Heat Resistant Clear Material Needed…

[James GirdlerParticipant @jamesgirdler65405]

Eltex Greenhouse Heater viewing glass

[James GirdlerParticipant @jamesgirdler65405]

Hi all,

I'm after some ideas for a clear product which is good a heat resistance.

I have some old Eltex greenhouse heaters which need refurbing. The chimney/viewing tank, which draws the heat up into the heater has a small 60mm diameter circular viewing glass, pliable thin 1-1.5mm plastic, looks like fibreglass type material. Brittle, hard, bends, but breaks under too much pressure.

I wanted to find something similar I could cut into circles, with fairly good heat resistant properties. Will never be tons of heat, just a couple of wicks from the paraffin tank below.

I was thinking Polycarbonate sheet or PTFE, or would simple clear acetate laminating style sheeting work? Not sure if it will bubble.

Be interesting to know what this stuff is, it is made of layers, if you rub the surface it peels off until there is nothing left.

Thanks in advance

[Martin 100Participant @martin100]

The original is probably Mica

[Martin KyteParticipant @martinkyte99762]

Yes. Sounds like mica to me.

Martin

[not done it yetParticipant @notdoneityet]

Posted by Martin 100 on 06/01/2021 14:18:18:

The original is probably Mica

Almost certainly. Find a ‘skipped’ electric iron?

[GeorgineerParticipant @georgineer]

I'm certain it's mica, which is a mineral. Your windows would have been made of mica in its 'native' form. My father told me that a lot of mica used in electrical goods like irons is made (for cheapness) of loose mica flakes stuck together with something like shellac. The adhesive burns off when heated, and the mica falls to pieces if subsequently disturbed. Not ideal for a window!

George B.

[James GirdlerParticipant @jamesgirdler65405]

Amazing, thanks all, very helpful. I never thought of Mica, just ordered some small sheets up. Another questions, I need to cut 60mm circles, is it brittle to cut? I have some glass cutters, snips, but reckon a needle point to score the material and keep scoring until it cuts through.

[James GirdlerParticipant @jamesgirdler65405]

Posted by not done it yet on 06/01/2021 14:35:37:

Posted by Martin 100 on 06/01/2021 14:18:18:

The original is probably Mica

Almost certainly. Find a ‘skipped’ electric iron?

Sold an old iron for pennies recently, sods law!

[Andrew TinsleyParticipant @andrewtinsley63637]

You may have trouble trying to cut native mica into circles. I made a botch when I tried it, although it is done commercially. I suspect that a sharp circular punch might do the job.

Andrew.

[James GirdlerParticipant @jamesgirdler65405]

Posted by Andrew Tinsley on 06/01/2021 15:38:23:

You may have trouble trying to cut native mica into circles. I made a botch when I tried it, although it is done commercially. I suspect that a sharp circular punch might do the job.

Andrew.

Brilliant, thanks Andrew. I was thinking something similar. I'll see how it goes!

[Ramon WilsonParticipant @ramonwilson3]

James – Yes I would agree with others and say Mica too.

Not sure if this will be of use but recently on here I asked about cutting microscope glass. It was suggested by some that it may be able to be cut 'with a pair of scissors' under some water.

A quick google confirmed this is a method that could be adopted but in the end I didn't need to try it. Whether it would work with mica I have no idea but it might be worth thinking about.

Just a thought – Tug

[Rod RenshawParticipant @rodrenshaw28584]

Native mica is quite brittle and I wonder if a single point hole cutter, as used by plumbers to cut holes in water tanks might be safer than a punch. This would leave a small (1/4"? ) hole in the centre of the window but this is unlikely to matter in a greenhouse heater.

If there is little air movement in the greenhouse, then a paraffin heater may work well enough without a window at all.

Rod

[Jeff DaymanParticipant @jeffdayman43397]

If there is direct flame nearby, I would not recommend any polymeric material be used. There are some cyclic olefin polymers that will take 160 degrees C in service and some are flame retardant but none of them are rated for, or will stay clear, if exposed to flame. PTFE is opaque by the way, not clear/transparent.

Ordinary tempered glass as used in gas and wood fireplace doors would be my recommendation for use near direct flame, as it will take quite a lot of heat and will withstand rapid cooling from high heat as well, in case someone opens a door and lets a cold draught in. This material has to be cut before tempering. It will shatter if attempting a cut after tempering. Best thing to do would be to find pre-cut and tempered pieces the right size. It is usually not expensive.

Pyrex glass would also be excellent but it is much more expensive usually.

You may be able to find round gauge face glasses in Pyrex or tempered glass. If not, is there room to mount a square or rectangular glass piece in front of or behind the 60 mm opening, in a sheetmetal holding frame?

Glass will be much more durable than mica or composite mica board.

Just food for thought.

Edited By Jeff Dayman on 06/01/2021 16:44:15

[SteviegtrParticipant @steviegtr]

I tried to picture what the op was saying, when i remembered. As a much younger me we had 2 heaters at home ,which i think were the same heaters. They were called Aladin with a large base that held the fuel & a funnel around 5 or 6" diameter & stood about 20" high. They ran on paraffin. Is this the same type of heater. If so i remember the viewing window as a curved to the diameter clearish window. No help whatsoever to the question though. Now all i need to do is remember what i did 2 hours ago. !!!!.

Steve.

[PeroParticipant @pero]

Mica can be " cut " using a pair of sharp nippers – preferably of the end cutting variety. The type used in electronics would be suitable for this size of work. You need to nibble away of the edges until you reach the desired shape.

Pyrex would be suitable but would be difficult to cut to shape and ideally you should anneal the cut edge prior to use. A possible source, if you want to try it, is the base plate for a 3D printer. These can be acquired quite cheaply in the smaller sizes and possibly used uncut if it is possible to fit the square sheet behind the round hole.

Pero

[Paul LousickParticipant @paullousick59116]

Jame's question was for "a clear product which is good a heat resistance" for a " 60mm dia. viewing glass"

As far as I know, Micas are translucent to opaque with a distinct vitreous or pearly luster, and different mica minerals display colors ranging from white to green or red to black.

Therefore unsuitable foe a viewing glass.

Paul

[J HancockParticipant @jhancock95746]

Industrial boilers in small factories/hospitals, etc, have burner 'spyhole' glasses of about that size.

You could try your local British Steam Specialities BSS stockist.

[Mike PooleParticipant @mikepoole82104]

I notice that 60mm diameter Petri dish’s are available on eBay, they are 12mm deep so the edge would need removing. They are Borosilicate glass so would be heat resistant. Removing the edge might not be too easy though.

Mike

[SandgrounderParticipant @sandgrounder]

Can you change the window viewing area with a metal plate fitted with a different size and shape glass, if so the best you can get is 'transparent fused silica' glasses which are available for example on eBay, just looking at one which is 37mm sq by 1mm thick, about £6 inc P & P, this type of glass can stand very high temperatures and thermal shock and for a window like this should be OK for 1000C see link below.

https://accuratus.com/fused.html

[Nick Clarke 3Participant @nickclarke3]

Posted by Paul Lousick on 07/01/2021 05:26:20:

Jame's question was for "a clear product which is good a heat resistance" for a " 60mm dia. viewing glass"

As far as I know, Micas are translucent to opaque with a distinct vitreous or pearly luster, and different mica minerals display colors ranging from white to green or red to black.

Therefore unsuitable foe a viewing glass.

Paul

The originals were mica and obtainable as spares from ironmongers 'in the day'

However don't think for one moment that I am disagreeing with you – they were at best dimly transparent and became translucent or worse after use.

As an aside LBSC in his Live Steam Book (aka Shop, Shed & Road) suggests mica sheet wrapped round gauge glasses and secured with wire as gauge glass protectors!

[James GirdlerParticipant @jamesgirdler65405]

Brilliant, thanks all! I have ordered some stove mica from a very helpful chap, I should have been more specific, not overly necessary being completely clear, it's only enough to view the size of the flame.

Also need to drill some small holes into it with a hss or ceramic tipped bit, so mica will be great. Thanks again. Will send some photos when done.

[John HinkleyParticipant @johnhinkley26699]

James,

I'm a bit late for you maybe, but when we lived in rural France, we had a log burning fire with glass windows in the doors. One broke and I went to the local fire dealers. He directed me to a glazier/ glass supplier who cut up some high temperature glass to size for me, specifically for this application. I dare say similar is available in the UK and they should be able to cut it into circles and drill holes in it, too. That way you only pay for the finished article.

John

[Adam MaraParticipant @adammara]

There is an interesting article about mica on the British Mica Company website, it will stand up to 900c, and the largest piece found was 330 tons!

Many years ago, as a country ironmonger we used to sell sheet mica for oil heaters and slow combustion stoves, the memory is fading, but I'm pretty sure we used to cut it with normal scissors. Happy days!

[Nick Clarke 3Participant @nickclarke3]

Posted by John Hinkley on 07/01/2021 10:03:31:

James,

I'm a bit late for you maybe, but when we lived in rural France, we had a log burning fire with glass windows in the doors. One broke and I went to the local fire dealers. He directed me to a glazier/ glass supplier who cut up some high temperature glass to size for me, specifically for this application. I dare say similar is available in the UK and they should be able to cut it into circles and drill holes in it, too. That way you only pay for the finished article.

John

Somewhere in the house I have a small book, just post ww2 by George Wakefield on how to make a photographic enlarger.

It asks for a 2.25×3.25 piece of flashed opal glass and a similar sized piece of heat absorbing glass – but if you were concerned it might shatter you could ask for that to be supplied cut into a series of strips, obtainable direct from Chance Brothers Glass, Oldbury.

In more normal times I drive home down the M5 past the remains of the Chance works I wonder at a company supplying such a small order from the factory!

Autres temps, autres mœurs (excusing my pronunciation and spelling!)

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