a major hidden danger when overhauling high ratio planetary drives?

A

Reverse torque lockup.

92
Q

What are some telltale signs that indicate the overall condition of a planetary gear box?

A
  • stress cracks
  • heat rings
  • embedded metal particles
93
Q

What is the purpose of an oil scraper? It what happens if it is not installed close enough to the edge of the gears?

A

Scrape excess oil off the gears and distribute it to the bearings via the oil dam.

If the scraper is not mounted close enough to the edge of the gears it will not scrap enough oil to lubricate the bearings.

94
Q

When assembling a gear box that has oil dams why is it super important to inspect and clean all dam reservoirs and passageways leading to bearings?

A

A cracked scraper could lead to catastrophic failure of a broken piece fell into the gears

95
Q

Two types of gear tooth pitting?

A
96
Q

If new gears are not available what can be used to hand dress the teeth?

A

Tapered oilstones (abrasive files) with low viscosity light oil to remove sharp edged spots and burrs

Never use power driven rotary stones

97
Q

How can you check for residual magnetism?

And what is residual magnetism?

A

Good quality compass

Caused by production shops not running their magnetic tables and chunks through for the time required to demagnetize the gear.

98
Q

How can a welder be used to reverse residual magnetism in a gear box?

A

By wrapping the welding cable around the gear box then using the welder

Or

Strip down gear box and demagnetize

Red Seal Study Prep (5 decks)

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