The machine is subjected to various energies in use, and the functions of these energies mainly include: (1) The function of the surrounding medium energy, including the function of the operators, repairers and environmental conditions performing tasks;
(2) Internal energy sources related to the operation of machinery and the work of various institutions, such as various loads, vibrations, temperature, etc.;
(3) Latent energy (internal stress of castings and internal stress of assembly) accumulated in mechanical materials and parts during manufacturing and assembly.
These energies mainly exist in the form of mechanical energy, thermal energy, and chemical energy. When the energy reaches a certain value, it will cause harmful processes to appear, causing changes in the initial performance and state of mechanical parts, such as when matched with a certain power and speed. At this time, a harmful friction process will occur with each other, and the result of friction will cause wear of the mating pair and change the movement of the mating pair. It can be seen that with the development of harmful processes, the parts will be damaged first, which is specifically manifested as wear, deformation, cracks, fatigue, corrosion, etc. The appearance of damage causes changes in the structural parameters of mechanical parts, such as dimensional tolerances and geometric tolerances. , Change of fit clearance, etc.
Changes in structural parameters have led to changes in mechanical function output parameters, such as changes in mechanical output power and speed. With the further expansion of the damage degree, the structural parameters of mechanical parts gradually exceed the allowable value. If the structural parameters of the mechanical parts exceed the allowable value and the function output parameters do not exceed the allowable limit range, it is considered that the machine has a potential failure and the corresponding state is an abnormal state. At this time, it should be eliminated through maintenance; if the structure parameter exceeds the limit , The function output parameter also exceeds the allowable value, it is considered that the machine has a functional failure, and the corresponding state is the failure state. At this time, the corresponding failure should be eliminated through repair. If the machine is used for a long time, the structural parameters of its main parts have reached the limit value, and the system function output parameter is seriously exceeded, and the economic efficiency of use will be significantly reduced. At this time, the machine is in a state of extreme technology and needs to be overhauled or updated.
Characteristic analysis of mechanical failure
Mechanical failures are inseparable from mechanisms such as wear, corrosion, fatigue, and aging. According to the general process of mechanical failure formation, mechanical failures mainly have the following characteristics:
(l) Potentiality. Various damages will occur to the machinery in use, and the damage causes changes in the structural parameters of the parts. When the damage develops to the extent that the structural parameters of the parts exceed the allowable value, the machine will have potential failures. Because there is a certain margin (safety factor) in the mechanical design, even if the structural parameters of some parts exceed the allowable value, the function output parameters of the machine are still within the allowable range, that is, the machine does not have a functional failure. It usually takes a long period of time to develop from potential failure to functional failure, because through lubrication, cleaning, tightening, adjustment and other means, the development of damage can be eliminated or slowed down, so that potential failures can be controlled or even eliminated to a certain extent. The potential of mechanical failures can be reduced through maintenance to reduce the occurrence of functional failures, thereby greatly extending the service life of the machinery.
(2) Gradual onset. Since the occurrence of processes such as wear, corrosion, fatigue, and aging are closely related to time, the occurrence of mechanical failures is mostly related to time. In use, mechanical damage is gradually generated, the structural parameters of parts and components are also slowly changed, and the mechanical performance gg# number also gradually deteriorates. Most of the failures may be tested and monitored by the instrument in advance. The probability of failure is related to the time of machine operation. The longer the machine is used, the greater the probability of failure. The gradual occurrence of failures makes most mechanical failures preventable. Failure diagnosis and condition-based maintenance are based on this foundation.
(3) Wearability. The processes of mechanical wear, corrosion, fatigue, and aging are accompanied by changes in energy and quality, and the process is irreversible. It is manifested as the degree of mechanical aging gradually intensified, and more and more failures. With the increase of use time, although the elimination of local faults can restore the performance of the machine, the failure rate of the machine is still rising, and new faults will continue to appear. At the same time, the elimination of damage is also incomplete, and maintenance cannot restore the performance of the machine to the state before use. The wearability of mechanical failure determines the difference between the level and depth of mechanical maintenance, and the mechanical failure distribution model cannot be simply described by exponential distribution.
(4) Fuzziness. In the use of machinery, due to the influence of various use and environmental conditions, the damage and the change of output parameters have a certain degree of randomness and dispersion. At the same time, due to the influence of factors such as materials and manufacturing, various limit values, The initial value also has a different distribution. The output parameters of the same machine under different use environments also have different distributions over time, which leads to a certain degree of dispersion in parameter changes and failure judgment standards, which makes the occurrence and judgment of mechanical failures The standards have a certain degree of ambiguity. The ambiguity of mechanical faults adds a certain degree of difficulty to the diagnosis and discrimination of mechanical faults, and it also requires that the research of mechanical faults must be combined with macroscopic and microscopic.
(5) Diversity. In mechanical use, due to the simultaneous effects of wear, corrosion, fatigue, and aging, the same component often has multiple failure mechanisms, resulting in multiple failure modes, such as shaft bending, wear, and fatigue fracture. These faults are not only different in fault mechanism and manifestation, but also in different distribution models and different levels of influence at all levels, which makes the faults show diversity. The diversity of mechanical failures requires separate studies of failures according to different mechanisms and modes.