What Is a Bearing? Types, Selection, Mounting and Failure Analysis

A bearing (rolling bearing) is a machine element that supports a rotating shaft and makes rotation possible with very low friction thanks to rolling elements (balls or rollers) running between inner and outer rings. Bearings play a critical role in almost all mining equipment, including crushers, vibrating screens, conveyors, feeders, screw washers, pumps and electric motors. An unexpected bearing failure can stop an entire plant because of a relatively inexpensive part.

In this guide we take a comprehensive look at what a bearing is, bearing types, bearing selection for mining equipment, bearing housings and sealing solutions, correct mounting and lubrication methods, failure modes and spare bearing planning.

What Is a Bearing and How Does It Work?

A bearing basically consists of four parts:

• Inner ring: Fitted on the shaft and usually rotates with it.
• Outer ring: Sits in the bearing housing.
• Rolling elements: Balls or rollers (cylindrical, tapered, spherical/barrel, needle).
• Cage: Keeps the rolling elements evenly spaced.

In plain bearings (bushings) the shaft slides on an oil film, whereas in rolling bearings the load is carried by the rolling elements. This reduces friction and heat, lowers starting resistance and makes maintenance more predictable. However, under very high shock loads and in some large crushers (e.g. the cone crusher eccentric) bronze-bushed plain bearings are preferred. See our cone crusher eccentric bushing guide on this subject.

Bearing Types

The most common bearing type on crushing and screening equipment is the spherical roller bearing, which can carry heavy, shock loads and tolerate shaft deflection.

Special Bearings for Vibrating Screens

On vibrating screens, bearings run at high speed under loads that constantly change in direction and magnitude. Special spherical roller bearings developed for screen applications are therefore used, with greater internal clearance (usually C3 or C4 radial clearance class) and reinforced cages. Fitting a standard bearing to a screen’s eccentric shaft is one of the most common causes of premature failure. For the screen eccentric mechanism and bearing replacement see our vibrating screen guide.

Radial Internal Clearance (C2, CN, C3, C4)

Radial internal clearance is the total play between the bearing rings before mounting. An interference fit and heating during operation reduce this clearance. Bearings with greater clearance such as C3 or C4 are selected for high-temperature, tight-fit and vibrating applications. The wrong clearance class causes the bearing to “preload itself” in operation, overheat quickly and fail.

Bearing Housings and Sealing

A bearing housing carries the outer ring of the bearing, connects it to the equipment and protects it from the environment. The types most used in mining are split plummer block housings (such as SNL/SD types), flanged housings and housings machined specifically for the equipment.

• Split housings: The top cap can be removed to reach the bearing; common for conveyor pulleys and large shafts.
• Locating and non-locating arrangement: On a shaft, one bearing is fixed axially and the other is left free to allow for thermal expansion. This arrangement is achieved with locating rings. The wrong arrangement creates excessive axial load on the bearings.
• Sealing: In dusty and wet environments, labyrinth seals, double-lip seals, V-rings and grease-purged multi-stage (taconite-type) seals are used. A large share of bearing failures is caused by dust and water entering through inadequate seals.

For impact crusher main shaft bearings and sealing see our impact crusher main shaft and rotor bearings guide, and for jaw crusher bearings our eccentric shaft and bearings guide.

Bearing Selection for Mining Equipment

Correct Mounting

A significant proportion of bearing failures is caused not by the bearing itself but by incorrect mounting.

1. Cleanliness: The work area, shaft, housing and tools must be clean. A new bearing should be taken out of its packaging just before mounting.
2. Measurement: Shaft and housing diameters, ovality and surface condition should be measured. A worn shaft will make a new bearing fail quickly too.
3. Heat mounting: Interference-fit bearings should be heated in a controlled way with an induction heater before fitting on the shaft. Never strike a bearing directly with a hammer; impact creates dents (brinelling) in the raceways. Heating with an open flame also damages the bearing material.
4. Tapered-bore bearings: On bearings mounted on an adapter sleeve or tapered shaft, radial clearance reduces as the bearing is driven up the taper. The correct tightness is achieved by measuring the reduction in radial clearance with feeler gauges or by checking the axial drive-up distance.
5. Alignment: Check housing alignment and coupling alignment. Misalignment creates extra load and vibration in the bearings.
6. Lubrication: The initial grease fill should follow the manufacturer’s recommendation; the housing must not be overfilled.

Lubrication: Grease or Oil?

• Grease lubrication: Used on most crushers, conveyors and some screens. Grease quantity and interval depend on bearing size, speed and temperature. Too much grease makes the bearing overheat; too little causes metal-to-metal contact and wear.
• Oil lubrication: Preferred for high-speed and high-temperature applications (some screens, VSI cartridges, gearboxes). Oil level, cleanliness and change interval are critical.
• Centralised lubrication systems: Reduce human error across many lubrication points and deliver regular small quantities.

Mixing different types of grease can cause compatibility problems; if the grease type is changed, the old grease should be cleaned out.

Bearing Failure Modes and Causes

Condition Monitoring

Bearing failures usually develop with warning signs weeks in advance rather than suddenly. These signs can be monitored by:

• Temperature: Regular measurement with non-contact thermometers or fixed sensors.
• Vibration analysis: Bearing damage produces characteristic frequencies in the vibration spectrum.
• Ultrasonic listening: Used to detect lack of lubrication and early damage.
• Grease and oil analysis: Tracking metal particles and contamination.

For applying these methods across a plant, see our predictive maintenance guide.

Counterfeit Bearing Risk and Reliable Supply

Counterfeit bearings imitating well-known brands are found on the market. Although they look like the originals, they can fail very quickly because of low-quality steel, faulty heat treatment and poor precision. Using counterfeit bearings is a serious damage risk, especially on heavily loaded equipment such as crushers and screens. Buy bearings from reliable suppliers, check the packaging and markings, and use the manufacturer’s verification channels when in doubt.

Spare Bearing Planning

• Draw up a list of all bearings in the plant (equipment, position, bearing number, housing type, sealing).
• Keep bearings for critical equipment (primary crusher, main conveyor, screens) in stock.
• Stock variety can be reduced by standardising bearing numbers.
• Store bearings flat, in their original packaging, in a dry, clean and vibration-free place.
• Keep adapter sleeves, nuts, lock washers, seals and locating rings in stock together with the bearings.

Field Example

Suppose that at a plant the eccentric bearings of a vibrating screen fail every few months. Inspection after removal shows that the bearings are standard general-purpose C3 bearings and bear signs of overheating. It also emerges that the housing was being packed full of grease during greasing. When screen-specific bearings are used and the grease quantity is reduced to the manufacturer’s value, bearing life increases markedly.

Frequently Asked Questions

What does a bearing do?

It supports the rotating shaft, reduces friction and transfers the load to the housing, so the machine runs with less energy, less heat and a longer life.

What types of bearing are there?

The main types are deep groove ball, self-aligning ball, cylindrical roller, tapered roller, spherical roller, needle and thrust bearings.

Is a bearing housing the same as a bearing?

No. The bearing housing is the part that carries and protects the bearing; the bearing is the machine element with rolling elements inside it.

How can bearing life be extended?

Through correct bearing selection, clean and correct mounting, suitable lubrication, good sealing and regular condition monitoring.

Is bearing heating normal?

A brief temperature rise can be seen on first running and after fresh greasing; the temperature should then stabilise. A continuous rise is not normal.

How to Read Bearing Numbers

Bearing numbers show the bearing type, dimension series and bore diameter. In a common designation, for example, the first digits indicate the bearing type and series, and the last two digits (within a certain range) give one fifth of the bore diameter. Prefixes and suffixes indicate the internal clearance class (C3, C4), cage type, sealing, tapered bore (K) and special application features. Tapered-bore bearings, for instance, carry the suffix “K”, while bearings specific to vibrating screen applications are marked with special suffixes that vary by manufacturer.

When replacing a bearing, pay attention not only to the basic number but also to the suffixes. A bearing with the same basic number but a different internal clearance or cage type can cause early failure, especially in screen and crusher applications.

Spare Bearing and Housing List by Equipment

Step-by-Step Bearing Replacement

1. Stop, lock out and tag the equipment; disconnect belts and couplings.
2. Remove the old bearing with a suitable puller or hydraulic nut. Keep the bearing for later inspection.
3. Clean the shaft and housing; measure diameters, ovality and surface damage.
4. Check the number, suffixes and clearance class of the new bearing.
5. Fit the bearing after heating it with an induction heater within the manufacturer’s temperature limits, or, for tapered-bore bearings, tighten it while measuring the reduction in radial clearance.
6. Fit the locating rings to suit the locating/non-locating arrangement.
7. Fill the housing with the correct amount of grease and fit the seals.
8. Check alignment and set belt tension.
9. Start up and monitor temperature and vibration in the first hours.

Bearing replacement on screen eccentric mechanisms, conveyor pulleys and crushers requires expertise on site. Our service, maintenance and repair team can help.

Glossary

• Radial internal clearance: The radial play between the bearing rings (C2, CN, C3, C4).
• Adapter sleeve: A tapered sleeve that secures a tapered-bore bearing to a cylindrical shaft.
• Brinelling: Indentations in the raceway caused by impact or static overload.
• Labyrinth seal: A non-contact seal that blocks dust by forming a tortuous path.
• Taconite seal: A grease-purged multi-stage sealing arrangement for very dusty environments.
• L10 life: The calculated life that 90% of bearings running under the same conditions are expected to reach.

CSP Mühendislik Support

CSP Mühendislik supplies bearings and bearing housings for your crushers, screens, conveyors and feeders and provides mounting and service, maintenance and repair. You can find the parts you need on our spare parts, vibrating screen spare parts and belt conveyor spare parts pages.