Heat Resistant Clear Material Needed...

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

The original is probably Mica

Yes. Sounds like mica to me.

Martin

Almost certainly. Find a ‘skipped’ electric iron?

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.

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.

Sold an old iron for pennies recently, sods law!

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!

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

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

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

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.

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

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

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.

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

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

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!

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.