1. The harm of diesel engine
Diesel mills, also known as burnt tiles, are common quality faults in diesel engine testing and work processes. In the event of a rolling failure, first of all, the lighter needs to change the bearing bush on the locomotive, the workload and work are difficult, and the quality of the repair is not guaranteed accordingly; in the case of heavy, the diesel engine must be lifted off the locomotive for disassembly and repair. If the bearing bush burns, the crankshaft journal strain and the superheat discoloration deformation, the body main bearing hole is overheated and discolored, the rework amount is even larger, the bearing bush, the crankshaft and the body need to be replaced, and the repair cycle is long and the maintenance cost is high. Secondly, the diesel engine is the heart and traction power of the diesel locomotive. If the diesel engine is run in the locomotive, the machine will break the accident, which will not only bring a large economic loss and reputation loss to the production enterprise, but also directly affect the railway transportation. Smooth and safe.
In order to prevent the diesel engine from being crushed, the diesel locomotive manufacturers have made a series of prevention and rectification measures for the main factors that may cause the diesel engine to be rolled, and adopted a series of prevention and rectification measures. However, due to the complexity of the cause of the diesel engine grinding, the diesel engine is still very windy. Hard to avoid and completely solve. In order to reduce the economic loss caused by the diesel mill, the author analyzes how the damaged body is repaired after the diesel engine is crushed.
2. The structure of the main bearing of diesel engine and the accuracy analysis of the body
The body is the skeleton of the diesel engine, and the main bearing hole of the body is formed by the main bearing housing and the main bearing cover assembled therewith through the main bearing bolt and the horizontal pulling bolt. When the main bearing bore of the main body is installed with the main bearing bush and the crankshaft, the main bearing of the diesel engine is formed. The main bearing of the diesel engine is an open-closed sliding bearing, which consists of two semi-circular alloy tiles. The lubrication method is pressure lubrication, and the lubricating oil film is formed to generate load capacity, so that the diesel engine works normally.
The body is made of alloyed ductile iron. The precision of the main bearing hole is very high. It is also the assembly and processing reference for the cam hole, cylinder hole and other key elements. The company produces a new type of high-power, low-emission, low-fuel consumption diesel engine with high precision. The body consists of 9-stop main bearing holes. The main bearing hole diameter is 265+0.0320mm, and the cylindricity is 0.025mm. Degree 0.03mm; full length straightness 0.10mm. In order to ensure the machining accuracy of the main bearing hole of the machine body, the main bearing hole machining is completed by the gantry machining center, and the machining accuracy is controlled by strict precision detection. Generally, the precision of the machining is performed by the collimator and the bridge distance and the coordinate measuring machine. Inspection must meet the design requirements of the pattern.
3. The state of the main bearing hole of the body after the diesel engine is milled
When the diesel engine crankshaft works in the main bearing hole of the machine body, if the minimum thickness of the oil film is less than the microscopic unevenness of the surface of the part for some reason, the oil film will be destroyed and the bearing capacity will be lost, so that the crankshaft main journal and the main bearing hole of the main body are installed. The inner bearing surface is in direct contact and enters a semi-dry friction and dry friction state. If it is operated in this state, the bearing bush will wear and heat quickly, and the alloy layer of the bearing bush will be completely melted at a high temperature, causing the crankshaft to be crushed. Therefore, the crankshaft, the bearing bush and the body are seriously damaged after the diesel engine is crushed. The three-coordinate measurement of the body of several milled diesel engines shows that the hole diameter of the main bearing bore becomes smaller and the cylinder is out of tolerance, the adjacent bearing and the full-length straightness of the main bearing hole are out of tolerance, and the bearing pad is stuck in serious cases. On the crankshaft, the shaft rotates to strain the surface of the main bearing bore.
4. Repair method of the body after grinding
Since the main bearing hole is the reference for other important holes and faces on the body, the accuracy requirement is high. Therefore, the most important and important point of repairing the main bearing hole is that the center position of the main bearing hole must be constant. Because once the center position of the main bearing hole changes, the center distance and parallelism of the left and right cam holes to the main bearing hole, the size and position accuracy of the left and right cylinder holes to the main bearing hole, the gear hole and the center distance of the pump hole will change and be out of tolerance. . At this time, even if the accuracy of the spindle hole is repaired, the body cannot be reused due to the failure of the important size and accuracy. How to ensure that the center of the main bearing hole of the machine is unchanged and can repair the spindle hole? The most efficient and simple method is to replace the main bearing cap and rework the main bearing bore after the cap change. Because the main bearing cap is a weak component in the main bearing bore composed of the main bearing cap and the main bearing housing; it is also the most stressed component in the diesel engine operation. When the diesel engine is working, the main bearing cap is underneath, and it also needs to bear the gravity of the part. Therefore, the main bearing cap of the diesel engine is most likely to be deformed after the grinding, and the cylindricity of the main bearing hole is excessively poor, causing the straightness to be out of tolerance. Therefore, it is feasible to replace the semi-finished main bearing cap and then re-machine the machining center to perform correction processing on the body. The following describes the process and method of repairing the crushed body:
(1) Disassemble the milled diesel engine, remove all the accessories installed on the body, and clean the body to make the body to be repaired in a relatively clean state.
(2) Reassemble the main bearing caps of each block according to the machining assembly requirements.
(3) The three-axis precision detection of the body, measuring the size, coordinates and shape and position accuracy of the main bearing holes of each block.
(4) Replace the semi-finished main bearing caps (semi-circle reserve 2.0mm machining allowance) for the gears with severe tolerance (generally the bearing block) and reassemble all the spindle cover gears.
(5) The machine tool performs calibration processing, which is the key to the body repair. One is to correct the center of the main bearing hole of the first and the ninth gear; the other is to correct the center of the adjacent hole of the cover block; and the third is to correct the semicircle center of the main bearing seat of the cover. The correction error must be controlled within 0.01mm; the fourth is to control the spindle aperture size during processing, so as not to enlarge the aperture. If the ninth main bearing cap is replaced, the two ends of the thrust stop must be leveled during the machining process to ensure that the two sides face the common axis AB perpendicularity of 0.03 mm.
(6) Manual detection and three-coordinate precision detection of the body.
(7) Remove the main bearing caps of each gear, clean the deburring flash, and remove the rust and grease from the body.
5. Inspection after the body is repaired
Accuracy inspection after repairing the body is a very important task. Firstly, the accuracy state of the repaired part of the body should be checked. At the same time, it is necessary to retest the accuracy of the non-repaired key parts such as the accuracy of the camshaft hole and the cylinder bore, because the accuracy of these parts is directly Affect the performance of the body. The inspection contents of the main bearing hole of the main body mainly include the following points:
(1) Manual inspection. The inner diameter of the aperture was measured from the left, middle, and right positions of the aperture (30° interval) by an inner diameter micrometer; the surface roughness of the hole was examined.
(2) Three-coordinate measurement. Three-coordinate measuring the main bearing hole diameter, cylindricity, Y/Z coordinates, adjacent and full-length straightness on the body; the corresponding accuracy of the camshaft hole and cylinder bore.
(3) Pressure tile inspection. The aperture size detection and the three-coordinate measurement are inspections of the point-picking method, which should be macroscopic inspection; since the main bearing housing hole is already the finished product size, it is basically inaccessible during processing. However, the microscopic deformation caused by the tile is difficult to measure. How to measure the base microscopic deformation? According to the requirements of assembly and use, the method is to check the bearing of the main bearing hole, and the contact between the surface of the aperture and the surface of the tile is required to be ≥80%.
Pressure tile inspection method: disassemble the main bearing cap and wipe the main bearing seat and the main bearing cap hole surface cleanly; at the same time, wipe the back surface of the bearing bush cleanly, evenly apply a layer of red powder on the back surface of the tile; In the semi-circular hole of the main bearing seat and the main bearing cap, the main bearing cap is installed in the main bearing seat, and the main bearing cap is loosened and tightened according to the assembly requirements of the main bearing cap, and the main bearing cap is disassembled to inspect the tile back and the main bearing housing. And the red bearing powder indentation on the surface of the semi-circular hole of the main bearing cap. If the contact surface of the pressure tile is not up to standard, it must be repaired by the fitter and coated.
6. Conclusion
The key to the repair of the tile body is to ensure that its center position is unchanged. Replacing the main bearing cap is the most efficient and simple method. For the serious damage of the diesel engine, the main bearing hole is deformed greatly, the main bearing seat is deformed by the strain. After the cover is processed, the accuracy of the main bearing hole cannot be restored. The main bearing hole needs to be repaired by the coating repair process, but the coating amount is applied. Generally, it should be controlled within 0.1mm; for local damage is serious, local welding repair method can be adopted when coating is not possible, but preheating should be carried out before welding repair, the welding repair process should be lightly tapped, and should be kept after welding. Let stress release, control deformation and prevent cracking, and process after a period of aging. After repairing and reassembling the use of more than 10 crushed tiles, they all meet the requirements for use.
It is worth noting that the repaired mill body should pay great attention to the internal surface cleaning and derusting work before assembly and use; at the same time ensure the cleanliness of the oil passages and mating surfaces of the body; in addition, check the surface quality of each hole and surface of the body. If there is no flaws, strains and locating pins of each spindle seat, because the main bearing bore will have an impact on the positioning pin after the bearing, it will easily make the original positioning pin become the clearance fit, so that the main bearing cap Inaccurate positioning or loosening due to looseness.
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