【Daily Question】Lubricant Monitoring Management (Open-ended question)

The parameters monitored by our company are viscosity, moisture, mechanical impurities, flash point, and acid value. The qualifying standard is the national standard for new oil; there is no corporate standard (please provide a corporate standard – +5 wealth points if one is available).

Lubricating oil is a technology-intensive product, 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. 　　1. General physical and chemical properties Each type of lubricant has its common 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 refining, 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 parent categories 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 amounts of carbon, oxygen, and sulfur in its composition increase. 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 a density in between, while those with a high content of alkanes have the lowest density. 　　(3) Viscosity Viscosity reflects the internal friction of an oil and is an indicator of its lubricity 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 performance; otherwise, the performance is worse. (5) Flash point: The flash point is an indicator of the evaporativity of oil products. The lighter the fraction of the oil, the greater its volatility, and the lower its flash point as well. Conversely, the heavier the distillate of the oil, the lower its volatility, and the higher its flash point. At the same time, the flash point is 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. Given 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. It is generally believed that a flash point 20 to 30°C higher than the operating temperature ensures safe use. (6) Freezing point and pour point: The freezing point refers to the highest temperature at which the oil stops flowing under specified cooling conditions. The solidification of oils differs significantly from that of pure compounds. There is no definite solidification temperature for oils; the so-called “solidification” simply means that the oil, as a whole, loses its fluidity. It does not mean that all of its components have turned 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. Lubricating oils with a high pour 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. The lower the pour point of lubricating oil, the higher its production cost, resulting in unnecessary waste. Generally, 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 oils with low freezing points may also have low-temperature viscosity and viscosity-temperature properties that do not meet the requirements. Both the freezing point and the pour point are indicators of the low-temperature flowability of oils; there is no fundamental difference between them, only slight variations in the methods of measurement. 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, but 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 the “total acid number (TAN)”. The base number is an indicator of the amount of basic substances in lubricating oil; its unit is mgKOH/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” generally refers only to the “total acid value,” which is also expressed in mgKOH/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 there is in lubricating oil, 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 content has different meanings for various types of oils; for base oils or oils without additives, ash content can be used to determine the degree of refinement 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 to replace ash. The method is: after burning the oil sample but before ashing, add a small amount of concentrated sulfuric acid to convert the metal elements of the additives into sulfates. 　　(11) Residue The dark, charred residue that forms after oil products are heated, evaporated, and burned under specified experimental conditions is called residue. Carbon residue is an important quality indicator for lube oil base stocks; it is a parameter specified to determine the properties and degree of refinement of lubricating oils. In lubricant base oils, the amount of residue is determined not only by its chemical composition but also by the degree of refining of the oil. The main substances that cause residue formation 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 deeper the refining of the oil product, the lower its residue value. Generally speaking, the lower the carbon residue value of the base oil, the better. Currently, many oils contain additives containing metal, sulfur, phosphorus, and nitrogen elements; these additives result in a high carbon residue value. Consequently, the carbon residue of oils with additives has lost its original purpose in carbon residue determination. 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. 2. 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 application properties. The higher the quality requirements, or the greater the specificity of the oil, the more prominent its special physical and chemical properties become. The test methods that reflect these special physicochemical properties are briefly described as follows: (1) Oxidation stability. Oxidation stability indicates the anti-aging performance of lubricants; many 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. During use, oxidation occurs, gradually leading to the formation of various substances such as aldehydes, ketones, acids, gums, and asphaltenes. Oxidative stability refers to the ability to inhibit the formation of these substances that are detrimental to the usability of the oil. 　　(2) Thermal stability Thermal stability refers to a lubricant’s ability to withstand high temperatures; in other words, it is the lubricant’s 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 decomposing 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 low-melting-point, soft (or plastic) extreme pressure film, which provides resistance to impacts as well as high loads and high temperatures. (4) Corrosion and rusting Oxidation of oils or the effect of additives often leads to corrosion of steel and other non-ferrous metals. In corrosion tests, copper strips are generally placed in oil and left at 100°C for 3 hours, after which the changes in the copper are observed ； The corrosion test involves the formation of rust on the steel surface under the influence of water and moisture. To determine the rust resistance, 30 ml of distilled water or artificial seawater is added to 300 ml of test oil, after which a steel rod is placed in it and stirred at 54°C for 24 hours; thereafter, it is checked whether 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) Antifoam property: 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 it is also difficult for such foam to disappear. 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 the like. 　　(6) Hydrolytic stability Hydrolytic stability indicates the stability of oils under the action of water and metals (mainly copper). When an oil has a high acid value, or contains additives that decompose into acidic substances when exposed to water, this parameter 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) Anti-emulsification property: Industrial lubricants often inevitably become mixed with some cooling water during use. If the lubricant’s anti-emulsification property is poor, 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; this 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 with 40 ml of distilled water and vigorously stirred at a certain temperature for a specified period of time; thereafter, the time it takes for the oil layer, water layer, and emulsion layer to separate into 40 ml, 37 ml, and 3 ml respectively 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, allowing it to stand for 5 hours, and then measuring the volumes of oil, water, and the emulsion layer. 　　(8) Air release value: This requirement is specified in the hydraulic oil standards. 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; in severe cases, it may even render the hydraulic system unfit for use. The method for measuring this property is similar to that for antifoaminess, except that it measures 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 that have 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 acts during use, causing the high-molecular polymers in the oil to be broken down, which reduces the viscosity of the oil and affects 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 　Solubility is usually expressed by the aniline point. The solubility limit and aniline point of composite additives vary depending on the oil grade; the limit values for low-ash oils are higher than those for overbased oils, and those for monograde oils are higher than those for multigrade 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-grade oils and energy-saving oils. 　　(13) Rust resistance: This refers specifically to the special physical and chemical properties that anti-rust greases should possess. The testing methods include humidity tests, salt spray tests, laminating 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 physical and chemical properties of greases In addition to their general physical and chemical properties, greases designed for specific purposes possess special physical and chemical properties as well. 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 greases 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 Each type of oil should possess its own unique special properties in addition to its general 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 ensure them.

The basic properties of lubricating oils include general physical and chemical properties, special physical and chemical properties, and bench test simulations. 　　1. General physical and chemical properties Each type of lubricant has its common 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 refining, 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 parent categories 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 amounts of carbon, oxygen, and sulfur in its composition increase. 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 a density in between, while those with a high content of alkanes have the lowest density. 　　(3) Viscosity Viscosity reflects the internal friction of an oil and is an indicator of its lubricity 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 performance; otherwise, the performance is worse. (5) Flash point: The flash point is an indicator of the evaporativity of oil products. The lighter the fraction of the oil, the greater its volatility, and the lower its flash point as well. Conversely, the heavier the distillate of the oil, the lower its volatility, and the higher its flash point. At the same time, the flash point is 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. Given 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. It is generally believed that a flash point 20 to 30°C higher than the operating temperature ensures safe use. (6) Freezing point and pour point: The freezing point refers to the highest temperature at which the oil stops flowing under specified cooling conditions. The solidification of oils differs significantly from that of pure compounds. There is no definite solidification temperature for oils; the so-called “solidification” simply means that the oil, as a whole, loses its fluidity. It does not mean that all of its components have turned 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. Lubricating oils with a high pour 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. The lower the pour point of lubricating oil, the higher its production cost, resulting in unnecessary waste. Generally, 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 oils with low freezing points may also have low-temperature viscosity and viscosity-temperature properties that do not meet the requirements. Both the freezing point and the pour point are indicators of the low-temperature flowability of oils; there is no fundamental difference between them, only slight variations in the methods of measurement. 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, but 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 the “total acid number (TAN)”. The base number is an indicator of the amount of basic substances in lubricating oil; its unit is mgKOH/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” generally refers only to the “total acid value,” which is also expressed in mgKOH/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 there is in lubricating oil, 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 content has different meanings for various types of oils; for base oils or oils without additives, ash content can be used to determine the degree of refinement 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 to replace ash. The method is: after burning the oil sample but before ashing, add a small amount of concentrated sulfuric acid to convert the metal elements of the additives into sulfates. 　　(11) Residue The dark, charred residue that forms after oil products are heated, evaporated, and burned under specified experimental conditions is called residue. Carbon residue is an important quality indicator for lube oil base stocks; it is a parameter specified to determine the properties and degree of refinement of lubricating oils. In lubricant base oils, the amount of residue is determined not only by its chemical composition but also by the degree of refining of the oil. The main substances that cause residue formation 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 deeper the refining of the oil product, the lower its residue value. Generally speaking, the lower the carbon residue value of the base oil, the better. Currently, many oils contain additives containing metal, sulfur, phosphorus, and nitrogen elements; these additives result in a high carbon residue value. Consequently, the carbon residue of oils with additives has lost its original purpose in carbon residue determination. 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. 2. 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 application properties. The higher the quality requirements, or the greater the specificity of the oil, the more prominent its special physical and chemical properties become. The test methods that reflect these special physicochemical properties are briefly described as follows: (1) Oxidation stability. Oxidation stability indicates the anti-aging performance of lubricants; many 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. During use, oxidation occurs, gradually leading to the formation of various substances such as aldehydes, ketones, acids, gums, and asphaltenes. Oxidative stability refers to the ability to inhibit the formation of these substances that are detrimental to the usability of the oil. 　　(2) Thermal stability Thermal stability refers to a lubricant’s ability to withstand high temperatures; in other words, it is the lubricant’s 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 decomposing 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 low-melting-point, soft (or plastic) extreme pressure film, which provides resistance to impacts as well as high loads and high temperatures. (4) Corrosion and rusting Oxidation of oils or the effect of additives often leads to corrosion of steel and other non-ferrous metals. In corrosion tests, copper strips are generally placed in oil and left at 100°C for 3 hours, after which the changes in the copper are observed ； The corrosion test involves the formation of rust on the steel surface under the influence of water and moisture. To determine the rust resistance, 30 ml of distilled water or artificial seawater is added to 300 ml of test oil, after which a steel rod is placed in it and stirred at 54°C for 24 hours; thereafter, it is checked whether 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) Antifoam property: 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 it is also difficult for such foam to disappear. 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 the like. 　　(6) Hydrolytic stability Hydrolytic stability indicates the stability of oils under the action of water and metals (mainly copper). When an oil has a high acid value, or contains additives that decompose into acidic substances when exposed to water, this parameter 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) Anti-emulsification property: Industrial lubricants often inevitably become mixed with some cooling water during use. If the lubricant’s anti-emulsification property is poor, 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; this 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 with 40 ml of distilled water and vigorously stirred at a certain temperature for a specified period of time; thereafter, the time it takes for the oil layer, water layer, and emulsion layer to separate into 40 ml, 37 ml, and 3 ml respectively 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, allowing it to stand for 5 hours, and then measuring the volumes of oil, water, and the emulsion layer. 　　(8) Air release value: This requirement is specified in the hydraulic oil standards. 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; in severe cases, it may even render the hydraulic system unfit for use. The method for measuring this property is similar to that for antifoaminess, except that it measures 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 that have 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 acts during use, causing the high-molecular polymers in the oil to be broken down, which reduces the viscosity of the oil and affects 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 　Solubility is usually expressed by the aniline point. The solubility limit and aniline point of composite additives vary depending on the oil grade; the limit values for low-ash oils are higher than those for overbased oils, and those for monograde oils are higher than those for multigrade 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-grade oils and energy-saving oils. 　　(13) Rust resistance: This refers specifically to the special physical and chemical properties that anti-rust greases should possess. The testing methods include humidity tests, salt spray tests, laminating 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 physical and chemical properties of greases In addition to their general physical and chemical properties, greases designed for specific purposes possess special physical and chemical properties as well. 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 greases 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 Each type of oil should possess its own unique special properties in addition to its general 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 ensure them.

Viscosity, moisture, acid value, flash point, and mechanical impurities, in accordance with national standards

Viscosity, moisture, acid value, flash point, and mechanical impurities

For properties such as viscosity, flash point, pour point, moisture, acidity, and mechanical impurities, there are no corporate standards, so testing is carried out externally. Based on the oil change criteria for various oils, SHS

Our company is rather lazy – we hardly analyze the lubricant; we just replace it on a regular basis. However, our heat transfer oil needs to be analyzed regularly: open flash point, dynamic viscosity, moisture content, mechanical impurities, acid value, density, color, and the presence of water-soluble acids and bases.

Consistency: Consistency refers to the degree to which grease resists deformation under external forces. Consistency is generally expressed by the cone penetration value; the greater the consistency, the lower the cone penetration value, and the greater the plastic strength. Consistency grade: NLGI (National Lubricant Grease Institute) divides it into nine grades, ranging from 000 to 6, a total of nine grades. Penetration: Penetration is a measure of the consistency of grease. The greater the cone penetration, the softer the grease. The depth to which a standard cone can sink into grease at a certain temperature within 5 seconds, measured in units of 1/10 mm, indicates the difficulty of introducing grease into the lubrication points. Drop point: The drop point refers to the temperature at which the first drop of grease falls from the hole in the testing apparatus under specified conditions (it is not the melting point); it roughly determines the maximum operating temperature of the grease. For soap-based fats, the operating temperature should be 20–30°C below their dropping point. Evaporability: Also known as evaporation loss, it refers to the weight percentage of loss due to the evaporation of grease under specified temperature conditions; the lower the evaporation loss, the better. The volatility of grease mainly depends on the properties of the lubricating oil and its distillation composition. Mechanical stability: Also known as structural stability or shear stability, it refers to the ability of grease to prevent changes in its consistency when subjected to mechanical shear; the smaller the change in consistency, the better the mechanical stability. Oxidation stability: Also known as chemical stability, it refers to the ability of grease to resist oxidation caused by heat and oxygen in the air during long-term storage or use at high temperatures. It is a key indicator of a grease’s resistance to aging, and can be determined using the oxygen bomb method. Colloidal stability: Colloidal stability indicates the tendency of a grease to release oil during use, transportation, and storage, or its ability to maintain its colloidal structure. It is important for greases used in high-temperature and high-load applications. Wear resistance: Wear resistance refers to the ability of grease to prevent wear on the contacting surfaces by maintaining an oil film on the surface of moving parts. The method for determining wear resistance generally involves using a four-ball machine to measure the critical load PB value ； Sintering load PD value ； Comprehensive wear index. OK values measured by Timken testing machines, etc. Water resistance: Also known as the water spray test, water resistance refers to a grease’s ability to resist being washed away by water, or its ability to withstand damage to its structure caused by the absorption of moisture. Under certain conditions, the mass percentage of grease washed away by water is determined; the lower the amount lost, the less the change in its properties when exposed to water. Low-temperature performance: One of the important indicators for measuring the low-temperature performance of grease is the low-temperature torque, which refers to the degree to which the grease prevents the rotation of bearings operating at low speeds in cold conditions (below -20°C). The low-temperature torque of a grease is expressed as the average of the starting torque and the torque after 60 minutes of operation. Corrosion resistance (protective property): Corrosion resistance refers to the ability of grease to prevent the metal in contact with it from corroding. It is used to measure the grease’s capacity to protect metals from rusting under wet and hot conditions, with the requirement that the metal not be corroded at room temperature and in high humidity conditions. Pumpability: Pumpability refers to the ease with which grease can be delivered, under pressure, to locations such as the nozzles in the distribution system and the tips of grease guns. Resistance to rubber swelling: Resistance to rubber swelling refers to the ability of grease to prevent excessive dissolution, penetration, or swelling and deformation of rubber products such as seals. Grooving tendency: The grooving tendency refers to the propensity of grease to form grooves when it is in continuous operation within bearings; the unworked portion of the grease adjacent to the raceways forms the walls of these grooves, serving to provide sealing and an oil reservoir. Cavitation sensitivity: In the grease distribution system, cavities form due to pressure drops, preventing the grease from reaching the suction point. Some lipids are prone to this phenomenon, that is, they are sensitive to cavitation. Cohesion: Cohesion refers to the molecular attraction that exists between the particles of a given substance, causing them to attract and stick together; it acts to hinder the flow of grease. Adhesion: Adhesion refers to the ability of grease to adhere to the surface of the bearing raceways it is lubricating. Thixotropy: The property in which the viscosity of a grease decreases when subjected to shear, and increases again once the shear is stopped.

Each type of lubricant has a set of quality standards, and manufacturers control production in accordance with these criteria; only products that pass the inspections are allowed to leave the factory and enter the market. 　　There are a wide variety of lubricants, each with different applications. Their specifications fall into two categories: common specifications, which must be met by all or most lubricant products, although the specific values vary ； Another category is those where, due to different uses, each variety has its own set of specifications. 　　The first category can be further divided into three subcategories: 1. Physical and chemical properties – These indicate the internal quality of the product, as well as the basic physical and chemical characteristics of the lubricant; they represent minimum requirements. These properties are generally determined in the laboratory using glass instruments according to standard methods, which is a time-efficient and quick process. Examples include viscosity and flash point, and their measurement is usually required every time during production. In recent years, many automated instruments for measuring physical and chemical parameters have been developed; they not only save labor and increase the speed of measurement but also reduce human-induced measurement errors and improve accuracy. 　　2. Performance indicators These represent the properties that lubricants should possess during use, such as oxidation resistance, antifoaming capacity, and extreme pressure resistance. There are standard methods for testing these properties, but the testing equipment is complex and expensive; it requires more time and labor compared to other indicators. It also demands certain skills from the operators, and some small lubricant manufacturers do not have the capability to use such equipment. In addition to checking product quality, these indicators can also be used in the development of new products. It is not necessary to conduct this test on every batch of products in production; rather, it is done only when there are changes in the raw materials, processes, or formulas, as a quality assurance measure. 　　3. Simulation bench test The equipment used for this test is a dedicated standard testing machine or a representative engine actually in use; the test conditions simulate typical operating scenarios in real-world applications. Therefore, the test results can best reflect the performance of the lubricant under actual use, and they provide the most convincing assessment of the quality of the lubricant. Standard test methods exist for simulated bench tests, and these methods require a great deal of manpower, resources, and time during testing; only enterprises with sufficient scale or financial resources can undertake them.

1. Physicochemical properties: These indicate the internal quality of the product and represent the basic physicochemical characteristics of lubricants; they are also essential requirements. They are generally determined in the laboratory using glass instruments according to standard methods, which is a time-saving, labor-saving, and rapid process. Properties such as viscosity and flash point are usually measured every time during production. 2. Performance indicators These represent the properties that lubricants should possess during use, such as oxidation resistance, antifoaming capacity, and extreme pressure resistance. There are standard methods for testing these properties, but the testing equipment is complex and expensive; it requires more time and labor compared to other indicators. It also demands certain skills from the operators, and some small lubricant manufacturers do not have the capability to use such equipment. In addition to checking product quality, these indicators can also be used in the development of new products. 3. Standards: The quality grades are classified according to the API (American Petroleum Institute) classification system. Gasoline engine oils are identified with letters starting with S, such as SE, SJ, S, etc. Diesel engine oils are denoted with a letter C at the beginning, such as CD, CF, CH, etc. Gear oil is denoted by G, such as G-4, G-5, etc. The further the sub-letter goes, the higher the quality grade of the oil product. In addition to the API standards, there are other authoritative organizations that have established their own standards for evaluating the quality of engine oils. Now let us introduce to you several international organizations that are responsible for assessing the quality grades of engine oils. ACEA is an organization that many people are familiar with; it is the Association of European Automobile Manufacturers. It was established in May 1991 to replace CCMC, which was the Association of Automobile Manufacturers in the European Common Market and served as ACEA’s predecessor, carrying out functions similar to those of ACEA. The ACEA organization revises its automotive lubricant specifications every two years, with some of its criteria being identical to those of API. There is also an organization called ILSAC, which stands for the International Lubricant Standardization and Certification Committee. It is jointly formed by the United States Automobile Manufacturers Association and the Japan Automobile Manufacturers Association. In October 1990, ILSAC issued test specification GF-1 for engine oils used in automobiles. JASO, the Japanese Automobile Standards Organization, is also one of the agencies responsible for evaluating vehicle engines. It is composed of Japanese oil companies, additive manufacturers, automobile manufacturers, and other Japanese organizations; the standards it develops are applicable in Japan and the Pacific region, serving as a complement to the API testing standards. The U.S. military, the German military, and the French military have also established their own standards to ensure the quality of military aircraft oils. In addition to the aforementioned international organizations, some well-known automobile manufacturers have also established their own standards. For example, companies such as Cummins in the United States, Mercedes-Benz, BMW, Volkswagen, Porsche in Germany, and Volvo in Sweden have all established their own oil testing standards, which are stricter and more rigorous than the API standards. A total of 7 companies in China have met the API standards, and even fewer have passed the oil testing standards set by automobile manufacturers. Currently, the domestic lubricant manufacturer with the most such certifications is Beijing United Petrochemical Co., Ltd. Countries around the world and various companies establish specifications for automotive fuels primarily to ensure that the lubricants produced by manufacturers meet the requirements of vehicle use; therefore, when purchasing lubricants, consumers must check whether the manufacturer has been certified by such authoritative organizations.