Yoke type track rollers have an internal design very similar to that of a needle or cylindrical roller bearing. They comprise thick-walled outer ring with a profiled outside surface and needle roller and cage assemblies or full complement needle roller or cylindrical roller sets. Yoke type track rollers can support high radial loads as well as axial loads arising from slight misalignment and skewed running. They are suitable for cam gears, bed ways, conveying equipment etc.
Yoke type track rollers with a crowned outside surface are standard type since they are often inclined in relation to the mating track and edge stress must be avoided. The radius of curvature of the outside surface is R500mm. However, yoke type track rollers with cylindrical running surface are available for certain applications.
NPB yoke type track rollers are available:
● without flange rings
● with flange rings
Yoke type track rollers without flange rings
Yoke type track rollers supplied without flange rings have two designs and variants:
● with or without an inner ring
● open or sealed with two integral flanges in the outer ring
The bearings without flanges are designed for applications where associated components can limit axial movement of the outer ring. Bearings without inner ring are suitable for arrangements where the shaft can be hardened and served as the raceway. Yoke type track roller with an inner ring have a slightly extended inner ring to enable the necessary of outer ring.
STO and RSTO design yoke type track rollers
STO design yoke type track rollers have extended inner ring（fig1）, while RSTO design don’t have an inner ring（fig2）. Both designs of bearings are only available in open type, making it possible to mount each component separately. The bearings are pre-greased. STO and RSTO are the only designs of track rollers that can be lubricated with oil, if the bearings are lubricated with oil, the grease that pre-supplied should be cleaned out.
NA22…2RS and RNA22…2RS design yoke type track rollers
The needle roller and cage assembly is axially guided between two integral flanges in the outer ring and forms a non-separable unit with the outer ring. NA22…2RS design yoke type track rollers have an inner ring that can be mounted individually（fig3）. RNA22…2RS design track rollers do not have an inner ring and are used where the shaft can be hardened and ground（fig4）.
Both of these designs are fitted with contact seals made of oil and wear-resistant acrylonitrile-butadiene rubber (NBR). They are designed for applications where contamination is light to moderate and where moisture or water spray can not be avoided.
fig 3 fig4
Yoke type track roller with flange rings
Yoke type track roller with flange rings are non-separable units and are available in different designs and varients:
● with gap-type, labyrinth, polyamide or rubber seals
● with needle or cylindrical rollers
● with one or two rows of rollers
● with a cage-guided or a full complement roller set
Depending on the designs, the flange rings are either pressed-on or loose. The yoke type track rollers with flange rings are suitable for applications where the thrust forces that induced during the shaft is not horizontal need to be accommodated by the flange rings.
NATR design yoke type track rollers
NATR type track rollers are fitted with needle roller and cage assembles（fig5）, the flange rings are pressed on the inner ring and formed a gap-type seals with the outer ring.
NATV design yoke type track rollers
NATV design track rollers are similar to the NATR design, except that they comprise full complement of needle rollers（fig6）. Therefore, they can accommodate higher load.
NATR and NATV design yoke type track rollers, designation suffix PP
NATR and NATV design yoke type track rollers with designation suffix PP have axial sliding rings made of polyamide 66 on both side（fig7&fig8）. In the radial direction, the sliding ring forms a narrow labyrinth seal with the outer ring to protect against coarse contaminants. In the axial direction, the sliding ring serves as a contact seal to reliably retain grease in the bearing.
NUTR design yoke type track rollers
The NUTR design yoke type track rollers（fig9） are based on double row full complement cylindrical roller bearing. The outer ring comprises two integral flanges to axially guide the rollers. A loose flange on both side of the inner ring axially guided the outer ring via the roller sets, this enable the bearing to accommodate high axial forces induced when operating in a tilted position.
The bearings are provided with metal angular ring that pressed into the outer ring on both sides. The sheet metal angular ring extend over the flange rings hold the bearing components together and form efficient labyrinth seals.
PWTR…2RS design yoke type track rollers
PWTR…2RS design yoke type track rollers （fig10）have a contact seal which is protected and integrated with a metal angular ring that pressed into the outer ring on both sides. The seals make these bearing particularly suitable for operation under pollutant conditions. The metal sheet angular rings extend over the flange rings to hold the components together.
The three integral flanges in the outer ring axially guide the two full complement roller sets separately to minimize friction in the roller, thereby reducing heat generated by the bearing. The loose flanges on both sides provide axial guidance for the outer ring via roller sets. This enable the rollers to accommodate axial loads occurred when operating in a tilted position.
The large space between two roller sets enables to fill more grease. The large grease fill and efficient sealing structure make the rollers to operate longer between maintenance intervals.
NNTR…2ZL design yoke type track rollers
NNTR…2RZL design yoke type track rollers（fig11） comprise two full complement cylindrical rollers and can accommodate very heavy radial loads. The track rollers have a lamellar seal that inserted into the outer ring and flange shoulder on both sides and provide support to hold the bearing together. Three integral flanges in the outer ring axially guide the two rows of full complement rollers separately to minimize friction in the bearings, thereby reducing the amount of heat generation. The two loose flanges axially guide the outer ring via the roller complements. This enable the track rollers to accommodate relatively heavy constant axial loads that occur when bearings operate in inclined position.
Profile of the outer ring running surface
NPB yoke type track rollers with crowned outer ring running surface are as standard since the bearings are usually operated in inclined position and edge stress must be avoided.
The crowned running surface has a radius of 500mm for the following track roller designs:
● STO and RSTO designs
● NA22…2RS and RNA22…2RS designs
● NATR and NATV without designation suffix
In the case of NNTR..2ZL, the bearings with outer diameter D≤260mm have Radius=10000mm,and outer diameter D≥290mm have Radius=15000mm.
NPB also provide yoke type track rollers with improved crowned profile of the outer ring running surface. The modified line contact provides even better load distribution than the standard radius. The modified line contact provides a higher degree of stiffness while reducing wear between the outer ring running surface and the track.
The following yoke type track roller designs have improved crowned profile:
● NATR and NATV designs with suffix PP
● NUTR design and PWTR..-2RS design