During long-term storage, the physical and chemical properties of grease will change due to the influence of external temperature, humidity and the action of oxygen in the air. In addition, due to the mixing of mechanical impurities such as dust, sand cores, rust, and moisture, as well as contamination by microorganisms, its performance will also be reduced.

　　Changes in the storage stability of grease are generally manifested as drop point drop, increase or decrease in penetration, decrease in free base, and increase in free organic acid. Corrosion test failed, bearing leakage increased and mechanical stability deteriorated.

　　The storage stability of grease is related to its composition and storage conditions. Hydrocarbon-based grease has good colloid stability and is not easy to absorb water. Sodium-based and calcium-based greases are easy to absorb water. Lithium-based greases thickened with low-viscosity oil have poor colloidal stability and serious oil separation. Silicone oil and diester grease do not evaporate at room temperature. Pentonite greases have good water resistance. Phthalo bronze grease does not oxidize with air below 350℃.