I. Mechanical failure
(1) the concept of mechanical failure
Mechanical equipment lost the state of the specified performance, known as mechanical failure.
(2) the type of mechanical failure
1, according to the speed of failure classification
(1)Gradual failure
(2) sudden failure
(3) compound failure
2, according to the consequences of failure classification
(1)Functional failure
(2)Parameter failure
3, according to the degree of harm classification of the fault
The frequency of the failure degree of impact level to eliminate the degree of urgency
Very easy to occur A major fault needs to be removed immediately
Easy to occur Level 2 major fault as soon as possible to eliminate
Occasionally occurrence of three-level major fault production interval excluded
Rarely Occurs Level 4 major fault Troubleshooting during major maintenance
In addition, it can also be divided into actual faults that have occurred and potential faults that have not occurred; it can also be divided into man-made faults and natural faults according to the cause or nature of the faults. In short, the purpose of studying the type of failure is to analyze the impact of various faults on the function of equipment, parameters, components failure form, so as to take improvement measures in the design, use, reduce or eliminate the occurrence of failure to ensure the safety of personnel and machinery.
(3) the law of mechanical failure
Mechanical failure over time called the law of mechanical failure law. With the life of the characteristic curve, also known as “bath curve” to describe the efficiency of mechanical failure with the use of time change relationship.
The life characteristic curve is divided into three stages:
The first stage is the early failure period, that is, due to the design and manufacture of storage and transport installation and other reasons caused by early failure. Its failure rate is high, but easy to discharge.
The second stage is the normal operation period, also known as the random failure period. Machine by running and, adjustment, the failure rate gradually decreases and tends to stabilize. Within this phase only sudden failures, the general failure rate is small. This phase characterizes the effective life of the machinery.
The third stage for the wear and tear failure period, due to wear and tear of parts, corrosion, fatigue and other reasons caused by the rise in failure rate, when the machine for overhaul, replacement of parts to reach life, strengthen maintenance, can extend the service life. But the general overhaul costs may be higher, the performance of the machine after the overhaul is often not as good as the new machine.
(4) the cause of mechanical failure
Understanding the reasons for the occurrence of failure, for reasonable maintenance equipment to extend its service life, and then take effective measures to prevent the occurrence of failure, has important practical significance.
The causes of mechanical equipment failure are varied, summarized as follows: (1) the impact of mechanical equipment defects themselves (2) the impact of environmental factors (3) the impact of time factors
Second, the failure of mechanical parts form
(A) deformation failure
Deformation failure parts embodied as follows
Can not withstand the prescribed load; can not play a prescribed role; and other parts of the operation of interference. Deformation of a part in some way diminishes the function of the provisions, can be plastic or elastoplastic deformation of the basic type: size deformation or volume deformation (growth or shrinkage) and shape deformation (such as bending and warping).
Elastic deformation failure.
The amount of deformation is varied in the elastic range and is a matter of stiffness. Rods, columns, shaft parts, parts driven by friction and other elastic deformation will bring failure problems. The main factors affecting the elastic deformation: the shape of the part, size, the elastic modulus of the material, the working temperature of the part and the size of the load
Plastic deformation failure.
Is the applied stress exceeds the yield limit of the part material when the obvious plastic deformation. Plastic deformation factors: In addition to the elastic deformation in the impact factors, there are material defects, improper use, design errors, etc., which is especially bad heat treatment is more prominent. Such as high-frequency quenching of gear teeth, may cause cracks due to improper temperature control.
Warpage deformation failure: is a kind of and direction often produce complex regular deformation and eventually formed a warped shape and lead to failure.
(B) fracture failure
1. fracture classification
(1) according to the nature of fracture
ductile fracture – material fracture before the occurrence of obvious macro plastic fracture.
brittle fracture refers to the fracture of the material before fracture does not occur or a small macroscopic visible plastic deformation occurs.
Toughness – brittle fracture – also known as quasi-brittle fracture. Is a plastic and brittle fracture mixed.
(2) By fracture path.
Fracture along the crystal, fracture through the crystal, mixed crystal fracture.
2. Fracture analysis method
Room temperature tensile or impact specimens of metal materials, macroscopic observation of the fracture can be seen in the fracture can be divided into three different areas: fibrous area, radial area and shear lip area.
(1) Corrosion failure
Corrosion is a metal exposed to the active medium environment and a surface loss, is the result of chemical and electrochemical action.
Corrosion failure has several basic types: (1) uniform corrosion (2) pitting corrosion (3) crystal corrosion
(2) wear and tear
Parts of the working surface of the material, due to the surface friction or media washing and continuous loss of the phenomenon called wear. Wear is the main form of failure of the parts.
Wear is also divided into adhesive wear, abrasive wear and surface fatigue wear.
The general law of mechanical wear: mechanical equipment in operation, the parts of the wear is not the same, but the development of wear has a common law. The mechanical wear process is divided into three stages: (1) the “running together” stage (2) the stable wear stage (3) the acute wear stage.
Methods and ways to prevent and reduce wear: (1) Correct material selection is the key to improve wear resistance. (2) Try to ensure liquid lubrication, correct and reasonable lubrication of equipment can effectively reduce the wear of equipment parts and prolong the service life of equipment. (3) the use of a variety of surface treatment methods: such as rolling, chemical surface heat treatment, chrome plating, spraying, etc.”) correctly carried out (5) the structural design of the friction pair (6) the correct maintenance and use of the equipment has a great impact on the life of the equipment