Comprehensive Analysis of Lubricant Characteristics in the Market

author: Yibuzz_XiaoYiChong

2026-01-28

1. Classification of Lubricants

Lubricants come in a wide variety and are typically classified into four major categories based on their physical state: liquid lubricants, semi-solid lubricants, solid lubricants, and gaseous lubricants. Additionally, according to the national standard GB/T498-1987, lubricants and related products are categorized as Class L products, so all lubricant codes begin with the letter "L."

- Liquid Lubricants: These include mineral oils, synthetic oils, animal and vegetable oils, and water-based liquids.
- Semi-Solid Lubricants (Greases): These are semi-fluid pastes at room temperature and pressure, made by mixing base oils with thickeners in specific proportions.
- Solid Lubricants: These substances exist in a solid state between friction interfaces, providing lubrication. Common solid lubricants include soft metals, metal compounds, organics, and inorganics such as molybdenum disulfide, graphite, and polytetrafluoroethylene (PTFE).
- Gaseous Lubricants: Similar to liquids, gases also follow the physical laws of fluids and can act as lubricants under specific conditions. Common gaseous lubricants include air, helium, nitrogen, and argon.

2. About Lubricating Oils

Lubricating oil, a type of liquid lubricant, primarily refers to mineral and synthetic oils, especially mineral oils. Globally, annual production of mineral lubricating oil exceeds 20,003 tons, accounting for over 95% of total lubricant production.

- Lubricating Oil Codes and Their Meanings: The codes for lubricating oils follow the GB/T7631.1-1987 standard, comprising category, type, and numerical values in the format: Category + Type + Number.
- Category: Indicates the classification of petroleum products, with "L" representing lubricants.
- Type: Groups products based on application scenarios, e.g., A for total loss system oils, C for gear oils. The first letter in the type column represents the product type, which may also include additional letters for further subdivision.
- Number: Represents viscosity grade, equivalent to the kinematic viscosity at 40°C (unit: mm²/s). According to GB/T3141-1994, there are 20 viscosity grades, such as 2, 3, 5, 7, 10, etc.
For example, L-AN100 represents a total loss system oil with a viscosity grade of 100 mm²/s. At 40°C, its kinematic viscosity ranges from 90 to 110 mm²/s, with an intermediate value of 100 mm²/s.

Key Quality Indicators of Lubricating Oils:

- Color: The color of lubricating oil is closely related to the refining degree of the base oil and the additives used. During use or storage, oxidation may cause the oil to degrade and change color, indicating its condition. For instance, milky white oil may indicate water or bubbles, while darkening may signal oxidation or contamination.
- Viscosity: Viscosity measures the internal friction resistance of the oil and is a critical factor for classification, grading, quality assessment, and selection. Dynamic viscosity measures internal friction under specific shear stress, while kinematic viscosity measures internal friction under gravity. China categorizes lubricating oils into 20 viscosity grades for easier classification and selection.

3. ISO Viscosity Classification

Viscosity is a critical quality indicator for lubricating oils. If the viscosity is too low, it can lead to the formation of semi-liquid lubrication or boundary lubrication, accelerating wear of friction pairs and potentially causing oil leakage. Conversely, excessively high viscosity can affect the fluidity, penetrability, and heat dissipation of the lubricating oil, increase internal friction resistance, make starting difficult, and result in higher power consumption. Therefore, selecting an appropriate viscosity is key to ensuring sufficient lubrication for friction pairs.

In addition, the viscosity-temperature characteristics of lubricating oil are also an important consideration. These characteristics describe how the properties of lubricating oil change with temperature. Currently, the viscosity index (VI) is commonly used to measure the quality of viscosity-temperature characteristics. A higher VI indicates that the viscosity changes less with temperature, making the oil more suitable for applications with variable or wide temperature ranges.

At the same time, the pour point and freezing point are important indicators of the low-temperature performance of lubricating oil. The freezing point refers to the highest temperature at which the lubricating oil ceases to flow under specified cooling conditions, while the pour point indicates the lowest temperature at which the oil can still flow under specific conditions. In practical applications, the pour point more effectively reflects the low-temperature fluidity of the oil, so it is now more commonly used internationally to characterize the low-temperature performance of lubricating oils.

Furthermore, the flash point and acid value are also significant parameters of lubricating oil quality. The flash point is the lowest temperature at which the oil's vapor, mixed with air under specified conditions, ignites briefly when exposed to a flame. The acid value refers to the mass of potassium hydroxide required to neutralize the organic acids in 1g of lubricating oil. It not only reflects the refining depth of new oil but also indicates the degree of oxidative deterioration of used oil during operation.

- Water Content: The water content in lubricating oil is a critical indicator. When the temperature drops below 0°C, water can worsen the viscosity-temperature characteristics of the oil. As the temperature rises, water vaporizes, creating bubbles that disrupt the oil film, causing emulsification and reducing viscosity, thereby impairing lubrication performance.
- Mechanical Impurities: These refer to all suspended and settled solid impurities in lubricating oil. Such impurities can damage the oil film and accelerate wear of the friction pairs.
- Carbon Residue: Carbon residue refers to the coke-like residue formed when lubricating oil is heated and undergoes vaporization and decomposition in the presence of air. Its percentage in the oil reflects certain properties of the lubricating oil.

4. Common Types of Lubricating Oils

Loss System Lubricating Oil: Loss system lubricating oil mainly refers to Group A oils within the L-class lubricants. L-AN oil is a commonly used loss system oil, refined from mineral oil. In older standards, it was referred to as machine oil or mechanical oil, with viscosity grades ranging from L-AN5 to L-AN150, divided into 10 levels. At 40°C, its kinematic viscosity ranges from 4.41 to 165 mm²/s, with a pour point not exceeding -5°C and a flash point between 80°C and 180°C. It is mainly suitable for light-load and general machinery loss lubrication systems or short oil change cycle oil-immersed lubrication systems, but is not suitable for circulating lubrication systems.

Gear Oil: Gear oil, categorized as Group C in L-class lubricants, is specifically designed for lubricating gear transmission systems, including worm gear sets. It must possess appropriate viscosity, excellent thermal stability, oxidation resistance, outstanding extreme pressure anti-wear properties, anti-emulsification, shear stability, and rust and corrosion resistance. This type of lubricant is typically formulated by adding specific additives to refined mineral or synthetic oils.

Gear oil can be divided into three main categories: industrial enclosed gear oils, industrial open gear oils, and automotive gear oils. Industrial enclosed gear oils are further subdivided into seven grades—L-CKB, L-CKC, L-CKD, L-CKE, L-CKS, L-CKT, and L-CKG—to meet lubrication needs under various working conditions. Additionally, industrial open gear oils are available in four grades: L-CKH, L-CKJ, L-CKL, and L-CKM.

Industrial Open Gear Oil: Industrial open gear oils include various types such as L-CKH, L-CKJ, and L-CKM. Currently, China adheres to petrochemical industry standards, categorizing these oils into five grades—68, 100, 150, 220, and 320—based on their mid-range kinematic viscosity at 100°C.

Compressor Oil: Compressor oil is classified as Group D in L-class lubricants, specifically designed to lubricate internal friction components of compressors. It includes air compressor oil, gas compressor oil, refrigerating machine oil, and vacuum pump oil, each suited for different working conditions of compressors. The current grading standard divides them into five levels: 32, 46, 68, 100, and 150.

For air compressor oil, there are several types such as L-DAA, L-DAB, L-DAC, L-DAG, L-DAH, and L-DAJ, designed for different compressor types and conditions to meet various lubrication needs. For instance, L-DAA compressor oil is suitable for reciprocating compressors with discharge pressures below 1 MPa, while L-DAB compressor oil is suitable for medium, high-pressure, and multi-stage reciprocating compressors.

Additionally, there are gas compressor oils such as L-DGA, L-DGB, L-DGC, L-DGD, and L-DGE, each designed for compressor lubrication under different pressures and gas types. Refrigerating machine oil is another important category of lubricants.

Refrigerating machine oil is specifically designed for compression refrigeration machines. It requires a low pour point, good oxidation resistance, and moderate viscosity. National standards classify refrigerating machine oils into four grades: L-DRA/A, L-DRA/B, L-DRB/A, and L-DRB/B. Different grades are suitable for different types of refrigeration compressors, such as ammonia refrigeration compressors and large-capacity Freon refrigeration compressors.

Additionally, vacuum pump oil is characterized by high flash points, viscosity indices, and good oxidation stability, suitable for lubricating and sealing volumetric vacuum pumps and Roots vacuum pumps. Depending on gas corrosion and vacuum levels, vacuum pump oils are available in six types: L-DVA, L-DVB, L-DVC, L-DVD, L-DVE, and L-DVF.

Moreover, turbine oil is another essential lubricant. It is primarily used for lubricating high-speed turbines, turbine generators, and large hydroelectric generators. Turbine oils are classified into four grades based on viscosity: 32, 46, 68, and 100, further divided into steam turbine oils and gas turbine oils.

Lastly, hydraulic oil, though not part of the aforementioned categories, also plays a crucial role in industrial lubrication.

Hydraulic oil belongs to the H group of L-class lubricants. It is referred to as hydraulic oil when used as a working medium in hydrostatic systems (hydraulic transmission systems) and as hydraulic transmission oil when used in hydrodynamic systems (hydrodynamic transmission systems). Hydraulic oil has a variety of viscosity grades, including 10, 15, 22, 32, 46, 68, 100, and 150. Additionally, the oils used in hydraulic systems are categorized into 17 varieties, such as L-HH, L-HL, L-HM, etc., while those used in hydrodynamic systems are divided into two types: L-HA and L-HN.

Furthermore, there is bearing oil, another type of lubricant, which belongs to the F group of L-class lubricants. Bearing oil is primarily used for lubricating precision machine tool main bearings and other high-speed sliding bearings. It can also serve as a lubricant for general bearings or as oil for hydraulic systems. According to the SH/T0017-1989 industry standard for bearing oil, L-FC bearing oil, classified as an antioxidant and anti-rust type bearing oil, includes multiple grades and is suitable for lubricating various industrial machinery.

Lastly, we must consider grease. Grease is a gel-like lubricating material with unique semi-solid characteristics, positioned between liquid and solid states. It is synthesized from base oil, thickener, and additives under high temperatures and can also be regarded asa thickened lubricating oil. When writing grease codes, specific rules must be followed to ensure accuracy and standardization.

5. Classification and Coding of Lubricants

Lubricants, as an essential category of petroleum products, rely heavily on their classification and coding systems. In lubricant product nomenclature, "L" represents the basic category. The grouping of lubricating oils is determined by their application scenarios, represented by corresponding letters such as A, C, D, E, F, G, H, M, P, T, Z, etc. These letters not only appear at the beginning of the product type but may also be accompanied by additional letters to specify the variety further.

Moreover, numbers play a role in indicating viscosity grades in lubricant coding. These numbers correspond to the kinematic viscosity value at 40°C, measured in mm²/s. According to the GB/T3141 "Industrial Liquid Lubricants—ISO Viscosity Classification" standard, there are 20 available viscosity grades. For instance, L-AN100 denotes a total loss system lubricant with a viscosity grade of 100 mm²/s.

- Quality Indicators of Grease: As a unique lubricating material, the quality indicators of grease are of critical importance. Penetration (or cone penetration) is a commonly used indicator to evaluate the hardness (i.e., consistency) of grease. It reflects the depth to which a standard cone penetrates the grease under specified conditions. Additionally, moisture content is a significant indicator, as it directly affects the protective, chemical, and mechanical properties of the grease.
- Dropping Point: The dropping point, an essential indicator of grease, refers to the lowest temperature at which grease begins to melt and drops its first fluid droplet during heating. This indicator is crucial for determining the maximum temperature the grease can withstand during use. Typically, the maximum operating temperature of grease should be 20–30°C lower than its dropping point.
- Mechanical Impurities: Mechanical impurities in grease mainly include solvent-insoluble substances, such as inorganic salts, dust, and sand particles introduced from external sources. These impurities act as abrasives during friction, damaging the oil film and accelerating wear.
- Soap Content: Soap content, expressed as a mass percentage, indicates the amount of soap in grease and reflects its hardness. The soap content significantly influences the performance and effectiveness of grease.

6. Common Types of Lubricating Greases

- Calcium-Based Grease: Calcium-based grease uses natural calcium fatty acid as a thickener, thickening medium-viscosity mineral lubricating oil. It appears as a light yellow to dark brown paste, is not easily soluble in water, has strong water resistance, and offers good pumpability. Calcium-based grease is suitable for lubricating medium and low-load mechanical equipment in industries such as industrial, agricultural, and transportation sectors. However, due to its low dropping point, its usage temperature is limited. Therefore, it has been gradually replaced by more advanced greases like lithium-based grease in medium to heavy-load or high-temperature applications.
- Sodium-Based Grease: Sodium-based grease is made by thickening medium-viscosity mineral or synthetic lubricating oil with natural sodium fatty acid soap. It has a dark yellow to dark brown appearance and excellent high-temperature performance, capable of operating for extended periods at working temperatures of 120°C. However, its water resistance is relatively poor. Sodium-based grease is suitable for lubricating friction parts in industrial and agricultural machinery that are not exposed to water and operate under high temperature and medium to low loads. Its operating temperature range is below 120–135°C.
- Aluminum-Based Grease: Aluminum-based grease uses aluminum fatty acid as a thickener, forming a smooth, transparent paste ranging from light yellow to dark brown after thickening mineral oil. It has excellent water resistance and is insoluble in water, making it ideal for lubricating mechanical friction parts in humid environments and low-temperature conditions (below 50°C). According to the SH/T0371-1992 standard, only one grade, ZU-2, is available, with a penetration range of 230–280 and a dropping point of 75°C.
- Lithium-Based Grease: Lithium-based grease is made by thickening medium-viscosity mineral or synthetic oil with natural or synthetic lithium fatty acid soap. This grease appears light yellow to dark brown and features excellent water resistance, mechanical stability, rust resistance, and oxidative stability. It is suitable for a wide temperature range of -20°C to 120°C, making it an ideal lubricant for various machinery such as electric motors, automobiles, and tractors. Lithium-based grease is available in three grades: ZL-1, ZL-2, and ZL-3, with penetration values ranging from 220 to 340 and a dropping point not lower than 170–180°C.

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