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Epoxy piston or not?

Posted: Fri Jan 13, 2017 10:50 am
by sbooder
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.

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Re: Epoxy piston or not?

Posted: Sat Jan 14, 2017 3:29 am
by Trevor
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

Re: Epoxy piston or not?

Posted: Sat Jan 14, 2017 3:35 am
by shadowjack
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.

Re: Epoxy piston or not?

Posted: Sat Jan 14, 2017 3:59 am
by Trevor
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

Re: Epoxy piston or not?

Posted: Sat Jan 14, 2017 4:19 am
by shadowjack
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.

Re: Epoxy piston or not?

Posted: Sat Jan 14, 2017 4:48 am
by Trevor
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

Re: Epoxy piston or not?

Posted: Sat Jan 14, 2017 5:37 am
by thanh-cuibap
this video may be help you ! i not yet made Epoxy piston ..


Re: Epoxy piston or not?

Posted: Sat Jan 14, 2017 12:43 pm
by sbooder
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?

Many thanks.

Re: Epoxy piston or not?

Posted: Sat Jan 14, 2017 6:17 pm
by thanh-cuibap
Hi sbooder !
if you have lathe you may be make piston aluminium 6061-it not good for run a long time but it is easy to find and to make ,you have experience ...and after you can make with brass, bronze,cast iron
http://www.stirlingengineforum.com/view ... 6&start=60
http://www.stirlingengineforum.com/view ... f=1&t=2136

Re: Epoxy piston or not?

Posted: Sun Jan 15, 2017 1:36 am
by Ian S C
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