High temperature plastics

[andrew lynerParticipant @andrewlyner71257]

I have a Pavoni Lever Espresso maker. A thing of beauty with chrome and S/S. The standard handles are hard black plastic and I am trying to change to prettier wood.

I am trying to replace the boiler filler plug and am experimenting with Utile on an aluminium base for strength. I have a problem with my first design because the wooden 'skirt' appears to have split due to stress and or temperature (higher than 100C, for the steaming). The split could be because my fit of the wooden skirt round the metal spigot is too tight to cope with the expansion of the metal. Making another wooden piece is a bit long winded if it's just going to crack because of excess temperature.

I want to try a plastic 'core' which will support a 2mm thread about 35mm diameter, with a wood cover.

I see plastic knobs, handles etc, on cooking equipment that can cope easily with the requirement but I can't find anything that would be machinable. PTFE took my eye but that would be far too expensive.

I'm sure some of you have experience of wood at high temperatures. What would you do?

[andrew lynerParticipant @andrewlyner71257]

I want to make a screw-in plug for a coffee boiler

[John HaineParticipant @johnhaine32865]

Corian – certainly resists boiling temperatures. Lovely to machine (at least by milling – I haven't tried turning but I'm sure it would be equally good with a sharp tool. (Used in pen making.)

Available in a wide range of colours and finishes (for kitchen worktops). If you find a kitchen fitter that works with it he would probably let you have some scrap, one gave me a nearly complete sample kit with ~50 nice chunks of all the colours which are useful for small jobs. Or look on eBay for Corian pen blanks.

[Michael GilliganParticipant @michaelgilligan61133]

PEEK would be my choice: **LINK**

https://www.curbellplastics.com/Research-Solutions/Materials/PEEK

… but if price is a concern, you will probably need to watch ebay for offcuts

MichaelG.

[David George 1Participant @davidgeorge1]

Try Delrin for a heat resistant plastic.

David

[andrew lynerParticipant @andrewlyner71257]

Thanks for the alternatives guys. As it will not be 'on show', I tihink I will try the lower cost delryn. It performs at up to 120C, apparently and that would be easily enough for the temperatures of the low pressure boiler.

[bernard towersParticipant @bernardtowers37738]

It’s proper name is Acetal and is available in loaded versions for greater strength but have the advantage it is a proper machining plastic machining to tolerances very closely something that cannot be said for Nylon 66 and the Ptfe family. Noggin end good for quality plastics(just a satisfied customer.)

[Andy StopfordParticipant @andystopford50521]

Acetal is pretty much the same thing as Delrin, and it tends to be a bit cheaper. Some people suggest that acetal is more suited to machining, whilst Delrin is optimised for moulding. I've only used acetal, so I can't comment on their comparative merits, but it would be fine for your requirements I should think.

Tufnol is another possibility, it's more rigid than acetal/delrin/nylon which are all a bit 'squidgy' in small sections.

[bernard towersParticipant @bernardtowers37738]

Be careful if using tufnol as it has a grain which may affect the strength of you component in a certain direction. The grain is flat with plate (gears) and with bar is rollled so does limit its uses in tension(eg threaded fittings).

[andrew lynerParticipant @andrewlyner71257]

OTOH, my problem may not be to do with the insert material at all but the thin skirt of wood (which has split) and the clearance between metal and plug. Could the wood just be splitting due to a tight fit and a bit too much stress on a thin section of wood.

Perhaps a bit more wood and a bit less metal would give the wood an advantage? I must say, the wood (utile) does seem very brittle after getting that hot. There are wooden versions of the plastic on high end versions of my machine so it must be possible.

[Andy StopfordParticipant @andystopford50521]

Have you tried looking here, Andrew:

https://www.home-barista.com/forums/

There is much information on repairs, modification etc. of the La Pavoni Europiccola and related models

[Jeff DaymanParticipant @jeffdayman43397]

Melting points (in degrees F) and max recommended service temperatures (in degrees C) are shown in the attached screenshot photos. I work with plastics in industry and use these tables as general guides.

Note that PPO (polyphenylene oxide) (one brand name is Noryl) has slightly higher melt temp than Acetal (one brand name is Delrin) and is about the same cost and availability. When Acetal degrades at high heat during / after it melts, the fumes and by-products can be nasty. Less so with PPO.

The polysulfones (PSU) have excellent high temp perfomance and are sometimes cheaper and more affordable than PEEK.

Just food for thought.

[garyParticipant @gary44937]

good choice of coffee maker i have had one for six years and it is used every day. good luck with your project.

[andrew lynerParticipant @andrewlyner71257]

Posted by gary on 18/02/2022 05:22:04:

good choice of coffee maker i have had one for six years and it is used every day. good luck with your project.

Mine is quite a bit older than that and keeps going well with very few replacement bits. There are a few quirky aspects of the design, of course; the flange between the boiler and the group head is, to my mind, 90 degrees wrong, to deal with the torque from the lever. The familiar bubbling from the gasket would not occur and the force on the bolts (and boiler) would be a lot less if the two bolts were over and under.

But the coffee is lovely and the ceremony of grinding, measuring, squeezing, steaming and pouring makes a great start to the day. It all fascinates the grandchildren, despite they fact that they are not too keen on the coffee taste and smell.

[Roderick JenkinsParticipant @roderickjenkins93242]

Noggin End do small quantities of PEEK for reasonable prices **LINK**

HTH,

Rod

[peak4Participant @peak4]

If you have access to a vacuum pump, one possibility would be to stabilise the wood before machining; it's a method often used by knife makers.
Essentially evacuate a vessel containing your wood and a resin; as the air is re-admitted, the resin is drawn into the pores of the wood.
I did mention it on a different thread, but "Cactus Juice" is one such resin, but I'm not sure if it is readily available in the UK in small quantities.
Maybe have a look around the pen makers forums, whilst you're researching Corian.

Bill

[PETER ROACHParticipant @peterroach92938]

Polycarbonate seems not to have been mentioned, but would be economically and within the temperature zone. Else use a thermoset rather than a thermoplastic. Most pan lids etc with handle use these materials,e.g. bakerlite and melamine type materials or mould/ machine a piece from “plastic Steel” an epoxy resin, even Araldite?

Peter

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