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Millwright Level 2 > Gear Drives > Flashcards

Gear Drives Flashcards

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1
Q

What are the two types of gear drives?

A

Open - light duty

Enclosed gear drives

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2
Q

What do gear drives do?

A

Transmit force and motion

Connects shafts using a gear train

Reduce speed and increase torque by using reduction unit

Increase speed by using a overdrive unit

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3
Q

What is diametral pitch (DP)?

What is pitch diameter (PD)?

A

Total number of teeth on a gear divided by the pitch diameter.

DP = N / PD

PD= (NxOD)/(N+2)

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4
Q

What is the formula to figure out pitch diameter?

A

PD = (N x OD) / (N + 2)

N = number of teeth 
OD = outside diameter
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5
Q

What is needed to achieve a correct fitting gear assembly (mesh)?

A

Diametral pitch

Pressure angle

Tooth profile

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6
Q

What is the rack?

A

The spur gear with a straight pitch line and straight sided teeth.

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7
Q

What are the pressure angles of the spur gears?

A

14.5 or 20 degrees

20 degrees is preferred

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8
Q

How can you tell if the spur gear is 14.5 or 20 degree pressure angle?

A

A gear gauge

Or

measure the width of the teeth at the top and bottom.

If the bottom is wider than the top it is a 20 degree pressure angle

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9
Q

What is backlash?

A

The amount of play between mating teeth.

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10
Q

What is the purpose of backlash?

A

Allow for tooth expansion due to heat

Prevent interference with incoming and outgoing teeth

Allow lubrication to escape

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11
Q

What should be taken into consideration when deciding gear materials?

A

Load

Speed

Method of lubrication

Tooth form

Noise levels

Environment

Temperature

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12
Q

What material of gear can carry the most load and highest torque?

A

Steel gears that are heat treated.

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13
Q

What is the benefit of cast iron gears?

A

Easy to machine

Inexpensive

Has good wear resistance

Run quit

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14
Q

When are non ferrous metal gears used?

A

When corrosion resistance, cost or low weight is important.

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15
Q

Why would non metallic gears be used l?

A

Quite operation at high speeds

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16
Q

What are the 4 typical shaft arrangements?

A

Shafts parallel to each other

Centreline intersecting a right angles

Centreline crossing at right angles

Special cases when intersection of shafts is not 90 degrees

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17
Q

What are the two types of spur gears?

A

External

Internal

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18
Q

Can internal spur gears operate the same loads and speeds as external?

A

Yes but internal spur gear is a lot quieter

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19
Q

In a spur gear drive what is the pinion and what one is the gear?

A

The smaller gear is the pinion and larger is the gear

20
Q

What does a rack and pinion spur gear do?

A

They are used to covert rotary motion to linear motion.

Ex: open and close chute doors

21
Q

What is the standard angle for helical gears?

A

45 degrees

22
Q

How can you tell if a helical gear is left or right angle?

A

Place the bore of the gear vertically, if the teeth slope downward from right to left that means they are:

Right hand

23
Q

Single helical gears connecting parallel shafts must have?

A

The same helix angle

Same diametral pitch

Same pressure angle

Correct centre distance

Be of opposite hand

24
Q

True or false? When parallel shafts are connected by a single set of helical gears, the shafts develop axial thrust?

A

True

25
Q

How must you compensate for axial thrust?

A

Axial thrust bearings

26
Q

How can you determine direction of thrust?

A

The thrust of the driven shaft is always opposite to the direction of thrust of the drive shaft.

27
Q

How can single helical gears connect crossing shafts?

A

By meshing two of the same hand gears are meshed together

28
Q

Can double helical gears reduce thrust on a parallel shaft?

A

Yes, the thrust generated on one of the gears is counteracted by the thrust set up in the other gear mounted on the same shaft

29
Q

Where can herringbone gears often be found?

A

Slow turning, heavy loads

30
Q

Where are the teeth cut on bevel gears?

A

Teeth are cut on the surface of a cone

31
Q

In bevel gears what is the smaller gear called? What is the larger gear called?

A

Small gear = pinion

Large gear = Ring gear

32
Q

Where would find bevel gears?

A

To connect shafts that intersect, usually right angles.

Usually are a matched set

33
Q

If a bevel gear has a pitch cone angle of 90 degrees it is called a ______?

A

Crown gear

Crown gears are disc shaped

34
Q

If the pitch cone angle is greater than 90 degrees it is called a ________?

A

Internal bevel gear

Internal bevel gear is cup shaped

35
Q

How do you determine the bevel gears direction?

A

By viewing from the back looking toward the apex.

36
Q

When are mitre gears used?

A

Mitre gears are used to change shaft direction without alternating the drive.

37
Q

What is the ratio and pitch cone angle of mitre gears?

A

1:1 and 45 degrees

38
Q

When is a hyoid gear used?

A

When transmitting power between shafts that cross but do not intersect.

39
Q

What are some advantages of hypoid gears over spiral bevel gears?

A

For the same ratio, their pinion is increased in diameter

Higher ratio’s can be achieved with the same strength

They are extremely smooth running

Connect Shafts that do not intersect

40
Q

Do hypoid gears require extreme pressure lubricants?

A

Yes

Because of the sliding action that takes place between the teeth.

41
Q

When are worm and worm wheels used?

A

To connect shafts that cross

42
Q

What are the helical teeth around the worm shaft called?

A

Threads

43
Q

How do you calculate the gear ration on a worm and wheel set?

A

Dividing the number of teeth on the worm gear and dividing it by the number of starts on the worm.

44
Q

What are the three different contact patterns worm gearing sets can have when they are in the correct positions?

A

Non throated contact

Throated contact

Double throated contact

45
Q

What is non throated contact?

A

In non throated gear sets the teeth on the worm all have the same depth and linear pitch

46
Q

What is throated contact?

A

In throated contact, the tooth forms of the worm gear are modified to give better contact between the worm and worm gear

47
Q

What is the purpose of a reduction unit?

A

Reduce speed and increase torque

Millwright Level 2 (15 decks)

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