Graphite Piston

[nemt]

I can remember they used carbon as pistonrings on compressor psitons. These were used to provide "oil less" air meant for the use in controlequipment like levelcontrols etc. working on compressed air. The lab also used this, what we called "instrument"air. The area I am talking about is the process industry. More precise AKZO. They produced salt and made Chlorine and hydrogen out of is by means of electrolysis. Lots of controlinstruments, all working on air.
Nemt

 

[shred]

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.

I used one of those hex pencils for the piston on my stirling fan. Worked well. Since then I found some graphite with 1" diameters as well as odd-shaped chunks, but I've not actually used those yet.

 

[carbide_burner]

Thanks for all the replies everyone!
I managed to find a telephone number for a company that supplies graphite to industry. I believe they use it mainly for EDM (electric discharge machining), and electrodes in ovens. It can be cut in any size and shape your heart desires.

Problem is that the graphite shop is not nearby, and I would like to investigate alternatives. There is a shop in town that sells any plastic known to man, and they have a product called "VESCONITE". It is a hard, easy machinable, self lubricating plastic. Used for suspension bushings etc. as well as high load, high temp applications where lubrication is a problem. My brother recently made inserts for his lathe steady in place of the brass inserts, and it works great! He used it to support aluminium tubes in the machine, and it merely polished the surface of the tube!

Has anyone tried something like this? or is graphite the final answer?

In the meantime I'll contact the graphite shop, and find out if they'll sell a small piece to a small customer AND drop it in the mail...

 

[bentprop]

Just a thought,old transistor radios used to have a graphite rod for the aerial.Is that a useful material,or junk?

 

[Bogstandard]

BP,

It's not graphite, it is ferrite. Dump it.

Someone on here tried it a few months ago.

John

 

[baldrocker]

Slightly ot how does delrin perform as pistons?
Paul aka Baldy

 

[CrewCab]

how does delrin perform as pistons?

I made a cylinder using Delrin and it worked just fine ;D

CC

 

[baldrocker]

Thanks mate
BR

 

[Stan]

carbide_burner: I don't know what the reason was for your question on uses for graphite. If was for uses in model engines. Here are a couple: On engines like Stirlings where you need a piston rod seal, it works great. Just make the hole oversize and machine a piece of graphite for a tight fit in the cap and a sliding fit on the piston rod.
It also makes good bearings for slow turning shafts with light loading. I don't know how it would do on high speed (10K+) shaft. I will try it for crankshaft bearings on the next engine I build.

The last piston I made was 1.125" OD with a .40" wall thickness. It fell on the concrete floor off the bench and didn't break. I don't advise this as a test procedure as I expected it to shatter.

My method of turning in the lathe is to cover everything with multiple paper towels so that they can be picked up frequently and the cuttings put into a plastic garbage bag. I turn at low speed (about 100 RPM) and that keeps all the cuttings on the lathe. Speed seems to have little effect on the surface quality and even at low speed you can easily cut.0005" or .050". Speed up the spindle and you are in a black fog.

 

[carbide_burner]

I was wondering if it could be used for bearings, so yes, you answered my question thanks. I found a generator slipring brush and I have since made the piston using it. What a mess it made!!! Took me a day or two to get rid of the "touch anything and get black" problem!