Maintenance is an effective means to restore the performance of engineering machinery and extend its service life. However, in the actual operation process, some use and maintenance personnel have many wrong practices, affecting the normal use of engineering machinery.
1. Avoid adding machine oil only
Engine oil is essential in the use of diesel engines, mainly playing the role of lubrication, cooling and cleaning. Therefore, many drivers will pay attention to check the oil quantity of the lubricating oil and add it according to the standard, but they ignore the inspection of the lubricating oil quality and the replacement of the oil that has gone bad, resulting in that some moving parts of the engine always operate in poor lubrication environment, thus accelerating the wear of various parts. Under normal circumstances, the loss of oil is not great, but it is easy to pollute, thus losing the role of protecting diesel engines. During the operation of a diesel engine, a lot of waste (carbon smoke, carbon deposits, and fouling resulting from incomplete combustion of fuel oil) enters the engine oil. For new or overhauled machinery, there will be more impurities after trial operation. If only the impurities are added and not replaced, they will be put into use in a hurry. In addition, even if the oil is replaced, some drivers will not thoroughly clean the oil channel due to their lack of maintenance experience or convenience, so that mechanical impurities remain in the oil sump and oil road.
2.Avoid butter spread
(1) butter the cylinder washer. Butter is a common grease used in engineering machinery repair, which can play the role of lubrication and sealing. As a result, some repairmen apply a layer of butter to the cylinder gasket when installing the cylinder gaskets, thinking that this increases the seal of the diesel engine. However, this will affect the performance of the diesel engine. Cylinder gasket is the most important sealing element between the cylinder block and cylinder cover. It can not only seal the high temperature and high pressure gas generated in the cylinder, but also seal the cooling water and oil in the cylinder block. If installed in the cylinder MATS and butter, when the cylinder head bolt is tightened, part of the butter will be squeezed into the cylinder in the channel and the oil duct, stay in the cylinder gasket between the butter in cylinder work, due to the effect of high temperature, part will shed cylinder combustion, others remain in the combination of the cylinder block and cylinder head, cylinder pad, cylinder head and the body plane between aperture, high temperature and high pressure gas from impact cylinder pad, easily damaged cylinder pad, cause air leakage. In addition, the butter under the high temperature for a long time will produce carbon accumulation, resulting in premature aging and deterioration of cylinder pads. Do not use butter when installing cylinder gaskets.
(2) butter the tyre nut. To tighten the nuts easily and prevent rust, a number of repairmen grease the nuts and bolts of tires. This is actually a mistake. Because the tire nut is tightened, the thread has the characteristic of self - locking. This is because the spiral Angle of the thread is less than the equivalent friction Angle between the threads. In a given bolt connection, the spiral Angle is a certain value, while the equivalent friction Angle varies with the friction state between threads. Obviously, the equivalent friction Angle between the threads decreases and the self-locking performance of the bolt joint decreases. Therefore, never apply grease or grease to the bolts and nuts of tires. In doing so, the nuts will become loose and even lead to accidents.
3. Avoid the installation of cylinder sleeves and new piston products without selection
When replacing cylinder bushing and piston, it is considered that the new cylinder bushing and piston are standard parts with interchangeability. In fact, the cylinder sleeve and piston dimensions have a certain tolerance range.
If the maximum size of the cylinder sleeve with the minimum size of the piston, will make the fit gap too large, resulting in weak compression, starting difficulties. Therefore, it is necessary to check the size grouping code of standard cylinder liner and piston when replacing the cylinder liner and piston. The size grouping code of standard piston and piston must be the same as the size grouping code of standard cylinder liner. Only in this way can the standard fit gap be ensured between the two. In addition, the cylinder sleeve and piston with the same grouping code shall be installed, and the gap of cylinder plug shall be checked before loading. In order to ensure the assembly standard, a test shall be carried out before installing the cylinder, so as to avoid loading the counterfeit and shoddy defective products.
4. Don't check the plunger travel margin
In the spot-test of the plunger pump, many maintenance personnel do not pay attention to check the plunger travel margin. The stroke allowance of the plunger refers to the amount of upward movement of the plunger after the CAM top to the top stop on the camshaft. After adjusting the oil supply start time, the reason to check the travel allowance is that the travel allowance of plunger is related to the wear of plunger and sleeve. After the plunger and sleeve wear, the plunger should move up for a period to start oil supply, thus delaying the start time of oil supply. When the adjustment bolts are unscrewed or thick adjustment pads are replaced, the lowest position of the plunger is moved upward to reduce the stroke margin of the plunger. Therefore, in the maintenance and debugging of the fuel pump, the stroke margin should be checked first to determine whether the fuel pump is also allowed to adjust. During inspection, the following methods shall be adopted according to the different structure of the injection pump: a) rotate the camshaft, lift the plunger to the top stop, remove the oil valve and seat, and measure with depth vernier. B) after the plunger is pushed to the top stop, use a screwdriver to pry the plunger spring's seat so that the plunger rises to the highest point. The gauge is then inserted between the flat surface of the plunger and the tappet adjusting bolt. The standard travel allowance of the plunger is about 1.5mm, and the limit travel allowance after wear should not be less than 0.5mm.
5. No accurate measurement of cylinder clearance
When measuring cylinder clearance, do not measure in the direction of the piston skirt perpendicular to the piston pin hole, but in the other direction. The structure of aluminum alloy piston is characterized by small on the top and large on the bottom, which is a cone, and the section of skirt is elliptic, so the cylinder gaps along the circumference are not equal. When measuring, the regulation takes the ellipse long axis direction clearance is accurate, measure the piston skirt section perpendicular to the piston pin hole direction clearance. In this way, the measurement is more convenient and accurate, and in the reciprocating movement, the direction of the piston skirt perpendicular to the piston pin hole is worn greatly due to the action of lateral pressure. Therefore, when measuring cylinder clearance, the direction of the piston skirt should be measured perpendicular to the piston pin hole.
6. Do not heat the piston with open flame
Because the piston and piston pin is interference fit, so when installing a piston pin, should first make the piston thermal expansion, at this time, some of the maintenance personnel will put the piston on the flame heating directly, so it is very wrong, because each part of the piston, uneven heat bilges cold shrink degree would be different, firing can make the piston balance, easy to cause deformation; The surface of the piston can also be attached with soot, reducing the service life of the piston. If the piston is cooled naturally after reaching a certain temperature, its metallographic structure will be damaged and its wear resistance will be greatly reduced, and its service life will be significantly shortened. When the piston pin is installed, the piston can be put in hot oil uniform heating to slow expansion, do not directly heat with open flame.
7. Do not polish the bearing shell with abrasive cloth
For some inexperienced repairers, scraping tile is a relatively difficult job. Since the scraping tile technology is difficult to master, it is difficult for the bearing shell to meet the technical requirements. For this reason, in order to increase the contact area between the bearing shell and the crankshaft when replacing the bearing shell with abrasive cloth. This method is highly undesirable in practical maintenance because the abrasive particles on the emery cloth are hard while the bearing shell alloy is soft. In this way, the sand can be easily embedded into the alloy when grinding, and the diesel engine will accelerate the wear of the shaft neck and shorten the service life of the crankshaft.
8.Don't screw the bolts too tight
In the disassembly and installation process of engineering machinery, bolts in many parts have specified torque requirements, such as transmission box, cylinder cover, wheel hub, connecting rod and front bridge, etc., and tightening torque is specially specified in the specification, which cannot be changed at will. But many users mistakenly believe that it is safer to tighten a bit, but twisting too tightly can cause screws or bolts to break, or may cause a failure due to thread slips.
9.Avoid high tire pressure
Tire inflation pressure of wheel engineering machinery is an important factor to determine its service life and efficiency. Too much or too little air pressure can affect a tyre's life, and it's not good for safe driving, especially in hot summer. Scientific inflation standard should be: take the standard air pressure of the tire as the benchmark, as the temperature changes, adjust the air pressure of the tire slightly. For example, summer should be 5%-7% lower than winter because, taking into account the high temperature in summer, the air is heated and the pressure is increased. On the contrary, winter must reach the standard pressure or slightly lower.
10. Don't add cold water to the water tank
Excessive engine operation, poor heat dissipation or a lack of water in the tank can cause the tank to open. If cold water is added immediately, the cylinder head and cylinder body will burst. Therefore, once the water tank is found to be open, emergency measures should be taken to stop the operation so that the diesel engine cooling water will cool itself.
Circle friends, the above 10 types of situations are easy to summarize the problems of the net friends, do you not notice these problems? If you're not paying attention, be sure to. A machine is like a man. If you don't treat it well, it won't treat you well either. Love it, maintain it!
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