Deformation failure mechanism and removal measures

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Deformation failure mechanism of packaging machinery parts and its removal measures

in the failure of packaging machinery and equipment, wear is the main factor. The deformation of the components of the packaging machinery often increases the wear of the components and leads to equipment failure

the phenomenon that the size or shape of parts changes due to the force during the operation of packaging machinery is called deformation. The deformation of packaging machinery parts, especially the basic parts or running parts, will seriously affect the working quality and service life of packaging machinery and equipment

deformation mechanism of metal parts

the deformation process of metal parts can be divided into elastic deformation stage and plastic deformation stage. Practice has proved that plastic deformation has a great influence on the performance and life of parts in the two kinds of deformation

the mechanism of elastic deformation of metal materials is that there are mutually balanced forces between metal atoms - suction and pressure. Attraction makes atoms close to each other; Pressure keeps atoms from getting too close together. Under normal circumstances, atoms occupy the position where these two forces maintain equilibrium. When an external force is applied to make the atomic spacing close or far away, the corresponding repulsive resistance or attractive resistance will inevitably occur, and a new balance will be established with it. When the external force is removed, a new imbalance appears, and the atoms return to the original position of mutual balance. This is also the mechanism of elastic deformation, that is to say, elastic deformation is the result of reversible changes in the distance between atoms caused by external forces

the mechanism of plastic deformation of metal materials is that the plastic deformation of metals is caused by the slip or twinning of metal crystals, and the slip of crystals is the main one. The metals of mechanical parts are almost polycrystalline, and most of them are alloys. The plastic deformation of polycrystals and alloys is much more complex than that of single crystals because of the different orientation of each lattice, the existence of grain boundaries, and the existence of solute atoms or heterotropism in the alloy, which hinder and restrict the deformation of each grain

the effect of plastic deformation on the automatic uniform cooling of the specimen and the properties of constant temperature metal is that work hardening will occur. With the increase of plastic deformation, the strength and hardness of the material will gradually increase, and the plasticity and toughness will gradually decrease. Plastic deformation also makes the metal easy to rust, not resistant to corrosion and causes internal stress, resulting in the deformation of metal parts

stress and deformation in the cooling process of parts

during the cooling process of mechanical parts from high temperature, internal stress will be generated due to uneven volume changes of parts connected and mutual restraint. When the internal stress exceeds the strength limit of the part material, the part will break; When the internal stress exceeds the yield limit of the part material but does not reach the strength limit, the part will be deformed; When the stress is less than the elastic limit, it will exist in the form of residual internal stress after years of unremitting efforts. Although there is no difference in the appearance of the parts, when the parts are cut off during cutting, the balance of the original internal stress will be destroyed and the parts will be deformed. When parts are sent for heat treatment or put into use, due to the superposition of heat treatment stress or external load and internal stress, parts may deform or even fracture

reasons for deformation of packaging machinery parts during use

as mentioned earlier, deformation will occur when the stress of the parts exceeds the material yield limit. According to the reasons for the stress of parts, the reasons for the deformation of parts of packaging machinery and equipment in the process of use can be roughly analyzed from the aspects of blank manufacturing, machining, repair quality and use

(1) factors in blank production. The blank of packaging machinery parts, whether forged, cast or welded, has a process of cooling from high temperature in the manufacturing process. In this cooling process, internal stress will be generated, and this internal stress will cause deformation of parts

(2) machining factors if the blank is machined under stress, the balance of internal stress will be destroyed after cutting part of the surface. Due to the redistribution of internal stress, parts will be deformed. In addition, in the process of cutting, due to the action of cutting force and cutting heat, great plastic deformation will also occur on the surface of parts, so internal stress will also occur. This residual internal stress, like the internal stress formed in blank manufacturing, will cause the deformation of mechanical parts

(3) factors in terms of repair quality. During the overhaul of packaging machinery and equipment, if you do not know that the parts have been deformed, and the deformation factor is not taken into account when formulating the repair process, it will often cause greater deformation or increase the damage of deformation

(4) factors in use if the packaging machinery and equipment work in a relatively harsh environment, or under extreme load conditions, when the temperature is relatively high, the mechanical parts will be deformed

if the design is not fully considered, the unreasonable layout of parts and components will also cause deformation

measures to reduce the damage of deformation

there are many reasons for the damage of deformation of parts of packaging machinery and equipment, so the measures to reduce the damage of deformation should also be comprehensively considered from the aspects of design, manufacturing, repair, use and so on. At present, the deformation of equipment parts is inevitable. The only way is to study the deformation law of parts and reduce the harm of deformation

(I) scientific design

when designing packaging machinery and its parts, we should not only fully consider how to realize the action of the mechanism and the strength of the parts, but also fully consider the stiffness and deformation of the parts and what problems will occur in the process of manufacturing, assembly and use

when designing packaging machinery and equipment, reasonably arrange various parts and components, improve the stress condition of parts, and reduce the deformation of parts and components; When designing mechanical parts, try to make the wall thickness of parts uniform, which can reduce the temperature difference during hot processing, so as to achieve the effect of reducing the deformation of parts

(II) careful manufacturing

when formulating the blank manufacturing process, we should pay attention to the problem of deformation and take various process measures to reduce the residual stress of the blank. After the blank is made, and in the subsequent machining process, sufficient processes to eliminate internal stress must be arranged to strive to reduce the residual internal stress in the parts

in machining, rough machining and finish machining are divided into two processes, and a period of storage time is reserved in the two processes, which is conducive to the elimination of internal stress; In the process of machining, we should try to keep the process benchmark for repair, which can reduce the error caused by different benchmarks in repair and processing. When manufacturing the crankshaft, if the ejector pin hole is cut off by the subsequent process, and another pin hole is made when grinding the crankshaft during repair, the error will increase

in order to reduce the stress and deformation of parts after machining, for more important or complex parts, natural aging or artificial aging treatment should be carried out again after finishing. For some particularly precise parts, such as indexing and measuring mechanisms, several aging treatments should be arranged between finishing processes

(III) repair with good quality

as the deformation of mechanical parts is inevitable, it is not only necessary to check the wear of the mating surface during the overhaul of packaging machinery and equipment, but also to carefully check and repair the mutual position accuracy. Therefore, during the overhaul of packaging machinery and equipment, the maintenance standard that must ensure that the system is preheated for more than 20 minutes should be formulated, and the special measuring tools and special clamping tools that are simple, reliable and easy to operate should be designed

since the deformation of parts under the action of internal stress is usually completed within 12 ~ 20 months, special attention should be paid to the inspection and repair of the deformation of mechanical equipment during the first overhaul to restore it to the specified mutual position

in the machining of packaging machinery and equipment during overhaul, the positioning benchmark must be reasonably selected; Measures should also be taken to reduce stress and deformation for some hot working or pressure processing processes during overhaul

(IV) reasonable use

packaging machinery and equipment must be operated in strict accordance with the procedures in the process of use, and overload operation and local high temperature must be avoided as far as possible, so as to reduce the occurrence of part deformation. (end)

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