Three Fault Analysis And Solutions Of Compressors
Any mechanical product will inevitably suffer from various faults after it has been used for a period of time. One is the use method, the other is the environment in which the machine is located, which may cause mechanical damage. Air compressor is no exception. Moreover, the failure frequency of mine air compressor is higher than that of the general air compressor, because the environmental dust of mine air compressor is comparable. Now let's analyze some common faults.
1. Common failures and their causes
Inadequate exhaust: Inadequate exhaust compared to the compressor design. Considerations may be given mainly to the following:
(1) Breakdown of intake filter; blocked dirt, reduced exhaust volume, long suction pipe, and small diameter cause increased suction resistance which affects the air volume. Clean the filter regularly.
(2) Reduction of compressor speed reduces exhaust volume: improper use of air compressor because the exhaust volume of air compressor is designed according to a certain altitude, suction temperature, and humidity. When it is used on the plateau above the above standards, the suction pressure decreases, etc., and the exhaust volume will inevitably decrease.
(3) Cylinders, pistons, and piston rings are worn seriously and out of tolerance, which increases the relevant clearance and leakage, affecting the exhaust volume. In case of normal wear, the fragile parts, such as piston rings, should be replaced in time.
(4) Gas leakage occurs due to a lax packing box, which reduces gas flow. The reason is first that the stuffing box itself is not qualified in manufacture; secondly, it may be that the center of the piston rod and stuffing box is not well aligned during installation, resulting in air leakage due to wear and strain; generally, the stuffing box is filled with lubricant, which acts as lubrication, sealing and cooling.
(5) The effect of the failure of suction and exhaust valves of the compressor on exhaust volume. Metal debris or other debris fall between the seat and valve disc and close loosely to form a leak. This not only affects the exhaust volume, but also the change of stages and temperatures. Lack of contact between valve seat and valve disc results in air leakage which affects the exhaust volume. One is the manufacturing quality problem, such as warpage of valve disc, and the other is the leakage caused by severe wear of valve seat and disc.
2. Causes of abnormal exhaust temperature
(1) Exhaust temperature is not normal. Theoretically, the factors influencing the increase of exhaust temperature are intake air temperature, pressure ratio, and compression index (for air compression index K=1.4). The factors that affect the high suction temperature are: low efficiency of intermediate cooling or scaling in the intercooler mostly affects heat exchange, then the suction temperature of the rear stage must be high and the exhaust temperature will be high. Leakage of the air valve and piston ring will not only affect the exhaust temperature but also change the pressure between stages. As long as the pressure ratio is higher than normal, the exhaust temperature will increase. Besides, water-cooled machines, lack of water, or insufficient water will cause the exhaust temperature to rise.
(2) Abnormal pressure and lower exhaust pressure. If the amount of air discharged by the compressor can not meet the flow requirement of the user at the rated pressure, the exhaust pressure must be reduced. Therefore, it is a phenomenon that the exhaust pressure is reduced, in essence, the exhaust volume can not meet the requirement of the user. At this time, we have to change to another machine with the same exhaust pressure and large exhaust volume. The main reason that affects the abnormal pressure between stages is the leakage of the air valve or the leakage of air after piston ring wear. Therefore, we should find out the reasons and take measures from these aspects.
(3) Overheating fault. Overheating occurs at friction points between crankshaft and bearing, crosshead and sliding plate, packing, and piston rod when the temperature exceeds the specified value. Consequences of overheating: one is to accelerate the wear between friction pairs; the other is that the excessive heat accumulates continuously to burn the friction surface and cause major accidents of the machine due to burning. Reasons for overheating of bearings are as follows: uneven fit of bearings with journals or too small contact area; bent bearing skewed crankshaft, too small lubricant viscosity, blocked oil circuit, oil pump failure resulting in oil breakage, etc. When installing, no leveling, no clearance, no alignment of the main shaft and motor shaft, the tilt of both shafts, etc.
3. Other Reasons
(1) Crankshaft fracture. Most of its breakage occurs at the corner transition between journal and shaft arm due to the following reasons: transition fillet is too small, r < 0.06d (d is crankshaft journal); the fillet is not treated during heat treatment, which results in stress concentration at the junction; the fillet is machined irregularly with a sudden change of local section; long-term overload operation, and some users increase speed to increase output so that they are subject to stress. Force condition deteriorates; the material itself is defective, e.g. sand holes in castings, shrinkage, etc.
(2) Fracture of the connecting rod. There are several situations as follows: connecting rod screw breaks due to plastic deformation caused by long-term use of connecting rod screw; eccentric load caused by poor contact between screw head or nut and big end face can be up to seven times the pure axial tension of bolt. Therefore, no slight deflection is allowed, the contact should be evenly distributed and the maximum distance between the contact points should not exceed 1/8 of the circumference, i.e. 450; the quality of bolt material processing is questionable.
(3) The piston rod is broken mainly at the threads connected with the crosshead and at the threads fastening the piston. These two are the weak points of the piston rod. Fractures occur frequently due to design negligence, carelessness in manufacturing, and operational reasons. If there are no problems in the design, processing, and material, the preload must not be too great during installation, otherwise, the piston rod will break when the maximum force reaches the yield limit. After a long-term operation, due to excessive wear of the cylinder, the piston in the horizontal row will sink, resulting in additional loads at the connection threads, and further running may cause the piston rod to break, which should be paid special attention during maintenance. Besides, it is possible to break the piston rod when it is subjected to a strong impact due to damage in other parts.
(4) The cylinder and head are broken. Main reasons: For a water-cooled machine, if you forget to drain the cooling water in the cylinder and cylinder head after shutdown in winter, the cooling water will freeze and break the cylinder and cylinder head, especially in the northern part of China, you must drain the cooling water after shutdown; because the water interruption during operation is not found in time, the temperature of the cylinder rises and the cooling water is suddenly put in, causing the cylinder to burst. The cylinder will hit the cylinder head and break it because of the small dead-point clearance, loose piston nut, metal falling into the cylinder, and plug coming out on the piston.
Because the high-pressure stage valve of the compressor is not tight, the high-pressure and high-temperature gas returns to the cylinder and generates high temperature near the exhaust valve. When carbon deposits exist, they will cause an explosion. To avoid accidents, it is necessary to repair the exhaust valve, check the leaking parts, and eliminate the faults at this time.
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