Cam Followers

Due to their thick-walled outer rings, cam followers can absorb high radial loads. With axial guidance through the retaining flanges of the bolt and the pressed-on end disc, these bearing designs tolerate axial loads. The size of the permissible load is determined by the internal design.

When a cam follower runs on a straight or curved counter raceway, the contact under radial load causes an elastic (oval) deformation of the outer ring. For this reason, these bearing types have an outer ring that has an enlarged cross-section compared to standard bearings, where the forces are transmitted directly into the housing via the outer ring (without significant deformation). As a result, the outer ring is able to absorb increased bending stresses and the associated deformations.

However, the deformation means that a smaller area of the raceway is loaded (reduced contact zone) and the load is therefore distributed over fewer rolling elements, which in turn has an effect on the dynamic and static load ratings.

The load ratings C_rw und C_{0r w} are decisive for the service life calculation. In the context of a service life calculation in accordance with DIN ISO 281, the following applies:

C_{0r w} = C_0r

C_{r w} = C_r

The permissible effective radial loads F_r und F_0r take bending stresses in the outer ring into account. The bending stresses must not exceed the permissible strength values of the material. If the data sheets do not contain any values for F_r und F_0r, the following applies:

F_0r = C_{0r w}

F_r = C_{r w}

The dynamical load rating characterises the radial load at which 90 % of a group of identical cam followers can perform 1 million revolutions without material damage due to fatigue in the rolling contact.

The elastic deformation of the outer ring has an effect on the load distribution between the rolling bearing elements and reduces the load calculated in accordance with the ISO standards for bearings. The effective dynamic load rating C_{r w} applies to dynamically loaded rotating bearings. C_{r w} is used to calculate the basic rating life. The permissible dynamic radial load Fr must not be exceeded. If Fr is not specified, the effective dynamic load rating C_{r w} applies instead. This must also not be exceeded by the existing radial load. If the static load C_{0r w} is lower than the dynamic load rating C_{r w} , then C_{r w} applies.

The static load rating characterises a static radial load in the centre of the contact surface of the rolling element raceway under the highest possible load in relation to the plastic deformation of the cam followers.

The effective load rating C0r w applies to statically loaded bearings at standstill or infrequently occurring rotary movements. The static load safety factor can be calculated using C0r w.

On the other hand, the permissible static radial load F0r must not be exceeded. If F0r is not specified, the effective static load rating C0r w applies instead. The lower value applies as the maximum permissible load. In some applications, the permissible load of cam followers is limited by the bending and shear strength of the stud and the strength of the outer ring and not by the load rating of the needle roller or cylindrical roller bearing. The maximum permissible static load, which is limited by these strengths, is therefore specified.

In addition to the permissible radial load of the bearing, the permissible radial load of the counter raceway must also be taken into account.

Like all rolling bearings, cam followers are subject to a minimum load. If the load falls below this, the rolling elements cannot roll cleanly. This increases the risk of sliding friction. Sliding causes the lubricating film in the contact area to be broken, resulting in metal-to-metal contact, which greatly increases both friction and adhesive wear. The minimum load is an important factor, especially for cam rollers, which are often subjected to rapid start-stop loads or high accelerations. If these requirements cannot be met, DLC coatings, application-specific lubrication concepts or cam followers of a smaller size series should be considered.

The maximum amount of grease that a bearing can accommodate is a function of the free space available inside the bearing. This means that it is the volume that is created between the outer rolling element raceway and the inner rolling element raceway, minus the volume of the rolling elements and the additional space that may be available due to sealing concepts, two rolling element raceways, etc. Ideally, relubrication should be carried out regularly, even if the initial filling still has full lubricating properties.

In cam followers with needles the large number of needles takes up most of the available space, leaving little room for the lubricant. It primarily fills the cavity between neighbouring rolling elements and the inner or outer raceway. The main cause of premature wear is a lack of lubricant. The greater the grease filling, the longer the product will last in most common applications. Excess grease is carried to the outside as a protective function by centrifugal force and with the help of the sealing lip structure (incl. groove geometry).

In cam rollers with cylinders as rolling elements, the cavities between the rollers and the raceways are larger, although there are fewer of them. However, there is additional space for lubricant in the area between the roller pairs and between the rollers and seals. As a result, there is up to four times more grease in cam rollers of the same size than in cam rollers with needles.

For KIS cam followers, an EP-additivated, fully synthetic high-performance grease (consistency class NLGI 2) is used as standard, which has been specially developed for use in applications subject to high radial loads (even in highly oscillating operation). It combines the advantages of a synthetic base oil and a special lithium complex thickener with those of a state-of-the-art additive package.

It is an excellent choice due to its wide temperature range, high mechanical stability and exceptional load-bearing capacity. The effort required for a reliable grease supply is significantly reduced by using this product. The lubricant can be used with grease guns, automatic relubrication systems and centralised lubrication systems.

All lubricants suitable for rolling bearing lubrication can be used to lubricate the counter raceway. However, there are also applications in which the counter raceway must remain unlubricated. If lubrication is not possible, wear must be expected, particularly under high loads and high reciprocal speeds. In these cases, please contact our technical support team.

Relubrication cycles can only be determined under operating conditions. At the latest, however, when the first traces of tribocorrosion can be recognised in the tribological system.

The permissible speeds stated on the data sheets are empirical values. They are not generally exact values and may deviate upwards or downwards depending on the operating conditions and application of the rotary solution under real conditions and may therefore be modified.

The speeds must be reduced or determined more precisely for

• Loads > 0.05 * C_{0r w}
• Bearing variants with needles as rolling elements
• Difficult lubrication conditions (incl. counter raceway)
• High sealing requirements (higher contact friction)
• Tight radial internal clearance tolerances
• Additional axial loads
• Insufficient heat dissipation
• Need for a high-viscosity lubricant

Oil-lubricated cam followers can generally be operated at a 50% higher speed than grease-lubricated solutions, whereby the rolling element guidance has a much greater influence on the maximum speed. Intermittent operation can also further increase this value.

In the case of a sealed cam roller with cylinders, the speed is limited by the maximum permissible surface speed of the seal.

Cage-guided (usually plastic) rolling elements also reduce internal friction and offer a larger lubricant reservoir than full complement (needle roller) variants. However, lower load ratings must now be taken into account, as fewer and shorter rolling elements are used due to the cage volume.

Possible methods for calculating the rating life are the nominal and modified nominal rating life calculation in accordance with DIN ISO 281 and the extended calculation of the modified reference rating life in accordance with DIN ISO 281-4.

The basic rating life is the number of revolutions reached or exceeded by 90 % of a sufficiently large number of identical bearings at constant load and speed before the first signs of material fatigue occur.

These methods are described under load-bearing capacity and service life. For support and

cam rollers, the following values are used:

• for C_r the effective dynamic load rating C_{r w}
• for C_0r the effective basic static load rating C_{0r w}
• for C_ur the effective fatigue limit load C_{ur w}

The service life is the service life actually achieved by a support roller, cam roller or track roller and can deviate significantly from the calculated nominal service life.

Deviations between the nominal service life and the service life are due to wear or fatigue:

• misalignment between the track roller and the mating track
• deviating operating data
• Too small or too high operating clearance
• Very high impact loads, static overload
• Contamination of the track roller
• Operating temperature too high
• Insufficient lubrication
• Oscillating bearing movement with very small swivel angles that cause rippling
• Wear between the outer ring shell surface and the counter raceway
• Vibration stress and ripple formation
• Preliminary damage during assembly

Due to the variety of installation and operating conditions, the service life cannot be calculated exactly in advance and can be estimated most reliably by comparison with similar installation cases.

Great care must be taken when installing cam rollers to ensure trouble-free running:

• Cam followers must be protected from dust, dirt and moisture. Contamination can lead to increased wear and premature failure
• Do not overcool cam rollers. Condensation may lead to corrosion in the bearings and bearing seats
• Keep the assembly area dust-free and clean
• Check the axle seat for dimensional, shape and positional accuracy and cleanliness
• Lightly oil the seating surfaces of the bearing rings or rub in solid lubricant
• Apply lubricant to the bearings after installation
• Final functional check of the bearing

Depending on the application, the following tools are suitable:

• Induction heating devices in compliance with the manufacturer's instructions regarding seal and lubricant
• Heating cabinets with heating up to +80 °C
• Mechanical or hydraulic presses: Use mounting sleeves that are in contact with the entire circumference of the bearing ring end faces
• Hammers and mounting sleeves: Apply blows centred on the sleeve

Cam followers with eccentrics allow the fitter to adjust the radial position of the bearing relative to its carrier housing. This is particularly useful when several cam roller bearings are carrying a load and inaccuracies during assembly prevent the standard bearings from distributing the load evenly. Eccentric adjustment can also reduce wear on raceways.

• Do not transfer installation forces via the rolling elements
• Do not damage seals
• No impacts on the bearing rings

The removal option should already be taken into account when designing the bearing position. For reuse:

• Avoid direct impacts on the bearing rings
• Avoid dismounting forces via the rolling elements
• Only clean bearings when they have been removed
• No hard flame

• If possible, fit the cam followers using an assembly press as shown in the illustration
• Do not hit the thrust collar of the roller stud
• The lubrication hole must not be located in the loaded zone and is labeled on the collar side of the roller stud.

• Fit the grease nipple before fitting the bearings
• Drive-in grease nipples are supplied with the cam followers. These must be pressed in correctly before fitting the bearings. Only the enclosed grease nipples may be used.
• For lubricating the cam rollers with the central lubrication adapter.
• If lubrication is applied via the locating bore, the axial lubrication holes in the cam roller must be sealed with the grease nipples before installation.

The highest point of the eccentric is marked on the roller journal side, where the radial lubrication hole is also located.

• Cam followers each have a lubrication hole for relubrication:
• on the collar side of the roller journal
• on the end face on the thread side, from an outside diameter of 22 mm
• on the shaft of the roller stud, from outer diameter 30 mm with additional lubrication groove

Commissioning and relubrication, important to note:

• Cam followers with an eccentric cannot be relubricated via the shaft, as the eccentric ring covers the lubrication hole.
• For lubrication, only use grease guns with needle point nozzles that have an opening angle of 60°.
• Before commissioning the lubrication holes and supply lines, they must be filled with grease to prevent corrosion, and lubrication can be carried out at the same time.
• Lubrication is made more difficult if a rolling element is positioned above the radial lubrication hole. For this reason, relubrication must be carried out when the bearing is at operating temperature and rotating, as well as before standstill and before longer interruptions in operation.
• The same lubricant must be used for relubrication as for the initial lubrication. If this is not possible, the miscibility and compatibility of the lubricants must be checked. Relubrication is carried out until a fresh grease collar forms at the sealing gaps. The old lubricant must be able to escape from the bearing unhindered.