Lub oil and transmission theory 2 Flashcards
what are the two main uses of a gearbox?
- to change the speed of rotation from the prime mover
- to change direction of the rotation
what is the max ratio limit for a single gear reduction?
15:1
what is a pinion?
the gear that is driving.
what is a wheel?
the gear being driven.
what is the advantage of a dual tandem gear reduction ?
halves the load so smaller pinions can be used
why are quill shafts important?
to flex with the gears to counteract flexing of the boat which would cause de-meshing of gears.
what are the 3 ancillaries of a gearbox?
Shaft brake
thrust block
turning gear
what is a straight spur gear?
the teeth area parallel to the shaft it rotates on.
used in low speed applications as they are single contact gears so make lots of noise.
what is a helical gear?
the teeth are at a angle to the shaft allowing for multiple teeth contact making the stronger and quitter but the teeth push the gears away creating friction.
why do we need thrust bearing with helical gear
to prevent the gears moving which causes friction.
what problem does double helical gears fix?
they remove the need for thrust bearings as they are counteract the thrust of the other side of the gear.
why do we use worm wheels and some of the characteristics?
they allow driving of shafts at 90 degrees to each other
high gear reduction
self locking
good for manual turning gears
what pressure does the pressure switch kick in at and when is it tested?
18.5psi or less
and tested every 24hrs
what is the job of the serckstat?
to regulate the lubricant temperature.
what are the 8 components of a gearbox
pinions
wheels
input/ output
casing
thrust bearings
bearings
sump (holds oil)
Shafts
what is the purpose of the shaft brake?
to stop the shaft and hold it still
what are the checks done on a shaft brake?
on application
no fire risk exists
all brake pads are applied
shaft is stationary
on removal
all pads are clear
there are no fire dangers exists
the shaft is rotating
what is the purpose of thrust blocks?
to absorb any thrust from the shaft when the ship flexes and moves ahead and stern
what is the purpose of turning gear?
to manual turn the gearbox over for maintenance and to align the shaft for dry docking.
what is the purpose of the Plummer block and how is it lubricated?
to support the shaft with out absorbing thrust from it. lubricates the shaft and its self using dynamic lubrication(Michell principle)
what is dynamic lubrication?
the picking up of oil from a sump by having the shaft spin off centre slightly causing a wedge of oil to form
what are the purpose of bulkhead glands and how is it lubricated?
to maintain a water and air tight seal between compartments
lubricated with grease and grease nipples
what is the purpose of the stern seal?
to maintain water tight integrity as the shaft passes through the ships hull.
has a emergency inflatable(uses LP air) seal if the main one fails
what is the purpose of the A brackets and how is it lubricated?
to support the shaft out side of the hull
have a main and intermediate bracket
lubricated using seawater (hydrodynamic lubrication)
what are the 3 sections of a shaft?
thrust shaft (links gear box to the intermediate shaft)
intermediate shaft
tail shaft
how is the thrust shaft connected to the intermediate shaft?
using flanges, nuts and bolts
what is the purpose of the SKF coupling?
used to connect the intermediate shaft and tail shaft
consist of a inner and outer sleeve that use a interference fit to hold the shaft and is then fully seated with high pressure oil.
what are the two difference types of propeller?
fixed propeller
controllable pitch propeller
what are the parts of the Plummer block?
a casing
dipstick (not Hallie’s)
journal pads
oil cooler
