Summary of 15 years' experience of the hottest con

2022-10-18
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Summary of 15 years' experience in construction machinery! Have you made these mistakes

because some maintenance personnel are not clear about the structure and principle of construction machinery, do not carefully analyze the cause of the fault, and cannot accurately judge the fault location, they blindly dismantle and unload the machinery with the idea of "probably, almost", as a result, not only the original fault is not eliminated, but also new problems appear due to poor maintenance skills and processes. Therefore, when the machinery fails, it should be detected through the detection equipment. If there is no detection equipment, the most likely failure position can be determined through the traditional fault judgment methods and means such as "ask, see, check and try", combined with the structure and working principle of construction machinery. When judging the faults of construction machinery, the "elimination method" and "comparison method" are commonly used, which are carried out in the order from simple to complex, from appearance to interior, from assembly to components. By all means, it is forbidden to "blindly dismantle and disassemble without asking for anything"

2. The phenomenon of blindly replacing parts and blindly "replacing parts and repairing" exists to varying degrees. It is relatively difficult to judge and eliminate the faults of construction machinery. Some maintenance personnel always use the method of replacement test, no matter large or small parts, as long as they think that the parts and components that may cause faults are replaced one by one, the results are not only that the faults are not eliminated, but also that the parts and components that should not be replaced are replaced at will, Increased consumer spending. There are also some faulty parts that can be repaired to restore their technical performance without complex repair processes, but maintenance personnel require users to replace new parts and blindly adopt the method of "replacement and repair", resulting in serious waste. The above practices of blind replacement test and blindly replacing repairable parts still exist in some repair units to varying degrees. During maintenance, the cause and position of the fault should be carefully analyzed and judged according to the fault phenomenon. The repair method should be adopted to restore the technical performance of the parts that can be repaired, and the practice of blindly replacing parts should be avoided

3. It is common to fail after assembly without checking the quality of new parts.

before replacing parts, some maintenance personnel do not do technical inspection on new parts and directly install them on construction machinery after taking them. This practice is unscientific. At present, the quality of spare parts sold in the market is uneven, and some fake and shoddy parts are confused; There are also some accessories whose performance changes due to long inventory time. If they are not tested, they often cause failures after assembly. Before replacing new parts, necessary inspections and tests must be carried out, including appearance and performance tests, to ensure that the new parts are free of faults and eliminate unnecessary troubles caused by them

4. Do not pay attention to the model of accessories, and the phenomenon of substitution or misuse of accessories is common.

when repairing construction machinery, the phenomenon of substitution or misuse of accessories is still common. Some accessories are feasible for emergency substitution, but it is harmful and unhelpful to use for a long time, affecting the safety and technical performance of machinery. Some maintenance personnel have less understanding of the mechanical structure and principle, and many spare parts are inconsistent with the models, but they believe that as long as they can be installed, they do not consider whether they can give full play to the technical performance of the machinery. Therefore, when repairing construction machinery, try to use the original model of accessories, and do not use other models of accessories instead, let alone misuse

5. Do not pay attention to the selection of bolts, and the phenomenon of disordered use of bolts is more prominent

in the maintenance of construction machinery, the phenomenon of disordered use of bolts is also more prominent, because the bolt performance and quality do not meet the technical requirements, resulting in frequent mechanical failures after maintenance. The special bolts used in construction machinery, such as transmission shaft bolts, cylinder head bolts, connecting rod bolts, flywheel bolts, fuel injector fixing bolts, etc., are made of special materials through special processing, with high strength and strong shear resistance, ensuring reliable connection and fixation. In the actual maintenance operation, some maintenance personnel found that these bolts were damaged or missing, and they couldn't find the standard bolts at that time. Some took other bolts at will to replace them, and some processed them by themselves. These bolts left hidden trouble for the later use of construction machinery due to poor material or unqualified processing technology. Some parts need "fine thread self tightening" bolts, copper bolts and copper plated bolts with "small pitch", but ordinary bolts are used instead, resulting in bolt loosening and disassembly difficulties; Some bolts will have tensile, deformation and other defects after use. Some technical requirements stipulate that the bolts must be replaced after disassembly and assembly for several times. Because the maintenance personnel do not understand these conditions, repeated use of unqualified bolts for many times is also easy to lead to mechanical failure or accidents. Therefore, in the maintenance of construction machinery, when the bolts are damaged or lost, the bolts that meet the requirements should be replaced in time, and the bolts should not be used indiscriminately

6. The improper tightening method of bolts is more serious

most of the fixing or connecting bolts in various parts of construction machinery have tightening torque requirements, such as fuel injector fixing bolts, cylinder head bolts, connecting rod bolts, flywheel bolts, etc., some specify tightening torque, some specify tightening angle, and also specify tightening sequence. Some maintenance personnel think that anyone can tighten the bolts, which is irrelevant. They don't tighten the bolts according to the specified torque and sequence (some don't know the requirements of tightening torque and sequence at all), don't use torque (kg) wrenches, or use force adding rods at will, and tighten them by feeling, resulting in a great difference in tightening torque. The torque is insufficient, and the bolts are easy to loosen, resulting in punching the cylinder gasket, loose bearing bush, oil leakage and air leakage; When the torque is too high during "1025", the bolt is easy to stretch and deform, even break, and sometimes damage the threaded hole, affecting the repair quality. Therefore, when repairing construction machinery, the bolts must be tightened according to the specified torque and sequence to prevent mechanical failures caused by excessive, too small or improper sequence of bolt tightening torque

7. There are many phenomena that do not pay attention to the fitting clearance of parts and components.

the fitting clearance between piston and cylinder liner, piston ring "three clearances", piston crown clearance, valve clearance, plunger clearance, brake shoe clearance, driving and driven gear meshing clearance, bearing axial and radial clearance, valve stem and valve guide fitting clearance of diesel engines have strict requirements, which must be measured during maintenance, For the parts that do not meet the gap requirements, the emerging 3D technology is also a new medium to adjust or replace the sculpture. In the actual maintenance work, there are a lot of phenomena of blindly assembling parts without measuring the fitting clearance, which lead to early wear or ablation of bearings, oil burning of diesel engines, difficult starting or deflagration, broken piston rings, parts collision, oil leakage, air leakage and other faults, and sometimes even serious mechanical damage accidents due to improper fitting clearance of parts and components

8. It is not uncommon for couples or components to be replaced in pairs or in sets

there are many couples in construction machinery, such as plunger pair, outlet valve pair and injector needle valve pair of diesel engine fuel system; Driving and driven gears in the main reducer of the drive axle; Valve block and valve rod in hydraulic control valve; The valve core and valve sleeve in the full hydraulic steering gear are specially processed and ground in pairs when they are manufactured in the factory. The matching is very precise. They are always used in pairs within the service life and must not be interchanged; Some mutually matched components, such as piston and cylinder liner, bearing bush and journal, valve and valve seat, connecting rod big end pad cover and rod body, have a relatively good fit after running in for a period of time. During maintenance, attention should also be paid to assembly in pairs, not to string; Diesel engine connecting rod, piston, fan belt, high-pressure oil pipe, excavator central swivel oil seal, bulldozer main clutch adhesive tape joint, etc. These machines use a set of accessories at the same time. If they are damaged, they must be replaced in complete sets. Otherwise, due to the large difference in the quality of accessories, different degrees of old and new, and different length and size, the diesel engine will run unsteadily, the hydraulic system will leak oil, and the load concentration will be serious The replaced parts are easy to be damaged early. In the actual maintenance work, it is not uncommon for some people to replace the above parts in pairs or in sets in order to reduce expenses and some people do not understand the technical requirements, which reduces the maintenance quality of construction machinery, shortens the service life of parts, and increases the possibility of failure, which should be paid enough attention to

9. When assembling, the parts are installed reversely from time to time.

when repairing construction machinery, some parts are assembled with strict direction requirements. Only when they are installed correctly can the parts work normally. Some parts have no obvious external features and can be installed in both positive and negative directions. In actual work, they are often installed in reverse, resulting in early damage of parts, failure of machinery to work normally, damage accidents of construction machinery, etc

such as engine cylinder gasket, unequal distance valve spring (such as F6L912 diesel engine), engine piston, piston ring, fan blade, gear oil pump side plate, skeleton oil seal, thrust washer, thrust bearing, thrust gasket, oil deflector, fuel injection pump plunger, clutch friction disc hub, transmission shaft universal joint, etc. when installing these parts, if you do not understand the structure and installation precautions, they are most likely to be installed reversely, It causes abnormal operation after assembly and leads to the failure of construction machinery. Therefore, when assembling parts, maintenance personnel must master the structure and installation direction requirements of parts and components, and cannot assume blindly installation

10. The maintenance method is irregular, "treating the symptoms but not the root cause"

when repairing construction machinery, some maintenance personnel do not take the correct maintenance method, and think that emergency measures are omnipotent, replacing "maintenance" with "emergency", and there are still many phenomena of "treating the symptoms but not the root cause". For example, the frequently encountered "repair by welding with capital injection from batel and United Soybean Board" is an example. Some parts could have been repaired, but some maintenance personnel often adopt the method of "welding dead" to save trouble. After the connecting thread of the hydraulic cylinder earring and the cylinder piston rod is damaged, the direct welding method is used, so that the oil seal of the cylinder can not be replaced after being damaged, and the oil leakage is serious; When it is found that the working device moves slowly or the steering is difficult, do not check the cause of the fault, and blindly increase the working pressure of the system, resulting in too high system pressure, which is easy to damage oil seals, pipelines, hydraulic components, etc; In order to make the diesel engine "powerful", artificially increase the fuel supply of the fuel injection pump and the fuel injection pressure of the fuel injector. These irregular maintenance methods can only be used for emergencies, but cannot be used for a long time. The cause of the fault must be found out fundamentally, and the regular maintenance methods should be adopted to eliminate the fault, which should attract the attention of maintenance personnel

11. The use of gaskets is not standardized, and the phenomenon of random use still exists

there are many kinds of gaskets used between the mating surfaces of construction machinery parts, including asbestos pads, rubber pads, cardboard pads, cork pads, felt pads, non-ferrous metal pads (copper pads, aluminum pads), copper (steel) asbestos pads, insulation pads, spring pads, flat pads, etc. Some are used to prevent oil leakage, water leakage, air leakage and electric leakage between the mating surfaces of parts, and some are used to tighten and prevent looseness. There are different regulations and requirements for the timing and occasion of the use of each type of gasket. When repairing construction machinery, the use of gaskets is not standardized or even disorderly, which leads to frequent leakage between the mating surfaces, and the bolts and nuts loosen and loose by themselves, affecting the normal use of construction machinery. If the engine cylinder gasket is too thick, the compression ratio will be reduced and the engine will be difficult to start; Fuel injector and gas

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