Classification and Application of Grease Base Oils

Grease is primarily composed of base oil (70%~90%), thickener, and additives. As the core carrier of grease, base oil directly defines its key performance limits and application scopes. Below is a detailed breakdown of its classification, characteristics, and application scenarios based on base oil types and industry standards.

I. Mineral Oil-Based Base Oils

They correspond to Group I, II, and III in the API base oil classification (Group III oils are sometimes categorized as synthetic hydrocarbons due to their deep hydroisomerization process and performance approaching that of synthetic hydrocarbons).

1. Characteristics

Boasting abundant raw material sources, low production costs, and mature, stable processes, their comprehensive performance meets the requirements of most conventional operating conditions, making them the most widely used base oil type to date.

2. Application

Suitable for manufacturing various general-purpose and cost-effective greases, they are mainly used to lubricate ordinary machinery under normal temperature, medium-low speed, light-to-medium load, and non-extreme environments, covering basic civil and industrial fields such as bearings of general mechanical equipment, gearboxes, and textile machinery.

II. Synthetic Oil-Based Base Oils

When mineral oil-based base oils fail to meet the demands of harsh operating conditions (e.g., wide temperature ranges, extreme pressure, and strong chemical corrosion), synthetic oil-based base oils become the preferred solution. Classified by chemical structure, they fall into the following categories, all belonging to Group V API base oils except PAO, which is classified as Group IV.

 (I) Synthetic Hydrocarbon Oils (SHC)

The core type is polyalphaolefin (PAO), one of the most widely applied categories in synthetic oils.

1. Characteristics

They offer a wide temperature adaptation range (excellent low-temperature fluidity with a pour point below -60℃ and strong high-temperature oxidation stability, resisting aging and degradation during long-term service). Among synthetic oils, PAO stands out for its cost-effectiveness with controllable costs. Featuring a non-polar molecular structure, it exhibits excellent compatibility with most rubbers and plastics without causing swelling or shrinkage. However, its sealing adaptability to ethylene-propylene-diene monomer (EPDM) rubber is suboptimal.

2. Application

PAO is widely used in grease formulations requiring a wide temperature range and long service life. Typical applications include automotive wheel bearing grease, aerospace equipment grease, grease for construction machinery operating under low temperatures, and bearing grease for precision instruments.

 (II) Ester Oils

1. Characteristics

Ester oils deliver outstanding lubricating load-carrying capacity, high oil film strength, and excellent extreme pressure and anti-wear properties, along with good low-temperature fluidity and stable viscosity-temperature characteristics. As polar molecules, they readily adsorb onto metal surfaces to form a robust lubricating film. However, their polarity tends to cause moderate swelling of some rubber seals—a property that can be leveraged in specific scenarios to enhance sealing performance and prevent medium leakage, but requires caution in applications demanding strict dimensional accuracy. Their heat resistance and oxidation stability surpass those of mineral oils.

2. Application

Often blended with PAO in high-performance grease and engine oil formulations, the combination of polyurea thickener and ester oil is widely recognized as a premium high-temperature, long-lasting lubrication solution in the industry. It is extensively used in harsh lubrication scenarios such as automotive generators, starter bearings, high-temperature motor bearings, high-temperature components of metallurgical equipment, and special industrial machinery.

 (III) Polyethylene Glycol (PAG) Oils

1. Characteristics

PAG oils offer excellent rubber compatibility, particularly with sealing materials like natural rubber and EPDM, effectively preventing seal aging and failure. They generate minimal carbon deposits, ensuring high cleanliness, and feature low toxicity

and superior environmental friendliness. Their viscosity-temperature characteristics and oxidation stability are also better than those of mineral oils.

2. Application

They are mainly used in lubrication scenarios involving direct contact with rubber components, including refrigeration compressors, braking systems, sealing parts of hydraulic systems, and rubber components in household appliances.

 (IV) Silicone Oils

1. Characteristics

Silicone oils boast the widest temperature adaptation range (covering -60℃ to 250℃, with special grades capable of withstanding over 300℃), exceptional oxidation stability, and consistent performance under long-term high-temperature conditions. They are highly hydrophobic and offer excellent electrical insulation properties. However, their key drawback is poor lubricating load-carrying capacity and insufficient extreme pressure and anti-wear performance, making them unsuitable for heavy-load steel-on-steel friction pairs.

2. Application

They are suitable for lubrication scenarios requiring high temperature, light load, corrosion resistance, and electrical insulation, such as the assembly and operation lubrication of plastic/rubber components, O-ring seal lubrication, high-temperature oven bearings, precision instruments, and insulation protection of electrical equipment.

 (V) Perfluoropolyether (PFPE) Oils

As a top-tier category in synthetic oils, PFPE oils excel in adapting to extremely harsh operating conditions.

1. Characteristics

They exhibit extremely high chemical inertness, resisting strong acids, strong alkalis, strong oxidants, and various corrosive media. With top-tier heat resistance and oxidation stability among synthetic oils, they produce no carbon deposits during long-term use. Their main disadvantage is extremely high production costs, which limits their application scope.

2. Application

Designed specifically for extreme environments, PFPE oils are used in chemical equipment (corrosion-resistant pumps, valves), oxygen systems, aerospace vehicles, copier fuser rollers, semiconductor manufacturing equipment, and other harsh conditions where ordinary lubricating greases cannot survive, such as strong corrosion, high temperature, and high purity requirements.