homemade rigidizer #2

[Vito]

I'm forced on starting new threads with the same subjects due to forum problems, which someone should solve. PROMPTLY.

it's really frustrating, not being able to post anything...somebody take care of it. I've already lost about 6 posts, together worth 1 hour of writing...

 

anyhow, here's a reply to frosty from previous thread...

Yes Frosty but what are you using currently to liquify the mix and make it workable, so you can spread it on? Water?

 

Actually, could you please explain why use zirconium silicate in the first place? It doesn't want to dissolve in the mix, it doesn't vitrify under ''our'' use, why is it there then?

And also, shouldn't the kaolin act as a binder and the matrix for the zirconium? Afterall, kaolin will vitrify under the temperatures which we use.

Why just not use more kaolin instead of using more zirconium? Something like 75% kaolin and 25%zirconium+water until you make it very thin?

 

What makes zirconium so invaluable in that mix?

 

Thank you for clearing things up, I appreciate your answers and your help that you're willing to share.

[timgunn1962]

As I understand it, the Zirconium Silicate is intended to work as an IR reflective component in the coating. The idea is that IR radiation is reflected back from the walls to the workpiece where it can do the most good.

ITC100 is the best known IR reflective coating, but is somewhat spendy. I am not sure if it uses Zirconium Silicate or Zirconium Oxide as the IR reflective component.

I have used both commercial rigidizer and a 10%-by-weight solution of 140 tw Sodium Silicate in water to mix with the 2 parts Zirconium Silicate/One part China clay. Both seem to work reasonably well. Just using plain water seems to work much less well (poor adhesion).

Using higher concentrations of Sodium Silicate seems to be a bad idea, though it may just have been that I didn't let it dry enough before firing. Whichever it was, I got something like stalagtites last time I was careless over quantities. I think I prefer the commercial rigidizer.

[Vito]

tim thanks for answering, will take your advice in consideration.
...offcourse you prefer the commercial rigidizer...so would I but I can't find one in the EU area of the globe....frustrating.

Best, Vito

[Frosty]

I was Forbidden out for the 4th. time.

Short recipe. I'm going to try mixing some of the castable refractory I'm using for the fire contact surface in my new forge as a slip with zirconium silicate and suing it for a kiln wash. I'll let everybody know how it works.

I'm getting really REALLY tired of Invision Services cruddy software!

Frosty The Lucky.

[timgunn1962]

I have no great difficulty sourcing Rigidizer in the UK. Price is not actually too bad; under 20 GBP for 5 litres over-the-counter. 

Both Unifrax and Morgan Thermal Ceramics certainly have distributors in Europe, though my Google-fu is weak and I can't find any actually in Slovenia.

 

[Vito]

Frosty thanks, report how it goes

Timgunn, I will check the suppliers you have mentioned.

One more thing; do you guys think that coating ceramic blanket with a thin layer of refractory prior to coating it with something reflective, would decrease forge efficiency? 
I'm suspicious on refractory sucking up heat... that would probably be minimal? 

Thank you and all the best, Vito

[timgunn1962]

It depends a bit on your setup, but theoretically it increases the thermal conductivity and reduces the insulation value. However, I don't see any real downside in practice. The added thermal mass is minimal, so it's effect on heating time is also minimal.

Making a thin mix of china clay in rigidizer and sloshing it on gets a fairly deep rigidized layer with a thin shell of porcelain once fired. It is much more resilient than untreated fibre and doesn't shed the fibres. This advantage more than offsets any theoretical reduction in efficiency. 

If you do it, you only really get one shot at it. The rigidizer solution/suspension soaks in, but the clay particles are filtered out by the blanket and get trapped in the top layer. If you try to add more after this, the clay layer on the surface tends to form a barrier to the liquid and you just make a mess.

I do it and then paint on my poor-mans IR-reflective coating. 

[Frosty]

Porcelain sounds good but it's kaolin and unless you want to keep your forge/kiln above 2,000f for a number of hours it isn't going to vitrify. I THOUGHT that's what it did but discovered otherwise, ITC company recommends regular re-coating ovens, kilns, etc.

Wet the ceramic blanket before coating or the blanket will dry the wash too quickly and it won't bond well. I have a double lined forge 3/4" hard liner with 1" kaowool outer insulating liner. It's as bullet proof and a concrete dance floor but takes more time and fuel to run. It's a trade off and depends on what you do.

Frosty The Lucky.

[timgunn1962]

I reckon its taken a good 6-8 hours each time to get mine fired and the blanket properly dried out. That's after giving it a good couple of weeks air drying.

With a steel shell and the relatively low-permeability clayed lining, there's no short route out for the water vapour and it mostly needs to be driven out of the ends, rather slowly. Once it's properly dry, it gets the last couple of hours at 1300 degC or thereabouts (2370 degF or a good welding heat for most folk).

I'd like to try building a forge in a mesh shell because I think it would help a lot with the drying and firing time, but I've not found anything suitable at the right price yet. Galvanized would probably be ok because the outer surface temperature is low and the Carbon Monoxide risk means it'll only ever get used outside anyway, but I'm still reluctant to risk it.

[Frosty]

I hang a light bulb in a cast shell to speed drying without checking it. I think you're curing your liner material correctly it's better to go too slow than too quickly.

I recommend stainless steel stove pipe for pipe forge shells. It's more IR reflective, tougher and . . . well, shiny doesn't really count. It doesn't need special tools and you can buy things like wall brackets off the shelf, they make excellent legs. A little drilling and bending of sheet metal for mounts, hinge points, etc. and ss poprivets and it's golden. A 24" length of 10" SS stove pipe needs to be trimmed and there's all the stock you'll ever need for accoutrements.

I've got an old forge made from galvy and though it's nearly 30 years old and never given a whiff of smoke I've had guys turn and run. Literally. That's the only forge I get out if they wanted me to teach them anything. Some folk shouldn't be allowed to use tools.

Frosty The Lucky.