What are needle roller bearings, where do they go, and why you might need them
Ball or roller bearings make up the majority of rolling element bearings. Spherical, needle, tapered, and cylindrical bearings make up the majority of the roller bearing family. The tiniest and lightest members of the roller bearing family are needle roller bearings. Because of this, they provide unique benefits for some applications, especially those that call for less weight and space. The bearings’ operational features and nomenclature are largely attributed to their high roller length-to-diameter ratio. In essence, roller bearings for needles have:
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greater load capacity compared to same OD single-row ball or roller bearings.
the capacity to manage a stiffer, bigger shaft in a particular application.
Outstanding rolling properties in a compact cross section.
often less expensive than machined counterparts, particularly for the drawn-cup kind.
Rollers with needles
A full complement of loose needle rollers placed directly between a housing and a shaft that has been machined and hardened is the most affordable kind of needle roller bearing. Hardened end washers often offer axial placement. This kind is used in a variety of applications, such as those in which the outer raceway has a hardened and ground gear bore.
When all application criteria are satisfied and assembly is simple, a bearing with a small cross section and high load capacity is formed by all of the rollers. With the lowest cost per pound of capacity, this rolling bearing is especially advantageous in situations where production rates warrant the use of automated assembly equipment.
There are several end configurations for needle rollers. In order to lessen roller-end stress concentrations caused by misalignment or deflection of one or both raceways under load, controlled shapes have also been devised. Optimized bearing performance and more uniform stress distribution are brought about by controlled contour refinement.
Needle roller bearings with drawn cups
Drawn-cup needle roller bearings work similarly to loose rollers but in a unitized arrangement for convenience of handling and installation. With precision, low-carbon strip steel is drawn to create the outer shell, which functions as the outer raceway and is case hardened. Because no further machining is required, this bearing is cost-effective.
A complete set of trunnion-end needle rollers is mechanically retained by the cup’s turned-in lips (picture). These lips also serve as tight-fitting barriers that keep lubricant in place and keep out extraneous objects.
The load ratings of full-complement drawn-cup needle bearings are on par with or higher than those of ball and roller bearings with similar OD. Greater shaft diameters on which the bearings directly act are made possible by thin cross sections. This kind works well in settings that are static, slowly revolving, or oscillating due to the numerous contact lines that the loaded rollers produce.
Drawn-cup caged bearings are similar to their full-complement counterparts in many ways, including the fact that they work well in low-hardness housings. Compared to full-complement bearings, they can withstand higher speeds, shaft misalignment, and load deflection, but their load capacity is lower.
The advantages at high speeds and slopes with respect to the bearing centerline come from the cage architecture. The one-piece cage creates the best roller stability by effortlessly guiding and holding the rollers.
The cage’s open sections improve lubricant circulation and offer the grease storage space required by a prelubricated bearing. Integral seals that are optional aid in retaining grease and keeping impurities out.
Cage and roller assemblies for needles
In addition to offering control over operating radial internal clearances, the caged assembly design ensures proper load distribution between rollers and raceways. In addition, it can operate at high speeds and can withstand load deflection or shaft misalignment.
The user’s ability to maintain housing and shaft tolerances is essentially the sole restriction on managing clearance because the assembly has a housing as its outer racetrack and a shaft as its inner raceway. Numerous high-speed planetary pinions and other applications with low to moderate applied load are ideal for these systems.
Sturdy needle rollers
The outer ring of this bearing is machined and ground, and is somewhat thick. The through-hardened, one-piece, channel-shaped outer ring can withstand far greater shock and overload than casehardened drawn-cup bearings. The installation in a split housing is made possible by the considerable outer ring cross section.
Heavy-duty needle roller bearings can tolerate high speeds and misalignment because they have a cage to divide and guide the rollers. Certain split designs allow for installation in hard-to-reach places, including on crankshafts of engines.
Thrust cage and needle roller assemblies
These assemblies, which employ a reinforced steel cage to contain a complement of needle rollers, are made to support axial loads in constrained spaces. Thrust needle bearings offer better frictional properties and a significantly larger load capacity, even though they often occupy no more space than a standard thrust washer.
You can obtain individual hardened thrust washers in different thicknesses to achieve the required raceway quality if neighboring surfaces are not able to be hardened to the required level of 58 Rc or similar. High velocities and axial stresses are not a problem for thrust needle roller and cage combinations. Because they offer less friction in constrained spaces, they are frequently utilized in automatic gearboxes.
Tracker wheels
These are used with equipment that is track-type or cam-controlled. A robust outer ring is incorporated into the unit structure to withstand the severe rolling and shock loads that are characteristic of these applications.
There are two fundamental designs for various mounting configurations. The integrated stud type is for cantilever installation, and the yoke type is for straddle or clevis mounting. The ductile core of the stud gives it resilience against shock loads. Installation is made easier by a hexagonal wrench socket or a slot for a screwdriver in the stud head.
Certain variants are quite typical. Internal self-lubricating resin thrust washers are a common feature of sealed track rollers. To reduce unequal loading caused by deflection or misalignment during mounting, crowned outer rings may be supplied. During installation, eccentric studs allow the outer ring to be adjusted radially toward the track or cam surface.
Needle bearings in airframes
These bearings are made to specifically address the requirements of the aircraft industry in airframe applications, even though they are frequently used elsewhere. Heavy outer rings are a part of the unit structure to support large static or oscillating loads. High-carbon chrome steel is used for the bearing rings and rollers, and most exterior surfaces have protective coatings applied to them.
Certain kinds can be mounted in housings because of their lighter cross section. Some are designed to be used as track rollers. Wider and with two rows of rollers, bearings designed to withstand higher rolling loads (picture). Self-aligning varieties are intended for applications where deflection or difficulty with alignment during assembly exist.