Cam Followers

Thanks to their thick-walled outer rings, cam followers can absorb high radial loads. With axial guidance provided by the retaining flanges of the stud and the pressed-on end washer, these bearing designs tolerate axial loads. The magnitude of the permissible load is determined by the internal design.

When a cam follower runs on a straight or curved mating track, the contact under radial load causes an elastic (oval) deformation of the outer ring. For this reason, these bearing types have an outer ring with an enlarged cross-section compared to standard bearings, where the forces are transmitted via the outer ring directly into the housing (without significant deformation). This enables the outer ring 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 thus distributed over fewer rolling elements, which in turn affects the dynamic and static load ratings.

The load ratings C_rw and C_{0r w} are decisive for the rating life calculation. For a rating life calculation according to DIN ISO 281, the following applies:

C_{0r w} = C_0r

C_{r w} = C_r

The permissible effective radial loads F_r and 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 values for F_r and F_0r, the following applies:

F_0r = C_{0r w}

F_r = C_{r w}

The dynamic load rating denotes 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 affects the load distribution between the rolling elements and reduces the load calculated according to the ISO standards for bearings. The effective dynamic load rating C_{r w} applies to dynamically loaded rotating bearings. The basic rating life is to be calculated with C_{r w}. The permissible dynamic radial load F_r must not be exceeded. If F_r is not specified, the effective dynamic load rating C_{r w} applies instead. This must likewise not be exceeded by the actual radial load. If the static load rating C_{0r w} is lower than the dynamic load rating C_{r w}, then C_{r w} applies.

The static load rating denotes a static radial load at the centre of the contact area between rolling element and raceway under the highest possible load, with respect to the plastic deformation of the cam follower.

For statically loaded bearings, at standstill or with rarely occurring rotary movements, the effective load rating C_{0r w} applies. The static load safety factor is to be calculated with C_{0r w}.

This is contrasted by the permissible static radial load F_0r, which must not be exceeded. If F_0r is not specified, the effective static load rating C_{0r w} applies instead. The smaller value in each case applies as the permissible maximum 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 or cylindrical roller bearing. The maximum permissible static load limited by these strengths is therefore specified.

In addition to the permissible radial load of the bearing, the permissible radial load of the mating track must also be observed.

Like all rolling bearings, cam followers are also subject to a minimum load. If this is not reached, the rolling elements cannot roll properly. This increases the risk of sliding friction. Sliding breaks through the lubricant film in the contact zone and leads to metal-to-metal contact, which causes both friction and adhesive wear (smearing) to rise sharply. The minimum load is an important parameter, particularly for cam followers, which are often exposed 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 dimension series should be considered.

The maximum amount of grease a bearing can hold is a function of the free space available inside the bearing. This means the volume 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 present due to sealing concepts, two rolling element raceways, etc. Ideally, relubrication should be carried out regularly, even if the initial fill 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 lubricant. It primarily fills the cavity between adjacent rolling elements and the inner or outer raceway. The main cause of premature wear is a lack of lubricant. The larger the grease fill, the longer the product lasts in most common applications. As a protective function, excess grease is carried outwards by centrifugal force and with the help of the sealing lip structure (including the groove geometry).

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

For KIS cam followers, an EP-additivated, fully synthetic high-performance grease (consistency class NLGI 2) is used as standard, which was specially developed for use in applications with high radial loads (including heavily 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.

Thanks to its wide temperature range, high mechanical stability and exceptional load-carrying capacity, it is an excellent choice. The effort required for a reliable grease supply is considerably 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 mating track. However, there are also applications in which the mating track must remain unlubricated. If lubrication is not possible, wear must be expected, particularly under high loads and high alternating speeds. In these cases, please feel free to contact our technical support.

Relubrication intervals can only be determined under operating conditions – at the latest, however, when the first signs of tribocorrosion become visible in the tribological system.

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

Speeds must be reduced or determined more precisely in the case of:

• Loads > 0.05 * C_{0r w}
• Bearing variants with needles as rolling elements
• Difficult lubrication conditions (including mating track)
• High sealing requirements (higher contact friction)
• Tight radial 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, although rolling element guidance has a much stronger influence on the maximum speed. Intermittent operation can also raise this value further.

With a sealed cam follower 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 provide a larger lubricant reservoir than full complement roller (or needle) variants. However, lower load ratings must then be taken into account, as fewer and shorter rolling elements are used due to the cage volume.

Possible methods for the rating life calculation are the basic and modified basic rating life calculation according to DIN ISO 281 and the extended calculation of the modified reference rating life according to DIN ISO 281-4.

The basic rating life is the number of revolutions that 90 % of a sufficiently large group of identical bearings will reach or exceed at constant load and speed before the first signs of material fatigue occur.

These methods are described under load-carrying capacity and rating life. For support rollers and cam followers, the following values are used:

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

The service life is the actual life achieved by a support roller, cam follower or track roller and can deviate significantly from the calculated basic rating life.

Deviations between basic rating life and service life result from wear or fatigue due to:

• Misalignment between track roller and mating track
• Deviating operating data
• Operating clearance too small or too large
• Very high shock loads, static overload
• Contamination of the track roller
• Excessive operating temperature
• Insufficient lubrication
• Oscillating bearing movement with very small swivel angles, causing false brinelling
• Wear between the outer ring outside surface and the mating track
• Vibration loads and false brinelling
• Pre-damage during mounting

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

Great care must be taken when mounting cam followers to ensure trouble-free operation:

• Cam followers must be protected against dust, dirt and moisture. Contamination can lead to increased wear and premature failure
• Do not overcool cam followers. 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, geometric and positional accuracy and cleanliness
• Lightly oil the seating surfaces of the bearing rings or rub them with solid lubricant
• Supply the bearing with lubricant after mounting
• Final functional check of the bearing arrangement

Depending on the application, the following tools are suitable:

• Induction heating devices, observing the manufacturer’s instructions regarding seal and lubricant
• Heating cabinets with heating up to +80 °C
• Mechanical or hydraulic presses: use mounting sleeves that bear against the entire circumference of the bearing ring end faces
• Hammer and mounting sleeves: strike the sleeve centrally

With cam followers with an eccentric collar, the fitter can adjust the radial position of the bearing relative to its support housing. This is particularly useful when several cam follower bearings carry a load and mounting inaccuracies prevent the standard bearings from distributing the load evenly. The eccentric adjustment can also reduce wear of the tracks.

• Do not transmit mounting forces through the rolling elements
• Do not damage the seals
• No blows to the bearing rings

The possibility of dismounting should already be considered when designing the bearing position. For reuse:

• Avoid direct blows to the bearing rings
• Avoid dismounting forces through the rolling elements
• Only clean bearings in the dismounted state
• No hard flame

• Mount cam followers with a mounting press wherever possible, as shown in the figure
• No blows to the thrust collar of the roller stud
• The lubrication hole must not lie in the loaded zone and is marked on the collar side of the roller stud.

• Fit grease nipples before mounting the bearings
• Drive-in grease nipples are supplied with the cam followers. These must be properly pressed in before the bearings are mounted. Only the supplied grease nipples may be used.
• For lubricating the cam followers with the centralised lubrication adapter.
• If lubrication is carried out via the locating bore, the axial lubrication holes in the cam follower must be closed with the grease nipples before mounting.

Cam followers must be axially secured with a hexagon nut. The slot or hexagon at the end of the roller stud allows the bearing to be held with a spanner while tightening the fastening nut and the eccentric collar to be adjusted. In the case of strong vibrations, special serrated lock washers or self-locking nuts according to DIN 985 can also be used.

Axial fastening – important to note:

The tightening torque of the fastening nuts must be strictly observed in order to guarantee the permissible radial load. If it cannot be observed, an interference fit is required. With self-locking nuts, an increased tightening torque and the instructions of the nut manufacturer must be observed.

The highest point of the eccentric collar is marked on the roller stud 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 stud
• on the end face on the thread side, from an outside diameter of 22 mm
• on the shank of the roller stud, from an outside diameter of 30 mm with an additional lubrication groove

Commissioning and relubrication – important to note:

• Cam followers with an eccentric collar cannot be relubricated via the shank, as the eccentric ring covers the lubrication hole.
• For lubrication, only use grease guns with pointed needle nozzles that have an opening angle of 60°.
• Before commissioning, the lubrication holes and supply lines must be filled with grease for corrosion protection reasons; lubrication can be carried out at the same time.
• Lubrication is made more difficult if a rolling element is positioned over the radial lubrication hole. Relubrication should therefore be carried out while the bearing is warm from operation and rotating, as well as before standstill and before longer interruptions in operation.
• The same lubricant as used for initial lubrication must be used for relubrication. If this is not possible, the miscibility and compatibility of the lubricants must be checked. Relubricate until a fresh collar of grease forms at the seal gaps. The old lubricant must be able to escape freely from the bearing.