Insulating board that won't drop powder as it is touched

hi, i am currently making a small tempering / bluing box using a PID controller and ceramic heater.

the insulation is a bit of an issue. Ideally I would like it to be 25mm thick but less will not hurt. i dis some reseach and went fot Calcium silicate for its insulation characteristics. the box will be heat to around the 300 celcius point..

The issue with calcium silicate is it is so powdery i can see each time i take off or put on the lid white powder will drop in.

So has anyone any ideas of an alternative. There's vermiculite but is this as bad for crumbling/ how about fibre cement. The idea is to keep the heat in to reduce heat up times and help maintain a constant temperature as much as possible.

Hope you are all well.

Chris

You can try these as they make an insulation board which is a mixture board.

2. COMPOSITION CAS NO.
Synthetic calcium silicate hydrate 1344-95-2
Mica 12001-26-2
Vermiculite 1318-00-9
Cellulose fibre 9004-34-6

Company: Promat UK Limited
Calcium silicate board containing the substances The Sterling Centre, Eastern Road
detailed below Bracknell RG12 2TD
Tel: 01344 381400 Fax: 01344 381401

David

Jake Sutton, a brilliant clockmaker, described using a bluing box in Horological Journal last July and mentioned a useful mod to reduce the heating of the outside of the housing. This was to use Rockwool-type roofing insulation rather than vermiculite.

Thanks David, I think it might well be an idea to give these people a call tomorrow and pose my question of what is not going to drop powde inside/

Chris

I’ve been looking for mater for a similar application. Thanks for the ‘heads up’ on this one.

I’ve found a link on t’internet:-

**LINK**

John.

I’ve been looking for mater for a similar application. Thanks for the ‘heads up’ on this one.

I’ve found a link on t’internet:-

**LINK**

John.

The under face of the insulating lid can be protected with a thin steel sheet to stop powder crumbling off. Ideally polished stainless, but ordinary tin-plate will do. (Old biscuit tin.)

Although the sheet will get hot inside the oven the outer insulation will still work as normal. Whilst the steel sheet absorbs a certain amount of heat, keeping it thin means it won't waste much.

The sheet could be secured to the insulating lid by a small diameter stainless steel* bolt. A convenient wooden handle could be attached to the bolt on the cold side.

Though the steel will cool fairly quickly, take care when handling the hot lid!

Dave

* Stainless conducts heat much less well than ordinary steel.

I have 2 full sheets of A60 insulation board. The modern equivalent of asbestos sheet 12 or20 mm thick. Not as efficient as silica or ceramic fibre but solid. I can let you have some for a few beer tokens ! Ceramic fibre with a rigidiser would work or even a pre formed tube, this would make it easy to construct. PM me if I can help. Noel

Then on reflection by far the best idea would be American K23 firebricks in a thin steel box. These can be cut with a knife or hacksaw and glued together with air setting cement. 3" will keep 1500*c in. It's used in the lining of pottery kilns Etc Bricks cut in half would give you1.5" thickness.There so light they will float.  I built a furnace 25 years ago of this material, carted it all over the country and it's still going strong.  N.

Edited By noel shelley on 29/03/2020 15:47:33

Do you have a product called Pratleyperl in the UK? It is made from the mineral perlite. A really remarkable thermal insulator and is mostly used in bead form and laid on your ceiling for insulation. It is also used mixed with cement to plaster house walls for insulation, which I have done to my house on the Namibian West Coast and the result is great - huge reduction in heating/cooling requirements. . Raw beads weigh about 100kg/cubic meter. Also, mixed with cement, used to insulate ovens, furnaces, cryogenic storage, etc.

Basically mix, dry, with cement in 3:1 volume, then add water till a firm mix, and form into the shape you want. A test I performed was to make a 25mm thick slab, about 200mm square, and cure well. An Oxy-Acetylene hot flame played onto one face till the surface was orange/red, with the flat of my hand up against the opposite side - warm but far from uncomfortable to keep my hand there!

You can make any shape you want, and it does not seem to powder much, unless you rub two like surfaces together.

The only heat insulator that would not do that is probably in the family of ceramics.

Joe

This is a very low temperature so why not use vermiculite board? Stands up to hot red heat and at 300c won't even tarnish.

Thanks Guys,

Lots of ideas here. Is vermiculite less powdery than the calcium silicate, if it is fine.

Chris

Would painting with a solution of water glass (sodium silicate) solve the problem?

Vermiculite board is the stuff CuP alloys sell to make brazing hearths, see **LINK**

Vermiculite/skamolex will be fine, the only thing that spoils it is getting flux on it.

Thanks Neil,

I guess the thing to do is try vermiculite.

Chris

Rockwool? After all someone who has made one recommends it.

Thanks John,

Rock wool is on my radar though its lack of total rigidity needs to be appraised. In the design I am using the hot plate will sit on the insulation as well as the lid. Is it rigid enough...that is the question, it certainly solves the powder issue though.

Chris

Another angle is to make a thin stainless steel box or find a suitable shape in cooking utensil and surround with rockwool. Need some kind of asbestos paper substitute Kaowool? for electrical insulation or are you making a big box with a hot plate inside it?

Hi,

I would agree with Dick that painting it with a solution of water glass (sodium silicate) would fix the problem. Years ago I made a small oven for use in a lab and it was insulated with a putty of powdered asbestos and sodium silicate solution. It was plastered on and dried by turning the oven on. The surface was stable and I used it for years.

Regards,

Alan

Thanks for this at first glance it didn't seem plausable but if you second it it must be. Also carbonising it apparently may help. a little experimentation as always may be a good idea.

Chris