01

The shelf life of grease

1.General Shelf Life Range

The shelf life of grease usually ranges from 1 to 5 years, and the specific duration depends on various factors. Under ideal storage conditions, the shelf life of unopened ordinary grease may be close to 5 years, while that of some special or high-performance greases may be shorter, approximately 1 to 2 years.

2.Factors Affecting Shelf Life

Temperature: The appropriate storage temperature is crucial for the shelf life of grease. Generally speaking, grease should be stored in a cool and dry place, and the ideal storage temperature is between -10°C and 30°C. If it is exposed to a high-temperature environment (such as above 40°C) for a long time, the base oil in the grease is prone to volatilization, and the additives may decompose, thus shortening the shelf life. In a low-temperature environment (such as below -20°C), the structure of the grease may change, but if it returns to the appropriate temperature and the structure is not damaged, the impact on the shelf life is relatively small.

Humidity: A high-humidity environment easily causes the grease to absorb water, resulting in emulsification and deterioration of the grease. If the humidity exceeds 80%, the metal soap thickener in the grease may react with water, causing the grease to lose its lubricating properties and shortening the shelf life.

Illumination: When exposed to sunlight or strong light for a long time, some components in the grease will undergo photochemical reactions, accelerating deterioration. For example, ultraviolet rays may cause the decomposition of antioxidants in the grease, reducing the antioxidant capacity of the grease and thus affecting the shelf life.

Type of Base Oil: Grease is composed of base oil, thickener and other components. Different types of base oils, such as mineral oil and synthetic oil, have different chemical stabilities. Mineral oil-based grease has relatively poorer chemical stability compared to synthetic oil-based grease, and its shelf life may be shorter. For example, under good storage conditions, the shelf life of mineral oil-based grease may be 2 to 3 years, while that of synthetic oil-based grease can reach 3 to 5 years.

Type of Thickener: Common thickeners include lithium-based, calcium-based, and complex lithium-based, etc. Different thickeners have an impact on the stability of the grease. For example, the grease with lithium-based thickener has better stability and a relatively longer shelf life. The grease with calcium-based thickener may have a relatively shorter shelf life due to reasons such as being prone to absorb water.

Additive Components: To improve the performance of the grease, additives such as antioxidants and rust inhibitors are added. The quality and content of additives will affect the shelf life of the grease. If the content of additives such as antioxidants is sufficient and of good quality, the grease can better resist oxidation and other deterioration processes, and the shelf life will be extended.

3.Storage Conditions

Temperature: The appropriate storage temperature is of great importance for the shelf - life of grease. Generally, grease should be stored in a cool and dry place, and the ideal storage temperature is between - 10°C and 30°C. If it is in a high - temperature environment (such as above 40°C) for a long time, the base oil in the grease is easy to volatilize and the additives may decompose, thus shortening the shelf - life. In a low - temperature environment (such as below - 20°C), the structure of the grease may change. However, if it returns to the appropriate temperature and the structure is not damaged, the impact on the shelf - life is relatively small.

Humidity: A high - humidity environment easily causes the grease to absorb water, resulting in the emulsification and deterioration of the grease. If the humidity exceeds 80%, the metal soap thickener in the grease may react with water, causing the grease to lose its lubricating performance and shortening the shelf - life.

Illumination: When exposed to sunlight or strong light for a long time, some components in the grease will have photochemical reactions and accelerate deterioration. For example, ultraviolet rays may decompose the antioxidants in the grease and reduce the antioxidant capacity of the grease, thus affecting the shelf - life.

02

The Issue of Using Expired Grease

1.Reasons Why It Is Not Recommended to Use

Performance Degradation: In expired grease, the base oil may have partially volatilized, resulting in a reduction in the lubricating performance of the grease. For example, in high-speed rotating mechanical parts, using expired grease may not be able to provide a sufficient oil film to reduce friction, increasing the risk of component wear.

Oxidation and Rancidity: Over time, grease will undergo oxidation reactions and produce acidic substances. The content of acidic substances in expired grease may increase, which will not only corrode metal parts but also damage the structure of the grease itself, causing changes in its consistency and preventing it from effectively adhering to the surface of parts to play a lubricating and protective role.

Increased Impurities: During storage, expired grease may be contaminated with impurities such as dust and moisture. These impurities will exacerbate the wear of mechanical parts and may also clog the oil passages and filters in the lubrication system, affecting the normal operation of the lubrication system.

2.Considerations for Special Situations

For some non-critical, low-speed, and light-load equipment, if after detailed inspection and evaluation, it is found that there are no obvious changes in the appearance and consistency of the expired grease and there is no better substitute available, it can be used with caution in the short term. However, during the use process, the operating condition of the equipment needs to be closely observed. Once any abnormality is detected, the grease should be replaced immediately. Nevertheless, this approach carries certain risks and is not suitable for high-precision, high-value equipment with strict lubrication requirements.