Gears, Flashcards
What are the 4 types of Fixed speed gear box drives
Parallel drives
Angle drives
Compound drives
Planetary gear systems
What is Dedendum
The part of the tooth that lies between pitch Circle and the route diameter of the gear
What is Backlash
The amount to play between meeting teeth it is the difference between tooth space and tooth with measured and thousands of an inch
Some shaft mounted reducers use a device to absorb torsion load shock, what is this device called?
Spring type torque arm
What’s a indication of gear wear?
Backlash, uneven wear
What is a Internal spur gear
Teeth mesh inside larger gear. Rotate same direction quieter than external due to more teeth engaged
Gear materials
Ferrous metals,
Non ferrous metals,
Non metallic materials
What are the Two profiles of teeth?
Involute or straight
Types of Ferrous metals gears
Steel gears- when heated, greatest loads and torque
Cast iron- easy to machine , cheap, good wear resistance and runs quieter but more brittle
Stainless steel- corrosive resistance
What is the Spiral mitre shaft arraignment
Intersecting
The Drive gear does what
Power in. Is the input gear, caused mating gear to turn
Double helical gears
Opposite hand - same shaft. Thrust generated is counteracted by thirst set up
What is a Speed reducer
Slower output speed than input . Occurred when small gear drives larger gear. More torque less speed
What is the Hypoid shaft arrangement
Crossing
What is Straight bevel , shaft arrangement
Intersecting
What is the Herringbone shaft arraignment
Parallel
Types of gears?
External/internal spur gears, Rack and pinion spur gears, Helical gears,(single and double) Herringbone gears, Straight bevel Spiral bevel, Hypoid, Spiral mitre, Worm and worm gears
Involute tooth profile have what
Slight curve on face of gear teeth.
What do worm gears and worm wheel
Connect shafts that cross. Helical teeth around worm called thread. May bore more than one start.
What is worm and wheel shaft arraignment
Crossing
Spiral bevel gears have what arraignment
Intersecting
What are Bevel gears?
Used to connect shafts that intersect usually at right angles.
What are External spur gears?
Teeth on the outside of both pinion and gear, connected shafts roster in opposite directions unless a idler is used
What is a Non throated worm gear
Teeth have same depth, meshing is only one or two points on teeth
When spur gears are mounted in a gear box, the correct c-c distance is
Half the sum of the pitch diameters . Insured proper meshing
What are Hypoid gears
Used for transmitting lower between shafts that cross but don’t intersect. Usually a 90° angle.
Planetary gears can be either
Spur or helical deign
What is Straight tooth profile gears
Have straight faces and flanks. Very noisy. Not suitable for high speed or high power applications unless speeds are low.
Non ferrous metals
Bronze- tough and wear resistance, easy to cast and machine
Aluminum- lightweight
Internal gear sets have gears moving how?
Both in same direction
What are Straddle mounted gears
Mounted between 2 bearings. Stronger and has less deflection under life than overhung
What is a Mesh pattern
A mesh pattern describes the area of contact between two meeting teeth
What are Helical gears
Similar to spur gears except gear teeth are at an angle to the bore of the gear. Two or more teeth mesh at same time , smooth and quiet
The distance that one thread advances during one revolution is called?
Lead
What is End play
When the gear or shaft is allowed to move axially, for some arrangement end play is required. For others is damages gear train
What are the Conditions for gear meshing
Diameter pitch
Pressure angle
Tooth profile
What does a idler gear do
Between drive and driven gear, connect two gears with a center to center distance thaf is greater than the diameter of the gears
What is a Mounting distance?
Distance from the back of the gear hub to the apex
What is the Double helical shaft arrangement
Parralel
A major hidden danger with high ratio planetary drives is what?
Reverse torque lock up.
What is a Speed increaser
Faster output speed, larger gear drives a smaller gear. Less torque more speed
What is Preloading a bearing
Giving bearing less than 0 axial clearance
What is the Driven gear
Power out. Output gear forces to turn
What is the External and internal spur shaft arrangement
Parralel
Do Gears have slippage?
False
What are Mitre gears
1:1 ratio - cone angle of 45°
Change shaft direction without altering drive ratio
What are 3types of Shaft arraignment
Parallel
Centrelines intersecting at 90°
Centrelines crossing at 90°
A Pressure angle has what?
14.5% or 20%
Gears with angle of 20% have more stregth and wear resistance because they have fewer teeth on pinions
Bevel gears that have there teeth cut Parralel to the axis of their bore called
Straight bevel gears
Purpose of backlash
Allow for tooth expansion(heat)
Allow lube to escape,prevent interference with incoming and outgoing teeth
A Throated worm has what
Better contact between worm and wheel, single throated outline of worm gear teeth curved match shape of worm
Diffence between spur and helical gears?
Spur do not have axial thrust but are weaker and nosier at high speeds.
Helical gears are stronger and quieter but have some axial thrust
Characteristics of a spur gear
Teeth cut parallel to bore, smaller gear is called pinion, do not generate axial thrust p
On a gear box the lubricant should be changed when
Every 20,000 service hours or after 4gears. In case of extreme conditions a earlier change can be recommended
The point in which the cones pivot is called(bevel gears)
Apex
Straight mitre shaft arraignment
Intersecting
What is a Direct drive
Input and output speed are same speed 1:1
What is a Gear train?
When two or more gears mesh or work together as a unit
What is Rack and pinion shaft arrangement
One shaft only
What is Addendum
The part of the tooth that lies between the pitch of a circle and the outside diameter of the gear
When a odd number of gears mesh?
Rotation in same direction
What are Herringbone gears
Two helical gears abbutted - often used on slow turning heavy loads
What is a Over hung gear
Has a bearing supper on only one side. Keep close to bearing for more support
What are Non metallic gears
Quiet at high speeds, natural or synthetic
Plastic, laminated phenolic, carbon fibre.
What are examples of light application open gear drives
Small conveyers,textile machinery, small er engine lathes
3 parts of a planetary gear system
1sun gear
- Carrier with planted gears mounted to it
- Ring gear
When a even number of gears mesh the last rotates in?
Opposite direction
Compound gear train must have
Three or more shafts and four or more gears. Good where higher reduction or speed is important
When a Parralel shaft is connected by single set of helical gears the shaft develops axial thrust. The direction depends on
Whether shaft is a drive or driven, direction of rotation, the hand and gear on the drive shaft.
Single helical shaft arrangement
Parallel or crossing
If two members of plantetary gears are locked up
Produces direct drive
What are Single helical gears
Same helix angle, diamtrel pitch, pressure angle, correct center distance
Causes of gear wear?
Lack of lube,
Abrasives in gear train,
Incorrect tooth contact
Extended heavy loads
What is a Rack and pinion
Used to convert rotary motion to a liberal motion and vice versa. Used to open and close chute doors, large air valves etc
Can you use layout out blue for checking gear mesh?
No
