Q. We have some gear shafts with chrome plating on the bearing journals. The parts have been fluorescent penetrant inspected and the inspection service has told us the chrome has a condition known as "banding". Is that the same as micro cracking? How does banding occur? Thanks for your time and consideration.
A. In a post chrome grinding scenario, "banding" refers to a slight discoloration due to over heating. In such a case, there could be visual cracks, tears or spiral patterns within the band. A mild case may just be discoloration.
"Banding" refers to a symmetrical band around the outside diameter that is commensurate with the wheel position and/or wheel contact area. This might be caused by the grinding wheel being plunged in too fast and too deep while the part is rotating in a stationary position. Another possible cause might be insufficient coolant which lubricates the process and minimizes friction.
"Spiraling" or "barber poling" is the same visual discoloration pattern of overheating only the wheel or the part is traversing left to right during the wheel contact phase and the affected area is in a spiral pattern like a course thread.
Best of luck.