Delrin vs. Graphite

[WSHBaker]

Does anyone have prior experience using Delrin in place of graphite for pistons and/or bearings in LTD Stirling Engines? It was suggested to me by a materials type person that it has an exceptionally low coefficient of friction as well as the ability to hold close dimensional tolerances and machinability.

[jutz]

I haven't worked with the LTD engines but I much prefer working with Delrin than graphite; it's cleaner and doesn't eat up tools. The main concern would be the difference in thermal expansion. The Delrin's expansion coefficient is easy enough to find but the graphite's will depend on the resin matrix in which it is bound which could be difficult to ascertain. If the plans suggest sources for the graphite, they may be able to provide the data.

Incidentally, you may get more replies on this if you repost it in the General Discussion forum.

[NAMPeters]

Another concern is the ability of Delrin to absorb water which will affect its dimensions. Also Delrin comes in many grades and with different fillers so you need to be more specific in your question.