Gear Drives Flashcards
What is the difference between a speed reducer and a speed increaser gear drive in terms of the relationship between the size of the drive gear and the driven gear?
Pinion: smaller gear, does more work
if pinion gear drives it is is a speed reducer unit
if gear drives it it is a speed increaser unit
What degree of pressure angle do most new gears have?
20 DEGREES
What is the difference between gear tooth clearance and backlash
Tooth clearance: distance between the top of the tooth of one gear and the bottom of meshing tooth space
Backlash: amount of SIDE clearance of a gear tooth when two teeth mesh
Pinion gear
smaller gear
Idler gear
an intermediate gear used to make the driver and driven gears rotate in the same direction
gear ratio
ratio between number of teeth on driven gear to the teeth on the driver gear
Pressure angle
determines shape of tooth. All meshing gears should have some Pressure angle. The slant at the top
Diametral potch
SIZE of gear teeth that specifies the number of teeth per inch of the gear’s pitch diameter.
Clearance
distance between top of tooth of gear and bottom of the meshing gear
Backlash
side clearance between two meshing gears
What are the two formulas for calculating the number of teeth in a gear
N= OD x DP - 2
N=PD x DP
What are the three major configurations of spur gear drives
External
Internal
rack and pinion
What are the disadvantages of spur gears when compared with other gear types
- Noisier
- more vibration
- limited to low or moderate speeds
- only two teeth can mesh at once so its not as smooth sets
what are the four types of bevel gears commonly used in industry
straight
spiral
zero bevel
hypoid
What are the are the advantages of helical gears
- greater tooth length=greater load and power capabilties
- more teeth meshing
- smoother and quieter
- load is spread over entire surface of tooth
Why would a double helical gear used rather than a single helical gear?
the problem is shaft end, or axial thrust,
double helical gears create equal but opposing forces to cancel out the thrust
Herringbone gears are more difficult and expensive to machine than standard helical gears, but where are these types of gears preferred
They are preferred where you need stronger and used with very heavy loads and high speeds
When are bevel gears mainly used
Intersecting shafts
When are worm gears generally used, and what advantages do they have
- high ratios in compact areas
- quieter, less vibration because of sliding contact
- handle shock loads well
What is meant by the statement “Worm gears tend to be self locking”?
self locking is when motion cannot be started by applying torque to the output shaft (worm gear)
What is the another name for a bevel gear that have the same number of teeth and 90 degree shafts
miter gears
To ensure that a gear drive cannot be reversed what should you use
backstop
Which type of gearbox approaches 99 efficiency?
helical gearbox
service factor
constant used to multiply the horsepower by a multiplier in the selection of gearbox
most common gear profil
The involute gear profile where the profiles of the teeth are involutes of a circle
The contact between teeth occur at a single instantaneous point
gears of difference pressure angles are
NOT interchangeable
pitch diameter
is the diameter of that instantaneous point to the opposite side
straight bevel gears
have same advantage/disadvantage as spur gears so speed and gear ratio should be kept low
They are angled
spiral bevel gears
are bevel gears that provide the advatnage that helical gears do for spur gears.
smoother
less noise
higher speeds
higher loads
