Fault types
Due to the time of the failure, the content and cause of the failure are also different. Therefore, the fault can be divided into initial fault, sudden fault and aging fault.
1. Initial failure
The fault occurred in the debugging stage and within two or three months after the start of operation is called the initial fault. The reasons are as follows:
1) poor component processing and assembly
If the grinding of the inner hole of the component does not meet the requirements, the burr of the part is not cleaned, the installation is not clean, the parts are installed in the wrong way, the assembly is defective, the tightening torque of the fastening screw is not appropriate, the material of the parts does not meet the requirements, and the quality of the purchased parts (such as sealing ring and spring) is poor.
2) design mistakes
Design components, the parts of the material selection is not appropriate, unreasonable processing technology requirements. Insufficient understanding of the features, performance and functions of components leads to improper selection of components in circuit design. The designed air handling system can not meet the requirements of pneumatic components and systems. Circuit design error.
3) the installation does not meet the requirements
During installation, the components and pipes are not cleaned by blowing, so that dust, sealing material fragments and other impurities are mixed in, resulting in the failure of the pneumatic system. There is bias load when installing cylinder. No effective measures have been taken to prevent loosening and vibration of pipelines.
4) poor maintenance and management, such as not discharging condensed water in time, not timely filling oil mist device, etc.
2. Sudden failure
The sudden failure of the system during the stable operation is called sudden failure. For example, the oil cup and water cup are made of polycarbonate material. In the air cargo pipeline, residual impurities mixed with the components, suddenly make the relative moving parts stuck; Spring suddenly broken, hose suddenly burst, electromagnetic coil suddenly burned; A sudden power failure causes the loop to misoperate.
Some sudden failures are premonitory, such as the emergence of impurities and moisture in the air discharged, indicating that the filter has failed, should be timely found out the cause, to eliminate, do not become a sudden failure. However, some sudden failures are unpredictable, so safety protection measures can only be taken to prevent them, or some vulnerable spare parts can be prepared, so as to timely replace the failed components.
3. Aging failure
Individual or a few components after reaching the service life of the fault is called aging fault. It is possible to predict roughly the duration of aging failure by reference to the date of production, start date, frequency of use of the components in the system, and certain symptoms that have occurred, such as abnormal sound and increasing leakage.
The following two commonly used fault diagnosis methods are empirical method and thrust analysis method.
1. Empirical method
Based on practical experience, and with the aid of a simple instrument, diagnosis fault location, find out the cause of the fault method, known as the empirical method. The empirical method can be carried out according to the four words "look, smell, ask and cut" of TCM patients.
1) hope
For example; See the movement speed of the executive element abnormal change; Whether the pressure indicated by each pressure gauge meets the requirements and whether there is a big fluctuation; Whether the quality of lubricating oil and the amount of dripping oil meet the requirements; Whether the condensed water can be discharged normally; Whether the air discharged from the exhaust port of the reversing valve is clean; The indicator light of the solenoid valve is normal; Whether the fastening screw and pipe joint are loose; Pipes are free from distortion and flattening; There is no obvious vibration; There is no change in the quality of processed products.
2) smell
Including ear and nose smell, such as cylinder and reversing valve when there is no abnormal sound; When the system stops working but has not been relieved, there is no air leakage everywhere, the sound volume of air leakage and its daily changes; Electromagnetic coil and sealing ring have no special smell due to overheating.
3) ask
That is, consult the technical archives of the pneumatic system to understand the system's work procedures, operational requirements and main technical parameters; Review product samples to understand the function, structure, function and performance of each component; Check the maintenance inspection record, understand the daily maintenance work; Visit the field operators to understand the operation of the equipment, and understand the signs before and when the fault occurs; Understand the problems and troubleshooting.
4) to cut
Such as touching the relative motion of the external feel and temperature, electromagnetic coil temperature rise. If you feel hot after touching for two seconds, you should find out the reason. There is no vibration feeling in the cylinder, pipe, etc., and there is no crawling feeling in the cylinder, and there is no air leakage in the touch of the joints and components.
The empirical method is simple and feasible, but due to the difference of each person's feeling, practical experience and judgment ability, there will be some limitations in fault diagnosis.
2. Inferential analysis method, which USES logical reasoning and step by step approximation to find the real cause of the fault, is called inferential analysis method.
(1) reasoning steps
From the symptoms of the fault to the real cause of the fault, you can follow the following three steps:
1) deduce the essential cause of the fault from the symptoms of the fault.
2) from the nature of the fault, deduce the common reasons that may lead to the fault
3) deduce the real cause of the failure from various possible common reasons.
(2) reasoning method
The principle of reasoning is: from simple to complex, from easy to difficult, from the surface to the inside to analyze one by one, to eliminate the impossible and non-main reasons for failure; Check the components that have been adjusted or replaced before the fault occurs; Give priority to the common causes of high failure rate.
1) instrument analysis method
Use instruments such as pressure gauges, differential pressure gauges, voltmeters, thermometers, electric stopwatches and other electronic instruments to check whether the technical parameters of the system or components meet the requirements.
2) departmental suspension law
Temporarily shut down part of the working conditions of the pneumatic system and observe the effect on the fault signs.
3) trial proof
Some working conditions of pneumatic system are changed tentatively, and the influence on fault sign is observed.
4) comparative method
Replace the same components in the system with standard or qualified components, and determine whether the replaced components are invalid by comparing their working conditions.
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