Friction Bearings Flashcards
_____ bearings have a sliding contact between a shaft and the bearing. A special, low friction material lines the housing and directly contacts and supports the shaft, separated by a thin layer of lubricant.
Friction Bearings
Friction bearings are also referred to as: (3)
- Plain Bearings
- Sleeve bearings
- Journal bearings
The _____ of a bearing is its outer casing.
Housing aka Pillow block
the principal parts of a friction bearing are the: (4)
- Base
- Base bolt slots
- cap
- cap bolt holes
Housings can be made of one of the following materials: (3)
- Cast iron
- Cast steel
- Fabricated steel
This housing material would be ideal for light to medium loads
cast iron
This housing material would be ideal for light to heavy loads
cast steel
This housing material is for special jobs
fabricated steel
the choice of bearing housing, and the friction bearing, depend on: (4)
- Load
- Rotational(rubbing) speed
- direction of pull
- support design
Bearings have a nominal size, such as 2 7/16”. This is the size of the:
bore
The dimension from the base to the shaft center is important for:
installation and alignment
Note: this is also known as the eye of the bearing
There are two kinds of flat bearings, which differ in their housings: (2)
solid and split bearings
Solid bearings are used when speed and load are:
low
solid bearings are used in locations where the load is applied to the ___ part of the bearing
top
Solid bearings must be slid on or off of the shaft, which means that the bearings must be installed as an:
assembled unit
A two bolt split bearing is used for what size load?
light to medium load
A two bolt split bearing is used for what size load?
medium to heavy load
____ bearing housings are used for drives in either of the following situations:
- when a load is applied parallel to the horizontal
- when the bearing is mounted on a vertical support
Angle bearings
Some heavy duty machines in industrial plants have the bearing housing base cast as an integral part of the machine. Either babbitted or fit with shells or liners. This is an:
Integrated bearing
What are the 3 join designs of split bearing housings? (3)
- Flat joints
- Gib in the joint
- angle joint
When the split bearing housing joints have a “step” in them, they keep the cap from moving sideways. This combines the rigidity of a solid block with the advantages of split construction. What style joint is this?
Gib joints
Note: Allows bearing limited side loading
Journal bearings and pillow block bearings with anti-friction material liners are commonly used for ____ to ____ speed and for _____ to ____ loads.
low to medium speed
light to heavy loads
Journal bearings and pillow block bearings with anti friction material liners can be used for ultra high speeds with _____ lubrication only under exact conditions
Air jet lubrication
ex: main bearings on a turbine
when selecting bearing lining material, it should be: (5)
- softer than shaft material
- low coefficient of friction
- wear-resistant
- a good heat conductor, remain stable with heat changes
- readily available
Metallic bearing materials must have a low:
coefficient of expansion
metallic bearing materials ____ ____ with water, mild acids, alkalis, salts, or other materials.
react chemically
Materials for metallic liners include: (5)
- Babbitt
- Brass
- Bronze
- Sintered Bronze
- Aluminum
This metallic bearing liner material is for general use
Babbitt
These metallic bearing liner materials are for higher speeds and heavier loading than babbitt: (2)
- Brass
- Bronze
This metallic bearing liner material is common in hydraulic pumps
Aluminum
This metallic bearing liner material is porous with a built in oil supply:
Sintered bronze
Note: oil to bronze ratio is 1:2 by volume
Non metallic bearing liners include: (3)
- Nylon
- Polyurethane
- phenol laminates
Nylons, polyurethanes and other synthetic bearing materials are sometimes called _____ bearing materials
Plastic
The advantage of plastic bearings is that they are generally inert to most ___ and ____
Mild acids and alkalis
The lubricant for plastic bearings can be oil or grease, but ____ is sometimes used
Water
With ____ rubbing speeds and ____ operating temperatures, some grades of nylon run with no lubrication
Low and Low
Note: Plastic bearings have varying, but higher coefficients of heat expansion VS metallic bearing materials.
Some synthetic materials _____ when saturated with water
expand
This non-metallic bearing liner has layers of cotton or other natural fibers bonded with resin. They are strong, shock resistant, and compatible with most fluids
Phenol Laminates
______ is a common anti-friction lining material for bearings. It melts at a temperature of 288C (550F) or less. In a liquid state, it fills all cracks, voids and irregularities in a casting, giving a smooth surface to match the shaft surface.
Babbitt
____ can be used in badly worn bearing housings
Babbitt
____ based babbitts are the hardest and toughest
Tin
tin based babbitt with very high tin content is sometimes called ____ babbitt. Used in heavy service and extreme pressures
nickel
Introducing a small percentage of ___ to a tin based babbitt gives a slightly softer material
lead
____ based babbitt are cheaper and used for light loads at low speeds
Lead based babbitt.
Note: this is when lead replaces the majority of the tin. up to 10% tin and 75% lead
When pouring babbitt, 275C-285C (495F-545F) is:
Melting point
When pouring babbitt, 343C-371C (650F-700F) is:
Pour Point
When pouring babbitt, 25C-28C (40F-50F) is
complete solidification point
If babbitt is overheated, the ____ _____ of the material is greatly reduced
Service life
Babbitt is held in position in a bearing casting by ___ which are grooves or slots in the casting
Keys
Note: Any bearing liner to be re-babbitted must have the keys cleaned out
A ____ or dummy shaft is used to shape and size bearings
Mandrel
Note: must be several inches longer than the widest bearing to be poured
A mandrel with side pieces helps you to:
quickly center the mandrel in the bearing housing
Poured babbitt is held in position with a ring held in place by a backing of:
babbitt putty
pouring babbitt can be ______ and is usually done by a designated millwright in the plant
dangerous
When you pour babbitt into a bearing and mandrel assembly, make sure the assembly has been heated to 94C (200F) first to remove any free water or surface moisture. This is because:
Free water causes a “blow back” or explosion
Preparation for babbitting is critical, the vertical and horizontal shaft positions are _____ ____.
Most important
when a thin skin of babbitt must be firmly attached to a metallic backing, a ____ process is used. Similar to brazing a brass coating.
Tinning
Any bearing (regardless of shape or material) must prepared carefully. You must check: (4)
- Surface Finish (area of contact)
- Running Clearance
- Lubrication Entry
- Grooves (for distributing lubrication)
Hand tools, such as scrapers, used for fitting bearings may be a commercial product or:
Hand made tool
After the bearing has been babbitted, the corners of the bottom half must be ____ to keep the shaft from binding
relieved
With babbitt, the top edge of the bearing must be _____ almost to the corners. This channels the lubricant to the shaft.
Chamfered
Note: Chamfer is often greater for grease than with oil
With babbitt, always cut grooves into the ____ section of the bearing
unloaded
A one piece or solid bearing used in an inverted position may need to be lubricated through the ____ of the bearing
Base
After the chamfers and/or oil grooves are cut into the load bearing surfaces, check the bearing for ______. to do this, lightly coat a mandrel in mechanics bluing and rotate it in the bearing.
contact
When a bearing is assembled, there must be a small amount of ____ between the shaft and bearing cap.
Clearance
Shims are made from material that will not _____
Compress
shims are made from materials that are not affected by _______
oil
These are 3 materials you can make shims from: (3)
- Sheet packing
- Tin plate
- Brass shim stock
What is the advantage and disadvantage of slip-in shims?
Advantage: Cap doesn’t need to be fully disassembled for installation
Disadvantage: Can lose the shims easier
The amount of clearance set into a friction bearing depends upon ______ and company policy.
Machine design
Some machines with a constant load toward the base of the bearing do not have a ______
fitted cap
Note: Cap merely keeps out foreign material and supplies lubricant
As a general rule, with constant one direction load and rotation, bearing clearance can be from ____ to ____
Medium to loose
As a general rule, with reversing rotation and fluctuating loads, bearing clearance can be from _____ to _____
medium to tight
as a general rule, with reciprocating action, bearing clearance must be _____
tight
What are three ways you can check bearing clearance on a shaft? (3)
- Feeler gauge
- Plastigage/lead wire
- Dial indicators
____ are two piece liners installed in a bearing housing. They are usually held in position by pins, dowels, screws, special bearing designs, compression, or combinations of those.
Shells
When shells are first installed, they frequently extend past the face of the bearing by a small amount. This is known as the _____
Crush or Crush allowance
With bearing shells, when the cap and other shell is installed and fasteners are torqued to the correct tension, the shells are forced into ____ ____ with the housing
Full Contact
Shells can be installed and used in two cases: (2)
- No adjustment for wear
- Wear adjustment is obtained by shims
One advantage of shell liners is that they may be _____ by taking the weight of the shaft off the liner.
removed
_____ are one piece liners and can be made from any of the common bearing materials.
Bushings
With a bushing, fit and clearance are usually set by the dimensions machined into the housing and bushing. It is held in position by: (3)
- Press fit
- Press fit and dowels
- Dowels with clamping action between cap and base
Small bushings can be ____ to bring the bore to the correct diameter.
Reamed
Larger diameter bushings sometimes require _____ or scraping
Honing
If the bushing is supplied with an oil hole, you must align it to the supply line when pressing in the bushing. With some bushings, the oil line must be _____ after installation.
Drilled.
Note: Should be scraped to remove high spots caused by drilling
When a bushing is worn it must be replaced as there is no:
Adjustment for clearance
Friction bearings are usually considered radial load bearings with limited ____ capacity.
Thrust
Note: Thrust (axial force) is usually controlled with other components
The thrust in a plain bearing is controlled by a shaft collar fastened to the shaft, or by a thrust washer backed by a hub. Such a design is good for: (3)
- Low speeds
- light to medium intermittent thrust loading
- simple lubrication
Thrust of a shaft is controlled by the shaft shoulder and a collar that adjusts the amount of:
End float
Note: If the shaft shoulder is not high enough, you may add a collar or other machined component to contact the bearing surface. Good for high speed applications.
End float is:
The amount a shaft moves axially in a bearing
The liner material that covers the ends of bearings may be made of any of the following materials: (3)
- solid babbitt poured in the bearing
- shells made of brass or bronze
- brass shell with a tinned babbitt wear face
Some bearings are designed to carry both radial and thrust forces without the use of other components. Such setups require:
shaft and bearing liner material to have matching parallel grooves
Note: no adjustment for end float, and lubrication can be a problem
This bearing is a special thrust bearing designed to take high speeds and heavy loads:
Kingsbury thrust bearing
The basic design of a kingsbury thrust bearing consists of: (2)
- Revolving ring with flat contact surface
- Stationary ring with a number of flat contact surfaces of a low friction material.
Note: material of stationary ring can either be brass, bronze, or a tinned on high capacity babbit on a brass backing
With a kingsbury thrust bearing, the lubricant is supplied to the center of the bearing and distributed via:
Centrifugal force
What two styles do kingsbury bearings come in: (2)
- Fixed pad
- Floating or tilting pad
This bearing is a positioning device or guide for linear motion.
Guide bearing
Normally has thin layer of bearing material on its surface and operates with lubrication
This bearing is a split journal bearing mostly used for high peripheral speeds and shaft stabilization. The shoes are machined cylindrically to fit freely in grooves in a retaining ring.
Pivoted shoe bearing
Note: This bearing operates similar to the flat, tilting pad, kingsbury bearing
The surfaces of the shoes and rings on a pivoted shoe bearing are _____ _____ and low friction. The bearing is dowelled so the halves can only be joined one way
corrosion resistant
On a pivoted shoe bearing, each shoe has its own oil inlet, which helps to: (2)
- Lower operating temperature
- Keep it uniform
