What Is an Allostatic Load?

Static load rating is one of the most important technical characteristics of rolling bearings.

Together with the rated dynamic load, it constitutes two basic aspects of the rolling bearing load performance. The rated static load indicates the ability of the bearing to resist permanent deformation, and the rated dynamic load indicates the ability of the bearing to withstand fatigue failure.

Compared with the old standard GB4662-84 (equivalent to ISO76-1978), the amendment made in GB / T4662-93 is substantial. The definition of static load rating, calculation formula, theoretical and experimental basis, and practical effects are all related The past is not consistent. In its essence, it is a new concept in the field of rolling bearing technology. The calculation of the static load safety factor Fs of the static load bearing helps to determine whether the selected bearing has a sufficient static load rating.

For bearings that must run smoothly and have extremely low noise, a high value of FS is required; where only moderate running noise is required, a smaller FS can be selected; generally the following values are recommended:

FS = 1.5 ~ 2.5 is suitable for low noise level;

FS = 1.0 ~ 1.5 is suitable for general noise level;

FS = 0.7 ~ 1.0 is suitable for medium noise level.

The rated static load CO [KN] has been listed in the table for each product specification

Static load bearing bearing cleaning

When disassembling the bearing for maintenance, first record the appearance of the bearing, confirm the remaining amount of lubricant, and take a sample of the lubricant for inspection before washing the bearing. As cleaning agents, gasoline and kerosene are commonly used. The cleaning of the disassembled bearing is divided into coarse cleaning and fine cleaning, which are respectively placed in the container, and the bottom of the metal mesh pad is first placed so that the bearing does not directly contact the dirt of the container. During rough cleaning, if the bearing is rotated with dirt, it will damage the rolling surface of the bearing and should be paid attention to. In the rough cleaning oil, use a brush to remove any stickies. After it is approximately clean, switch to fine cleaning. Fine cleaning is to carefully wash the bearing while rotating it in the cleaning oil. In addition, the cleaning oil should always be kept clean.

Overhaul and judgment of static load bearings

In order to determine whether the disassembled bearing can be used, it should be checked after the bearing is cleaned. Check the condition of the raceway surface, rolling surface, mating surface, the wear of the cage, the increase of the overall eccentric bearing clearance, and any irrelevant reduction in dimensional accuracy and damage. For non-separable small ball bearings, use one hand to support the inner ring horizontally, and check whether the outer ring is smooth.

High temperatures often indicate that the bearing is already in an abnormal condition. High temperature is also harmful to the lubricant in the I bearing. Sometimes overheating of the bearing can be attributed to the lubricant of the spherical bearing. If the bearing is operated at a temperature exceeding 125 degrees Celsius for a long time, it will reduce the bearing life. The causes of high temperature bearings include: insufficient lubrication or excessive lubrication, lubricants contained in magazines, excessive load, damage to overall eccentric bearings, insufficient clearance, and high temperature friction caused by oil seals. Both the rolling elements of the bearing and the raceway surfaces of the inner and outer rings are subject to cyclical pulsating loads, resulting in cyclically varying contact stresses.

When the number of stress cycles reaches a certain value, fatigue spalling occurs on the working surfaces of the rolling elements or the inner and outer ring raceways. If the bearing is overloaded, this fatigue will be exacerbated. In addition, the bearing is not installed properly, the shaft is bent, and the raceway peeling phenomenon will also occur. Fatigue spalling of the bearing raceway will reduce the running accuracy of the shaft, causing the mechanism to vibrate and noise. Burnt outer spherical bearings have tempered colors on their raceways and rolling elements. The causes of burns are generally insufficient lubrication, the quality of the lubricant does not meet the requirements or deterioration, and the bearing assembly is too tight. The uneven pits on the contact surface between the roller raceway and the roller of the bearing indicate the plastic deformation of the overall eccentric bearing. The reason is that under the action of a large static or impact load on the bearing, the local stress on the working surface exceeds the yield limit of the material. This situation generally occurs on low-speed rotating bearings.

Static load bearing preparation

1. Remove the decorative cover and dust cover of the bearing head;

2. Remove the tire nut and tire, taking care not to hurt the thread of the tire bolt. In the case of a disc brake, the brake should be removed and used to remove the lock ring or pin.

3. Remove the bearing with special tools;

4. Scrape off the old grease in the bearings, journal and bearing cavity, clean the bearing and journal with a cleaning agent and wipe dry with a cloth, and finally clean the bearing cavity with a cloth.

5. Check the bearings and bearing races, and find that there are cracks, fatigue peeling and loose bearing rollers, etc. The bearings should be replaced. If pitting is found on the bearing race, the bearing should also be replaced.

6. Check the fit between the bearing inner diameter and the journal. The fit clearance should not be greater than 0.10mm. When measuring the journal, it should be measured at the upper and lower two parts of the vertical ground (the largest wear part). If the fit clearance exceeds the specified use limit, the bearing should be replaced to restore the normal fit clearance. Burrs and pits on the journal are not allowed to reduce the gap.

7. After all parts meet the requirements, grease the inner bearing and put it in the bearing.

8. When applying grease to the bearing cavity, care should be taken to squeeze the grease into the bearing until the grease comes out from the other side of the bearing. Apply a thin layer of grease to the bearing cavity and shaft cap to prevent rust. Be careful not to apply too much grease in the bearing cavity, otherwise it will affect heat dissipation and braking.