Lubricating Grease Indicators

Viscosity

Definition: A measure of the internal friction resistance of oil, i.e., its fluidity. Colloquially, it refers to the "thickness" of the oil.

Importance: As the most critical indicator of lubricating oil, it directly determines oil film thickness and lubrication capacity. Excessively high viscosity causes increased resistance, higher energy consumption, and difficult startup; excessively low viscosity leads to easy oil film rupture and subsequent wear.

Unit: Usually expressed in mm²/s (cSt, Centistokes). Common test temperatures are 40°C and 100°C.

Viscosity Index (VI)

Definition: An indicator measuring the degree of viscosity change with temperature.

Importance: A higher VI indicates less viscosity variation with temperature, enabling stable lubrication performance over a wider temperature range. This is a key advantage of high-performance lubricants such as synthetic oils.

Pour Point

Definition: The lowest temperature at which oil can flow under specific conditions.

Importance: Reflects the low-temperature startup performance of lubricating oil. A lower pour point means better fluidity in extremely cold environments, facilitating easier machine startup.

Flash Point

Definition: The lowest temperature at which the mixture of oil vapor and air ignites instantaneously when exposed to an open flame.

Importance: Indicates the volatility and safety of oil. A higher flash point means lower volatility and higher safety during use, especially in high-temperature environments.

2. Key Chemical Indicators

These indicators reflect the chemical composition and stability of lubricating oils.

Total Acid Number (TAN)

Definition: The milligrams of potassium hydroxide required to neutralize the acidic components in 1 gram of lubricating oil.

Importance: Used to measure oil aging (oxidation) degree. During service, oil oxidizes to form organic acids, causing a gradual increase in TAN. An excessively high TAN indicates severe oil deterioration and the need for replacement.

Total Base Number (TBN)

Definition: The amount of acid required to neutralize all basic components in 1 gram of lubricating oil, converted to the equivalent milligrams of potassium hydroxide.

Importance: Primarily used for engine oils. It represents the oil's ability to neutralize acidic substances (such as sulfuric acid and nitric acid) generated by combustion, preventing corrosion. Oils with high TBN are typically used in high-sulfur fuel engines or heavy-duty engines.

3. Important Performance Indicators

These indicators evaluate the actual service performance of lubricating oil through simulation tests.

Oxidation Stability

Definition: The oil's ability to resist degradation from reactions with oxygen.

Importance: Determines the service life of the oil. Oils with good oxidation stability are less prone to forming carbon deposits, sludge, and acidic substances, allowing longer oil change intervals.

Demulsibility

Definition: The oil's ability to separate from water.

Importance: Critical for circulating systems (such as gearboxes and turbine oil systems) operating in humid environments or with potential water contact. Oils with good demulsibility can separate from water quickly for easy drainage.

Foaming Characteristics

Definition: The oil's tendency to resist foam formation and its ability to dissipate foam rapidly once formed.

Importance: Foam can rupture the oil film, resulting in poor lubrication, reduced oil pump efficiency, and potential cavitation.

Extreme Pressure & Anti-Wear (EP/AW) Performance

Definition: The oil's ability to prevent wear, scuffing, and welding of metal surfaces under high-load/high-pressure conditions.

Test Methods:Four-Ball Test: Measures wear scar diameter and sintering load;Timken OK Load: Measures the maximum load without scuffing.

Importance: A key indicator for heavy-duty oils such as gear oils and hydraulic oils.