There are different types of bearings, with different shapes, materials, lubrication or operating principles. By far the most common bearing is the plain bearing, in which friction contacting surfaces are used, often lubricated with oil or graphite. A plain bearing can be nothing more than the support surface of a hole through a shaft, or a flat surface on which another element rests, which is defined as a non-discrete device. In the case of a layer of Babbit metal "Babbitt (metal)") fused to the substrate to facilitate sliding, this is referred to as a semi-discrete device; and when it is in the form of a separable sleeve then it is a discrete support surface. With proper lubrication, plain bearings often provide completely acceptable precision, life, and friction at minimal cost, and are therefore widely used.

However, there are many applications where a specific type of bearing can improve machinery efficiency, accuracy, service intervals, reliability, operating speed, size, weight, and purchasing and operating costs.

There are at least 6 common types of bearings,[20]​ each of which works on different principles:.

• - Sliding bearing, which consists of a shaft that rotates in a hole. There are several specific styles: bushing, plain bearing, sleeve bearing, rifle bearing, composite bearing").

• - Bearing, in which the rolling elements placed between the rotating and stationary grooves prevent sliding friction. There are two main types:

• Ball bearing, in which the rolling elements are spherical balls

• Bearings with cylindrical, conical or spherical rollers.

• - Ruby bearing"), a plain bearing in which one of the bearing surfaces is made of an ultra-hard glassy material such as sapphire to reduce friction and wear.

• - Fluid bearing, a non-contact bearing in which the load is supported by a liquid or gas (as in an air bearing).

• - Magnetic bearing, in which the load is supported by a magnetic field.

• - Flexion bearing"), in which the movement is supported by a load element that can bend.

The movements commonly allowed by the bearings are:.

• - Radial rotation, like the rotation of a turbine shaft.

• - Linear movement, like the movement of a drawer.

• - Spherical rotation, as in the kneecaps.

• - Hinge movement, typical of doors and joints such as elbows and knees.

Reducing friction in bearings is often important to optimize their efficiency, to reduce wear and to facilitate prolonged use at high speeds, avoiding overheating and premature bearing failures. Essentially, a bearing can reduce friction by virtue of its shape, its material, or by introducing and containing a fluid between surfaces or by separating the surfaces with an electromagnetic field.

• - By shape: bearings that use spheres or rollers, or bending bearings.

• - By material: the nature of the bearing material used is taken advantage of, as in the case of low surface friction plastics.

• - By fluid: the low viscosity of a fluid layer is used, which serves as a lubricant or as a pressurized medium to prevent the two solid parts from touching, or by reducing the normal force between them.

• - By fields: they use electromagnetic fields to prevent moving parts from rubbing against each other.

• - By air pressure: pressurized air is used to prevent solid parts from touching.

Even combinations of some of these systems can be used within the same bearing. An example is bearings in which a plastic material is used for the cage that separates the rollers/balls, which in turn reduces friction due to its shape and finish.

The design of bearings varies depending on the size and directions of the forces they must withstand. The forces may be predominantly radial (Radius (geometry)), axial (thrust bearings) or bending forces perpendicular to the main axis.

Different types of bearings have different operating speed limits. They are generally specified as maximum relative surface velocities, often expressed in ft/s or m/s. Slewing bearings typically describe performance in terms of the product "DN", where "D" is the mean diameter (often in mm) of the bearing and "N" is the rotational speed in revolutions per minute.

In general, there is considerable overlap in speed ranges between bearing types. Plain bearings generally handle only the lowest speeds, rolling element bearings allow for faster spins, followed by fluid bearings and finally magnetic bearings, ultimately limited by centripetal force exceeding the strength of the material.

In some applications support loads are generated from different directions, but the bearings only tolerate a limited play or "tilt" (angle with respect to the normal direction of the shaft) as the applied load changes. One source of movement is gaps or "plays" in the bearing. For example, a 10mm shaft in a 12mm hole has a clearance of 2mm.

Allowed play varies greatly depending on use. For example, a wheelbarrow wheel supports radial and axial loads. Axial loads can involve hundreds of newtons (Newton (unit)") of force to the left or right and it is generally acceptable for the wheel to wobble up to 10mm under the varying load. In contrast, a lathe can position a cutting tool with an accuracy of ±0.002 mm using a ball screw supported by rotating bearings, which must withstand axial loads of thousands of newtons in any direction.

A second source of motion is the elasticity of the bearing itself. For example, the balls in a bearing have a certain flexibility, and under load they deform into a slightly flattened shape. The groove that the rollers travel also has an elastic behavior, and develops a slight dent where it receives the pressure of the balls.

The stiffness of a bearing is related to how the distance between the parts that are separated varies with the applied load. In rolling element bearings, it is linked to the tension supported between the balls and the grooves they run through. With fluid bearings, it is due to how the spacing between the parts varies with fluid pressure (when properly loaded, fluid bearings are typically stiffer than rolling element bearings).

Los cojinetes de fluidos y magnéticos pueden tener una vida útil prácticamente indefinida. En la práctica, existen cojinetes de fluido que soportan cargas elevadas en plantas hidroeléctricas que han estado en servicio casi continuo desde alrededor de 1900 y que no muestran signos de desgaste.[21]​.

La vida útil de los cojinetes de los elementos rodantes está determinada por la carga, la temperatura, el mantenimiento, la lubricación, los defectos del material, la contaminación, la manipulación, la instalación y otros factores. Todos estos factores pueden tener un efecto significativo en la vida útil de un rodamiento. Por ejemplo, la vida útil de los rodamientos en una aplicación se prolongó drásticamente al cambiar la forma en que se almacenaban los rodamientos antes de su instalación y uso, ya que las vibraciones durante el almacenamiento provocaban problemas con el lubricante incluso cuando la única carga sobre el rodamiento era su propio peso;[22]​ el daño resultante es a menudo un falso punzonamiento.[23]​ La vida útil de los rodamientos se determina mediante valores estadísticos: varias muestras de un rodamiento dado, a menudo exhibirán una vida útil según una campana de Gauss, y algunas muestras presentarán una vida significativamente mejor o peor. Su vida útil varía porque la estructura microscópica y la contaminación varían mucho, incluso cuando macroscópicamente parecen idénticas.

Service life L10

Bearings are often specified to give "L10" life (outside the US it may also be referred to as "B10"). It is the duration over which ten percent of the bearings in that application can be expected to have been out of service due to classical material fatigue failure (and not any other failure mode caused by lack of lubrication, incorrect mounting or other problems), or, alternatively, the period of time over which ninety percent will continue to function. Bearing life L10 is a theoretical life and may not represent the actual life of a given bearing. Bearings are also classified using the C value (static load). This basic load rating is a reference value, and not an actual load value.

For plain bearings, some materials give a much longer life than others. Some of John Harrison's clocks still work after hundreds of years due to the guaiac wood used in their construction, while his metal clocks rarely work due to wear problems.

In a plain bearing, two bushings move in direct contact, sliding by friction. In order to keep friction as low as possible, appropriate materials and lubricants are selected. Lubricants have the function of creating a sliding film that separates the two materials or prevents direct contact. Babbitt metal is usually used as the bushing material.

As the two parts touch, wear on the contact surfaces limits their useful life. The generation of a lubricating film that separates the two parts of the mechanism through complete lubrication requires an additional system to raise the pressure of the lubricant. This system is used only on large machines, with large sliding bearings. Slip resistance causes the conversion of part of the kinetic energy into heat, which means that the parts that support the bearing bushings must be very resistant both mechanically and thermally.

Bending bearings are based on the elastic properties of the material of a piece that is repeatedly bent. Some materials fail after being subjected to repeated bending, even at low loads, but careful material selection and proper design can make the life of flexing bearings indefinite.

Although a long bearing life is often desirable, sometimes it is not necessary. Harris, 2001 describes a bearing for a rocket engine oxygen pump that achieved only a few hours of life, but a value well above the tens of minutes of life strictly necessary.[22]​.

Composite material bearings.

Depending on their particular specifications, composite bearings can operate for up to 30 years without maintenance.

Oscillating bearings.

For bearings used in oscillating applications, specific approaches are used to calculate L10.[24]​.

External factors

The useful life of a bearing is affected by many parameters that are not controlled by the manufacturer that supplied it. For example, bearing mounting, temperature, exposure to the external environment, lubricant cleanliness, or passage of electrical currents. High-frequency electronic inverters can induce eddy currents in a bearing, which can be suppressed by using a ferrite core.

The temperature and physical characteristics of the supporting microsurfaces will determine the amount of friction at the contacts between the solid parts.

Certain elements and fields reduce friction while increasing speeds.

The forces expected for the working regime and the degree of mobility allow determining the amount of load that the type of bearing can support.

Alignment factors can play a detrimental role in wear, although this problem can be effectively mitigated by computerized monitoring of its evolution, and almost definitively, with types of bearings that practically completely avoid friction, such as magnetic levitation bearings or bearings made of air or other pressurized fluids.

There are many methods of mounting bearings, generally using an interference fit.[25] Press fit and shrink fit involve inserting a bearing into a hole or shaft. In these cases, it is important to keep the inside diameter of the housing and the outside diameter of the shaft within very tight limits, which may involve one or more reaming operations, several facing and drilling operations, tapping, and threading operations.[26] Alternatively, the desired interference fit can also be achieved by adding a tolerance ring.

Muchos rodamientos requieren mantenimiento periódico para evitar fallos prematuros, aunque otros muchos apenas requieren mantenimiento. Estos últimos incluyen varios tipos de cojinetes de polímero, fluidos y magnéticos, así como cojinetes de elementos rodantes que se describen con términos que incluyen "cojinete sellado" y "sellado de por vida", que incorporan un sellado para mantener fuera la suciedad y evitar que se escape la grasa que los lubrica. Se usan con éxito en muchas aplicaciones, brindando un funcionamiento libre de operaciones de mantenimiento, aunque en algunos casos no pueden usarse de manera efectiva.

Los rodamientos no sellados a menudo tienen un punto de engrase destinado a facilitar la lubricación periódica con una aceitera, o una recámara para ser llenada periódicamente con aceite. Antes de la década de 1970 no eran habituales, y el engrasado era una actividad más común que en la actualidad. Por ejemplo, los chasis de los automóviles solían requerir "trabajos de lubricación" casi tan a menudo como los cambios de aceite del motor, pero los chasis de los automóviles de hoy en día en su mayoría están sellados de por vida. Desde finales de 1700 hasta mediados de 1900, la industria dependía de muchos trabajadores llamados engrasadores&action=edit&redlink=1 "Engrasador (ocupación) (aún no redactado)") para lubricar la maquinaria con frecuencia.

Actualmente, las máquinas de fábrica suelen tener "sistemas de lubricación", en los que una bomba central suministra cargas periódicas de aceite o grasa desde un depósito a través de "líneas de lubricación" a los diversos "puntos de lubricación" en las superficies de apoyo de la máquina, los cojinetes, o los bloques de almohada"). La sincronización y el número de dichos "ciclos de lubricación" se regulan mediante el control computarizado de la máquina, utilizando un controlador lógico programable o sistemas de control numérico, así como mediante funciones de operación manual cuando se necesitan ocasionalmente. Este proceso automatizado es la forma en que se lubrican todas las máquinas herramienta asistidas electrónicamente modernas y muchas otras máquinas de fábrica actuales.

También se utilizan sistemas de lubricación similares en máquinas no automatizadas, en cuyo caso se dispone de una bomba manual que se supone que el operador de la máquina debe bombear una vez al día (para máquinas en uso constante) o una vez a la semana. Estos se denominan "sistemas de un solo paso" por su principal punto de accionamiento: un solo tirón de una manija sirve para lubricar la máquina completa, en lugar de una docena de posiciones diferentes alrededor de la máquina donde usar una aceitera o una lata de aceite.

El sistema de lubricación dentro de un motor moderno de automóvil o camión es similar en concepto a los sistemas de lubricación mencionados anteriormente, excepto en que el aceite se bombea continuamente. Gran parte de este aceite fluye a través de pasajes perforados o fundidos en la culata "Culata (motor)") y en el bloque del motor, llegando a través de estos conductos directamente a los cojinetes y saliendo a chorros a otros lugares para proporcionar un baño de aceite. La bomba de aceite simplemente bombea constantemente, y cualquier exceso de aceite bombeado escapa continuamente a través de una válvula de alivio hacia el sumidero del cárter.

Muchos rodamientos en operaciones industriales de alto ciclo necesitan lubricación y limpieza periódicas, y muchos requieren un ajuste ocasional, como un ajuste de precarga, para minimizar los efectos del desgaste.

La vida útil del rodamiento suele ser mucho mayor cuando se mantiene limpio y bien lubricado. Sin embargo, muchas aplicaciones dificultan un buen mantenimiento. Un ejemplo son los rodamientos de la cinta transportadora de una trituradora de rocas, están continuamente expuestos a partículas abrasivas duras. La limpieza es de poca utilidad por la dificultad que implica, y porque el rodamiento se ensucia nuevamente tan pronto como el transportador reanuda la operación. Por lo tanto, un buen programa de mantenimiento podría lubricar los cojinetes con frecuencia, pero no incluir ningún desmontaje para la limpieza. La lubricación frecuente, por su naturaleza, proporciona un tipo limitado de acción de limpieza, al desplazar el aceite o la grasa más antiguos (llenos de arena) por una carga nueva, que a su vez acumula arena antes de ser desplazada por el próximo ciclo. Otro ejemplo, son los cojinetes de las turbinas eólicas, que dificultan su mantenimiento ya que la góndola se coloca al aire en zonas de viento fuerte. Además, la turbina no siempre funciona y está sujeta a un comportamiento operativo diferente en diferentes condiciones climáticas, lo que hace que la lubricación adecuada sea un desafío.[27]​.

Detection of failures in the outer race of rolling element bearings

Bearings are widely used in today's industries and therefore their maintenance becomes an important task. Rolling elements tend to wear easily due to metal-to-metal contact, leading to failures in the outer race, inner race, and rollers themselves. It is also the most vulnerable component of a machine because it is often under high load and high operating speed conditions. Regular diagnosis of rolling element bearing failures is essential for industrial safety and machine operations, as well as reducing maintenance costs or avoiding downtime. Between the outer court, the inner court and the ball, the outer court tends to be more vulnerable to failures and defects.

Rolling elements can excite the fundamental frequency of the bearing component when they pass a damaged spot on the outer race. Therefore, it is necessary to identify the natural frequency of the bearing outer race and its harmonics. Bearing failures create impulses and result in strong harmonics of the failure frequencies in the vibration signal spectrum,[28]​ which are sometimes masked by adjacent frequencies in the spectra due to their low energy. Therefore, very high spectral resolution is often needed to identify these frequencies during fast Fourier transform analysis.

The fundamental frequency of a bearing with free boundary conditions is 3 kHz. Therefore, to use the resonance bandwidth method of a bearing component to detect the failure at an early stage, an accelerometer with a high-frequency measurement range must be used, and data must be recorded for a long period. A characteristic failure frequency can only be identified when the extent of the failure is severe, such as the presence of a hole in the outer race. Failure frequency harmonics are a more sensitive indicator in the bearing outer race. For more rigorous detection of faults in defective bearings, waveform and spectrum analysis techniques will help reveal them. However, if high-frequency demodulation is used in envelope analysis to detect characteristic bearing failure frequencies, maintenance professionals must be more careful in the analysis due to the influence of resonance, which may or may not contain failure frequency components.

The use of spectral analysis as a tool to identify bearing failures faces complex challenges due to problems such as low energy, low signal sharpness, or cycloseasonality. High resolution is often desired to differentiate components of the failure frequency from other adjacent high-amplitude frequencies. Therefore, when sampling the signal for fast Fourier transform analysis, the sample length must be large enough to provide adequate frequency resolution in the spectrum. Additionally, keeping calculation time and memory within limits and avoiding unwanted truncations can be demanding. However, a required minimum frequency resolution can be obtained by estimating bearing failure frequencies and other vibration frequency components and their harmonics as a function of shaft speed, misalignment, operating frequency, or gearbox effect.[29]​.

Lubricant confinement

Some bearings use a thick grease (lubricant) for lubrication, which is filled into the spaces between the bearing surfaces, also known as a "packing". The grease is held in place by a plastic, leather or rubber gasket (formerly known as a stuffing box) that covers the inner and outer edges of the bearing race to prevent lubricant from escaping.

Bearings can also be packaged with other materials. Historically, railroad car wheels used sleeve bearings filled with "waste" or loose pieces of oil-soaked cotton or wool fiber confined in so-called axle boxes, and later transitioned to solid cotton pads.[30]

ring oiler

The bearings can be lubricated with a metal ring that moves freely on the central rotating axis of the bearing. This ring hangs inside a chamber containing lubricating oil. As the bearing rotates, viscous adhesion moves oil up the ring and deposits it on the shaft, where it migrates to the bearing to lubricate it. Excess oil is expelled and accumulates in the chamber again.[31]​.

Splash lubrication

A rudimentary form of greasing is "splash lubrication"). special plastic deflectors that spread oil randomly around the inside of the mechanism.[32]​.

Pressure lubrication

For high-speed, high-power machines, loss of lubricant can result in rapid heating of the bearings and damage due to friction. Also in dirty environments, the oil can become contaminated with dust or debris that increases friction. In these applications, a fresh supply of lubricant can be continuously available to the bearing and all other contact surfaces, and the excess can be collected for filtering, cooling and possibly reuse. Pressure lubrication is commonly used in large, complex internal combustion engines in those parts of the engine where directly splashed oil cannot reach, such as in the upper valve assemblies.[33] High-speed turbochargers also typically require a pressurized oil system to cool the bearings and prevent them from burning due to turbine heat.

Composite bearings

Composite bearings are designed with a self-lubricating polytetrafluoroethylene (PTFE) liner with a laminated metal backing. The PTFE liner offers consistent, controlled friction and durability, while the metal backing ensures the composite bearing is robust and able to withstand high loads and stresses over its long life. Its design also makes it lightweight: one-tenth the weight of a traditional bearing.[34]​.

There are many different types of bearings. Research into new designs is constant, in order to reduce friction, increase bearing payload and increase momentum build-up and speed.

Below are the terms for the different types of bearings and their parts, and their corresponding English equivalents:

Below are formulas for sizing a boat propeller bearing and an illustrative example:.

Calculation of the dimension of a ship's main engine thrust bearing:.

Example:.

The effective power of the engine is a manual data, often given in (hp), which must be converted to (kg/cm²). Assume a power of 3350 hp and a propeller efficiency of 0.6.

• - data with which the thrust bearing surface is cleared.

• - Wikimedia Commons hosts a multimedia category on Bearing.

• - ISO dimensional system and bearing numbers.

• - Complete review on bearings, University of Cambridge.

• - A glossary of bearing terms.

• - How bearings work.

• - Kinematic Models for Design Digital Library (KMODDL) – movies and photos of hundreds of models of mechanical systems in operation at Cornell University. It also includes an e-book library of classic mechanical design and engineering texts.

• - Types of bearings, University of Cambridge.

• - Bearings, in Wordpress.

• - Bearings - Rincón del Vago.

• - How they work: the bearings.

• - Anti-friction bearings.

• - What are friction bearings and how do they work?

• - (Bearings or bearings) Types of bearings in Rodamientos.mx.

Contenido

La invención del rodamiento, en forma de rodillos de madera que sostienen un objeto que se mueve, es muy antigua, y puede ser anterior a la invención de la rueda utilizada para el transporte que gira sobre un cojinete liso.[5]​.

Aunque a menudo se afirma que los egipcios usaban troncos "Tronco (botánica)") como rodillos situados debajo de plataformas de arrastre, es una especulación moderna.[6]​ Los propios dibujos del período del Antiguo Egipto encontrados en la tumba de Dyehutyhotep muestran el proceso de mover enormes bloques de piedra empleando trineos con los patines lubricados con líquidos que constituirían una forma de cojinetes de deslizamiento.[7]​ También hay dibujos egipcios de superficies de deslizamiento lisas preparadas con herramientas manuales.[8]​.

Los vehículos con ruedas que utilizaban cojinetes lisos debieron aparecer entre el 5000 y el 3000 a. C.[9]​.

El primer ejemplo conocido de un cojinete con elementos rodantes es un rodamiento de bolas de madera que sostiene una mesa giratoria de época romana, encontrada entre los restos de los barcos de Nemi (hallados junto a la villa imperial de Calígula en el lago de Nemi, en Italia), que datan del año 40 d. C.[10]​[11]​.

Leonardo da Vinci incorporó dibujos de cojinetes de bolas en su diseño para un helicóptero alrededor del año 1500. Este es el primer dibujo que testimonia la idea de utilizar rodamientos en un diseño aeronáutico. Sin embargo, Agostino Ramelli (1531-1610) sería el primero en publicar un libro con bocetos de rodamientos de rodillos y de empuje. Un problema con los cojinetes de bolas y de rodillos es que las bolas o los rodillos rozan entre sí, lo que provoca una fricción adicional, que se puede reducir separándolos mediante jaulas. El cojinete de bolas enjauladas fue descrito originalmente por Galileo en el siglo XVII.[12]​.

El primer rodamiento de rodillos enjaulado práctico fue inventado a mediados de la década de 1740 por el relojero británico John Harrison para su cronómetro marino H3, donde se empleaba un cojinete para permitir un movimiento oscilante de baja amplitud, pero también usó un cojinete similar en una aplicación verdaderamente rotatoria en un reloj contemporáneo.[12]​.

industrial era

The first recorded modern patent for a ball bearing was granted to Philip Vaughan, a British inventor and forgemaster who devised the first design of a ball bearing at Carmarthen in 1794. His was the first modern ball bearing design, with the balls rolling in a perimeter groove cut into the shaft body.[13] Bearings played a key role in the nascent Industrial Revolution, allowing new machinery to operate more efficiently.

The first plain and rolling element bearings were made of wood, followed shortly by bronze ones. Throughout their history, they have been made from many materials, including ceramic, sapphire, glass, steel, bronze, other metals, and various plastics (such as nylon, polyacetal, polytetrafluoroethylene, or high-density polyethylene), which are still used today.

Watchmakers produce "jeweled" watches that use ruby ​​plain bearings to reduce friction, allowing for more accurate timekeeping.

Even the most basic materials can have good durability. For example, wooden bearings can still be seen in antique clocks or in hydraulic mills where water provides cooling and lubrication.

The first patent for a radial-style ball bearing was granted to Jules Suriray, a Parisian bicycle mechanic, on August 3, 1869. The bearings were later installed in the bicycle with which James Moore "James Moore (cyclist)" won the world's first road bicycle race, the Paris-Rouen "Paris-Rouen (cyclist race)") in November 1869.[14]

In 1883, Friedrich Fischer "Friedrich Fischer (inventor"), founder of the company FAG"), developed a method for serially grinding and polishing balls of equal size and precise sphericity, which laid the foundation for the creation of an independent bearing industry. His hometown, Schweinfurt (Germany) "Schweinfurt (Germany)"), later became a world-leading center for the production of ball bearings.

The modern, self-aligning design of ball bearings is attributed to engineer Sven Wingquist of the ball bearing manufacturing company SKF in 1907, when he was granted Swedish patent No. 25406.

Henry Timken, a visionary 19th-century carriage manufacturing businessman, patented the tapered roller bearing in 1898. The following year he formed a company to produce his innovation. For more than a century, the company grew to manufacture bearings of all types, including the use of specialty steels in a diverse range of related products and services.

Erich Franke invented and patented the wire fence bearing in 1934. His focus was on a bearing design with the smallest possible cross section that could be integrated into the housing design. After the Second World War, together with Gerhard Heydrich, he founded the company Franke & Heydrich KG (today Franke GmbH) to promote the development and production of ball bearings.

Richard Stribeck's extensive research[15]​[16]​ on ball bearing steels led him to identify the metallurgy of the commonly used 100Cr6 steel (AISI 52100)[17]​, whose coefficient of friction varies depending on the pressure received.

Designed in 1968 and then patented in 1972, Bishop-Wisecarver co-founder Bud Wisecarver created guide wheels with V-groove bearings, a type of linear motion bearing, whose grooves are formed by 90-degree V-shaped grooves.[18]​.

In the early 1980s, Pacific Bearing founder Robert Schroeder invented the first bi-material plain bearing whose size was interchangeable with linear ball bearings. This bearing had a metal casing (aluminum, steel or stainless steel) and a layer of Teflon-based material connected by a thin adhesive layer.[19]​.

Today, ball and roller bearings are used in many applications that include a rotating component. Notable examples are ultra-high speed bearings used in dental drills, aerospace bearings on the Mars Rover, wheel bearings and gearboxes in automobiles, deflection bearings in optical alignment systems, bicycle wheel hubs, and air bearings used in coordinate measuring machines.

There are different types of bearings, with different shapes, materials, lubrication or operating principles. By far the most common bearing is the plain bearing, in which friction contacting surfaces are used, often lubricated with oil or graphite. A plain bearing can be nothing more than the support surface of a hole through a shaft, or a flat surface on which another element rests, which is defined as a non-discrete device. In the case of a layer of Babbit metal "Babbitt (metal)") fused to the substrate to facilitate sliding, this is referred to as a semi-discrete device; and when it is in the form of a separable sleeve then it is a discrete support surface. With proper lubrication, plain bearings often provide completely acceptable precision, life, and friction at minimal cost, and are therefore widely used.

However, there are many applications where a specific type of bearing can improve machinery efficiency, accuracy, service intervals, reliability, operating speed, size, weight, and purchasing and operating costs.

There are at least 6 common types of bearings,[20]​ each of which works on different principles:.

• - Sliding bearing, which consists of a shaft that rotates in a hole. There are several specific styles: bushing, plain bearing, sleeve bearing, rifle bearing, composite bearing").

• - Bearing, in which the rolling elements placed between the rotating and stationary grooves prevent sliding friction. There are two main types:

• Ball bearing, in which the rolling elements are spherical balls

• Bearings with cylindrical, conical or spherical rollers.

• - Ruby bearing"), a plain bearing in which one of the bearing surfaces is made of an ultra-hard glassy material such as sapphire to reduce friction and wear.

• - Fluid bearing, a non-contact bearing in which the load is supported by a liquid or gas (as in an air bearing).

• - Magnetic bearing, in which the load is supported by a magnetic field.

• - Flexion bearing"), in which the movement is supported by a load element that can bend.

The movements commonly allowed by the bearings are:.

• - Radial rotation, like the rotation of a turbine shaft.

• - Linear movement, like the movement of a drawer.

• - Spherical rotation, as in the kneecaps.

• - Hinge movement, typical of doors and joints such as elbows and knees.

Reducing friction in bearings is often important to optimize their efficiency, to reduce wear and to facilitate prolonged use at high speeds, avoiding overheating and premature bearing failures. Essentially, a bearing can reduce friction by virtue of its shape, its material, or by introducing and containing a fluid between surfaces or by separating the surfaces with an electromagnetic field.

• - By shape: bearings that use spheres or rollers, or bending bearings.

• - By material: the nature of the bearing material used is taken advantage of, as in the case of low surface friction plastics.

• - By fluid: the low viscosity of a fluid layer is used, which serves as a lubricant or as a pressurized medium to prevent the two solid parts from touching, or by reducing the normal force between them.

• - By fields: they use electromagnetic fields to prevent moving parts from rubbing against each other.

• - By air pressure: pressurized air is used to prevent solid parts from touching.

Even combinations of some of these systems can be used within the same bearing. An example is bearings in which a plastic material is used for the cage that separates the rollers/balls, which in turn reduces friction due to its shape and finish.

The design of bearings varies depending on the size and directions of the forces they must withstand. The forces may be predominantly radial (Radius (geometry)), axial (thrust bearings) or bending forces perpendicular to the main axis.

Different types of bearings have different operating speed limits. They are generally specified as maximum relative surface velocities, often expressed in ft/s or m/s. Slewing bearings typically describe performance in terms of the product "DN", where "D" is the mean diameter (often in mm) of the bearing and "N" is the rotational speed in revolutions per minute.

In general, there is considerable overlap in speed ranges between bearing types. Plain bearings generally handle only the lowest speeds, rolling element bearings allow for faster spins, followed by fluid bearings and finally magnetic bearings, ultimately limited by centripetal force exceeding the strength of the material.

In some applications support loads are generated from different directions, but the bearings only tolerate a limited play or "tilt" (angle with respect to the normal direction of the shaft) as the applied load changes. One source of movement is gaps or "plays" in the bearing. For example, a 10mm shaft in a 12mm hole has a clearance of 2mm.

Allowed play varies greatly depending on use. For example, a wheelbarrow wheel supports radial and axial loads. Axial loads can involve hundreds of newtons (Newton (unit)") of force to the left or right and it is generally acceptable for the wheel to wobble up to 10mm under the varying load. In contrast, a lathe can position a cutting tool with an accuracy of ±0.002 mm using a ball screw supported by rotating bearings, which must withstand axial loads of thousands of newtons in any direction.

A second source of motion is the elasticity of the bearing itself. For example, the balls in a bearing have a certain flexibility, and under load they deform into a slightly flattened shape. The groove that the rollers travel also has an elastic behavior, and develops a slight dent where it receives the pressure of the balls.

The stiffness of a bearing is related to how the distance between the parts that are separated varies with the applied load. In rolling element bearings, it is linked to the tension supported between the balls and the grooves they run through. With fluid bearings, it is due to how the spacing between the parts varies with fluid pressure (when properly loaded, fluid bearings are typically stiffer than rolling element bearings).

Los cojinetes de fluidos y magnéticos pueden tener una vida útil prácticamente indefinida. En la práctica, existen cojinetes de fluido que soportan cargas elevadas en plantas hidroeléctricas que han estado en servicio casi continuo desde alrededor de 1900 y que no muestran signos de desgaste.[21]​.

La vida útil de los cojinetes de los elementos rodantes está determinada por la carga, la temperatura, el mantenimiento, la lubricación, los defectos del material, la contaminación, la manipulación, la instalación y otros factores. Todos estos factores pueden tener un efecto significativo en la vida útil de un rodamiento. Por ejemplo, la vida útil de los rodamientos en una aplicación se prolongó drásticamente al cambiar la forma en que se almacenaban los rodamientos antes de su instalación y uso, ya que las vibraciones durante el almacenamiento provocaban problemas con el lubricante incluso cuando la única carga sobre el rodamiento era su propio peso;[22]​ el daño resultante es a menudo un falso punzonamiento.[23]​ La vida útil de los rodamientos se determina mediante valores estadísticos: varias muestras de un rodamiento dado, a menudo exhibirán una vida útil según una campana de Gauss, y algunas muestras presentarán una vida significativamente mejor o peor. Su vida útil varía porque la estructura microscópica y la contaminación varían mucho, incluso cuando macroscópicamente parecen idénticas.

Service life L10

Bearings are often specified to give "L10" life (outside the US it may also be referred to as "B10"). It is the duration over which ten percent of the bearings in that application can be expected to have been out of service due to classical material fatigue failure (and not any other failure mode caused by lack of lubrication, incorrect mounting or other problems), or, alternatively, the period of time over which ninety percent will continue to function. Bearing life L10 is a theoretical life and may not represent the actual life of a given bearing. Bearings are also classified using the C value (static load). This basic load rating is a reference value, and not an actual load value.

For plain bearings, some materials give a much longer life than others. Some of John Harrison's clocks still work after hundreds of years due to the guaiac wood used in their construction, while his metal clocks rarely work due to wear problems.

In a plain bearing, two bushings move in direct contact, sliding by friction. In order to keep friction as low as possible, appropriate materials and lubricants are selected. Lubricants have the function of creating a sliding film that separates the two materials or prevents direct contact. Babbitt metal is usually used as the bushing material.

As the two parts touch, wear on the contact surfaces limits their useful life. The generation of a lubricating film that separates the two parts of the mechanism through complete lubrication requires an additional system to raise the pressure of the lubricant. This system is used only on large machines, with large sliding bearings. Slip resistance causes the conversion of part of the kinetic energy into heat, which means that the parts that support the bearing bushings must be very resistant both mechanically and thermally.

Bending bearings are based on the elastic properties of the material of a piece that is repeatedly bent. Some materials fail after being subjected to repeated bending, even at low loads, but careful material selection and proper design can make the life of flexing bearings indefinite.

Although a long bearing life is often desirable, sometimes it is not necessary. Harris, 2001 describes a bearing for a rocket engine oxygen pump that achieved only a few hours of life, but a value well above the tens of minutes of life strictly necessary.[22]​.

Composite material bearings.

Depending on their particular specifications, composite bearings can operate for up to 30 years without maintenance.

Oscillating bearings.

For bearings used in oscillating applications, specific approaches are used to calculate L10.[24]​.

External factors

The useful life of a bearing is affected by many parameters that are not controlled by the manufacturer that supplied it. For example, bearing mounting, temperature, exposure to the external environment, lubricant cleanliness, or passage of electrical currents. High-frequency electronic inverters can induce eddy currents in a bearing, which can be suppressed by using a ferrite core.

The temperature and physical characteristics of the supporting microsurfaces will determine the amount of friction at the contacts between the solid parts.

Certain elements and fields reduce friction while increasing speeds.

The forces expected for the working regime and the degree of mobility allow determining the amount of load that the type of bearing can support.

Alignment factors can play a detrimental role in wear, although this problem can be effectively mitigated by computerized monitoring of its evolution, and almost definitively, with types of bearings that practically completely avoid friction, such as magnetic levitation bearings or bearings made of air or other pressurized fluids.

There are many methods of mounting bearings, generally using an interference fit.[25] Press fit and shrink fit involve inserting a bearing into a hole or shaft. In these cases, it is important to keep the inside diameter of the housing and the outside diameter of the shaft within very tight limits, which may involve one or more reaming operations, several facing and drilling operations, tapping, and threading operations.[26] Alternatively, the desired interference fit can also be achieved by adding a tolerance ring.

Muchos rodamientos requieren mantenimiento periódico para evitar fallos prematuros, aunque otros muchos apenas requieren mantenimiento. Estos últimos incluyen varios tipos de cojinetes de polímero, fluidos y magnéticos, así como cojinetes de elementos rodantes que se describen con términos que incluyen "cojinete sellado" y "sellado de por vida", que incorporan un sellado para mantener fuera la suciedad y evitar que se escape la grasa que los lubrica. Se usan con éxito en muchas aplicaciones, brindando un funcionamiento libre de operaciones de mantenimiento, aunque en algunos casos no pueden usarse de manera efectiva.

Los rodamientos no sellados a menudo tienen un punto de engrase destinado a facilitar la lubricación periódica con una aceitera, o una recámara para ser llenada periódicamente con aceite. Antes de la década de 1970 no eran habituales, y el engrasado era una actividad más común que en la actualidad. Por ejemplo, los chasis de los automóviles solían requerir "trabajos de lubricación" casi tan a menudo como los cambios de aceite del motor, pero los chasis de los automóviles de hoy en día en su mayoría están sellados de por vida. Desde finales de 1700 hasta mediados de 1900, la industria dependía de muchos trabajadores llamados engrasadores&action=edit&redlink=1 "Engrasador (ocupación) (aún no redactado)") para lubricar la maquinaria con frecuencia.

Actualmente, las máquinas de fábrica suelen tener "sistemas de lubricación", en los que una bomba central suministra cargas periódicas de aceite o grasa desde un depósito a través de "líneas de lubricación" a los diversos "puntos de lubricación" en las superficies de apoyo de la máquina, los cojinetes, o los bloques de almohada"). La sincronización y el número de dichos "ciclos de lubricación" se regulan mediante el control computarizado de la máquina, utilizando un controlador lógico programable o sistemas de control numérico, así como mediante funciones de operación manual cuando se necesitan ocasionalmente. Este proceso automatizado es la forma en que se lubrican todas las máquinas herramienta asistidas electrónicamente modernas y muchas otras máquinas de fábrica actuales.

También se utilizan sistemas de lubricación similares en máquinas no automatizadas, en cuyo caso se dispone de una bomba manual que se supone que el operador de la máquina debe bombear una vez al día (para máquinas en uso constante) o una vez a la semana. Estos se denominan "sistemas de un solo paso" por su principal punto de accionamiento: un solo tirón de una manija sirve para lubricar la máquina completa, en lugar de una docena de posiciones diferentes alrededor de la máquina donde usar una aceitera o una lata de aceite.

El sistema de lubricación dentro de un motor moderno de automóvil o camión es similar en concepto a los sistemas de lubricación mencionados anteriormente, excepto en que el aceite se bombea continuamente. Gran parte de este aceite fluye a través de pasajes perforados o fundidos en la culata "Culata (motor)") y en el bloque del motor, llegando a través de estos conductos directamente a los cojinetes y saliendo a chorros a otros lugares para proporcionar un baño de aceite. La bomba de aceite simplemente bombea constantemente, y cualquier exceso de aceite bombeado escapa continuamente a través de una válvula de alivio hacia el sumidero del cárter.

Muchos rodamientos en operaciones industriales de alto ciclo necesitan lubricación y limpieza periódicas, y muchos requieren un ajuste ocasional, como un ajuste de precarga, para minimizar los efectos del desgaste.

La vida útil del rodamiento suele ser mucho mayor cuando se mantiene limpio y bien lubricado. Sin embargo, muchas aplicaciones dificultan un buen mantenimiento. Un ejemplo son los rodamientos de la cinta transportadora de una trituradora de rocas, están continuamente expuestos a partículas abrasivas duras. La limpieza es de poca utilidad por la dificultad que implica, y porque el rodamiento se ensucia nuevamente tan pronto como el transportador reanuda la operación. Por lo tanto, un buen programa de mantenimiento podría lubricar los cojinetes con frecuencia, pero no incluir ningún desmontaje para la limpieza. La lubricación frecuente, por su naturaleza, proporciona un tipo limitado de acción de limpieza, al desplazar el aceite o la grasa más antiguos (llenos de arena) por una carga nueva, que a su vez acumula arena antes de ser desplazada por el próximo ciclo. Otro ejemplo, son los cojinetes de las turbinas eólicas, que dificultan su mantenimiento ya que la góndola se coloca al aire en zonas de viento fuerte. Además, la turbina no siempre funciona y está sujeta a un comportamiento operativo diferente en diferentes condiciones climáticas, lo que hace que la lubricación adecuada sea un desafío.[27]​.

Detection of failures in the outer race of rolling element bearings

Bearings are widely used in today's industries and therefore their maintenance becomes an important task. Rolling elements tend to wear easily due to metal-to-metal contact, leading to failures in the outer race, inner race, and rollers themselves. It is also the most vulnerable component of a machine because it is often under high load and high operating speed conditions. Regular diagnosis of rolling element bearing failures is essential for industrial safety and machine operations, as well as reducing maintenance costs or avoiding downtime. Between the outer court, the inner court and the ball, the outer court tends to be more vulnerable to failures and defects.

Rolling elements can excite the fundamental frequency of the bearing component when they pass a damaged spot on the outer race. Therefore, it is necessary to identify the natural frequency of the bearing outer race and its harmonics. Bearing failures create impulses and result in strong harmonics of the failure frequencies in the vibration signal spectrum,[28]​ which are sometimes masked by adjacent frequencies in the spectra due to their low energy. Therefore, very high spectral resolution is often needed to identify these frequencies during fast Fourier transform analysis.

The fundamental frequency of a bearing with free boundary conditions is 3 kHz. Therefore, to use the resonance bandwidth method of a bearing component to detect the failure at an early stage, an accelerometer with a high-frequency measurement range must be used, and data must be recorded for a long period. A characteristic failure frequency can only be identified when the extent of the failure is severe, such as the presence of a hole in the outer race. Failure frequency harmonics are a more sensitive indicator in the bearing outer race. For more rigorous detection of faults in defective bearings, waveform and spectrum analysis techniques will help reveal them. However, if high-frequency demodulation is used in envelope analysis to detect characteristic bearing failure frequencies, maintenance professionals must be more careful in the analysis due to the influence of resonance, which may or may not contain failure frequency components.

The use of spectral analysis as a tool to identify bearing failures faces complex challenges due to problems such as low energy, low signal sharpness, or cycloseasonality. High resolution is often desired to differentiate components of the failure frequency from other adjacent high-amplitude frequencies. Therefore, when sampling the signal for fast Fourier transform analysis, the sample length must be large enough to provide adequate frequency resolution in the spectrum. Additionally, keeping calculation time and memory within limits and avoiding unwanted truncations can be demanding. However, a required minimum frequency resolution can be obtained by estimating bearing failure frequencies and other vibration frequency components and their harmonics as a function of shaft speed, misalignment, operating frequency, or gearbox effect.[29]​.

Lubricant confinement

Some bearings use a thick grease (lubricant) for lubrication, which is filled into the spaces between the bearing surfaces, also known as a "packing". The grease is held in place by a plastic, leather or rubber gasket (formerly known as a stuffing box) that covers the inner and outer edges of the bearing race to prevent lubricant from escaping.

Bearings can also be packaged with other materials. Historically, railroad car wheels used sleeve bearings filled with "waste" or loose pieces of oil-soaked cotton or wool fiber confined in so-called axle boxes, and later transitioned to solid cotton pads.[30]

ring oiler

The bearings can be lubricated with a metal ring that moves freely on the central rotating axis of the bearing. This ring hangs inside a chamber containing lubricating oil. As the bearing rotates, viscous adhesion moves oil up the ring and deposits it on the shaft, where it migrates to the bearing to lubricate it. Excess oil is expelled and accumulates in the chamber again.[31]​.

Splash lubrication

A rudimentary form of greasing is "splash lubrication"). special plastic deflectors that spread oil randomly around the inside of the mechanism.[32]​.

Pressure lubrication

For high-speed, high-power machines, loss of lubricant can result in rapid heating of the bearings and damage due to friction. Also in dirty environments, the oil can become contaminated with dust or debris that increases friction. In these applications, a fresh supply of lubricant can be continuously available to the bearing and all other contact surfaces, and the excess can be collected for filtering, cooling and possibly reuse. Pressure lubrication is commonly used in large, complex internal combustion engines in those parts of the engine where directly splashed oil cannot reach, such as in the upper valve assemblies.[33] High-speed turbochargers also typically require a pressurized oil system to cool the bearings and prevent them from burning due to turbine heat.

Composite bearings

Composite bearings are designed with a self-lubricating polytetrafluoroethylene (PTFE) liner with a laminated metal backing. The PTFE liner offers consistent, controlled friction and durability, while the metal backing ensures the composite bearing is robust and able to withstand high loads and stresses over its long life. Its design also makes it lightweight: one-tenth the weight of a traditional bearing.[34]​.

There are many different types of bearings. Research into new designs is constant, in order to reduce friction, increase bearing payload and increase momentum build-up and speed.

Below are the terms for the different types of bearings and their parts, and their corresponding English equivalents:

Below are formulas for sizing a boat propeller bearing and an illustrative example:.

Calculation of the dimension of a ship's main engine thrust bearing:.

Example:.

The effective power of the engine is a manual data, often given in (hp), which must be converted to (kg/cm²). Assume a power of 3350 hp and a propeller efficiency of 0.6.

• - data with which the thrust bearing surface is cleared.

• - Wikimedia Commons hosts a multimedia category on Bearing.

• - ISO dimensional system and bearing numbers.

• - Complete review on bearings, University of Cambridge.

• - A glossary of bearing terms.

• - How bearings work.

• - Kinematic Models for Design Digital Library (KMODDL) – movies and photos of hundreds of models of mechanical systems in operation at Cornell University. It also includes an e-book library of classic mechanical design and engineering texts.

• - Types of bearings, University of Cambridge.

• - Bearings, in Wordpress.

• - Bearings - Rincón del Vago.

• - How they work: the bearings.

• - Anti-friction bearings.

• - What are friction bearings and how do they work?

• - (Bearings or bearings) Types of bearings in Rodamientos.mx.