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Second Year Millwright > Gearing And Variable Speed Drives > Flashcards

Gearing And Variable Speed Drives Flashcards

0
Q

What are the two types of gear drives

A

Open gear drives and enclosed gear drives

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1
Q

What are gears?

A

Positive power transmission devices that do not slip

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2
Q

Which gear drive system has more wear and why

A

The open drive system has more wear because of contaminants

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3
Q

How are you enclosed gear drives lubricated?

A

By either grease or oil

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4
Q

What is a gear set

A

Matched pairs of gears manufactured together

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5
Q

What is a gear train?

A

When two or more gears mesh or work together

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6
Q

What is a pinion?

A

When two gears have a different number of teeth, the lower number is called the pinion

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7
Q

What is a crown gear?

A

In a bevel and hypoid gear set, the larger set is called a crown gear or a ring gear

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8
Q

What is drive and driven gear

A

Drive=power in

Driven=power out

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9
Q

What is direct drive?

A

When the input and output is the same speed. It is often used to change directions.

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10
Q

What happens when speed is reduced?

A

The output has an increase in torque. The result is a mechanical advantage

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11
Q

What is an overhung gear?

A

It has a bearing support on only one side

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12
Q

What is a straddle mounted gear?

A

Gears that are mounted between bearings

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13
Q

What is a compound gear train?

A

They have three or more shafts and four or more gears

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14
Q

What is preloading of bearings?

A

Giving the bearing less than zero axial clearance. This is common with tapered roller bearings in a worm gearbox

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15
Q

What can an increase in backlash be an indication of?

A

Gear wear

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16
Q

What is a floating gear or shaft?

A

Where the fear or shaft is allowed to float axially to its best position

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17
Q

Describe how to tell if a helix angle gear is LH or RH

A

When viewing from the shaft angle, if the teeth point up to the right, it’s a RH and vice versa

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18
Q

Parallel shafts must have what combination of angled gears?

A

Must use opposite hand gears

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19
Q

Crossing over shafts must have what combination of angled gears?

A

They must have the same hand gears (such as in a worm gear)

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20
Q

Describe a worm and worm wheel gear set

A

The worm is the smaller gear, and the worm wheel is is the larger circle gear

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21
Q

What is the drive side of gear teeth?

A

Most gearboxes rotate in one direction most or all of the time,so the wear is I the drive side of the teeth, and the side that doesn’t make contact is the coast side

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22
Q

What is the addendum?

A

The top half of the teeth

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23
Q

What is the dedendum?

A

The bottom half of the tooth

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24
What is the whole depth?
The addendum plus dedendum
25
What is the clearance?
The space between the bottom land of one gear, and top land of the meshing gear. It allows for lubricant, thermal expansion, and gear runout
26
What is the working depth?
The addendum, plus the dedendum, minus the clearance
27
What is the circular pitch?
Also called the gear pitch, it is the distance from the center of one tooth to the center of the next tooth, at the pitch circle
28
What is the pitch circle?
The diameter, at the pitch circle. It is approximately in the middle of the gear teeth.
29
What is crowning?
A slight curve on the face of the tooth from side to side
30
What is pressure angle?
It is the angle on the side of the tooth. Also known as the angle on the line of action which is the point of contact as the gear turns. The two common angles are 20° and 14.5°
31
What is a helix angle?
The angle of the tooth from the shaft axis of the gear is called the helix angle
32
Why are steeper helix angles stronger and smoother tooth action?
They are stronger because they have a longer line of contact however they have more sliding friction and create axial thrust
33
What is a start?
A term that describes the number of threads starts on the worm in a worm gear box
34
What is backlash?
It is the clearance between the gear teeth at the pitch line
35
What is diametral pitch?
It indicates to the size. It is the number of teeth on the gear divided by the pitch diameter
36
Binding can because by several factors. What are they?
Lack of backlash or clearance between the meeting Teeth, incorrect center distance between gears, gear center out of tolerance, bent shafts or shaft deflection
37
For gears to mesh properly, what must happen?
``` Same diametral pitch Same pressure angle of the teeth Correct hand of gear Shafts in correct position Same helix angle ```
38
How do you determine the rotation of odd and even gear combinations?
Even number of gears=opposite direction | Odd number=same direction
39
What do idler gears do?
Main function is to change direction. They can also change the center distance
40
What are the three common shaft positions?
Parallel, intersecting, crossing over at 90
41
What are spur gears?
Straight teeth, must be used in parallel shaft position. They generate no axial thrust.
42
What does a rack and pinion gear set do?
Transfers circle motion into linear motion
43
When is there maximum power transmission between teeth?
At the pitch line when the teeth meet it becomes a rolling action, that is the maximum transfer point. As they are coming into mesh it is a sliding action
44
What do some helical gears need in the oil?
They need an EP additive in the oil
45
What is a gear ratio of a mitre gear set?
They are always 1:1 and always at 90 degrees
46
Why are helical gears popular?
They are stronger because of the linear contact and have more teeth in contact at one time
47
What is benefit of double helix gears?
The opposite hand helixes cancel out the axial thrust
48
What are herringbone gears?
They are similar to double helical gears, but there is no gap in the middle, it comes to a point. They are recommended for high speed and heavy loads.
49
What are spiral bevel gears?
Stronger than straight bevel gears, and give a smoother transfer of power because they have more teeth in contact at the same time.
50
What is different about zerol bevel gears?
Because the teeth are curved they have more contact area, but the produce no axial thrust
51
Why are hypoid gears stronger than spiral bevel gears?
They have a larger pinion, have extensive sliding action, and because they are crossing over shafts, it can be straddle mount
52
What makes a worm gear self locking?
1 or 2 starts, and usually 30:1 ratio at least
53
What is worm lead?
The distance by which one tooth on the worm will advance in one turn PitchX# of starts=lead
54
Who do you determine gear ratio of a multistart worm gear?
worm wheel teeth divided by number of starts
55
What is a throated worm?
It is a worm shaped like an hourglass
56
Which arrangement gives the most tooth contact in a worm gear drive.
A double throated gear set
57
How should the worm wheel be set up?
It should be set up so the the contact is slightly towards the leaving side of the worm wheel
58
What are the components of a planetary gear set?
Sun gear, planetary gears with carrier, ring gear
59
What are concentric reducers?
The input and output shafts are on the same plane
60
What is an offset horizontal drive gearbox?
The input and output shafts are on a different plane.
61
How must torque arms be aligned?
90° angle between output and point of torque arm
62
What device do gearbox manufacturers use to absorb torsion shock load?
Spring type torque arm
63
Why is residual magnetism in rebuilt gearboxes bad?
Magnetism attracts and particles to wear surfaces
64
A good mesh pattern between gears that are mated is indicated by?
A central tooth pattern and not contacting on either edge
65
What is a mating gear mesh pattern?
The shiny metallic surfaces that show up when one tooth drives another
66
What are the two operational ranges that all variable speed mechanical drives operate in?
Constant torque and constant horsepower | Constant torque is when output speed is below input speed
67
How fast can leaf chain drives go?
Below 3000 rpm
68
Describe a PIV
A positively infinite variable speed reducer. Only good up to 900 rpm and requires EP lubrication
69
When should oil be changed in a chain drive?
Every 2000 hours. The oil will be full of metal flakes. This is normal
70
What are the three major components of the torque converter
The input impeller, the follower turbine, and the stater
71
How is output speed and power changed on the variable Fill scoop tube hydraulic Drive
By changing the amount of oil in the rotating case
72
What are the three basic spur gear arrangements
External, internal, rack and Pinion

Second Year Millwright (8 decks)

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