Monthly Archives: Jan 2017


Parameters of Bearing Selection

Allowable Bearing installation Space

To install a bearing in target equipment, the allowable space for a rolling bearing and its adjacent parts is generally limited so the type and size of the bearing must be selected within such limits. In most cases, the shaft diameter is fixed first on the basis of its rigidity and strength by the machine designer; therefore, the bearing is often selected based on its bore size. There are numerous standardized dimension series and types available for rolling bearings and the selection of the optimum bearing from them is an important task.

Load and Bearing Types

Load magnitude, type and direction of applied load are to be considered in bearing type selection. The axial load carrying capacity of a bearing is closely related to the radial load capacity in a manner that depends on the bearing design.

Permissible Speed and Bearing Types

Bearings to be selected with response to rotational speed of equipment in which bearing is to be installed; the maximum speed of rolling bearings varies depending, not only the type of bearing, but also its size, type of cage, loads on system, lubrication method, heat dissipation, etc. Assuming the common oil bath lubrication method, the bearing types are roughly ranked from higher speed to lower.

Misalignment of Inner/Outer Rings and Bearing Types

 The inner and outer rings are slightly misaligned because of deflection of a shaft caused by applied loads, dimensional error of the shaft and housing, and mounting errors. The permissible amount of misalignment varies depending on the bearing type and operating conditions, but usually it is a small angle less than 0.0012 radian. When a large misalignment is expected, bearings having a self-aligning capability, such as self-aligning ball bearings, spherical roller bearings and bearing units should be selected.

Rigidity and Bearing Types

When loads are imposed on a rolling bearing, some elastic deformation occurs in the contact areas between the rolling elements and raceways. The rigidity of the bearing is determined by the ratio of bearing load to the amount of elastic deformation of the inner and outer rings and rolling elements. The higher the rigidity that bearing possess, better they control elastic deformation. For the main spindles of machine tools, it is necessary to have high rigidity of the bearings together with the rest of the spindle. Consequently, since roller bearings are deformed less by load, they are more often selected than ball bearings. When extra high rigidity is required, bearings negative clearance. Angular contact ball bearings and tapered roller bearings are often preloaded.

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The correct way to mount a bearing

Industry Challenges: A loose fit for a bearing will lead to relative movement between mating components, resulting in fretting, smearing, scoring, wear, excessive heat, and/or fracture. A extra-tight fit will reduce the bearing’s internal clearance, which will increase the operating temperature of the bearing in operation. Increase in mounting forces required, but can lead to fracture of bearing’s.

Introduction : When a bearing is mounted without proper care — without utilising the correct knowledge and tools — the bearing’s service life will be cut short. As per the industry estimates, estimated 16 percent of all premature bearing failures are due to poor fitting and the lack of knowledge) of the right fitting tools. The  best practices for mounting a bearing can avoid future problems and extend bearing performance and service life. This will be visible, in the efficiency and productivity of an operation with an increase in machinery uptime.

Methods : The primary methods for proper mounting of a bearing are classified as “cold” or “hot,” as per the shaft diameter or bearing inner diameter. Cold mounting, or mechanical mounting, generally is recommended for small- and medium-sized bearings.

Hot mounting will be for larger bearings; and hydraulic techniques should be used when mounting especially large bearings. Tools have been developed to take care of  each particular bearing needs.

In cold mounting, the wrong practice of using a hammer and pipe for the job is not recommended as will damage the raceways. This can also allow contamination to enter the bearing or, if not done properly, a pipe can slip and impact the rolling element of the bearing. The best practice recommended is to use fitting tools to eliminate the possibility of damage from force, not acting in line with the shaft and bearing position. Fitting tools ensure the proper force is applied to both bearing rings and isolates the rolling elements from impact force, thus assuring a more reliable installation and limiting the risk of damage.

Hot mounting, where the bearing is pre-heated, provides a fool proof solution to allow for a bearing’s inner ring expansion and subsequently easier installation, while maintaining specified interference fit or tolerances after the job is completed. It also saves time , free from any risk of lower flash point of the used oil being used , free from dirt entering the rolling elements and acting as abrasives.

For example, conventional hot oil baths raise the probability of contamination (and premature bearing failure) and flashing. Other techniques (such as exposure to an open flame) fall short, too, and can be potentially dangerous. Induction heating is highly recommended, which involves heating bearings to be mounted prior to installation to allow for a high degree of control, efficiency and safety.



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