A ball bearing is a rolling element type pad that uses a ball to keep the split between bearing races.
The purpose of ball bearings is to reduce rotational friction and support radial and axial loads. It achieves this by using at least three races to load the ball and send the load through the ball. In most applications, one race is stationary and the other is attached to a rotating assembly (eg hub or pivot). When one of the pads rotates, it causes the ball to spin as well. Because the balls roll over, they have a much lower friction coefficient than if two flat surfaces are rubbing together.
Ball bearings tend to have lower load capacity for their size than other rolling-type bearing pads due to the smaller contact area between the ball and the races. However, they can tolerate some misalignment of the inner and outer races.
Video Ball bearing
Histori
Although the bearing has been developed since ancient times, the first recorded modern patent on ball bearing was awarded to Philip Vaughan, a Welsh inventor and iron expert who created the first design for ball bearings at Carmarthen in 1794. His first modern-ball design, with a ball running along the groove in the assembly assembly.
Jules Suriray, a Paris bike mechanic, designed the first radial ball bearings in 1869, which was then mounted on a winning bike dumped by James Moore in the world's first bicycle race, Paris-Rouen, in November 1869.
Maps Ball bearing
General design
There are several common ball bearing designs, each offering a variety of performance trade-offs. They can be made from a variety of materials, including: stainless steel, chrome steel, and ceramics (silicon nitride (Si 3 N 4 )). Hybrid ball bearings are padded with ceramic balls and metal races.
Corner contact
Ball bearings contact angles use axial asymmetric races. Axial load passes through a straight line through the bearings, while the radial load takes a sloping path that acts to separate axial races. So the angle of contact on the inner race is the same as that of the outer race. More angular contact bearings support combination loads (loading in both radial and axial directions) and bearing contact angles should be matched to their respective relative proportions. The larger the contact angle (usually in the range of 10 to 45 degrees), the higher the supported axial load, but the lower the radial load. In high speed applications, such as turbines, jet engines, and dentistry equipment, the centrifugal force generated by the ball alters the angle of contact on the inner and outer races. Ceramics such as silicon nitride are now regularly used in such applications because of their low density (40% of steel). These materials significantly reduce centrifugal force and function well in high temperature environments. They also tend to wear in a way similar to steel bearings - rather than cracked or broken like glass or porcelain.
Most bicycles use angular contact pads in the headset because the force on this pad is in the radial and axial direction.
Axial
Axial ball bearing or push using side-by-side races. Axial loads are transmitted directly through bearings, while radial loads are less supported and tend to separate races, so larger radial loads tend to damage bearing.
Deep-groove
In the deep-groove radial bearing, the racing dimension approaches the dimension of the ball that runs inside it. The deep-groove bearings support higher loads than the shallower grooves. Like angular contact bearings, deep groove bearings support radial and axial loads, but with no angular contact options to allow a choice of the relative proportions of this load capacity.
Preloaded pairs
The basic types of bearings above are usually applied in the preloaded pairs method, in which two individual pads are rigidly tied along the rotating shaft to face each other. This increases the axial runout by taking ( preloading ) the required small clearance between ball bearing and race. Pairing also provides the benefit of evenly distributing the load, almost doubling the total load capacity compared to single bearings. Angular contact bearings are almost always used in opposite pairs: the asymmetric design of each bearing supports axial loads in only one direction, so the opposite pair is required if the application demands support in both directions. Preloading styles should be carefully designed and assembled, as they reduce the capacity of the axial bearing force, and may damage the bearing if applied excessively. Coupling mechanisms may only face joint bearings directly, or separate them with shim, bushing, or pivot features.
Type of construction
Conrad
The Conrad ball bearing was named after its inventor Robert Conrad, who was awarded British patent 12,206 in 1903 and US patent 822,723 in 1906. The pad was assembled by placing the inner ring into an eccentric position. relative to the outer ring, with two rings in contact at one point, resulting in a large gap across the contact point. The ball is inserted through the gap and then distributed evenly around the bearing assembly, causing the ring to become concentric. The assembly is finished by installing a cage into the ball to maintain their position relative to each other. Without the enclosure, the balls will eventually get out of position during the operation, causing the pads to fail. The cage does not carry the burden and only serves to maintain the position of the ball.
Conrad bearings have the advantage that they are able to withstand radial and axial loads, but have lower load capacity losses due to the limited number of balls that can be loaded into the bearing assembly. Probably the best known industrial ball bearer is the Conrad style in the groove. Bearings are used in most mechanical industries.
Slot-fill
In the slot-fill radial pads, the inner and outer races are notched on one face so that when the notches are aligned, the ball may slip in the resulting slot to assemble the pads. fill bearings have the advantage that more balls can be assembled (even allowing complete designs), resulting in a higher radial load capacity than Conrad bearing with the same dimensions and material types. However, slot-fill bearings can not carry significant axial loads, and slots cause discontinuities in races that can have small but detrimental effects on strength.
Racing is relief
Reliable racing ball bearings are 'relieved' as the name suggests because it basically has either the OD of the inner ring reduced on one side, or the ID of the outer ring rises on one side. This allows a large number of balls to be strung into races inside or outside, and then press fitting over the relief. Sometimes the outer ring will be heated to facilitate assembly. Like slot-fill construction, the relieved race construction allows more spheres than Conrad's construction, up to and including the full complement, and the number of extra balls provides additional load capacity. However, a relieved race cushion can only support a significant axial load in one direction ('away from' a relieved race).
Cracked race
Another way to fit more balls into a radial ball bearing is to "radial" (slicing) one ring along the path, insert the ball in, reassemble the cracked part, and then use a pair of steel bands to grasp the parts cracked rings together parallel. Again, this allows more spheres, including a full ball complement, but unlike with slot fills or racing relief construction, it can support significant axial loadings in both directions.
Rows
There are two row designs: single line pad and double line pads. Most ball bearings are a one line design, which means there is one row of ball bearings. This design works with radial and thrust loads.
The double line design has two rows of ball bearings. The disadvantage is that they require better alignment than one-line pads.
Flanged
Pads with flanges in the outer ring simplify the axial location. Housing for such bearings may consist of uniform diameter holes, but the inlet surface of the housing (which may be the outer or inner surface) should be done completely normal on the axis of the hole. However, flanges are very expensive to produce. A more effective arrangement of the outer ring bearing, with the same benefit, is the curve of a snap ring on one or both ends of the outer diameter. The instant ring assumes the function of the flanges.
Shelled
The enclosure is usually used to secure the ball in a Conrad-style ball bearing. In other types of construction, they can reduce the number of orbs depending on the shape of the particular enclosure, and thereby reduce the load capacity. Without the enclosure, the tangential position is stabilized by shifting two convex surfaces to each other. With the cage, the tangential position is stabilized by the shear of the convex surface on a suitable concave surface, which avoids dents in the sphere and has a lower friction. The caged roller bearing was invented by John Harrison in the mid-18th century as part of his work on chronographs.
Hybrid ball bearings with ceramic ball
Ceramic ball bearings can weigh up to 40% less than steel ones, depending on size and materials. This reduces centrifugal loading and skidding, so hybrid ceramic bearings can operate 20% to 40% faster than conventional bearings. This means that the outer track path gives slightly inward force against the ball as the pads rotate. This reduction of force reduces friction and rolling resistance. Lighter balls allow the bearing to rotate faster, and use less energy to maintain its speed.
Ceramic balls are usually louder than race. Due to wear and tear, with time they will form a groove in the race. This is better than wearing a ball that will leave them with the possibility of flat flats that significantly impair performance.
While ceramic bearing hybrids use ceramic balls in places made of steel, they are built with inner and outer steel rings; then the hybrid title . While the ceramic material itself is stronger than steel, it is also more rigid, resulting in increased pressure on the rings, and hence the load capacity decreases. Ceramic balls are electrical insulation, which can prevent 'arcing' failure if the current has to pass through the pads. Ceramic balls can also be effective in environments where lubrication may not be available (as in space applications).
In some settings only a thin ceramic layer is used on a metal ball bearing.
Complete Ceramic Bearing
This pads utilize ball and ceramic racing. These bearings are resistant to corrosion and rarely require lubrication if at all. Due to the stiffness and hardness of the balls and races, these bearings are noisy at high speeds. Ceramic rigidity makes the pads brittle and can crack under load or impact. Because both balls and races have the same hardness it can cause chipping at high speeds of both balls and this race can cause splashes.
Self-aligning
The self-aligning ball bearings, such as the Wingquist pads shown in the drawing, are constructed with inner rings and ball assemblies contained within the outer ring which have a round raceway. This construction allows the bearings to tolerate small angle misalignment resulting from improper shaft or housing deflection or mounting. Bearings are used primarily in the setting of bearings with very long shafts, such as transmission shafts in textile factories. One disadvantage of self-aligning ball bearings is that the load rating is limited, because the outer raceway has very low oscillations (the radius is much larger than the ball radius). This led to the discovery of a spherical roller bearing, which has a similar design, but uses a roll instead of a sphere. Also the roller thrust roller bearing is an invention derived from the findings by Wingquist.
Operating conditions
Age
Countless life for bearings is based on the load it carries and the speed of its operation. The standard industrial bearing life used is inversely proportional to the load of cubed bearings. Maximum bearing nominal load, is for a lifespan of 1 million rotations, which at 50 Hz (ie 3000 RPM) is the lifespan of 5.5 hours of work. 90% of the bearings have at least the lifetime, and 50% of bearings have a lifespan of at least 5 times longer.
The calculation of standard industrial life is based on Lundberg and Palmgren's work done in 1947. The formula assumes life is limited by metal fatigue and that the distribution of life can be explained by the Weibull distribution. Many variations of the existing formula include factors for material properties, lubrication, and loading. Factoring for loading can be seen as a tacit recognition that modern materials show the different relationships between the load and life of Lundberg and Palmgren determined.
Failure mode
If the bearing does not rotate, the maximum load is determined by the force causing the deformation of elements or plastic raceways. Indentation caused by elements can concentrate pressure and produce cracks in components. The maximum load for a not-so-slow spinning bearing is called a static "static" load.
Also if the pads do not rotate, the oscillating force on the pads may cause bearing impact damage or rolling elements, known as brinelling. A second low form called false brinelling occurs when the bearing only spins across the short arc and pushes the lubricant out of the rolling element.
For rotating bearings, dynamic load capacity indicates a load that holds the bearings for 1,000,000 cycles.
If the bearing is spinning, but is subjected to a heavy load that lasts shorter than a revolution, the static max load must be used in the calculation, since the bearings do not rotate during the maximum load.
If sideways torque is applied to the deep-groove radial bearing, the uneven force in the ellipse is applied to the outer ring by the rolling element, concentrating on two regions on the opposite side of the outer ring. If the outer ring is not strong enough, or if it is not sufficiently supported by the supporting structure, the outer ring will change its shape to an oval shape from the torsion voltage to the side, until the gap is large enough for rolling elements to escape. The inner ring then appears and the structure collapses.
The sideways torque on the radial pad also applies pressure on the cage that holds the rolling elements at the same distance, since the all-rolling elements try to glide together in the highest torque sideways location. If the cage collapses or breaks apart, group elements rolling together, the inner ring loses support, and can get out of the center.
Maximum load
In general, the maximum load on the ball bearing is proportional to the outside diameter of the bearing width bearing time (where the width is measured in the direction of the shaft).
Bearings have static charge ratings. It is based on not exceeding a number of plastic deformations in the raceway. This rating can be exceeded by a large amount for a particular app.
Lubrication
For bearing to function properly, it should be lubricated. In most cases the lubricant is based on elastohydrodynamic effects (by oil or fat) but working on extreme temperatures of dry lubricated bearings is also available.
For bearings to have a nominal life at nominal maximum load, it should be lubricated with a lubricant (oil or fat) that has at least a minimum dynamic viscosity (usually denoted by the Greek letter ) is recommended for that pad.
The suggested dynamic viscosity is inversely proportional to the bearing diameter.
The recommended dynamic viscosity decreases with the rotating frequency. As a rough indication: less than 3000 RPM , suggested viscosity increase by a factor of 6 for a 10-factor velocity reduction, and for more than 3000 RPM , the recommended viscosity decrease by a factor of 3 for an increase of 10 speed factors.
For bearings where the mean outer diameter of the bearing and the diameter of the shaft hole is 50 mm , and it rotates at 3000 RPM , the suggested dynamic viscosity is 12 mmÃ, ²/s .
Note that the viscosity of the dynamic oil varies greatly with temperature: an increase in temperature 50-70Ã, Â ° C causes the viscosity to decrease by a factor of 10.
If the lubricant viscosity is higher than recommended, the lifetime of the pads increases, roughly proportional to the square root of the viscosity. If the lubricant viscosity is lower than recommended, the lifetime of the bearings decreases, and how much depends on the type of oil used. For oils with an EP additive ('extreme pressure'), its age is proportional to the square root of dynamic viscosity, just as the viscosity is too high, while for the regular oil age proportional to the lower viscosity square. of the recommended viscosity is used.
Lubrication can be done with grease, which has an edge normally stored in a cushion that releases lubricating oil as it is compressed by the ball. This provides a protective barrier for metal bearing from the environment, but has the disadvantage that this grease should be replaced periodically, and the maximum load bearing decrease (because if the pads become too warm, the fat melts and runs out of pads). The time between replacement grease decreases very strong with the bearing diameter: for span bearing 40 mm, the grease should be replaced every 5000 working hours, while for the 100 mm be replaced every 500 working hours.
Lubrication can also be done with oil, which has a higher maximum overload, but it takes some way to keep the oil in the pads, as it usually tends to run out of it. For oil lubrication it is recommended that for applications where the oil does not become warmer than 50Ã, ° C , the oil should be replaced once a year, while for applications where the oil does not become warmer than 100 à ,  ° C , oil should be replaced 4 times per year. For car engines, oil becomes 100Ã,  ° C but the engine has an oil filter to maintain oil quality; therefore, oil is usually changed less frequently than oil in a cushion.
The load direction
Most bearings are intended to support loads perpendicular to the shaft ("radial load"). Can they also bear axial load, and if so, how much, depending on the type of cushion. Thrust bearings (commonly found in lazy arrangements) are specifically designed for axial loads.
For single-line deep-groove ball bearings, SKF documentation says that the maximum axial load is about 50% of the maximum radial load, but also says that "light" and/or small "pads" can take axial loads that are 25% of the maximum radial load.
For single-row end-contact ball bearings, axial loads can be about 2 times the max radial load, and for axial load the maximum cone is between 1 and 2 times the maximum radial load.
Conrad-style ball bearings will often show elliptical cutting contacts under axial load. That means that either the ID of the outer ring is large enough, or the inner ring OD is small enough, thus reducing the contact area between the ball and the raceway. When this happens, it can significantly increase the pressure in the pads, often invalidating general rules about the relationship between radial and axial load capacity. With this type of construction other than Conrad, one can further reduce the ID of the outer ring and increase the inner ring OD to prevent this.
If both axial and radial loads are present, they can be added vectors, to produce the total load on the bearings, combined with the nominal maximum load can be used to predict lifespan. However, to correctly predict the life of the ISO/TS 16281 ball bearing ratings should be used with the help of calculation software.
Avoiding unwanted axial load
Part of a rotating bearing (either axle or outer loop) should be fixed, while for non-rotating parts this is not required (so it can be left to slip). If the pad is loaded axially, both sides must be fixed.
If the shaft has two bearings, and the temperature varies, the shaft shrinks or expands, therefore it is unacceptable for both bearings to be repaired on both sides of them, since the shaft extension will exert an axial force that will destroy this bearing. Therefore, at least one bearing should be able to slide.
A 'free fit slide' is one in which at least there is a 4 Âμm clearance, possibly because surface-surface roughness is made on a lathe normally between 1.6 and 3.2 Âμm.
Fit
Bearings can withstand maximum load only if the marriage is the right size. Bearing manufacturers provide tolerance for shaft and residential compatibility so that this can be achieved. Material and hardness can also be determined.
Fittings that are not left to slip are made into a diameter that prevents slipping and consequently the mating surface can not be brought to a position without coercion. For small pads this is best accomplished by pressing because of tapping with a hammer bearing and shaft damage, while for large bearings, the required force is so large that there is no alternative to heat one section before it is installed, so thermal expansion allows while sliding fit.
Avoiding torsional load
If the shaft is supported by two bearings, and the centerline of this bearing rotation is not the same, then a large force is applied to the pads that can destroy it. Some very small misalignments are acceptable, and how much depends on the type of pads. For bearings specifically designed to 'align oneself', an acceptable misalignment is between 1.5 and 3 degrees arc. Pads that are not designed to align themselves can receive a misalignment of just 2-10 minute arcs.
Apps
In general, ball bearings are used in most applications that involve moving parts. Some of these apps have special features and requirements:
- The hard drive pads are usually very round, and are said to be the best form of ball production, but this is no longer true, and more and more are replaced with fluid pads.
- German ball bearing factories were often subjected to allied air bombing during World War II; such is the importance of the ball being brought into the German war industry.
- In horology, the company Jean Lassale designed a clock movement that uses ball bearings to reduce the thickness of movement. Using a 0.20 mm ball, Caliber 1200 is only 1.2 mm thick, which is still the thinnest mechanical watch movement.
- The aerospace bearings are used in many applications on commercial, private and military aircraft including pulleys, gearboxes and jet engine shafts. Materials include M50 steel tool (AMS6491), Chrome carbon steel (AMS6444), AMS5930 corrosion resistance, 440C stainless steel, silicon nitride (ceramic) and titanium carbide-coated 440C.
- The skateboard wheel contains two bearings, which are subject to axial and radial loads varying in time. Most commonly used 608-2Z bearing (deep groove ball bearing from series 60 with 8mm diameter bore)
- Yo-Yos, there are ball bearings in the midst of many new ones, ranging from beginner to professional or competition level, Yo-Yos.
- Many restless spinner toys use multiple ball bearings to gain weight, and to allow rotating toys.
Setting
The size of the ball increases as the series increases, for each inner diameter or outer diameter (not both). The larger the ball the greater the load carrying capacity. Series 200 and 300 are the most common.
See also
- How Ball Bearings Are Made - Manufacturing Process
- Screw ball
- Bearings (mechanical)
- Bearing Specialist Association
- Brinelling, common failure mode
- Linear bearings
- Thrust bearing
- Spherical roller bearings
References
External links
- Ball bearing in Curlie (based on DMOZ)
- Bearing Modeling using Wolfram
Source of the article : Wikipedia
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