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I. Eccentric wear of crank pin bearing bush
The connecting rod transmits the thrust acting on the piston to the crank axle, and converts the rotation motion of the crank axle into the reciprocating motion of the piston, in a compressor of our company, the first grade crank pin tile eccentric wear frequently damaged the black gold falling off in a period of time, and the direction of eccentric wear has been unchanged, mainly analyzed from the following aspects.
1. Carefully inspect the clearance of crank pin bearing, the gap between Cross pin and cross head and connecting rod big and small head tile, the gap between Cross Head and slide six points, and the ovality of crank pin shaft, the new cross pin was replaced to ensure the clearance of each part.
2. The parallelism of the big and small head holes of connecting rod is detected by special tools, and the parallelism of the cross pin hole to the first grade crank pin shaft is also detected by special tools. The degree of parallelism is not more than 0.02-0.03, within the allowed range.
3. The design value of the beating of the piston rod should not exceed 0.07mm/full stroke, and after the above three points are confirmed to be correct within the design scope, it only takes 3 days to drive after the unit is overhauled, the eccentric wear of crank pin tile still occurs. Finally, it is found that due to the problem of the alignment of the crank coupling, the farthest side of the crank is skewed, which is the most obvious, thus causing the eccentric wear of the crank pin tile, the problem of eccentric wear of the crank pin Bush is completely solved by rectifying the coaxial degree between the crank axle and the motor and adjusting the gap between the main shaft bush.
II. Damage of crank pin axle neck)
Due to the mistake of the original design of the compressor, after the transformation, the operating force of the first-level piston is larger, and the specific pressure of the first-level crank pin tile is larger. Frequently damage the first grade tile, first grade piston and connecting rod.
For large and medium-sized compressors, the allowable maximum specific pressures of the spindle neck and crank pin axle neck bearings are 4-5mpa and 9.0MPa respectively. Under the condition of maintenance quality assurance, through adjusting the reasonable clearance of crank pin tile, improve the oil supply condition oil circuit and oil pressure adjustment, form an effective oil film, and through the adjustment of the first inlet pressure, the selection of bearing bush with appropriate pressure solves the damage of bearing Bush caused by unbalance, and further solves the damage of crank pin axle neck.
III. Handling of cross pin
During the operation of compressor, the fracture of the cross pin end face pressing screw and the falling off of the cross pin will cause very serious accidents. Therefore, the gap between the cross pin and the connecting rod small head tile should be paid great attention, in addition, what is more important is that there should be no gap between the cone surface of the cross-head pin and the cross-head body, because theoretically, once there is a gap, the contact will be linear contact, which has a great influence on the transmission force and the stability of the unit, therefore, it is required that the contact area of the matching and research should be above 80%. If there is a gap between the new spare parts pin and the cross pin hole, the cross pin must be repaired according to the taper of the cross pin hole. As for the cross cone hole, it must not be repaired, because once the cross cone hole is repaired, it is likely to cause the change of the axial position of the pin in the future, which will affect the positioning and the supply of lubricating oil, if the deviation of the pin is too large, it can be fixed and filed on the lathe by measuring the radial size, and then grind, but it is better to use the appropriate cone pin of spare parts.
4. Damage of piston and piston rod
In the use of compressor, the first-class piston is broken and the piston rod is broken. The connection between the piston rod and the piston must be firm and accurate, the both ends of the piston and the support surface of the piston rod should be matched with each other and fastened according to the specified fastening torque. The two halves of the piston (cast aluminum) the joint surface of the inner ring should be closely attached and the gap of the joint surface of the inner ring and the outer ring should not appear. This point should be paid great attention to, because the gap of the joint surface of the inner ring will generate alternating stress and shorten the life span of the piston, while the clearance of the outer ring causes the inner cavity of the piston to enter into the compressed gas, making the internal volume become the residual clearance volume of the cylinder to some extent, which has bad effects on the efficiency of the compressor and the lifespan of the piston, therefore, each part of assembling piston should be checked carefully. In addition, the mechanical properties and smoothness of the force surface of the piston tail rod also have great influence on the service life of the piston rod.
V. Abnormal handling of piston rod beating
In general, the beating of the piston rod is the final verification result of the compressor alignment, which should be within the allowed range, under the condition that the cylinder is correctly aligned with the cross slide, the allowable horizontal and radial jitter of piston rod should be one tolerance band, namely ± 0.00015 mm/mm stroke, and the maximum should not exceed ± 0.064mm, and the vertical radial jitter should also consider the slight change of the deflection of piston rod, etc. Even if the overdifference is still from one side to the other side in the process of making a table, the value continues to increase or decrease, and it can be eliminated as long as the adjustment of horizontal level and serial positioning in all directions is adopted. However, in the process of detection, the following abnormal situations are found: in the process of the piston movement, the vertical jitter of the piston rod has always been relatively good, but only in the dead center on both sides suddenly has a wide range of jitter change, the horizontal jitter is better. After excluding the influences of the gap between each part, such as the gap between big and small head tiles of connecting rod, the gap between Cross Head and the gap between dead center of cylinder, it is found that there are problems of the piston ring crossing, which leads to the sudden change of the beating amount of piston rod, the processing method is to remove the abrasion of the inner wall of the cylinder by grinding the shoulder, adjust the piston ring's cross-distance value, and then eliminate the abnormal phenomenon of the piston rod's jitter.
