Revisiting the Bad Old Days

  Unless you are involved with rebuilding old equipment, it may be entirely possible to never see a tooth flank with “progressive pitting.” Yes, once upon a time, boys and girls, we actually sent gears out into the field knowing that users would be calling us within months to report that the tooth flanks were no longer smooth and shiny. We had a well-rehearsed script handy to explain about the gears “wearing themselves in” and that the process would eventually slow down and, hopefully, stop. There were lots of snake oil additives sold to cure the problem — some of which actually helped — and in most cases the drives delivered an acceptable amount of service life in some very demanding applications. The inevitable transition to surface hardened gearing took millions of dollars in capital equipment and the re-education of the American gear engineer and his customer; but if a modern process line gearbox ever gets a real “pit,” alarm bells will go off. It has been almost thirty years since the transition began, twenty since the through hardened products receded into legacy status. Some companies are on their second or third generation of surface hardened products and barely see any business for their old lines. Others still service a large installed base and have to field the occasional call from a new mechanic at an old installation. AMGA has recently updated the already excellent ANSI/AGMA 1010 Appearance of Gear Teeth/Terminology of Wear and Failure. A copy of it ought to be on the desk of every mill maintenance manager. Gear service technicians know it is the best way to identify problems and explain the causes of common problems. Many technicians can ignore those ugly pitting photos secure in the knowledge that their products will never have to “wear themselves in.”