Gear Drives Flashcards
What are the two types of gear drives?
Open - light duty
Enclosed gear drives
What do gear drives do?
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
What is diametral pitch (DP)?
What is pitch diameter (PD)?
Total number of teeth on a gear divided by the pitch diameter.
DP = N / PD
PD= (NxOD)/(N+2)
What is the formula to figure out pitch diameter?
PD = (N x OD) / (N + 2)
N = number of teeth OD = outside diameter
What is needed to achieve a correct fitting gear assembly (mesh)?
Diametral pitch
Pressure angle
Tooth profile
What is the rack?
The spur gear with a straight pitch line and straight sided teeth.
What are the pressure angles of the spur gears?
14.5 or 20 degrees
20 degrees is preferred
How can you tell if the spur gear is 14.5 or 20 degree pressure angle?
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
What is backlash?
The amount of play between mating teeth.
What is the purpose of backlash?
Allow for tooth expansion due to heat
Prevent interference with incoming and outgoing teeth
Allow lubrication to escape
What should be taken into consideration when deciding gear materials?
Load
Speed
Method of lubrication
Tooth form
Noise levels
Environment
Temperature
What material of gear can carry the most load and highest torque?
Steel gears that are heat treated.
What is the benefit of cast iron gears?
Easy to machine
Inexpensive
Has good wear resistance
Run quit
When are non ferrous metal gears used?
When corrosion resistance, cost or low weight is important.
Why would non metallic gears be used l?
Quite operation at high speeds
What are the 4 typical shaft arrangements?
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
What are the two types of spur gears?
External
Internal
Can internal spur gears operate the same loads and speeds as external?
Yes but internal spur gear is a lot quieter
In a spur gear drive what is the pinion and what one is the gear?
The smaller gear is the pinion and larger is the gear
What does a rack and pinion spur gear do?
They are used to covert rotary motion to linear motion.
Ex: open and close chute doors
What is the standard angle for helical gears?
45 degrees
How can you tell if a helical gear is left or right angle?
Place the bore of the gear vertically, if the teeth slope downward from right to left that means they are:
Right hand
Single helical gears connecting parallel shafts must have?
The same helix angle
Same diametral pitch
Same pressure angle
Correct centre distance
Be of opposite hand
True or false? When parallel shafts are connected by a single set of helical gears, the shafts develop axial thrust?
True
How must you compensate for axial thrust?
Axial thrust bearings
How can you determine direction of thrust?
The thrust of the driven shaft is always opposite to the direction of thrust of the drive shaft.
How can single helical gears connect crossing shafts?
By meshing two of the same hand gears are meshed together
Can double helical gears reduce thrust on a parallel shaft?
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
Where can herringbone gears often be found?
Slow turning, heavy loads
Where are the teeth cut on bevel gears?
Teeth are cut on the surface of a cone
In bevel gears what is the smaller gear called? What is the larger gear called?
Small gear = pinion
Large gear = Ring gear
Where would find bevel gears?
To connect shafts that intersect, usually right angles.
Usually are a matched set
If a bevel gear has a pitch cone angle of 90 degrees it is called a ______?
Crown gear
Crown gears are disc shaped
If the pitch cone angle is greater than 90 degrees it is called a ________?
Internal bevel gear
Internal bevel gear is cup shaped
How do you determine the bevel gears direction?
By viewing from the back looking toward the apex.
When are mitre gears used?
Mitre gears are used to change shaft direction without alternating the drive.
What is the ratio and pitch cone angle of mitre gears?
1:1 and 45 degrees
When is a hyoid gear used?
When transmitting power between shafts that cross but do not intersect.
What are some advantages of hypoid gears over spiral bevel gears?
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
Do hypoid gears require extreme pressure lubricants?
Yes
Because of the sliding action that takes place between the teeth.
When are worm and worm wheels used?
To connect shafts that cross
What are the helical teeth around the worm shaft called?
Threads
How do you calculate the gear ration on a worm and wheel set?
Dividing the number of teeth on the worm gear and dividing it by the number of starts on the worm.
What are the three different contact patterns worm gearing sets can have when they are in the correct positions?
Non throated contact
Throated contact
Double throated contact
What is non throated contact?
In non throated gear sets the teeth on the worm all have the same depth and linear pitch
What is throated contact?
In throated contact, the tooth forms of the worm gear are modified to give better contact between the worm and worm gear
What is the purpose of a reduction unit?
Reduce speed and increase torque
