Maintenance is an effective means to restore the technical performance of construction machinery, eliminate faults and hidden troubles, and prolong the service life of machinery. There are still many technical problems in the maintenance. The existence of these problems can easily lead to the low quality of machinery maintenance and poor reliability of equipment, thus causing losses to consumers and even major construction machinery accidents. This paper analyzes the common technical problems encountered in the maintenance of construction machinery, which is definitely worth a visit!
1. It is common to fail to correctly judge and analyze faults and blindly dismantle and unload.
Because some maintenance personnel were not clear about the structure and principle of the engineering machinery, did not carefully analyze the cause of the fault, and could not accurately judge the fault location, they blindly dismantled and unloaded the machinery with the idea of "roughly, almost". As a result, not only the original fault was not eliminated, but also new problems occurred due to poor maintenance skills and processes. One bulldozer failed to work due to insufficient diesel power. The maintenance personnel disassembled and disassembled the PT fuel injection pump and fuel injector, but the cause of the failure was not found. One fuel injection pump was replaced for test, and the failure remained. In the final inspection, the fault was caused by too much impurities and moisture in the diesel used. However, this disassembly led to a significant decline in the performance of the PT fuel injection pump and insufficient power of the diesel engine. Therefore, in case of mechanical failure, it is necessary to detect 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" and in combination with the structure and working principle of construction machinery. "Elimination method" and "comparison method" are commonly used to determine the faults of construction machinery. They are carried out in the order from simple to complex, from appearance to interior, from assembly to components. 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 replacement test method. No matter the large or small parts, as long as they think that the parts that may cause the fault are replaced one by one, the results are not only that the faults are not eliminated, but also that the parts that should not be replaced are replaced at will, which increases the expenses of consumers. One excavator went to a factory for maintenance due to difficult steering, and the manufacturer replaced the vane pump (steering pump), overflow valve, steering cylinder and other parts to no avail. After that, it was found that the fault was caused by the aging glue inside a hydraulic oil pipe from the steering oil tank to the vane pump, resulting in insufficient hydraulic oil flow and pressure. Some faulty parts can be repaired to restore their technical performance. For example, the generator, starter, oil cooler, gear oil pump, etc. can be repaired without complex repair process. However, the maintenance personnel require the user to replace new parts and blindly adopt the method of "replacement and repair", resulting in serious waste. The above practice of blind replacement test and blindly replacing repairable parts still exists in some repair units to varying degrees. During maintenance, the cause and position of the fault shall be carefully analyzed and judged according to the fault phenomenon. For the parts that can be repaired, the repair method shall be adopted to restore the technical performance, and the practice of blindly replacing parts shall 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 conduct technical inspection on new parts, but directly install them on construction machinery after taking them, which is unscientific. At present, the quality of spare parts sold in the market is uneven, and some fake and shoddy spare parts are confused; There are also some parts whose performance changes due to long inventory time. If they are not tested, they often cause failures after assembly. One Shanghai 120a bulldozer, the engine oil cooler of the diesel engine was frozen and cracked, resulting in water in the engine oil. A new engine oil cooler was replaced, and the engine was started for test. Water was still in the engine oil. Other parts were checked, and the cause of the fault was not found. After that, the side cover of the new engine oil cooler was removed. It was found that the oil sealing ring at the side cover was not compacted, resulting in the mixing of engine oil and water. The reason was that the quality of the engine oil cooler was not up to standard. One ZL50 loader, the engine oil pressure of the diesel engine is too low. It is analyzed that the engine oil filter is blocked. A new engine oil filter is replaced, and the engine oil pressure is still low during the test run. After that, all parts that may lead to low oil pressure were checked or replaced, but the oil pressure still could not rise. Finally, the diesel engine was reluctantly used without finding the cause of the fault and low oil pressure. As a result, the diesel engine was burnt and seized, the crankshaft was broken, and the connecting rod was bent, resulting in a loss of more than 10000 yuan. After inspection, it was found that the replaced oil filter element (primary filter) had been blocked by too much rust, because the filter had been stored for a long time, resulting in internal rust. Therefore, necessary inspection and test must be carried out before replacing new parts, including appearance and performance test, to ensure that the new parts are free from faults and eliminate unnecessary troubles caused by them.
4. Do not pay attention to the model of accessories. It is common to substitute or misuse accessories.
In the maintenance of construction machinery, the substitution or misuse of accessories is still common. Some accessories are feasible for emergency substitution, but long-term use is harmful and unhelpful, affecting the safety and technical performance of machinery. Some maintenance personnel know little about the mechanical structure and principle, and many spare parts are inconsistent with the models, but they think 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. For example, the 4120f diesel engine should use a 350 Watt generator, but uses a 500 Watt generator, wasting power; ZL50 loader uses qd274 starter, but QD50 starter is used. Due to insufficient power, it is difficult to start the diesel engine; The piston, valve and rocker arm of 135 series supercharged and non supercharged diesel engines are not common, but they are often mixed, which makes the diesel engine difficult to start, reduces the power, and even leads to serious parts damage accidents. 1 set of 6135ZD supercharged diesel engine, due to the misuse of non supercharged diesel engine piston, the diesel engine will not catch fire after assembly. After replacing the prototype piston (supercharged), the diesel engine will start smoothly; The substitution of high-pressure oil pipe, fuel injection nozzle coupling and plunger coupling of different models of diesel engine results in the change of fuel injection quantity and fuel supply advance angle; Replace qualified 名媛直播 with defective 名媛直播, split pins with iron wires and nails, and cylindrical pins with steel bars and old bolts. The quality cannot be guaranteed and long-term use is not allowed. 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 them.
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 indiscriminate use of bolts is still quite prominent. Because the performance and quality of bolts do not meet the technical requirements, mechanical failures occur frequently after maintenance. The special bolts used for 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. They have high strength and strong shear resistance, ensuring reliable connection and fixation. In the actual maintenance work, some maintenance personnel found that these bolts were damaged or missing. They could not find the standard bolts at that time. Some of them were replaced by other bolts at random, and some of them were processed by themselves. These bolts were poor in material or unqualified in processing technology, which left hidden trouble for the later use of construction machinery. The six bolts connecting the planetary gear carrier and the shell of the wheel reducer in the rear axle of type 74 II excavator bear a large torque, The six bolts were broken and damaged. Some maintenance personnel used other bolts or processed them by themselves. They often broke again because of insufficient bolt strength; Some parts need "small pitch" fine thread self tightening bolts, copper bolts and copper plated bolts, but ordinary bolts are used to replace them, resulting in bolt loosening and disassembly difficulties. For example, the fixing nuts of diesel engine exhaust manifold are mostly made of copper to prevent heating or use for too long, which is difficult to disassemble. However, in actual maintenance, ordinary nuts are mostly used, which is very difficult to disassemble after a long time; 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 shall be replaced in time, and the bolts shall not be used indiscriminately.
6. The improper tightening method of bolts is 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 do not tighten the bolts according to the specified torque and sequence (some do not know the tightening torque and sequence requirements at all), do not use torque (kg) wrenches, or use force adding rods at will. They tighten the bolts by feeling, resulting in a great difference in tightening torque. The torque is insufficient, and the bolts are easy to loose, resulting in punching the cylinder gasket, loose bearing bush, oil and air leakage; If the torque is too large, the bolt is easy to stretch and deform, even break, and sometimes damage the threaded hole, affecting the repair quality. One ZL50 loader and the torque converter threw hydraulic oil outward. After inspection, the 24 bolts connecting the pump wheel and cover wheel were not tightened according to the specified sequence and torque. Therefore, during the maintenance of construction machinery, the bolts must be tightened according to the specified torque and sequence, so as to prevent the machinery failure caused by excessive, too small or improper sequence of bolt tightening torque.
7. There are a lot of phenomena that do not pay attention to detecting the fitting clearance of parts.
Diesel engine piston and cylinder liner fit clearance, 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 fit clearance, etc. all types of models have strict requirements, which must be measured during maintenance, and the parts that do not meet the clearance requirements must be adjusted or replaced. In the actual maintenance work, there are quite a few phenomena of blind assembly of parts without measuring the fitting clearance, resulting in early wear or ablation of bearings, oil burning of diesel engines, difficult starting or deflagration, broken piston rings, impact of parts, oil leakage, air leakage and other faults, and sometimes even serious mechanical damage accidents due to improper fitting clearance of parts. After a Nissan 6db-10p diesel engine was overhauled, the test run lasted about 30 minutes, and then the starter did not catch fire. Check that the oil fluid and oil circuit were normal. After the engine was shut down for 30 minutes, it could start to catch fire again, but after 30 minutes of operation, it stopped. Later, it was checked that the cause of the fault was that the clearance between the plunger of the injection pump was too small. After the temperature of the diesel engine increased, the plunger expanded and collided with the oil outlet valve, so it could not supply oil normally in a reciprocating motion and shut down automatically. After the shutdown and cooling, there was a certain clearance between the plunger and the oil outlet valve, so the oil can be supplied normally.
8. It is not uncommon for couples or components to be replaced in pairs or in sets.
There are many coupling parts in construction machinery, such as plunger pair, outlet valve pair and needle valve pair of diesel engine fuel system; Driving and driven gears in the drive axle main reducer; 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 grinded in pairs during factory manufacturing. 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, are relatively well matched after running in and use for a period of time. During maintenance, attention should also be paid to assembly in pairs rather than string; The diesel engine connecting rod, piston, fan belt, high-pressure oil pipe, oil seal of excavator central swivel, adhesive tape joint of bulldozer main clutch, etc. all these machines use one set of accessories at the same time. If they are damaged, they must be replaced in 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 complete 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 mechanical parts, and increases the possibility of failure, which should be paid enough attention to.
9. During assembly, parts and components are installed reversely from time to time.
During the maintenance of construction machinery, some parts and components are assembled with strict direction requirements. Only when they are installed correctly can the normal operation of parts and components be ensured. 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. For example, engine cylinder gasket, unequal distance valve spring (such as F6L912 diesel engine), engine piston, piston ring, fan blade, gear oil pump side plate, framework oil seal, thrust washer, thrust bearing, thrust gasket, oil deflector, fuel injection pump plunger, clutch friction disc hub, transmission shaft universal joint, etc. during installation, these parts are most likely to be installed reversely without understanding the structure and installation precautions, resulting in abnormal operation after assembly, Cause the failure of construction machinery. If a 4120f diesel engine emits blue smoke after replacing the piston ring, it may be caused by excessive oil filling or "matching" of the piston ring. Check that the oil quantity is normal. Remove the piston connecting rod group of one cylinder. It is found that the piston rings are not "matched", but the gas rings are installed reversely. Check that the piston rings of other cylinders are also installed reversely. The machine uses an inner grooved twisted gas ring. During installation, the inner notch is required to face upward, and the maintenance personnel just installed it reversely. As the piston "pump oil" phenomenon is very easy to occur when the inner grooved piston ring is installed reversely, the oil will run up along the notch of the ring to the combustion chamber for combustion. Another example is that the working oil pump of ZL50 loader is equipped with two skeleton oil seals. The correct installation direction of the oil seal is: the oil seal lip on the inner side is inward, and the oil seal lip on the outer side is outward. This can not only prevent the working pump from pumping the oil in the hydraulic oil tank into the gearbox through the variable speed pump, but also prevent the variable speed pump from pumping the oil in the gearbox into the hydraulic oil tank through the working pump (the working pump and the variable speed pump are installed side by side and driven by a shaft gear), The author has encountered two cases of oil channeling fault caused by the oil seal of the oil pump. Therefore, when assembling parts, maintenance personnel must master the structure and installation direction requirements of parts, and do not take it for granted.
10. The maintenance method is irregular, and "treating the symptoms but not the root cause" is still a common method used by some maintenance units.
In the maintenance of construction machinery, some maintenance personnel do not adopt correct maintenance methods and think that emergency measures are omnipotent. There are still many phenomena that "emergency" is used to replace "maintenance" and "treating symptoms but not root causes". For example, the frequently encountered "welding instead of repair" is an example. Some parts could have been repaired, but some maintenance personnel often use the "welding dead" method to save trouble. One 12V135 diesel engine fuel injection pump camshaft keyway was loose due to wear and the semicircular key was not fixed firmly. The keyway should have been milled again. However, the maintenance personnel directly welded the camshaft and the fuel injection pump connecting plate together, which made it impossible to disassemble and difficult to repair later. After the connecting thread between 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 it is damaged, and the oil leakage is serious; When it is found that the working device moves slowly or the steering is difficult, the fault cause is not checked, and the working pressure of the system is blindly increased, resulting in too high system pressure, which is easy to damage the oil seal, pipeline, 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 can not be used for a long time. The cause of the fault must be found out fundamentally, and regular maintenance methods should be adopted to eliminate the fault, which should attract the attention of maintenance personnel.
