# ECCENTRICITY LEADING OVERHEATING OF BEARINGS

27/11/2020

Continuing our series on concentricity (out of alignment). As the previous post mentioned, eccentricity causes many problems that affect the life of Bearings. In this article, ICV World will focus on the issue of bearing overheating.

## 1. Calculating the concentricity of Bearings

As we all know, Bearings are divided into two categories: ball bearings and roller bearings. Ball bearings have a point contact ball surface, and roller bearings have a line contact surface. Roller bearings have better load capacity but generate more heat than ball bearings.

For single-row tapered roller bearings, the eccentric angle is only allowed about 1 minute (1/60 of 1 degree). Some manufacturers use logarithmic deformations that increase the eccentric angle value to 3 minutes (3/60 of 1 degree).

Point-contact Ball bearings

Line-contact Roller bearings

Let's see the following example. The picture below is a vertical centrifugal pump, with a 24 inch distance between the bearing centers of the two bearings and a shaft diameter of 4 inches. Self-aligning cylindrical roller bearings (self-balancing) are installed at one end of the shaft so they are less susceptible (due to shaft oscillation) to errors due to the out of centering of the two bearing holes (bearing eccentricity).

Suppose, the inside diameter of the shaft is 8 inches. To maintain the eccentricity for about 1 minute (1/60 of 1 degree), we need to solve a simple geometric relationship:

tan (1 minute) = c / L

In which: c: concentricity

L: distance between 2 bearing centers

Inferred: c = 12 inches x tan (1/60 degrees) = 0.003 inches (1mil = 0.01 inch = 0.025mm = 25.4 microns)

If concentricity is within 3 mils, the bearings may operate within the permissible concentricity. Anything higher will result in overheating and damage to Bearings.

## 2. Overcoming of eccentricity in Bearings

Road contact patterns, roller ball geometry and many other factors play an important role in minimizing the amount of heat generated.

Typically, Taper Roller Bearing is designed to be fitted at one end of the shaft instead of a Cylindrical Roller Bearing. As shown in figure 1, the cylindrical roller bearing on ​​the upper pillow is mounted face-down together, and on the lower pillow, the tapered roller bearing (self-balancing capability) is installed.

## 3. Other causes of overheating Bearings

However, it must be added that, in addition to the loss of concentricity (out of alignment), there are many other causes that lead to the phenomenon of bearings hotter than normal, such as:

- Using the wrong type of lubricating oil

- Too much oil

- Oil contaminants

- Selecting and assembling the wrong type of bearing

- Operating conditions too harsh, overloaded ...