Designs and variants

SKF standard assortment

The assortment of SKF spherical roller bearings is the widest available on the market. The standard assortment includes:
  • CC, CA and E design bearings
  • sealed bearings
  • bearings for vibratory applications
  • bearings for wind energy applications

All SKF spherical roller bearings are SKF Explorer bearings and almost all bearings are available with the option of a tapered bore. Depending on the bearing series, the tapered bore has:

  • a taper 1:12 (designation suffix K)
  • a taper 1:30 (designation suffix K30)

For sizes and variants not listed in the product table, contact SKF.

CC, CA and E design bearings

CC design bearings

  • have two stamped window-type steel cages, an inner ring without flanges and a floating guide ring centred on the inner ring (fig. 1)
  • are indicated in the product table by the designation suffix C or CC
  • are indicated in the product table by the designation suffix EC or ECC for larger bearings and have an optimized internal design for increased load carrying capacity

CA design bearings

  • have a machined double prong-type brass cage, an inner ring with a retaining flange on both sides and a floating guide ring centred on the inner ring (fig. 2). The flanges on the inner ring are designed to keep the rollers in place when swivelling the bearing during mounting or maintenance and are not designed to guide the rollers or accommodate any axial load.
  • are indicated in the product table by the designation suffix CA
  • are indicated in the product table by the designation suffix ECA for larger bearings and have an optimized internal design for increased load carrying capacity

E design bearings

  • have two stamped window-type steel cages, an inner ring without flanges and a floating guide ring centred on the inner ring (d ≤ 65 mm) or on the cages (d > 65 mm) (fig. 3)
  • are indicated in the product table by the designation suffix E
  • have an optimized internal design for increased load carrying capacity

For additional information about the suitability of cages, refer to Cages.

Annular groove and lubrication holes

  • CC and CA design bearings are available with an annular groove and three lubrication holes in the outer ring (designation suffix W33) or three lubrication holes in the outer ring (designation suffix W20) (fig. 4).
  • SKF E design bearings (fig. 3) have an annular groove and three lubrication holes as standard. This feature is not identified in the bearing designation (no designation suffix).
Sealed bearings
  • have the same features and internal design as open spherical roller bearings
  • are available with a cylindrical bore as standard
  • are supplied grease lubricated and should not be washed
  • are equipped with an annular groove and three lubrication holes in the outer ring, except for those with the designation suffix W
  • are fitted with a contact seal, on one or both sides, made of one of the following materials:
    • sheet steel reinforced NBR (designation suffix CS or RS)
    • sheet steel reinforced HNBR (designation suffix CS5 or RS5)
    • sheet steel reinforced FKM (designation suffix CS2)

For additional information about the materials → Seal materials.

The seals are fitted in a recess on the outer ring and seal against the inner ring (fig. 5). On larger bearings, the seals are fixed by a retaining ring (fig. 6).

Bearings sealed on both sides are lubricated for the life of the bearing and are virtually maintenance-free (→ Grease life for sealed bearings). They are filled with one of the following greases (table 1):
  • SKF LGEP 2 grease (designation suffix VT143) as standard
  • SKF LGHB 2 grease (designation suffix GEM) or LGWM 2 grease (designation suffix GLE) on request
For additional information about greases → Lubrication.

Grease life for sealed bearings

The grease life for sealed bearings is presented as L10, i.e. the time period at the end of which 90% of the bearings are still reliably lubricated, and depends on the load, operating temperature and speed factor. It can be obtained for bearings with standard SKF LGEP 2 grease (designation suffix VT143) from:

The grease life is valid under the following operating conditions:
  • horizontal shaft
  • inner ring rotation
  • operating temperature within the green temperature zone of the grease (→ table 1)
  • stationary machine
  • low vibration levels
  • load ratio Fa/Fr ≤ e (→ product table)
  • rotational speed below the limiting speed (→ product table) and below the limits listed in table 2

For other operating conditions, the grease life can be estimated by multiplying the relubrication interval for open bearings (→ Relubrication) by a factor of 2,7.

Relubrication of sealed bearings

When the required service life is longer than the grease life, the bearings may require relubrication. A suitable grease quantity to relubricate sealed bearings can be obtained using

Gp = 0,0015 D B

where
Gp
=
grease quantity [g]
D
=
bearing outside diameter [mm]
B
=
bearing width [mm]

The grease should be applied slowly through the lubrication holes in the outer ring, preferably while the bearing is rotating to avoid damaging the seals. SKF recommends relubricating with the same grease as the initial fill.

WARNING

Bearings with designation suffix CS2 have seals made of FKM (fluoro rubber). FKM exposed to an open flame or temperatures above 300 °C (570 °F) is a health and environmental hazard! It remains dangerous even after it has cooled.

Read and follow the safety precautions under this WARNING.

Bearings for vibratory applications
  • are available in the 223 series
  • are available with a cylindrical or tapered bore
  • have C4 radial internal clearance as standard
  • are equipped with an annular groove and three lubrication holes in the outer ring
  • are available with a PTFE coated cylindrical bore (designation suffix VA406), which prevents fretting corrosion between the shaft and the bearing bore, for shaft thermal elongation in non-locating bearing positions that have a rotating outer ring load. Therefore, shafts do not require special heat treatments or coatings.
  • are manufactured to one of the following designs:
    • E/VA405 bearings (fig. 7) have two surface-hardened stamped window-type steel cages, an inner ring without flanges and a guide ring centred on the inner ring or on the cages
    • EJA/VA405 and CCJA/W33VA405 bearings (fig. 8 and fig. 9) have two surface-hardened stamped window-type steel cages, an inner ring without flanges and a guide ring centred on the outer ring raceway

Acceleration
Vibratory applications induce accelerations of the rollers and cages in the bearings. This puts extra demands on the bearing design. SKF spherical roller bearings for vibratory applications can withstand considerably higher accelerations than corresponding standard bearings. The permissible acceleration depends on the lubricant and the mode of acceleration.

  • Mode 1

    The bearing is subjected to a rotating outer ring load in combination with a rotating acceleration field, or an internally induced angular acceleration field due to rapid speed variations. These accelerations cause the unloaded rollers to generate cyclic loads on the cages. Examples: vibrating screens (fig. 10), exciters, planetary gears and general arrangements subjected to rapid starts or rapid speed variations.

  • Mode 2

    The bearing is subjected to impact loads, which generate a linear acceleration in a constant radial direction, causing the unloaded rollers to “hammer” the cage pockets. Example: acceleration generated when rail wheels roll over rail joints (fig. 11).

Road rollers, where the roller is vibrating against a relatively hard surface, are subjected to a combination of mode 1 and 2 acceleration. Values for the permissible acceleration are listed in the product table and are valid for oil lubricated bearings. The values are expressed in multiples of g, where g is the acceleration of gravity (g = 9,81 m/s2).

System solutions for vibrating screens

In addition to single bearings for vibrating screens, SKF has developed fault detection and bearing arrangements that can improve performance, reduce maintenance and monitor machine condition in vibratory equipment.

WARNING

PTFE coatings exposed to an open flame or temperatures above 300 °C (570 °F) are a health and environmental hazard! They remain dangerous even after they have cooled.

Read and follow the safety precautions under this WARNING.

Bearings for wind energy applications
  • are available in the 240 series, from d ≥ 530 mm
  • are designed explicitly for wind turbine main shafts
  • have an optimized internal geometry with large diameter rollers and increased contact angle for increased axial load carrying capacity (fig. 12)
  • have a roller-guided cast iron cage for increased robustness
  • have no guide ring
  • have a wide outer ring lubrication groove and six lubrication holes
  • are indicated in the product table by the designation suffix BC

Customized bearings

SKF can customize bearings to meet the needs of applications where the bearings are subjected to unique operating conditions. For example, bearings for:
  • printing presses, paper mills or high-precision coating systems
  • very arduous operating conditions, e.g.continuous casters
  • bearings for high-speed applications
  • mounting with loose fit on roll necks
  • railway vehicles

Bearings for high-speed applications

  • have 50% higher limiting speeds than standard bearings
  • are available in the 223, 232, 240 and 241 series in a special execution
  • are identified by the designation suffix VA991
  • address a market need in multi-megawatt industrial gearboxes
For additional information about application-specific spherical roller bearings, contact SKF.
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