Technical Questions and Answers for Lubricating Grease Industry

The main ingredients of grease?

Base oil: Base oil accounts for 65% - 98% of grease and is the dispersing medium of thickener. The choice of base oil directly affects the lubricity, evaporation, low temperature and compatibility of sealing materials.

(2) Thickener: Thickener accounts for about 2%-35% of grease. Generally, it is dispersed in liquid lubricant in colloidal state, forming spatial network structure, or dispersed in base oil only in the form of dispersed phase, which plays the role of adsorbing and restricting the flow of base oil. Thickener selection directly affects the mechanical stability, high temperature resistance, colloid stability and water resistance of grease.

(3) Additives: Additives account for about 0-10% of grease, which can improve some performance of grease. According to the performance requirements of lubricating grease, additives such as structure improver, antioxidant, metal passivator, rust inhibitor, extreme pressure agent, oiliness agent, antiwear agent and wire drawing agent can be added. According to different requirements, molybdenum disulfide can be added into additives.

Molybdenum disulfide is added as an additive in various oils to form a colloidal state which is absolutely non-cohesive, thus increasing lubricity and extreme pressure of oils and fats.

What are the basic functions of grease?

The two basic functions of grease are lubrication and protection

(1) Lubrication: Grease can reduce the surface wear of two friction pairs in relative motion;

(2) Protective effect: grease can isolate or reduce the contact between the surface of friction pairs or objects and corrosive substances, play the role of reducing or slowing down the chemical action on the surface of materials erosion and damage, adding molybdenum disulfide in grease can strengthen the anti-corrosion, water resistance and other functions of grease.

What are grease additives?

Antioxidants: amines, phenols, sulfides;

(2) Antirust agents: carboxylic acid and its derivatives, petroleum sulfonate, etc.

(3) Oily agents: higher fatty acids, higher alcohols, animal and vegetable oils, esters;

(4) Extreme Pressure Agent and Oil Resistant Agent: Phosphorus Compound and Chalcogenide Compound;

Solid lubricants: molybdenum disulfide, graphite, PTFE, etc.

Grease dropping point

The dropping point is the temperature at which the grease is heated in a prescribed container, and the grease becomes liquid at high temperature and begins to drip. One of the indicators used to reflect the performance of grease at high temperature, but the dropping point can not determine the temperature of grease alone. The difference of antioxidant capacity of different kinds of base oils, the catalytic effect of thickeners on the oxidation of base oils and the selection of antioxidant additives are also the determinants of lubricating grease service temperature.

The dropping points of different kinds of greases are different:

Calcium soap-based grease: dropping point 80-100 C

Sodium soap-based grease: dripping point 130-180 C

Lithium soap-based grease: dropping point 170-200 C

Compound soap and non-soap greases: dropping point > 260 C

Molybdenum disulfide as a good solid lubricant can be applied to the working temperature range from 270 C to 1000 C.

Lubricating grease taper penetration

Cone penetration is an index to measure the consistency and hardness of grease. It refers to the depth of the cone falling into the sample under specified load, time and temperature conditions. Its unit is 0.1mm. The greater the cone penetration, the softer the grease, and vice versa.

The measurement of working cone penetration has two meanings:

(1) Indicates the fluidity of grease.

(2) The grades of greases are classified according to the working cone penetration range.

Shear stability of grease

Shear stability refers to the property that grease is mechanically sheared and taper penetration is not easy to change. It can be understood as a result of shearing, the gelling agent micelles were cut off or the structure changed.

Shear stability is mainly judged by working stability. The working stability of the cone penetration tester is to detect the cone penetration after working 100,000 times.

Corrosion Resistance of Lubricating Grease

The corrosion resistance of grease is determined by copper corrosion test. A polished copper sheet was immersed in a certain amount of samples and heated to 100 C according to the product standard for 24 hours. At the end of the test period, the copper sheet was taken out and compared with the standard color plate after washing to determine the corrosion level. Copper sheets can be judged to be qualified without any change in green or black.

Molybdenum disulfide has strong corrosion resistance. Adding molybdenum disulfide into grease as an additive can effectively improve the corrosion resistance of grease.