Construction machinery maintenance 10 "no", who did it?

Maintenance is an effective means to restore the technical performance of engineering machinery, eliminate faults and eliminate hidden troubles, and prolong the service life of machinery. There are still many technical problems in the maintenance. The existence of these problems easily leads to poor quality of mechanical maintenance and poor equipment reliability, which causes 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. It is impossible to correctly judge the analysis of faults, and the phenomenon of blindly dismantling and unloading is commonplace.

 

Some maintenance personnel are unclear about the structure and principle of the construction machinery, do not carefully analyze the cause of the failure, can not accurately determine the fault location, blindly dismantle the machinery with the "probably, almost" idea, the result is not only the original fault is not ruled out, and Due to poor maintenance skills and craftsmanship, new problems have arisen. One bulldozer had a problem that the diesel engine was insufficiently powered and the machine could not work. The maintenance personnel disassembled and disassembled the PT fuel injection pump and the injector and found the cause of the failure. The replacement of one fuel injection pump test, the fault remains. The final inspection failure was caused by excessive internal impurities and moisture in the diesel used, and this disassembly caused the performance of the PT fuel injection pump to drop significantly, and the diesel engine power was insufficient. Therefore, when the machine fails, it must be tested by the testing equipment. If there is no testing equipment, it can be determined through traditional fault judgment methods and means such as “question, see, check, test”, combined with the structure and working principle of the construction machinery. The most likely area of ​​failure. When judging the failure of construction machinery, the "exclusion method" and "comparative method" are generally used, and the order is from simple to complex, and the internal and the first assembly are re-assembled in the order of the first and the first assembly, and it is forbidden to "disregard the indiscriminate, blindly dismantling and unloading." ".

 

2, blindly replace parts, blindly "changing parts repair" phenomenon exists to varying degrees.

 

It is relatively difficult to judge and eliminate the failure of construction machinery. Some maintenance personnel have always adopted the method of replacement test. Regardless of the large and small parts, as long as it is considered that the parts that may cause the failure, the test is replaced one by one, the result is not eliminated, and Replace the parts that should not be replaced at will, increasing the cost of consumers. 1 excavator, due to steering difficulties to a factory maintenance, the manufacturer replaced the vane pump (steering pump), relief valve, steering cylinder and other parts also did not help, and found that the cause of the failure is a hydraulic oil pipe steering the tank to the vane pump The internal aging rubber is removed, resulting in insufficient hydraulic fluid flow and pressure. There are also some faulty parts that can be repaired to restore their technical performance, such as generators, starters, oil coolers, gear oil pumps, etc., which can be repaired without complicated repair processes, but the maintenance personnel require users to replace new parts. The method of “replacement repair” is adopted blindly, resulting in serious waste. The above-mentioned blind replacement test and the practice of replacing the repairable parts are still present to varying degrees in some repairing units. During maintenance, the cause and location of the fault should be carefully analyzed and judged according to the fault phenomenon. The repaired parts should be repaired to restore technical performance and eliminate the blind replacement of parts.

 

 

 

3, do not check the quality of new parts, the problem of failure after assembly is more common.

 

Before replacing the parts, some maintenance personnel do not perform technical inspections on the new parts and directly install them on the construction machinery. This is unscientific. At present, the quality of spare parts sold on the market is uneven, and some counterfeit and shoddy parts are mixed with beads; some accessories have changed performance due to excessive inventory time. If they are not tested, they often cause failure after assembly. A Shanghai 120A bulldozer, diesel engine oil cooler freeze crack, resulting in water in the oil, replace a new oil cooler, start the test machine, the oil is still in the water, and other parts were checked, and the cause of the failure was not found. After disassembling the side cover of the new oil cooler, it was found that the sealing oil ring at the side cover was not compacted, resulting in mixing of the oil and water, because the quality of the oil cooler was not good. One ZL50 loader, the diesel engine oil pressure is too low, the analysis is that the oil filter is clogged, replaced with a new oil filter, the test machine oil pressure is still low. After inspection or replacement of all parts that may cause low oil pressure, but the oil pressure can not be raised, and finally barely used in the case of failure to find the cause of the failure, low oil pressure, resulting in diesel engine burning shaft, crankshaft The fracture and the connecting rod are bent, and the loss is more than 10,000 yuan. After the inspection, the replacement oil filter element (strainer) has been blocked by excessive rust, because the filter is stored in the stock for a long time and causes internal rust. Therefore, it is necessary to carry out necessary inspection tests before replacing new parts. The tests include appearance and performance tests to ensure that the new parts are free from malfunctions and prevent unnecessary troubles caused by them.

 

4, do not pay attention to the type of accessories, the substitution or misuse of the accessories is more common.

 

When repairing construction machinery, the substitution or misuse of accessories is still common. Some accessories are feasible for emergency use, but long-term use is harmful and affects the safety and technical performance of the machine. Some maintenance personnel have little understanding of the mechanical structure and principle, and many parts and components do not match the model, but they believe that as long as they can be installed, it is not considered whether the mechanical performance of the machine can be exerted. For example, the 4120F diesel engine should use a 350 watt generator, but use a 500 watt generator, which wastes power. The ZL50 loader uses the QD274 starter, but uses the QD50 starter. Due to insufficient power, the diesel engine is difficult to start; Unlike non-supercharged diesel engines, pistons, valves, rocker arms, etc. are not common, but mixed phenomena often occur, making diesel engines difficult to start, reducing power, and even causing serious damage to the machine. A 6135ZD turbocharged diesel engine, due to the misuse of the non-supercharged diesel engine piston, the diesel engine does not catch fire after assembly. After replacing the original type piston (boost type), the diesel engine starts smoothly; different types of diesel engine high pressure fuel pipe, fuel injection The nozzle coupler and the plunger coupler are substituted, which causes the fuel injection quantity and the fuel supply advance angle to change; replace the qualified product with the defective product, replace the split pin with iron wire and iron nail, replace the cylindrical pin with steel bar and old bolt, etc., quality There is no guarantee that long-term use will never be allowed. Therefore, when repairing construction machinery, the original type of accessories should be used as much as possible, and other types of accessories should not be used instead, and it should not be misused.

 

5, do not pay attention to the selection of bolts, the phenomenon of chaotic use of bolts is more prominent.

 

When repairing construction machinery, the phenomenon of indiscriminate use of bolts is still prominent, because 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, injector fixing bolts, etc., are specially processed with special materials, which have high strength and strong shear resistance. Ensure that the connection is fixed and reliable. In the actual maintenance work, some maintenance personnel found that when these bolts were damaged or missing, they could not find the standard bolts at the moment, and some of them were free to take other bolts instead, and some of them were replaced by their own. These bolts were unqualified due to poor materials or processing techniques. The late use of construction machinery leaves hidden troubles. The six bolts of the 74-type II excavator rear axle wheel reducer connecting the planetary carrier and the wheel reducer housing are subjected to large torque, and the six bolts are broken. Damage, some maintenance personnel use other bolts or self-processing substitutes, often broken due to insufficient bolt strength; some parts need to use "small pitch" "small buckle self-tightening" bolts, copper bolts, copper-plated bolts, but Replacement with ordinary bolts results in loose bolts and difficulty in disassembly. For example, diesel engine exhaust manifold fixing nuts are mostly made of copper, which is difficult to disassemble when heated or used for a long time. However, in actual maintenance, most of them are used. Ordinary nuts, it is 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, when repairing the construction machinery, when the bolt is damaged or lost, it is necessary to replace the bolts that meet the requirements in time, and avoid using the bolts.

 

6. The improper tightening method of bolts is more serious.

 

Many 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 of them specify tightening torque, some specify tightening angle, and also specify tightening order. Some maintenance personnel think that anyone who tightens the bolts will do it, it does not matter, do not tighten according to the specified torque and order (some do not understand the tightening torque and sequence requirements), do not use the torque (kg) wrench, or use the afterburner at will, Tightening by feeling, the tightening torque varies greatly. If the torque is insufficient, the bolt is prone to loosening, which will cause the cylinder liner to be damaged, the bearing bush to loosen, oil leakage, and air leakage. If the torque is too large, the bolt is easy to be stretched and deformed, or even broken, and sometimes the threaded hole is damaged, which affects the repair quality. One ZL50 loader, the torque converter slammed the hydraulic oil, and it was checked that the 24 bolts connecting the pump wheel and the cover wheel were not tightened in the specified order and torque. Therefore, when repairing construction machinery, be sure to tighten the bolts according to the specified torque and order to prevent mechanical failure due to excessive tightening torque, too small or improper sequence.

 

 

 

7, not paying attention to the detection of parts with the gap phenomenon is a lot.

 

Diesel piston and cylinder sleeve clearance, piston ring "three gaps", piston clearance, valve clearance, plunger clearance, brake shoe clearance, main driven gear meshing clearance, bearing axial and radial clearance, valve stem With the valve guide clearance, etc., all types of models have strict requirements, must be measured during maintenance, parts that do not meet the clearance requirements should be adjusted or replaced. In the actual maintenance work, there are many phenomena of blindly assembling components without measuring the clearance, which leads to early wear or ablation of the bearing, diesel engine oil burning, difficulty in starting or deflagration, piston ring breaking, mechanical impact, oil leakage, and air leakage. If the fault occurs, sometimes even due to improper fitting of the parts, the mechanical damage will occur. After the overhaul of a Nissan 6DB-10P diesel engine, the test machine will run out for 30 minutes or so, and then the starter will not catch fire. Check the oil and oil lines and other normal conditions. After 30 minutes of shutdown, start the fire again, but run for 30 minutes. Turn off the fire by yourself. Later, the reason for the fault was that the plunger of the fuel injection pump was too small. After the temperature of the diesel engine increased, the plunger expansion and the oil discharge valve were in conflict with each other. The oil could not be reciprocated normally and the oil was extinguished by itself. After the machine was cooled down, the plunger and the oil were discharged. There is a certain gap between the valves to supply oil normally.

 

8. It is not uncommon to have a pair or a complete set of replacement parts or components.

 

There are many coupling parts on the construction machinery, such as the plunger pair of the diesel fuel system, the outlet valve pair, the injector needle pair coupler; the main and driven gears in the transaxle final drive; the valve in the hydraulic control valve Blocks and valve stems; spools and valve sleeves in full hydraulic steering gears. These mating parts are specially machined in the factory and are ground in pairs. They are perfectly matched and are always used in pairs during the service life. , can not be interchanged; some mutual cooperation components, such as piston and cylinder liner, bearing bush and journal, valve and valve seat, connecting rod head tile cover and shaft, etc., after a period of running-in use, relatively better cooperation, in When repairing, you should also pay attention to the assembly in pairs, do not string; diesel engine connecting rod, piston, fan belt, high pressure oil pipe, excavator central rotary joint oil seal, bulldozer main clutch tape section, etc., these one machine use a set of accessories at the same time The damage must be replaced in a complete set. Otherwise, due to the large difference in the quality of the parts, the different degrees of old and new, and the different lengths and lengths, the diesel engine may be unstable, the hydraulic system may leak oil, and the load may be concentrated. Like severe, early replacement parts easily damaged. In the actual maintenance work, in order to reduce expenses, some people do not understand the technical requirements, it is not uncommon to replace the above parts in an unpaired or complete set, which reduces the maintenance quality of the construction machinery, shortens the life of the machine parts, and increases the occurrence of faults. The possibility should be given enough attention.

 

 

 

9. When the assembly is reversed during assembly, it may occur.

 

When repairing construction machinery, some parts and components have strict direction requirements, and only correct installation can ensure the normal operation of the parts. Some parts have external features that are not obvious, and can be installed both positively and negatively. In actual work, the reverse condition often occurs, resulting in early damage of the parts, mechanical failure to work properly, and engineering machinery damage accidents. Such as engine cylinder liner, unequal valve spring (such as F6L912 diesel engine), engine piston, piston ring, fan blade, gear pump side plate, skeleton oil seal, thrust washer, thrust bearing, thrust washer, oil retaining ring , fuel injection pump plunger, clutch friction disc hub, drive shaft universal joint, etc., these components are not easy to install and reverse when installing, if they do not understand the structure and installation precautions, resulting in abnormal work after assembly, resulting in construction machinery The failure occurred. If a 4120F diesel engine replaces the piston ring, the diesel engine emits blue smoke. Considering that the oil may be excessively filled or the piston ring is “opposite”. Check that the oil quantity is normal. Remove the piston rod set of one cylinder and find that the piston ring is not “opposite”, but the air ring is reversed. Check that the piston rings of the other cylinders are also reversed. The machine uses an inner grooved twisted air ring. The inner cut is required to face upwards during installation. The maintenance personnel just reversed it. Because the inner cut groove piston ring is reversed, the piston “pump oil” phenomenon is easy to occur, so that the oil is cut along the ring. The upper part is burned into the combustion chamber. Another example is the ZL50 loader working oil pump 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 outer oil seal lip is outward, which prevents the working pump from pumping the oil in the hydraulic oil tank. Driving the gearbox through the variable speed pump also prevents the variable speed pump from pumping the oil in the gearbox into the hydraulic tank through the working pump (the working pump and the variable speed pump are installed side by side, driven by a shaft gear), and I have encountered two For example, the oil pump oil is sealed due to the oil pump oil package. Therefore, maintenance personnel must master the structure and installation direction requirements of the components when assembling the components. Do not blindly install them.

 

10, the maintenance method is not formal, "treatment of the standard is not a cure" is still the means used by some maintenance units.

 

When repairing construction machinery, some maintenance personnel do not take correct maintenance methods, and believe that emergency measures are omnipotent. There are still many phenomena of “emergency” generation of “maintenance” and “treatment of the symptoms without treatment”. As often encountered in the "repair by welding", is an example, some parts can be repaired, but some maintenance personnel to save trouble, but often use the "weld death" method. The camshaft keyway of a 12V135 diesel engine fuel injection pump is loose due to wear and looseness. The semi-circular key is not fixed firmly. It should be solved by re-milling the keyway, but the maintenance personnel directly weld the camshaft and the fuel injection pump together, resulting in the It cannot be dismantled and it is difficult to repair in the later period. After the hydraulic cylinder earrings and the piston rod connecting rod of the cylinder are damaged, the direct welding method is used, so that the oil seal of the cylinder cannot be replaced after the oil seal is damaged, and the oil leakage is serious; when the working device is found to be slow or difficult to turn, the cause of the failure is not checked, and the system is blindly adjusted. The working pressure causes the system pressure to be too high, 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 increase the fuel injection pressure of the injector. These irregular maintenance methods can only be used for emergency, but they cannot be used for a long time. The cause of the failure must be fundamentally detected. Regular maintenance methods should be used to eliminate the fault and should be brought to the attention of maintenance personnel.