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Multi-Row Cylindrical Roller Bearings

Four-row (fig 1) and six-row cylindrical roller bearings (fig) are used almost exclusively for the roll necks of rolling mill stands, calenders and roller presses. Their friction is low compared with other roller bearings. As they are normally mounted with an interference fit on the roll neck, they are particularly suitable for rolling mill applications where the rolling speed is high.

Fig 1. Four-row cylindrical roller bearing

Fig 2. Six-row cylindrical roller bearing

The low bearing cross section allows for relatively large roll neck diameters in comparison with the roll diameter. Since very many rollers can be incorporated, the radial load carrying capacity is exceptionally high.

Multi-row cylindrical roller bearings are only able to accommodate radial loads. They are therefore mounted together with deep groove or angular contact ball bearings, or with tapered roller bearings, either radial or thrust designs, which take up the axial loads.

The four-row and six-row cylindrical roller bearings are of separable design, i.e. the ring or rings with integral flanges and the roller and cage assemblies can be mounted independently of the free rings, or all bearing components can be mounted separately. This considerably simplifies bearing mounting, maintenance and inspection. A certain limited axial displacement of the shaft with respect to the housing can be accommodated within the bearing.

SKF four-row cylindrical roller bearings have a cylindrical bore and some sizes are also available with tapered bore. Bearings with tapered bore can be adjusted during mounting to give a certain radial internal clearance or a defined preload.

Four-row cylindrical roller bearings with cylindrical bore

SKF four-row cylindrical roller bearings with cylindrical bore are available in many designs dictated by the application or by maintenance considerations. The various designs differ basically in the number of inner and outer rings as well as in the number of loose or integral flanges on the outer ring. There are also differences in cage design and in the number of rollers per cage pocket.

For bearing arrangements (up to 8,5 m/s rolling speed) where the bearings are mounted with a loose rather than an interference fit on the roll neck, in order, for example, to enable rapid roll replacement in the chocks, SKF four-row cylindrical roller bearings are supplied in special designs. To largely compensate for the disadvantages of the loose fit (the inner rings wander on the seat which can damage both bearing and seat), these bearings have a helical groove in the bore and/or lubrication grooves in the side faces of the bearing rings (fig).These grooves enable the mating surfaces to be efficiently lubricated.

Bearings which have one or more of these features are identified in the product table by the following letters

DesignationFretures
Ghelical groove in bearing bore
Wlubrication grooves in side faces of bearing
WIlubrication grooves in side faces of inner ring
WOlubrication grooves in side faces of outer ring
W33Annular groove and three lubrication holes in outer ring

The letters appear under the heading "Design" in the product table following the design identification, e.g. BC4.10/W33GW.

DesignSKF produces four-row cylindrical roller bearings with cylindrical bore in many designs. Those shown in the product table are briefly described in the following.

BC4.1 designTwo outer rings each with three integral flanges. One inner ring. Two roller guided double pronged machined brass cages. With or without annular groove and/or lubrication holes in the outer rings (fig).

BC4.2 designTwo outer rings each with three integral flanges, and with an intermediate ring between the two outer rings. One inner ring. Two roller guided double pronged machined brass cages. With or without annular groove and/or lubrication holes in the outer rings (fig).

BC4.3 designTwo outer rings each with an integral central flange and two loose flange rings; one intermediate ring. One inner ring. Two roller guided double pronged machined brass cages. With or without annular groove and/or lubrication holes in the outer rings (fig).

BC4.4 designTwo outer rings each with two integral flanges. One inner ring. Two window-type cages of brass (two rollers per cage pocket) (fig).

BC4.5 designOne outer ring with three loose guide rings and two loose flange rings. One inner ring. Two double pronged machined brass cages. With or without annular groove and/or lubrication holes in the outer ring (fig).

BC4.6 designOne outer ring with five integral flanges. One inner ring. Four roller guided pronged cages of brass. With annular groove and lubrication holes in the outer ring (fig).

BC4.7 designTwo outer rings each with three integral flanges. Two inner rings. Two roller guided double pronged cages of brass. With or without annular groove and/or lubrication holes in the outer rings (fig).

BC4.8 designTwo outer rings each with an integral central flange and two loose flange rings; one intermediate ring. Two inner rings. Two roller guided double pronged machined brass cages. With or without annular groove and/or lubrication holes in the outer rings (fig).

BC4.9 designTwo outer rings each with three integral flanges. Two inner rings. Pierced rollers and four pin-type cages of steel or brass. With or without annular groove and/or lubrication holes in the outer rings (fig).

BC4.10 designTwo outer rings each with an integral central flange and two loose flange rings; one intermediate ring. Two inner rings. Pierced rollers and four pin-type cages of steel or brass. With or without annular groove and/or lubrication holes in the outer rings (fig).

BC4.11 designTwo single row outer rings each with one integral flange and one double row outer ring with integral central flange and two intermediate rings. Two inner rings. Pierced rollers and four pin-type cages of steel (fig).

BC4.12 designTwo outer rings each with an integral central flange and two loose flange rings; one intermediate ring. Two inner rings. Four pressed steel cages. With or without annular groove and/or lubrication holes in the outer rings (fig).

BC4.13 designTwo outer rings each with two integral flanges. Two inner rings. Two double row window-type machined brass cages (two rollers per cage pocket) (fig).

BC4.14 designTwo outer rings each with an integral central flange and two loose flange rings; one intermediate ring. Four inner rings. Pierced rollers and four pin-type cages of steel or brass. With or without annular groove and lubrication holes in the outer rings (fig).

BC4.15 designTwo flangeless outer rings. Two inner rings each with three integral flanges. Pierced rollers and four pin-type cages of steel. With lubrication holes in the outer rings (fig).

BC4.16 designOne outer ring with three loose guide rings and two loose flange rings. One extended inner ring. Two roller guided double pronged machined brass cages. With or without annular groove and/or lubrication holes in the outer ring (fig).

BC4.17 designTwo outer rings each with three integral flanges. Two inner rings, one of which is extended. Two roller guided double pronged machined brass cages. With or without annular groove and/or lubrication holes in the outer rings (fig).

BC4.18 designTwo outer rings each with an integral central flange and two loose flange rings; one intermediate ring. Two inner rings, one of which is extended. Two roller guided double pronged machined brass cages. With or without annular groove and/or lubrication holes in the outer rings (fig).

BC4.19 designTwo outer rings each with an integral central flange and two loose flange rings; one intermediate ring. Two inner rings, one of which is extended. Pierced rollers and four steel pin-type cages. With or without annular groove and/or lubrication holes in the outer rings (fig).

BC4.20 designTwo outer rings each with an integral central flange and two loose flange rings; one intermediate ring. Two inner rings, one of which is extended and has a concentric shoulder. Pierced rollers and four steel pin-type cages. With annular groove and lubrication holes in the outer rings (fig).

BC4.21 designTwo outer rings each with an integral central flange and two loose flange rings; one intermediate ring. Two extended inner rings, one of which has a concentric shoulder. Pierced rollers and four steel pin-type cages. With annular groove and lubrication holes in the outer rings (fig).

Four-row cylindrical roller bearings with tapered bore

There is relatively little demand for four-row cylindrical roller bearings with tapered bore; this is reflected in the relatively small number of sizes and designs manufactured by SKF. The designs differ principally from those of the four-row bearings with cylindrical bore in that the inner ring is usually in one piece and generally has a taper of 1:12. A few relatively wide bearings have inner rings with a tapered bore of 1:30.

BC4T.1 design Two outer rings each with three integral flanges. One inner ring. Two roller guided double pronged machined brass cages. With or without annular groove and/or lubrication holes in the outer rings (fig).

BC4T.2 design Two outer rings each with three integral flanges. One intermediate ring between the two outer rings. One inner ring. Two roller guided double pronged machined brass cages. With annular groove and lubrication holes in the outer rings (fig).

BC4T.3 design Two outer rings each with a central integral flange and two loose flange ring; one intermediate rings. One inner ring. Two roller guided double pronged machined brass cages. With or without annular groove and/or lubrication holes in the outer rings (fig).

BC4T.4 design One outer ring with three loose guide rings and two loose flange rings. One inner ring. Two double pronged machined brass cages. With or without annular groove and/or lubrication holes in the outer ring (fig).

BC4T.5 design Two outer rings each with a central integral flange and two loose flange rings, one intermediate ring. One inner ring. Pierced rollers and four steel pin-type cages. With or without annular groove and/or lubrication holes in outer rings (fig).

BC4T.6 design Two outer rings each with a central integral flange and two loose flange rings, one intermediate ring. Two inner rings. Pierced rollers and four steel pin-type cages. With annular groove and lubrication holes in outer rings (fig).

BC4T.7 design Two outer rings each with three integral flanges. One extended inner ring. Two roller guided double pronged machined brass cages. With annular groove in the outer rings (fig).

BC4T.8 design One outer ring with three loose guide rings and two loose flange rings. One extended inner ring with a lead-in. Two double pronged machined brass cages. With or without annular groove and/or lubrication holes in the outer ring (fig).

Sealed four-row cylindrical roller bearings

SKF four-row cylindrical roller bearings can also be supplied as sealed bearings, with a seal at one side or at both sides of the bearing. The seals are double lip radial shaft seals. Compared with open bearings, sealed bearings offer the following advantages:

  • Longer service life.
  • Reduced grease consumption.
  • Longer relubrication intervals.
  • Grease leakage and contamination of the rolling emulsion are prevented.

Thus the sealed bearings satisfy modern economic and ecological demands.

The radial shaft seals are made of hydrogenated acrylonitrile butadiene rubber (HNBR) with pressed steel reinforcement and have a steel garter spring to provide the necessary pressure for the seal lip on the counterface. The permissible sliding speed is 25 m/s. The seals have high thermal and chemical resistance and can be operated in the temperature range 20 to +140 C.

Designs SKF sealed four-row cylindrical roller bearings are produced with cylindrical bore; two designs are available.

BC4.22 design Two outer rings with integral central flange, one intermediate ring and two loose flange rings fitted with a double-lip radial shaft seal. Two inner rings with one integral flange. Four pressed steel window-type cages. With annular grooves and lubrication holes in outer ring (fig).

BC4.23 design Two outer rings with integral central flange, one intermediate ring and two loose flange rings, one fitted with a double-lip radial shaft seal. Two inner rings with one integral flange. Four pressed steel window-type cages. With annular grooves and lubrication holes in outer ring (fig).

Six-row cylindrical roller bearings

Six-row cylindrical roller bearings (fig) are used primarily for small cold rolling mills for flat products where the rolling forces are considerable at the same time as rolling speeds are high. The bearings have an outer ring with two loose flange rings and three loose guide rings, between which the six rows of rollers are radially guided. Three double pronged machine brass cages retain the rollers. The inner ring is without flanges so that limited axial displacements of the roll neck with respect to the chock can be accommodated within the bearing itself.

DimensionsThe dimensions of the four-row cylindrical roller bearings are not standardized. However, in many cases the bore and outside diameters correspond to Diameter Series 9 or 0 to ISO 15:1998.

The dimensions of the six-row cylindrical roller bearings of series NNU 69 and NNU 60 are in accordance with ISO 15:1998.

TolerancesSKF four-row cylindrical roller bearings are produced with the normal accuracy for roll neck bearings, i.e. dimensional accuracy to tolerance class P6 and running accuracy to tolerance class P5 specifications.

SKF six-row cylindrical roller bearings are manufactured to Normal tolerances.

Internal clearanceSKF four-row cylindrical roller bearings are normally produced with the C3 or C4 radial internal clearance required for rolling mill bearings. Bearings for mounting with a loose fit on the roll necks ("G" design) generally have C2 radial internal clearance.

SKF six-row cylindrical roller bearings are produced with the radial internal clearance specified on the order.

The clearance values, where standardized, conform to ISO 5753:1991 and are given in table 1 for bearings with cylindrical bore and in table 2 for bearings with tapered bore. They are valid for unmounted bearings under zero measuring load.

Influence of operating temperatures on bearing materials

SKF multi-row cylindrical roller bearings are subjected to a special heat treatment as standard so that they can be operated at temperatures up to +150 C without any inadmissible dimensional changes occurring. To order, and against a surcharge, bearings can be dimensionally stabilised for operating temperatures up to +200 C (designation suffix S1) or up to +250 C (designation suffix S2). An advantage of this special heat treatment is that the bearings can be mounted with a greater degree of interference than is possible with standard bearings. For further information please contact the SKF application engineering service.

CagesSKF multi-row cylindrical roller bearings, depending on size and also application, are produced with the following cages:

  • Two or three double pronged machined brass cages (fig).
  • Two double row window-type cages of brass (fig).
  • Four window-type cages of pressed steel (fig).
  • Four pin-type cages of steel (fig).
  • Four pronged machined brass cages (fig).

Minimum loadTo achieve satisfactory operation, multi-row cylindrical roller bearings, like all ball and roller bearings, must always be subjected to a given minimum load, particularly if they are to operate at high speeds or are subjected to high accelerations or rapid changes in the direction of load. Under such conditions the inertia forces of the rollers and cage, and the friction in the lubricant, can have a detrimental effect on the rolling conditions in the bearing arrangement and may cause damaging sliding movements to occur between the rollers and the raceways.

The requisite minimum load to be applied to multi-row cylindrical roller bearings can be estimated using

where

Frm = minimum radial load [kN]

kr = minimum load factor (see product data)

n = operating speed [r/min]

dm = mean diameter of bearing

= 0,5 (d + D) [mm]

When starting up at low temperatures or when the lubricant is highly viscous, even greater loads may be required. The weights of the components supported by the bearing, together with the external forces, generally exceed the requisite minimum load. If this is not the case, the multi-row cylindrical roller bearing must be subjected to an additional radial load.

Equivalent dynamic bearing load

P = Fr

Equivalent static bearing load

P0 = Fr

Supplementary designationsThe designation suffixes used to identify certain features of SKF multi-row cylindrical roller bearings are explained in the following.

DesignationFretures
A, B, C, D, EModifications to the original design. Combinations of these letters are also used, e.g. DC. The actual modification is specific to the individual bearing and is given on the drawing.
C2Radial internal clearance smaller than Normal
C3Radial internal clearance greater than Normal
C4Radial internal clearance greater than C3
HA1Inner and outer rings of case-hardened steel
HA2Outer ring of case-hardened steel
HA3Inner ring of case-hardened steel
HA4Inner and outer rings and rollers of case-hardened steel
HB1Bainite hardened inner and outer rings
HB2Bainite hardened outer ring
HB3Bainite hardened inner ring
KTapered bore, taper 1:12
K30Tapered bore, taper 1:30
MMachined brass cage
P5Dimensional and running accuracy to ISO tolerance class 5 (better than P6)
P6Dimensional and running accuracy to ISO tolerance class 6 (better than Normal)
VJ202Bearing set of double row bearings
W33Annular groove and three lubrication holes in outer ring

Mounting instructionsKnowledge and experience are of particular importance where four-row cylindrical roller bearings are concerned. The individual components must be mounted in the correct order. Parts which belong together are marked with letters (fig). In addition, all components of the bearing are marked with the same serial number, so that there is no risk of mixing components if several bearings are to be mounted at the same time. However, the inner rings and inner ring pairs are fully interchangeable and need not have the same serial number as the outer ring(s).

In the majority of applications the load is of constant direction, so that only approximately a quarter of the outer ring is under load. For this reason, the side faces of the outer rings are divided into four zones indicated by I to IV. The markings for load zone I are also joined by a line across the outside surface of the outer rings.

When the bearing is mounted for the first time it is usual to position zone I in the direction of action of the load. Depending on the operating conditions, the outer rings should be turned through 90 after a period of service so that a new zone comes under load. The recommended period is approximately 1 000 operating hours and the bearings should be inspected. The turning should take place at a suitable roll change.

If skilled personnel is not available to mount the bearings it is advisable, particularly where large bearings are concerned, to request the assistance of SKF service personnel. Further details of the SKF mounting service will be supplied on request.

Detailed mounting instructions are also supplied with all bearings.


Cylindrical roller bearings | Single row cylindrical roller bearings | Double row cylindrical roller bearings | Multi-row cylindrical roller bearings | Single row full complement cylindrical roller bearings | Double row full complement cylindrical roller bearings | Multi-row full complement cylindrical roller bearings | Split cylindrical roller bearings

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This page is still under construction. All bearing information remains the property and copyright of SKF Group.