plain bearings Flashcards
name 3 types of radial loads?
stationary
osculating load
reciprocating load
stationary load?
present on bearings supporting a horizontal rotor
oscillating load?
act on bearings in the crank end of connecting rods in engines.
much smaller clearances
advantages of split bearings?
very high load capacity ,high precision ,inexpensive to replace, quick to change out, available in over sizes and undersizes, wide range of material can be used in their construction
spherical seated bearings are usually used where?
turbines with a vary long span between bearings
what are bushings?
type of plain bearing that has not been split and can handle radial and axial loads
advantages of a wrapped bushing?
high fatigue strength
available in pre-finished sizes that are oversized until installed
(should only be used in lightly loaded non critical applications.
what is a solid bushing?
bored out of a solid piece of bearing material ( lead,bronze, teflon)
advantages of solid bushings?
can be bored out to non standard sizes,easily made from suitable round stock
they can accommodate deep lubricant grooves
limitations of solid bushings?
do not have the fatigue strength of wrapped bushings
what is a floating bushing?
consists of an outer bushing with a loosely fitted inner bushing
applications of water lubricated bushings?
used when water is continuously flushing the bearing and makes it impossible to retain any other lubricant
limitations of water lubricated bushings?
only suitable for light loads such as vertical shafts with out side load.
pre lubricated bushings are made of?
porous material soaked with lubricant ,lubricant squeezed out under load
dry lubricated bushing?
can run dry or with lubricants
available with large range of liner materials
not good for high speeds or heavy loads
hydro dynamic bearing is ?
most widely used type of plain bearing
depends on rotation of shaft to drag oil into the loaded area
at normal speed the bearing is supported on a full film of oil
What kind of Bearing at start up has virtually no oil in the loaded area which results in dry rubbing friction and boundary lubrication
Hydro dynamic bearings
Hydro dynamic bearings are designed to carry any load at?
Very high speeds
And unsteady load at high speeds, and develop a condition called what?
oil whirl
hydrostatic bearings are found on equipment that operate to?
To slowly to form a Hydro dynamic film or to operate with heavy shock loads. I can breakthrough Hydro dynamic film.
What is the minimum speed on a hydrostatic Bearing?
There is no minimum speed load supporting film can be provided at zero speed
Full film of the oil with no dry rub in friction or boundary lubrication on start up
Where is an oil left journal Bearing commonly used
Large turbines and compressors this bearing uses hydrostatic pressure to lift the shaft off the Bearing surface before it starts to turn and continues to support it until reaches a speed with the Hydro. Dammit lubrication can take over.
Jacking oil must be up to what on a oil lift journal bearing
Must be up to pressure before the shaft just turned, if not, could result in immediate destruction of the Bearing
Where is a hybrid bearing used?
Used in situations where there is an imbalance such as an Ecentric weight on the load or that causes radial load to increase as speed increases
What does a thrust bearing do?
Function of a thrust bearing us to hold a shaft Axially in the required positions
Where are magnetic bearings used?
They are used on large, high-speed, central, fugal compressors
What is compressive strength?
Bearing material must be strong enough to support the shops load at maximum operating temperature
What is fatigue resistance?
Is the resistance of the bearing material to cracking and flaking by loads that increase and decrease in rapid cycles, fatigue resistance can be increased by keeping the liner material as thin as possible to allow the backing to handle the stress
What is high embeddability
Determines how well a material handles contaminants without failing
what is deformability?
Allows the material to yield to misalignment or inperfections in the shaft, insurers all parts of the bearing carry a share of the load
what is wet ability?
Ability to retain a film of lubricant
What is compatibility?
Must not seize or weld to journal under rubbing conditions, such as during start up
What is Babbitt?
Babbitt is a white metal alloy is composed of soft alloys, such as tin lead copper and add atimony
Lead provides the bearing properties while bronze or copper, provides the strength
Where is Teflon used?
It is used for light duty bushings and it is used in bronze matrix for extra strength
What are some advantages of Teflon?
It is self lubricating. It is chemically inert
It can be used with soft journals
What are the disadvantages of Teflon?
It is limited by temperature it emits poisonous gas when burned it absorbs water
What is a limitation of aluminum alloys?
They have less embeddability and conformability than babit
What is false loading?
A small chip or burr can cause a bearing to support the load on only part of its surface. It results in premature wear
What is crush and spread?
crush-crush and spread ensure the insert is mated tightly to the bearing housing bore.
Spread is the amount that the insert diameter is wider than the bearing housing diameter
Using a vernier, check the journal for taper, and out of round to check for out of round three measurements are taken at what intervals
60 deg intervalls
true or false-Plane bearings can be either journal bearings to support radialloads or thrust bearings to sport axial loads
true
true or false ?Water lubricated bearings are made of rubber but can be nylon or Teflon.
true
true or false–Dry bushings are made of graphite, or Teflon or a bronze matrix containing graphite or Teflon.
true
What kind of bearings are found on equipment that operate two slowly to form a Hydro dynamic film
hydrostatic bearings
What is another name for the tilting pad thrust bearing?
Kingsbury
Where are magnetic bearings used?
large high speed centrifugal compressors
Where are gas lubricated bearings used?
They are used for lightly loaded, high-speed applications
Use a driver and a ____ when removing a bushing?
adapter
