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.