kevingambrell

Hi

Took the piston out of a TE that had clocked up about 12 hors running yesterday to find the string piston ring all but gone, turned to muck each end of the cylider.
Not wanting to repeat this I machined a piston ring 11thou over bore from Delrin angle split the ring and put it in the packing groove. Put the lot back together and steamed the engine. After 20 mins running the piston runs in the bore better than any ring set up iv ever used! smooth and seals very well.
Dont think it would work for super heated steam but on saturated it seems just fine. Il post an update after 15-20 hours.

kevin

Bunkerbarge

Could you let us know what Delrin is, sounds interesting.

kevingambrell

Hi
Delrin is one of the family of engineering plastics, its a very low friction self lubricating material made by DuPont and is some times called Polyoxymethylene or POM. Its used in a vast list of applications from body piercings to turbine seals. I use it in large amounts for bearings on telescope drives (part of our main work).
Good stuff.

Kevin

alan2525

what were the original ones that went to goop made from - cast iron? :O

I've heard people using delrin for nuts on cross slides on machines but haven't been too convinced about it's life expectancy.

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kevingambrell

The old piston ring was graphite yarn, it had lasted many many hours but as with most yarn rings it had lost some of its seal before it was mashed. I wouldnt use cast iron rings in a engine with a bore less than 1.5 inches. i doubt there would be any bennefit.

Delrin makes superb nuts for lite use I wouldnt want it in a cross slide i must say. Its like any material used in the correct place its superb at its job. As a lite duty bearing its hard to better it. I used to use Nylatron but after being introduced to Delrin i kept with it on most fixed bearing that have small loads.
The one big advantage with Delrin is if you get swarf or grit in the nut/ bearing it will tend to sink into the surface of the Delrin and not do too much damage to the shaft that the bearing is on.

Be warned it grows after machining! if you machine Delrin and let it sit over night it can grow a thou or so.

alan2525

Do you know of any sites which would provide guidelines on what lubricants are suitable for use with various types of plastics?

I've used some ptfe dry lubricant which deplasticized some styrene that caught the overspray one time and have a project which is going to be reliant on styrene and acrylic in close proximity to drivetrain components.

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kevingambrell

Hi Alan
Go with silicone grease from a dive shop its inert to almost everything out there. It lubricity is not perfect but it wont destroy any of the plastics your going to come across on a day to day basis.
I restore vintage fountain pens for a hobby and its the only grease thats safe on all pen materials.
PTFE dry lube is still in a carrier most likely iso propane or butane based if in a spray can. PTFE on its own is reasonably inert but i wouldnt want it on styrene.

kevin

bsm

Hi Kevin

How are the Delrin piston rings holding up? A couple of questions if you don't mind.
1) what size bore are you using them in.
2) what is the Delrin angle that you mention in your post of April 3 2007?

Thanks

Bruce

kevingambrell

Hi Bruce

Just Pm'd you on the traction engine site.

The Delrin rings are fine after many hours of steaming (probably 60 hours plus) plus the bore is as it was before the ring was installed no marks no wear and it runs fine on less steam oil. One engne has a 5/8th bore the other has a 1.5 inch bore.

The angle I cut at was about 45 degrees rather than just splitting the ring across its radius. I have since made one in a coil form fora slightly larger engine.

I dont think id go back to compressed packing or cast iron rings. I will be trying an Aluminum piston with delrin rings later this year. Mostly in an attempt to reduce teh mass of the piston. I had also played with the idea of a piston with feather edge seals machined in. May still try that if time lets me.

Cheers kevin