Maintenance is an effective means to restore the technical performance of engineering machinery, eliminate failures and eliminate hidden dangers, and extend the service life of machinery. There are still many technical problems in maintenance. The existence of these problems can easily lead to low quality of mechanical maintenance and poor equipment reliability, which can cause consumers to suffer losses and even major engineering machinery accidents. This article analyzes the common technical problems encountered in the maintenance work of construction machinery, it is definitely worth a look!
1. Failure to judge and analyze faults correctly, and the phenomenon of blind demolition and unloading are commonplace.
Some maintenance personnel are unclear about the structure and principle of construction machinery, and do not analyze the cause of the failure seriously, and cannot accurately determine the location of the failure. With the idea of "probably, almost", they blindly dismantle and disassemble the machinery. Due to poor maintenance skills and craftsmanship,
There are new problems. One bulldozer had a fault that the diesel engine was insufficient in power and the machine could not work. The maintenance staff disassembled and disassembled the PT fuel injection pump and fuel injector and found no cause of the failure. Replace one fuel injection pump to test and the failure remains. The final inspection failure was due to the internal impurities and excessive moisture in the diesel used, but this disassembly caused the performance of the PT fuel injection pump to be significantly reduced, and the power of the diesel engine was insufficient. Therefore, when the machine fails, it must be detected by the detection equipment. If there is no detection equipment, the traditional fault judgment methods and means such as "ask, see, check, test" and other methods, combined with the structure and working principle of the construction machinery, can be determined The location where the failure is most likely. When judging the failure of construction machinery, the "elimination method" and "comparison method" are generally used, in order from simple to complex, first appearance and then internal, first assembly and then components, avoiding "regardless of indiscriminate, blind dismantling and unloading ".
2. Blind replacement of parts, the phenomenon of "replacement repair" exists to varying degrees.
It is relatively difficult to judge and eliminate construction machinery faults. Some maintenance personnel always use the replacement test method, regardless of the large and small parts, as long as it is considered to be the part that may cause the failure, one by one replacement test. Replace parts that should not be replaced at will
It has increased consumer spending. One excavator was repaired by a factory due to steering difficulties. The manufacturer replaced the vane pump (steering pump), overflow valve, steering cylinder and other parts to no avail. Later, it was found that the cause of the failure was a hydraulic tubing from the steering tank to the vane pump The internal aging glue is removed, resulting in insufficient hydraulic fluid flow and pressure. There are also some faulty parts that can be completely restored to their technical performance through repairs, such as generators, starters, oil coolers, gear oil pumps, etc. failures, which can be repaired without complicated repair processes, but maintenance personnel require users to replace new parts, Blindly adopt the "replacement repair" method, causing serious waste. The above-mentioned blind replacement test and blind replacement of repairable parts still exist in some repair units to varying degrees. During maintenance, the cause and location of the fault should be carefully analyzed and judged according to the fault phenomenon. The repairable parts should be repaired to restore the technical performance, and the practice of blindly replacing parts should be eliminated.
3. Without checking the quality of new parts, the problem of failure after assembly is relatively common.
Before replacing parts, some maintenance personnel do not perform technical inspection on the new parts, and install them directly on the construction machinery after they are taken. At present, the quality of spare parts sold on the market is uneven, and some counterfeit and inferior parts are mixed in the fish head; some parts have changed their performance due to the long inventory time. If they are not tested, they often cause failures after assembly. A Shanghai 120A bulldozer, diesel engine oil cooler freezes and cracks, resulting in water in the oil. Replace the oil cooler with a new one, start the test machine, the water still enters the engine oil, and check other parts. No cause of the failure was found. After disassembling the side cover of the new oil cooler, it was found that the oil seal at the side cover was not compacted, which caused the mixing of oil and water, because the quality of the oil cooler was not enough. One ZL50 loader, the diesel engine oil pressure is too low, the analysis is that the oil filter is clogged, a new oil filter is replaced, and the test engine oil pressure is still low. After checking or replacing all the parts that may cause low oil pressure, but the oil pressure still cannot be increased, and finally it was used reluctantly without finding the cause of the failure and the low oil pressure. As a result, the diesel engine burned the bush, crankshaft Broken and bent connecting rods cost more than 10,000 yuan. After the inspection, the replacement oil filter element (coarse filter) has been blocked by too much rust. The reason is that the filter has been kept in stock for a long time, resulting in internal rust. Therefore, before replacing a new accessory, it is necessary to carry out the necessary inspection tests, including appearance and performance tests, to ensure that the new accessory is free of trouble, and to avoid unnecessary trouble caused by it.
4. The model of the accessories is not paid attention to, and the substitution or misuse of the accessories is more common.
When repairing construction machinery, the substitution or misuse of accessories is still relatively common. Some accessories are feasible for emergency substitution, but long-term use is harmful and unhelpful, affecting the safety and technical performance of the machinery. Some maintenance personnel have little understanding of the mechanical structure and principles, and many parts and models do not match, but they think that as long as they can be installed, they do not consider whether they can play the technical performance of the machine. For example, the 4120F diesel engine should use a 350-watt generator, but a 500-watt generator, wasting power; the ZL50 loader uses a QD274 starter, but uses a QD50 starter. Due to insufficient power, the diesel engine is difficult to start; 135 series supercharger The pistons, valves, and rocker arms of non-supercharged diesel engines are not versatile, but they often mix up, making it difficult for the diesel engine to start, reducing power, and even causing serious damage to the machine parts. One 6135ZD supercharged diesel engine, due to the misuse of the non-supercharged diesel engine piston, the diesel engine does not start to fire after assembly. After replacing the original model piston (supercharged type), the diesel engine starts smoothly; the high-pressure fuel pipe and fuel injection of different types of diesel engines The replacement of spout and plunger parts has resulted in changes in the amount of fuel injection and the advance angle of fuel supply; replacing defective 名媛直播 with defective 名媛直播, replacing cotter pins with iron wires and nails, replacing cylindrical pins with steel bars and old bolts, etc., quality There is no guarantee that long-term use is never allowed. Therefore, when repairing construction machinery, the original model accessories should be used as much as possible, and other types of accessories should not be used as substitutes, not to mention misuse.
5. I don't pay attention to the selection of bolts, and the phenomenon of messy use of bolts is more prominent.
In the maintenance of construction machinery, the phenomenon of indiscriminate use of bolts is still more prominent. The performance and quality of bolts do not meet the technical requirements, resulting in frequent mechanical failures after maintenance. Special bolts used in construction machinery, such as drive shaft bolts, cylinder head bolts, connecting rod bolts, flywheel bolts, fuel injector fixing bolts, etc., are made of special materials through special processing, which has high strength and strong shear resistance. Ensure the connection and fixation are reliable. In the actual maintenance work, some maintenance personnel found that these bolts were damaged or missing, and they could not find the standard bolts at once. Some of them were randomly replaced by other bolts, and some were processed and replaced by themselves. These bolts were given poor quality or processing technology. The late use of construction machinery leaves hidden dangers. The 6 bolts connecting the planetary gear carrier and the wheel reducer housing in the rear axle wheel reducer of the 74 type II excavator bear a large torque, and these 6 bolts break Damaged, some maintenance personnel use other bolts or process their own substitutes, and they often break again due to insufficient bolt strength; some parts need to use "small pitch" "fine buckle self-tightening" bolts, copper bolts, copper-plated bolts, but The use of ordinary bolts instead causes the bolts to loosen themselves and make it difficult to disassemble. For example, the fixing nuts of diesel exhaust manifolds are mostly made of copper, which prevents them from being heated or used for too long. It is not easy to disassemble, but they are mostly used in actual maintenance Ordinary nuts are very difficult to disassemble for a long time; some bolts will have defects such as stretching and deformation after use, and some technical requirements After disassembly times must get a new bolt, for maintenance personnel do not understand these cases, the repeated use of substandard bolts, also easily lead to mechanical failure or accidents. Therefore,
If the bolt is damaged or lost, replace the bolt that meets the requirements in time, and avoid using the bolt indiscriminately.
6. The situation of improper bolt tightening is more serious.
Most of the fixing or connecting bolts of various parts of construction machinery have tightening torque requirements, such as injector fixing bolts, cylinder head bolts, connecting rod bolts, flywheel bolts, etc. Some specify the tightening torque, some specify the tightening angle, and also specify the tightening order. Some maintenance personnel think that anyone will do the bolt tightening, it does not matter, do not tighten in accordance with the specified torque and sequence (some do not understand the tightening torque and sequence requirements at all), do not use torque (kg) wrenches, or use stiffeners at will Tightening by feeling leads to a large difference in tightening torque. If the torque is insufficient, the bolts are prone to loosen, resulting in broken cylinder liners, loose bearing bushes, oil leakage, and air leakage. When the torque is too large, the bolts are easily stretched and deformed, or even broken, and sometimes the threaded holes are damaged, affecting the repair quality. 1 ZL50 loader, the torque converter throws the hydraulic oil outwards. After inspection, the 24 bolts connecting the pump wheel and the cover wheel are not tightened in the specified order and torque. Therefore, when repairing construction machinery, be sure to tighten the bolts in accordance with the specified torque and order to prevent the machine from malfunctioning due to excessive tightening torque, too small, or improper order.
7. There are many phenomena that do not pay attention to detecting the fit clearance of parts.
Diesel engine piston and cylinder liner clearance, piston ring "three clearance", piston top clearance, valve clearance, plunger clearance, brake shoe clearance, main and driven gear mesh clearance, bearing axial and radial clearance, valve rod With the clearance of the valve guide, all types of models have strict requirements.
Measurements must be made, and parts that do not meet the clearance requirements must be adjusted or replaced. In the actual maintenance work, there are many phenomena of blindly assembling parts without measuring the fit gap, resulting in early wear or ablation of the bearing, diesel engine oil burning, difficult starting or deflagration, broken piston ring, mechanical parts impact, oil leakage, air leakage Such failures sometimes result in serious mechanical damage accidents due to improper clearance of parts. After a Nissan 6DB-10P diesel engine is overhauled, the test machine will automatically shut down after about 30 minutes of operation. Then start the engine and it will not catch fire. Check that the oil and oil lines are normal. After 30 minutes of shutdown, it can start to fire again, but after 30 minutes of operation Turn off the flame by yourself. Later, the cause of the fault was checked because the plunger clearance of the fuel injection pump was too small. After the temperature of the diesel engine increased, the plunger expanded and the fuel outlet valve conflicted. There is a certain gap between the valves and the oil can be supplied normally.
8. It is not uncommon for pairs or components to be replaced in complete sets.
There are many couples on the construction machinery, such as the plunger pair of the diesel engine fuel system, the fuel outlet pair, and the injector needle valve pair couple; the main and driven gears in the main reducer of the drive axle; the valves in the hydraulic control valve Blocks and valve stems; valve cores and valve sleeves in full hydraulic steering gears, etc. These mating couples are specially processed at the factory and grinded in pairs, the coordination is very precise, and they are always used in pairs during the service life , Must not be interchangeable; some mutually coordinated components, such as pistons and cylinder liners, bushes and journals, valves and valve seats, connecting rod head covers and shafts, etc., after a period of running-in use, the relative cooperation is better. When repairing, you should also pay attention to assembly in pairs, not to make strings; diesel engine connecting rods, pistons, fan belts, high-pressure oil pipes, excavator central rotary joint oil seals, bulldozer main clutch rubber joints, etc. These machines use a set of accessories at the same time If damage occurs, it must be replaced in a complete set. Otherwise, due to large differences in quality of parts, different old and new sizes, and different lengths and sizes, it will cause unstable operation of the diesel engine, oil leakage in the hydraulic system, and concentrated load Like severe, early replacement parts easily damaged. In the actual maintenance work, it is not uncommon for some people to replace the above parts in unpaired or 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 life of machine parts, and increases the occurrence of failures. The possibility should be given enough attention.
9. There are occasions when parts are reversed during assembly.
When servicing construction machinery, some parts have strict directional requirements. Only correct installation can ensure the normal operation of parts. The external features of some parts are not obvious, and they can be installed both positive and negative. In actual work, they are often reversed, resulting in early damage of parts, machinery not working properly, and accidents of construction machinery damage. Such as engine cylinder liner, unequal 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 washer, oil retaining ring 、 Injection pump plunger, clutch friction disc hub, transmission shaft universal joint, etc., these components are most likely to be reversed if they do not understand the structure and installation precautions during installation. The failure occurred. For example, after a 4120F diesel engine replaces the piston ring, the diesel engine emits blue smoke. It may be caused by too much oil filling or the "pair" of the piston ring. Check that the amount of engine oil is normal, remove the piston connecting rod set of one cylinder, and find that the piston ring is not "paired", but the gas ring is reversed. Check that the piston rings of other cylinders are also reversed. The machine uses an internally cut grooved twisted air ring. The inner cut is required to be upwards during installation. The maintenance personnel just installed it reversely. When the internally cut piston ring is reversed, the "pump oil" phenomenon of the piston is prone to occur, which causes the oil to cut along the ring. It went up into the combustion chamber and burned. Another example is that the ZL50 loader working oil pump is equipped with two skeleton oil seals. The correct installation direction of the oil seal is: the inner oil seal lip is inward, and the outer oil seal lip is outward. It can also prevent the variable speed pump from driving the oil in the transmission 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 For example, due to the oil pump oil packaging, the oil-to-liquid channeling failure is caused instead. Therefore, when assembling parts, maintenance personnel must master the structure and safety of the parts
The installation direction requires that blind installation cannot be taken for granted.
10. The maintenance method is not formal, and "fixing the symptoms but not the cause" is still a common method used by some maintenance organizations.
In the maintenance of construction machinery, some maintenance personnel do not take the correct maintenance method, and believe that emergency measures are omnipotent. Instead of "maintenance" with "emergency", there are still many phenomena of "fixing the symptoms but not the cause". For example, "welding instead of repair" is often encountered. Some parts can be repaired, but some maintenance personnel often use the method of "welding to die" to save trouble. A 12V135 diesel engine fuel injection pump camshaft keyway is loose due to wear, and the semicircular key is not fixed firmly. It should be solved by re-milling the keyway, but the maintenance personnel directly welded the camshaft and the injection pump connection disk together The location cannot be disassembled, and it is difficult to maintain it later. After the connection thread of the hydraulic cylinder earring and the piston rod of the hydraulic cylinder is damaged, the method of direct welding is used, so that the oil seal of the cylinder cannot be replaced after the damage, and the oil leakage is serious. Working pressure
The pressure of the system is too high, which is easy to damage the oil seals, pipelines, hydraulic components, etc. In order to make the diesel engine "vigorous", artificially increase the fuel supply of the fuel injection pump and increase the fuel injection pressure of the fuel injector. These irregular maintenance methods can only be used for emergency, but cannot be used for a long time. The cause of the failure must be fundamentally detected, and a formal maintenance method should be adopted to eliminate the failure, which should be brought to the attention of the maintenance personnel.
