PEEK plastic for sliding steam valve

Has anyone tried PEEK as the material for sliding valves?. I found an old discussion that partially covers this question in the forums **LINK**  which discourages the material for use in piston valves, but I think that the described problems should not happen in a sliding valve. Any experiences?

I also have a secondary question: I have been pointed to "Iglidur X" from IGUS for the same purpose (by an IGUS representative). The specs seem very similar to PEEK, but I am unable to find the actual base polymer of said IGUS branded material. Can it be just PEEK filled with some particular or proprietary fillers?

Edited By John Lluch on 25/11/2017 12:05:01

Edited By John Lluch on 25/11/2017 12:05:58

Iglidur looks a very impressive material, John

**LINK**

https://www.igus.co.uk/iPro/iPro_02_0005_0000_GBen.htm?c=%7BC%7D&l=%7BL%7D

I would think it worth a try, if you can get a suitable shape to work with.

MichaelG.

Hi Michael,

Thanks for your reply.

I have an offer from the local IGUS representative for 20 mm diameter round bar, 200 mm length, of the "Iglidur X" material. Price is 23.32 EUR (plus transport). Not totally cheap, but fairly affordable and enough quantity to make several parts. The rep said the material "should" stand superheated steam, but I guess that's an uncommon application.

A interesting application of PEEK is 3D printing replacement bits for people's skulls!

A reel of filament costs more than my printer did!

PEEK melts at about 340 deg C. There are grades that are rated to work at 250 deg C but with reduced properties. Glass transition temp (where properties start to change, in plastics) of PEEK starts around 140 deg C.

With saturated steam at low pressures PEEK may work OK as a sliding valve. It will not likely work with superheated steam at high temp and pressure, even briefly.

A general caution - PEEK or other plastics should not ever be used as pressure vessels at all.

A note on IGUS products - the resins used are excellent for stated purposes under stated conditions. They will not work well outside those conditions, and I doubt IGUS would endorse them for steam valve service under any conditions since there are so many variables with steam valve service. IGUS simply do not talk about the actual composition of their resins due to fierce competition in their market. There are a lot of lookalike similar products being imported from the far east that do not perform well at all, so it is best to buy direct from IGUS if you want something.

I saw several hundred PET pressure vessels in the supermarket this morning. At room temperature the pressure in a bottle of fizzy drink is about 60PSI, comparable to some lower-pressure steam boilers.

Doug McHard used to wrap them in fibreglass tape and use them at ridiculously high pressures (for compressed air powered aircraft). He pointed out it was VERY important not to scratch them.

I found this online - together with a warning that under some conditions they can fail at 50PSI. the internet seems to accept 150PSI. Bear in mind these figures don't include safety margins:

Thank you for contacting The Coca-Cola Company via our Web site.

The amount of PSIs (pounds of pressure per square inch) that a package is able to withstand depends on the volume of carbonation and is based on the product rather than on the package. At lower temperatures, the pressure is lower; at higher temperatures, the pressure is higher.

A can is able to withstand over 100 PSIs.
A 6.5 ounce glass bottle can withstand 225 PSIs.
A 16 ounce bottle can withstand 175 PSIs.
A PET bottle can withstand 250 PSIs depending on the temperature.

I hope this information is helpful. If you have additional questions or comments, please visit our Web site again.

Gina M. L'Heureux
The Coca-Cola Company
Industry and Consumer Affairs

I make bait pumps and i have tried all kinds of plastics the best and hardest wearing is Oilon green and its a lot cheaper than peek

The usage of a high-performance polymer (HPP) like PEEK, impregnated PTFE etc for piston valve bobbins led me to many hours of research.
Expansion is the problem. If you bear with this brief narrative about piston valves, it might aid your thinking about PEEK for slide valves altho' of course the situation is different.
If you machine a HPP bobbin to slide nicely at ambient temp then it WILL seize at steam temperature. Keith Wilson and many others have reported this. Advice is the tedious process of putting the whole casting in the domestic oven set to the temp of the steam your boiler pressure will produce. You are then supposed to keep skimming the bobbins - a thou or two at a time - until they slide at this elevated temp. Well....yes, that's good except that at ambient temp, there's damn-all contact between the bobbin and the piston valve bore. So that means you'll never get the engine to run on compressed air and starting up on steam will also be problematic.
John, you don't write whether your valves are to run on CI or GM. I found that carbon-fibre impregnated PEEK "PEEK CA30" had the best properties in terms of relatively low linear expansion and wear resistance at moderate superheated steam temp. It is not cheap and judging by how quickly it blunts a HSS cutting tool, I'm a bit apprehensive about use on GM surfaces, but it should be OK with CI.
This offers some comparative data:-

I purchased the PEEK CA30 from Davis Ind Palstics and found them very helpful.

Edited By Fowlers Fury on 25/11/2017 17:08:22

Hi Jeff and Fowlers.

Thanks for your replies.

The matting surface may be Stainless Steel 303 grade (yes I know this is very uncommon). So in theory suitable for a sliding valve made in plastic.

I would REALLY like to know what's the actual base polymer of the "Iglidur X" material from IGUS. I hate that they provide all kind of mechanical and property data at low to moderate temperatures but fail to give the same data at their upper range of working temperatures. According to their spec: "With a permitted long-term application temperature of 250°C, the iglidur® X tolerates even 315°C on a short term. Like in all thermoplastics, the compressive strength of iglidur® X decreases with rising temperature".

Well, that's nice to know, but to what extend? It looks as they are marketing a material for high temperatures only to fail to give actual data at these temperatures (?)

**LINK**

Their specs make me think on this: "Ok, the material isn't going to melt that easily, but you better don't use it at all if you are serious about high temperature"

That's why I ultimately asked for your practical advice which I appreciated.

Edited By John Lluch on 25/11/2017 18:10:09

A bit off topic, but I now that one heritage railway has used a PTFE/PEEK type bearing material in coupling rods with complete success. I've probably got the material spec hidden in my records somewhere. Id be interested to know if anyone has done this on amodel and had success.

Edited By duncan webster on 25/11/2017 19:03:34

If you DID manage to find out the composition of these Iglidur plastics, you'd find they are actually a blend of PEEK and other additives (to assist moulding and for friction reduction etc, as they are intended for bearing applications). I recently looked into the use of some of their bearing plastics for a high temp application (170C long term) but the cost of Igus materials is ruinous for cost sensitive (automotive) products. There are similar materials available from competitor suppliers of speciality polymers (EMS, Solvay etc) but as suggested, Igus guard the actual composition very carefully, as do their competitors.

Murray

As per what I have found, many if not all manufacturers state the base polymer for their compositions, and most of them also the type of fillers embedded. Of course, they will not provide the exact formulation but at least you have an idea of what's in there so you can compare specs with other manufacturers of similar products.

IGUS seem to be the exception. They are extremely secretive about the actual polymers being used, which in my opinion makes difficult to know what alternatives you may have from other manufacturers. They are also more expensive, and they tend to say that their products are the solution for everything, so you end trusting them without really knowing what you are buying, which makes the purchase a bit frustrating and uncertain. I honestly dislike this way of selling things, which is not saying that it may be bad for them, because I may end buying their Iglidur X product anyway.

Edited By John Lluch on 25/11/2017 21:16:05

That kind of behaviour seems reminiscent of US practice, where often mundane materials are dressed up as miracle (and expensive) products. The MSDS cloaks the fact, typically quoting "industrial secret" or somesuch. It seems to be common practice over there.

Obviously, making it difficult to know what you are getting or what equivalent product could be used from a competitor acts to protect their margins. But it also often indicates that you are paying through the nose. If you know your speciality polymer chemistry, or know somebody who does, you can find a cheaper alternative. And no, sorry - it's not me!! BTW, I may be wrong but i believe Igus make bearing components, not polymers, so if I'm correct they will be buying the bulk material in from a third party.

Murray

Edited By Muzzer on 26/11/2017 12:42:40

+1 for Muzzer's comments.

The significant variation in physical properties of HPPs impregnated with materials such as mica, graphite, carbon fibre etc means it's essential to know what is the base HPP and how the additions modify its physico/chemical properties.

As he also implies, production of the HPP itself is hi-tech and distributors will normally just machine the bulk product into saleable sizes. The HPPS, PEEK and PES were developed by ICI and their synthesis is complex e.g.
cpsm.kpi.ua/polymer/1994/2/415-422.pdf
My choice of PEEK CA30 grade was based on readilly available data and key properties such as expansion due to heat and water absorption, thermal stability, creep etc.
Without such data, you're asking for trouble in an untried and unproven application IMHO.

Have a look at Solvay´s site for Ketaspire

**LINK** and download the processing and design guide. Look out for KT880-SL30 or FW30. The mechanicals don´t match exactly.

Or look at Victrex´s website **LINK** and look at PEEK FC30.

Both have some simple temperature data (tensiles etc.).

From the density and mechanicals you are probably looking at a higher melt viscosity PEEK grade with about 30% carbon fibre, some graphite and PTFE in it (+ some other non-reinforcing filler eg. mica to lower the mechanicals a bit more).

The crucial temperature is the glass transition temperature of PEEK at 143°C.

Thanks for your replies. They are all very helpful.

So it looks to me that the best material for this must be PEEK with Carbon Fibre + PTFE and graphite. Eventually, I found this material on the RS-Online site (**LINK**).

Its not clear what's the original manufacturer, but based on the RS specs it seems to me that it could be Victrex PEEK 450FC30 (**LINK**) I am also comfortable with a statement on the RS site and elsewhere that PEEK has excellent resistance to superheated steam.

Of course, there's still the "iglidur X" material offer that I keep from IGUS, which is cheaper than the material found on the RS-Site. It may turn that "Iglidur X" is just a rebranded version of the "Victrex PEEK 450FC30", because the specs are suspiciously similar. But I think I will finally discard any products from IGUS despite having found them cheaper, as they do not give me enough confidence or information.

Maybe someone can suggest where to buy the "Victrex PEEK 450FC30" or equivalent product at a better price than RS-Online, so I stop looking further?

There aren´t too many producers of PEEK, its high processing temperature makes it expensive to compound and extrude. The base polymer is also expensive.

Igus seem to offer preformed liners. The trouble with machining a sleeve from rod is that you throw most of it away, okay for prototyping but you would extrude/injection mould it if you scale up. . You will also need a bit of practice to see how it machines.

Drake in the US **LINK** seem to equate 450FC30 with the Solvay Ketaspire KT820SL30 (but see the caveat at the bottom of the page).

Try Victrex tech service (Fleetwood/Thornton Cleveleys in the UK), they might know who supplies small quantities in the UK or around Europe.

John,
As I wrote (& mistyped) in my first post Davis Industrial Plastics were extremely helpful considering I was a small-time buyer. Despite PEEK CA30 (C-fibre PEEK) not being listed on their website, they were prepared to sell an off-cut from 20mm thick sheet at a very reasonable price. Since you're making slide valves I assume sheet is more use than it was to me when making rings.

The material can be hell to machine in that it will blunt HSS tools quickly, whereas sharp TC-tipped tools have no problem with it. Nevertheless it is easy to shave with a sharp blade and a file will produce a smooth flat surface.

I was going to make my slide valve out of carbon loaded PTFE, but this stuff looks better. I'll hold off until you tell us whether it's successful.

Edited By duncan webster on 27/11/2017 18:39:39

Hi Fowlers, Following your advice I just sent an email to Davis Industrial Plastics. I asked for a bearing grade PEEK. Let's see what they reply.

Duncan, It may take some time before I am able to post any result. Unfortunately, I'm partially disabled due to a chronic illness, and everything takes a lot of time for me. I also need a lot of time to rest. Maybe you want to try the material too, if you have some opportunity. Said that, I wonder if you have already some previous experience with carbon loaded PTFE. I would like to know too how the reinforced PTFE works.

Edited By John Lluch on 27/11/2017 19:46:24