[b]1 Characteristics and Classification of Machine Tool Lubrication Systems[/b] Machine tool lubrication systems occupy a very important position in the overall machine tool. Their design, debugging, and maintenance play a vital role in improving machining accuracy and extending the service life of the machine tool. Modern machine tool guideways, lead screws, and other sliding pairs are basically lubricated using centralized lubrication systems. A centralized lubrication system uses a hydraulic pump to supply lubricating oil at a certain displacement and pressure to all the distributors in the main and secondary oil circuits of the system. The distributors then distribute the oil to each lubrication point according to the required amount. Simultaneously, a controller monitors the lubrication time and frequency, provides fault alarms, and stops the machine, achieving automatic lubrication. The characteristics of centralized lubrication systems are timed, quantitative, accurate, and efficient operation; they are convenient and reliable to use, which helps to improve machine life and ensure performance. Centralized lubrication systems can be classified according to the lubrication elements used: damping lubrication systems, progressive lubrication systems, and volumetric lubrication systems. **2. Single-Line Damped Lubrication System** This system is suitable for machine tool lubrication points requiring relatively low oil volume and periodic oil supply. It utilizes a damped distributor to distribute the pumped oil to the lubrication points in a specific ratio. It is generally used in circulating systems but can also be used in open systems. The oil volume at each lubrication point can be controlled by time. This lubrication system is very flexible, allowing for more or fewer lubrication points, and can be installed by the user. When one point becomes blocked, it does not affect the use of other points, making it widely applicable. **3. Progressive Lubrication System** The progressive lubrication system mainly consists of a pump station and a progressive plate distributor, and can be equipped with a control device for monitoring. Its features include the ability to alarm and terminate operation upon blockage at any lubrication point to protect the equipment; accurate metering and high pressure; it can use not only thin oil but also grease lubrication. It can handle up to 100 lubrication points and pressures up to 21 MPa. The progressive distributor consists of a base plate, an end plate, and at least three intermediate plates. A single valve set can have up to 8 intermediate plates, lubricating 18 points. Its working principle involves the plungers in the intermediate plates sequentially actuating from a certain position to supply oil. If a blockage occurs at a point, the next outlet will not actuate, thus stopping the entire distributor's oil supply. A blockage indicator shows the location of the blockage, facilitating maintenance. [b]4. Volumetric Lubrication System[/b] This system uses a metering valve as a distributor to supply oil to the lubrication points. A pressure relay is installed in the system so that when the system oil pressure reaches a predetermined value, a signal is sent to delay and stop the motor. Lubricating oil is then supplied from the metering distributor. The system is unloaded through a directional valve and maintains a minimum pressure, allowing the metering valve distributor to replenish lubricating oil. The motor restarts, and this process repeats until the specified lubrication time is reached. This system typically operates at pressures below 50 MPa and can lubricate hundreds of points. It has a wide range of applications and reliable performance, but it cannot be used as a continuous lubrication system. The structural principle of the metering valve is as follows: it consists of two oil chambers, upper and lower. Under high pressure, the oil is pumped to the lubrication point. Under low pressure, the oil stored in the lower chamber is forced into the oil discharge chamber located in the upper chamber by its own spring return and cup-shaped seal. The discharge volume is 0.1-1.6 mL, and it can be combined according to actual needs. Figure 9-8 shows a volumetric lubrication system. [b]5 Four Cases of Lubrication System Fault Repair[/b] Fault Repair for Unsatisfactory Machining Surface Roughness Fault Phenomenon: When milling the machine frame plane of a CNC gantry milling machine with the right vertical tool post, it was found that the surface roughness of the workpiece did not meet the predetermined accuracy requirements. Analysis and Handling Process: After this fault occurred, the focus of troubleshooting was on checking the accuracy of the rolling bearings (especially the front and rear bearings of the spindle) in the spindle box of the right vertical tool post. However, unexpectedly, all rolling bearings were normal. Later, after research, analysis and detailed inspection, it was found that the four pipes that provide lubricating oil to the worm gear of the worktable and the nut strip fixed at the bottom of the worktable were basically not supplying oil. After adjusting the four needle-shaped throttle valves on the machine bed that control the oil flow of the four oil pipes, the lubricating oil flow was normalized, and the fault disappeared. Repairing a fault with high lubricating oil consumption: Fault symptom: The TH5640 vertical machining center experienced high lubricating oil consumption in its centralized lubrication station, requiring refilling every one day, and a significant amount of lubricating oil was clearly mixed into the cutting fluid. Analysis and handling process: The TH5640 vertical machining center uses a volumetric lubrication system. Initially, this fault was thought to be caused by too short a lubrication interval, frequent starts of the lubrication motor, and excessive lubrication, leading to high lubricating oil consumption in the centralized lubrication station. Changing the lubrication motor start interval from 12 minutes to 30 minutes improved the lubricating oil consumption in the centralized lubrication station, but the oil consumption remained high. Therefore, attention was focused on checking the lubrication lines. The lubrication lines were intact and there were no leaks, but it was found that there was particularly high levels of lubricating oil in the Y-axis leadscrew nut. Upon unscrewing the Y-axis leadscrew nut lubrication metering component, inspection revealed that the Y-shaped seal in the metering component was damaged. After replacing the lubrication metering component, the fault was resolved. Repairing Insufficient Guide Rail Lubrication: Fault Phenomenon: Insufficient lubrication of the Y-axis guide rail in the TH6363 horizontal machining center. Analysis and Handling Process: The TH6363 horizontal machining center uses a single-line damping lubrication system. Initially, it was thought that the lubrication interval was too long, leading to insufficient Y-axis lubrication. Changing the lubrication motor start interval from 15 minutes to 10 minutes improved the Y-axis guide rail lubrication somewhat, but the oil volume was still unsatisfactory. Therefore, attention was focused on checking the lubrication pipeline, which was found to be intact. Upon unscrewing the Y-axis guide rail lubrication metering component, it was discovered that the small hole in the metering component was blocked. After cleaning, the fault was resolved. Repairing Lubrication System Pressure Failure: Fault Phenomenon: In the TH68125 horizontal machining center, the lubrication system pressure failed to build up. Analysis and Handling Process: After assembling the TH68125 horizontal machining center, a lubrication test was conducted. This horizontal machining center uses a volumetric lubrication system. After power-on, the lubrication motor rotated, but the lubrication system pressure consistently failed to build up. The lubrication pump was found to be functioning normally, and pressurized oil was present at the lubrication station outlet. The lubrication lines were inspected and found to be intact. Inspection of the X-axis ball screw bearing revealed a significant amount of lubricating oil leaking from the bearing. The measuring element, model ASA-5Y, was examined. The manufacturer's lubrication manual indicated that ASA-5Y is for a single-line damping lubrication system, while the machine tool uses a volumetric lubrication system. Measuring elements from these two systems cannot be mixed. Replacing the volumetric lubrication system measuring element (ZSAM-20T) resolved the problem.