Bearings Flashcards
(39 cards)
Purpose
enables rotational or linear movement, while reducing friction and handling stress.
made up of a ball with internal and external smooth metal surfaces, to aid in rolling.
Radial load
Pulley, simply puts weight on the bearing in a manner that causes the bearing to roll or rotate as a result of tension.
Thrust load
Puts stress on the bearing but in a different way. a bearing that is used to support a bar stool is an example of a bearing that is subjected only to thrust load.
Examples of thrust load
car wheels carry a radial load when driving in a straight line. however when it goes around a corner is it subjected to thrust load.
Bearing loads
Axial loading (shaft longitudinal loads) radial loadings (shaft sideward loads) compound loads (both directions together) More suitable for uses in applications which require high speed high precision low torque and low vibration Larger load carrying capacity which makes them more suitable for applications requiring long life and endurance for heavy loads and shock loads
Plain bearings
consist of load carrying cylindrical inserts, made of hard wearing materials, such as cast iron, phosphor bronze, beryllium copper, white metal or special plastics.
oil supports the shaft preventing metal to metal contact.
Used?
they are used mainly in applications where the loads are relatively light and the motion is relatively continuous.
Spherical plain bearings
used in numerous push-pull rod applications and many other aircraft linkages. these bearings types serve primarily a force or load transporters and angular alignment.
Not intended for rotation, the rod end can be installed with grease nipple facilitating easy bearing maintenance.
maintenance free because they are self lubricating.
What are the several designs?
steel on steel (frequent maintenance) steel/sinter bronze composite Teflon TM (PTFE) fabric
Air bearings
also known as aerostatical or aerodynamical bearings are bearings that use a thin film of pressurised air to provide an exceedingly low friction load bearing interface between surfaces.
contact free.
they avoid problems such as friction, wear, particulates and lubricant handling.
Advantages
precision positioning, such as lacking backlash and static friction as well, as in high speed applications.
Uses of air bearings
used in precision machinery tools and fast running machines for example some small turbines.
Rolling element bearings
utilise cylindrical, tapered and spherical rollers running in suitably shaped raceways. while ball bearings employ steel balls which rotate in grooved raceways.
Ball bearings and tapered roller bearings accept both radial and axial loads whilst the other types of roller bearings may accept only radial loads.
Bearing types
Deep groove ball bearings Angular contact ball bearings self-aligning ball bearings cylindrical roller bearings needle roller bearings taper roller bearings spherical roller bearings toroidal or crowned roller bearings thrust ball bearings cylindrical roller thrust bearings needle roller thrust bearings spherical roller thrust bearings
Ball bearings
Consist of an inner and outer race separated by hardened steel balls.
relies on motion of the balls to reduce friction between the inner race carried on the shaft of the machine and the outer race which is normally fitted inside a housing on the stationary part of the machine.
constructed using single or double rows of balls, each row controlled by bronze or brass cage, but bearings which do not have a cage are often not used.
Ball bearings design
designed for radial or thrust loads or a combination of both and can operate in either direction of rotation, can be rigid or self aligning.
Ball bearings advantages
Cheapest and most commonly used type, produced in many designs and sizes, cannot be disassembled.
they can handle operational conditions and their maintenance is simple, relatively good load rating both in radial and axial directions, suitable for high and very high speeds, they require good alignment of the journal and bearing body.
Angular contact bearing
Orbital paths which are offset mutually in the direction of the bearing axis. designed to retain combined load with relatively large axial forces.
Are installed in pairs in opposite positions and as close to each other as possible.
can be paired, or double row bearings.
lower load rating than tapered roller bearings however can be used at higher speeds.
Roller bearings
consist of an inner and outer race separated by hardened steel rollers instead of balls. normally only used to support radial loads.
Three types of roller bearings
Cylindrical roller bearings
spherical roller bearings
tapered roller bearings
Spherical roller bearings
two rows of spherical rollers with a common spherical path on the outer ring.
have a high load rating, suitable for large loads with misaligned seating and deflections of shaft.
usually produced with cylindrical and tapered holes; non dismountable
Taper roller bearings
shape of a cone, cone shaped inner and a cup shaped outer race. rollers are tapered and made from hardened steel. this class of bearing can support radial loads in one direction only. contain two individual rows of bearings. mounted in pairs - back to back so that loads can be accepted in both directions.
Torodial (crowned) roller bearings
single row bearings with long, slightly spherical rolling elements; orbital paths of the outer and inner rings are concave and symmetrical along the axis running through the bearing centre
high radial load rating
reduce vibrations in seating, axial vibrations of the shaft are not transferred to the body.
Needle roller bearings
Special type of roller bearing which uses long, thin cylindrical rollers resembling needles.
rollers are only slightly longer than their diameter, but needle bearings typically have rollers that are at least four times longer than their diameter. support a greater load.
also thinner, so they require less clearance between the axle and the surrounding structure.
