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RKB produces cylindrical roller bearings in various design styles, sizes and dimension series. RKB heavy duty radial cylindrical roller bearings are designed to provide the highest possible radial capacity for the given cross section and to perform under heavy radial loads. These bearings incorporate improved internal proportions developed through computer assisted optimization studies, to make the maximum use of the total available cross-sectional area. The rollers have controlled contour to redistribute end stress concentration and provide more uniform distribution of the applied loads (suffix ZB). Their surface finishing maximizes lubricant film formation and optimizes rolling motion. The standard ISO assortment of RKB production program includes single and double row bearings with a cage that can accommodate heavy radial loads and operation at high speeds. A complete range in various executions of full complement of rollers suitable for more heavy loads at moderate speeds is also available. Large size bearings can be supplied with surface treated rollers (suffix B). In addition to the standard assortment, RKB cylindrical roller bearing range is comprehensive of open and sealed multi row for rolling mills in many executions and designes, backing bearings for cold rolling mills and indexing roller units for continuous furnace. Besides to the inch dimension series as per AFBMA specifications, RKB offers the American style series 5200 and 5300 metric cylindrical roller bearings with enhanced radial capacity due to its internal design proportions, with double ribbed outer ring and with manufacturing tolerances established for the interchangeable components. The single row cylindrical roller bearings are manufactured in various constructive versions, depending on the position of the ribs on the rings (e.g. bearing designation NU, NJ, NUP and N). Depending on size and design, the bearings are equipped as standard with one of the following cages: unhardened pressed steel roller centered, one-piece window type brass inner or outer ring centered, two-piece machined brass roller centered (suffix M) or outer ring centered (suffix MA) or inner ring centered (suffix MB) and steel pin-type for pierced rollers. Lubrication grooves in the guiding surfaces of machined brass cages are also available (suffix MAS and MBS). RKB cylindrical roller bearings undergo a special heat treatment of stress relieving which allows them to be operated up to a temperature of +150° C. The tolerances are in accordance with ISO 492:2002. The radial internal clearance, even smaller or greater than normal, is in accordance with the range class of ISO 5793 measured for unmounted bearings under zero measuring loads. The axial internal clearance for fixed design bearings, which can locate the shaft axially in both directions, is specified as per experienced rule. Bearings with no standard radial clearance or with special stated values required by specific applications can be supplied to special order. Bearings made of case hardened carburizing alloy steels can be produced for particular applications, where required (suffix HA1, HA2, HA3 and HA4). Besides, special treatments for rings and rollers are available (e.g. bainite quenching hardened for rings - suffix HB1 -, anti-wear surface treatment, etc.).

RKB double row angular contact ball bearings are equivalent to two single row paired angular contact ball bearings in the arrangement back-to-back or face-to-face. So they can accept radial loads together with axial loads acting in both directions. The width is narrower than the two equivalent single row bearings in pair.

The large double row angular contact ball bearings of RKB production range include bearings specially designed for rolling mills (bearing designation series 305 followed by three numbers).

The standardized items of the series ISO 32 and 33 have the filling slot and are non-separable, thus single direction axial loads should be applied.

The special bearings with drawing number of series 305 can have either split two-part inner ring or split two-part outer ring. They are non-separable and usually are mounted with radial play in the housing. In the bearings with split two-part inner ring the load lines refer to the back-to-back arrangement. The load lines of the bearings with split two-part outer ring are in the face-to-face arrangement.

The main dimensions of bearing series 32 and 33 are as per ISO 15 specifications. The dimensions of bearing series 305 do not follow any standards, but are internationally accepted and recognized in the rolling mill applications. The manufacturing tolerances conform to ISO 492 for normal class specification, but running accuracy grade is in accordance with P6 at least. These bearings are generally produced with a uniform axial internal clearance, but special values suitable for specific applications can be supplied on request.

The double row angular contact ball bearings in RKB production program are normally filled with two machined brass cage (one for each ball row).

RKB four-row taper roller bearings are installed as complete assemblies and take axial loads in addition to heavy radial loads, so that generally it is not requested separate thrust bearings in such arrangements. They are commonly used in rolling mill applications. For quick roll changes, the bearings have a loose fit on the roll necks, but there is the disadvantage that the inner rings wander on their seatings causing wear. To reduce these negative effects, RKB bearings have a helical groove in the bore and lubrication grooves in the side faces of the inner rings. These grooves enable lubricant to be supplied to the contact surfaces of the inner ring and seating. Since wear and shock resistance under heavy rolling loads is a requirement for roll neck bearings, highest quality carburizing grade bearing alloy steels are normally used in RKB four-row taper roller bearings. Besides, for large size bearings, pierced rollers and steel pin-type cage for maximum load ratings possible are applied. The induced thrust resulting from radial loading is cancelled within the double cones and it eliminates excessive loads on clamping and spacing members. RKB produces this style of bearings in two base designs, TQO and TQI configuration, where the main difference is the mutual arrangement of the roller complements and the number of inner and outer rings dictated by this. The TQO type is composed in its standard configuration of two double cone assemblies, one central double cup, two single cups and factory adjusted cup and cone spacers. The spacers of each bearing are face ground after accurate measurement of the distance between adjacent cups and cones to obtain the asked initial play (also defined as BEP - Bench End Play). So the bearing parts cannot be interchanged and they are individually marked for proper assembly. Lubrication grooves and oil holes are provided in the cup spacers and in the double cup. Furthermore, lubricant slots in the cones side faces and cone spacer permit the lubricant to go through the bearing to the roll neck. These bearings can be provided with lateral extension of the double cones used as sealing surface. This sealing feature offers better protection against hostile environment. For high speed rolling mill requirements, the TQO bearing sets may have tapered bore with features of high capacity, compactness and a mounting system that guarantees a positive interference fit on the roll neck. The TQI type is composed in its standard configuration of one double cone assembly, two single cone assemblies and two double cups. A four-separated individual single cup configuration is also available. This design facilitates the reworking of the bearing. These bearings are fitted with pressed steel cage or with pierced rollers and steel pin-type cage. The fact that contact angles diverge makes the bearings well suited to resist to warping and misalignment. The version with tapered bore that, with its three-cone design, assures easy assembly and disassembly (designation TQIT and TQITE) is also available. In RKB sealed TQOS type sets, four-row taper roller bearings have been developed to improve the lubrication in service. The incorporation of this type of bearing simplifies design, reduces grease consumption and routine maintenance requirements and attains longer service life. The seals, fitted on both sides of the bearing set, are produced in several designs depending on bearing size and application needs; the most common ones are the integrated lateral unitized seals (European version), the integrated lateral narrow seals (compact seal concept) and the loose flange lateral unitized seals (Japanese version). So the basic design with the garter seal, made by reinforced fluoro rubber and steel spring, is located in the integral external cups. Alternatively, the separate seal carrier flanges are matched to the cups and a chock type seal runs on extended surface of inner rings. Furthermore, RKB seals have been redesigned in new type to increase seal durability and efficiency: while maintaining an overall narrow profile, these seals optimize the available space by utilizing the area directly adjacent to or underneath the cage bore, with the result of the usage of longer rollers with consequent increased bearing capacity similar to open type version. RKB sealed four-row taper roller bearings are usually provided also with O-rings in the outboard cup outside diameter to seal contaminants from the bearing outer diameter and/or with a cone seal set designed to accommodate relative motion between inner rings and to prevent build-up of negative pressure (anti-vortex system technology for longer bearing life and less lubricant deterioration). Phosphate treatment for rings, rollers and spacers (suffix PT4) for anti-rust and anti-corrosion properties under water, alkalescent and acidescent working conditions is also available. RKB produces special executions of TQO made of four single cups and two double cone assemblies (design without spacers). Most of TQO and TQI four row taper roller bearings are manufactured with inch dimensions as per American AFBMA 19/1974 and as per RKB standard practice, dimensional and running accuracy grade is in accordance with class 2 or 4.

RKB single angular contact ball bearings are designed to accommodate combined loads acting in radial and axial direction. They can take axial loads in one direction only. When radially loaded, in the bearing occurs an axially acting load which has to be compensated. For this reason one bearing or paired bearings are mounted on each shaft end. These bearings are not separable and their use at relatively high speed is allowed. Manufactured in various constructive versions, they can be with different contact angles, depending on the application (suffix AC, A and B).

RKB produces two types of single row angular contact ball bearings: those of normal design and those intended for paired mounting (used respectively for tandem arrangement, DB and DF arrangements when axial loads have to be taken in both directions).

In the case of single row angular contact ball bearings the efforts between rings and rolling elements are transmitted at an angle to a plane perpendicular to the bearing axis. The value of this angle depends on the magnitude of the raceway radius, ball diameter and radial clearance in the bearing when the curvature centers of the raceway are in the same plane.

The main dimensions are in accordance with ISO/R 15. The values for the tolerance of the normal, P6 and P5 classes conform to ISO 492. Internal axial clearance or preload is obtained only when the bearings are mounted in the assembly and depends on the location of the second bearing which assures the shaft axial guiding.

RKB single angular contact ball bearings are fitted with a cage type depending on series and size: pressed steel sheet cage, machined brass cage guided on balls or on the inner ring and machined steel cage.

Large size paired 718 and 719 series bearings in DF and DB configuration for power transmission equipment are included in RKB production program.

FOUR-POINT ANGULAR CONTACT BALL BEARINGS

RKB four-point angular contact ball bearings are single row bearings where the raceway is designed to accommodate significant axial loads in both directions. Generally they have contact angle of either 35° or 45°. They need less axial space than double row or paired angular contact ball bearings. The four-point contact ball bearings have a split two-part inner (bearing designation QJ) or outer (bearing designation Q) ring, allowing a large number of balls to be incorporated, thus providing a high load carrying capacity. The bearings are of separable design of the parts.

To prevent rotation of the outer ring (when split inner ring) all the bearings with outside diameter over 160 mm are provided with locating slots (suffix N).

The main boundary dimensions are in accordance to ISO 15. The tolerances have values conform to ISO 492 and the normal class is for RKB standard production. The fitted cage is machined brass centered on outer ring for the standard common type QJ with split inner ring. RKB produces these bearings with normal axial internal clearance measured before mounting under zero measuring loads, but most sizes can also be supplied with greater or smaller clearance to special order.

RKB spherical roller bearings are self-aligning and consequently insensitive to the misalignment of the shaft relative to the housing and insensitive to shaft deflection or bending. The permissible value is up to 3.5° approximately depending on bearing series and size. These bearings have two rows of rollers with sphered raceway in the outer ring and two inner ring raceways inclined at the proper angle to the bearing axis. Used to operate in arduous conditions, leading in design, RKB spherical roller bearings can accommodate, in addition to high radial loads, axial loads acting in both directions. The production range of RKB spherical roller bearings comprises open bearings, sealed bearings (suffix 2CZ1) and bearings for vibratory applications (suffix ROVS). Besides, RKB offers spherical roller bearings customized for specific applications, as, for instance, bearings with split outer ring and wider outer ring for higher permissible misalignment (suffix WOR) or with increased width dimension and consequent larger rollers for milling applications (project designation SRB) or for the support of the rolls of cold rolling Pilger mills for tubes. RKB program includes the spherical roller bearings with both cylindrical and tapered bore (1:12 or 1:30 depending on series). Tapered bore bearings can either be mounted on tapered shaft seats or with sleeve on cylindrical shafts. Limiting load may result in lubrication problems, specially in the case of large bearings. So such bearings are provided with annular groove and lubrication holes in the outer and/or in the inner ring (suffix W33, W33X, W20, W26, etc.). Depending on the bearing series, size and/or application, RKB spherical roller bearings are manufactured in different constructive internal design versions (e.g. CA, MB, MA, CC, etc.). RKB small and medium size spherical roller bearings are usually fitted with pressed steel cage or one-piece machined brass cage where the bearings have a central guide rib on the inner ring and symmetrical rollers with large dimensions for increased carrying capacity. The bearings of normal design, with a central fixed rib, are fitted with machined brass or steel cage guided on the rollers or on the inner ring or outer ring raceway. The main dimensions are in accordance with ISO 15. The radial clearance can be normal, larger than normal (suffix C3, C4 and C5) or smaller than normal (suffix C2), measured on unloaded bearing in accordance with ISO 5753. RKB spherical roller bearings of all series and sizes are stress relieved. They undergo a special heat treatment so that they can be used up to an operating temperature of +150° C for long periods without inadmissible dimensional changes occurring. Some of RKB spherical roller bearings are also manufactured in the sealed version with contact seal on both sides. The seals are reinforced with steel sheet and made of an oil and wear resistant rubber (as nitrile butadiene for universal usage - suffix 2CZ1 - or fluoro base - suffix 2CZ - to withstand operating temperature up to about +200° C). In order to locate the spherical roller bearings with the tapered bore onto a cylindrical seating, the adapter (designation H) or withdrawal (designation AH) sleeves are the most commonly used components with large shafts with h9 and h10 tolerance. They are easy-to-mount on smooth or stepped shafts and require no additional location. Adapter sleeves are supplied along with lock nut and locking device (washer or clip). For large sized bearings, both adapter and withdrawal sleeves are provided with oil grooves and oil duct at the threaded side to enable the oil injection method to be used for easy mounting and dismounting (designation OH and AOH). All ISO series (also the outmoded series, such as 202 and 203) are in RKB manufacturing program with both straight bore (no suffix) and tapered bore (suffix K).

RKB taper roller thrust bearings have the following separable parts: shaft washer, housing washer and rolling element assembly. RKB manufacturing program includes the single direction type, the double direction type and the screw-down special type. RKB single direction taper roller thrust bearings are manufactured in two constructive versions, with tapered raceway on both washers or on only one. The rollers are radially guided by the rib of one washer. They have controlled contour to redistribute end stress concentration and provide more uniform distribution of the applied loads (suffix ZB). These bearings can also be produced in the version without the cage to obtain the maximum axial load carrying capacity (suffix V). The most common series are T type, TK type and 351 type. Bearings made of case hardened carburizing alloy steels can be produced for particular applications where required. RKB double direction taper roller thrust bearings are normally used in the rolling mill applications associated with a multi row cylindrical roller bearing. RKB produces this type of bearing in two constructive versions, either with central plane shaft washer and taper raceways in both housing washers or with both plane housing washers and taper raceways in the central shaft washer. A special sleeve is arranged between the two housing washers, so that, when mounting, no special adjustment of the bearing is required. As the double direction taper roller bearings are usually mounted with loose fit on the roll neck, the shaft washer is normally provided with one or two locating slots that, engaged with key-way or similar devices, prevent the shaft washer from rotating on the seating. If the load carrying capacity is not adequate to the expected life, TDIS type can be used in alternative. The most common series are 350 type, 351 type, 353 type and TTK type. RKB screw-down bearings are a special design of the single direction taper roller thrust bearings used for rolling mill arrangements. They are generally produced with case hardened carburizing alloy steels and with full complement of long rollers of large diameter to accommodate very heavy axial loads and shocks. In order to accept the angular movements of the screw spindle with respect to the support without detrimental effects on bearing performance, the bearings have one sphered washer that could be either the shaft or the housing washer. An additional concave sphered pressure plate can be supplied with the bearing. Usually screw-down bearings are custom-made to meet the specific requirements of different applications. The dimensions of taper roller thrust bearings are not standardized. The main boundary dimensions are produced with normal tolerances according to ISO 199:1979.