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Bearing installation skills

by:JNSN     2021-10-27
Bearing damage is commonplace, but did you know that 80% of bearings fail prematurely because they are not installed correctly. The correct installation of the bearing can not only increase the service life of the bearing and reduce the cost, but also greatly improve the production efficiency.

Bearing installation is very different from conventional parts and equipment. In order to achieve 'tight fit

Before installation, it is necessary to confirm whether the bearing is well preserved, which is an important prerequisite to ensure the installation of the bearing.

Bearing storage

Bearing storage has relatively strict requirements on the environment

●The storage environment such as a warehouse, the temperature should be maintained at 0-40 degrees, and the humidity should be maintained below 60%

●No large amount of dust and corrosive gas

New bearings will be packaged intact and equipped with anti-rust oil protection when they leave the factory. Try to maintain the original packaging before preparing for use to avoid or reduce the bearing products caused by failure to take protective measures. Something rusty happened.

Installation of the bearing

After ensuring that the properly stored bearing is intact, you can start the formal installation. Usually, you can 'install the elephant in the refrigerator' in three steps.

The first step is to make adequate preparations

● Clean and tidy operating space

As a precision component, the assembly process has higher requirements for operating space. A clean and tidy space is helpful to avoid Early damage to the bearing caused by the introduction of impurities.

●Prepare in advance the parts and tools needed during the installation process

Prepare in advance the necessary parts and tools during the entire installation process, including screws and nuts, threaded glue, gaskets, heaters (or freezer) , Spreader, torque wrench, inner and outer micrometer, magnetic seat, dial indicator (or dial indicator), feeler gauge, height gauge, spring scale, cleaning agent, rag, dust-free paper, and other auxiliary devices.

●Measure and record the dimensions of key parts in advance

According to the general bearing design, the rotating parts are required to have an interference fit, and the stationary parts can be selected for clearance fit. Compared with heavy shafts and bearing seats, bearings are a relatively disadvantaged group and will be affected by the shape of shafts or bearing seats. Before installation, it is necessary to measure and record the dimensions of key parts in advance to avoid the impact of the installation of unqualified parts on the bearing.

The second step is to choose the appropriate installation method.

We take the most common case where the inner ring rotates with an interference fit on the shaft and the outer ring has a clearance fit as an example to illustrate the installation method of the bearing.

For bearings with an interference fit, they are usually installed by heating the inner ring to expand or pressing directly into the press (only suitable for bearings with small dimensions).

● Heating and expansion of the inner ring

Heating method of the bearing inner ring: The bearing inner ring is usually heated by induction, heating furnace and oil bath. Do not use acetylene for heating, because it is random and uncontrollable, which may cause the bearing to overheat or even be scrapped.

Comparison of common heating methods:

Skills to master heating temperature: ordinary industrial bearings stipulate that the maximum heating temperature does not exceed 120 degrees Celsius, and the time does not exceed 8 hours; the maximum heating temperature of precision bearings does not exceed 66 degrees Celsius. In many cases, the bearing does not need to be heated to the highest temperature. The following formula can be used to calculate the amount of expansion ΔL caused by heating.

ΔLu003d α*ΔT*d

α: 11.7*10 -6 Metal thermal expansion coefficient

ΔT: The difference between heating temperature and ambient temperature (degrees Celsius)

d: bearing inner diameter (mm)

Although in theory, the installation can be completed as long as the heating expansion is greater than the interference, but in fact, the installation cannot be directly operated at this temperature. The temperature required for installation must be greater than this value. The time difference between heating and installation will cause a slight drop in temperature. In addition, the installation process cannot be completely aligned, and the minimum clearance reserved for the convenience of installation will also affect the installation. Therefore, the actual heating temperature selection needs to integrate the calculation results of this formula and the above factors.

For the same reason, if the outer ring needs to be frozen to install applications with interference fit, the same formula is used and the same factors are considered, but the inner diameter value of the bearing is replaced with the outer diameter value of the outer ring.

●Pressing in by a press

This method is only suitable for small size bearings.

First of all, the pressure needs to be matched in place. According to the formula, the required press tonnage can be calculated. Secondly, select the appropriate tooling to match the press head and the bearing parts to be pressed, usually the sleeve-like parts are in contact with the bearing parts all around. Finally, and one of the most important steps, the pressure should be directly applied to the parts that need to overcome the interference force. For example, if there is interference in the inner ring, the outer ring should not be pressed, and the raceway and rollers can be used to transfer the force to the inner ring to achieve press-fitting, which will cause damage to the bearing raceway.

The third step is post-installation inspection, double insurance

No matter which installation method is used, the inspection after installation can avoid the inadequate bearing press-fitting caused by negligence in some steps.

For the bearing installed by the press, if the fillet radius of the shoulder part is too large, so as to exceed the fillet of the bearing, then the inspection after installation will become a correction such as improper press-fitting, machining error, Necessary procedures for pre-order missed inspections and other problems.
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