“Zero” Maintenance Ball Screws

Hah – got your interest with that title, right?  But is there really such as component as a ball screw that requires zero maintenance?  First we should establish exactly what we mean by “zero” maintenance.  This can be one of two scenarios: either the ball screw has absolutely no lubrication, that is it runs dry; or the ball nut includes enough lubricant and is sufficiently protected such that no further maintenance is required for its lifetime.  BTW for either scenario the answer is pretty much “NO, it’s not possible!”  Here are the reasons.  For option 1, running dry, our long experience has been that a ball screw requires some minimum, albeit small, amount of lubricant in order to ensure smooth recirculation of the balls inside the nut.  We have tried using various dry lubricant coatings and found reality to be quite different from the marketing claims of the coating manufacturer.  The balls invariably tend to jam, especially under slow rotation and/or reversing.  Perhaps someone will develop a new dry lubricant coating that works better but for now we remain highly skeptical.  We have had however good success using balls made from silicon nitride which will be discussed in another blog.  Regarding option 2, that is loading the nut with lubricant and sealing it to prevent the lubricant from escaping, Steinmeyer has (for years) offered a highly effective dual stage wiper – our so-called combination wiper (consisting of external plastic and internal felt wipers).  However we tout this as a superior dual stage wiper, capable of protecting the nut from large particles as well as small ones, e.g. grinding dust and debris.  And the felt also acts as a lubricant reservoir, thus minimizing the maintenance requirement (and it can be re-filled).  We view this as a low maintenance solution, but not zero!  There are other wiper products on the market being touted as zero maintenance.  These are typically made from oil impregnated plastic.  The idea is to heat up the wiper, by pressing it against the shaft as it moves, such that the oil wicks out (not really a good idea in our opinion – that is deliberately adding heat to the shaft).  The concept is that as this wiper passes over the shaft it always leaves a thin film of oil behind. Of course it will do that only as long as there is any oil left. Once empty, you go back to regular lubrication (which is really not what you wanted in the first place), or you replace the wiper.  Low maintenance?  Maybe.  Zero?  Decidedly not.  The other issue with such a wiper is you do not get to choose the lubricant – the supplier does.  Oh well, you can’t win ’em all!

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