Bearings are mechanical elements used to support rotating or oscillating shafts. They reduce friction, absorb loads, and allow for more precise shaft rotation. There are many types of bearings, each with specific applications and design features.

The four common types of bearings are mainly based on different classification criteria, the following are two common ways of classification and the corresponding four types:

I. Classification according to the shape of rolling bodies

Ball bearings

The rolling body is spherical, suitable for bearing radial and smaller axial loads, with high limiting speed and precision.

Common types include deep groove ball bearings, angular contact ball bearings and so on.

Roller bearings

Rolling body is roller-shaped, suitable for bearing large radial and axial load, strong load carrying capacity.

Common types include cylindrical roller bearings, tapered roller bearings, spherical roller bearings and needle roller bearings.

Second, according to the force way classification

Radial bearing

Mainly bear radial load, that is, perpendicular to the axis of the load.

Common types include deep groove ball bearings, cylindrical roller bearings and so on.

Axial bearing

Mainly bear axial load, that is, parallel to the axis of the load.

Common types include thrust ball bearings, thrust roller bearings and so on.

In addition, bearings can also be classified according to other criteria, such as whether they can be centred into spherical and non-spherical bearings, and the number of columns of rolling elements into single row bearings, double row bearings and multi-row bearings.

The following are four common types of bearings:

1. Ball Bearings

   - Characteristics: Ball bearings use round balls as rolling elements that can roll between the inner and outer rings to reduce friction.

   - Applications: Suitable for applications that carry light to moderate loads and require high speed rotation, such as electric motors, wheels, precision instruments, etc.

2. Roller Bearings 

   - Characteristics: Roller bearings use cylindrical rolling elements, and they can withstand greater loads than ball bearings.

   - Application: They are suitable for applications with heavy loads, such as industrial machinery, gearboxes, bearing housings and so on.

3. Plain Bearings

   - Characteristics: Plain bearings do not have rolling elements, but rely on lubricants to form an oil film on the bearing surface to reduce friction.

   - Application: Suitable for low speed, heavy load or intermittent motion applications, such as propeller shafts in ships, crankshaft bearings in internal combustion engines, etc.

4. Spherical Bearings

   - Characteristics: Spherical bearings allow the shaft to be angularly adjusted within them to compensate for shaft misalignment.

   - Application: Suitable for applications where shaft misalignment needs to be accommodated, such as steering knuckles, mechanical arm joints, etc.

In addition to these four basic types, there are other special types of bearings such as:

- Thrust Bearings : used to withstand axial loads.

- Combined Bearings: Combine the characteristics of different types of bearings for complex applications.

- Magnetic Bearings: use magnetic forces to levitate the shaft with little or no friction.

Each bearing type has its own specific design, materials and application, and choosing the right type of bearing is critical to ensuring the performance and longevity of your machinery and equipment.

How to choose the right type of bearing

Selecting the right type of bearing is a comprehensive decision-making process that requires consideration of several factors. Below are some key steps and considerations to help you select the right type of bearing:

1. Load Characteristics:

   - Size: Determine the magnitude of the load that the bearing will be required to carry (radial, axial or both).

   - Direction: whether the load is unidirectional or multidirectional.

   - Nature: whether the load is static, dynamic or shock.

2. operating speed:

   - The speed at which the bearing will operate. High speed rotation may require the use of ball bearings, while low speed applications may be suitable for plain bearings.

3. accuracy requirements:

   - Determine if the application requires a high precision bearing, such as in precision instruments or machining.

4. environmental conditions:

   - Consider the environment in which the bearing will operate, including temperature, humidity, corrosive substances, cleanliness, etc.

5. Mounting space and design constraints:

   - The size and design of the bearing must accommodate the existing mechanical design.

6. Maintenance and lubrication:

   - Consider whether regular maintenance and lubrication is required. For example, plain bearings usually require more frequent lubrication.

7. cost:

   - Consider the initial cost of the bearing and the long-term maintenance costs.

The following are specific steps for selecting a bearing type. 

1. Determine the load:

   - For radial loads, roller or ball bearings may be required.

   - If the load is axial, thrust bearings are a better choice.

   - If the load is complex, spherical or combination bearings may be required. 

2. Consider speed:

   - High speed rotations usually use ball bearings.

   - Low speeds or intermittent motion may be suitable for plain bearings.

3. Evaluate accuracy requirements:

   - High precision applications may require precision bearings.

4. assess the environment:

   - Corrosive environments may require bearings made of special materials.

   - High or low temperature environments require specially designed bearings. 

5. Consider installation and maintenance:

   - Select a bearing type that is easy to install and maintain.

   - Consider lubrication methods and frequency. 

6. Cost-benefit analysis:

   - Compare the life, performance and cost of different types of bearings.

7. Consult the manufacturer or an expert:

   - Consult the bearing manufacturer or application engineer before making a final decision.

By considering the above factors, you can choose the type of bearing that best suits your application, ensuring the reliability and efficiency of your machinery and equipment.

How the bearing is lubricated:

The way a bearing is lubricated does vary from one type of bearing to another. The way a bearing is lubricated depends on a number of factors, including the type of bearing, operating conditions, load characteristics, speed, and so on. The following are some common bearing types and their corresponding lubrication methods:

1. Ball and roller bearings:

   - These types of bearings are usually lubricated with oil or grease.

   - For high-speed bearings, oil-mist lubrication or oil-air lubrication may be used to keep the lubrication film stable.

   - Under heavy load or high temperature conditions, special high temperature grease or oil may be required.

2. Sliding bearings:

   - Sliding bearings are usually lubricated with oil because they rely on an oil film to reduce wear.

   - Lubrication can be provided by a recirculating lubrication system that ensures a constant supply of fresh oil.

   - Grease may also be used for low speed or intermittent operation.

3. Ceramic bearings:

   - Ceramic bearings may require special lubricants because ceramic materials have different lubrication requirements than metals.

   - Usually a high quality lubricant or grease is used.

4. self-lubricating bearings:

   - These bearings are designed with lubricating materials already included, such as solid lubricants, and usually do not require additional lubrication.

   - In some applications, self-lubricating bearings can also be used with oil or grease to extend their life. 

5. Spherical and tapered bearings:

   - These bearings are usually lubricated with grease, especially where large clearances are required or seals are needed.

The following are some of the characteristics of the different lubrication methods:

- Grease: Suitable for most bearings, easy to apply and capable of maintaining lubrication for a long period of time, but requires periodic replenishment.

- Lubricant: Suitable for high speed or high temperature applications, requires a lubrication system to maintain the oil film, and may need to be changed more frequently.

- Oil-air lubrication: Suitable for high-speed, high-temperature or heavy-duty applications, provides good lubrication but requires a specialised oil-air lubrication system.

- Oil Mist Lubrication: Suitable for high speed bearings, provides continuous lubrication through oil mist, but requires an oil mist generator and ventilation system.

Choosing the correct lubrication method and lubricant is critical to ensuring bearing performance and life. Improper lubrication can lead to premature bearing wear, failure or even damage. Therefore, the bearing manufacturer's recommendations and the requirements of the specific application should be consulted when determining the lubrication programme.

Overall, there are many different types of bearings, and which type to choose depends on the specific application scenario and requirements. When selecting bearings, a number of factors such as load size, direction, rotational speed, precision, working environment, etc. need to be considered to ensure that the bearings can meet the requirements of the equipment and extend the service life.