The precision piston rod is the key component of compressor, the straightness and surface strength standards of which are very high. For example, there is a product that is 52.5 mm in diameter, 620mm in length, op0.019 mm in cylindricity standard, surface strength standard is ≥50HRC.
In the nitriding environment of ionic vapor, the 24-hours’ nitrided layer can only reach to 0.2 mm. The lower the temperature is, the longer the nitriding time is needed. Due to its thin nitriding layer, the machining processing takes place before nitriding.
Because of the high temperature of the nitriding, there may be corresponding deformation of the precision piston rods. At that time, the piston rod meets the standard of finished product, and has got high surface strength. There is no way to use the mechanical processing to fix the deformation, only the straightening way can be used to adjust the form variable within a reasonable range.
The straightening precision of the common pressure straightening machine, whether it's old straightening or hot straightening, is affected by human factors. After general nitriding treatment, part of the product has the bending shape variable of 0.1~ 0.3mm, this tiny shape variable can not meet the standard with pressure straightening machine. According to the bold trial and practice test, we choose bending and knocking vibration for straightening.
Use two pieces of V-shaped iron to support both sides of the precision piston rod, settle the dial indicator in the middle of the rod, rotate the piston rod vigorously, record the shaking condition and mark the high and low points. Press the high point down by 5~10 mm with the pressing plate, and keep still. The bending stress will be stable by beating the rod body several times with a copper rod.
Remove the pressing plate, check the shaking condition of precision piston rod again.If the condition exceed the standard, we can do the straightening again, until the rod reaches the standard. Good patience and experience are required during the straightening. If a batch of products is straightened in this way, the shaking condition should be checked again after five days of placement. As long as there’s no springback of the piston rod, it means the straightening is practicable.
