Alb. Mod. Plain Bearings Flashcards
In regards to the journal, it is normally machined to _____ _______ than the rest of the shaft
Closer tolerances, in regards to dimensions and finish
Plain bearings can be journal bearings, which support _____ loads
Radial
Plain bearings can be thrust bearings, which support _____ loads
axial
The two main functions of a journal bearing are: (2)
- Hold a journal
- support radial load
The 3 most common radial loads are: (3)
- Stationary load
- Oscillating load
- Reciprocating load
_____ radial loads generally act in one direction and on one area of the bearing
Stationary
_____ radial loads shift through an arc of less than 180°. The fluid film is much thinner, but stronger than a stationary load. Surface finish and oil cleanliness are more important than on a stationary load.
Oscillating
____ radial loads shift 180° from one side of the bearing to the other. The fluid film is much thinner, but stronger than a stationary load. Surface finish and oil cleanliness are more important than on a stationary load.
Reciprocating
Journal bearings can either be: (2)
Split in half or
One piece, also called a bushing
Thin shell split bearings have the following features: (4)
- Thin shell seated in a strong housing with accurate bore
- Flexible
- Thin overlay on steel backing (Most common overlay is babbitt)
- Shell can have intermediate layers to assist bonding
Thin shell split bearings are a lightweight bearing that can withstand:
High loads
Note: Originally developed for automotive engines
Thin shell split bearings have a high load capacity because they are:
High precision
This bearing is lightweight, has a compact housing, is quick to change out, and inexpensive to replace.
Thin shell split bearing
This bearing has a consistent quality and is available in a wide range of materials. It is available in both oversize and undersizes, which allows the grinding of the journal for reuse.
Thin shell split bearing
This split bearing may have a plain seat, or a spherical seat.
Thick wall split bearing
With a thick wall split bearing designed with a spherical seat, the spherical seat assists with:
aligning a heavy shaft with the bore during installation. Simplifies installation and ensures edge loading of the bearing is minimized
Bushings are a type of plain bearing that has not been split and can be designed to handle what two loads? (2)
Radial
Axial
The load and speed capacity of bushings is comparable to:
The load and speed capacity of split bearings of the same size
Direction of load is normally radial, but some bushings can accommodate an axial load using: (2)
Flanges
Thrust washers
Bushings can be used in the same applications as split bearings, the choice depends upon: (2)
- Ease of assembly
- parts on hand
This type of bushing consists of a thin shell lined with a soft bearing material:
Wrapped bushing
Note: Only available in stock sizes
Wrapped bushings have a high:
Fatigue strength
Pre finished bushings should only be used in lightly loaded, non critical applications as there is:
Variation in the diameter after installation
These bushings are bored out of a solid piece of bearing material, such as lead, bronze or teflon. Can be easily made for emergency repairs, and can accommodate deep lubrication grooves
Solid bushing
Note: Do not have the fatigue strength of wrapped bushings. Must be reamed to final diameter after installation
This type of bushing consists of an outer bushing with a loosely fitted inner bushing.
Floating bushing
This type of bushing can support a lightly loaded but high speed shaft, or be used with heavily loaded slow speed journals:
floating bushing
Water lubricated bushings are normally made from this material, since it is slippery when wet
Rubber
Note: In some applications, nylon or PTFE is used
Water is excellent for _________ which makes the water lubricated bushings very durable. Used when water is constantly flushing the bearings and makes retention of any other lubricant impossible.
Heat dissipation
What are two limitations of water lubricated bushings? (2)
- Only suitable for very light loads
- corrosion resistant journals must be used.
Why can you only use water lubricated bushings in a light load application?
Water has a very low film strength.
Note: These bushings can only be used, for example, on vertical shafts without side loads.
____ bushings are either made from a porous material soaked with lubricant, or have a lining made with pockets of lubricant.
Pre lubricated bushings.
A porous bronze bushing is also known as: (2)
- Sintered bronze bushing
- Oilite bushing
A porous bronze bushing is pre charged with oil by soaking the bushing in oil at ____ °C for ____ minutes
90 C (194 F) for 30 minutes
porous bronze can hold up to ____ % its volume in oil
30
With porous bronze bushings, the higher the oil capacity, the:
Lower the strength
Pre lubricated bushings are used where:
It is not practical to supply lubricant from the outside
Due to poor heat distribution, pre lubricated bushings are more suitable for:
Start/stop applications
Pre lubricated bushings are not suitable for high temperatures, as the:
Oil evaporates
Pre lubricated bushings are intended for ___ loads
light
____ bushings are made of a slippery material, such as graphite or PTFE. The can also be made of a bronze matrix containing graphite or PTFE, which oozes from the matrix under pressure
Dry lubricated bushings
What are the features of dry lubricated bushings? (3)
- Can be solid or lined
- can run dry or with lubricant (increases speed rating)
- Are available in a very large range of materials
Dry lubricated bushings are ideal for these two situations: (2)
- start and stop applications
- positions where lubrication is impossible, such as high heat areas
Dry lubricated bushings are not suitable for: (2)
- High speeds
- Heavy loads
____ bearings are one of the most widely used types of plain bearing. Designed to develop a full film of lubricant when the journal is up to speed
hydrodynamic bearing
A hydrodynamic bearing depends on the rotation of the shaft to drag the oil into the loaded area. It can be a split bearing or bushing. An oil inlet is located:
In the unloaded area
In order for a hydrodynamic bearing to get a full film of lubricant under the loaded area, the journal must turn at a designated:
Minimum speed
With a hydrodynamic bearing, what happens when you run under the minimum speed?
The lubricant film breaks down and the journal contacts the bearing, resulting in severe wear
With a hydrodynamic bearing, the ___ determines the minimum speed
load
Most of the wear on a hydrodynamic bearing occurs:
at start up, before the supporting film has developed
Hydrodynamic bearings can be designed to carry:
Any load at very high speeds
The actual load on a hydrodynamic bearing can exceed 300 PSI and speeds can be up to 15000 f/m (80m/s). They can be designed to run at _____ RPM at lower loads
200, 000
For steady loads that are moderate to heavy, hydrodynamic bearings usually have a plain circular bore with a chamfer at the area of the split, which:
assists in the formation of the oil wedge
Note: this is the most common design
Bearings that reciprocate may include a ________ oil distribution groove, which reduces the load rating by about half, but provides a continuous supply of lubricant to all areas of the bearing
circumferential
An ____ groove is sometimes used to ensure distribution of oil across the width of the bearing
axial groove
Note: slow speed bearings requiring grease lubrication also use axial/distribution grooves in the unloaded area
An unsteady load at high speeds can develop a condition called:
Oil whirl
Causes oil whip, which results in the shaft breaking through the film and destroying the surface of the bearing
What are two methods used to create oil wedges at different locations around the shaft to hold it in position, preventing oil whirl? (2)
- Lobed bearing (light applications)
- tilting pad style (heavier applications)
Note: clean oil is important for tilting pad style bearings, as deposits can form and seize the pads
An added feature that became widely used on tilting pad bearings is:
directed lubrication
directed lubrication has what 4 advantages over oil bath lubrication, on tilting pad bearings? (4)
- reduces temperature of pads (20 C or 68 F)
- Increases load capacity
- reduces power consumption
- reduces oil flow, smaller lube system can be used
Plain hydrodynamic bearings can sometimes be found in: (4)
- Turbines
- Gearboxes
- Engines
- Compressors
____ bearings are found in equipment which runs too slow to develop a hydrodynamic film
Hydrostatic
Hydrostatic bearings require_____ to provide a pressurized film of lubricant to support the shaft
External pump
This type of bearing can be a split bearing or a bushing. Oil is admitted through holes into pockets(recesses) in the loaded and unloaded areas. Holes are fitted with restrictors to regulate the pressure, and control shaft position within the bearing.
Hydrostatic bearing
This bearing has no minimum speed, and results in no wear at startup
Hydrostatic bearing
On a hydrostatic bearing, you can expect load and speed limits to be lower than a hydrodynamic bearing. This is due to:
Turbulence in the oil developing in the pockets as speed increases. Turbulence will reduce the film strength.
Note: very high loads can be supported if there is zero speed or only a few feet per minute
Hydrostatic bearings are used where:
Shaft load may change suddenly, but position must be accurately maintained
____ bearings are used with a heavy, unsteady load, in a compact area, where speeds aren’t sufficient for hydrodynamic lubrication
hydrostatic
the _____ bearing is a special type of hydrostatic bearing with pressurized oil entering under the loaded area only
oil lift journal bearing
the oil lift journal bearing uses hydrostatic pressure to lift the journal on startup, until:
hydrodynamic lubrication can take over
Hybrid bearings depend on both hydrodynamic and hydrostatic lubrication, however can only support a full load when:
both are operating together
hybrid bearings are used when there is an:
imbalance, such as an eccentric weight on a rotor increasing radial load as speed increases
The function of a thrust bearing is to:
Hold a shaft axially in the required position
a thrust bearing consists of:
one or multiple support surfaces perpendicular to the shaft axis
With a thrust bearing, a ____ attached to the shaft rides against the thrust bearing to limit axial movement. This may also me forged and machined as part of the shaft.
thrust collar
Various designs of thrust bearings are used, including: (3)
- Flat plate
- Tilting pad
- Tapered land
This type of thrust bearing is the simplest and cheapest to manufacture, and limited to light loads.
Flat plate
With a vertically mounted flat plate thrust bearing, it can be oil submerged or oil fed, if it is oil fed, the feed should be to the:
inner diameter
This thrust bearing is also referred to as a profiled pad thrust bearing. Provides a greater load capacity than flat plate, due to superior hydrodynamic lubrication. Has flat lands on the pad to prevent excessive pressure on start up.
Tapered land thrust bearing
This thrust bearing is a stationary base ring fitted with tilting segments of bearing material. The thrust collar transmits the axial load to the tilting segments.
tilting pad thrust bearing
the tilting pad thrust bearing is also known as: (2)
Kingsbury bearing
michell bearing
The tilting pads on tilting pad bearings are made of:
Babbitt on a steel backing
In regards to a tilting pad thrust bearing, the thrust collar performs what two functions?
- Transmits thrust load
- Draws lubricant into loaded areas
Some assemblies of a tilting pad thrust bearing include tilting pads on both sides, this is to:
provide thrust control in both directions
Note: often used with reversing loads
On a tilting pad thrust bearing, directed lubrication replaces the oil bath with:
Spray nozzles between the pads
On an oil lift thrust bearing, jacking oil is required to:
separate the pads from the thrust collar on start up, until higher speeds are achieved
Note: It is also required when there is a heavy load on a vertical shaft
Special bearings are bearings that support the journal with something other than oil or grease, such as: (2)
- Gas
- Magnetic field
Magnetic bearings now perform better than:
Oil bearings
Gas can be used instead of oil in what applications?
light load high speed applications
Wear resistance decreases as ______ increases
compressive strength
_____ is the resistance of a material to flaking and cracking 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 material to take the stress
_____ determines how well a material handles contaminants without failing
embeddability
_____ allows a material to yield to misalignment or imperfections in the shaft. ensures all parts of a bearing share the load.
Deformability (conformability)
____ is a materials ability to retain a film of lubricant
wetability
____ allows rapid transfer of heat
good thermal conductivity
____ allows a material to resist wear from the acids in oxidized oils
good corrosion resistance
____ is a materials ability to bond to a backing material
bondability
Materials in a journal and bearing must be ____ to ensure parts don’t seize or weld.
compatible
____ is used for light duty bushings, and is used in a bronze matric for extra strength. It is self lubricating, chemically inert, and can be used with soft journals. It’s limited by temperature, absorbs water, and emits a poisonous gas when burned
Teflon
aluminum/___ and aluminum/___ alloys were developed specifically for bearings.
tin, silicone
the aluminum/___ alloy consists of free ___ in an aluminum matrix.
Tin.
Note: tin provides the bearing material and the aluminum provides the strength.
The aluminum/silicone alloy was developed for:
extra strength
____ bearing materials are more embeddable and more corrosion resistant than copper/lead or lead bronze, less expensive and can run with softer shafts than copper or bronze alloys, have a higher load rating than babbitt, and can be bonded to steel backings
aluminum/tin and aluminum/silicone
Note: Less conformability and less embeddability than babbitt
A small chip or burr in a housing can cause ___ when seating a bearing in a housing
false loading
____ is the distance that a new insert protrudes above a split line of a housing
crush
____ is the amount that the insert diameter is wider than the bearing house diameter
Spread
The coating in the housing is required to prevent ___ from migrating out of the casting and destroying the bearing, as well as preventing corrosion
sand
To check if a journal is out of round:
three measurements are taken at 60° intervals
To check if a journal has developed a taper:
three measurements are taken at 60° intervals at both ends and the middle of the journal
When installing a bearing, the insert should be cleaned and ____
lightly lubricated
When installing or removing a bushing, what tool can help avoid damaging the bushing and the housing?
Adapter and Driver
What could you do to repair a damaged bore before installing a bushing?
bore the housing oversize and sleeve it
What two things can help with installation of a bushing?
Lightly lubricate the bushing, and slightly chamfer the outside and inside edges of the bushing
A solid bushing almost always has to be ____ to its final diameter, after installation
reamed
Thrust collars must be checked for ____ with a dial indicator
runout
____ and ____ is never recommended with oilite bearings.
Honing and grinding.
Note: use a sharp cutting tool instead
When scraping babbitt for a smooth surface contact area, you want to repeat until you have points of contact at least 1/8” in diameter, over at least ____ % of the bearing
85%
Correct ____ in a journal bearing is critical to the formation of an oil film
clearance
When checking clearance, is a lift check, aka bump check, considered accurate?
No.
But it will show if the bearing is worn and needs further attention
What is the most accurate way of checking clearance?
Measure the bearing bore and journal with a vernier micrometer. Subtract journal diameter from bore diameter to calculate clearance.
How would you adjust clearance on a connecting rod bearing housing?
shims
