Rolling bearings support and guide, with minimal friction, rotating or oscillating machine elements – such as shafts, axles, or wheels – and transfer loads between machine components. Rolling bearings provide high precision and low friction and therefore enable high rotational speeds while reducing noise, heat, energy consumption, and wear. They are cost-effective and exchangeable machine elements that typically follow national or international dimension standards.
The two basic types of rolling elements distinguish the two basic types of rolling bearings:
• Ball → Ball bearing
• Roller → Roller bearing
Balls and rollers are different in how they make contact with the raceways.
Balls make point contact with the ring raceways. With increasing load acting on the bearing, the contact point becomes an elliptical area. The small contact area provides low rolling friction, which enables ball bearings to accommodate high speeds but also limits their load-carrying capacity.
Rollers make line contact with the ring raceways. With increasing load acting on the bearing, the contact line becomes somewhat rectangular in shape. Because of the larger contact area and the consequently higher friction, a roller bearing can accommodate heavier loads, but at lower speeds, than a same-sized ball bearing.
Rolling bearings are classified into two groups based on the direction of the load they predominantly accommodate:
Radial bearings accommodate loads that are predominantly perpendicular to the shaft. Some radial bearings can support only pure radial loads, while most can additionally accommodate some axial loads in one direction and, in some cases, both directions.
Thrust bearings accommodate loads that act predominantly along the axis of the shaft. Depending on their design, thrust bearings may support pure axial loads in one or both directions, and some can additionally accommodate radial loads (combined loads). Thrust bearings cannot accommodate speeds as high as same-sized radial bearings.
The contact angle determines which group the bearing belongs to. Bearings with a contact angle ≤ 45° are radial bearings, and the others are thrust bearings.
Rolling bearings are used in various applications, including machines and vehicles, to reduce friction between moving parts. To ensure proper functioning, it is essential to maintain the right tolerances during the manufacturing process. Tolerance refers to the allowable variation in size and shape of the bearing components to ensure that the bearing operates correctly. The rolling bearing tolerance can be defined as the permissible range of variation in the dimensions and geometrical characteristics of the bearing components, such as inner and outer rings, rolling elements, cages, and their assembly. There are several types of rolling bearing tolerances, including:
1. Dimensional tolerance: This refers to the allowable variation in the size of the bearing components, such as the inner and outer diameter of the rings, the width of the rings, and the diameter of the rolling elements.
2. Form tolerance: This refers to the allowable variation in the shape of the bearing components, such as the roundness of the inner and outer rings, the roundness of the rings, and the shape of the rolling elements.
3. Position tolerance: This refers to the allowable variation in the position of the bearing components concerning each other, such as the alignment of the inner and outer rings and the parallelism of the bearing faces.
4. Running accuracy: This refers to the allowable variation in the operating characteristics of the bearing, such as the radial and axial runout, the radial and axial clearance, and the torque and noise level.
The rolling bearing tolerance is usually specified by international standards, such as the ISO (International Organization for Standardization) and the ABMA (American Bearing Manufacturers Association). These standards define the maximum allowable deviation in dimensions and geometrical characteristics, and the manufacturing process should ensure that the bearing components and their assembly fall within the specified tolerance limits.
In conclusion, the rolling bearing tolerance is a critical factor in ensuring the proper functioning of the bearing, and it is necessary to maintain the right tolerances during the manufacturing process to ensure the bearing's reliability and longevity.
Rolling bearing fits and tolerances refer to the relationship between the bearing and it’s mating parts or shaft/housing. The fit determines how tightly the bearing is installed on the shaft or in the housing, while the tolerance specifies the allowable variation in the dimensions and geometrical characteristics of the bearing components and their mating parts.
There are three types of rolling bearing fits:
1. Clearance fit: In this type of fit, the bearing is slightly smaller than the shaft or housing bore, allowing for a small amount of radial or axial movement. The clearance fit is typically used in low-speed applications, such as electric motors, to allow for thermal expansion and contraction of the shaft or housing.
2. Interference fit: In this type of fit, the bearing is slightly larger than the shaft or housing bore, requiring some force to install the bearing onto the shaft or in the housing. The interference fit ensures that the bearing is securely held in place and minimizes any radial or axial movement. Interference fits are typically used in high-speed or heavy-duty applications, such as industrial machinery or automotive transmissions.
3. Transition fit: In this type of fit, the bearing is designed to have both clearance and interference fit characteristics. The bearing is installed with a slight interference fit initially, but as it rotates, it loosens up and creates a small clearance. Transition fits are used in applications where some amount of clearance is required during operation but where a secure fit is needed initially.
The tolerance for rolling bearings refers to the allowable variation in the dimensions and geometrical characteristics of the bearing components, such as the inner and outer rings, rolling elements, cages, and their assembly. The tolerance values are specified by international standards, such as the ISO (International Organization for Standardization) and the ABMA (American Bearing Manufacturers Association). The tolerance values are typically specified as upper and lower limits for various dimensions and geometrical characteristics, and the manufacturing process should ensure that the bearing components and their assembly fall within the specified tolerance limits.
In conclusion, rolling bearing fits and tolerances are critical factors in ensuring the proper functioning of the bearing, and it is necessary to select the appropriate fit and maintain the right tolerances during the manufacturing process to ensure the bearing's reliability and longevity.
Friction is an important consideration in the design and operation of rolling bearings. Friction is the force that resists motion when two surfaces come into contact with each other. In rolling bearings, friction is caused by the interaction between the rolling elements (such as balls or rollers) and the raceways (inner and outer rings).
When a load is applied to a rolling bearing, the rolling elements come into contact with the raceways and roll along them. Friction occurs at the contact points between the rolling elements and the raceways, which creates heat and causes wear on the bearing surfaces.
The amount of friction in a rolling bearing is influenced by several factors, including the bearing design, the lubrication, and the operating conditions. Some factors that can increase friction in a rolling bearing include high loads, high speeds, inadequate lubrication, contamination, and misalignment.
Excessive friction can lead to several problems, including increased heat generation, wear and damage to the bearing surfaces, reduced bearing life, and increased energy consumption. Therefore, reducing friction in rolling bearings is essential to maximize bearing performance and improve efficiency.
Several methods are used to reduce friction in rolling bearings, including the use of high-quality bearing materials, optimizing the bearing design and tolerances, selecting appropriate lubrication, and minimizing external factors such as misalignment and contamination.
In conclusion, friction is an important factor to consider in the design and operation of rolling bearings. Reducing friction in rolling bearings is crucial to ensure optimal performance and longevity of the bearing.
Rolling bearing lubrication is critical to the proper functioning and longevity of the bearing. Lubrication is used to reduce friction between the bearing components, dissipate heat, prevent wear, and protect against corrosion. Here are some basics of rolling bearing lubrication:
1. Types of lubricants: Rolling bearings can be lubricated with various types of lubricants, including oil, grease, and solid lubricants. The selection of the lubricant depends on the bearing design, operating conditions, and the application requirements.
2. Oil lubrication: Oil lubrication is commonly used in high-speed or heavy-duty applications. The oil is usually circulated through the bearing using a pump, and excess oil is drained back into the reservoir. Proper oil viscosity, temperature, and cleanliness are essential for effective lubrication.
3. Grease lubrication: Grease lubrication is widely used in low to medium-speed applications. Grease is a semi-solid lubricant that is applied to the bearing in a measured amount and held in place by the sealing system. The choice of grease type, consistency, and amount is critical for effective lubrication.
4. Solid lubricants: Solid lubricants, such as molybdenum disulfide or graphite, are used in applications where the bearing is exposed to high temperatures, radiation, or vacuum conditions.
5. Lubrication frequency: The frequency of lubrication depends on the bearing design, operating conditions, and the type of lubricant used. Over-lubrication and under-lubrication can both lead to bearing failure, so it is essential to follow the manufacturer's recommendations for lubrication frequency and amount.
6. Lubrication contamination: Lubrication can become contaminated with dirt, moisture, or other particles, which can reduce its effectiveness and lead to bearing failure. Proper storage, handling, and filtering of the lubricant are essential to prevent contamination.
In conclusion, rolling bearing lubrication is critical to the proper functioning and longevity of the bearing. Proper selection of lubricant type, frequency, and amount, as well as proper storage and handling, are essential to ensure effective lubrication and prevent bearing failure.