In their catalogs, manufacturers include a variety of conventional needle roller bearings; in addition, they provide both standard variants and custom designs.
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Seals
Sealing solutions for radial needle bearings are many. One or two seals may be supplied with a bearing. Usually, they are lip-contact seals that provide mild, continuous shaft contact for minimal drag and positive sealing. A general-purpose bearing oil is prepacked into the majority of sealed bearings.
Closed End
In designs where the shaft does not have to extend past the bearing, bearings—especially the drawn-cup variety—may have one end closed to offer good sealing. If the open end needs more defense against impurities, it can also be shut.
Relubrication Provisions
To make relubrication easier, drawn-cup bearings can be equipped with an oil hole in the middle of the cup OD. The outer ring OD of heavy-duty models has an oil hole and lubrication groove. Inner rings with holes and lubricating grooves are also available.
The plastic cages
These provide a more affordable option with better performance and are frequently utilized in certain applications where loads and environmental conditions are recognized.
Performance elements
To achieve the required bearing performance, choosing the appropriate needle bearing is not enough. Bearing functioning is influenced by a number of distinct parameters, such as the housing, raceway surface hardness and quality, and lubrication.
The Lubrication
Lubrication with oil is often preferable. It eliminates certain impurities, facilitates simpler injection into the bearing load zone, and allows for faster speeds by serving as a coolant. The best techniques include mist, oil splash, and positive feed.
Grease lubrication of bearings may be necessary under certain situations. Relubricate the system if at all feasible via a fitting in the housing or shaft, preferably through the stationary component.
In situations when relubrication is not feasible, caged bearings can offer a longer prelubricated life as they typically have a larger grease storage capacity. In these kinds of applications, grease life determines bearing life, and life estimates have to take it into consideration. Seals can aid in lubricant retention and foreign matter exclusion.
Surfaces of raceways
The geometry and material of the raceway determine bearing performance.
Hardness
The versatility of needle roller bearings to employ mating surfaces as inner or outer raceways, or both, is one of its key advantages. Usually, bearing load values are determined by using a raceway hardness of 58 Rc or above. If it is smaller, the bearing-raceway combination’s capacity is also less. Treatments such as case hardening, through hardening, and induction hardening are all appropriate. Use different inner rings if the shaft cannot be hardened to 58 Rc. Find those with the shoulders or snap rings on the shaft.
Finishing
Keeping a healthy lubrication coating between rollers and raceways requires a well-finished racetrack. High points are allowed to pierce the film over a rough surface, which speeds up fatigue and eventually seizing. On the Ra scale, the inner raceway finish should not be coarser than 16 minutes; nevertheless, improved microfinishes can significantly increase life. If the outside raceway finish is finer than 16 minutes, you will obtain the greatest results for complete complements of needle rollers or roller and cage assemblies. Make sure there are no nicks or scratches on the raceway surfaces.
The study of geometry
Perfect cylinders are the ideal raceway surfaces for radial needle roller bearings. Any deviation from the optimum might shorten bearing life and raise noise levels. As a result, the shaft and housing’s roundness should be maintained at 0.0003 inches, or half the suggested manufacturing tolerance, whichever is less. Reduced bearing fatigue life and increased roller stress can result from raceway taper. A situation in which the raceway design leads to nonuniform roller contact—for example, because of surface flaws or inadequate surface straightness—may be much more harmful. Furthermore, rollers must not protrude past the raceway’s surface. Early failure and stress concentrations may result from this.
For full-complement bearings, the shaft slope with respect to the bearing centerline should generally not be greater than 0.0010 in./in.; for caged bearings, it should be 0.0015 in./in. Slope can be better tolerated by shorter bearings.
The Housings
In order to guarantee that the thin outer shell of drawn-cup needle bearings is appropriately shaped and rounded, proper installation is necessary for their successful operation. Usually, an arbor press and a basic tool are enough to push the bearing into place. Axial location attributes are typically not necessary.
If made of steel or high-grade iron, the housing section may be as small as one and a half to two times the bearing section. A comparable section could be sufficient for a light alloy housing, but choosing appropriately reduced housing bore dimensions is essential for correct bearing size and rounding.
If the load is stationary with respect to the housing, heavy-duty needle bearings are installed in housings with a tight transition fit; if the load rotates with respect to the housing, the bearings are mounted with a clearance fit. Find the outer rings axially using a housing shoulder, snap ring, or other effective method, regardless of fit.
Applications
These days, weight, space, and energy consumption reduction are the main design trends. A compact solution to frictional issues is offered by needle roller bearings because of their narrow cross section and light weight.
Their distinct benefits are especially acknowledged in the two-cycle engine, automobile, and agricultural and construction equipment industries. Here, torque converters, suspensions, U-joints, auxiliary equipment, and gearboxes (as well as other gearbox applications) are typical uses for needle bearings.
In a similar vein, needle bearings are found in several parts of household appliances, including spindles, idler pulleys, pump clutches, and gearboxes. The narrow radial cross section also helps to reduce weight in portable power equipment.
Several varieties of needle bearings, for instance, perform numerous crucial tasks in an automatic gearbox. In the bores of planetary gear sets, full complement configurations of needle rollers and needle roller and cage assemblies are commonly utilized. Chaindrive sprockets hold needle bearings with drawn-cup cages installed in them. In shaft support locations, similar bearings are replacing bushings for increased efficiency.
When a spinning component is placed between a stationary support or between two counter-rotating components, thrust needle roller and cage assemblies are frequently used. Common uses involve sustaining moderate to high axial stresses in torque converters between the impeller and stator or between planetary sun gears and their carriers.
These are typically unitized bearings made up of two unique thrust washers that serve as raceways in addition to the thrust needle roller and cage assembly. Other elements to improve or control lubricant flow may be incorporated. These bearings are usually made to order in order to satisfy specific performance and space constraints.
The car engine is one application where needle bearings are now useful. Here, sliding valve lifters and traditional bushings are replaced with unique needle roller bearings, which assist lower friction at important contact areas within the valve train.
In certain automobile engines, special needle roller bearings are also used at the rocker arm pivot point. These bearings assist increase performance and fuel efficiency by taking the role of sliding bushings.
These kinds of bearings now have more options because to developments in contact stress analysis, surface finish specification, and manufacturing techniques. Further ensuring adaptability to unique application demands is geometric optimization of component profiles.