Graphite Piston

[carbide_burner]

I'm busy investigating options for a first project, and I'm keen on builing something simple that will yield results without investing too much time and effort. I am looking at "A simple lamina flow engine" of witch I found info elsewhere in the forum. http://www.stirlingengines.org.uk/thermo/lamina.html

Question: Where on earth will I find graphite for the piston? Is this a material that is readily available and used in industry? and secondly: How is a conrod typically connected to a graphite piston? Is the piston maybe left solid with a hole tapped in the back f it?

Thanks for any help and comments.

 

[Powder keg]

Ebay is our friend)

Wes

 

[Stan]

Search ebay for EDM graphite. With Stirling engines you are trying for light weight pistons so the graphite piston can be made with a hollow skirt and a thin top. Put a countersunk hole in the top for a small flat head machine screw and put a crosshead inside the piston skirt. HTH

 

[gilessim]

Try goldsmith/silversmith suppliers, I got some 16mm and 19mm graphite rods from one, they are used for stiring molten metal, they also had graphite crucibles!

Giles

 

[mklotz]

Look for EDM rods and supplies from your local metalworking suppliers.

For instance, here in the States, a popular supplier is Enco and they have...

http://www.use-enco.com/CGI/INLMK3?PMK0NO=936052

I can't help with specific suppliers in South Africa (BTW, thanks for putting location in profile) but there must be someone supplying EDM shops with their consumables.

 

[tmuir]

Try goldsmith/silversmith suppliers, I got some 16mm and 19mm graphite rods from one, they are used for stiring molten metal, they also had graphite crucibles!

Giles

I never even thought of that even though I've walked past them dozens of times when I buy my silver and gold for making jewellery.
I'm not planning on building anything with graphite pistons yet but thats handy to know.
Is it as durable or the same as EDM graphite mentioned above?

 

[Loose nut]

Look for anyone in your area that makes graphite seals for pumps etc. they might "give" you some.

 

[SmoggyTurnip]

: How is a conrod typically connected to a graphite piston? Is the piston maybe left solid with a hole tapped in the back f it?

Thanks for any help and comments.

I have been wondering about this as well.

 

[Stan]

Quote from: carbide_burner on August 04, 2008, 08:11:11 AM
: How is a conrod typically connected to a graphite piston? Is the piston maybe left solid with a hole tapped in the back f it?

Thanks for any help and comments.

I have been wondering about this as well


Read my reply about six posts up.

 

[SmoggyTurnip]

Search ebay for EDM graphite. With Stirling engines you are trying for light weight pistons so the graphite piston can be made with a hollow skirt and a thin top. Put a countersunk hole in the top for a small flat head machine screw and put a crosshead inside the piston skirt. HTH

I guess I don't understand what the machine screw is for. Does the graphite get tapped? Can graphite be tapped?

 

[Bogstandard]

Methinks this calls for a quickie grotsketch.

I suppose rather than using a c/sunk screw you could try to tap the graphite and epoxy a threaded rod in there for the crosshead to screw onto.

Bogs

 

[SmoggyTurnip]

Thanks again Bog's! I gotta get that CAD package you have one of these days.

 

[Bogstandard]

Smogs,
If you want a copy, you can buy it from most stationers, it's called Crap-O-Cad, and comes in a box with a felt tip pen and a sheet of paper. Quickest Cad package on the market, both for learning and using.

Bogs

 

[Stan]

Thanks John. Nothing like a piece of talking paper to get an idea across. I think graphite creates a whole new learning experience. On the last graphite piston I made, the top was so thin that I had to countersink the crosshead to accommodate an 82° screw. Not much run time but with the low friction, the piston head hasn't broken.

BTW: I am awaiting delivery of a block of virgin EDM graphite 2" x 4" X 13" that I got on ebay. With that I will be able to make graohite pistons all the way up to 4". I just may make a giant fire eater!

 

[Bogstandard]

Stan,

I get discarded EDM profiles from the aerospace industry. They can only be remachined about 3 times and are then thrown away. So however big you can get turbine blades, I should in theory be able to obtain some of that size. But at the moment I have enough to do about 100 pistons, so I am not pushing for any more, unless I start to believe in reincarnation.

John

 

[Mcgyver]

John, can you get crap-o-cad to do a stress analysis of that piston seriously though, what sort of wall/end thickness would you think is practical to machine? I've not worked this stuff before but my perception is that it is quite fragile?

 

[Bogstandard]

Mcgyver,

I truthfully can't tell you, I have only played about with graphite a small amount, getting ready for my assault on all things Stirling. All I can say is that when I machined it using collets, it was stronger than I thought it would be, and machined really nice with a very small radius, round nosed tool, it came out with a glass like finish. I also tried lapping it with newspaper on a piece of flat plywood, and the results were very encouraging, it might have been even better wrapped around a thin parallel.

The only true downside that I found, was that myself and the dog looked like Al Jolson when we were finished. So a face mask and protective clothing are a must, oh! and gloves, unless you want her indoors to nail you to the wall, because of all the black handprints everywhere, don't ask, all I can say the dog was still grey tinged a few days later. Not too worried about the lathe though, it is a good lubricant.

Hoped this has helped in some way.

John

 

[carbide_burner]

Look for anyone in your area that makes graphite seals for pumps etc. they might "give" you some.

That's a good idea! There is a specialist seal manufacturer just around the corner from where I work. I'll stop by and speak to them today.

While on the graphite topic: Is graphite ever used for making anything but pistons?

 

[rickharris]

Lots / most art shops have these http://www.utrechtart.com/dsp_view_product.cfm?classId=1510&subclassID=151012&brandname=&item=32441

The one I have is 12 mm hex shaped - they come in various hardness although as yet I have no experience of machining them.

 

[PTsideshow]

It is also used in glass working and bead making they have smal paddles and larger blocks. For forming the hot glass.
You can shop where the rocketeer's shop for the raw material for model rocket nozzles.
http://www.graphitestore.com/index.asp
http://www.aeroconsystems.com/graphite/index.htm
Or check out you local glass working shop.
And I believe the first one had some info on machining it.
;D