Equipment maintenance, fault diagnosis methods, and inspection of components

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1. Concept: Equipment maintenance is one of the main aspects of equipment management during its usage period. During use, the components of a device gradually experience wear, deformation, breaking, rusting, and other such issues. Equipment repair is a technical process that involves disassembling and reassembling, as well as making adjustments to the entire device or its individual components, in order to replace or fix worn-out parts when the device malfunctions due to changes in its technical condition. The goal is to restore the device’s functionality or precision and maintain its good condition. In other words, equipment repair is a technical activity carried out to restore the functionality of equipment when its technical condition deteriorates to a certain critical level. For the repair of equipment, a prevention-oriented approach must be adopted, and the appropriate maintenance method should be selected based on the nature of the enterprise’s production, the characteristics of the equipment, and the role it plays in the production process. By employing various methods such as routine inspections, periodic checks, condition monitoring, and diagnostics, it is necessary to accurately understand the technical condition of the equipment, enhance the planning for repairs, and thoroughly prepare the technical and production aspects prior to carrying out those repairs. During repairs, new processes, technologies, materials, and modern scientific methods should be actively employed to ensure repair quality, reduce downtime, and lower repair costs. At the same time, necessary improvements and repairs are carried out in conjunction with maintenance to enhance the reliability and maintainability of the equipment, thereby fully utilizing its efficiency. Equipment maintenance is the technical activity carried out to maintain and restore the ability of equipment to perform its designated functions, including upkeep and repair. The method of equipment maintenance implies a maintenance strategy. Equipment management emphasizes the use of different maintenance methods for various types of equipment; it stresses that equipment maintenance should follow the objective laws governing the physical movement of the equipment. While ensuring production continues, maintenance resources should be utilized efficiently in order to achieve the most economical lifecycle costs. 2. Post-maintenance: Post-maintenance refers to the repair of certain production equipment that are not included in the preventive maintenance plan; repairs are carried out after a failure occurs or when the equipment’s performance or accuracy drops to a level that no longer meets the production requirements. Adopting a reactive maintenance strategy (i.e., repairing only when it breaks) can maximize the service life of the main components, resulting in cost-effective maintenance. After-sales maintenance, as a maintenance strategy, differs from the original and outdated approach of post-repair fixes. After-sales maintenance is not applicable to equipment that has a significant impact on production. Its typical areas of application include: 1) Equipment for which repairs after a failure-induced shutdown will not result in any losses to production ； 2) Equipment whose repair techniques are not complex and for which spare parts can be provided promptly ； 3) Some equipment with low utilization rates or that has backups. 3. Preventive maintenance: Maintenance activities that are carried out in accordance with pre-established repair plans and technical requirements, in order to prevent a decline in equipment performance and accuracy or to reduce the failure rate, are known as preventive maintenance. Implementing preventive maintenance on key and important equipment is an essential task for carrying out the \"prevention first\" principle stipulated in the equipment management regulations. There are mainly the following types of preventive maintenance. (1) Regular maintenance: Regular maintenance is a preventive maintenance activity carried out at scheduled times, and it has a periodic nature. It determines the repair interval, repair type, repair content, and repair workload in advance, based on the failure patterns of the components. It is mainly applicable to batch production equipment and power equipment with stable and continuous operation, for which the patterns of equipment wear are already known. The current systems for regular equipment maintenance consist primarily of planned preventive maintenance and planned warranty systems. 1) The planned preventive maintenance system is abbreviated as the planned pre-maintenance system. It is a equipment maintenance system that carries out maintenance, inspection, and repair of equipment based on the patterns of wear and tear, as well as predetermined repair schedules and the equipment’s structure, in order to ensure that it remains in good technical condition at all times. 2) The planned warranty system is also known as the maintenance and repair system. It is a repair system that combines maintenance and scheduled inspections. (2) Condition monitoring maintenance: This is a type of preventive maintenance that involves carrying out repairs based on the technical condition of the equipment, according to actual needs. It is based on condition monitoring and technical diagnosis to understand the progression of equipment degradation; by enabling high-level prediction, it allows for the scheduling of preventive repairs, also known as predictive maintenance. The basis of this maintenance approach is to use the large amount of information generated from various inspections, maintenance activities, operations, and repairs – particularly diagnosis and monitoring – to make accurate assessments through statistical analysis regarding the degree of equipment degradation, the locations where failures have occurred (or are likely to occur), and the trends in the equipment’s technical condition, so as to determine the appropriate type of maintenance to carry out. This allows for full control over maintenance activities, proper preparation before repairs, and coordination with production plans; it not only improves the equipment’s availability but also maximizes the service life of the components. Due to the limitations imposed by advances in diagnostic technology, it is primarily applicable to critical equipment, as well as high-utilization precision, large-scale, and rare-type equipment – in other words, equipment for which it is worthwhile to invest in diagnosis and monitoring in order to minimize the consequences of failures and avoid unnecessary maintenance activities. It represents the future direction for equipment maintenance in enterprises; as stated in the Equipment Management Regulations, \"Enterprises should actively adopt a equipment maintenance approach based on condition monitoring.\" 3. Improving maintenance: Measures taken to eliminate inherent defects or frequent failures in equipment by modifying its local structure and component design, and to enhance its reliability and maintainability through repairs, are known as improving maintenance. The concepts of improved maintenance and technical renovation of equipment are different. The main difference is that the former aims to improve the reliability and maintainability of individual parts, thereby reducing the equipment’s failure rate as well as maintenance time and costs; whereas the latter aims to compensate for the intangible wear and tear of the equipment, thus enhancing its performance and accuracy. Equipment repair categories: The repair categories for preventive maintenance include major repairs, medium repairs, itemized repairs, and minor repairs. 1. Major repair: Equipment major repair is the type of planned maintenance that involves the most work. It is a type of repair that involves comprehensive restoration of machinery and equipment. It is used when the standard parts of the equipment are severely worn, resulting in the loss of most of its precision and performance; only through comprehensive repair can its functionality be restored. Major equipment repairs require the complete disassembly of the equipment, repair of the components that serve as references for maintenance, replacement or repair of worn parts; all guide rail surfaces must be polished and ground; the electrical system of the equipment also needs to be repaired and adjusted ； Repair the attachments of the equipment and refurbish its appearance, thereby completely eliminating the defects present before the repair and restoring the equipment to its specified accuracy and performance. To compensate for the invisible wear and tear of equipment, major repairs should also be combined with the use of new technologies, processes, and materials to upgrade, improve, and modify the equipment, thereby enhancing its efficiency. 2. Medium repair: Medium repair involves replacing or fixing the main components of machinery and equipment, as well as a number of other worn parts. It also includes checking and adjusting the entire mechanical system, tightening all components, and correcting the benchmarks of the machinery and equipment, in order to ensure that the equipment is restored to its proper standards and technical requirements. Medium-term maintenance is a type of planned repair characterized by frequent occurrences, short intervals between repairs, relatively low workload, short duration for each repair, and lower costs. The workload of a medium repair lies between that of a major repair and a minor repair, and the requirements for a medium repair are lower than those for a major repair. In the implementation of mid-overhaul in our country, it is commonly noted that \"aside from the lack of painting, a mid-overhaul is difficult to distinguish from a major overhaul.\" Therefore, many companies have eliminated the medium repair category. 3. Item repair: Project repair (abbreviated as item repair) refers to targeted partial repairs aimed at addressing defects that degrade the accuracy and performance of equipment. During maintenance, local disassembly and inspection are generally carried out to replace or repair defective parts; when necessary, the reference components are also repaired locally and their coordinates are adjusted, thereby restoring the performance and accuracy of the repaired section. Xiang Xiu’s workload depends on the actual circumstances. Xiangxiu emerged as a result of continuous reforms in practice, based on a summary of the positive and negative experiences gained from implementing the equipment preventive maintenance system in the past, and alongside the wider adoption of condition-based maintenance. Under the planned preventive maintenance system, the differences in factors such as the factory-quality of specific equipment, operating conditions, load rates, and the quality of maintenance are often overlooked. Instead, planned repairs are scheduled according to a uniform repair cycle structure and intervals, which leads to two problems: first, some components of the equipment are still in good technical condition, yet scheduled for medium or major repairs, resulting in unnecessary repairs; second, when the technical condition of the equipment has deteriorated to the point where it can no longer meet the requirements of the production process, no planned repairs are carried out due to the fact that the repair deadline has not yet arrived, leading to neglect of maintenance. Using item-based maintenance can avoid the aforementioned drawbacks, as well as reduce downtime and maintenance costs. Especially for single critical pieces of equipment or specialized devices used in assembly line production, repairs can be carried out during production breaks (such as holidays), thereby ensuring the smooth continuation of production. 4. Minor repairs: Minor repairs represent the type of planned maintenance with the least amount of work involved. They refer to routine minor fixes for equipment that is maintained using a condition-based (monitoring) approach. The tasks involved in minor repairs include addressing issues identified through daily inspections and periodic checks; removing relevant components for inspection, adjustment, or replacement, as well as fixing any defective parts in order to restore the equipment’s normal functionality ； For equipment that requires regular maintenance, the tasks involved in minor repairs mainly consist of replacing or repairing those parts that have failed or are about to fail during the maintenance interval, based on the known patterns of wear and tear, as well as making adjustments to ensure the equipment’s proper operational capacity. 5. Regular precision adjustment: Regular precision adjustment involves periodically adjusting the geometric accuracy of precision, large-scale, and low-volume machine tools to bring it to (or close to) the specified standards. The cycle for precision adjustment is generally 1 to 2 years. Adjusting the timing is best done in seasons with minimal temperature changes. Performing regular precision adjustments helps maintain the stability of the machine tool’s precision, thereby ensuring product quality. 6. Regular preventive testing: For equipment with high safety requirements, such as power equipment, pressure vessels, electrical equipment, and lifting and transportation equipment, professionals carry out tests at specified intervals and in accordance with established requirements. These tests include checks on pressure resistance, insulation, resistance, grounding, safety devices, indicating instruments, load capacity, limiters, brakes, etc. Through experiments, problems can be identified in a timely manner, potential hazards can be eliminated, or repairs can be scheduled. Repair cycle and repair cycle structure: The equipment repair cycle and repair structure are based on the theories of equipment wear and friction, and serve as the foundation for planning repairs. 1. Repair cycle: The repair cycle refers to the time interval between two consecutive major repairs, or the time from when new equipment starts to be used until its first major repair (expressed in terms of actual operating hours or output). The repair cycle is determined comprehensively based on factors such as the equipment’s structure, process characteristics, production type, the allowable wear limit of components, and the level of maintenance. The decisive factors are the service life of the main components and the working shifts. Different device types and production conditions result in different repair cycles. 2. Repair cycle structure: The repair cycle structure refers to the types, frequencies, and sequence of planned maintenance tasks that should be carried out within a single repair cycle. Different devices or different repair systems can have different repair cycle structures. 3. Repair interval: The repair interval refers to the time between two consecutive repairs (regardless of whether they are major, medium, or minor repairs). The interval period is primarily determined based on the actual operating hours of the equipment, the service life of the wear parts, as well as routine maintenance and inspection activities. The role of equipment maintenance: 1. Equipment suffers from both intangible and tangible wear during use. Intangible wear refers to the decline in the economic value of equipment over time, as well as due to the emergence of newer equipment and advances in technology, even before the equipment is put into use or while it is in use. Physical wear of equipment refers to the decline in its performance over time as it is used. Equipment fails due to factors such as wear and tear, corrosion, and deformation under stress, which results in a loss of its utility. Through maintenance, it is possible to influence, control, or compensate for this wear and degradation. Scientific and reasonable maintenance enables equipment to operate for a long time under normal conditions, reduces the occurrence of failures and the resulting downtime losses, and lowers production costs. 2. Wear and tear represents a deterioration in the functional capabilities of a device’s physical structure as well as a decrease in its value. Maintenance involves restoring the functional capabilities of the device due to wear and tear, as well as compensating for the loss in its value. From an investment perspective, each repair represents an addition of value or an investment for the future. 3. Maintenance is an important component of production costs. Reducing maintenance expenses means lowering production costs and increasing the profitability of the enterprise. As business competition intensifies, reducing maintenance costs has become an issue of concern for the business community. According to statistics, maintenance costs account for 70% of the total cost over the equipment’s life cycle. 4. Extension of the significance of maintenance: Through maintenance, it is possible not only to restore the functionality of equipment but also to improve its performance, extend the lifespan of its components. Moreover, through feedback, the design department can refine its designs, thereby enhancing the inherent reliability of the equipment. 5. Objectives and guidelines for equipment inspection (maintenance). The core issue in equipment maintenance is to determine appropriate maintenance strategies for various types of equipment, based on their degree of wear and degradation, in conjunction with the company’s business objectives; plans are then formulated and implemented. To reduce equipment failure rates, it is not sufficient to simply repair the faulty equipment; instead, the company’s production conditions, maintenance techniques, maintenance organization, and maintenance resources must all be taken into consideration to determine how to carry out equipment maintenance. Therefore, maintenance in enterprises is not merely about repairing faulty equipment or minimizing the life-cycle cost of individual devices; rather, it aims to achieve the overall efficiency of the enterprise. To this end, it is necessary to optimize the decision-making for maintenance. Optimization of maintenance decisions includes the selection of maintenance plans, maintenance timing, maintenance methods, maintenance organization, maintenance resources, and repair techniques. Maintenance mode and selection of maintenance strategies 1. Classification of equipment maintenance (1) Daily equipment maintenance The main tasks of daily maintenance include lubricating the equipment, cleaning it, conducting inspections, and fixing minor faults; these activities are part of the self-maintenance process. Minor repairs, which include the inspection, adjustment, tightening of equipment, as well as partial disassembly and repair, are also included in routine maintenance. (2) Major overhaul of a single piece of equipment: Such an overhaul involves completely disassembling the equipment, inspecting, cleaning, repairing, replacing, and reassembling all its components, as well as making adjustments (such as adjusting the clearances in mechanical transmissions and setting and verifying parameters of electrical and internal control systems). It also includes testing, trial operation, acceptance, and commissioning of the equipment. (3) System shutdown for major repairs: For continuous production lines and process industries, production plants or factories represent complex production systems. The complete system shutdown for major maintenance involves all production units, main equipment, and utility systems. Therefore, a very strict and comprehensive management procedure must be established for the shutdown overhaul of the entire system, creating a tightly integrated management system that comprises procedures such as equipment maintenance planning, construction organization, maintenance techniques, resource control, safety measures, quality assurance, site management, and the start-up and shutdown of production. 2. Methods and Selections for Equipment Maintenance (1) Maintenance Methods: As production equipment becomes more complex, maintenance techniques improve, and technologies for monitoring equipment condition and diagnosing faults continue to evolve, along with innovations in maintenance theory, maintenance methods are also constantly developing and changing, giving rise to a variety of maintenance approaches and combined maintenance models. The commonly used maintenance methods at present include the following: 1) Planned maintenance, 2) Preventive maintenance, 3) Corrective maintenance, 4) Production maintenance, 5) Reactive maintenance, 6) Predictive maintenance, 7) Condition-based maintenance, 8) Reliability-based maintenance, 9) Utilization-centered maintenance. (2) Selection of maintenance methods There are generally three strategies for selecting maintenance methods: reactive maintenance, scheduled maintenance, and condition-based maintenance. The main factors affecting the choice of maintenance method are the failure characteristics of the equipment, its reliability, and the cost of maintaining it. 1) Fault characteristics of the equipment. It is mainly determined by the manufacturer from a design perspective, including the service life of the components and their wear condition. The users of the equipment make modifications based on the specific operating conditions and their experience, thereby determining or influencing the failure characteristics and service life of the equipment. 2) The validity of the equipment. This is proposed based on the importance of the equipment in production, the technical difficulty of maintenance, and economic feasibility. Especially intensive-type facilities require a high degree of efficiency, such as urban transportation systems, power supply systems, water supply systems, and highly automated manufacturing plants. The determined device effective life is too low, resulting in an increase in failures ； Excessive effectiveness leads to over-maintenance and high operating costs. 3) Maintenance costs. What amount needs to be invested as a cost to achieve the desired equipment efficiency, including both direct and indirect maintenance costs. Direct repair costs generally include the labor, materials, equipment, spare parts, energy, and inspection expenses incurred by the repair department that are directly used for repairs. Indirect maintenance costs include preparation costs, downtime costs, startup costs, and additional fees. In deciding on the optimal maintenance approach, the indirect maintenance costs of certain equipment should be given priority. Routine after-maintenance is suitable for non-critical equipment, where the losses caused by failures are minor, the consequences of those failures are not severe, or redundant equipment is available. Regular maintenance is suitable for equipment with distinct failure cycles, or for some important devices whose failure cycles are not obvious, provided that the failure patterns and wear conditions of the equipment are known. For continuous production systems, the schedule for regular equipment maintenance is determined based on the production plan and the operating condition of the equipment. Condition-based maintenance is suitable for important or critical equipment. By utilizing monitoring techniques, it is possible to analyze and diagnose the location, cause, severity, and development trend of equipment failures, as well as to determine the timing and scope of repairs, thereby avoiding excessive repair costs associated with planned or preventive maintenance. Of course, the choice of repair method is based on a comprehensive consideration of factors such as the fault characteristics of the equipment, its role in production, the characteristics of production, and repair costs. A combined maintenance approach can also be adopted. Common methods for diagnosing equipment failures, as well as for inspecting and examining mechanical components. The common simple methods for condition monitoring include auscultation, tactile inspection, and observation. 1. Auscultation: When the equipment is operating properly, the sounds produced always have a certain rhythm and pattern. By becoming familiar with and mastering these normal melodies and rhythms, one can use their auditory sense to detect any abnormal noises such as heavy, harsh, strange, or chaotic sounds coming from the equipment, and thus identify potential issues like looseness, collisions, or imbalance inside the equipment. By tapping the part with a hammer and listening for any cracking noises, it is possible to determine whether cracks have formed. An electronic stethoscope is a vibration acceleration sensor. It converts the vibration conditions of the equipment into electrical signals and amplifies them; workers use headphones to listen to the vibrations of the operating equipment, thereby enabling qualitative measurement of those sounds. By measuring the signals at the same measurement point at different times, under the same rotational speed and under the same operating conditions, and comparing them, it is possible to determine whether there is a fault in the equipment. When crisp and high-pitched noises are heard from the headphones, it indicates a high vibration frequency; usually, this is caused by local defects or tiny cracks in components that are relatively small in size but have relatively high strength. When the headphones produce a muffled, low-frequency noise, it indicates that the vibration frequency is low; generally, this is due to large cracks or defects in components that are relatively large in size and have relatively low strength. When the noise coming from the headphones increases compared to normal, it indicates that a fault is developing; the louder the sound, the more severe the fault. When the noise coming from the headphones appears intermittently in a chaotic manner, it indicates that a component or part is loose. 2. Touch sensing method: The tactile sense of the human hand can be used to monitor changes in the temperature, vibration, and clearance of equipment. The nerve fibers in the hands are sensitive to temperature, allowing them to detect temperatures down to 80°C with relatively high accuracy. When the temperature of the component is around 0°C, it feels icy to the touch; prolonged contact can cause a piercing pain. At around 10°C, it feels cool to the touch, but it is generally tolerable. At around 20°C, it feels slightly cool to the touch; as contact time increases, it gradually becomes warmer. At around 30°C, it feels slightly warm to the touch, providing a comfortable sensation. At around 40°C, it feels warm to the touch, with a slight burning sensation. At around 50°C, it feels quite hot to the touch; if one presses with the palm for an extended period, sweating will occur. At around 60°C, it feels very hot to the touch, but it is generally tolerable for up to 10 seconds. At around 70°C, it feels scorching hot to the touch; one can generally only tolerate it for about 3 seconds, and the area touched by the hand turns red very quickly. When touching, touch it first and then feel it more carefully to estimate the temperature rise of the component. By shaking the component by hand, it is possible to sense the gap size of 0.1mm–0.3mm. By touching the components with your hand, you can sense changes in the intensity of vibration and whether shocks are generated, as well as the movement of the slide. Using a thermometer equipped with a surface thermocouple probe to measure the surface temperature of components such as rolling bearings, sliding bearings, spindle boxes, and motors offers the advantages of rapid identification of the location of thermal abnormalities, accurate data, and a convenient testing process. 3. Observation method: The human eye can be used to check whether there is any looseness, cracks, or other damage in the components of the equipment ； It is possible to check whether the lubrication is proper, as well as to detect any signs of dry friction or leaks ； It is possible to examine the quantity, size, and characteristics of metal particles in the fuel tank sediment in order to assess the wear level of related components ； It is possible to monitor whether the device is moving properly and whether any abnormal phenomena occur ； It is possible to view the various gauges installed on the device, which indicate its operating status, in order to monitor changes in the data. Product quality can be checked, and the device’s operating condition can be assessed by using measurement tools and by directly observing the surface condition. By conducting a comprehensive analysis of the various observations, it is possible to determine whether there is a fault in the equipment, identify the location of the fault, assess the severity of the fault, and determine its cause. A simple method for monitoring wear conditions by using instruments to observe the wear particles collected from the equipment’s lubricant is the magnetic plug method. Its principle involves inserting a magnetic plug into the lubricating oil to collect the iron particles generated by wear; by using a reading microscope or simply observing with the naked eye, the size, quantity, and shape of these particles are examined in order to determine the degree of wear on the surface of mechanical parts. The magnetic plug method can be used to observe the larger particle sizes that appear in the later stages of wear of mechanical parts. During inspection, if small abrasive particles are found in small quantities, it indicates that the equipment is operating properly ； If large abrasive particles are detected, it is necessary to pay close attention and closely monitor the operating condition of the equipment ； If large particles are found repeatedly in succession, it is a sign that a failure is imminent; the machine should be stopped immediately for inspection to identify and resolve the issue. How to inspect mechanical components: Component inspection is an important part of the mechanical maintenance process. Through inspection, the technical condition of the machinery and its components is determined, as well as the corrective actions that need to be taken. Subsequently, inspections are also used to assess the technical quality of the machinery after repairs. 1. Main aspects of part inspection In mechanical maintenance, parts are generally inspected one by one, and the main aspects of this inspection can be divided into the following categories: 1) Inspection of the geometric accuracy of parts. Geometric accuracy includes dimensional accuracy as well as shape and position accuracy. However, in maintenance work, the focus is sometimes not on the geometric dimensions of individual parts, but rather on the relative fit between them, which is often an important aspect of the inspection process. Common precision requirements for shape and position during maintenance include roundness, cylindricity, concentricity, coaxiality, parallelism, and perpendicularity. 2) Inspection of surface quality: The inspection of the surface quality of parts during maintenance work is not limited to checking the surface finish; it also involves checking for defects such as scratches, burns, and roughness on the surfaces of used parts. 3) Inspection of mechanical properties: Given the characteristics of mechanical maintenance, in addition to checking the hardness, which is one of the mechanical properties of the material used for parts, other parameters are generally not examined. However, certain properties that arise during part manufacturing and maintenance, such as balance and spring stiffness, cannot be ignored. 4) Inspection for hidden defects: During the manufacturing process, parts may have inherent defects such as inclusions and voids, and microscopic cracks may form during use. These defects cannot be detected directly through ordinary observation and measurement, but they can have serious consequences for the machinery; therefore, during mechanical maintenance, certain components must be thoroughly inspected purposefully. 2. Methods of part inspection There are many methods for inspecting parts, and new inspection technologies are constantly evolving. However, based on the actual practices of mechanical maintenance, it can be summarized into the following aspects: 1) Visual inspection method. This is a method that does not require examining the equipment; instead, it relies on the inspector’s intuitive sense to assess the technical condition of the parts. This method is simple, and it also makes it easier to identify defects in the numerous components that are disassembled during mechanical maintenance; therefore, it remains useful. However, this method cannot be used to inspect parts with high precision requirements, and it demands that the inspector have extensive experience. 2) Instrument and tool inspection method: A large amount of inspection work is carried out using instruments and tools. Due to the varying principles of operation and types of instruments and tools, they can be classified into general-purpose measuring tools, specialized measuring tools, mechanical instruments and meters, optical instruments, electronic instruments, etc. 3) Physical inspection method: This is a technique that utilizes physical quantities such as electricity, magnetism, light, sound, and heat, as well as the changes they cause in the workpiece, to determine the technical condition of the parts. The implementation of this method is also combined with instrument and tool inspection methods. This method is typically used to detect hidden defects inside parts without damaging the parts themselves; it is commonly known as non-destructive testing. Non-destructive testing techniques have been developing increasingly in recent years, and the methods widely used in production today include magnetic particle testing, penetrant testing, ultrasonic testing, and radiographic testing. 3. Visual inspection of parts 1) Visual inspection: This is the main aspect of visual inspection in terms of part evaluation; issues such as fractures and macroscopic cracks in the parts, obvious bending and warping, burns and scratches on the surface of the parts, as well as severe wear, can usually be identified with the naked eye. To improve the accuracy of visual inspection, a magnifying glass can also be used in some cases. To compensate for the limitations of vision in inspecting the interior of certain walls, optical fibers can also be used as endoscopes for light transmission. 2) Auditory inspection: A method that relies on the auditory capabilities of the human ear to determine whether mechanical parts have defects is an established inspection technique. This method has been used for the routine inspection of railway vehicles for decades. During inspection, the part under examination is tapped; when there are no defects in the part, the sound is clear, while if there are internal shrinkages, the sound becomes dull. If cracks appear internally, the sound is hoarse. Thus, by listening to the different sounds, it is possible to determine whether the part has any defects. 3) Tactile inspection: By touching the surface of the part with your hand, you can sense its surface condition. By shaking the mating parts relative to each other, it is possible to sense their fitting condition. For machines that are in operation, by touching their components, it is possible to sense their temperature level, thereby assessing the condition of their mechanisms. 4. Measures to ensure the quality of part inspection: 1) Strictly adhere to technical standards. Most mechanical parts and components come with specified technical standards, which serve as the basis for inspection work. Unless there is reliable evidence suggesting that these standards need to be modified, it is essential to strictly comply with them; it is absolutely not permissible to lower these standards in order to use substandard parts. 2) Select inspection equipment according to the requirements of the items being inspected. In addition to choosing the equipment based on the nature and scope of the inspection tasks, special attention should be paid to the accuracy requirements. For example, when measuring length and a precision of within 1 mm is required, a steel ruler is sufficient ； When a precision of around 0.1 mm is required, a vernier caliper is generally used ； When a precision of 0.01 mm is required, a micrometer or dial indicator is needed ； When a precision of 0.001 mm is required, a comparator is needed. If the accuracy of the inspection equipment is lower than the accuracy required for the object being tested, it is simply impossible to meet the quality inspection requirements, and care must be taken to prevent this. 3) Improve the technical level of inspection operations. The technical level of inspection operations has a direct impact on the accuracy of inspections; whether it is self-inspection by maintenance personnel or inspections carried out by specialized inspectors, it is necessary that the operators be proficient in using the inspection equipment and understand the requirements for inspecting the specific items. To this end, it is necessary to focus on improving inspection techniques; specialized training should be provided for the use of special and important inspection equipment, and the personnel responsible for inspections should remain relatively stable. 4) Reducing inspection errors: Any inspection result is inevitably subject to errors, whose impacts are multifaceted. To prevent and eliminate such errors, the following measures should be taken: (1) Inspection equipment has its own accuracy level; it is necessary to calibrate it regularly and take proper care of it to maintain its desired accuracy ； (2) Correct the errors caused by temperature; among the environmental factors that affect inspection accuracy, the impact of temperature is the greatest. Factors such as the effect of linear expansion in length measurements, and changes in properties caused by temperature variations in electronic devices, all require necessary corrections in more precise measurements ； (3) Errors caused by improper operation or inaccurate reading are mostly random errors; therefore, the average of multiple measurements can be taken to **reduce the magnitude of these errors. 5) Establish sound and reasonable inspection rules and regulations. A proper inspection system serves as an organizational guarantee for effective inspection work; it is necessary to establish post responsibility systems to clarify duties and ensure that everyone is accountable. Additionally, it is advisable to implement certain acceptance and handover systems as well as measurement calibration systems.