What is the relationship between the colloidal stability of high temperature grease and oil separation?
December 03, 2021
The ability of high temperature grease to resist oil separation during long-term storage and use is called colloidal stability. Generally speaking, if the gel stability of the grease is good, the oil content is difficult, and if the gel stability is poor, the oil content is easy. The stability of high temperature grease colloid depends on its composition and structure. Different raw materials, formulations and cooling conditions have an impact on the colloidal stability of the dispersion system. Generally speaking, the increase of the viscosity of the Base Oil of high-temperature grease will increase the stability of its colloid. However, if the viscosity is too high, the growth of soap crystals will be hindered, and the high-temperature grease made is unstable. At the same time, the chemical composition of the base oil will also affect the stability of the high-temperature grease colloid. The compatibility between paraffin base oil and soap is not good, and it is difficult to use it to make stable grease, while the high temperature grease made with naphthenic base oil is more stable. In addition, when the soap content is too small, the high-temperature grease is easy to separate the oil, and the increase in temperature and storage time will increase the oil separation. High-temperature grease is beneficial in the use of a small amount of oil separation, and the separated oil can play a lubricating effect. However, if the oil separation speed is too fast, the base oil is lost too much, and the life of the high-temperature grease will be shortened.
How to separate grease: There are two ways of grease separation: static oil separation and dynamic oil separation. In addition to the quality factor of the grease itself, these two factors can also cause oil separation. Static oil separation: Affected by storage conditions, storage temperature, storage time, vibration of the container during storage, and whether the grease surface is smooth, oil separation is more obvious in any of the following situations 1. Low base oil viscosity (ISO68 and below) 2. Low grease viscosity (NLGI00, NLGI0, NLGI1) Under normal storage period and storage conditions, the oil separation under these conditions will not affect the performance of the grease. Dynamic oil separation: Dynamic oil separation is mainly used for mechanical extrusion or high temperature of lubricating grease. Dynamic oil separation has a great influence on the use of grease and should be controlled. The following conditions can cause or aggravate dynamic oil separation: 1. Mixing different greases: The colloidal structure of the thickener is destroyed, resulting in oil separation. 2. Vibration or centrifugal force: Continuous vibration or centrifugal force will cause the grease to separate. 3. Grease is contaminated: Dust falls into the grease, so pay attention to sealing during storage. 4. Too much grease is added: it will lead to high temperature, resulting in increased oxidation of grease, and rapid separation of base oil and thickening agent. 5. Mechanical reasons: improper installation of equipment and high load, such as improper selection of clearances, resulting in poor lubrication and high temperature bearing operation. 6. Grease drying: The dry grease adheres to the equipment and blocks, the base oil flows out from both sides, the viscous agent accumulates on the block, the local lubrication is poor, the temperature rises, and the high temperature aggravates the separation of base oil and viscous agent. Therefore, the old grease should be removed when changing the oil.
