6.9 Flashcards
what is the direction of the teeth on a straight cut spur gear
parallel to the shaft’s axis
when are external spur gears used
when a change of speed is required and the shafts are parallel
when are internal spur gears used
when a change of speed is required whilst not increasing the size
what are the benefits of a helical spur gear
carry heavier loads at higher speeds compared to same sized spur gears and run quieter and smoother
what are the two types of helical gears
single and double
what is a problem caused by a single helical gear that is removed by a double helical gear
a single helical gear produces an axial load on the bearing, but the teeth in the opposite direction cancel that out
when are bevel gears used
when 2 different shafts intersect
what is the key aspect of a hypoid gear
the shafts are not intersecting
what is the main problem for hypoid gears
they suffer from heavy sliding so need very heavy lubricant
what is a key advantage of worm gears
they cannot be back driven
what is a rack and pinion gear system used for
transmitting rotating movement into linear movement or vice versa
what is the mechanical and speed ratio if both gears have the same teeth number
both are 1
what is the speed ratio if the drive gear is 8 teeth and the driven gear is 16 teeth
1:2 which means 1/2 the speed
what is the mechanical advantage if the drive gear is 8 teeth and the driven gear is 16 teeth
2:1 which means 2 times
what is the relationship between gear speed and mechanical advantage
as the speed increases the mechanical advantage decreases and vice versa
what direction is an even number in a gear chain
the opposite to the drive gear
what direction is an odd number in a gear chain
the same as the drive gear
when calculating speed ratio and mechanical advantage in a gear chain what gears are used
the first and last gear
what is the primary type of gear used for reduction in aircraft engines
epicyclic (planetary) gears
what happens if the gear teeth are too high when joined together
the load is on the small part of the teeth so it will break quicker and easier
what happens if the gear teeth are too low when joined together
the teeth will not be lubricated
what part of the gear teeth is best for contact with each other
the middle section
what is gear backlash
the clearance between the gear teeth and the meshing point
what is a belt
a loop of flexible material used to mechanically link or dive 2 or more rotating shafts
what happens if the belt is crossed over
the direction of the driven shaft will be reversed
what are the two main belt types
friction drive belts and positive drive belts
what do friction drive belts need
require tension to have the correct amount of friction
what do positive belts rely on
engagement of teeth on the belt with grooves on the pulley
why are flat belts not advisable for high speeds
they are more likely to slip off
what makes a v belt better than a flat belt
it is wedged into the pulley groove making less likely to slip out
how do positive (synchronous) belts work
the belt and pulley work in the same way as a chain as they have teeth that are engaged by the pulley
what are v belt pulleys used for
transmitting power between parallel axis
what is the difference between a synchronous belt pulley and belt
the teeth are on the pulley rather than the belt
what does a stepped or cone pulley drive allow the user
to change the speed ratio and mechanical advantage of the gears without changing the belt
what equipment uses a stepped or cone pulley drive
a pillar drill
how does a chain and sprocket drive work
a roller chain engages with 2 or more toothed wheels called sprockets
what is a leaf chain and what is it used for
a chain made of only link plates and pins used for tensile strength by pulling at either end
what is an advantage of chain drives
the chain cannot slip off
what is a disadvantage of chain drives
heavy, noisy and more expensive
