Analysis of common technical problems during construction machinery maintenance

No importance is attached to the selection of bolts, and the confusing use of bolts is more prominent.

During the maintenance of construction machinery, the phenomenon of misuse of bolts is still quite prominent, because the performance and quality of bolts do not meet the technical requirements, resulting in frequent mechanical failures after maintenance.

Specialized bolts used in construction machinery, such as drive shaft bolts, cylinder hood bolts, rod bolts, flywheel bolts, oil sprayer fixed bolts, etc., are made of special materials after special processing, and their strong strength and resistance to crushing are strong, ensuring joint and fixed reliability.

In actual maintenance operations, some maintenance personnel find these bolts damaged or missing, cannot find standard bolts for a moment, and some randomly retrieve other bolts to replace them. Some of the bolts are self-made and used for replacement. These bolts are of poor material or substandard processing processes, leaving a fault problem in the later use of construction machinery. The six bolts in the rear bridge wheel side decelerator connecting the planetary shaft and the wheel side decrease housing of the 74 type II excavator bear a large torque. These six bolts broke and were damaged, and some maintenance personnel used other bolts or made their own work for them, often breaking again because the bolts were not strong enough; Some parts need to use "fine-fast" bolts with "small screw sizes," copper bolts, copper-plated bolts, but ordinary bolts are used instead. This has led to the phenomenon of bolts loosening themselves and being difficult to disassemble, such as the fixed nuts for the exhaust manifold of diesel engines are mostly made of copper, which prevents heating or being used for too long and is not easy to disassemble. However, in actual maintenance, most of the ordinary nuts are used, which is very difficult to disarm during a long time; Some bolts will exhibit defects such as stretching and deformation after use, and some technical requirements require that new bolts must be replaced after several tear-downs. Because the maintenance personnel do not understand these conditions, the substandard bolts are repeatedly used, which is also easy to cause mechanical failure or accidents. Therefore, when repairing construction machinery, when bolts are damaged or lost, replace the required bolts in a timely manner, and never use them indiscriminately.

2 The problem of improper bolt tightening method is more serious.

Most of the fixed or joined bolts in various parts of construction machinery have a tightening torque requirement, such as a jet fixed bolt, a hood bolt, joint bolt, and a flying wheel bolt. Some specify the tightening force, some specify the angle of tightening, and at the same time, the order of tighten.

Some maintenance personnel, thinking that screwing up the bolts is something that everyone can do, doesn't matter, and doesn 't screw it according to the prescribed torque and order (some don't understand that there are torque torque or order requirements). Use no torque (kg) wrench, or use the lever at will and tighten it on the feel of the feel, resulting in a large difference in the tightening torque.

The torque is insufficient, and the bolts are prone to loosening, leading to the breaking of the cylinder liner, loosening of the shaft, oil and gas leakage; The torque is too high, the bolt is prone to stretching and deformation, even breaking, and sometimes damages the screw hole, which affects the quality of repair. 1 ZL50 loading machine, torque converter to throw liquid oil, after inspection is due to the connection pump wheel and cover wheel 24 bolts are not tightened according to the prescribed order and torque.

Therefore, when maintaining construction machinery, it is necessary to tighten the bolts with the prescribed torque and order to prevent the machinery from being broken because the bolt tightening torque is too large, too small or incorrectly.

3. There are many phenomena that do not pay attention to detecting the gap between parts and components.

Diesel piston and cylinder casing compatibility gap, piston ring "triple gap," piston top gap, valve gap, The residual gap of the column, the brake flap gap, the roding gap of the main moving gear, the axial and radial gap of the bearing, the matching gap of the valve rod and the valve catheter, etc. All types of machinery have strict requirements, and measurement must be made during maintenance, and parts that do not meet the gap requirements must be adjusted or replaced.

In actual maintenance work, there are many phenomena of blind assembly of parts without measuring the matching gaps. This causes early wear or corrosion of bearings, oil burning of diesel engines, difficulty in starting or bursting, broken piston rings, impact of parts, oil leakage, gas leakage and other failures, sometimes even due to improper spacing of parts and components, leading to serious mechanical damage accidents.

After the major repair of a Nissan 6DB-10P diesel engine, the test engine stopped its own fire for about 30 minutes, then it started the engine without catching fire, check the oil fluid, the oil path, etc. After stopping and placing it for 30 minutes, it could start the fire again, but after 30 minutes of operation, it stopped its self-fire. Later inspection of the cause of the failure is due to fuel injection pump plunger clearance is too small, diesel engine temperature, the plunger expansion and delivery valve conflict, not the normal reciprocating movement of fuel supply and self-flameout, shutdown cooling, plunger and delivery valve and there is a certain gap between the normal supply.

It is also not uncommon to replace a pair or component in pairs or in sets.

There are many couplings in construction machinery, such as the plug side, the oil outlet valve side, and the nozzle needle side couplings in the diesel fuel system; Main and moving gears in the drive bridge main gearbox; The valve blocks and valve bars in the hydraulic control valve; The valve cores and valve casings in the fully hydraulic steering gear, etc., are specially processed when manufactured in the factory, grinded in pairs, and the combination is very accurate, always used in pairs during the life of use, and cannot be interchangeable; Some of the components that cooperate with each other, such as pistons and cylinders, shafts and collars, valves and valve seats, joint heads and butts, etc., after a period of wear and use, they are relatively good together. When repairing, care should also be taken to assemble in pairs and not string together; Diesel joints, pistons, fan belts, high-pressure oil pipes, excavator central turning joint oil seals, bulldozer owner clutch ducts, etc. These machinery use a set of accessories at the same time. When damage occurs, it is necessary to replace it in a set, otherwise, due to the large difference in the quality of the parts, the different degree of new and old, and the different length and short dimensions, it will cause the diesel engine to operate unsteadily, the hydraulic system to leak oil, the load concentrated phenomenon is serious, and the replacement parts are prone to early damage. In the actual maintenance work, some people are trying to reduce expenses, some are not aware of the technical requirements, It is not uncommon for the above parts to be replaced in pairs or in sets, which reduces the maintenance quality of construction machinery, shortens the life of the components, and increases the possibility of failure, and should be given sufficient attention.

5. Sometimes parts are turned back during assembly.

When repairing construction machinery, some parts assembly has strict direction requirements, and only proper installation can ensure the normal working of the parts. Some parts are not obvious external features, and both sides can be installed, and often there are cases of partial assembly in actual work, leading to early damage to parts, machinery not working properly, and construction machinery damage accidents.

Such as engine cylinder liner, non-equidistant valve spring (such as F6L912 diesel engine), engine piston, plug ring, fan blade, gear pump side plate, skeleton oil seal, thrust washer, Thrust bearings, thrust gaskets, oil ring, fuel injection pump plunger, clutch friction disk hub, drive shaft universal joint, etc., these parts in the installation, if you do not understand the structure and installation precautions, the most easily reverse, resulting in abnormal work after assembly, resulting in construction machinery failure. If a 4120F fuel oil machine replaces the plug ring, the fuel oil machine takes blue smoke, consider that it may be too much oil filling or the plug ring "counterpart." Check that the oil quantity is normal. Remove the piston joints in one cylinder and find that the piston loop is not "aligned," but the air ring is turned back. Check that the cylinder rings are also turned back in all other cylinders. The machine uses an internal socket type twisted gas ring. When it is installed, the internal socket is required to be facing up, and the maintenance personnel correctly installed it. Because the internal cylinder piston ring is very easy to cause a piston "pumping oil" phenomenon when it is loaded back, causing the oil to escape up the ring socket to burn in the combustion room. Also, if the working oil pump of the ZL50 loader is equipped with 2 skeleton oil seals, the correct orientation of the seals is: the inner lip of the seal is inward and the external lip of the oil seal is outward, so as to prevent the working pump from entering the hydraulic oil tank through the transmission pump into the transmission. It is also possible to prevent the transmission pump from injecting oil from the transmission into the hydraulic oil tank through the working pump (the working pump and the transmission pump are installed side by side and are driven by an axle gear). The author has encountered two cases of oil leakage failures caused by the oil encapsulation of the oil pump. Therefore, when assembling parts, maintenance personnel must master the structure and installation direction requirements of the parts, and cannot imagine blind installation.