Who has the specifications for various types of lubricants?

Lubricating oil is a technology-intensive product that is a mixture of complex hydrocarbons, and its actual performance in use is the result of a combination of complex physical or chemical processes. The basic properties of lubricating oils include general physical and chemical properties, special physical and chemical properties, and bench test simulations. General physical and chemical properties: Each type of lubricant has its common general physical and chemical properties, which indicate the inherent quality of that product. For lubricating oils, these general physical and chemical properties are as follows: (1) Appearance (colority) – The color of the oil often reflects its degree of refinement and stability. For base oils, generally the higher the degree of refinement, the more thoroughly the hydrocarbon oxides and sulfides are removed, and the lighter the color becomes. However, even under the same refining conditions, the base oils produced from crude oils of different sources and base stocks may vary in color and transparency. For new finished lubricants, due to the use of additives, color has lost its original significance as an indicator of the degree of refinement of the base oil. (2) Density. Density is the simplest and most commonly used physical property indicator for lubricating oils. The density of lubricating oil increases as the amount of carbon, oxygen, and sulfur in its composition rises; therefore, at the same viscosity or the same relative molecular mass, lubricating oils with a high content of aromatics, as well as those with high levels of gums and asphalts, have the highest density, those with a high content of naphthenes have an intermediate density, and those with a high content of alkanes have the lowest density. (3) Viscosity: Viscosity reflects the internal friction of oil and is an indicator of its viscosity and fluidity. Without the addition of any functional additives, the higher the viscosity, the greater the strength of the oil film and the poorer its fluidity. (4) Viscosity index: The viscosity index indicates the extent to which the viscosity of an oil changes with temperature. The higher the viscosity index, the less the viscosity of the oil is affected by temperature, indicating better viscosity-temperature properties; conversely, the lower the viscosity index, the worse these properties are. (5) Flash point: The flash point is an indicator of the evaporativity of oil products. The lighter the distillate of an oil product, the greater its volatility, and the lower its flash point. Conversely, the heavier the distillate of the oil, the lower its volatility, and the higher its flash point. At the same time, flash point is also an indicator of the fire hazard of petroleum products. The hazard level of oils is determined based on their flash point: oils with a flash point below 45°C are considered flammable, while those with a flash point above 45°C are considered combustible. It is strictly prohibited to heat oils to their flash point temperature during storage and transportation. At the same viscosity, the higher the flash point, the better. Therefore, when selecting lubricating oil, users should choose based on the operating temperature and the working conditions of the oil. Generally, it is believed that a flash point 20–30°C higher than the operating temperature ensures safe use. (6) Freezing point and pour point: The freezing point is the highest temperature at which an oil product ceases to flow under specified cooling conditions. The solidification of oils is very different from that of pure compounds. Oil does not have a definite freezing temperature; the so-called “freezing” simply means that it loses its fluidity as a whole, and not all of its components turn into solids. The freezing point of lubricating oil is an important quality indicator that reflects its flowability at low temperatures. It is of great significance for production, transportation, and use. Lubricants with a high freezing point cannot be used at low temperatures. On the contrary, in areas with higher temperatures, there is no need to use lubricants with a low freezing point. Because the lower the freezing point of the lubricating oil, the higher its production cost, resulting in unnecessary waste. Generally speaking, the freezing point of lubricating oil should be 5~7°C lower than the lowest temperature of the operating environment. It is particularly important to note that when selecting lubricants for low temperatures, a comprehensive consideration of the oil’s freezing point, viscosity at low temperatures, and viscosity-temperature characteristics is necessary. Because for oils with a low pour point, their low-temperature viscosity and viscosity-temperature characteristics may also fail to meet the requirements. Both pour point and freezing point are indicators of a petroleum product’s low-temperature fluidity; there is no fundamental difference between them, except that their determination methods are slightly different. The freezing point and pour point of the same oil product are not exactly equal; generally, the pour point is 2–3°C higher than the freezing point, though there are exceptions. (7) Acid value, alkali value, and neutralization value. The acid value is an indicator of the acidic substances contained in lubricating oil, with the unit being mgKOH/g. The acid value is divided into strong acid value and weak acid value; the sum of the two gives the total acid value (abbreviated as TAN). What we usually refer to as the “acid value” actually means “Total Acid Number (TAN)”. The base number is an indicator of the amount of basic substances in lubricating oil, and its unit is mg KOH/g. Alkalinity is also divided into strong alkalinity and weak alkalinity; the sum of the two is the total alkalinity (abbreviated as TBN). What we usually refer to as “alkalinity” actually means “Total Base Number (TBN)”. The neutralization value actually includes the total acid value and the total base value. However, unless otherwise specified, the so-called “neutralization value” actually refers only to the “total acid value”, and its unit is also mg KOH/g. (8) Moisture: Moisture refers to the percentage of water contained in the lubricant, usually expressed as a weight percentage. The presence of water in lubricating oil can destroy the oil film formed by the lubricant, reducing its lubricating efficiency, accelerating the corrosion of metals by organic acids, causing equipment to rust, and leading to the formation of sediment in the oil. In short, the less moisture in the lubricant, the better. (9) Mechanical impurities: Mechanical impurities refer to precipitates or colloidal suspensions present in lubricating oil that are insoluble in solvents such as gasoline, ethanol, and benzene. Most of these impurities are sand, gravel, iron shavings, and other such substances, as well as some organometallic salts that are insoluble in solvents and resulting from additives. Generally, the mechanical impurities in lubricant base oils are kept below 0.005% (levels below 0.005% are considered to be absent). (10) Ash and sulfuric ash: Ash refers to the non-combustible substances that remain after burning under specified conditions. The composition of ash is generally considered to be various metal elements and their salts. Ash has different meanings for different types of oils. For base oils or oils without additives, ash can be used to determine the degree of refining of the oil. For oils with metal salt additives (new oil), ash content becomes a means to quantitatively control the amount of additives added. Abroad, sulfuric acid ash is used in place of ash. The method is to add a small amount of concentrated sulfuric acid before burning the oil sample and then conducting ashing, so as to convert the metal elements of the additive into sulfates. (11) Residue: The charblack residue formed after the heating, evaporation, and combustion of oil under specified experimental conditions is called residue. Residue is an important quality indicator for lubricant base oils; it is a parameter specified to determine the properties of the lubricant and the degree of its refining. In lubricant base oils, the amount of carbon residue is related not only to its chemical composition but also to the degree of refining of the oil. The main substances that cause carbon residue in lubricants are gums, asphaltenes, and polycyclic aromatic hydrocarbons present in the oil. Under conditions of insufficient air, these substances decompose and condense under high heat to form residue carbon. The greater the degree of refining of the oil, the lower its residue value. Generally speaking, the lower the carbon residue value of the base oil, the better. Today, many oils contain additives such as metals, sulfur, phosphorus, and nitrogen, which result in high carbon residue values; as a result, the carbon residue value of oils with additives loses its original meaning in carbon residue testing. Mechanical impurities, moisture, ash, and residue are all quality indicators that reflect the purity of oil products, indicating the degree of refinement of the lubricating base oil. Special physical and chemical properties: In addition to the aforementioned general physical and chemical properties, each type of lubricant should also possess special physical and chemical characteristics that reflect its specific usage properties. The higher the quality requirements or the greater the specificity of an oil, the more prominent its special physical and chemical properties become. The test methods that reflect these special physical and chemical properties are briefly described as follows: (1) Oxidation stability. Oxidation stability indicates the anti-aging performance of lubricants; some industrial lubricants with a long service life are required to meet this criterion, making it a special property specified for such types of lubricants. There are many methods for determining the oxidation stability of oils. Basically, a certain amount of oil is oxidized at a specific temperature for a set period of time in the presence of air (or oxygen) and metal catalysts, after which the acid value, changes in viscosity, and the formation of precipitates in the oil are measured. All lubricating oils have different tendencies toward auto-oxidation, depending on their chemical composition and the external conditions they are exposed to. Oxidation occurs over time as it is used, gradually producing substances such as aldehydes, ketones, acids, as well as gums and asphaltenes. Oxidation stability is the property that prevents the formation of these substances that are detrimental to the use of oil products. (2) Thermal stability: Thermal stability refers to a lubricant’s ability to withstand high temperatures, that is, its resistance to thermal decomposition, which is expressed by the thermal decomposition temperature. Requirements for thermal stability have been established for some high-quality anti-wear hydraulic oils, compressor oils, and similar products. The thermal stability of oils depends primarily on the composition of the base oil; many additives with low decomposition temperatures tend to have an adverse effect on the stability of the oils ； Antioxidants also cannot significantly improve the thermal stability of oils. (3) Oiliness and extreme pressure properties: Oiliness enables the polar substances in lubricants to form a strong physicochemical adsorption film on the metal surfaces at the points of friction, thereby providing resistance to high loads and frictional wear. Extreme pressure properties, on the other hand, involve the polar substances in lubricants breaking down due to frictional chemical reactions under high temperatures and high loads at the metal surfaces in question; these substances then undergo frictional chemical reactions with the surface metal to form a soft (or plastic) extreme pressure film with a low melting point, which provides protection against impacts as well as high loads and high temperatures. (4) Corrosion and rust: Due to the oxidation of oils or the effect of additives, corrosion of steel and other non-ferrous metals often occurs. In a corrosion test, copper strips are typically placed in oil and left at 100°C for 3 hours; thereafter, any changes in the copper are observed ； In the corrosion test, rust forms on the steel surface under the action of water and water vapor. To determine the anti-corrosion properties, 30 ml of distilled water or artificial seawater is added to 300 ml of test oil; a steel rod is then placed in it. The mixture is stirred at 54°C for 24 hours, after which it is checked whether any rust has formed on the steel rod. Oils should have resistance to metal corrosion and rust prevention; in industrial lubricant standards, these two properties are typically required to be tested. (5) Antifoamability: During operation, lubricants often form foam due to the presence of air. This is especially true when the oil contains surfactant additives, as foam is more likely to form and is also difficult to dissipate. Foam formation during the use of lubricant can damage the oil film, cause sintering of the friction surfaces or increase wear, accelerate the oxidation and deterioration of the lubricant, and also cause air blockages in the lubrication system, affecting the circulation of the lubricant. Therefore, antifoamability is an important quality indicator for lubricants and similar products. (6) Hydrolytic stability. Hydrolytic stability indicates the stability of oil products under the action of water and metals (mainly copper). When the acid number of an oil product is high, or when it contains additives that readily decompose into acidic substances upon contact with water, this indicator often fails to meet the required standards. Its determination method involves adding the test oil to a certain amount of water, mixing and stirring it with a copper sheet at a specified temperature for a certain period of time, and then measuring the acid number of the water layer and the weight loss of the copper sheet. (7) Emulsion resistance: Industrial lubricants often inevitably become mixed with some cooling water during use. If the lubricant lacks good emulsion resistance, it will form an emulsion with the water that has mixed in, making it difficult to remove the water from the bottom of the circulation tank – which can lead to poor lubrication. Therefore, anti-emulsibility is a very important physicochemical property of industrial lubricants. For ordinary oils, 40 ml of the oil sample is mixed vigorously with 40 ml of distilled water at a certain temperature for a specified period of time, after which the time it takes for the oil layer, water layer, and emulsion layer to separate into 40-37-3 ml is observed ； Industrial gear oil is prepared by mixing the oil with water, stirring at a certain temperature and at 6,000 revolutions per minute for 5 minutes, then allowing it to stand for 5 hours, after which the volumes of oil, water, and the emulsion layer are measured. (8) Air release value: This requirement is specified in the hydraulic oil standards, because in hydraulic systems, if the air dissolved in the oil is not released in a timely manner, it will affect the accuracy and sensitivity of hydraulic transmission; in severe cases, it will fail to meet the requirements for using such hydraulic systems. The method for measuring this property is similar to that for antifoaming capacity, except that it determines the time it takes for the air (mist) dissolved within the oil to be released. (9) Rubber sealing performance: In hydraulic systems, rubber is commonly used as a sealing material. In mechanical devices, oils inevitably come into contact with various sealing components. Oils with poor sealing properties can cause the rubber to swell, shrink, harden, or crack, thereby affecting its sealing ability; therefore, it is necessary for the oil to have good compatibility with rubber. Hydraulic oil standards require a rubber sealing index, which is measured by the change that occurs in a rubber ring of a certain size after being immersed in oil for a specified period of time. (10) Shear stability: In oils to which thickeners have been added, mechanical shear during use can break down the high-molecular polymers present in the oil, resulting in a decrease in its viscosity and thereby affecting proper lubrication. Therefore, shear stability is a specific physical and chemical property that must be measured for such oils. There are many methods for measuring shear stability, including the ultrasonic shear method, the nozzle shear method, the Wicks pump shear method, and the FZG gearbox shear method; all of these methods ultimately aim to determine the rate of viscosity decrease in the oil. (11) Solubility The solubility is usually expressed by the aniline point. The solubility limit aniline point of composite additives varies with different grades of oils; the limit value for oils with low ash content is higher than that for highly basic oils, and the limit value for single-grade oils is higher than that for multi-grade oils. (12) Volatility: The volatility of the base oil is related to fuel consumption, viscosity stability, and oxidation stability. These properties are particularly important for multi-stage oils and energy-saving oils. (13) Rust resistance: This refers specifically to the special physical and chemical properties that rust-preventing greases should possess. The testing methods include humidity tests, salt spray tests, lamination tests, and water displacement tests; in addition, there are also greenhouse tests and long-term storage tests. (14) Electrical properties: Electrical properties are unique characteristics of insulating oils, including the dielectric loss angle, dielectric constant, breakdown voltage, pulse voltage, etc. The degree of refinement of the base oil, as well as impurities and moisture, all have a significant impact on the electrical properties of the oil. (15) Special physicochemical properties of greases In addition to their general physicochemical properties, greases designed for specific applications possess special physicochemical characteristics. Greases with good water resistance are required to undergo a water test ； For low-temperature grease, low-temperature torque needs to be measured ； Multi-effect lubricants need to be tested for extreme pressure and wear resistance as well as rust prevention properties ； Long-life lubricants require bearing life tests and similar procedures. There are also corresponding test methods for measuring these properties. (16) Other special physical and chemical properties: In addition to their general properties, each type of oil should have its own unique special properties. For example, the cooling rate of quenching oil needs to be determined ； The emulsification stability of the emulsified oil needs to be determined ； The anti-creep coefficient of hydraulic guide rail oil needs to be measured ； The dispersion of oil mist needs to be measured for spray lubricants ； The freezing point and flocculation point of refrigeration oil need to be measured ； Low-temperature gear oil needs to be tested for pitting, etc. All these properties require a special chemical composition of the base oil, or the addition of certain special additives to be ensured