A bearing is a machine element that limits the motion relative to just the desired movement, and reduces friction between moving parts. The bearing design may, for example, provide free linear movement of moving parts or for free rotation around the fixed axis; or, it may be prevent movement by controlling the normal power vector that holds the moving parts. Most pads facilitate the desired movement by minimizing friction. Bearings are broadly classified according to the type of operation, permissible movement, or towards the load (force) applied to the parts.
Swivel bearings retain rotating components such as axle or axle in mechanical systems, and transfer axial and radial load from load source to the supporting structure. The simplest form of cushion, plain bearing , consists of a rotating shaft in a hole. Lubrication is often used to reduce friction. In ball bearings and roller bearings , to prevent shear friction, rolling elements such as rollers or balls with circular cross-sections are located between racecars or bearing journal assemblies. A wide variety of bearing designs exist to enable application demands to be properly met for maximum efficiency, reliability, durability and performance.
The term "bearing" comes from the verb "to bear"; bearing into machine elements that allow one part to bear (ie, to support) others. The simplest bearing is a surface bearing, cut or shaped into parts, with varying degrees of control over shape, size, roughness and surface location. Another bearing is a separate device that is attached to the engine or engine part. The most sophisticated bearing for the most demanding applications is a very precise device; Its manufacture requires some of the highest standards of current technology.
Video Bearing (mechanical)
History
The invention of rolling bearing, in the form of wooden rollers that hold, or hold, a moved object is very ancient, and may precede the invention of the wheel.
Although it is often claimed that Egyptians use roller bearings in the form of tree trunks under a sled, this is a modern speculation. They are portrayed in their own drawings at Djehutihotep's grave as moving the massive stone blocks over the sled with a fluid-lubricated runner that will become a common bearing. There are also images of Egyptian cushions used with hand drills.
The earliest recovery example of a rolling element bearing is a wooden ball bearing supporting a rotating table of the remains of the Roman Nemi ship on Lake Nemi, Italy. The wreck was dated 40 BC.
Leonardo da Vinci combines ball bearing images in design for helicopters around 1500. This is the first recorded use of bearings in space design. However, Agostino Ramelli was the first to publish a roller sketch and a thrust bearing. The problem with balls and roller bearings is that the ball or rub rub against each other causing additional friction that can be reduced by attaching a ball or roller inside the enclosure. The captured or caged ball bearings were originally depicted by Galileo in the 17th century.
The practical caged-roller bearings were first discovered in the mid-1740s by the horoscopist John Harrison for his H3 sea timekeeper. It uses pads for very limited oscillation motions but Harrison also uses similar bearings in applications that actually spin in contemporary clock regulators.
Industrial era
The first recorded modern patent on ball bearing was awarded to Philip Vaughan, the British inventor and expert who created the first design for ball bearings in Carmarthen in 1794. The first modern ball-bearing design, with the ball running along the grooves in the axle assembly.
Bearings play an important role in the newborn Industrial Revolution, allowing new industrial machinery to operate efficiently. For example, they see usage for holding wheels and axles to reduce the enormous friction from dragging objects by making friction action at shorter distances as the wheel spins.
The first plain and rolled bearing is a wood that is closely followed by bronze. During their historical bearings have been made of many materials including ceramics, sapphires, glass, steel, bronze, metals and other plastics (eg, nylon, polyoxymethylene, poletrafluoroethylene, and UHMWPE) are all used today.
Watchmakers produce "gem" watches using ordinary sapphire pads to reduce friction thus allowing more precise time storage.
Even basic materials can have good endurance. For example, wooden pads can still be seen today in long hours or in water mills where water provides cooling and lubrication.
The first patent for radial-style ball bearing was given to Jules Suriray, the Paris bike mechanic, on August 3, 1869. The cushion was then mounted to the winning bike ridden by James Moore in the world's first bicycle race, Paris-Rouen, in November 1869.
In 1883, Friedrich Fischer, founder of FAG, developed an approach for milling and ball milling of the same size and precise roundness by using the appropriate production machine and forming the foundation for the creation of an independent bearing industry.
The design of modern and self-aligned ball bearings was associated with Sven Wingquist from SKF ball-bearing maker in 1907, when he was awarded the No. 1 Swedish patent. 25406 on the design.
Henry Timken, a 19th century visionary and innovator in cart manufacturing, patented tapered roller bearings in 1898. The following year he formed the company to produce innovation. Over a century the company grows to make bearing of all kinds, including special steel and various related products and services.
Erich Franke invented and patented the cable race in 1934. The focus is on bearing design with the smallest possible cross section and that can be integrated into the enclosing design. After World War II he co-founded with Gerhard Heydrich Franke & amp; Heydrich KG (today Franke GmbH) to encourage the development and production of cable racing bearings.
Richard Stribeck's extensive research on steel balls identifies the commonly used metallurgical 100Cr6 (AISI 52100) showing the coefficient of friction as a function of pressure.
Designed in 1968 and later patented in 1972, Bishop-Wisecarver founder Bud Wisecarver created the wheel guide wheel groove, a linear motion bearing type consisting of both external and internal 90 degree veen angles.
In the early 1980s, founder of Pacific Bearing, Robert Schroeder, invented the first plain bi-material bearings that were interchangeable in size with linear ball bearings. This bearing has a metal shell (aluminum, steel or stainless steel) and a Teflon-based material layer connected by a thin adhesive layer.
Today ball and roller bearings are used in many applications that include rotating components. Examples include ultra high-speed bearings in dental workouts, Mars Rover aerial bearings, gearboxes and wheel bearings in automobiles, flexible bearings in optical alignment systems, bicycle wheel hubs and air bearings used in Coordinate Gauges.
Maps Bearing (mechanical)
General
By far, the most common bearing is a plain bearing, a bearing that uses surfaces in abrasive contact, often with lubricants such as oil or graphite. Ordinary bearings may or may not be discrete devices. This may be nothing more than a hole-bearing surface with a shaft passing through it, or from a planar surface that carries another (in this case, not a discrete device); or perhaps a metal layer bearing either fused with a substrate (semi-discrete) or in the form of a separate arm (discrete). With appropriate lubrication, ordinary bearings often provide accurate, life, and friction that are fully acceptable at minimal cost. Therefore, they are very widely used.
However, there are many applications where more suitable bearings can improve efficiency, accuracy, service intervals, reliability, operating speed, size, weight, and cost of purchasing and operating machines.
Thus, there are many types of bearings, with various shapes, materials, lubrication, operating principles, and so on.
Type
There are at least 6 types of common bearings, each of which operates on a different principle:
- Plain pads, consisting of a rotating axis in a hole. There are several special styles: bushing, journaling pads, sleeve pads, rifle bearings, composite bearings.
- Rolling-bearing elements, in which scrolling elements are placed between playback and stationary races prevent shear friction. There are two main types
- The bearing ball, where the scrolling element is a soccer ball
- Roller bearings, where scrolling elements are cylindrical, pointed, and round rollers
- Jewel bearings, ordinary bearings in which one of the bearing surfaces are made of ultrahard glass gemstones such as sapphire to reduce friction and wear
- Fluid pads, non-contact bearings in which the load is supported by gas or liquid,
- Magnetic pad, where load is supported by magnetic field
- Flexible pads, in which motion is supported by a curved load element.
Motions
Common movements allowed by bearings are:
- Radical rotation eg. shaft rotation
- linear motion eg. drawer
- ball rotation, e.g. ball and socket joints
- hinge hinge such as door, elbow, knee
Friction
Reducing friction on the pads is often important for efficiency, to reduce wear and to facilitate longer use at high speeds and to avoid overheating and premature bearing failure. Basically, the pads can reduce friction by shape, by the material, or by introducing and containing fluids between surfaces or by separating surfaces with electromagnetic fields.
- With shape , gain the advantage usually by using a ball or roller, or by forming a flexible bearing.
- With material , utilizing the bearing material properties used. (Examples will use plastics that have low surface friction.)
- With liquid , exploit the low viscosity of the fluid layer, such as the lubricant or as a pressurized medium to keep the two solids from touch, or by reducing the normal force between the two.
- With the field, utilizing an electromagnetic field, such as a magnetic field, to keep the solid parts in touch.
- Air pressure exploits air pressure to keep solid components from touching.
This combination can even be used in the same bearing. An example is where the cage is made of plastic, and it separates the rollers/balls, which reduce friction by shape and finish.
Loading
The bearing design varies depending on the size and direction of the force required to support it. The forces may be predominantly radial, axial (thrust bearing), or bending moments perpendicular to the major axis.
Speed ​​
Different types of bearings have different operating speed limits. Speed ​​is usually determined as the relative maximum surface velocity, often specified ft/s or m/s. Rotational bearings typically represent performance in terms of DN products where D is the average diameter (often in mm) of bearings and N is the rotation rate in revolutions per minute.
Generally there is a fairly overlapping range of speed between bearing types. Ordinary bearings usually handle only lower speeds, faster rolling element bearings, followed by fluid pads and ultimately endless magnetic bearings by centripetal forces that overcome the strength of the material.
Play
Some apps apply bearing loads from various directions and only accept restricted games or "slop" due to load changes being applied. One source of motion is the gap or "play" in relation. For example, a 10 mm axle in a 12 mm hole has a 2 mm game.
Allowed play varies greatly depending on usage. For example, wheel carts support radial and axial loads. Axial loads may be hundreds of left or right newton powers, and are usually acceptable for wheel swaying as much as 10 mm under varying loads. Instead, the lathe can position the cutting tool for Ã, Â ± 0.002 mm using a ball screw held by rotating the pads. Bearings support the axial load of thousands of newtons in both directions, and must hold the lead ball screw up to Ã, Â ± 0.002 mm at various loads
Stiffness
The second source of motion is the elasticity in the bearing itself. For example, the balls in the ball bearings are like rigid rubber, and under the deformation of the load from the round to the slightly flattened shape. The race is also elastic and develops a bit of a dent in which the ball presses it.
The bearing rigidity is how the spacing between the parts separated by the bearings varies with the applied load. With rolling element bearings this is caused by ball and race tension. With fluid pads, this is due to how fluid pressure varies with the gap (when filled properly, fluid pads are usually more rigid than rolling elemental pads).
Service life
- Fluid and magnetic pads
Fluid and magnetic pads can have unlimited practical service life. In practice, there are fluid bearings that support high loads in hydroelectric power plants that have been operating almost continuously since about 1900 and which show no signs of wear and tear.
- Rolling element bearing
The rolling elements of bearing life are determined by the load, temperature, maintenance, lubrication, defects of materials, contamination, handling, installation and other factors. These factors can all have a significant effect on bearing life. For example, the bearing life in one application is dramatically extended by changing the way the pads are stored prior to installation and use, since vibrations during storage cause lubricant failure even when the only load on the bearings is its own weight; the resulting damage is often wrong brinelling. Life bearings are statistics: some samples of given bearings often indicate the service life bell curve, with some samples showing a life that is significantly better or worse. Bearing life varies because microscopic structures and contamination vary greatly even if they look macroscopically identical.
L10's Life
Bearing is often determined to give life "L10" (outside of the United States, this can be referred to as "B10" life.) This is the life where ten per cent of bearings in such applications can be estimated to fail due to the failure of classical fatigue (and no other mode failures such as lubrication lubrication, incorrect installation etc.), or, alternatively, a life in which ninety percent will still operate. The L10 life of bearing is a theoretical life and may not represent life bearing services. Bearings are also rated using C 0 (static loading). This is the base load rating as a reference, and not the actual load value.
- Plain pads
For ordinary bearings, some materials provide a longer life than others. Hours of John Harrison are still operating after hundreds of years because lignum vitae is used in their construction, while metal clocks rarely run due to potential wear.
- Flexible pads
Flexible pads depend on the elastic properties of the material. Flexible pads bend a piece of material repeatedly. Some materials fail after repetitive bending, even at low loads, but careful selection of materials and cushioning design can make the life of the cushioning pads unlimited.
- Short term bearings
Although long bearing life is often desirable, sometimes it is not necessary. Tedric A. Harris described the pads for a motor oxygen pump rocket that provided several hours of life, far more than a few dozen minutes of life required.
Composite bearing
Depending on the customized specification (backing material and PTFE compound), the composite bearing can operate for up to 30 years without treatment.
The bearings oscillate
For cushions used in oscillatory applications, a special approach for computing L10 is used.
External factors
Bearing life is affected by many parameters that are not controlled by bearing manufacturers. For example, mounting pads, temperature, exposure to the external environment, lubricant cleanliness and electric current through bearings etc. High frequency PWM inverters can induce currents in bearings, which can be suppressed by using choking ferrite.
Temperature and micro-surface field will determine the amount of friction by the touch of the solid.
Elements and certain fields reduce friction, while increasing speed.
Power and mobility help determine the amount of load that bearings can carry.
The alignment factor can play a destructive role in wear and tear, but is overcome by the aid of computers that signal and type non-polishing pads, such as magnetic levitation or airfield pressure.
Treatment and lubrication
Many bearings require periodic maintenance to prevent premature failure, but many others require little care. The latter include various types of fluid and magnetic pads, as well as rolling element bearings described by the term including sealed seals and sealed seals for . It contains a seal to keep dirt and grease coming in. They work successfully in many applications, providing maintenance-free operations. Some apps can not use them effectively.
Unkeeped bearings often have fat fittings, for periodic lubrication with grease pistols, or oil cups for periodic filling with oil. Prior to the 1970s, sealed bearings were not found on most machines, and oiling and greasing were more common activities than now. For example, the automotive chassis used to require "lubricant work" is almost as frequent as engine oil change, but the current car chassis is mostly closed for life. From the late 1700s to the mid-1900s, industry relied on many workers called oilers to lubricate machines often with oil cans.
Current mill machinery typically has a lubricating system, where the central pump serves a periodic oil or fat charge from the reservoir through the lubricating lane to various lubricating points on the surface bearing machine, carrying journal, pillow block, and so on. The cycle time and number of lubricants is controlled by computerized computer controls, such as PLCs or CNCs, as well as with manual replacement functions when occasionally required. This automated process is how all modern CNC machine tools and many other modern factory machines are lubricated. A similar lubrication system is also used on non-working machines, where there are hand pumps that should be pumped by the operator's machine on a daily basis (for machines that use constant) or once a week. This is called a one-shot system from their main selling point: a pull on one handle to lubricate the whole machine, not a dozen pumps from alemite or oil rifles can be in a dozen different positions around the machine.
The oil system in a modern automotive or trucking machine is similar in concept to the above mentioned lubricating system, except that the oil is pumped continuously. Much of this oil flows through drilled or dumped channels into engine blocks and cylinder heads, out through direct ports into bearings, and sprays to other places to provide oil baths. The oil pump only pumps continuously, and excess oil is pumped constantly out through the relief valve back into the sump.
Many bearings in high cycle industrial operations require regular lubrication and cleaning, and many require occasional adjustments, such as pre-load adjustments, to minimize wear effects.
Bearing life is often much better when the bearings are kept clean and well lubricated. However, many applications make good care difficult. For example, bearings in stone crusher conveyors are exposed continuously to hard abrasive particles. Cleaning is of little use, since cleaning is expensive but the pads are contaminated again as soon as the conveyor is back in operation. Thus, a good treatment program may lubricate the pads regularly but does not include dismantling for cleaning. Frequent lubrication, by its very nature, provides a limited act of cleaning, by removing older oils or fats (filled with oil) with new charge, which in itself collects the sand before it is transferred in the next cycle.
Detecting outer hollow bearing track error
Rolling element bearings are widely used in the industry today, and hence the maintenance of these bearings becomes an important task for maintenance professionals. Rolling element bearings wear out easily due to metal-to-metal contact, which creates errors in outer races, deep races and balls. It is also the most vulnerable engine component because it is often under high load and high running speed conditions. Regular diagnostics from bearing element bearing faults are essential for industrial safety and machine operation along with reduced maintenance costs or avoid shutdown time. Among outdoor races, races and deep balls, outsiders tend to be more vulnerable to errors and defects.
There is still room for discussion as to whether the rolling elements excite the natural frequency of bearing components when it passes an error on an outsider race. Therefore we need to identify the natural frequencies beyond the bearing and its harmonics. Fault pads create impulses and generate powerful harmonics of the frequency of interference in the vibration signal spectrum. The frequency of these interferences is sometimes covered by adjacent frequencies in the spectrum due to their small energy. Therefore, very high spectral resolution is often required to identify these frequencies during FFT analysis. The natural frequency of rolling element bearings with free bounding conditions is 3 kHz. Therefore, to use the beam component resonant bandwidth method to detect bearing errors in the early stages, high frequency accelerometer ranges must be adopted, and data obtained from the long duration need to be obtained. Frequency characteristics of errors can only be identified when the error rate is severe, such as the presence of holes in the outer races. Harmonic frequency interference is a more sensitive indicator of outer bearing errors. For a more serious detection of the damage caused by waveform errors, spectrum and envelope techniques will help reveal these errors. However, if high frequency demodulation is used in envelope analysis to detect the frequency of bearing error characteristics, maintenance professionals should be more careful in the analysis because of resonance, as it may or may not contain error frequency components.
Using spectral analysis as a tool to identify errors in bearings faces challenges due to problems like low energy, signal smearing, cyclostationarity etc. High resolution is often desirable to differentiate the frequency components of errors from frequencies adjacent to other high amplitudes. Therefore, when the signal is taken for FFT analysis, the length of the sample must be large enough to provide an adequate frequency resolution in the spectrum. Also, keeping time calculations and memory within limits and avoiding unwanted aliasing may be demanding. However, the minimum required frequency resolution can be obtained by estimating the bearing error frequency and other vibration frequency components and harmonics due to shaft speed, misalignment, line frequency, gearbox etc.
Packaging
Some pads use a thick lubricant for lubrication, which is pushed into the gap between the bearing surfaces, also known as packing . Fats are held in place by plastic, leather, or rubber gasket (also called glands ) that cover the inside and outside edges of the bearing race to keep fat from escaping.
Bearings can also be packed with other materials. Historically, wheels on rail cars used sleeve pads packed with waste or loose pieces of cotton or wool fibers soaked in oil, then solid cotton solids were used.
Ring oiler
Bearings can be lubricated by a loosely rising metal ring on the central bearing rotary shaft. The ring hangs into a space containing lubricating oil. As the bearings rotate, the viscous adhesion pulls the oil up the ring and into the shaft, where the oil moves to the cushion to lubricate it. Excess oil is discarded and collected in the pond again.
Splash lubrication
Some engines contain a lubricant pool at the bottom, with gears partially immersed in a liquid, or a crankshaft that can swing down into the pool when the device is operating. The spinning wheel throws oil into the air around them, while the crankshaft slaps on the surface of the oil, splashing it randomly on the inside surface of the machine. Some typical small internal combustion engines contain special plastic flue wheels that randomly disperse the oil around the inside of the mechanism.
Pressure lubrication
For high-speed and high-power engines, the loss of lubricants can cause fast heating and frictional breakage. Also in a dirty environment, oil can be contaminated with dust or dirt that increases friction. In this application, the supply of new lubricants can be continuously supplied to bearings and all other contact surfaces, and the advantages can be collected for filtering, cooling, and possible reuse. The oiling pressure is generally used in large and complex internal combustion engines in parts of the engine where sprinkling oil can not reach, as upwards to the overhead valve assembly. High-speed turbochargers also typically require pressurized oil systems to cool the pads and keep them from burning out of heat from turbines.
Composite bearing
The composite bearing is designed with a self-lubricating polytetrafluroethylene (PTFE) liner with laminated metal support. PTFE liners offer consistent and controlled friction and durability while metal support ensures strong composite bearings and is able to withstand high loads and pressures over its long life. The design also makes it light-tenth the weight of a traditional rolling element bearing.
Type
There are many different types of bearings. Newer versions of the more enabling designs are under development being tested, which will reduce friction, increase bearing load, increase build-up momentum, and speed.
See also
References
External links
- A thorough review of the bearing, University of Cambridge
- Glossary of terms
- How to work pads
- Kinematic Model for Design Digital Library (KMODDL) - Films and photos from hundreds of mechanical system models working at Cornell University. Also includes a classic text book e-book on mechanical design and engineering.
- Types of bearings, Cambridge University
Source of the article : Wikipedia
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