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Fluorosint , mica filled ptfe

Wanted - source of fluorosint

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Michael Foster15/02/2010 19:55:33
13 forum posts

Does anyone know of a source of fluorosint,? I need a few inches to make the bobbins for the piston valves of my Euston, Martin Evans 8F, in 3.5" gauge. Also i would really like to hear from anyone with experience of using this material.
JasonB15/02/2010 20:09:14
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25215 forum posts
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Noggin End do it
 
Jason
Michael Foster21/02/2010 19:32:25
13 forum posts
Jason,
thanks for the info. I have been advised that a material called PEEK might do just as well - and it is considerably cheaper , so i will have a go with that ,
cheers,
mike
John Baguley22/02/2010 00:57:29
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Mike, if you are thinking of making the complete bobbin from PEEK, I would not advise it. The expansion is too much. For a running fit at operating temperatures the valve will have to be a very sloppy fit when cold. I experimented with the material for my Helen Long cylinders and eventually abandoned it. I now run bronze bobbins with PTFE heads. Works a treat.
 
John
Michael Foster22/02/2010 09:18:19
13 forum posts
John,
thanks v. much for that info. - disappointing  but good to know as i was banking on using it. Just to be clear, have you tried PEEK just for bobbin heads? also when you say 'I now run bronze bobbins with PTFE heads' are you using fluorosint?
cheers,
mike
John Baguley22/02/2010 12:15:53
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Hi Mike,
 
no, I didn't try the PEEK just for the heads. I was making the complete valve from it. I eventually abandoned it when the loco seized solid storming up the steep gradient at Chesterfield's track! Part of the problem though is the steam temperature as the loco has a very high degree of superheat and I think the cylinders run at something like 200°C when working hard.
 
I used ordinary plain PTFE for the new heads I made which seems ok. Like you, I found the price of Fluorosint slightly offputting! The beauty of Fluorosint though is that apparently it has a similar rate of expansion to bronze.
 
The PEEK may actually work for separate heads as the expansion does not seem to be so much of a problem so long as a bit of clearance is left between the bore of the head and the bobbin to allow it to 'squeeze' inwards when it expands. The PEEK does have a lower rate of expansion than plain PTFE, but still high compared to bronze etc. Incidently, the PEEK I used was PEEK bearing grade loaded with PTFE, graphite, and carbon fibre.
 
One good point that came out of the experiment is that I found the PEEK to be excellent for coupling rod bushes etc.!
 
John

Edited By John Baguley on 22/02/2010 12:22:10

Michael Foster22/02/2010 14:00:17
13 forum posts
John,
I 've bought the PEEK now on ebay ( at  a total of £6 for 10"  !!) so i will give it  a try - just for the heads as you suggest. So the next question is - where did you get the loaded PEEK from ? - and did you consider the glass loaded PEEK as an alternative which apparantely has a lower expansion rate,
mike
John Baguley22/02/2010 16:15:05
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517 forum posts
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I initially got the Peek bearing grade from RS but later got some from Davis Industrial Plastics which worked out a bit cheaper. If you go on the RS website and search for PEEK, it will come up with all the various grades available along with the data sheets. It's not cheap but not in the Fluorosint league fortunately!
 
I did look at the glass filled PEEK but I got the impression it's not suitable for bearing surfaces as the glass makes it quite abrasive (could be wrong though).
 
I presume you've got the plain stuff without additives?
 
John
Michael Foster22/02/2010 18:18:11
13 forum posts
John,
yes - just the basic PEEK. I've looked at RS , I never would have thought of them - so if the basic PEEK doesn't work out - I'll try the Bearing Grade at about £40 for a foot. Thanks again for all the info.
mike
 
Kevin Knowles24/01/2011 22:56:38
4 forum posts
Does this interest in fluorosint follow on from an article in one of the magazines?
If so, could anyone help me out with what issue this was. I kept my copy in a 'safe place' for when I needed it and can't remember where that place is!!!

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