Maintenance is an effective way to restore the technical performance of construction machinery, eliminate failures and eliminate hidden dangers, and extend the service life of machinery. At present, the domestic automobile repair industry has a considerable scale, and the construction machinery maintenance industry starts relatively late, and there are still many technical problems in the maintenance. The existence of these problems leads to poor quality of mechanical maintenance and poor equipment, causing consumers to suffer losses and even major construction machinery accidents. The author makes a brief analysis of the common technical problems encountered in the maintenance work of construction machinery, aiming to arouse the attention of the relevant personnel.
Bulldozer
1, it is common to fail to correctly diagnose and analyze faults. Some maintenance personnel, because of the structure and principle of the engineering machinery, not clear the cause of the failure, can not accurately judge the fault location, with the idea of "about, about" blindly dismantling the large machinery and unloading, the result not only the original fault has not been ruled out, but also because of maintenance skills and poor technology, there are new problems. 1 Nissan Komatsu bulldozers, lack of diesel engine power, machinery can not work, the maintenance personnel disassembly and decomposition of the PT injection pump and fuel injector has not found the cause of failure, the replacement of the 1 fuel injection pump test, the failure is still. The final inspection is due to the excessive internal impurities and excessive moisture in the diesel fuel, but this disassembly leads to a significant decline in the performance of the PT fuel injection pump and the insufficient power of the diesel engine. Therefore, after the failure of the machinery, it is necessary to detect the equipment through the detection equipment, such as no detection equipment, through the traditional methods and means of "asking, looking, checking, and trying", combining the structure and working principle of the construction machinery, to determine the most likely fault location. In determining the failure of engineering machinery, generally used "exclusion method" and "comparison method", according to the order from simple to complex, first appearance after the internal, first assembly and re components, should not be "indiscriminate, blind big dismantling and unloading".
2 blind replacement of parts, the phenomenon of "replacement repair" exists in varying degrees. The judgment and elimination of the fault of the engineering machinery is relatively difficult. Some maintenance personnel have always adopted the method of changing the parts, no matter the large parts and small parts, as long as it is considered possible to be a part of the failure, one of the replacement tests, the result is not troubleshooting, and the spare parts that should not be replaced will be replaced. Expenses of a fee. 1 74 type II excavators, because the steering difficulty to a factory maintenance, the manufacturer replaced the vane pump (steering pump), overflow valve, steering oil cylinder and other parts are also useless, the fault is found to turn the oil tank to the vane pump a hydraulic oil pipe internal aging glue off, resulting in liquid pressure oil flow and pressure is not due to. In addition, some failure parts can be repaired by repair, such as generators, starters, oil cooler, gear oil pump and so on. No complex repair technology can be used to repair them. But the maintenance personnel require the user to replace the new parts and take the "replacement repair" method to cause serious waste. . The above blind replacement test and the replacement of repairable parts are still in varying degrees in some repair units. In maintenance, the cause and location of the fault should be carefully analyzed and judged according to the failure phenomenon, and the repair methods should be taken to restore the technical performance of the repaired parts and eliminate the blind replacement of the parts.
3 do not check the quality of new parts. Problems after assembly are common. Before replacement of parts, some maintenance personnel do not make technical inspection of new parts, and then install them directly on construction machinery. This is not scientific. At present, the quality of the parts sold on the market is uneven, some counterfeit and inferior parts are mixed, and some accessories are too long in stock, the performance changes, such as unchecked, and often cause the failure after the assembly. 1 Shanghai 120A bulldozers, diesel engine oil cooler freeze cracking, lead to the oil in the water, the replacement of a new oil cooler, starting test machine, the oil still water, and check the other parts, not found the cause of the failure. After disassembling the new oil cooler side cover, it is found that the sealing oil ring at the side cover is not compacted, causing the oil and water to mix, because the quality of the oil cooler does not pass through. 1 ZL50 loaders, the diesel engine oil pressure is too low, the analysis is that the oil filter is blocked, a new oil filter is replaced, and the engine oil pressure is still low. After checking or replacing all the parts that may lead to low oil pressure, the oil pressure can not be raised. Finally, it is barely used under the condition that the fault is not found and the oil pressure is low. The result is that the diesel engine burns the shafts, the crankshaft fracture, the connecting rod bending, and the loss of more than 10000 yuan. After inspection, the change of the oil filter cartridge (coarse filter) has been blocked by too much rust, because the filter is kept in storage for a long time and causes internal rust. Therefore, the necessary inspection and testing must be carried out before the replacement of the new accessories, including the appearance and performance test, to ensure that the new accessories are not malfunction, and to eliminate the unnecessary trouble caused by it.
4 do not pay attention to accessories type, accessories substitution or misuse phenomenon is more common. In the maintenance of engineering machinery, the replacement or misuse of accessories is still common, and some accessories are feasible for emergency replacement, but long time use is harmful, affecting the safety and technical performance of the machinery. Some maintenance personnel are less aware of the mechanical structure and principle, many parts do not match, but think that if they can be installed on the line, do not consider the ability to play the mechanical performance. For example, the 4120F diesel engine should use a 350 Watt generator, but use a 500 Watt generator to waste the power; the ZL50 loader uses the QD274 type starting machine, but uses the QD50 type starting machine, because the power is insufficient, the diesel engine is starting difficult; the 135 series supercharging and non turbocharged diesel engines are often mixed with the piston, valve, rocker arm and so on. The phenomenon makes diesel engine start difficult and power decrease, and even cause serious damage to machine parts. 1 6135ZD turbocharged diesel engines have misused the piston of non turbocharged diesel engine. After assembly, the diesel engine starts without fire, and after replacing the prototype number piston (supercharged type), the diesel engine starts smoothly. Different types of diesel engines are replaced by high pressure oil pipes, nozzle couple parts and plunger pairs, resulting in the change of fuel injection and oil supply advance angle. By replacing the qualified 名媛直播 with defective 名媛直播, replacing the opening pin with wire and iron nails, replacing the cylindrical pin with steel bars and old bolts, the quality can not be guaranteed, and the long-term use is not allowed. Therefore, in the maintenance of construction machinery, should try to use the original type of accessories, can not be replaced by other types of accessories, more can not be misused.
5 do not pay attention to the selection of bolts, the use of bolts is chaotic. In the maintenance of construction machinery, the phenomenon of misuse of bolts is still more prominent, because the bolt performance and quality do not meet the technical requirements, resulting in frequent mechanical failure after maintenance. Special bolts used in engineering machinery, such as drive shaft bolts, cylinder head bolts, connecting rod bolts, flywheel bolts, and fixed bolts of fuel injector, are specially made with special materials, which have strong strength, strong shear resistance, and ensure the connection and fixed reliability. In the actual maintenance work, some maintenance workers find that these bolts are damaged or missing, some of them can not find the standard bolt for a moment. Some are taken in place of other bolts at will. Some of them are replaced by themselves. Because of the poor material or processing technology, these bolts leave hidden trouble for the later period of the construction machinery, and the 74 type II excavator is used. The 6 bolts of the rear axle wheel side decelerator connecting the planet wheel frame and the wheel side reducer shell bear greater torque. The 6 bolts are broken and damaged. Some maintenance personnel use other bolts or self processing, often when the bolt strength is not enough, some parts need "small screw pitch" "fine buckle". The self tightening bolt, copper bolt and copper plated bolt are replaced by ordinary bolts, which lead to the phenomenon of self loosening and disassembling of the bolts. For example, the diesel engine exhaust manifold fixed nut is mostly copper, preventing heat from being heated or using long time is not easy to disassemble, but in actual maintenance, most of the nut is used, time is one time. Long disassembly is very difficult; some bolts will have defects such as stretching, deformation and other defects after use. Some technical requirements require new bolts to be replaced after several times of disassembly and disassembly. Because the maintenance personnel do not understand these conditions, repeated use of unqualified bolts may also lead to mechanical failure or cause. Therefore, in the maintenance of construction machinery, when the bolt is damaged or missing, it is necessary to change the required bolts in time and avoid using bolts.
The improper tightening method of 6 bolts is more serious. Most of the fixed or connected bolts of the construction machinery have the tightening torque requirements, such as the fixed bolt of the injector, the cylinder head bolt, the connecting rod bolt, the flywheel bolt and so on. Some stipulate the tightening torque, some stipulate the tightening angle, and also stipulate the tightening order. Some maintenance personnel, believe that tightening bolts will do, irrelevant, not in accordance with the specified torque and order tightening (some do not understand the tightening torque and order requirements), no torque (kg) wrench, or random use of the force rod, tightened by feeling tightened, leading to a great difference in tightening torque. When the torque is insufficient, the bolt is easily loosened, which causes the cylinder liner, loose axle bush, oil leakage and gas leakage; the moment is too large, the bolt is easy to stretch and even break, and sometimes it will damage the thread hole, which affects the repair quality. 1 ZL50 loaders, the torque converter to throw hydraulic oil, after inspection is due to the connection of the pump wheel and cover wheel 24 bolts are not in accordance with the prescribed order and torque tightening. Therefore, in the maintenance of engineering machinery, we must tighten the bolts in accordance with the prescribed moment and order to prevent the mechanical failure caused by too much tightening torque, too small or improper order of the bolt tightening torque.
7, there are quite a few phenomena that do not pay attention to the clearance of parts. Diesel engine piston and cylinder liner clearance, piston ring "three gap", piston top clearance, valve clearance, piston clearance, brake shoe clearance, main and subordinate gear meshing clearance, axial and radial clearance of bearing, valve rod and valve guide, all types have strict requirements and must be measured in maintenance. It is necessary to adjust or replace parts that do not meet the requirements of clearance. In the actual maintenance work, there are many phenomena of blind assembly of spare parts without measuring matching clearance, which lead to early wear or erosion of bearing, diesel engine oil, starting difficulty or deflagration, piston ring break, machine parts impact, oil leakage, leakage and so on. Sometimes, it may even cause mechanical strict due to the improper coordination of the gap between zero components. The occurrence of a heavy damage to the accident. After 1 Nissan 6DB-10P diesel engine overhaul, the test machine runs for 30 minutes to extinguish its own fire, and then does not catch fire, check oil, oil and other normal. After stopping for 30 minutes, it can start to catch fire again, but it runs for 30 minutes and goes out on its own. After the diesel engine temperature rises, the plunger expansion and the oil outlet valve are incompatible, and the fuel supply can not be normal reciprocating. After the shutdown, the plunger and the oil outlet valve have some clearance and can supply oil normally.
8 it is not rare that pairs or components are replaced. There are many even parts in the engineering machinery, such as the plunger pair of the diesel fuel system, the oil outlet valve pair, the injection nozzle needle valve pair, the main and the driven gear in the main drive axle reducer, the valve block and stem in the hydraulic control valve, the valve core and the valve sleeve in the full hydraulic steering gear and so on. These matching couples are specially added when they are manufactured in the factory. The work, made of pairs, is very precise and is very precise. It is not interchangeable during the service life. Some components, such as piston and cylinder sleeve, axle bush and shaft neck, valve and valve seat, connecting rod large head and rod, are used for a period of time. At the same time, we should also pay attention to the pair assembly, do not make string; diesel engine connecting rod, piston, fan belt, high pressure oil pipe, excavator central rotary joint oil seal, bulldozer main clutch adhesive tape, and so on. These machines use a set of accessories at the same time, the damage must be changed more, otherwise, because of the large difference of quality of parts, Different new and old age and different length and short size will lead to unstable operation of diesel engine, oil leakage in hydraulic system, serious load concentration, easy damage of replacement parts and so on. In the actual maintenance work, in order to reduce expenses, some people do not know the technical requirements, unpaired or complete replacement of the above parts are not rare, reducing the maintenance quality of the engineering machinery, shortening the life of the machine parts, increasing the possibility of failure, and should pay enough attention.
9 when assembling parts, the reverse happens. In the maintenance of construction machinery, some parts have strict direction requirements. Only proper installation can ensure the normal work of components. The external features of some parts are not obvious, both positive and negative can be installed. In actual work, there are often reverse conditions, which lead to the early damage of the parts, the normal work of the machinery, the damage of the engineering machinery and so on. Such as engine cylinder liner, unequal distance valve spring (such as F6L912 diesel engine), engine piston, piston ring, fan blade, gear oil pump side board, skeleton oil seal, thrust washer, thrust bearing, thrust gasket, oil retaining ring, injection pump plunger, clutch disc hub, drive shaft universal joint, etc. During installation, if you do not understand the structure and installation matters needing attention, it will be the most difficult to install, resulting in abnormal work after assembly, resulting in the failure of construction machinery. If the 1 4120F diesel engine changes the piston ring, the diesel engine smokes blue smoke, considering that it may be caused by too much oil injection or the "counterpart" of the piston ring. Check the oil oil is normal, remove the piston rod group of one cylinder, find the piston ring not "opposite", but the gas ring is installed back, check the other cylinder piston rings are also installed. The machine uses the internal cutting slot type twisted gas ring, when the installation requires the internal incision upwards, the maintenance personnel are exactly installed, because the piston ring in the inner cutting slot is very easy to appear the piston "pump oil" phenomenon, so that the oil moves along the ring incisive to the combustion chamber. For example, 2 skeleton oil seals are installed on the ZL50 loader's working oil pump. The correct installation direction of the oil seal is: the oil seal lip of the inner side and the outside oil seal lip, so that the pump can prevent the oil from the hydraulic oil tank to enter the gearbox through the variable speed pump, and also prevent the transmission pump to enter the oil in the gearbox through the working pump. In the hydraulic tank (the work pump and the transmission pump are installed side by side, driven by a shaft gear), the author has encountered two cases of oil fluid channeling failure caused by the oil pump oil package. Therefore, when assembling parts, maintenance personnel must grasp the structure and installation requirements of parts and components.
10 the maintenance method is not regular. "Temporary solution is not a permanent cure" is still used by some maintenance units. In the maintenance of engineering machinery, some maintenance personnel do not take the correct maintenance methods, think that the emergency measures are omnipotent, "emergency" instead of "maintenance", "management of the standard" phenomenon is still a lot of phenomenon. If often encountered "to repair welding", is one example, some parts can be repaired, but some maintenance personnel plan to save trouble, but often use "welding death" method. The camshaft key slot of the injection pump camshaft of the 1 12V135 diesel engine is not fixed because of the loose wear and the semicircle key. This should be solved by means of re milling key grooves, but the maintenance personnel directly weld the camshaft and the fuel injection pump joint together, which can not be dismantled, and the later maintenance is difficult. After the damage of the connecting thread of the hydraulic cylinder earrings and the piston rod of the oil cylinder, the oil seal can not be replaced after the damage of the oil seal by direct welding, and the oil leakage is serious. When it is found that the working device is slow or difficult to turn, the working pressure of the system is blinded and the pressure of the system is blinded, so the pressure of the system is too high and the oil seal is easily damaged. In order to make the diesel engine "strong", the fuel supply quantity of the fuel injection pump and the injection pressure of the injector are increased artificially. These irregular maintenance methods can only be used for emergency, but they can not be used for a long time. It is necessary to find out the causes of the failure fundamentally, and take regular maintenance methods to eliminate the failure, and should cause the attention of the maintenance personnel.
11 the use of gaskets is not standardized, and the phenomenon of casual use still exists. There are many types of gaskets used in the construction machinery parts, including asbestos pads, rubber pads, cardboard mats, cork pads, felt mats, nonferrous metal mats (copper pads, aluminum mats), copper skin (steel skin) asbestos pads, insulation pads, spring mats, flat mats, etc. Some are used to prevent oil leakage, leakage, leakage, leakage and some fastening and loosening effects. There are different rules and requirements for the timing and occasion of each type of gasket. In the maintenance of engineering machinery, the use of the gasket is not standardized or even disorderly, which leads to frequent leakage, loosening and loosening of bolts and nuts, which affects the normal use of engineering machinery. If the engine cylinder pad is too thick, the compression ratio is reduced, the engine is difficult to start, and the copper gasket is used between the fuel injector and the cylinder head, such as the use of the asbestos pad instead of the asbestos pad, which can easily cause the erosion of the injector, and the oil pump and the injection pump are too thick, which leads to the shortage of oil transportation and oil delivery pressure. Oil engine power drop, such as leaking spring mat, locking pad, seal pad, causing loose joint, easy to happen loosening or oil leakage and so on. Because of the hole in the middle of the gasket, forgetting the opening of the hole leads to the blockage of the oil channel and the waterway, and the phenomenon of the engine burning the shafts and the water tank often happens. It reminds us that when maintenance personnel repair engineering machinery, remember that "gaskets are small and useful."
12 "small pieces" do not pay much attention to the problem, because the "small" loss of "big" leads to an increase in malfunction. In the maintenance operation, some maintenance personnel often pay attention to the maintenance of fuel injection pump, oil pump, piston, cylinder sleeve, piston ring, hydraulic oil pump, control valve, brake, steering system and other parts, but ignore the maintenance of "small pieces" such as filter, overflow valve and all kinds of instruments. They believe that these "small pieces" do not affect the maintenance. Mechanical work, even if the damage is not important, as long as the mechanical dynamic can be used, which is not known, it is the lack of maintenance of these "small pieces", leading to the early wear and tear of the machinery, shorten the service life. Such as diesel filter, oil filter, air filter, hydraulic oil filter, water thermometer, oil thermometer, oil thermometer, oil pressure meter, induction plug, sensor, alarm, preheating plug, oil filter screen, tank cover, oil tank cover, oil mouth cover, butter nozzle, storage tank, storage switch, storage battery box, fuel injection These "small pieces" are essential for the normal work and maintenance of the engineering machinery and are essential for the extension of the service life of the machinery. In the maintenance operation, if the maintenance is not paid attention to, it often causes the failure of the engineering machinery. It happened. 1 74 type II excavators, because the clutch 6 separate arm fixed screws do not wear lock pin, the use of 1 fixed screws off and broken, leading to the clutch disc, separation bearing, bearing seat serious damage, the clutch can not work normally. 1 TL180 bulldozers, air filter core damage, the use of personnel did not change in time, mechanical use for a long time, diesel engine power decline, inspection found that the piston, cylinder, piston ring, valve and so on serious wear and tear. The above two failures are caused by ignoring the maintenance of "small pieces". They should be taken as warning.
13 maintenance taboo forget mind, hidden trouble frequent. When repairing engineering machinery, some maintenance personnel do not understand some problems that should be paid attention to in maintenance, which leads to the often "habit" errors in the disassembly and disassembly, which affects the maintenance quality of the machinery. If the cylinder head of a hot car is disassembled, it is easy to cause the deformation crack of the cylinder head; when the piston pin is installed, the piston pin is not heated directly into the pin hole, which leads to the increase of the deformation of the piston and the increase of the ellipticity; the crankshaft main axle bush or the back of the connecting rod is added with copper pad or paper pad, which is easy to block the oil path and causes the accident of burning the bearing shaft; in the maintenance of the firewood When the oil machine is overused to scrape the axle bush, the antifriction alloy layer on the surface of the axle bush is scraped off, leading to the early wear of the axle steel back and the crankshaft, and the disassembly of the bearing, the pulley and other parts without the use of the tension device, hard knocking, easily causing the deformation or damage of the parts and parts, and opening the new piston, cylinder liner and nozzle couple. When the parts such as plungers and parts are used, the properties of the parts are changed by burning the oil or wax on the surface of the parts, which is not conducive to the use of parts.
14 cleaning and cleaning of parts are not thorough. Early damage and corrosion often occur. In the maintenance of construction machinery, it is important to correctly remove the oil and impurities on the surface of the components to improve the repair quality and prolong the service life of the machine. Due to the lack of attention to the cleaning of parts, improper selection of cleaning agents and improper cleaning methods, the early wear and corrosive damage of parts are caused by some repair units. If the cylinder liner is not completely removed, the carbon in the piston ring groove, the sundries in the bolt hole, and the sand in the hydraulic element, the bolt torque is insufficient, the piston ring is broken easily, the cylinder pad is ablated, and the hydraulic components are worn early. When the engineering machinery is overhauled, we do not pay attention to the removal of oil or impurities such as diesel filter, oil filter, hydraulic oil filter, diesel engine water jacket, radiator surface, lubricating oil and oil channel, so as to reduce the maintenance work and reduce the failure operation time of the construction machinery. When cleaning the components, the repair personnel must select the cleaning agent correctly. The cleaning of various parts should be based on their different requirements for cleanliness, and correct selection of different cleaning agents; two, prevent corrosion and rust of parts. To ensure the quality of parts and components, corrosion of parts should be prevented, especially for precision parts. Therefore, when cleaning, the alkaline cleaning agent (especially the alkali cleaning agent) is not used to clean the aluminum alloy parts (such as the aluminum alloy cylinder head), and the copper parts (such as the main valve of the thermostat) can not be cleaned with strong acid cleaning agent to minimize the corrosion of the machine parts. Three, the different parts and parts should be classified and cleaned. Aluminum alloy parts and copper parts should not be cleaned in alkaline or acid cleaning agents. Rubber parts should not be cleaned with other steel parts in steam, diesel and acid and alkaline detergent.
