A Closer Look at Needle Bearings: Types and Characteristics

Needle roller bearings have needle rollers as rolling elements. Needle roller bearings are defined where cylindrical rolling elements are classified as needle rollers if the rolling element diameter is ≦6 mm and the ratio of the rolling element diameter to the rolling element length is Dw/lw＜1:3. These bearings are known for their high load-carrying capacity and ability to operate in tight spaces with limited radial and axial clearance. Their use at high speeds is restricted.
The types of needle roller bearings we are discussing are Drawn Cup Needle Roller Bearings with Closed End, Drawn Cup Needle Roller Bearings with Open Ends, Machined Needle Roller Bearings, Aligning Needle Roller Bearings, and Inner Rings.
This article will take a closer look at these different types and discuss their various characteristics.

What are the characteristics of needle bearing?

A defining feature of needle roller bearings is their use of long, slender cylindrical rollers, with a length-to-diameter ratio of 3 to 10. This contrasts sharply with the shorter rollers found in conventional bearings. The extended roller design is not merely for space-saving; it’s a strategic choice that significantly enhances radial load capacity without increasing the bearing’s radial size.

The elongated nature of these rollers enables a more extensive contact area with the raceways. This extended contact zone allows for a more effective distribution of loads over a broader surface area. Consequently, needle bearings boast a superior capacity to handle higher radial loads, a critical factor in many engineering applications.

The compactness of needle bearings is one of their most appealing attributes. Despite their high load-bearing capacity, these bearings maintain a significantly smaller radial section height compared to traditional roller bearings. This makes them exceptionally suitable for applications where radial space is limited but high load capacity is essential.

While needle bearings are adept at handling high radial loads, they are generally not designed to withstand high axial or thrust loads. Their suitability for high-speed operations is contingent on various factors like bearing design, lubrication, and operational conditions. Engineers must carefully consider these parameters, as needle bearings might not be optimal for applications requiring very high speeds.

In their standard form, needle bearings exhibit limited tolerance to misalignment between the shaft and housing. However, certain designs incorporate features to accommodate slight misalignments, expanding their application scope.

Drawn Cup needle bearings

Drawn cup needle roller bearings are the more common type of needle bearing and are designed with a thin-walled outer ring and a needle roller and cage assembly. Full complement needle roller bearings, have the maximum number of rollers with no cage, which results in a higher load-carrying capacity. 

Drawn cup needle roller bearings with open and closed ends both have a very small radial section. Drawn Cup needle roller bearings are thin walled with drawn cup outer rings and needle roller and cage assemblies which become a complete unit. The outer rings conform to the dimensional and geometrical accuracy of the housing bore during fit up.

The dimensional and geometrical accuracy of drawn cup needle roller bearings with open and or closed ends conforms to DIN618 standards. The main dimensions of the bearings correspond to DIN 618:2008 and ISO 3245:2015. Nominal dimensions of bearings applied directly to a shaft inner ring can be used if necessary. 

If axial locating elements such as shoulders and snap rings are not used, the housing bore can be produced easily and particularly economically. This also allows simpler mounting and dismounting of the bearings.

Overview of needle bearing designs and structures 

All types of Needle bearings are designed with a cylindrical rolling element. The needle bearings with the highest speed capability are designed with a cage where rollers are guided, which maintains spacing and reduces friction. Full Complement type needle roller bearings have rollers not separated by a cage. With only a few exceptions, the cages are made from sheet steel. Bearings with a plastic cage have the suffix “TV.”

The outer ring of a needle bearing can be stamped steel or hardened steel depending upon the type, where rollers are made from hardened steel. 

Comparison with other types of roller bearings 

Compared to other types of roller bearings, such as cylindrical and spherical roller bearings, needle bearings have smaller cross-sections and are used in completely different applications. 

Components of a Needle Roller Bearing

Needle roller bearings are essential components in various machinery and equipment. Let’s look further at the key components of a needle roller bearing:

• Outer Ring. The outer ring is typically the stationary part of the bearing and provides support and housing for the other components. It is usually made from hardened steel to withstand external loads and ensure dimensional stability.
• Inner Ring. The inner ring is mounted on the rotating shaft and is responsible for transmitting the load from the rotating element (such as a shaft) to the rollers. Like the outer ring, it is also made from high-quality steel and may have a raceway for the needle rollers to move along.
• Needle Rollers. Needle rollers are the load-carrying elements in a needle roller bearing. These cylindrical, needle-shaped rollers have a much smaller diameter compared to their length, allowing them to handle high radial loads efficiently. They roll within the raceways of the inner and outer rings, distributing the load evenly.
• Cage or Retainer. The cage or retainer is an integral part of needle roller bearings, serving to maintain proper spacing and alignment of the needle rollers. It prevents direct contact between adjacent rollers, reducing friction and wear while also enhancing the overall stability of the bearing.
• Raceways. The raceways are groove-like channels or paths in the inner and outer rings. They guide the movement of the needle rollers, ensuring they remain in place and distribute the load evenly. The shape and design of these raceways may vary depending on the specific application and type of needle roller bearing.
• Seals and Shields. Needle roller bearings may include seals or shields to protect the internal components from contaminants, such as dust, dirt, and moisture. Seals provide better protection but may increase friction, while shields offer some protection while maintaining lower friction.

Main industries and equipment in which needle roller bearings

Needle bearings such as Drawn Cup Needle Roller Bearings with Closed End, Drawn Cup Needle Roller Bearings with Open Ends, and Machined Needle Roller Bearing. Those with Aligning Needle Roller Bearings and Inner Rings are commonly used in the automotive industry, where they are used in transmissions, engines, and gearboxes. They are also used in the aerospace industry, where they are applied in aircraft engines and landing gear. In the industrial equipment industry, needle bearings are used in a wide range of applications, including printing presses, textile machinery, and machine tools. 

Benefits and challenges of using needle bearings

The main benefit of using needle bearings is their high load-carrying capacity and ability to operate in tight spaces. However, they are more prone to wear and fatigue due to their high contact stresses. In applications where misalignment or shock loads are present, there may be better choices than needle bearings. 

Installation and selection of needle bearings 

Proper handling and storage of needle bearings are important to ensure their longevity and performance. Needle bearings should be stored in a clean and dry environment and should not be exposed to moisture or corrosive materials. During installation, it is important to ensure that the bearings are properly aligned and lubricated. The selection of the appropriate needle bearing for a specific application will depend on several factors, including the load requirements, operating conditions, and design envelope. 

Conclusion 

Needle bearings are a crucial component in industrial applications that require high radial load capacity within a limited space. By selecting the right type of needle bearing, handling, storing, and maintaining them correctly, you can ensure optimal performance and longevity of your machinery and equipment. 

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