Bearing greases are used in a wide range of applications and work conditions vary greatly. Performance requirements for bearing greases vary from machine to machine.The performance of bearing grease is a comprehensive reflection of the composition and preparation technology of bearing grease.The evaluation of the performance of bearing grease is not only decisive in production and research but also essential in the selection and inspection of bearing grease by the service department.According to the specific conditions of grease parts used in automobile and construction machinery, the basic requirements of bearing grease are: proper consistency, good high and low temperature performance, good extreme pressure, good resistance to water, corrosion, rust and stability, etc.
The concept of the thickness of the bearing grease to express the structure of the system is to determine the degree of deformation of the bearing grease structure under the specified shear force or shear rate.It is an important performance index related to the retention and sealing performance of the bearing grease on the lubricated part and the pumping and filling mode of the bearing grease.Bearing grease is used at certain lubrication points because it has a certain consistency which gives it a certain resistance to loss.Bearing greases of different consistencies are used under different working conditions such as mechanical speed, load and ambient temperature. Therefore, consistency is an important indicator of bearing greases.
The consistency grade of bearing grease can be expressed by coning degree.The taper degree of the bearing grease is the depth at which the standard cone of the specified weight is inserted into the bearing grease sample at the specified time and temperature, expressed in (L /10)mm.Determination of coning degree of bearing grease may be conducted in accordance with the method specified in Determination of Coning Degree of Bearing Grease (GB/T269-91).Bearing grease coning usually includes four kinds of non-working coning generally does not represent the consistency of bearing grease in the middle as effectively as working coning usually it is best to use working coning when testing bearing grease.Extended working tapering is applicable to tapering measured over 60 times.Determination of cone penetration of bearing grease: release the cone assembly from the cone penetration meter at 25 degrees to a depth of 5s for the cone to be immersed separately
Determine the four coning degrees of bearing grease.
The coning degree reflects the deformation and flow performance of bearing grease under the condition of low shear rate.The higher the taper value, the softer the fat, that is, the smaller the consistency, the easier the deformation and flow;The lower the taper value, the harder the grease, that is, the greater the consistency, the less deformation and flow.It can be seen that coning degree can effectively represent the consistency of bearing grease, which is an important basis for selecting bearing grease.The cone penetration range is used to classify the consistency grade of bearing grease in China.
2. High temperature performance
Temperature has a great influence on the fluidity of bearing grease. When the bearing grease becomes soft, its adhesion decreases and it is easy to be lost.In addition, under higher temperature, the evaporation loss of bearing grease is easy to increase.The main reasons for the failure of bearing grease are the shrinkage of gel and the evaporation loss of base oil, that is, the speed of the clearance process of bearing grease is related to its service temperature.Bearing grease with good high temperature performance can maintain its adhesion property at high service temperature and the deterioration and failure process is also slow.The high temperature performance of bearing grease can be evaluated by such indexes as drop point, evaporation degree and bearing loss.