Characteristics of lubricating grease products

Each type of grease should have special physicochemical properties that characterize its usage characteristics in addition to general physical and chemical properties. The higher the quality requirements or the stronger the specificity of the oil, the more outstanding its special physical and chemical properties become.

1. Oxidation stability

Oxidation stability indicates the anti-aging performance of lubricating grease. Some industrial greases with long service life have this index requirement, so it becomes a special performance required by these kinds of oils. There are many methods to determine the oxidation stability of oil products. Basically, a certain amount of oil is oxidized in the presence of air (or oxygen) and metal catalysts at a certain temperature for a certain period of time, and then the acid value, viscosity changes, and precipitation formation of the oil products are measured. All lubricating greases have different automatic oxidation tendencies depending on their chemical composition and external conditions. Oxidation occurs during use, resulting in the gradual formation of aldehydes, ketones, acids, colloids, asphaltenes, and other substances. Oxidation stability is the ability to inhibit the formation of substances that are detrimental to the use of oil products.

2. Hydrolytic stability

Hydrolytic stability characterizes the stability of oil products under the action of water and metals (mainly copper). When the oil has a high acid value or contains additives that easily decompose into acidic substances when in contact with water, this indicator is often unqualified. Its determination method is to add a certain amount of water to the test oil, mix and stir it at a certain temperature for a certain period of time, and then measure the acid value of the water layer and the weight loss of the copper sheet.

3. Emulsification resistance

Industrial lubricating grease often inevitably needs to be mixed with some cooling water during use. If the anti emulsification property of the grease is poor, it will form an emulsion with the mixed water, making it difficult for water to be released from the bottom of the circulating oil tank, which may cause poor lubrication. Therefore, emulsion resistance is an important physicochemical property of industrial lubricants. Generally, oil products are prepared by vigorously stirring 40m of test oil with 40ml of distilled water at a certain temperature for a certain period of time, and then observing the separation time of the oil layer, water layer, and emulsion layer into 40-37-3ml; Industrial gear oil is a mixture of test oil and water, stirred for 5 minutes at a constant temperature and 6000 rpm, left for 5 hours, and then measured for the milliliters of oil and water emulsion layer.

4. Thermal stability analysis

Thermal stability refers to the high temperature resistance of oil products, which is the resistance of lubricating grease to thermal decomposition, i.e. the thermal decomposition temperature. Some high-quality anti-wear hydraulic oils, compressor oils, etc. have put forward requirements for thermal safety. The thermal stability of oil mainly depends on the composition of the base oil, and many additives with lower decomposition temperatures often have adverse effects on the stability of the oil; Antioxidants cannot significantly improve the thermal safety of oil products.

5. Anti foaming property

During the operation of lubricating grease, due to the presence of air, foam is often produced, especially when the oil contains additives with surface activity, it is easier to produce "raw foam, and foam is not easy to disappear. The foam generated during the use of lubricating grease will damage the oil film, make the friction surface sintered or increase wear, promote the oxidation and deterioration of the grease, and also make the lubrication system air resistance, affecting its circulation. Therefore, anti foam property is an important quality indicator of lubricating grease.

6. Air release value

This requirement is included in the hydraulic oil standard because in hydraulic systems, if the air dissolved in the oil cannot be released in a timely manner, it will affect the accuracy and sensitivity of hydraulic transmission, and in severe cases, it will not meet the requirements of hydraulic system use. The method for measuring this performance is similar to that of anti foaming, but it measures the time it takes for air (mist) dissolved inside the oil to be released.

7. Rubber sealing performance

Rubber is mostly used as a sealing element in hydraulic systems, and oil in machinery inevitably comes into contact with some sealing elements. Oil with poor rubber sealing can cause rubber to swell, shrink, harden, and crack, affecting its sealing performance. Therefore, it is required that the oil and rubber have good adaptability. The rubber sealing index is required in the hydraulic oil standard, which is measured by the change of a certain size of rubber ring immersed in oil for a certain period of time.

8. Oil and extreme pressure

Oiliness refers to the formation of a strong physical and chemical adsorption film of polar substances in lubricating grease on the metal surface of the friction part, which plays a role in high load resistance and friction wear resistance. Extreme pressure refers to the decomposition of polar substances in lubricating grease on the metal surface of the friction part under high temperature and high load, and the frictional chemical reaction with the surface metal, forming a low melting point soft (or plastic) extreme pressure film, which plays a role in impact resistance and high load and high temperature resistance lubrication.

9. Corrosion and rusting

Due to the oxidation of oil or the effect of additives, it often causes corrosion of steel and other non-ferrous metals. The corrosion test generally involves placing a copper strip in oil, placing it at 100 ° C for 3 hours, and then observing the changes in copper; The corrosion test is conducted under the action of water and water vapor, which causes corrosion on the surface of steel. To determine the rust resistance, 30ml of distilled water or artificial seawater is added to 300m of test oil, and then the steel rod is placed inside it, stirred for 24 hours at 549C, and then observed for corrosion. Oil products should have anti metal corrosion and anti rust properties, which are usually required to be tested in the I industry lubricant standard.