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Second Year > Gears > Flashcards

Gears Flashcards

0
Q

Enclosed gear drives

A
  • gear drives inside a gearbox

- oil or grease lubricated

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1
Q

Open gear drives

A
  • exposed to the outside

- more excessive wear

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2
Q

Gear set

A

-matched pairs of gears made together intended to mate with eachother

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3
Q

Pinion

A
  • when two gears mess, the pinion is the smaller gear

- generally the drive gear

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4
Q

Crown gear (ring gear)

A

-the larger gear in a gear set

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5
Q

Direct drive

A
  • when the input speed of the gearbox is the same as the output speed
  • 1:1 ratio
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6
Q

Speed reducer

A
  • when a small gear drives a larger gear

- output has more torque but less speed

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7
Q

Speed increaser

A
  • a faster output speed than input speed

- larger gear drives a smaller gear

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8
Q

Mechanical advantage

A
  • when a speed reduction occurs in a speed reducer which is an increase in torque
  • the larger gear radius acts as a longer lever
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9
Q

Overhung gears (overhung load)

A
  • has a bearing support on only one side
  • tend to have more shaft deflection
  • be sure to keep them very close to the bearing for support
  • crossing over each other like worm gears
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10
Q

Straddle-mounted gears

A
  • mounted between two gears
  • much stronger and has much less shaft deflection under loads than overhung
  • hypoid gear set
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11
Q

Internal gears

A

-have teeth on the inside diameter of the gear

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12
Q

**Compound gear train

A
  • 3 or more shafts and 4 or more gears

- 4:1 reduction, 3:1 reduction, 5:1 reduction in a train - final is 60:1

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13
Q

Preloads

A
  • a bearing in a gearbox is done by giving the bearing less than zero axial clearance
  • done by mounting the gears with tapered roller bearing and preloading the bearings by adding or subtracting shims from the bearing supports
  • common in worm gearboxes
  • ensure they track don’t skid
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14
Q

Gear wear

A

-quick check of backlash tells us how much wear there is

-

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15
Q

Floating gear or shaft

A

-Not set or fixed on a shaft

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16
Q

Right-hand or left-hand

A
  • if the direction of the gear goes to the left, its left

- gears with the same hand have to be a crossing over arrangement and can’t be parallel

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17
Q

Worm & worm wheel gear set

A
  • have the same hand gear arrangement
  • high speed reduction
  • worm wheel is the larger gear
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18
Q

Addendum

A

-top half of the tooth

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19
Q

Dedendum

A

-bottom half of the tooth including the clearance

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20
Q

Whole depth

A

-total height of the whole tooth, which equals addendum plus dedendum

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21
Q

Working depth

A

-equals the addendum plus the dedendum minus the clearance

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22
Q

Clearance

A

-Allows room for lubrication, thermal expansion of the gear and gear runout

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23
Q

Circular pitch (gear pitch)

A

-the distance from the centre of one tooth to the centre of the next tooth at the pitch circle

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24
Q

Pitch circle

A

-diameter of the gear measured at the middle gear teeth

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25
Q

Crowning

A
  • to prevent loading on the tooth

- a gear tooth is cutting a slight curve on the face of the tooth from side to side

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26
Q

Pressure angles

A
  • The slope of the tooth
  • the angle between the line of action and the line of tangent to the pitch circle
  • Most common 20 degrees and 14.5 degrees
  • messing gears have to have the same pressure angle
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27
Q

Helix angle

A
  • angle of the tooth from the shaft axis of the gear
  • larger tooth, larger point of contact makes the gear stronger
  • bad thing is the larger the helix angle the more thrust loads develop
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28
Q

Starts

A
  • describes the number of thread starts on the worm gearbox

- the more starts, the faster the worm wheel advances in one turn

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29
Q

Involute

A
  • the face of the tooth on many gears has a radius across the flank and the face of the tooth
  • this makes meshing with mating gears quieter and smoother
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30
Q

Backlash

A
  • clearance measured at the pitch line
  • rotational arc clearance between a pair of mounted gears
  • backlash increases diametral pitch
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31
Q

Diametral pitch

A
  • number of teeth on the gear divided by the pitch diameter

- the size of the gear tooth

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32
Q

Mesh

A
  • the contact and action between the teeth is sliding until both the teeth are in contact at their pitch line.
  • when the teeth are in contact at the pitch line, the action is rolling until the teeth begin to slide out of mess and pull apart
  • point of maximum power
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33
Q

Involute tooth profile

A

-provides the smoothest tooth profile

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34
Q

Straight tooth profile

A

-very noisy

35
Q

Gear rotation direction

A
  • when an even number of gears mesh with each other, the last gear rotates in the opposite direction of the first
  • if an odd number of gears mesh with each other, the last gear rotates the same direction as the first
  • an internal gear set has both gears moving in the same direction
36
Q

Idler gears

A
  • Change the direction or keep it the same
  • can connect two gears with a centre to centre distance that is greater than the diameters of the gears
  • ask as moveable gears to set backlash and mesh patterns
37
Q

Speed vs. Torque

A
  • speed & torque are inversely proportional

- power in is the same as power out, gears make it so only the speed and torque change

38
Q

Parallel shaft position

A
  • spur gears
  • helical gears of opposite hand
  • double helical gears
  • herringbone gears
39
Q

Intersecting

A
  • shafts at 90 degrees to each but on the same plane
  • bevel gears
  • mitre gears
40
Q

Crossing over at 90 degrees

A
  • 90 degrees to each other but on different planes
  • worm gears
  • hypoid gears
  • helical gears of the same hand
41
Q

Spur gears

A
  • only suitable for shafts that are parallel to each other
  • teeth are straight
  • develop no axial thrust
  • noisy
  • not as strong as helix gears because of the length of the teeth
  • external, internal and rack and pinion
42
Q

External Spur Gear

A

-teeth cut on the outside of the gear blank

43
Q

Internal

A

-when a smaller, external cut gear meshes with a larger internal cut gear

44
Q

Rack & pinion

A
  • Converts rotary to linear
  • when spur gears are cut on a linear surface and mesh with a gear that has external teeth
  • during the maximum power transfer, the action is rolling, the torque is limited to one tooth in full contact at a time
45
Q

Single helical gears

A
  • stronger and have more teeth in contact at one time than a spur gear of the same size
  • meshing action is smoother
  • some require an EP additive in oil
  • increased sliding friction
46
Q

Double helical gears

A

-2 rows of helical teeth of opposite direction

-

47
Q

Herringbone gears

A
  • same as helical but no groove between the two sets of teeth
  • high speed applications
48
Q

Bevel gears

A

-most common intersect at a 90 degree angle

49
Q

Mitre gear

A
  • Ratio is 1:1
  • always intersect at 90 degrees
  • change in output shaft direction
  • develop axial loads
50
Q

Straight bevel “angular”

A
  • angular or 90 degrees

- low torque because of thin grooves on driven gear

51
Q

Spiral bevel gear

A
  • Stronger than straight and give a smoother transfer of power because they have more teeth in contact at the same time
  • have axial thrust
52
Q

Zerol bevel gears

A
  • Similar to straight but teeth are curved like those on spiral
  • no axial thrust
53
Q

Hypoid gear

A
  • A bevel gear that forms a drive between 2 shift that cross over at 90 degrees
  • very high sliding friction
54
Q

Worm gears

A
  • both worm and worm wheel are the same hand
  • worm is very quiet, smooth, steady with no vibration
  • 30:1 ratio and 1-2 starts is considered self locking
  • has excessive sliding action
55
Q

Worm lead

A
  • the distance by which one tooth on the worm advances in one turn
  • pitch x # starts=lead
56
Q

Planetary gear system

A
  • a sun gear, a carrier & a ring gear
  • draw three dots in a straight line down, R,C,S. Put an x in the hold gear, then draw a line from the line from the x to the driver
56
Q

Throated or non-throated worms

A
  • throated is shaped like a cylinder
  • non throated shaped like an hour glass
  • this has a large effect on how much tooth contact the gears have, which determines the power transfer capabilities of the gear set
57
Q

double throated

A

-maximum gear tooth contact. more contact least pressure

58
Q

worm gear contact

A

-set up so the contact between the teeth is slightly toward the leaving side of the worm wheel

58
Q

single reduction gearbox

A

-2 shafts with 2 gears, with one gear mounted on each shaft

59
Q

Double or multiple reduction gearbox

A
  • have at least 3 shafts and 4 gears

- input gear is small, output gear has to be larger

60
Q

concentric reducer

A

-have input and output shafts on the same plane

61
Q

Active or drive side flank

A

-driven tooth that is marked with bluing after gears are turned

62
Q

Correcting mesh pattern

A

-adjust shims. this doesn’t affect the preload, just the position of the wheel

63
Q

tolerance stack up (in new gears)

A

-any abnormal patterns disappear as the gears wear

64
Q

Proper belt tension

A

-as loose as possible without slipping

65
Q

tie rods (torque arms) on shaft mounted gearboxes

A

-mounted at 90 degrees between output and point of torque arm attachment

66
Q

fin fans

A

-force air through heat exchangers to release unwanted process heat

67
Q

Variable Speed drive

A
  • constant torque range occurs when the output speed is below the input speed
  • constant horsepower occurs when output speed is greater than the input speed
69
Q

Changing lubricant

A

-every 20,000 service hours or after 4 years

70
Q

Grease in bearings

A

-cleaned and packed every 10,000 service hours

71
Q

Wide belt drive

A
  • use adjustable diameter pulleys
  • turning a hand wheel so the driving pulley faces move either closer together or farther apart
  • this MUST be done while the unit is running
  • best performance is 1:1 ratio
72
Q

Offset reducer

A

-input shaft and the output shaft are usually on different planes

73
Q

Woodblock belts

A
  • a variable speed wide belt
  • Must be replaced when showing signs of lipping
  • for high torque and low speed
74
Q

Narrow Belt Drives

A
  • can be fixed centre drives where the driven and driver can’t be adjusted
  • they have an adjuster on one pulley which is manually to set the the input to output speeds at 1:1 to 8:1
75
Q

Hydrodynamic Variable Speed

A

-make it possible to regulate the torque by varying the amount of pressure fluid in the work cavity

76
Q

Variable speed chain drive

A
  • metal chains used for applications below 3000 rpm, where speed, positive drive, accuracy & long life are required
  • use leaf (laminated) chain
  • chains do not slip
  • change oil every 2000 hours to remove the metal flakes
  • require extreme pressure lubrication
77
Q

Closed loop hydrostatic variable speed drive

A
  • Input shaft connected to a variable displacement hydrostatic pump
  • output of the pump is routed through various pipes and components fixed displacement hydrostatic motor
  • oil returns from the motor goes back to pump completing the loop
79
Q

torque converter

A
  • oil leaving the impeller (pump) at high speeds, goes to the turbine (follower) then to stator.
  • stator takes the returning oil and redirects it back to the impeller blades on the inlet side. This action (stator) causes the torque to increase rapidly increase
80
Q

Variable Fill (snoop tube) Hydraulic drives

A
81
Q

Variable speed wet disc drive

A

-have constant input speed, usually 1760 rpm and an output of 0-1760 depending on the required speed of the load
-input has metal discs and output has sintered bronze discs
-a rotating hydraulic piston on the input shaft squeezes the discs together to transfer the power from input to output with slippage
usually have a cooler to handle the heat due to friction
-refinished by hand cross dressing with #600 wet & dry paper

82
Q

Gears meshing require

A
  • same diametral pitch
  • same pressure angle
  • same helix angle
83
Q

Face of the tooth

A

-contact point of the tooth on the addendum

84
Q

Gear rotation

A
  • odd number of gears are same direction

- even number of gears are opposite rotation

Second Year (19 decks)

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