Selection guidelines for different capping devices under various operating conditions. However, these guidelines cannot substitute for testing a shield or seal in its application. For additional information, refer to Integral sealing.

The seals, which are fitted in a recess on the outer ring, make good, positive contact with the recess, without deforming the outer ring. The capping devices are available as:

Shields

• are identified by the designation suffixes Z or ZS
• are primarily intended for applications where the inner ring rotates
• are fitted in the outer ring and form a narrow gap with the inner ring
• are made of stainless steel
• are supplied in different designs:
  • with designation suffix Z: either with (a) or without (b) an extension in the shield bore or the shield bore can extend into a recess in the inner ring (c)
  • fixed in the outer ring by a retaining ring and may extend into a recess (designation suffix ZS.
  • available on request: shields made of PTFE

Non-contact seals

• are identified by the designation suffix RZ
• provide better sealing effectiveness than shields
• can be operated at the same speeds as shields
• form an extremely narrow gap with the inner ring shoulder
• are made of sheet steel reinforced NBR (oil and wear-resistant)

Contact seals

• are identified by the designation suffixes RS1, RS1/VP311 or RS2
  • RS1 seals are made of sheet steel reinforced NBR and seal against the inner ring shoulder or against a recess in the inner ring side face.
  • Bearings with designation suffix VP311 are equipped with seals made of blue food-compatible NBR.
    The material is FDA and EC approved. FDA approval is based on compliance with CFR 21 section 177.2600 ‘Rubber articles intended for repeated use’ for use in contact with aqueous and fatty foods. EC approval is based on compliance with the overall migration requirements of the German BfR recommendation XXI for category 3 materials.
  • RS2 seals are similar to RS1 seals, but are made of sheet steel reinforced FKM.

Bearings capped on both sides are lubricated for the life of the bearing and are virtually maintenance-free. They are filled with one of the following greases:

• wide temperature range and low-noise grease LHT23 as standard
• GFJ food-grade grease, registered by NSF as category H1 (designation suffix VP311)
  The NSF registration confirms the grease fulfils the requirements listed in the US Food and Drug Administration’s guidelines under 21 CFR section 178.3570 (lubricant acceptable with incidental food contact for use in and around food processing areas).
• available on request: special non-toxic grease, registered by NSF as category H1 (designation suffix VT378)

The technical specifications of the various greases are listed in

Grease life for capped bearings

• is presented as L₁₀, i.e. the time period at the end of which 90% of the bearings are still reliably lubricated
• depends on:
  • the operating temperature
  • the nd_m value
  • grease performance factor (GPF)

The indicated grease life is valid for this combination of operating conditions:

• horizontal shaft
• inner ring rotation
• light load (P ≤ 0,05 C)
• operating temperature within the green temperature zone of the grease
• stationary machine
• low vibration levels

Where the operating conditions differ as described below, the grease life obtained from the diagram should be adjusted:

• vertical shafts → 50% of the obtained value
• heavier loads (P > 0,05 C) → apply reduction factor

When capped bearings must operate under certain extreme conditions, such as very high speeds or high temperatures, grease may appear on the capping diameter. For bearing arrangements where this would be detrimental, appropriate actions could be taken. For additional information, contact the SKF application engineering service.

• Certain sizes of SKF stainless steel deep groove ball bearings are also available with a flange on the outer ring (designation suffix R,. They:
  • can be supplied open or capped
  • are relatively easy to locate axially in the housing
  • enable easier and more cost-effective housing bore manufacture, no shoulders required

Depending on their design, series and size, SKF stainless steel deep groove ball bearings are fitted with one of the cages shown in table 4. The standard stamped stainless steel cage is not identified in the bearing designation. If non-standard cages are required, check availability prior to ordering.

When used at high temperatures, some lubricants can have a detrimental effect on polyamide cages.