Hi All,
First real post here. I am gathering bits to make my first Stirling engine and am going to use this for the power piston cylinder, as you can see I have started to modify it for purpose and the second photo has it lying in the position it will be used in, fixed to a central panel separating the two sides.
It seems near perfect for the job apart from the piston that it come with, it is not right for the job, so I was thinking of making an epoxy graphite powder mix piston. About 10% epoxy and 90% graphite.
Will this work and if not which material would be preferable please?
Thanks for any help.
Hi Sbooder - I have tried epoxy mixed with graphite powder and it worked, but not successfully for any length of time. The heat does cause a little concern to the epoxy, that however will depend on the epoxy you use. I guess you can only try it and see and you will need to have a real smooth bore with no ridges as the epoxy holding the graphite will score the piston like hell.
I like what you are doing for your engine and hope you make a good success with it. Looking forward to see your next lot of picsas you progress.
Trev
You will not be able to do 90/10 mix - it will not coat and will be like wet sand at best. 30/70 or 40/60 is more realistic.
Try first with other powder - like flour or starch.
Also outer layer will be probably 100% epoxy, so you will not get any self-librication if you do not machine piston to smaller diameter.
Nicely said Shadowjack, though I wouldn't use flour or starch as the piston will not hold together for any length of time. The adhesion would be weak at best. Lathing to a smaller size would certainly expose the graphite and as you say should do the trick.
Have you tried this before with any of your engines.
Trev
I suggested flour and starch not as working material, but for testing purposes - getting your ratios right, mixing technique, casting process etc.
I did not try casting piston, but researched topic in context of making epoxy granite for frames of diy lathes and mills - but did not try this either. You get better fill percentage if you have different grades of your filler - smaller ones filling voids between bigger ones.
Sorry about that Shadowjack - misinterpretation of the facts. I see what you mean. The idea works but I never got it to work for long periods due to some heat getting to the piston. He might have to water cool the piston jacket as well.
Trev
Thanks all for the feedback. I am not set on the epoxy path, so it would be good to know what materials others have used with success for the power piston with regards to a steel cylinder on the cold side?
Cast iron is number one on the list. You can read up on epoxy/JB Weld pistons in Boydhouse's free tin can Stirling Engine plans at the top of the index.
Ian S C
