Needle Bearing Guide

What do bearings do?

Bearings are a tiny component that is typically found around the moving parts within a machine, usually a shaft or a movable rail. The bearings are there to offer an extra support to the shaft or the movable parts. While a machine is operating and the shaft rotating, the bearings make sure that the shaft stays in place and rotates smoothly. The bearings also protect the areas around the shaft; isolated by the bearings, the neighboring areas will not be damaged by the rotating shaft. There are different types of bearings. There are two major types of bearing, the ball bearings and the rolling element bearings.

What are needle bearings?

The needle bearings are a type of rolling element bearings. They have rollers that have high length to diameter ratios. The needle bearings are used mostly in agriculture and construction equipment, automotive applications, small size engines, gear pumps, motors and sometimes aircraft controls. They are an essential component in the machinery to support the rotary shafts and protect the movable components. With the support from the bearings, the shaft gets to rotate faster and smoother; the vibration and noise that is generated when the machinery is running can also be minimized by the bearings.

Compared with other types of roller bearings, the needle bearings have much smaller rollers for a given bore size and the rollers are usually cylindrical. Though the needle bearings have the highest load capacity for a given radial space of all rolling bearings, their application is limited to bore diameters less than 10 inches. The general configuration of the needle bearings can be divided into two: the ones with full complement and the ones with cages. This design difference affects the capability of the needle bearings immensely.

Anatomy of the rolling element bearings

The anatomy of a rolling element bearing is not too complicated. There are three essential parts to make up a rolling element bearing: the inner ring, the outer ring and the rolling element. The rolling elements inside the bearing are called the rollers. The rollers come in with the shape of tiny round balls or cylinders. The typical configuration of a roller bearing is the inner ring and the outer ring wrapping the rollers in between. This setup allows the rotation force to be placed on the ball set, which is referred to as loading.

The fundamental principle of applying these tiny rollers inside the bearings is as this: it is always easier to roll a wheel than to slide a wheel on the ground because the rolling friction is lower than the sliding friction. With the rolling elements, the loading can be more efficiently spread and shifted. The two primary types of loading that a bearing takes on are the thrust loading and the radial loading. The bearings that work with a radial load are the bearings that rotate or roll in accordance with the shaft.

On the other hand, the thrust loading has to do with the angle that the force exerts. No matter which type of loading a roller bearing has to deal with, it functions as to reduce the friction between the bearing and the shaft and make the rotation smoother. A bearing can also protect the parts that support the shaft and make sure the shaft is positioned correctly.

Cages inside the needle bearing

There are two subtypes of needle bearings: the ones with cages and the ones without them. The cages are also called the retainers. The cages are the device that separates the rollers inside the rings. The caged needle bearings have smaller roller complements and lower load capacities than the ones with full complement. Smaller complements suggest few rollers. Since the space inside the bearing is limited, with cages within, there is less space to place the rollers. The full complement bearings are the ones without the cages so that there is more space for more rollers.

Without the retainers, the needle bearings can offer a more effective and inexpensive bearing assembly. Yet, the speed capability is moderate. With the roller retainers, the contact and friction between the rollers can be reduced. In other words, the key advantage of the caged needle bearings is that they have a higher speed capacity. The retainers also help to retain grease around the balls, which means they have greater lubricant capacity.

Causes of damage to needle bearings

The bearings wear out as the machine runs. Over time, the bearings can be damaged and need to be replaced. There are several causes that can possible make the bearings wear out more quickly than average. By knowing the possible causes and how to eliminate the causes, the bearings’ condition can be well maintained and the lifespan prolonged. The primary cause of the bearing damage can be the fatigue damage, poor lubrication, and introduction of contaminants into the bearings.

If there is a noticeable amount of dust around the needle bearing, it will positively increase the wear of the components in between the bearings and decrease the lifespan of the bearing. Therefore, it is crucial to keep the working environment clean. The lack of lubrication results in increased friction and the frequency of machine failure too. If the needle bearings are not installed properly, they can be damaged easier as well. There are particular installation tools for the installation of bearings. It is recommended to install the bearings with the tools to prevent poor installation and the bearings can last longer as a result.

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