For crankshafts with roundness and cylindricity errors exceeding 0.025mm in diameter below 80mm, or roundness and cylindricity errors exceeding 0.040mm in diameter above 80mm, they shall be polished according to the specified size (repair size). When the journal is badly worn and the repair size method cannot achieve the repair effect, the coating technology should be used for repair and then grinding to the specified size or repair size.
The repair dimension method is a common method to repair the wear of mating pair parts. It is a repair method to restore the correct shape and obtain a new repair size by means of mechanical processing, and then select another part with the corresponding size to match and restore the matching nature. For the crankshaft with little wear, the method of grinding can be used to make it reach the repair size.
The crankshaft with bending deformation must be corrected before grinding. Crankshaft grinding is usually done on the crankshaft grinder. In addition to the journal of crankshaft grinding surface size accuracy and surface roughness in accordance with technical requirements, must also meet the requirements of shape tolerance: grinding crankshaft must ensure that the main journal and the connecting rod journal each axis alignment and the parallelism between the two axes, limit the crank radius error and ensure the accuracy of connecting rod journal position Angle of each other.
Eccentric grinding and concentric grinding can be used for connecting rod journal. Concentric grinding method is to keep the axis position of the connecting rod journal unchanged after grinding, that is, the crank radius and distribution Angle remain unchanged. The Concentric method is often used in diesel engine crankshaft grinding. Eccentric grinding is done by positioning the surface of the worn connecting rod journal. Then the shaft centerline and the crank radius are changed, generally after grinding crank radius is larger than the original crank radius, increase the compression ratio, and each cylinder change is uneven, and the whole quality of the crankshaft center is not in the center of the crankshaft main journal online, cause crankshaft lopsided, additional dynamic load caused by turns. Therefore, in the connecting rod journal grinding, should reduce the increase of crank radius as far as possible, to ensure that the coaxiality error of the axis line of the same position connecting rod journal is not more than ±0.10mm, in order to ensure the balance of the crankshaft operation.
