Piston material?

[Alex]

Hi gang,

I want to build a laminar flow stirling engine but can't find graphite around here. Is there any other material which can be used as a piston?
Teflon came to my mind but it might not like the heat.

 

[Powder keg]

Where are you at? I have a piece you can have.

Wes

 

[compound driver 2]

Hi
Has any one had a go with machinable ceramic for a piston in one of these engines?
I had a small job a year or so back using the ceramic in the link bellow, it machines like butter
with a surface finish off the tool i didnt think was possible.

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=2255511

I still have the offcut from the job would like to find a use for it.

Cheers kevin

 

[tel]

How big is the piston? Dry cell batteries have a stick of graphite as their core.

 

[rickharris]

Hi gang,

I want to build a laminar flow stirling engine but can't find graphite around here. Is there any other material which can be used as a piston?
Teflon came to my mind but it might not like the heat.

graphite is obtainable in fairly large diameter rods, often hex, from art shops where it is sold as graphite sticks for drawing. They are about 1/2 inch in dia. Sometimes larger.

Teflon - is good to over 360 to 450 Deg C so a stirling should be no problem. HOWEVER be aware that you need to keep it below 360 to prevent toxic decomposition products. This includes when machining.

It is also recommended that you remove all tobacco products as they could get contaminated and when used give you more than lung cancer!.

Materials hazard sheet here
www2.dupont.com/Teflon_Industrial/en_US/assets/downloads/h75334.pdf -

It also seems to be the devil to chuck up and hold as it is so slippery.

 

[Alex]

Thanks for your input!

Wes, I live in Sweden so it might not be worth shipping, but thanks anyway! ;D

Teflon is easily available here so I think I'll have a go with that.

 

[Lyn S.]

I have used aluminum and leaded steel in brass cylinders. Also have used stainless steel in a bronze bore. Metal pistons can be made thin walled & light. They are lubricated with powdered graphite on a q tip swab. However graphite pistons work best.
Lyn S.

 

[compound driver 2]

Hi
Im going to echo the words of Rick Harris.

Be very careful working with Teflon, there are some links to its being carcenogenic even in dust form.
If you have to machine it wear a dust mask and hoover the machine after use.

cheers Kevin

 

[Rog02]

graphite is obtainable in fairly large diameter rods, often hex, from art shops where it is sold as graphite sticks for drawing. They are about 1/2 inch in dia. Sometimes larger.

Pure carbon rod of varying sizes is available through most full line welding suppliers. We call it "Hole Maker" as around here (the middle of Nowhere, redneck country) we use it when rebuilding tractor draw bars after the pin holes have wallowed out. I keep a stick of 1", 1 1/4", and 1 1/2" around the shop as those are the most common sizes I deal with. I think it is available in larger sizes.

Teflon - is good to over 360 to 450 Deg C so a stirling should be no problem. HOWEVER be aware that you need to keep it below 360 to prevent toxic decomposition products. This includes when machining.

It is also recommended that you remove all tobacco products as they could get contaminated and when used give you more than lung cancer!.

Materials hazard sheet here
www2.dupont.com/Teflon_Industrial/en_US/assets/downloads/h75334.pdf -

Yep! Teflon is some pretty evil stuff. I can tell you from over 37 years experience what it is like to live with PTFE poisoning. I tossed out all my teflon pots and pans sometime ago and went back to good old cast iron and stainless cookware. I can't do anything about the surgically installed stuff.

 

[DICKEYBIRD]

Great post Rog! I've been wanting to pick up some carbon rod for a Stirling engine and the stuff is cheap from a welding supplier.

Here's a link to a good source. Their information about using carbon as a dam to build up with weld and repair stuff is neat. You learn sumthin' new every day.
https://weldingsupply.securesites.com/cgi-bin/einstein.pl?Next::1:UNDEF:OR:47-143-000

 

[shred]

Is that "carbon" rod actually graphite?

http://www.jerry-howell.com/Pistons.html suggests not to use 'ordinary carbon', for whatever that is (in addition he doesn't like teflon either).

 

[Rog02]

Is that "carbon" rod actually graphite?

http://www.jerry-howell.com/Pistons.html suggests not to use 'ordinary carbon', for whatever that is (in addition he doesn't like teflon either).

Interesting question, Shred.

I did a quick search on graphite and found this.
http://www.mii.org/Minerals/photographite.html

From my experience of having carved some of the carbon rod, I would guess it is graphite as it carves easily with a pocket knife and has a slick feel to it when carved.

My best guess would be to e-mail the manufacturer and ask them.

 

[cfellows]

Carbon rod isn't the same as graphite and I'm pretty sure the carbon found in flashlight batteries is carbon rod, not graphite.

Chuck

 

[cfellows]

I just stumbled across this web site which sells small quantities of graphite in different forms. I don't know anything about the company, but it might worth checking out:

http://www.pocographiteonline.com

Chuck

 

[shred]

I think one big-volume graphite user is EDM machines, so if you know anybody in that industry, they may be able to get you some scraps.

 

[gilessim]

I made a discovery today, the place I go to get silver solder (here in Italy) is a supplier for goldsmiths etc. when I got home I was looking at their new catalogue and was surprised to see that they sell graphite lined crucibles and round graphite bar for stirring the molten metal!, they have it in 10-16-19mm x 600mm lengths, the 19mm costs about $22 a length, I'm sure goldsmith techniques must be pretty much the same the world over ,so it 's maybe worth a search in that direction!, these guys also sell little drops of copper, zinc ,tin ,etc. specially for casting.

Giles

 

[Lew Hartswick]

Carbon comes in all sorts of configurations. For example diamond is carbon in crystaylline form while
graphite is in tinny flat platelets form, then there is just plain garnules of unspecified shape and even
"buckey balls" which are another thing altogether. So if you need the "slippy" form be sure it's
graphite.
...lew...