【 Abstract 】 Lubrication of machine tools and cleaning of hydraulic systems are basic and important tasks in machine tool maintenance, which directly affect the performance of machine tools. By comparing case studies, we can fully enhance our understanding of the importance of machine tool lubrication and cleaning, which can help reduce the occurrence of machine tool failures, better utilize the overall performance of machine tools, and extend equipment lifespan.
【 Keywords 】 Machine tool; Hydraulic system; Lubrication; Cleaning; case
1. The significance and purpose of lubrication in ensuring smooth motion of machine tool friction pairs
Lubrication refers to the technical measure of improving the friction state of a friction pair to reduce frictional resistance and slow down wear. Usually, lubrication is achieved by adding lubricant to the friction pair. The common lubricants used by the chemical machinery company for machine tool lubrication include liquid lubrication (anti-wear hydraulic oil) and solid lubrication (graphite, molybdenum disulfide, etc.). Adding sufficient and corresponding effective lubricants can effectively reduce the metal wear of the motion pair, improve machine performance, extend machine life, and save energy.
1.1 Lubrication Function
Reduce friction coefficient: Adding appropriate lubricant to the contact surfaces of two opposing friction will form a friction reducing layer with a lubricating oil film, reducing friction coefficient, feeding frictional resistance, and reducing power consumption.
Reduce wear: Lubricants between friction surfaces can reduce wear caused by hard particle wear, surface corrosion, biting and tearing between metal surfaces, etc.
Prevent corrosion and protect metal surfaces: Avoid mechanical metal surfaces from rusting, corrosion, and damage.
Cleaning and rinsing: prevent the surface from being scratched by solid impurities, so that the processed steel surface has good quality and surface roughness.
1.2 Hazards of untimely lubrication and incorrect use of lubricating oil
Case 1: In the evening of mid May 2017, the DVT630 CNC vertical lathe produced by Qizhong Group made a piercing whistling sound while lifting the crossbeam of the machine tool, and the column felt a slight vibration. The operator stopped working in a timely manner and judged based on experience that the problem was with the column ball screw. The next day, the equipment management personnel, together with the manufacturer's after-sales personnel, inspected the machine tool and preliminarily determined that the possible cause of this phenomenon was: 1) damage to the connection between the ball screw and nut. 2) Due to the lack of lubricating oil, the surface of the ball screw rusted or scratched, resulting in a large amount of iron filings, which hindered the screw from rotating. Considering that the machine tool has not been put into production for a long time, we temporarily reject the possibility of 1 and use the possibility of 2 as the main problem to solve. Through PLC online monitoring, it was found that there was no start signal for the lubricating oil pump on the crossbeam. After replacing the signal wire, the problem still exists. After disassembling the two columns, it was found that the ball screw sealing gasket was damaged, causing the lubricating oil output from the column lubricating oil pump to be unable to adhere; The lubricating oil appears noticeably black; The lubricating oil pump is running low on oil. After taking corresponding measures, the whistling disappeared, but the vibration of the machine tool still existed. Afterwards, use high-grade lubricating oil (to reduce the impact of ambient temperature on the oil) and add solid lubricant (molybdenum disulfide) to enhance the adhesion of the lubricating oil on the ball screw. After the implementation of the method, the whistling and vibration disappeared. And there were no similar problems during the subsequent rainy season and high-temperature operations, with significant effects.
According to Case 1, it is crucial to maintain and upkeep the performance of the machine tool by using the correct lubricating oil in a timely and appropriate manner in the key friction pairs of the machine tool. The new machine tool in the case, due to the operator's lack of effective maintenance measures and failure to adopt correct lubrication methods and lubricants during regular maintenance, resulted in excessive wear of the friction pair and almost caused a serious equipment damage.
Case 2: The C61125E 15 meter horizontal lathe in the same workshop is an old machine tool that was put into operation in 1978. During regular maintenance, the operator pays special attention to the lubrication of the spindle box, chuck, guide surface, center frame, tailstock, and other components of the machine tool. The above components have not been shut down for maintenance in the past three years.
1.3 Key points of lubrication work
Comparing Case One and Case Two, it can be seen that lubrication work should be a key and persistent important task for equipment management and usage departments in the mechanical processing industry. A slight negligence may lead to unnecessary or even significant equipment accidents. In addition, as riveting and welding construction is the main process of the chemical machinery company, there are many impurities such as smoke and welding slag in the factory building. Therefore, when more precise machine tools and riveting and welding work areas coexist, the surrounding environment should be cleaned in a timely manner to prevent damage to the friction pair caused by large solid impurities.
2. The main lubrication management tasks
1) Three level filtration system; Storage filtration, distribution filtration, and oil injection filtration. 2) Five determinations: timing, personnel, quantity, regularity, and quality. 3) Strict inspection system and sound inspection records.
The Position and Function of Oil in Hydraulic Systems
The safe, reliable, and stable operation of hydraulic systems is the key to ensuring the normal operation of machine tools. Oil contamination is the main cause of hydraulic system failure and premature wear or damage of hydraulic components. Therefore, controlling hydraulic system oil pollution in machine tools has become the key to ensuring safe, efficient, and economical operation of equipment, and must be taken seriously.
2.1 Hazards of contamination in machine tool hydraulic systems
1) Oil contaminated particles enter the clearance between hydraulic components, intensifying surface friction of sliding components, scratching the accuracy and roughness of the mating surface, increasing leakage, shortening component life, and causing abnormal operation. 2) Polluting particles may clog the damping holes of hydraulic components, block the control valve ports, and prevent the hydraulic components from working properly. Especially for CNC machine tools, once the flow control valve is blocked, it means that the oil pressure information cannot be transmitted, causing the machine tool to stop running. 3) Oil contamination can cause changes in the viscosity of hydraulic oil, reducing its physical and chemical properties such as emulsification resistance and lubricity, leading to premature aging and failure of the oil, and causing various system failures. 4) According to equipment management records and monthly on-site comprehensive inspections and statistics, it was found that there are two main reasons for oil pollution in chemical machinery factory machine tools:
a. Solid pollutants: mainly include chips, welding slag, dust, burrs, etc.
b. Mixing water, cleaning oil, or other types of hydraulic oil.
According to statistics, the hydraulic system pollution caused by reason A is mainly concentrated in lathes, planers, and coils? Machine tools with exposed friction pairs; The hydraulic system pollution caused by reason B mainly manifests in drilling machines and boring machines.
2.2 Main measures to prevent contamination of machine tool hydraulic systems
1) Pay attention to daily maintenance, strengthen education for machine tool operators, and do a good job in routine maintenance and primary maintenance.
2) Regularly inspect and replace the oil tank filter element of the old machine tool, and clean the oil tank pipeline.
3) Before using the new machine tool, use a professional filter to inject new oil from the oil drum into the oil tank, and pay attention to the cleanliness of the oil delivery pipe to prevent impurities from entering the oil tank.
Two cases are presented to illustrate the impact of pollution in the hydraulic system of the oil tank on the use of machine tools and the effectiveness of cleaning.
Case 3: On April 21, 2018, the FBC200r CNC boring and milling machine produced by Shenyang Zhongjie Group experienced a situation where the machine spindle did not move and the oil pressure alarm signal repeatedly appeared, seriously affecting the production schedule. After on-site inspection and comparison with similar maintenance cases, it was determined that the hydraulic oil in the oil tank had deteriorated, causing a decrease in hydraulic oil viscosity and an output oil pressure that did not meet the requirements for starting the machine tool. After opening the spindle of the machine tool, it was found that the connecting valve port of the hydraulic oil pipe's return oil line was disconnected, and the return oil mixed with cooling cutting oil, water, etc., seriously polluting the hydraulic oil in the return oil tank and causing oil emulsification; In addition, the pollution of iron filings and dust has also caused the deterioration of engine oil. The above situation caused the spindle of the machine tool to stop rotating and the oil pressure alarm signal. After repairing and cleaning the return oil pipeline, thoroughly replacing the hydraulic oil in the oil tank, the alarm signal disappeared and the machine tool resumed operation.
Case 4: On June 10, 2018, the DVT1000 CNC vertical lathe chuck produced by Qizhong Group experienced a stoppage after rotating twice. Using a dial gauge to measure the floating height of the oil film, it shows only 0.03mm, while the designed floating height of the machine tool is between 0.08-0.15mm. It can be seen that the floating height of the chuck is insufficient, causing the machine tool to stop and protect itself. After inspecting the main components of the hydraulic system such as the machine tool oil tank, pipelines, and electrical components, it was found that the main problems were: 1) emulsification and blackening of oil accumulation in the hydraulic station oil tank in the pit; 2) Two of the four oil flow control valves and pressure valves are damaged; 3) There are signs of iron filings, welding slag, and dust invading the main oil tank, causing blockage in the main oil pipeline; It is basically concluded that the above reasons led to insufficient floating of the machine tool chuck. After taking corresponding measures, the machine tool was promptly restored to use.
The above case brings us inspiration: the hydraulic system is the key to the operation of machine tools, and ensuring the cleanliness of the hydraulic system mainly depends on ensuring the cleanliness of the hydraulic oil and pipelines. Only by timely and regular cleaning of the hydraulic system can the safety and stability of the machine tool system and machine tool be ensured.
2.3 Pollution Control of Machine Tool Hydraulic System
The pollution control of machine tool hydraulic system runs through the design, manufacturing, installation, use and maintenance process of hydraulic system. System pollution amount=original and newly generated pollutants in the system+invading pollutants in the system - pollutants filtered out by the system oil filter. Before putting machine tools and other equipment into use, all hydraulic components and pipelines in the hydraulic system must be pickled and cleaned to eliminate the possibility of impurities generated during the manufacturing process contaminating the oil; Daily maintenance: Strictly follow the maintenance procedures to regularly clean the hydraulic system; In the later stage of equipment life, due to factors such as material aging, it is necessary to update or undergo overall overhaul and maintenance according to the actual situation. The above content is directly related to the normal operation of the hydraulic system and should not be taken lightly.
2.4 Effects of Hydraulic Oil Temperature
In the post analysis of the hydraulic oil emulsification phenomenon in Case Three and Case Four, in addition to other cutting oil and water mixed hydraulic oils, the high temperature during the hydraulic oil circulation process was also the cause of hydraulic oil emulsification. Data shows that high temperatures can affect the thermal and oxidative stability of oil, causing changes in the chemical quality of the oil and resulting in emulsification. Emulsified and deteriorated oil can directly cause uneven oil film or even insufficient thickness, leading to insufficient pressure. In summer, especially during the Huangmei season unique to the Jianghuai region, the climate is humid and hot, and chemical fluids such as hydraulic oil are prone to deterioration. Based on this, we have learned a lesson and installed cooling devices for several heavy-duty machine tools that operate frequently throughout the year to ensure temperature control of the machine tool oil pressure system (oil temperature of 30 ℃ to 40 ℃ is appropriate).
3. Conclusion
Machine tools are common and direct production equipment in processing enterprises, and various malfunctions are inevitable during long-term use. Finding the right causes and solving them correctly can improve the performance of machine tools and extend the service life of equipment. And the inspection of machine tool lubrication and hydraulic system during regular maintenance is one of the important tasks. Only by doing this job well can we truly make good use of the machine tool and manage it well. This article only briefly explains the lubrication and cleaning of equipment in machine tool maintenance work. In the future, more problems will be encountered in more contact with machine tool maintenance. As long as we summarize and generalize carefully, we will definitely learn and master more knowledge about machine tool maintenance.
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2025-06-08