Maintenance Methods to Prevent Premature Damage of Koyo Thrust Ball Bearing
Maintenance Methods to Prevent Premature Damage of Koyo Thrust Ball Bearing
2022年3月25日
Physical and Chemical Indexes and Composition of Commonly Used lubricating Grease
Physical and Chemical Indexes and Composition of Commonly Used lubricating Grease
2022年3月25日

The Basic Functions of Lubricating Grease

  • Many scholars have done a lot of research work on the lubrication mechanism of grease, especially soap based grease. However, there is no unified understanding so far, which needs to be solved by further research in the future.Basic Precautions for Grease Storage
  • Generally speaking, most scholars believe that soap based grease is a three-dimensional network structure system composed of metal soap and base oil absorbed in soap. According to the concept of soap oil gel particle dispersion, saponin grease is a dispersing system with oil as dispersing medium and soap oil gel particles as dispersing phase. Therefore, there are the following views on the action mechanism of grease lubrication bearing.Basic Precautions for Grease Storage

The Basic Functions of Lubricating Grease

It is generally believed that due to the action of metal soap or thickener, the base oil is brought to the contact surface of friction pair, and the base oil is released by external force on this surface for lubrication. This view only sees that the base oil plays a real role in lubrication, which is only put forward according to the following test results, that is, the lubricating grease prepared by thickening the same base oil with different bowl chemicals has the same friction coefficient.

 Another view is that both base oil and thickener can play a lubricating role. This is based on the comparison test results of grease and separate base oil, and the relationship between the lubricating bearing performance of grease and the shear strength of blocker. A more comprehensive view is that the lubricating effect of grease is partly due to the role of base oil, but more importantly, it depends on the lubricating performance of base oil and thickener after the special combination of paste and base oil.Basic Precautions for Grease Storage

1) Thixotropy

The basic characteristic of grease is thixotropy. When an external force is applied, the flow of grease gradually softens and the viscosity decreases, but once it is at rest, the consistency increases (recovers) again after a period of time (very short). This characteristic is called thixotropy. This characteristic of grease determines that it can be lubricated in parts that are not suitable for lubricating oil lubrication, and shows its excellent performance.Basic Precautions for Grease Storage2) Viscosity

Grease is usually expressed by apparent viscosity or similar viscosity. When describing the viscosity of grease, the temperature and shear speed must be indicated. Similar viscosity indexes can be used to control its low-temperature fluidity and pumpability.Basic Precautions for Grease Storage

3) Strength limit

The strength limit of lubricating grease refers to the small shear stress required to cause the sample to start flowing, also known as the ultimate shear stress. The strength limit of grease is a function of temperature. The higher the temperature, the smaller the strength limit of grease. When the temperature decreases, the strength limit of grease becomes larger. Its size depends on the type and content of thickener and has a certain relationship with the process conditions of grease making.Basic Precautions for Grease Storage

4) Low temperature fluidity

One of the important indicators to measure the low-temperature performance of grease is the low-temperature torque, that is, the degree to which the grease blocks the rotation of low-speed flow bearing at low temperature (- 20 ° C). The Low-Temperature Torque of grease is expressed by the average value of starting torque and torque after rotating for 60mm.Basic Precautions for Grease Storage

5) Drop point the low temperature of lubricating grease when it reaches a certain fluidity under specified conditions is called drop point. The dropping point of lubricating grease is helpful to identify the type of lubricating grease and roughly estimate the high service temperature of lubricating grease. Generally speaking, for soap based grease, its service temperature should be 20 ~ 30 ° C lower than the dropping point. The higher the dropping point, the better its heat resistance.Basic Precautions for Grease Storage

 

Technical requirements for Timken non-standard bearing

Evaporation

  • The evaporation (degree) of grease indicates the degree of volatilization of grease when the grease is used for a long time under high temperature conditions. The smaller the evaporation, the better. The evaporation of grease mainly depends on the properties and fraction composition of lubricating oil.
  •  Colloidal stability
  • The colloidal stability of lubricating grease refers to the ability of lubricating grease to maintain the stability of colloidal structure at a certain temperature and pressure and prevent the precipitation of lubricating oil from lubricating grease, that is, the ability of lubricating grease to resist oil separation. 
  • Usually, the quantity of oil precipitated from lubricating grease is converted into mass fraction. The colloidal stability of lubricating grease reflects the oil trend of lubricating grease in long-term storage and practical application. If the colloidal stability of lubricating grease is poor, serious oil separation is easy to occur under the action of heating, pressure and centrifugal force, resulting in rapid reduction of service life, thickening and drying of lubricating grease and loss of lubrication.Basic Precautions for Grease Storage
  •  Oxidation stability
  • Oxidation stability refers to the ability of lubricating grease to resist the action of heat and oxygen and keep its properties from permanent change when it is stored for a long time or used at high temperature for a long time. Due to oxidation, the content of free alkali is often reduced or the content of free organic acid is increased, the dropping point is reduced, the appearance color is darker, there is a strange odor, the consistency, strength limit and similar viscosity are reduced, and corrosive products and substances that destroy the structure of lubricating grease are generated, resulting in the separation of soap and oil. 
  • Therefore, in the long-term storage of lubricating grease, it should be stored in a dry and ventilated environment to prevent sunlight exposure, and the changes of free alkali or free organic acid, corrosivity and other items should be checked regularly to ensure its quality and performance.The Basic Functions of Lubricating Grease
Basic Precautions for Grease Storage