polyurethane for seals

[wonky donky]

I have found 85 to 90 degree Shore A hardness polyurethane to be good for impact resistance.It is used for loading dock buffers for trucks to back into.For airgun parts I buy it in rod form and turn it, there is a trick to this to get a good finish.

Baz

Well is the "trick" a secret Barry or are you willing to to share with us? I've been turning 93 shore Polyurethane for some time to make piston seals. Getting the seal to work is not a problem, getting a good finish everytime is. This is typical.

I have used my dremel in a makeshift tool post holder with the lathe in reverse for grinding, made up holders to carry scalpels & hobby cutting tools, used stoned tool steel all to only achieve adequate parts.

Here is one of JB's BTW out of a modified BSA

I've also used Polyurethane for piston buffers similar to BSA's as well as pistons inside an alloy piston nose as well as rubber. Now I do know if you can get it right it does work, but I haven't as yet, not to my satisfaction anyway! The closest I got is with the piston in the nose. Using the buffer I either get no perceptible difference or I can feel a double "surge" & the result is a loss of Vo, as much as 70fps with a similar stroke to a non buffered set up.

I feel the solution will be very different for every rifle or even pellet to a point.

[T 20]

I bought a length, off that well known auction site, not cheap though

There's a plastics shop in Bedworth Nick, which would save you a bit of postage :-

http://www.theplasticshop.co.uk/cont...l#.U9Cm_2K9KSM



All the best Mick

[Shed tuner]

I've also used Polyurethane for piston buffers similar to BSA's as well as pistons inside an alloy piston nose as well as rubber. Now I do know if you can get it right it does work, but I haven't as yet, not to my satisfaction anyway! The closest I got is with the piston in the nose. Using the buffer I either get no perceptible difference or I can feel a double "surge" & the result is a loss of Vo, as much as 70fps with a similar stroke to a non buffered set up.

I feel the solution will be very different for every rifle or even pellet to a point.

Yeah, it's going be be very tricky as ideally you'd need both shock absorbing and damping properties... and we've very little space to work within!

[greenwayjames]

Here is one of JB's BTW out of a modified BSA

.

It would be interesting to know when JB did that work. I have tried to get him to do work on a springer but was told that he hadn't worked on springers for well over 20 years
I was given a hint that he was thinking of re-visiting his last spring airgun design that he developed while a partner at Titan back around 1990. He wouldnt give details only saying nothing like it has been seen before. "A totally different layout to the conventional thinking of what a spring air rifle should be" is what he said

[NickG]

let me know what you think of it, i have a sample here and made a few bits from it including one piston nose that has worked out very well, I also have run Nylotron noses which also worked well so we have 2 materials that look to be the ultimate choices.

Its not cheap though, thats the only bit that puts me off...you get what you pay for though

The place I use charged me about the same for ertalyte as delrin, and let me buy 1m instead of the minimum 3m for delrin

[NickG]

There's a plastics shop in Bedworth Nick, which would save you a bit of postage :-

http://www.theplasticshop.co.uk/cont...l#.U9Cm_2K9KSM



All the best Mick

that's the place I use ,they wanted £80 a meter for polyurethane

[vobster]

First test of Nicks O ring head in my hw97.

Fitting...
Nice fit to piston nose, better than many piston seals.
I lubed the O ring and cylinder with krytox 105 oil to prevent combustion.
The pressure of the O ring in the compression tube felt about right, the same as I'd expect from a standard piston seal.

First shots...
I started straight away with the chrono and a good batch of air arms 4.52.
Power was slightly down against the standard new shape weihrauch seal (20fps), but as this head short strokes the action a few mm I'd expect that.
Shot string was 750,752, 752,755,753,754,760,753,762,760,761
The action looks like its running in, and its going up in power with small increments. Power is now only 10fps behind the weihrauch seal.
When its fully run in I'll post up another string, it could take me a couple of weeks until I can find the time to put a tin of 500 through it though.

First impressions...
The rifle is much, much quieter.
It may be just my imagination, (and I wont discount that possibilty), but the firing cycle seems to be more tame when going form surge to recoil. In other words, I think the rifle is softer with less 'snap'

So, I'd say very interesting so far. I will be keeping Nicks O ring head in and get back to everyone.

[TonyL]

Nice one, Mr Vobster.

[greenwayjames]

First test of Nicks O ring head in my hw97.

Fitting...
Nice fit to piston nose, better than many piston seals.
I lubed the O ring and cylinder with krytox 105 oil to prevent combustion.
The pressure of the O ring in the compression tube felt about right, the same as I'd expect from a standard piston seal.

First shots...
I started straight away with the chrono and a good batch of air arms 4.52.
Power was slightly down against the standard new shape weihrauch seal (20fps), but as this head short strokes the action a few mm I'd expect that.
Shot string was 750,752, 752,755,753,754,760,753,762,760,761
The action looks like its running in, and its going up in power with small increments. Power is now only 10fps behind the weihrauch seal.
When its fully run in I'll post up another string, it could take me a couple of weeks until I can find the time to put a tin of 500 through it though.

First impressions...
The rifle is much, much quieter.
It may be just my imagination, (and I wont discount that possibilty), but the firing cycle seems to be more tame when going form surge to recoil. In other words, I think the rifle is softer with less 'snap'

So, I'd say very interesting so far. I will be keeping Nicks O ring head in and get back to everyone.

Is that a polyurathane piston head - you mention lubricating the O ring. Is Krytox compatible with rubber O ring material?

[nced]

Is that a polyurathane piston head - you mention lubricating the O ring. Is Krytox compatible with rubber O ring material?

Krytox is DESIGNED to be compatable with orings and for lubing metal. Here is a "sales pitch" from Dupont....
http://www2.dupont.com/Lubricants/en...ct%20Guide.pdf
http://www2.dupont.com/Lubricants/en...226_K20067.pdf

This statement may be of interest.
"Krytox oils and greases do not damage plastics or elastomers nor cause corrosion to metals."

[greenwayjames]

Thanks for that. It mentions GPL205 as being suitable for O ring assembly on the spec. sheet but I notice you mention Kryton 105. Is there any reason you use that for O ring lubrication? Excuse the ignorance.

[nced]

Thanks for that. It mentions GPL205 as being suitable for O ring assembly on the spec. sheet but I notice you mention Kryton 105. Is there any reason you use that for O ring lubrication? Excuse the ignorance.

It worked splendidly since all I really wanted was to form some sort of "wet edge" on the sealing oring, however the previous oils I tried would migrate past the seal and diesel. When testing the GPL 205 grease I slathered the piston and seal rather lavishly to actually prove the Dupont non-dieseling claims and sure enough...the stuff doesn't diesel. When I stripped the "205" and relubed with "105" I also didn't get any dieseling so it appears that BOTH forms will work well. I even tried the Krytox 105 OIL for internal lubing as well as the barrel latching detent and surprisingly it worked well for this purpose!

Since both the grease and oil worked well......currently I'm using Ultimox 225 for ALL internal lubing since it's advertized to have a wear and corrosion inhibiting component, but I must say that I had no issues with the Dupont GPL 205 either. To corrosion test the GPL 205 I took two degreased steel nails and wrapped them in a paper napkin that was soaked with a STRONG salt solution. After a couple days sitting here are a couple pics of the result.......

http://www.snapagogo.com/uploads/sou...rytoxTest2.jpg

Since I normally don't soak the internals of my R9 with strong salt water and then let it sit a couple days, I'm confident that there won't be any rusting of GPL205 lubed components under NORMAL use!

Sorry for the pic confusion.......for some reason one of the pisc from the hosting site won't post properly!

[greenwayjames]

Thank you for the information

[vobster]

Yes, as nced has said both krytox 205 and 105 work as a great lube for seals, but I find 105 takes far less running in before its consistent.

[greenwayjames]

Thank you for the information too