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I. Understand the properties of various lubricating materials. In lubrication work, it is first necessary to understand the relationship between lubrication and friction. The selection of lubricating materials depends on factors such as the clearance between the frictioning surfaces, the relative speed of movement of these surfaces, the material composition and manufacturing precision of the surfaces, the load applied to them, their position, orientation, and operating conditions, as well as the surrounding temperature and humidity. Secondly, it is necessary to understand the main quality indicators of lubricant materials, the quality of the base oils in these lubricants and the properties of the additives used in them, the performance characteristics of each type of lubricant, and the differences between various lubricants. For example, the oxidation resistance and antifoaming properties of HL32 hydraulic oil are better than those of HH32 hydraulic oil ； HM32 hydraulic oil has better wear resistance and emulsification resistance than HL32 ； The anti-crawling performance of HG32 hydraulic oil is better than that of HM32. Select the appropriate lubricant material based on the specific conditions of the equipment. For example, the ME1432B external grinder uses HG32 hydraulic oil, as this equipment is prone to crawling ； The M7340 frustum surface grinder uses HM32 hydraulic oil, as the coolant from this equipment easily mixes into the hydraulic oil. II. Pay attention to the integrity, sophistication, and rationality of the lubrication system. Lubrication is intended to reduce friction and extend the service life of equipment; a lack of lubrication in those areas can lead to serious consequences. An unreasonable lubrication system and insufficient supply of lubricating oil can also lead to lubrication failures in the equipment. In September 2002, the company manufactured 3 special double-end milling machines for production needs; the movement of the worktable was driven directly by a 7kW motor, and the lubrication between the worktable and the guide rails in the original design was provided via a manual pump. Since the lubricant tank is opaque and the oil level gauge window is small, it is not possible to see the oil level; therefore, it is impossible to determine whether oil has entered the guide rails when pressing the pump by hand ； The automatic lubrication system of this type of machine tool is unable to supply oil as needed ； The oil level is not easily visible; the guide rails are fully enclosed, making it difficult to detect problems during routine lubrication checks ； This lubrication device is installed on the lower side of the workbench guide rails; it has a small oil reservoir that holds only 100 ML of oil at a time, and it is prone to being covered by iron shavings from the products. All these inconveniences can easily lead to a lack of oil in the guideways of the workbench, thereby increasing frictional resistance and resulting in energy consumption. Additionally, the guideways are prone to scuffing and wear, which can damage the machine tool. Therefore, in January 2003, during the testing of this special aircraft, contact was immediately made with the design department to point out the irrationality of the lubrication system and request improvements. The improved lubrication system features a lubricant level gauge made of transparent plexiglass, allowing the oil level to be seen at a glance ； The oil supply is driven by a miniature motor, which is controlled by the main power supply; as long as the device is turned on, the lubrication motor operates, enabling automatic lubrication of the workbench ； The pressure of the lubrication system and the operating time of the lubrication motor can be controlled by a pressure relay and a time controller, thereby enabling automatic oil supply as required ； The lubricant circuit forms a closed loop, allowing the lubricant to be reused ； A standard centralized lubrication system is used, which facilitates the maintenance of the lubrication system. For example, in order to improve the production efficiency of its equipment, the company converted 30 conventional lathes such as C630-1, C6140F, and CA6140 into simple CNC lathes. During this conversion, the slide box was removed, and synchronous motors were used to move the vertical and horizontal guides. Since the lubrication between the large slide of the original machine and the bed rails was provided by a manual pump in the slide box, with the removal of the slide box and the lubrication tank as well, there is no lubrication mechanism between the large slide and the bed rails. Without the possibility of adding lubricant, this leads to wear of the rails due to lack of lubrication. Subsequently, relevant personnel were organized to rectify the equipment that had been modified but still lacked proper lubrication systems, ensuring adequate lubrication of the guide rails. Therefore, when modifying existing equipment or designing new equipment, special attention must be paid to the integrity, rationality, and sophistication of the lubrication system. It is not sufficient to focus only on the transmission system while ignoring the lubrication system; technical personnel should be involved to oversee and guide the process, ensuring the proper operation of the equipment after modification. III. Addressing the issue of cross-contamination between the cooling system and the lubrication system. There are numerous sources of contamination for oil; during equipment operation, such contamination arises mainly from wear of components in the hydraulic system, oxidation and degradation of the oil, as well as the intrusion of cutting fluid from the cooling system. The first two types of pollution are inevitable, while the latter type should be avoided as much as possible. Once this latter type of contamination occurs, the oil deteriorates within a short period of time. For example, the company has 27 Y5132 gear shaping machines manufactured by Nanjing No. 2 Machine Tool Factory. Such equipment has a significant flaw: the mixing of hydraulic oil and cutting fluid. The main cause of this is wear of the seals on the table clamping cylinders, which leads to leakage of hydraulic oil. This leaked hydraulic oil enters the cutting fluid tank, raising its level; as a result, the cutting fluid overflows into the lubricating oil tank. Since oily cutting fluids are generally not replaced regularly, and they contain many iron particles and impurities, even with a magnetic chip removal system, the concentration of fine particles in the oil remains high. Therefore, once any of this oil enters the hydraulic system, the damping holes in the hydraulic components get blocked, preventing the hydraulic system from functioning properly and forcing a shutdown. To prevent cutting oil from entering the lubricating oil tank, (1) an additional partition made of 2mm thick steel plate can be used to increase the height of the partition between the lubricating oil tank and the cutting oil tank, thereby preventing oil from overflowing from the cutting oil tank and contaminating the area around the machine tool when the oil level in that tank rises. (2) Since the hydraulic oil for machine tools and the cutting fluid are the same type of oil, both being HL32 hydraulic oil, it is permissible for these oils to mix with each other if, after filtration, the cutting fluid meets the requirements of the hydraulic system. Learning that the filter in the hydraulic system is of the XU-B50 x 100 type, improvements were made based on Plan (1): multiple rows of φ5mm holes were drilled in a 2mm-thick steel partition, and a filter screen with a precision of 100μm was installed on the side adjacent to the cutting oil tank. As a result of these improvements, the service life of the hydraulic oil was extended, and lubricant consumption was reduced. Of course, if it is a water-based cutting fluid, it is essential to strictly prevent the cutting fluid from entering the hydraulic system, as water can cause the lubricant to emulsify and deteriorate, preventing the creation of system pressure and thus preventing the machine from starting up. For machines such as the M7340A frustum surface grinder, the cutting fluid is soap water (prepared from tap water). If oil emulsification occurs due to the presence of this cutting fluid, it is necessary to first identify the source of the leakage before changing the lubricating oil; measures should be taken to repair the leaking area first, and then the oil should be replaced, preferably with HM32 hydraulic oil. In summary, for machine tools where cutting fluid easily enters the hydraulic oil, lubrication technicians must, based on the actual conditions and by fully understanding the structure of the machine tool as well as the properties of the cutting fluid, work together with relevant personnel to make appropriate improvements to the equipment in order to address the technical issue of cooling fluid entering the lubricating oil reservoir and ensure the proper operation of the hydraulic system. IV. Understand the schematic diagram of the equipment’s hydraulic system and the structure of hydraulic components. Hydraulics and lubrication are closely related; those working in lubrication technology should be familiar with the schematic diagram of the equipment’s hydraulic system. Because fault diagnosis in hydraulic system equipment is quite difficult, a fault may be caused by one factor or by multiple factors; meanwhile, one factor can also give rise to multiple faults. When certain faults occur in the equipment, people first think of oil quality issues and request an oil change; yet in fact, it is sometimes a fault in the hydraulic or transmission system that requires no oil change. For example, the grinding head of the Y7132 gear grinder manufactured by Qinchuan Machine Tool Factory operates at a slow speed; it can barely run for 3 hours in the morning, with the oil tank temperature reaching over 80°C, and it cannot be started in the afternoon. The device should be placed in a room with a constant temperature of around 20°C. At that time, it was not kept in an air-conditioned room, and due to the high weather temperatures, which exceeded 30°C, the first suspect factor was that the oil quality did not meet the requirements for use in hot weather. The technician requested that the oil be replaced. The device had only been in operation for 2 months since its last cleaning, oil change, and filling with HL46 hydraulic oil; a test of the oil in the tank showed that it was of good quality and had not deteriorated. The hydraulic system circuit was checked again; the hydraulic pump and hydraulic motor were operating normally, and the pressure in the hydraulic system was within normal limits. The three flow control valves were taken apart one by one to clean their valve cores, and everything appeared normal with no signs of blockage. However, the equipment malfunction still remained unresolved. Later, when the grinding head was lifted, it was found that the guide rails were lacking oil; as a result of excessive resistance, the grinding head could not move. By clearing the oil passages, the equipment malfunction was resolved. It can be seen from this that if lubrication technicians do not understand the schematic diagrams of hydraulic systems and the structure of hydraulic components, they will be unable to resolve this fault; moreover, they may replace qualified lubricating oil with substandard oil, resulting in unnecessary waste. Of course, inappropriate or degraded oil can also cause hydraulic system failures. For example, the MG1432A high-precision universal external grinder manufactured by Shanghai Machine Tool Factory will experience crawling if HL32 or HM32 hydraulic oil is used; however, this crawling problem is eliminated when HG32 hydraulic guide rail oil is used. Another example is the ME1332A external grinder manufactured by Shaanxi Machine Tool Factory; after 6 months of periodic oil changes, the oil deteriorated and the equipment’s guides started to wander. After cleaning the equipment and changing its oil, this wandering problem was eliminated. This shows that the type of oil can affect the performance of hydraulic systems, and changing the oil can resolve certain equipment failures. Similarly, certain faults can occur after periodic oil changes of the equipment. For example, the company had a HSS60BC gear grinding machine that was imported from the Swiss company MAAG in earlier years; oil was changed on a regular basis, and the new oil passed the necessary testing. Oil was then added to the machine following the strict \"three-filtering\" procedure. After the oil change, all functions of the machine operated normally, but the next day it was found that the machine’s gear trimming mechanism was not working. Since there was no impact, and the equipment failure occurred after a 12-hour shutdown, it cannot be a fault in the mechanical transmission system; rather, it must be a fault in the hydraulic system. Based on the hydraulic schematic, the flow control valve that regulates the movement of the control gear mechanism was removed, and its valve core was cleaned. However, the fault remained unresolved. Subsequently, the hydraulic schematic was analyzed again, and it was determined that only if this valve did not function could it cause the adjustment mechanism to stop working. The valve was then carefully cleaned with gasoline and blown out with compressed air, and this process was repeated several times; as a result, black particles as fine as hair strands were removed from the damping holes with a diameter of about φ1mm, and the equipment fault was thus resolved. Furthermore, lubrication technicians must frequently visit the production site to assess the lubrication status of the equipment, identify any issues promptly, and take corrective actions. At the same time, lubrication work should also be linked to the equipment’s maintenance records, and information from various sources should be collected to support lubrication services. For example, in February 2001, the company acquired a NOVA1000 CNC gear grinding machine from the German company HOFLER. The hydraulic oil tank had a capacity of 1000 L, and Mobil DTE24 hydraulic oil was used. Samples of the oil were taken for testing every six months, and the results were always satisfactory; therefore, no routine oil changes were carried out. By May 2002, it was learned from the equipment’s maintenance records that the imported filters had been replaced with domestic ones, which require replacement roughly once a month. Upon receiving this information, an oil change was performed on schedule, only to find that there was a layer of sludge at the bottom of the tank.