Technical FAQ

Basic principles for roller bearings

There is a total of six different basic types of roller bearings:

• ball bearings,
• cylinder roller bearings,
• needle bearings,
• tapered roller bearings,
• spherical roller bearings and
• toroidal roller bearings.

In this case, ball bearings are the most frequently used type of roller bearings.
Roller bearings are bearings in which rolling bodies - the rolling elements - reduce the frictional resistance between an outer ring and an inner ring. Roller bearings are used to fix shafts and axles and enable their rotation, for example the rotation of a wheel fixed to an axle. In such cases, rolling friction is the main occurrence between the three main components of outer ring, rolling elements and inner ring. The rolling friction in the bearing is fairly low since the rolling elements roll along hardened steel surfaces, which are provided with optimised lubrication, between the inner and outer rings.

Ball bearings or roller bearings are mostly manufactured in chromed steel which is hard, but also slightly susceptible to rust. When handling the bearings we recommend that you do not touch them without gloves in order to avoid forming possible rust locations at a later date.

Some bearings are also manufactured in stainless steel (VA/non-rusting). In most cases these bearings have loading limits due to the material used (mostly 1,4034).

The lifespan depends on numerous factors and ranges from between just a few hundred hours in the example of household devices, up to around 100,000 hours for running bearings in seagoing vessels.

Roller bearing models

As a basic principle we can differentiate between the loading direction of radio and axial bearings - also known as thrust bearings. The difference between these two bearing types is the contact angle. In a radial bearing the contact angle is between 0 and 45°, in an axial bearing it is between 45 and 90°.

In the case of radial bearings we can differentiate between

- deep groove ball bearings (single and double row),
- magneto ball bearings,
- angular ball bearings (singular and double row),
- four-point bearings,
- self-aligning ball bearings,
- cylinder roller bearings,
- tapered roller bearings,
- spherical roller bearings,
- self-aligning roller bearings,
- needle bearings,
- toroidal roller bearings and
- ball roller bearings

.

Axial bearings differentiate between

- axial deep groove ball bearings,
- axial cylinder roller bearings and
- axial self-aligning roller bearings

.
 

How do I choose the right bearing?

When selecting the right bearing there is a whole range of influencing magnitudes such as:

• radial force,
• axial force,
• rotational speed and speed,
• loading direction,
• deflection and tilting of the axle or shaft,
• the static and dynamic load factor,
• surrounding values such as temperature, dust load or vibrations in addition to
• installation conditions such as the stiffness of a machine housing in the area around the ball bearing location.

In practice, most searches are made for the three main dimensions:

• internal diameter
• external diameter
• width

In the case of roller bearings there is a wide range of different dimensions in accordance with DIN.
For this reason such bearings are mainly selected from online catalogues or books of tables.

Here you have the facility to search for dimensions.

Where can I find dimensions and technical information?

You can find all the technical information, drawings and dimensions in the manufacturer's bearing catalogues.
You can also find some basic information directly here at ekugellager.de.

Which bearing should I use at high operating temperatures?

Standard bearings can only be continuously operated up to a maximum operating temperature. Normally,
120°C is the maximum operating temperature, with brief peaks of up to 150°C.

In addition to the material for the inner and outer rings, and the rolling elements, you should also take the temperature limit into account for cage bearings and occasionally
seals. The permissible temperature range of the planned lubricant
must also be considered.

There are special bearings for high-temperature applications. These are
labelled with manufacturer-specific suffix letters. Here is a brief overview:

Kiln truck bearings SKF: VA201, for standard bearings –40 to +250°C, sheet steel cages filled with
polyalkylene glycol-graphite mixture Very strongly increased bearing air.
SKF: VA208, for high loadings of –150 to +350°C, graphics segment cage which ensures dry lubrication through graphite dust.
Very strongly increased bearing air.

Bearings with high-temperature or low-temperature grease ex-works: The works location is optimised for specific temperature ranges. The grease provides its full lubricating performance within this range.
SKF: GJN, grease for -30 to +150°C
SKF: LHT - grease for -40 to +140°C and further greases for medium and low ranges. Please also refer to the overviews in theSKF grease traffic light in the SKF catalogue.

Continuously increased temperatures restrict the service life of the bearing. We recommend you carry out an individual service life calculation in cooperation with the manufacturer.

2RS, 2RS1, 2RSH - How are these bearings different?

Bearings with suffix 2RS are sealed on both sides with plastic. The additional suffix letter into the 2RS,
in other words 1, 2, H, R, etc. is manufacturer-specific.

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

Which bearing seal is better - 2RS plastic seal or 2Z cover disc?

Which seal is more suitable depends on the application. The catalogue on the manufacturer website can inform you about the maximum permissible speeds and further
details.

2RS seals

• Threshold seals: bearings with these seals have a start-up torque and are not as freely-moving as other bearings.
• Splash water protection: bearings with splash water protection can also be used in damp environments. Please note that these do not protect against rust, and are also not suitable for permanent use underwater.
• Lower background noise: this type of seals minimise operating noises.
• Maintenance-free: these bearings are lifetime-greased and require no external lubrication.

2Z cover disks

• Gap seals: these bearings are the most easily-running of all bearings. The bearing grease remains in the gap and therefore acts as a seal.
• Susceptible to moisture: these bearings may not be used in damp environments.
• Lower background noise: the cover disks minimise operating noises.
• Maintenance-free: these bearings are lifetime-greased and require no external lubrication.

Open bearing / with 2Z cover disc / with 2RS plastic coating

What does "increased bearing air" mean (suffix C3)?

Bearing air is the way in which the inner ring is
moved from a limiting location to the opposite location paired with the outer ring, either radially or axially.

Standard bearings are also available in

• normal radial bearing air. The official suffix is "CN", but this is often not stated in the bearing description
  suffix. A 6205 deep groove ball bearing has normal bearing air CN.
• in "C3", the "air group" for slightly increased radial bearing air.
• "C4" designates even more increased radial bearing air.
• "C2" stands for reduced bearing air.

You can find bearing air tables in the roller bearing catalogues from various manufacturers.

Bearings with higher precision (suffixes P5, P6, etc.) also have
lower tolerances with the "radial bearing air" properties. You can also find these tables in manufacturers’ catalogues.