Selection Factors for Right Cam-Follower Bearing

To select the right cam follower bearing for a cam or track system, consider the size and type of load, speed, deflection, misalignment, and lubrication.

Loads, speeds and life requirements.

The magnitude and direction of the load will best affect the type and size of the bearing. For stud cam follower bearings, the strength and deflection limits determine the allowable load. To calculate bearing life, especially with varying loads, refer to the manufacturer's documentation or to the website.

Combined radial and axial load applications may require ball or taper roller bearings. Beware of shocks which can damage the inside and outside of the bearing components. Depending on the magnitude of the load, bends (also known as permanent deformation of raceways and raceways) can cause vibration and a higher shock load can cause bearings to fail.

Speed ​​limits are an important factor in determining the best ride. Full needle rollers usually have the lowest speed limit. Higher speeds are possible with cage needle bearings and sometimes with cylindrical or tapered roller bearings. Ball bearings withstand the highest speeds due to low internal friction. Check with the manufacturer for application specific speed limits.

Visit also: Needle Bearings Cam Follower Series

Misalignments and deflections.

Ring rollers reduce the stress caused by angular misalignment between cam followers and cams, but require approximately 20% more track capacity to accommodate the smaller contact area and higher contact stresses that result.

Cantilever bolts sag under load.

Factors affecting the amount of deflection include the corner radius in the upright body, the fit between the upright body and the upright (see illustration below), and the body material. To reduce this deformation, consider using a heavy block mounted on a pin or fork. For applications with subsequent deformations and axial loads that exceed the capacity of the needle bearing, use cylindrical rollers, ball bearings or taper roller bearings to support the axial load.

Lubrication.

Oil is the preferred lubricant for high speed cams because it cools bearings more efficiently and does not break down as quickly as grease. Oil is usually sprayed onto the bearings. Suitable for low speed cams and tracks. Most stud type cam followers are pre-filled with grease. For cam followers with studs, lubrication can be applied through axial and radial lubrication holes in the stud. For yoke bearings, apply grease through the mounting pin.

The oil or oil contained in the grease must have a viscosity of 20 cSt at the operating temperature of the bearing. Speed ​​is the primary factor in operating temperature, but load affects it as well. To estimate the operating temperature, compare the actual speeds and loads with the manufacturer's speed and dynamic loads. Temperature limits for general purpose greases are typically 225 to 250 ° F. For continuous operation, it is generally best to keep the temperature at least 50 ° F lower.

Lubrication intervals depend on the application. Bearings subject to heavy contamination, such as flushing, may require daily lubrication. However, in a clean environment, bearings can last a year or more before being relubricated. Some cam followers cannot be relubricated but have better seals and large grease reservoirs.

Selecting cam or track hardness.

Choosing the right hardness for the cam or track surface can be just as important as choosing the right bearing. An insufficiently strong cam or track will plastically wear or deform under load.

When dimensional accuracy is not critical, use flexible materials to reduce costs. For example, strain hardening of mild steel with little bearing wear at the rail surface is acceptable in some applications. For more delicate applications, use hardened tracks and cam surfaces (up to 60 HRC) to minimize wear.

The load capacity of a steel pallet, defined as the load it can withstand without plastic deformation on its surface, depends on the carrying size, strength and hardness of the pallet. Pallet lift ratings for specific cam followers are available from bearing manufacturers.

Maintenance of cam and track surfaces with lubrication is often difficult; however, coating these surfaces with oil or grease prevents excessive wear.

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