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Proper lubrication can effectively prevent abnormal wear of the friction pairs in equipment, stop lubricant leakage, and keep impurities and foreign objects from entering between the surfaces of these friction pairs. This helps to avoid a decline in the reliability of mechanical equipment and the occurrence of lubrication-related failures, thereby increasing equipment productivity and reducing operating and maintenance costs. 01 Manual Lubrication: Manual lubrication is the most common and simplest method. Generally, oil is supplied to the oil holes and nozzles using an equipment oil gun. After oil is injected into the oil holes, it flows along the mating surfaces of the friction pairs; due to uneven and discontinuous lubrication levels, as well as the lack of pressure, reliability depends on the operator’s awareness. Therefore, this method is only suitable for components and parts that operate at low speeds, under light loads, and in intermittent fashion, such as open-type machinery or machinery that is not used frequently. 02 Droplet oil lubrication: This type of lubrication relies on droplets of oil falling onto the parts that need lubrication, thanks to the weight of the oil itself. It features a simple design and is easy to use. Its drawback is that the oil supply amount is difficult to control, as mechanical vibration and low temperatures can both affect the amount of oil dripping. 03 Spraying Lubrication: Spraying lubrication involves using rapidly rotating parts or additional oil-spraying discs and plates to disperse oil in the form of droplets and supply it to the friction surfaces. It is primarily used in closed gear pairs and crankshaft bearings. The oil sump also channels the lubricant that splashes out to the bearings for lubrication. During splash lubrication, the circumferential speed of the parts or accessories should not exceed 12.5 m/s; otherwise, excessive foam and degradation will occur. Ventilation holes should be installed in the equipment to enhance air convection inside and outside the cabinet, thereby facilitating oil level indication. 04 Lubrication with oil ropes and oil pads: In this lubrication method, oils such as ropes, pads, or foam plastics are immersed in oil, and oil supply is achieved through capillary siphon action. The oil wick and oil pad themselves can act as filters, thereby keeping the oil clean and ensuring a continuous and even supply of oil. Its disadvantage is that the oil level is difficult to adjust; furthermore, when the moisture content in the oil exceeds 0.5%, the oil feed will stop. Additionally, the oil wick must not come into contact with the moving surface to avoid being trapped between the friction surfaces. To ensure a uniform oil supply, the oil level in the oil cup should be maintained at 3/4 of the total height of the oil wick, with a minimum of at least 1/3. It is commonly used in machinery with low to medium speeds. 05 Oil ring and oil chain lubrication: This lubrication method is used only for the lubrication of horizontal shafts, such as those in electric fans, motors, machine tools, and other similar devices. This method is very simple; it relies on rings or chains fitted around the shaft to carry oil from the oil reservoir to the shaft. This method is very reliable if a certain oil level can be maintained in the oil tank. The oil ring is preferably made as a single unit; it can also be designed in a modular format for easier assembly, but this should not hinder rotation. The diameter of the oil ring is generally 1.5 to 2 times larger than that of the shaft; a rectangular oil supply pattern is usually adopted, and several circular grooves can be machined on the inner surface ； When a smaller amount of oil is required, it is best to use lubrication suitable for horizontal shafts operating at speeds of 50–3000 r/min. If the speed is too high, the oil quantity carried by the oil ring will be insufficient when the speed is too low; in such cases, the oil ring may not even be able to rotate together with the shaft. The oil chain has a large contact area with both the shaft and the oil, so it can rotate along with the shaft at low speeds and carry more oil. Therefore, oil chain lubrication is most suitable for low-speed machinery. At high speeds, the oil is violently agitated, causing the chain to easily come apart; therefore, it is not suitable for high-speed machinery. 06 Forced Lubrication: Forced oil supply lubrication involves the pump delivering oil to the lubrication points. Since the oil under pressure can overcome the centrifugal force generated on the surfaces of rotating parts, a sufficient amount of oil is supplied, resulting in good lubrication effects as well as improved cooling performance. Compared to other methods, the forced oil supply lubrication method is easier to control, and the amount of oil supplied is more reliable. Therefore, it is widely used in various large-scale, heavy-duty, high-speed, precision, and automated mechanical devices. Forced lubrication can be further divided into three types: total loss lubrication, circulating lubrication, and centralized lubrication. (1) Total loss lubrication. This type of lubrication refers to a method in which the lubricating oil that has passed through the friction pair is not reused. It is used at the lubrication points of various devices that require a low amount of oil. Often, a moving machine or electric motor drives a piston pump to pump oil from an oil reservoir to these lubrication points; the supply of oil is intermittent, and the flow rate is adjusted by the stroke of the piston – at a slow pace, one drop of oil is delivered every few minutes, while at a faster pace, several drops are delivered per second. It can be used for individual lubrication, or several pumps can be combined for centralized lubrication. (2) Circulating lubrication. This type of lubrication involves the hydraulic pump pumping oil from the aircraft’s oil reservoir to the areas that need lubrication; the oil that has passed through these areas then returns to the oil reservoir for reuse in a circular process. (3) Centralized lubrication. Centralized lubrication involves a central oil tank supplying oil to multiple lubrication points. It is mainly used in mechanical equipment with numerous lubrication points, or even entire workshops or factories. This method can be operated manually as well as automatically to deliver an appropriate amount of lubricant. The advantages of centralized lubrication are: it allows connection to many components, can adapt to changes in the parts that require lubrication, enables precise distribution of lubricant, facilitates the automated production of various machines, permits pre-lubrication before machine startup, allows control over the flow of lubricant or the entire lubrication process, simplifies maintenance, and can stop the machine when there is a lack of lubricant or when the centralized lubrication system fails.