Main quality indicators of grease

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1. Appearance: Generally, a layer of grease 1–2 millimeters thick is applied onto clean, transparent glass, and the color, luster, transparency, fiber structure, consistency, impurities, oil separation, and uniformity of the grease are observed visually. (1) The quality of the fat can be simply determined by its appearance. (2) Determine whether the types of lipids match. For example, calcium and lithium-based greases are in the form of capillary creams, aluminum-based greases are transparent and thread-like, while sodium-based greases are in the form of long or short fibers ； Barium-based greases are short-fiber pastes, while molybdenum disulfide-based greases are gray-black creams, etc. (3) By testing whether it is viscous when pressed with fingers, the ease of drawing threads or thinning out, and the degree of adhesion, one can roughly assess the adhesiveness, protective properties, and mechanical stability of the fat. 2. Dropping point: It determines whether the grease meets the temperature requirements of the moving parts; the dropping point of the selected grease should be 20~30°C higher than the operating temperature of those moving parts. 3. Penetration: This value is an important indicator for selecting grease. A high penetration value indicates low consistency and good fluidity, which makes it suitable for pressure transmission through pipes; however, in high-temperature environments, an excessively high penetration value can lead to loss of material ； Grease with a low penetration value has high viscosity and poor flowability, resulting in poor lubricating performance in low-temperature environments. 4. Moisture: Free water in lubricating greases reduces their lubricity, mechanical stability, and chemical stability, leading to corrosion of the components. In calcium-based greases, 1.5–3% structural water is present, and when selecting such greases it is necessary to consider the relationship with the free water contained in them. 5. Mechanical impurities: Substances in lubricating grease that are insoluble in the ethanol-benzene mixture and distilled water are collectively referred to as mechanical impurities. Including dust, sand particles, metal powder, inorganic salts, minerals, etc., these substances can easily cause wear on mechanical components during use, and are difficult to filter out from greases. Therefore, strict measures must be taken to prevent the inclusion of such impurities during storage, transportation, and handling. 6. Free organic acids and free bases: (1) A small amount of free bases must be present in the lipids in order to neutralize the organic acids generated by oxidation during storage. It extends its lifespan, but an excess amount can cause the grease to separate and oil to separate out, reducing its lubricating properties. (2) The presence of free organic acids in grease is not allowed; when the grease becomes acidic, it damages the structural framework of the grease, causing it to soften and thin out, thereby reducing or eliminating its lubricating properties. 7. Hydrochloric acid-insoluble matter: Refers to the mechanical impurities in the grease that are insoluble in hydrochloric acid and petroleum ether. Their presence causes severe mechanical wear. The lower the value, the better the quality of the lipid. 8. Soap content: The value indicates the ratio of mineral oil to thickeners in the fat. The higher the soap content, the lower the oil content and the harder the fat; conversely, it is softer ； If the soap content is too high, the fat tends to harden, dry out, and become ineffective ； If the amount of soap is too low, the backbone of the lipid structure becomes weak, resulting in poor mechanical and colloidal stability; this makes it easy for the oil and soap to separate, leading to degradation and loss of effectiveness. 9. Corrosion test: No grease shall cause corrosion to metals. If fats contain excessive amounts of organic acids, bases, and active sulfides, their oxidation stability is poor; they tend to undergo oxidation reactions to form new organic acids, which can cause corrosion in moving parts. 10. Mechanical stability: It reflects the service life of the grease to a certain extent. The lower the value, the better its stability, and thus its service life is relatively longer ； Conversely, the higher the value, the worse its stability; it tends to thin out and leak during operation, increasing fuel consumption. 11. Colloidal stability: It is an indicator that measures the tendency of lipids to release oil during use, storage, and transportation. Greases with poor stability should not be used in mechanical equipment operating under high temperatures and heavy loads, and their shelf life cannot be too long. 12. Oxidation stability: The higher the value, the worse the stability. During storage and use, greases with poor oxidation stability are susceptible to oxidation by oxygen in the air, resulting in the formation of various organic acids that corrode metal surfaces. Additionally, this process can disrupt the colloidal stability of the grease, thereby reducing its service life and shortening it.