High temperature foam

[PETERg0rsq]

I have finally found the problem with my FRK rhubidium oscillator, and ready to start re-assembling it.

I have one problem though.

The lamp exciter sits in a sealed chamber, which is heated (and regulated) to about 112 degC.

This was originally insulated with an open cell foam material, which has now become very brittle, and disintegrates when touched. I needed to remove it to get at the lamp chamber heater circuit.

I therefore need to replace it.

I need a strip about 150mm long, 35mm wide and about 10mm thick. Looking at foam material specs I cant find anything that will run continuously at over 100 deg C.

Can anyone suggest anything suitable, that I can source reasonably easily.

thanks

peter

[Sean Williams]

Rockwoll loft insulation?

We use the commercial version to lag exhaust silencers

Alternatively, how about fire rope?

[ms660]

Solar hot water pipe foam insulation is good to 150 degrees C, it's cheap enough, normally it's thicker than 10 mm but you might be able to squeeze it in, you can stick it with high temp silicone (the red stuff) Google around.

Lawrence

[Silicon]

Does the foam need to be open cell? Is it purely a thermal barrier?

It might be possible to use an inner heat resistant material and then an outer insulation such as expanding foam to create a solid shell.
Some 2 part foams can be used up to 116 degrees C.

The temperature gradient across the inner insulation will reduce the temperature of the outer foam.

[PETERg0rsq]

Thanks for the ideas.

Rockwool is an option I hadnt thought about, but getting a very small quantity is a problem. Might experiment with some of the fibreglass loft insulation in the loft!

Hadn't heard about the solar insulation, so will investigate further.

Anyway I returned home early today, and the wife is out at work soooo.... You know what is comming

Put some samples of foam I could find around the house into the oven at 150 deg C

So far (after 1 hour) all of it has survived (except the polystyrene packing foam which is melting into a gue), so i will persevere with the experiment for as long as i can (or allowed to) and see if i can establish if any of it is suitable.

regards

peter

[ms660]

The solar pipe insulation is the same as the normal foam pipe insulation but higher temperature rating, it's pre slit up its length for fitting onto existing pipework, 1 metre lengths is a common stock size, you can cut that to length with a sharp knife or saw, you could cut that length to the width required, naturally it will be curved but you could stick it down with some pressure applied or tie it down tight if that is possible in your situation.

10 mm of bog standard rockwool or fiberglass probably wont give the same insulation qualities as foam, another fairly good insulator that will take high temperature and is stable is Duraboard (ceramic fiber based, available in 10 mm and other thicknesses) Normally it's in large sheets and costs a bit unless you know a friendly user.

Good luck whichever way.

Lawrence.

Might experiment with some of the fibreglass loft insulation in the loft!

It does peel apart in layers quite well and a bread knife is very good for cutting it.

[ms660]

Scissors is easier for cutting that stuff if it's thin or a sharp Stanley knife, used to install a lot of that stuff, the blades that are snapable are best for cutting deep stuff, just extend them out of the knife body to give a long cutting edge (not radio related but a good tip)

Lawrence

[PETERg0rsq]

Thanks for the information.

It looks like the solar pipe insulation is just what I need, so will give that a go.

My experiment, cooking foam in the oven, was curtailed when my wife returned home She couldnt understand the importance of what I was doing, over cooking dinner!

Anyway after 3 hours the polystyrene had melted completely, but non of the other foams seemed affected in any way, even the low density conducting foam, the closed cell PU, and the open cell foams. I will stick to something I know is rated high enough, so get hold of some solar pipe insulation.

Thanks again for the suggestions

peter

[Radio Wrangler]

There's also foamed PTFE tape which is used for making gaskets, that ought to be good at higher temperatures.

David

[Boater Sam]

I have some fireproof black foam, 50mm thick. It cuts down easily with a sharp knife so you could thin it down.

It is what is used for soundproofing machines and as prison mattresses.

It will withstand a blowlamp full on without charring at all.
I could send you a piece as per your size but it will be mid March before I get home.

[PETERg0rsq]

Thanks David ans Sam.

Never come across foamed PTF tape! Probably a bit to specialized to obtain the small quantity i need at short notice.

Thanks for the offer of the black prison mattresses However I am hoping to start re-assembling this weekend, so really need something I can obtain quick and local.

So a trip to my local plumbing merchant for solar pipe insulation seems the best option.

Peter

[hysteresis]

Originally Posted by PETERg0rsq

... Looking at foam material specs I cant find anything that will run continuously at over 100 deg C.

Silicone foam has a working temperature of just over 200°C, but may be difficult to obtain in small quantities.

Denser, silicone sponge (closed cell) occasionally appears on eBay, e.g:
http://www.ebay.co.uk/itm/SILICONE-R...#ht_860wt_1190
(it's the right thickness, but not the width that you specify).