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1. What are the types and functions of lubricants? The lubricants used in automobiles mainly include internal combustion engine oil, gear oil, brake fluid, and grease. Its functions are to reduce friction, minimize wear, dissipate heat, provide sealing protection, and ensure the proper operation of the vehicle. Lubricating oil can perform functions such as lubrication, cooling, flushing, sealing, protection, shock absorption, and load relief in machinery. 2. What are the main indicators of lubricating oil? The main parameters of lubricating oil include: viscosity, viscosity index, flash point and ignition point, ash content, and carbon residue value. 3. What properties should lubricating oil have? (1) Appropriate viscosity and good viscosity-temperature properties ； (2) Good cleaning and dispersion performance (3) Excellent antioxidant stability ； (4) Good wear resistance ； (5) Good anti-corrosion and rust prevention properties. (6) Good antifoaming properties. 4. What are the functions of lubricating oil? (1) Lubrication and wear reduction effects ； (2) Function of cooling engine components ； (3) Function of sealing the combustion chamber ； (4) Function of keeping engine components clean ； (5) Rust prevention and corrosion resistance. 5. How are lubricants in our country classified according to viscosity grades? China’s classification system for lubricant viscosity grades follows the SAE standards set by the Society of Automotive Engineers; there are eleven grades in total, namely 0W, 5W, 10W, 15W, 20W, 25W, 20, 30, 40, 50, and 60. In our country, engine oil with a viscosity grade of 40 is generally used in summer. In a few southern regions, engine oil with a viscosity grade of 50 is used. During winter, engine oil with a viscosity grade of 30 is typically used in the south. In the north, however, oils with viscosities of 10W or 15W are required; in very cold regions, even 5W oil is necessary. In addition, there are multi-grade oils (XW/XX) that can be used in both winter and summer, in both the northern and southern regions, and which also offer energy-saving benefits. “ W stands for (winter); the number before W (0, 5, 10, 15, 20) and the number after W (30, 40, 50) both represent the kinematic viscosity grade of the oil at 100°C. For 0W, 5W, 10W, 15W, 20W, and 25W, the maximum pumping limit temperatures are -35°C, -30°C, -25°C, -20°C, -15°C, and -5°C respectively. (The higher the number, the higher the operating temperature; grades with the suffix W are suitable for winter use.) ； Grade numbers without the suffix W, suitable for normal temperatures and summer ； If two numbers are combined, it indicates a multi-grade oil whose performance meets the requirements of both viscosity grades). 6. How are the operating temperature ranges for lubricants of different viscosity grades determined? The viscosity grades of lubricants and the approximate temperature ranges in which they can be used are shown in the table below: Viscosity Grade – Approximate Temperature Range (C); Viscosity Grade – Approximate Temperature Range (C). 0W: -55 to -10; 15W/40: -15 to 40; 5W/20: -30 to -5; 20W/40: -5 to 40; 10W: -20 to 10; 30: 0 to 40; 10W/30: -20 to 30; 40: 20 to 50; 15W/30: -15 to 30. 7. How are lubricants classified by quality in China? Answer: The standards for lubricants in our country have been aligned with international standards, with quality grades following the criteria set by the American Petroleum Institute (API). Gasoline engine oils are classified into SC, SD, SE, SF, SG, SH, and SJ based on their quality level (generally, the order of better oil quality and performance is from SC to SJ). Diesel engine oils are classified by quality level into CC, CD, CE, and CF-4 (generally, the order of better oil quality and performance is from CC to CF). 8. What do SAE30 and SE/CC represent? Answer: This is a multi-purpose internal combustion engine oil that can be used both as a gasoline engine oil and as a diesel engine oil. SE/CC indicates that when used as a gasoline engine oil, its quality meets the SE standard; when used as a diesel engine oil, it meets the CC standard ； SAE30 indicates that the SAE viscosity grade of this oil is 30. 9. What are the characteristics and application ranges of CC-grade diesel engine oil? Answer: CC-grade diesel engine oil has the ability to prevent precipitation at high and low temperatures, as well as to resist corrosion and rust. It is suitable for lubricating diesel engines with low boost pressure and medium load that do not have a turbocharger, such as the Huanghe NJ151, Hino, Mitsubishi, Isuzu, and other models. Currently, there are five grades of CC-grade diesel engine oils: 30, 40, 20W/20, 5W/30, and 15W/40. 10. What are the characteristics and application ranges of CD-grade diesel engine oil? Answer: CD-grade diesel engine oil possesses excellent capabilities in preventing deposits at both high and low temperatures, as well as anti-wear and anti-oxidation properties. It is primarily suitable for lubricating turbocharged diesel engines operating under heavy load conditions—such as currently imported heavy-duty, high-horsepower diesel vehicles, high-power construction machinery, and medium-turbocharged diesel engines. There are currently six grades of CD-grade diesel engine oil: 30, 40, 10W, 20W/20, 5W/30, and 15W/40. 11. What are the quality requirements for vehicle gear oil? (1) Good extreme pressure and anti-wear properties, which prevent scuffing and bonding on the gear surfaces; (2) Low groove formation temperature and good flowability at low temperatures, to ensure easy starting and normal operation of the vehicle in cold conditions; (3) Good oxidation stability, to enable long-term use under harsh conditions; (4) Good antifoaming properties; (5) Good rust resistance. 12. How is vehicle gear oil classified in our country? Answer: Classified by quality: Following the performance classification system for gear oils established by the American API (American Petroleum Institute), gear oils in China are divided into three grades: ordinary vehicle gear oil (GL-3), medium-load vehicle gear oil (GL-4), and heavy-load vehicle gear oil (GL-5). Their quality corresponds respectively to the US grades GC-3, GC-4, and GC-5. (In general, the good order of oil quality and performance is from GL-3 to GL-5.) Classified by viscosity: In China, the viscosity classification for vehicle gear oils follows the system established by the Society of Automotive Engineers (SAE). There are seven viscosity grades: 70W, 75W, 80W, 85W, 90, 140, and 250. The “W” designation indicates winter-use oils; SAE70W, 75W, 80W, and 85W are winter-use oils. Oils without the “W” designation are not winter-use oils, while 90 and 140 are designed for summer use. XXW/XX is a gear oil suitable for both winter and summer use. They are classified according to the kinematic viscosity at 100°C. The oils most commonly used in the market are SAE75W/90, SAE85W/90, and 85W/140; these are oils suitable for use in both winter and summer conditions. 13. Can grease replace lubricating oil? Answer: No. The main functions of lubricating grease are lubrication, sealing, and protection. Lubricants in machinery can serve purposes such as lubrication, cooling, cleaning, sealing, protection, vibration damping, and load relief. 14. Names and codes that should be noted and are familiar: API — American Petroleum Institute (classification system for quality and performance); SAE — Society of Automotive Engineers (classification system for viscosity grades). The letter ‘S’ (the same in China as abroad) indicates gasoline engine oil. ‘W’ denotes oil suitable for use in winter. ‘C’ (the same in China as abroad) indicates diesel engine oil. ‘G’ indicates gear oil. 15. What could be the sources of water in the hydraulic oil of injection molding machines? (1) Leakage from the condenser; (2) Water in the external air; (3) Oxidation of the oil itself; (4) Water contained in the oil added to it; (5) Human factors. 16. How to take oil samples? (1) Start sampling oil once the machine has reached its normal temperature under load. (2) When collecting oil, prepare a clean and suitable sampling bottle as well as oil extraction tools. (3) Under normal circumstances, the oil sampling point is located in the middle of the fuel tank. (4) The oil level in the sampling bottle should not be filled to capacity. (5) After taking the oil sample, quickly close the bottle cap to prevent contamination. (6) Clean the outside of the sampling bottle. (7) Attach a label to the sampling bottle and prepare it for testing. 17. What is the difference between hydraulic oil and power transmission fluid? They all use a liquid as a transmission medium to transfer energy. The liquid medium used in hydraulic systems that utilize the pressure energy of liquids is generally referred to as hydraulic oil ； The medium used in a transmission system that utilizes the kinetic energy of liquids to transfer energy is called hydraulic transmission fluid. These two types of oils have different requirements regarding the performance of the oil. The requirements for hydraulic transmission oil are often stricter than those for hydraulic oil. 18. What do European WEEE and RoHS mean? The European WEEE refers to the European Directive on Waste Electrical and Electronic Equipment, which requires our products to achieve improved environmental performance. And ROHS refers to the restriction of hazardous substances. This standard requires manufacturers to seek appropriate alternatives to replace substances containing lead, mercury, cadmium, hexavalent chromium, and bromides (including diphenyl bromide complexes and ethyl bromobenzene complexes) in the products they produce. This directive also presents more opportunities for lubricant manufacturers, while posing additional challenges. 19. What is counterfeit and inferior hydraulic oil? Generally, fake and inferior hydraulic oil has the following characteristics: (1) It uses low-quality base oils or diesel mixed with rubber to pretend to be any type of hydraulic oil. (2) Using ordinary hydraulic oil to pretend to be anti-wear hydraulic oil. (3) Some recycled oil is subjected to simple processing and then passed off as a certain brand of oil. These counterfeit and inferior hydraulic oils sometimes show no abnormalities in the short term during use; however, they may cause instability, rapid oil degradation, or severe wear of the pump, which severely affects the proper operation of the hydraulic system and the lifespan of its key components, thereby impacting product quality and production efficiency. 20. I often come across NAS8 and NAS5 in various oil product documents; what do they mean? NAS is the abbreviation for the National Academy of Sciences of the United States. NAS8 and NAS5 refer to the purity standards for oils; the lower the number, the higher the purity of the oil, which is more beneficial for the equipment during use. For example, the purity of NAS5 oil is much higher than that of NAS8 oil. 21. What is the main source of cutting heat? The main sources of cutting heat are shear heat and friction heat. 22. What effects can excessive heat during cutting have? Cutting overheating can cause: (1) expansion and deformation of the workpiece, (2) deterioration in the workpiece’s surface finish, (3) increased tool wear, (4) effects on the machining speed, and (5) higher production costs. 23. What is the appropriate storage temperature for cutting oil and cutting fluids? The storage temperature for cutting oil is typically between -5°C and 40°C, while the storage temperature for cutting fluid is between 5°C and 35°C. 24. What are the common extreme pressure additives used in cutting fluids? Common extreme pressure additives in cutting fluids are those containing phosphorus, chlorine, sulfur, and zinc. 25. What is an appropriate pH value for emulsified cutting fluids used in ferrous and non-ferrous metals? For ferrous metals (steel, iron, etc.), the pH value of the emulsion-type cutting fluid should be maintained between 9 and 9.5; for non-ferrous metals, it is advisable to keep it between 8.5 and 8.8. 26. What are the advantages of heat transfer using oil? The advantages of using heat transfer oil are: (1) low pressure, (2) low tendency to leak, (3) higher operating temperature, (4) longer lifespan. 27. What is the purpose of heating the furnace after adding new heat transfer oil to the heat transfer system? The purpose of boiling the oil is to remove water and some light components from it. It is for security reasons. 28. What are the criteria for constant heat transfer performance? The time interval between two heating cycles in a heat transfer furnace is the standard for consistent heat transfer performance. 29. What does “secondary compression” of an air compressor mean? The air generation process of a compressor is: intake → compression → exhaust. Therefore, after the compressor takes in air, compresses it, and expels it, there is still some air left inside the compressor that has not been completely expelled; this remaining air will be involved in the second compression cycle of the compressor. Therefore, it is called “secondary compression”. 30. What are the common methods for determining when an oil product needs to be replaced? Answer: The common methods for changing oil include: (1) the empirical oil-changing method, (2) the regular oil-changing method, and (3) the scientific testing-based oil-changing method. Among these, the scientific testing-based oil-changing method is the most accurate and reliable. 31. What are the common lubrication methods for oil lubrication? Answer: The common lubrication methods are as follows: (1) Manual lubrication, (2) Oil immersion lubrication, (3) Droplet lubrication, (4) Splashing lubrication, (5) Oil wick lubrication, (6) Oil mist lubrication, (7) Centralized lubrication. 32. What is emulsification? Emulsification is actually a phenomenon in which oil molecules and water molecules accommodate each other. It can be divided into two cases: (1) Oil molecules surround water molecules, i.e., the water-in-oil type; (2) Water molecules surround oil molecules, i.e., the oil-in-water type. The emulsification of oils is a physical change. The more common emulsion form is oil-in-water, which often appears milky white. 33. What are the two important methods for detecting the true degree of refinement of white oil? Two important methods for detecting the true degree of refinement of white oil are: (1) the hot acid test, which involves mixing white oil with concentrated sulfuric acid and heating it while shaking to determine the color of the acid layer ； (2) Ultraviolet absorption test method: This method measures the ultraviolet absorption value of white oil in the spectral range of 260–350 nm. The aromatic content in white oil is characterized by the amount of energy absorbed by the alkanes and cycloalkanes, while polycyclic aromatics indicate the degree of energy absorption. 34. What are the reasons for the decrease in oil viscosity in diesel engines? (1) Low-viscosity oil was added. (2) The viscosity regulator failed. (3) Fuel seepage (4) Heating of oil. 35. How to compare the advantages and disadvantages of two different high-temperature chain oils? Comparing two different high-temperature chain oils can be done from the following aspects: (1) the anti-wear performance of the chain oil; (2) whether it has low volatility; (3) whether it leaves behind low levels of residues. 36. What are the requirements for formulating high-quality lubricants? The requirements for formulating high-quality lubricants are as follows: (1) use of high-quality base oils, (2) balanced additives, (3) advanced formulation techniques and strict quality control.