Technical FAQ

Basic information on rolling bearings

We differentiate between six different types of rolling bearings:

  • ball bearings;
  • cylindrical roller bearings;
  • needle bearings;
  • tapered roller bearings;
  • barrel roller bearings;
  • and toroidal roller bearings.

Ball bearings are the most commonly used rolling bearings.
Rolling bearings are bearings in which rolling elements between an outer ring and an inner ring reduce frictional resistance. Rolling bearings are used to fix shafts and axles and allow them to rotate, for instance the rotation of a wheel attached to an axle. This results in rolling friction mainly between the three main components: the outer ring, the rolling elements and the inner ring. The rolling friction in bearings is quite low, as the rolling elements between the inner and outer ring roll on hardened steel surfaces that have been lubricated to optimise performance.

Ball bearings and rolling bearings are usually made of chromium steel, which, although hard, is subject to slight rusting. When working with bearings, we recommend that you do not touch them without wearing gloves in order to prevent any rust from forming.

Some bearings are also made from stainless steel (VA/Niro). These bearings usually have lower load limits due to the material used here (usually 1.4034). 

The lifespan depends on many factors and ranges from a few hundred hours, for example in household appliances, to around 100,000 hours in bearings used in deep-sea vessels. 


Types of rolling bearings.

In principle, it is possible to differentiate between radial and axial bearings – also called thrust bearings – depending on the loading direction.  The relevant contact angle is used to distinguish between the two types of bearings. In radial bearings the contact angle is between 0 and 45 degrees; for thrust bearings it is between 45 and 90 degrees.

Radial bearings can be separated into

- deep-groove ball bearings (single and double-row),
- magneto bearings,
- radial thrust ball bearings (single and double-row),
- four-point bearings,
- self-aligning ball bearings,
- cylindrical roller bearings,
- tapered roller bearings,
- barrel roller bearings,
- spherical roller bearings,
- needle bearings,
- toroidal roller bearings and
- ball roller bearings

.

Axial bearings can be separated into

- thrust ball bearings,
- cylindrical roller thrust bearings and
- spherical roller thrust bearings

.
 

How do I select the right bearing?

There are a number of factors involved in choosing the right rolling bearings, such as:

  • radial force;
  • axial force;
  • speed of rotation and speed;
  • loading direction;
  • deflection and misalignment of the axle or shaft;
  • the static and dynamic load rating;
  • environmental factors such as temperature, exposure to dust or vibrations;
  • and installation conditions, such as the stiffness of the machine housing in the area of the ball bearing. 

In practice , you generally base your search on three main dimensions:

  • Inner diameter
  • Outer diameter
  • Width

There are a wide range of rolling bearings of various dimensions in accordance with DIN (German Institute for Standardisation).
These are thus mainly selected from online catalogues or books of tables.

We allow you to search according to size.


Where can I find dimensions and technical information?

You can find all the technical details, drawings and dimensions in the bearing manufacturer’s catalogues.
You can find some basic information on ekugellager.de.

Which bearings should I use at high operating temperatures?

Standard bearings can only be used continuously up to a maximum operating temperature. As a rule, 120 °C is the maximum operating temperature, with short periods up to 150 °C.

In addition to the material for inner rings, outer rings and rolling elements, you also need to take into consideration the temperature limit for bearing cages and any seals.
You must also take into consideration the desired lubricant’s permissible temperature range.

There are special bearings for use in high temperatures. These are marked with manufacturer-specific suffixes.
Here is a brief overview:

SKF oven bearings : VA201, for conventional bearings −40 to +250 °C, sheet steel cage, lubricated with a polyalkylene glycol/graphite mixture.
Very high clearance.
SKF: VA208, for high demands from –150 to +350 °C, graphite segmented cage; graphite dust provides dry lubrication.
Very high clearance.

Bearings that come with a high or low-temperature grease as default: the factory lubrication is optimised for a particular temperature range.  The grease can provide its optimal lubricity in this range.
SKF: GJN, grease for –30 to +150 °C
SKF: LHT - grease for –40 to +140 °C and other greases for medium and low ranges.  You can also use the  SKF grease traffic light system  in the SKF catalogue as an overview.

Permanently high temperatures limit the lifespan of the bearings. We recommend requesting an individual bearing lifespan calculation from the manufacturer. 


2RS, 2RS1, 2RSH - what is the difference between these seals?

Bearings with the suffix 2RS are sealed with plastic on both sides. Additional characters after the 2RS,
i.e. 1, 2, H, R, etc.  are specific to the manufacturer.

2RS2 and 2RSH-bearings, however, have an improved double lip seal.


Which bearing seal is better – the 2RS plastic seal or the 2Z sealing shield?

Which seal is suitable depends on the intended use. For information on the maximum permissible speeds and other details, please refer to the catalogue on the relevant manufacturer’s website.

2RS seals

  • Contact seals: Bearings with these have a starting torque and do not move as freely as other bearings.
  • Splash protection: Bearings with splash protection can also be used in wet conditions. Please note that they do not offer protection from rust and are not suitable for continuous use under water.
  • Lower background noise: The seals minimise operating noise.
  • Maintenance-free: The bearings have been greased for the entire lifespan and do not require external lubrication.

2Z sealing shield

  • Gap seals: These bearings are some of the smoothest-running bearings. The bearing grease is situated in the gap and acts as a seal.
  • Susceptible to moisture: The bearings must not be used in wet environments.
  • Low background noise: The sealing shields minimise operating noise.
  • Maintenance-free: The bearings have been greased for the entire lifespan and do not require external lubrication.

Open bearings/with 2Z sealing shields/with 2RS plastic seals


What does increased clearance (suffix C3) mean?

The clearance is the path around which the inner ring moves relative to the outer ring, either radially or axially, from one end position to the other.

Common standard bearings are available in normal radial clearance.

  • The official suffix is “CN”, though this is usually not included in the bearing description suffix.
    A 6205 deep-groove ball bearing therefore has normal CN clearance.
  • The “C3” clearance group has a greater radial clearance.
  • "C4" means an even greater radial clearance.
  • "C2" signifies a lower clearance.

You can find tables showing the clearances in the various manufacturers’ rolling bearings catalogues.

Bearings with greater precision (suffixes P5, P6, etc.) also have lower tolerances for radial clearance.
You can find the relevant tables again in the manufacturers’ catalogues.