Gears Flashcards
0
Q
Enclosed gear drives
A
- gear drives inside a gearbox
- oil or grease lubricated
1
Q
Open gear drives
A
- exposed to the outside
- more excessive wear
2
Q
Gear set
A
-matched pairs of gears made together intended to mate with eachother
3
Q
Pinion
A
- when two gears mess, the pinion is the smaller gear
- generally the drive gear
4
Q
Crown gear (ring gear)
A
-the larger gear in a gear set
5
Q
Direct drive
A
- when the input speed of the gearbox is the same as the output speed
- 1:1 ratio
6
Q
Speed reducer
A
- when a small gear drives a larger gear
- output has more torque but less speed
7
Q
Speed increaser
A
- a faster output speed than input speed
- larger gear drives a smaller gear
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
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
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
11
Q
Internal gears
A
-have teeth on the inside diameter of the gear
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
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
14
Q
Gear wear
A
-quick check of backlash tells us how much wear there is
-
15
Q
Floating gear or shaft
A
-Not set or fixed on a shaft
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
17
Q
Worm & worm wheel gear set
A
- have the same hand gear arrangement
- high speed reduction
- worm wheel is the larger gear
18
Q
Addendum
A
-top half of the tooth
19
Q
Dedendum
A
-bottom half of the tooth including the clearance
20
Q
Whole depth
A
-total height of the whole tooth, which equals addendum plus dedendum
21
Q
Working depth
A
-equals the addendum plus the dedendum minus the clearance
22
Q
Clearance
A
-Allows room for lubrication, thermal expansion of the gear and gear runout
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
24
Pitch circle
-diameter of the gear measured at the middle gear teeth
25
Crowning
- to prevent loading on the tooth
| - a gear tooth is cutting a slight curve on the face of the tooth from side to side
26
Pressure angles
- 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
27
Helix angle
- 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
28
Starts
- describes the number of thread starts on the worm gearbox
| - the more starts, the faster the worm wheel advances in one turn
29
Involute
- 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
30
Backlash
- clearance measured at the pitch line
- rotational arc clearance between a pair of mounted gears
- backlash increases diametral pitch
31
Diametral pitch
- number of teeth on the gear divided by the pitch diameter
| - the size of the gear tooth
32
Mesh
- 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
33
Involute tooth profile
-provides the smoothest tooth profile
34
Straight tooth profile
-very noisy
35
Gear rotation direction
- 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
Idler gears
- 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
Speed vs. Torque
- speed & torque are inversely proportional
| - power in is the same as power out, gears make it so only the speed and torque change
38
Parallel shaft position
- spur gears
- helical gears of opposite hand
- double helical gears
- herringbone gears
39
Intersecting
- shafts at 90 degrees to each but on the same plane
- bevel gears
- mitre gears
40
Crossing over at 90 degrees
- 90 degrees to each other but on different planes
- worm gears
- hypoid gears
- helical gears of the same hand
41
Spur gears
- 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
External Spur Gear
-teeth cut on the outside of the gear blank
43
Internal
-when a smaller, external cut gear meshes with a larger internal cut gear
44
Rack & pinion
- 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
Single helical gears
- 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
Double helical gears
-2 rows of helical teeth of opposite direction
| -
47
Herringbone gears
- same as helical but no groove between the two sets of teeth
- high speed applications
48
Bevel gears
-most common intersect at a 90 degree angle
49
Mitre gear
- Ratio is 1:1
- always intersect at 90 degrees
- change in output shaft direction
- develop axial loads
50
Straight bevel "angular"
- angular or 90 degrees
| - low torque because of thin grooves on driven gear
51
Spiral bevel gear
- 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
Zerol bevel gears
- Similar to straight but teeth are curved like those on spiral
- no axial thrust
53
Hypoid gear
- A bevel gear that forms a drive between 2 shift that cross over at 90 degrees
- very high sliding friction
54
Worm gears
- 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
Worm lead
- the distance by which one tooth on the worm advances in one turn
- pitch x # starts=lead
56
Planetary gear system
- 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
Throated or non-throated worms
- 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
double throated
-maximum gear tooth contact. more contact least pressure
58
worm gear contact
-set up so the contact between the teeth is slightly toward the leaving side of the worm wheel
58
single reduction gearbox
-2 shafts with 2 gears, with one gear mounted on each shaft
59
Double or multiple reduction gearbox
- have at least 3 shafts and 4 gears
| - input gear is small, output gear has to be larger
60
concentric reducer
-have input and output shafts on the same plane
61
Active or drive side flank
-driven tooth that is marked with bluing after gears are turned
62
Correcting mesh pattern
-adjust shims. this doesn't affect the preload, just the position of the wheel
63
tolerance stack up (in new gears)
-any abnormal patterns disappear as the gears wear
64
Proper belt tension
-as loose as possible without slipping
65
tie rods (torque arms) on shaft mounted gearboxes
-mounted at 90 degrees between output and point of torque arm attachment
66
fin fans
-force air through heat exchangers to release unwanted process heat
67
Variable Speed drive
- 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
Changing lubricant
-every 20,000 service hours or after 4 years
70
Grease in bearings
-cleaned and packed every 10,000 service hours
71
Wide belt drive
- 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
Offset reducer
-input shaft and the output shaft are usually on different planes
73
Woodblock belts
- a variable speed wide belt
- Must be replaced when showing signs of lipping
- for high torque and low speed
74
Narrow Belt Drives
- 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
Hydrodynamic Variable Speed
-make it possible to regulate the torque by varying the amount of pressure fluid in the work cavity
76
Variable speed chain drive
- 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
Closed loop hydrostatic variable speed drive
- 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
torque converter
- 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
Variable Fill (snoop tube) Hydraulic drives
-vary the output speed and power by changing the amount of oil contained in the rotating case
-
81
Variable speed wet disc drive
-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
Gears meshing require
- same diametral pitch
- same pressure angle
- same helix angle
83
Face of the tooth
-contact point of the tooth on the addendum
84
Gear rotation
- odd number of gears are same direction
| - even number of gears are opposite rotation
