The precision piston rod is a key component on a compressor, with high standards for straightness and surface strength. For example, a certain product has a straight purity of 52.5mm, a length of 620mm, and a cylindricity standard of op0.019mm. The cylindrical surface requires wear resistance, and the surface strength standard is ≥ 50HRC. Generally, nitriding treatment is used for the process.
It can only reach a nitriding layer of 0.2 millimeters within 24 hours in an ion vapor nitriding environment, and the lower the temperature, the longer the nitriding time required. Because its nitriding layer is very thin, nitriding treatment is assigned as a process in the process, and mechanical processing is carried out before nitriding.
Due to the high nitriding temperature, it sometimes undergoes corresponding deformation after nitriding. At this point, it already meets the specifications and standards of the finished product, and the surface strength is very high. It is not possible to use mechanical processing methods for precision repair, and only the straightening method can be used to adjust the deformation within a reasonable range.
A common pressure straightening machine, regardless of whether it is hot or cold, has a straightening accuracy that is affected by human factors and can reach 1-2 millimeters. Generally, some products after nitriding treatment have a bending deformation of 0.1-0.3 millimeters, and this small deformation cannot be aligned with the standard using a pressure straightening machine. Based on bold attempts and practical testing, we have chosen the method of bending and knocking vibration for straightening.
Support both sides of the precision piston rod with 2 V-shaped iron blocks, place a dial gauge in the middle, rotate the piston rod vigorously, record the shaking value of the piston rod, and mark the high and low points on the rod. Use a pressure plate to collapse the bolt and press down the high point by 5-10 millimeters, maintaining it still. Use a copper rod to strike the rod several times to stabilize the bending stress.
Remove the pressure plate and recheck the runout of the precision piston rod. If the jump exceeds the standard, it can be straightened again until it meets the standard. Good patience and experience are required during this period. A batch of products were straightened using this method, and after being placed for 5 days, the runout value was rechecked. No rebound issues were found, indicating that this straightening method is feasible.