A bearing is a device to permit constrained relative motion between two parts, typically rotation or linear movement. Bearings may be classified broadly according to the motions they allow and according to their principle of operation as well as by the directions of applied loads they can handle.
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Bearing friction
Low friction bearings are often important for efficiency, to reduce wear and to facilitate high speeds. A ball bearing is an engineering term referring to a type of Rolling-element bearing which uses Balls to maintain the separation between the moving parts Essentially, a bearing can reduce friction by virtue of its shape, by its material, or by introducing and containing a fluid between surfaces.
- By shape, gains advantage usually by using spheres or rollers.
- By material, exploits the nature of the bearing material used. (An example would be using plastics that have low surface friction. )
- By fluid, exploits the low viscosity of a layer of fluid, such as a lubricant or as a pressurized medium to keep the two solid parts from touching.
- By fields, exploits electromagnetic fields, such as magnetic fields, to keep solid parts from touching.
Combinations of these can even be employed with the same bearing. An example of this is where the cage is made of plastic, and it separates the rollers/balls, which reduce friction by their shape and finish.
Principles of operation
There are at least six common principles of operation:
- sliding bearings, usually called "bushes", "bushings", "journal bearings", "sleeve bearings", "rifle bearings", or "plain bearings"
- rolling-element bearings such as ball bearings and roller bearings
- jewel bearings, in which the load is carried by rolling the axle slightly off-center
- fluid bearings, in which the load is carried by a gas or liquid
- magnetic bearings, in which the load is carried by a magnetic field
- flexure bearings, in which the motion is supported by a load element which bends. A mechanical bushing is a cylindrical lining designed to reduce friction and wear inside a hole or constrict and restrain motion of mechanical parts A mechanical bushing is a cylindrical lining designed to reduce friction and wear inside a hole or constrict and restrain motion of mechanical parts A journal bearing is a simple bearing in which a shaft, or "journal" or Crankshaft rotates in the bearing with a layer of Oil or A mechanical bushing is a cylindrical lining designed to reduce friction and wear inside a hole or constrict and restrain motion of mechanical parts A rolling-element bearing is a bearing which carries a load by placing round elements between the two pieces A jewel bearing is a bearing in which a metal Spindle turns in a jewel -lined pivot hole Fluid bearings are bearings which solely support the bearing's loads on a thin layer of liquid or gas A magnetic bearing is a bearing which supports a load using Magnetic levitation. In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges A flexure bearing is a bearing which allows motion by bending a load element
Loads
Bearings vary greatly over the forces and speeds that they can support.
Forces can be radial, axial (thrust bearings) or moments perpendicular to the main axis. A thrust bearing is a particular type of rotary bearing. Like other rotary bearings they permit rotation between parts but they are designed to support a high Axial
Speeds
Bearings vary typically involving some degree of relative movement between surfaces, and different types have limits as to the maximum relative surface speeds they can handle, and this can be specified as a speed in ft/s or m/s.
For rotational bearings generally performance is defined in terms of the product 'DN' where D is the diameter (often in mm) of the bearing and N is the rotation rate in revolutions per minute.
Generally in terms of relative speed of the moving parts there is considerable overlap between capabilities, but plain bearings can generally handle the lowest speeds while rolling element bearings are faster, followed by fluid bearings and finally magnetic bearings which have no known upper speed limit.
Life
Fluid and magnetic bearings can potentially give indefinite life.
Rolling element bearing life is statistical, but is determined by load, temperature, maintenance, vibration, lubrication and other factors.
For plain bearings some materials give much longer life than others. Some of the John Harrison clocks still operate after hundreds of years because of the lignum vitae wood employed in their construction, whereas his metal clocks are seldom run due to potential wear. John Harrison (24 March 1693 – 24 March 1776 was an English Clockmaker. Lignum vitae is the Heartwood of species of the genus Guaiacum, the trees of which are also called Guayacan.
Maintenance
Many bearings require periodic maintenance to prevent premature failure, although some such as fluid or magnetic bearings may require little maintenance.
Most bearings in high cycle operations need periodic lubrication and cleaning, and may require adjustment to minimise the effects of wear.
History and development
An early type of linear bearing was an arrangement of tree trunks laid down under sleds. This technology may date as far back as the construction of the Pyramids of Giza, though there is no definitive evidence. The Giza Necropolis stands on the Giza Plateau on the outskirts of Cairo, Egypt. Modern linear bearings use a similar principle, sometimes with balls in place of rollers.
The first plain and rolling-element bearings were wood, but ceramic, sapphire or glass can be used, and steel, bronze, other metals, and plastic (e. Wood is hard fibrous lignified structural tissue produced as secondary Xylem in the stems of Woody plants notably trees but also shrubs The word ceramic is derived from the Greek word κεραμικός ( keramikos) Sapphire (antique greek hyacinthos refers to gem varieties of the mineral Corundum, an Aluminium oxide (Al2O3 when it is a color other than Glass in the common sense refers to a Hard, Brittle, transparent Solid, such as that used for Windows many Steel is an Alloy consisting mostly of Iron, with a Carbon content between 0 Bronze is any of a broad range of Copper alloys, usually with Tin as the main additive but sometimes with other elements such as Phosphorus g. , nylon, polyoxymethylene, teflon, and UHMWPE) are all common today. Overview Nylon is a Thermoplastic silky material first used commercially in a nylon- Bristled Toothbrush (1938 followed more famously by Polyoxymethylene (POM in the USA also commonly known under DuPont 's brand name Delrin, is an Engineering plastic, a Polymer with the chemical Teflon is a Registered trademark and Brand name of the DuPont company for products made from three types of fluorine-containing polymers ( Fluoropolymers Ultra high molecular weight polyethylene ( UHMWPE) also known as high-modulus polyethylene ( HMPE) or high-performance polyethylene ( HPPE Indeed, stone was even used in various forms. Think of the "jeweled pocket watch", which incorporated stones to reduce frictional loads, and allow a smoother running watch. Of course, with older, mechanical timepieces, the smoother the operating properties, then the higher the accuracy and value. Wooden bearings can still be seen today in old water mills where the water has implications for cooling and lubrication.
Rotary bearings are required for many applications, from heavy-duty use in vehicle axles and machine shafts, to precision clock parts. The simplest rotary bearing is the sleeve bearing, which is just a cylinder inserted between the wheel and its axle. This was followed by the roller bearing, in which the sleeve was replaced by a number of cylindrical rollers. Each roller behaves as an individual wheel. A wheel is a circular device that is capable of rotating on its axis facilitating movement or transportation whilst supporting a load ( Mass) or performing labour in machines The first practical caged-roller bearing was invented in the mid-1740s by horologist John Harrison for his H3 marine timekeeper. Horology (from Greek ώρα, "hour time" and λόγος Logos, "study speech" lit John Harrison (24 March 1693 – 24 March 1776 was an English Clockmaker. This used the bearing for a very limited oscillating motion but Harrison also used a similar bearing in a truly rotary application in a contemporaneous regulator clock.
An early example of a wooden ball bearing (see rolling-element bearing), supporting a rotating table, was retrieved from the remains of the Roman Nemi ships in Lake Nemi, Italy. A rolling-element bearing is a bearing which carries a load by placing round elements between the two pieces The Roman Republic was the phase of the ancient Roman civilization characterized by a Republican form of government a period which began with the overthrow of the The Nemi Ships were huge and exceedingly luxurious Ships built by the Roman emperor Caligula in the first century AD at Lake Nemi. Lake Nemi (Nemorensis Lacus is a small circular Volcanic lake in the Lazio region of Italy 30 kilometers south of Rome, taking its name from Italy (Italia officially the Italian Republic, (Repubblica Italiana is located on the Italian Peninsula in Southern Europe, and on the two largest The wrecks were dated to 40 AD. Year 40 was a Leap year starting on Friday (link will display the full calendar of the Julian calendar. Leonardo da Vinci is said to have described a type of ball bearing around the year 1500. Leonardo di ser Piero da Vinci ( April 15 1452 – May 2 1519 was an Italian Polymath, having been a scientist Mathematician, Engineer One of the issues with ball bearings is that they can rub against each other, causing additional friction, but this can be prevented by enclosing the balls in a cage. The captured, or caged, ball bearing was originally described by Galileo in the 1600s. Galileo Galilei (15 February 1564 &ndash 8 January 1642 was a Tuscan ( Italian) Physicist, Mathematician, Astronomer, and Philosopher The mounting of bearings into a set was not accomplished for many years after that. The first patent for a ball race was by Philip Vaughan of Carmarthen in 1794. Philip Vaughan was a Welsh inventor and Ironmaster who Patented the first design for a Ball bearing in Carmarthen in 1794 Carmarthen ( Welsh Caerfyrddin - caer fort + Myrddin Moridunum is the County town of Carmarthenshire, Wales. Year 1794 ( MDCCXCIV) was a Common year starting on Wednesday (link will display the full calendar of the Gregorian calendar (or a
Friedrich Fischer's idea from the year 1883 for milling and grinding balls of equal size and exact roundness by means of a suitable production machine formed the foundation for creation of an independent bearing industry. Friedrich Fischer (1849–1899 from Schweinfurt, Germany is considered the father of the modern Ball bearing, having invented the process for milling standard bearings
The modern, self-aligning design of ball bearing is attributed to Sven Wingquist of the SKF ball-bearing manufacturer in 1907. MotorCycle is the title of a 1993 album by Rock band Daniel Amos, released on BAI Records. SKF, Svenska Kullagerfabriken AB, later AB SKF, is a Swedish bearing Company founded in 1907 supplying bearings seals Year 1907 ( MCMVII) was a Common year starting on Tuesday (link will display the full calendar of the Gregorian calendar (or a Common year
Henry Timken, a 19th century visionary and innovator in carriage manufacturing, patented the tapered roller bearing, in 1898. Henry Timken (1831 - 1909 was an inventor who was born in Bremen, Germany. The following year, he formed a company to produce his innovation. Through a century, the company grew to make bearings of all types, specialty steel and an array of related products and services.
The Timken Company (Sale $4,973. The Timken Company ( is a major manufacturer of Tapered roller bearings and specialty steels located in Canton, Ohio. 4M, 2006), The SKF company($6,195. SKF, Svenska Kullagerfabriken AB, later AB SKF, is a Swedish bearing Company founded in 1907 supplying bearings seals 1M, 2005), the Schaeffler Group (Private), the NSK company($5,344. NSK Ltd ( Japanese 日本精工株式会社 Nippon Seikō Kabushiki Kaisha;) inaugurated its business in November 1916 and produced the first Ball bearings 5M, 2006), and the NTN Bearing company($3,697. 8M, 2006) are now the largest bearing manufacturers in the world.
Types
There are many number of different types of bearings.
| Type | Description | Stiffness* | Speed | Life | Notes |
|---|---|---|---|---|---|
| plain bearing | rubbing surfaces, with lubricant | Good, provided wear is low, but some slack is normally present | low/moderate (often requires cooling) | moderate (depends on lubrication) | The simplest type of bearing, widely used, relatively high friction |
| Rolling element bearing | Ball or rollers are used to prevent or minimise rubbing | Good, but some slack is usually present | moderate-high (often requires cooling) | moderate (depends on lubrication, often requires maintenance) | Used for higher loads than plain bearings with lower friction |
| jewel bearing | off-center bearing rolls in seating | Low due to flexing | low | adequate (needs cleaning and lubrication requires maintenance) | Mainly used in low-load, high precision work such as clocks |
| fluid bearing | Fluid is forced between two faces and held in by edge seal | Very high | Very high- speeds usually limited by seals | Virtually infinite in some applications, may wear at startup/shutdown in some cases | Can fail quickly due to grit or dust or other contaminants. Stiffness is the resistance of an elastic body to Deformation by an applied Force. A mechanical bushing is a cylindrical lining designed to reduce friction and wear inside a hole or constrict and restrain motion of mechanical parts A rolling-element bearing is a bearing which carries a load by placing round elements between the two pieces A jewel bearing is a bearing in which a metal Spindle turns in a jewel -lined pivot hole Fluid bearings are bearings which solely support the bearing's loads on a thin layer of liquid or gas Maintenance free in continuous use. |
| magnetic bearings | Faces of bearing are kept separate by magnets (electromagnets or eddy currents) | low | Infinite | Infinite | Often needs considerable power. A magnetic bearing is a bearing which supports a load using Magnetic levitation. An electromagnet is a type of Magnet in which the Magnetic field is produced by the flow of an electric current. An eddy current (also known as Foucault current) is an electrical phenomenon discovered by French physicist Léon Foucault in Maintenance free. |
| Flexure bearing | Material flexes to give and constrain movement | low | Very high | Very high or low depending on materials and strain in application | Limited range of movement |
- - stiffness is the amount that the gap varies when the load on the bearing changes, it is distinct from the friction of the bearing
See also
External links
- How Bearings Work - Animations and functioning
- How Bearings Work - - Animations on www. A flexure bearing is a bearing which allows motion by bending a load element Friction is the Force resisting the relative motion of two Surfaces in contact or a surface in contact with a fluid (e A ball bearing is an engineering term referring to a type of Rolling-element bearing which uses Balls to maintain the separation between the moving parts Ball splines (Ball Spline bearings are a special type of Linear motion bearing that are used to provide nearly frictionless linear motion while allowing the member A mechanical bushing is a cylindrical lining designed to reduce friction and wear inside a hole or constrict and restrain motion of mechanical parts A combined bearing or combination Bearing includes a main body and a mating member Fluid bearings are bearings which solely support the bearing's loads on a thin layer of liquid or gas In Mechanical engineering and Tribology, Hertzian contact stress, is a description of the stress within mating parts A hinge is a type of bearing that connects two solid objects typically allowing only a limited angle of Rotation between them A journal bearing is a simple bearing in which a shaft, or "journal" or Crankshaft rotates in the bearing with a layer of Oil or In a Piston engine, the main bearings are the bearings on which the Crankshaft rotates usually plain or Journal bearings All A needle roller bearing is a bearing which uses small cylindrical rollers. Rolamite is a technology for very low Friction bearings developed by Sandia National Laboratories in the 1960s A rolling-element bearing is a bearing which carries a load by placing round elements between the two pieces mechanismen. be
- Early Bearing Failure Detection - Case study
- How to measure a bearing - Practical information on how to measure a bearing
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