Bearings are crucial components in CNC machining equipment. The working principle of a CNC machining center’s spindle relies on the drive of an electric motor and the support of bearings. The precision of CNC machining shop’s machines heavily depend on high-precision bearings as their main processing equipment. Among these bearings, milling cutter bearings are designed for milling operations and feature rotating tools with one or multiple cutting teeth. today in this blog, we will share with you different types of bearings and their properties.

What is a Bearing?

Bearings are components that “assist objects in rotating,” and as the name suggests, they are parts that support the “shafts” that rotate within machines. Machines that use bearings include automobiles, aircraft, generators, and more. Common household appliances like refrigerators, vacuum cleaners, and air conditioners also rely on bearings.

In these machines, bearings are responsible for providing support to the “shafts” that have components such as wheels, gears, turbines, rotors, and more, allowing these shafts to rotate smoothly.

What is the Purpose of Bearings?

  • Reducing Friction for Smoother Rotation，When a rotating “shaft” and its supporting components are in contact, friction inevitably occurs. Bearings are placed between the rotating “shaft” and the supporting components. Bearings serve to reduce friction, lower the friction coefficient during their motion, and ensure rotational accuracy. This results in smoother rotation and reduced energy consumption.
  • Protecting Rotating Support Components，The area between the rotating “shaft” and its supporting components experiences substantial forces. Bearings prevent damage to the rotating support components caused by these forces, ensuring that the rotating “shaft” maintains the correct position. In essence, bearings can handle radial loads and axial loads, keeping the rotating “shaft” in its proper place.

Common Bearing Types

Cylindrical Roller Bearings

The type designation for cylindrical roller bearings is “N.” These bearings have separable outer and inner rings and cannot withstand axial loads. The rollers are axially positioned by the flanges on the inner or outer ring. They have a substantial radial load-carrying capacity and can be used without an outer or inner ring.

Cylindrical roller bearings consist of a disk-shaped roller and a cylindrical body, forming a rolling bearing primarily designed to withstand radial loads but can also bear axial and torsional loads. The rollers in cylindrical roller bearings are arranged in parallel and separated by a cage, effectively preventing roller tilting or friction between rollers, thereby reducing the increase in rotational torque.

Characteristics of Cylindrical Roller Bearings

  • Excellent radial load-carrying capacity, suitable for heavy loads.
  • Can withstand significant axial impact loads and remain parallel to the shaft.
  • Excellent radial rigidity; minimal displacement at the contact point with the shaft.
  • Capable of withstanding some axial loads and possess self-lubrication ability at elevated temperatures.
  • Low friction coefficient, suitable for high-speed rotation, with an ultimate speed close to deep groove ball bearings.
  • Cylindrical roller bearings are separable; the inner or outer ring can be detached, facilitating installation and removal.

Applications of Cylindrical Roller Bearings

Cylindrical roller bearings are suitable for high-speed, high-load, and high-precision applications. They are widely used in large motors, machine tool spindles, axle boxes of vehicles, diesel engine crankshafts, automobiles, and more.

Self-Aligning Ball Bearings

The type designation for self-aligning ball bearings is “1”. The outer raceway surface of self-aligning ball bearings is spherical, centered around the bearing’s midpoint, allowing for automatic self-alignment. These bearings are generally not suitable for pure axial loads.

Self-aligning ball bearings consist of a circular ball and a cylindrical body located between the inner raceway ball surface and the outer raceway. They have a self-aligning function, where the outer diameter of the bearing cooperates with the inner diameter of the bearing seat on a spherical surface. This self-aligning function compensates for misalignment due to installation errors and deformations in the device’s base. Cage materials can include steel plates, synthetic resins, and more.

Self-aligning ball bearings structures

Cylindrical Bore

These bearings have two rows of steel balls and an arched raceway in the outer ring. Self-aligning ball bearings with cylindrical bores can actively self-align and accept angular misalignment between the shaft and bearing housing. They are suitable for conditions where there are bending or eccentricities in the shaft, resulting in low friction, even at high speeds, and minimal temperature rise.

Tapered Bore

Self-aligning ball bearings with tapered bores (typically with a taper of 1:12) have characteristics similar to those with cylindrical bores. However, they offer the additional advantage of adjusting bearing clearance when mounted on a tapered shaft. These bearings are often used in applications where there are large angular misalignments between two support shafts, and the alignment of the bearing housings is not strictly concentric. They can primarily withstand radial loads but can also handle some axial loads. Their versatility is second only to deep groove ball bearings, with slightly lower maximum speeds but higher load-carrying capacities.

Characteristics of Self-Aligning Ball Bearings

  • The outer raceway surface is spherical, allowing for automatic self-alignment.
  • Can withstand significant radial loads and some axial loads.
  • Long service life, even in harsh operating conditions.
  • Excellent sealing capabilities to prevent contamination and maintain optimal performance.

Applications of Self-Aligning Ball Bearings

Self-aligning ball bearings play a crucial role in various industries due to their ability to self-align, carry radial and axial loads, and provide extended service life, making them one of the most widely used types of bearings in the mechanical industry including electric motors, automotive, woodworking machinery, textile machinery, mining equipment, medical devices, fitness equipment, and general machinery,

Deep Groove Ball Bearings

The type designation for deep groove ball bearings is “6”. They primarily carry radial loads but can also handle small axial loads simultaneously. These bearings are mass-produced, have the lowest prices, and are the most widely used. Basic deep groove ball bearings consist of an outer ring, inner ring, a set of steel balls, and a set of cages. There are both single-row and double-row deep groove ball bearings. Deep groove ball bearings can also be categorized into sealed and open structures. Open bearings lack a sealing structure. Sealed deep groove ball bearings include dust-sealed and oil-sealed varieties.

  • Dust-sealed covers are made of stamped steel plates and are designed to prevent dust from entering the bearing raceways.
  • Oil-sealed types feature contact seals that effectively prevent grease from leaking out of the bearing.

Single-row deep groove ball bearings are denoted by the type code “6”, while double-row deep groove ball bearings are denoted by the type code “4”. They have a simple structure and are easy to use, making them the most common and widely used type of bearing.

Deep Groove Ball Bearing Structure

Compared to other bearing types, deep groove ball bearings have a simple structure and high manufacturing precision. Therefore, they are easy to mass-produce, resulting in lower manufacturing costs, and are used extensively. In addition to the basic types, there are various structural variations of deep groove ball bearings, including those with dust shields, rubber seals, snap ring grooves, and large load-carrying capacity with ball gaps, as well as double-row deep groove ball bearings.

Deep Groove Ball Bearing Principle

Deep groove ball bearings primarily carry radial loads but can also simultaneously handle both radial and axial loads. When subjected to only radial loads, the contact angle is zero. When deep groove ball bearings have a larger radial clearance and possess the characteristics of angular contact bearings, they can withstand significant axial loads. Deep groove ball bearings have very low friction coefficients and can operate at high speeds.

Advantages of Deep Groove Ball Bearing

  • Under normal conditions, deep groove ball bearings have higher efficiency than plain bearings and fluid dynamic lubricated bearings but lower than hybrid lubricated bearings.
  • They have relatively small radial clearances, and axial play can be eliminated by applying preload, resulting in high operational precision.
  • For the same shaft diameter, the width of deep groove ball bearings is smaller than that of plain bearings and sliding bearings, allowing for a compact axial structure in machines.
  • Most rolling bearings can simultaneously carry radial and axial loads, simplifying bearing assembly structures.
  • They consume less lubricant, are easy to seal, and require minimal maintenance.
  • They do not require the use of non-ferrous metals.
  • They have a high degree of standardization, making them suitable for mass production and cost-effective manufacturing.

Angular Contact Ball Bearings

Angular contact ball bearings are designated with the type code “7”. They can simultaneously bear both radial and axial loads, or individually handle axial loads and operate effectively at higher speeds. Since a single bearing can only withstand unidirectional axial forces, these bearings are generally used in pairs. The ability to bear axial loads is related to the contact angle α; the greater the contact angle, the greater the axial load it can handle.

Angular contact ball bearings consist of an inner ring, an outer ring, steel balls, and a cage. Contact between the inner and outer rings is facilitated by steel balls, allowing them to carry radial loads, axial loads, and torque. Angular contact ball bearings are characterized by their high load-carrying capacity, stiffness, and suitability for high-speed applications. The contact angle between the inner and outer rings is typically 15 degrees or 25 degrees, and the appropriate contact angle can be selected based on different operating conditions.

Principle of Angular Contact Ball Bearings

Angular contact ball bearings utilize the contact between steel balls to generate rolling friction, reducing frictional resistance and energy loss. Furthermore, due to the relatively small contact angle of angular contact ball bearings, rolling friction is smoother, leading to reduced noise and vibration. This makes angular contact ball bearings highly valuable in high-speed and precision-demanding mechanical equipment.

Advantage of Angular Contact Ball Bearings

Firstly, they possess high load-carrying capacity and stiffness, enabling them to withstand significant radial and axial forces. Secondly, angular contact ball bearings exhibit excellent high-speed performance, making them suitable for high-speed machinery. Additionally, their installation and adjustment are relatively simple, facilitating easier maintenance and repair. Most importantly, angular contact ball bearings have good self-aligning properties, accommodating uneven deformations of bearing seats while maintaining certain load-bearing capabilities.

Applications of Angular Contact Ball Bearings

In the machine tool industry, angular contact ball bearings are widely used in areas such as spindles, main transmissions, and support structures. In the wind power generation sector, they are employed in the transmission systems of wind turbines to withstand wind forces and convert them into electricity. In the automotive industry, angular contact ball bearings find applications in critical components such as suspension systems, transmissions, and engines. Furthermore, they are extensively used in applications like bearing vibration measurement instruments, precision instrument equipment, aerospace, and more.

Tapered Roller Bearings

Tapered roller bearings are designated with the type code “3”. They can simultaneously withstand radial and axial loads, and their outer rings can be separated. Similar to angular contact ball bearings, tapered roller bearings are generally used in pairs.

Tapered roller bearings consist of inner rings, outer rings, rollers, and retainers. Both the inner and outer rings have a conical shape, and the rollers roll within the conical surfaces, which is how they derive their name. Tapered roller bearings are capable of bearing both radial and axial loads, making them suitable for bidirectional force transmission. The angle between their inner and outer rings determines their load-carrying capacity and rotational stability.

Advantages of Tapered Roller Bearings:

  • High Load Capacity: Tapered roller bearings have a higher load-carrying capacity than ball bearings and cylindrical roller bearings of the same size. This makes them suitable for high-load and high-speed operations.
  • Rotational Stability: Precise control over the angle between the inner and outer rings ensures stable rotation and accurate transmission of the bearing.
  • High-Temperature and High-Speed Resistance: Tapered roller bearings are made from special materials and undergo heat treatment processes, making them resistant to high temperatures and high-speed rotations.
  • Ease of Installation and Maintenance: Tapered roller bearings have a simple structure, making them easy to install and disassemble, thus facilitating maintenance.

Applications of Tapered Roller Bearings:

Tapered roller bearings are widely used in various industrial equipment and machinery, including automobiles, ships, aircraft, construction machinery, metallurgical equipment, mining machinery, and more. They play a crucial role in transmission systems, capable of withstanding loads from different directions while ensuring stable rotation and transmission efficiency.

Spherical Roller Bearings

Spherical roller bearings are designated with the type code “2”. The performance and characteristics of spherical roller bearings are similar to spherical roller bearings, but they have a greater radial load-carrying capacity.

The center of the outer raceway of spherical roller bearings is the same as the bearing’s center, giving them automatic self-aligning capabilities. This enables them to compensate for installation errors or shaft deflection that would cause the inner ring to tilt. They are particularly suitable for heavy loads or vibrating conditions and are often referred to as “universal bearings.”

Spherical roller bearings have two rows of symmetrical spherical rollers. The outer ring has a shared spherical raceway, while the inner ring has two raceways inclined at an angle to the bearing’s axis. This design provides excellent self-aligning performance. Even when the shaft is subject to bending or installed off-center, the bearing can still function properly. The degree of self-alignment varies with the bearing’s size series, but generally allows for angular misalignment of 1 to 2.5 degrees. This type of bearing has a high load-carrying capacity and can withstand bidirectional axial loads in addition to radial loads. It also has good shock resistance. Typically, spherical roller bearings have lower allowable operating speeds.

Advantages of Spherical Roller Bearings:

  • High Temperature Resistance: Spherical roller bearings use high-quality materials and manufacturing processes, resulting in low friction coefficients and thermal expansion coefficients. This allows them to operate stably at high temperatures without deformation and with a long lifespan.
  • High Load-Carrying Capacity: Spherical roller bearings have larger rollers compared to other types of bearings, giving them a higher load-carrying capacity. They can withstand significant axial and radial loads.
  • Low Noise: Precision design and manufacturing reduce noise and vibration generation, resulting in quiet operation.
  • Self-Alignment: By adjusting the center axis of the bearing, spherical roller bearings can adapt to different operating conditions and load conditions.

Disadvantages of Spherical Roller Bearings:

  • Vibration: Spherical roller bearings can generate significant vibration when operating at high speeds, potentially causing instability in machinery.
  • High Noise: Due to rolling friction and vibration, spherical roller bearings can produce noise, affecting machine performance and the working environment.
  • High Precision Requirements: Spherical roller bearings are precision mechanical products that require high manufacturing precision, involving significant effort and time.
  • High Lubrication Requirements: Spherical roller bearings require the injection of lubricating oil during operation, demanding high-quality grease that doesn’t degrade easily and has a long service life.

Needle Roller Bearings

Needle roller bearings are designated with the type code “NA”. When the inner diameter is the same, needle roller bearings have a smaller outer diameter compared to other types of bearings, making them suitable for applications with limited space. They can have separable inner and outer rings, allowing for a small amount of axial misalignment during operation. They possess a large radial load-carrying capacity but generally do not have a cage, resulting in higher friction.

Needle roller bearings are a type of roller bearing with cylindrical rollers that are relatively thin and long in relation to their diameter. These rollers are called needle rollers. Despite their small cross-sectional size, needle roller bearings can still carry high loads. Needle roller bearings are equipped with thin and long rollers (roller diameter D≤5mm, L/D≥2.5, where L is the roller length). This compact radial structure means that when the inner diameter size and load capacity are the same as other types of bearings, the outer diameter is minimized. This makes them particularly suitable for support structures with limited radial installation dimensions.

Advantages of Needle Roller Bearings:

  • Low Friction: Needle roller bearings have low friction resistance, resulting in low power consumption, high mechanical efficiency, and easy starting.
  • Standardized Sizes: Needle roller bearings are standardized and interchangeable, making them easy to install, disassemble, and maintain.
  • Compact Structure: They have a compact structure, light weight, and smaller axial dimensions.
  • High Precision: Needle roller bearings offer high precision, high-speed performance, low wear, and long service life.
  • Some Bearings Offer Self-Alignment: Certain needle roller bearings have self-aligning capabilities.
  • Suitable for Mass Production: They are suitable for mass production with stable and reliable quality, and high production efficiency.
  • Lower Friction Torque: Needle roller bearings have lower friction torque compared to fluid dynamic pressure bearings, resulting in lower frictional heat generation. The starting friction torque is only slightly higher than the rotating friction torque.
  • Small Lubricant Requirement: They can operate normally with a small amount of lubricant and provide lubrication for an extended period during operation.
  • Can Handle Radial and Thrust Loads: Needle roller bearings can simultaneously handle combined radial and thrust loads.
  • Performance Insensitivity: The bearing’s performance is relatively insensitive to fluctuations in load, speed, and operating conditions within a large load-speed range.

Disadvantages of Needle Roller Bearings:

  • High Noise: Needle roller bearings can generate high noise levels.
  • Complex Bearing Seat Structure: The bearing seat structure is relatively complex, leading to higher costs.
  • Limited Fatigue Life: Despite proper lubrication, correct installation, and effective dust and moisture sealing, needle roller bearings can eventually fail due to fatigue on the rolling contact surfaces.

Thrust Ball Bearings

Thrust ball bearings are designated with the type code “5”. These bearings require a certain axial load during operation to prevent the steel balls from sliding in the raceways. At high speeds, there is a significant centrifugal force, causing wear and heating between the steel balls and the cage, which reduces the bearing’s lifespan. Therefore, these bearings have a lower maximum rotational speed.

Thrust ball bearings consist of three main components: an outer ring, an inner ring, and balls. There are one or more steel balls in the axial direction between the inner and outer rings, creating contact surfaces similar to raceways between them. The number of balls can be adjusted according to specific requirements to accommodate different loads and speed conditions.

Working Principle of Thrust Ball Bearings:

 When an external force acts on the shaft, the thrust load is transferred to the balls, and then it is transmitted to the bearing through the rolling contact surfaces between the balls and the inner and outer rings, generating the supporting force for the shaft.

Because the balls are arranged separately, frictional forces are relatively low, allowing the bearing to withstand significant axial loads.

Advantages of Thrust Ball Bearings:

  • High Load Capacity: Thrust ball bearings have a high load-carrying capacity and can withstand substantial axial loads.
  • Reduced Friction and Energy Consumption: Thrust ball bearings use steel balls and rolling contact surfaces, which reduce friction and energy consumption, thereby increasing the efficiency of mechanical equipment.
  • Compact Structure and Easy Installation: These bearings have a compact structure, are easy to install, and save space.
  • High Reliability and Durability: They offer high reliability and durability, can operate in various harsh environments, and reduce equipment maintenance and replacement costs.

Thrust Roller Bearings

Thrust roller bearings are a type of rolling bearing. Their working principle involves using rolling elements (rollers) to support axial loads between the outer raceway and the inner shaft (bearing housing). When axial loads act on the bearing, the relatively low rolling resistance of the rollers results in significantly reduced friction and wear during stable operation, thereby giving thrust roller bearings higher load-carrying capacity and a longer service life.

Types of Thrust Roller Bearings:

Cylindrical Thrust Roller Bearings (Type Code: 8): These bearings can withstand unidirectional loads. They have a much greater axial load-carrying capacity compared to thrust ball bearings and offer high rigidity while occupying less axial space. They are suitable for applications with lower rotational speeds. Cylindrical thrust roller bearings have a compact structure and strong load-carrying capacity, making them more effective for operation at low speeds. However, they tend to generate axial vibrations and noise at high speeds, so they are typically used in low-speed, high-load, or steady-load conditions.

Tapered Thrust Roller Bearings: Tapered thrust roller bearings are designated with type code 9. They are similar to cylindrical thrust roller bearings but allow for slightly higher rotational speeds. Tapered thrust roller bearings have a tapered roller structure, which results in higher rotational speeds, lower friction coefficients, and improved axial rigidity. Additionally, their adjustable preload capability makes them more widely used in industries such as engineering machinery and automotive applications.

Advantages of Thrust Roller Bearings

  • High Load Capacity: Compared to other types of roller bearings, thrust roller bearings have a higher load-carrying capacity and can withstand larger axial loads.
  • High Rotational Speed: Thrust roller bearings have a greater number of rolling elements (rollers), resulting in reduced rolling resistance during high-speed rotation. This characteristic allows for higher rotational speeds.
  • High Reliability: Thrust roller bearings are made from high-quality bearing steel and undergo precision manufacturing processes. This quality enables them to quickly adapt to different working environments, providing increased reliability and extended service life.

In summary

the selection of an appropriate bearing necessitates careful consideration of numerous factors. By evaluating various bearing types and their respective attributes, we aim to address your inquiries comprehensively. At KUSLA, our dedication lies in delivering a comprehensive range of bearing and fastener solutions tailored to your project’s precise requirements, ensuring a one-stop shopping experience.

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