Epoxy piston or not?

Discussion on Stirling or "hot air" engines (all types)
sbooder
Posts: 3
Joined: Thu Jan 12, 2017 2:41 am
Location: Briis-sous-Forges, France

Epoxy piston or not?

Postby sbooder » Fri Jan 13, 2017 10:50 am

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.

Image


Image
Kind regards,
Simon

Trevor
Posts: 169
Joined: Sun Nov 06, 2016 4:07 am

Re: Epoxy piston or not?

Postby Trevor » Sat Jan 14, 2017 3:29 am

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

shadowjack
Posts: 3
Joined: Sat Jan 07, 2017 3:43 pm

Re: Epoxy piston or not?

Postby shadowjack » Sat Jan 14, 2017 3:35 am

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.

Trevor
Posts: 169
Joined: Sun Nov 06, 2016 4:07 am

Re: Epoxy piston or not?

Postby Trevor » Sat Jan 14, 2017 3:59 am

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

shadowjack
Posts: 3
Joined: Sat Jan 07, 2017 3:43 pm

Re: Epoxy piston or not?

Postby shadowjack » Sat Jan 14, 2017 4:19 am

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.

Trevor
Posts: 169
Joined: Sun Nov 06, 2016 4:07 am

Re: Epoxy piston or not?

Postby Trevor » Sat Jan 14, 2017 4:48 am

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

thanh-cuibap
Posts: 147
Joined: Tue Sep 06, 2016 8:09 am
Location: Việt Nam

Re: Epoxy piston or not?

Postby thanh-cuibap » Sat Jan 14, 2017 5:37 am

this video may be help you ! i not yet made Epoxy piston ..
https://www.youtube.com/watch?v=7QrIAoc0Snc
https://www.youtube.com/watch?v=rxna7W8yhVE

sbooder
Posts: 3
Joined: Thu Jan 12, 2017 2:41 am
Location: Briis-sous-Forges, France

Re: Epoxy piston or not?

Postby sbooder » Sat Jan 14, 2017 12:43 pm

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.
Kind regards,
Simon

thanh-cuibap
Posts: 147
Joined: Tue Sep 06, 2016 8:09 am
Location: Việt Nam

Re: Epoxy piston or not?

Postby thanh-cuibap » Sat Jan 14, 2017 6:17 pm

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
viewtopic.php?f=1&t=2156&start=60
viewtopic.php?f=1&t=2136

Ian S C
Posts: 1970
Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: Epoxy piston or not?

Postby Ian S C » Sun Jan 15, 2017 1:36 am

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


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