Saturday, 2 December 2017

Fretting corrosion

Long ago I noticed friction fit connectors are not reliable in 3D printers: For example, 0.1" Molex connectors that are rated for 3A burn out when only carrying 1A motor currents. Even signal connectors on HydraRaptor lose contact and need re-seating occasionally. I figured it must be due to vibration and / or thermal expansion and contraction.

It is one of the reasons I choose the Melzi electronics for Mendel90, i.e. because it has screw terminals instead of Molex connectors that are common on other boards like RAMPS. While looking at some connectors for another project I came across the term "fretting corrosion", which is exactly the problem that causes failed connections when you have vibration or thermal movement. There is a marketing video explaining it here:

Basically contact mating points need to be gas tight to prevent corrosion and any relative movement breaks the gas tight seal. You can now get connectors that have sprung female parts to absorb any motion and prevent this mode of failure. Worth considering if you are designing a 3D printer.


  1. It should be noted that the failure mode in the video is limited to non-noble contact platings like tin.

    Gold-plated contacts are not nearly as affected - you'd have to wear through the gold layer for anything bad to happen.

    1. Motion at the mated terminals contact point, causes failure eventually in ALL applications! With gold plating first that contact motion wears through the gold, then fretting corrosion starts to occur (gold doesn't oxidize, therefore it can not fret, but it can wear through). Bottomline:
      > Reasonably priced connectors (push-on with/without latch) DO NOT prevent contact motion induced by wire motion
      > ALL Moving Wiring must be secured, strain relieved before the connector

  2. a drop of light machine oil will prevent corrosion also
    grease is commonly applied to any aluminum conx - this is especially formulated for aluminum

    1. no, oil or greases will not prevent fretting corrosion, these "may" delay the failure caused by fretting corrosion.. but if the mated terminal contacts are moving relative to each other .. it will eventually fail. Also, some lubricants make good terminal contact lubes and some DO NOT ... some turn to insulative crud with time/temp ... some cause floating of contacts ... and many do not reduce fretting ... there are purpose made contact lube products for reducing fretting corrosion, but it is really easier, probably cheaper, and certainly more reliable to just strain relive the wiring.

      (FYI - 30+ years engineering electrical connector solutions for computer & automotive applications)

    2. sorry. yes, delay is a much better word for it than prevent. nothing stops the failure of a movable contact over a long enough time if there is thermal expansion and vibration..
      a bandaid is a bandaid. only a cure is a cure. strain relief is a really good bandaid. gold is also good.

      in the humid environment where i live, i must periodically remove pcmcia cards with gold plated contacts and push them back in to re-establish reliable contact. on the stepper motor conx (also gold plated) i had to cure the problem- they are now
      but nothing lasts forever... so cure may not be the best word. the intended meaning is that the element retain integrity long enough to not be the cause of death.