rocket mass heater riser - precast molded ceramic fiber tube

Mud and I are working on a book.  This is the part about molded ceramic fiber risers.  We strong encourage everybody to share their experiences.  We hope that this thread will grow to ten pages of information about molded ceramic fiber risers.


The best. The sexy beast to beat!

$300 to $600. We are perpetually trying to find something as good for a lot less coin.  

If you don’t mind the expense (or tracking down a place that will sell it to you), it’s lovely.   2 inches thick and pretty light.   After seven years of heavy use it still looks brand new.  If we ever have a rocket mass heater that seems like it could work better, our first step is almost always to replace the riser with a molded ceramic fiber tube.  

Another perk is that there is zero construction involved.  Just set the tube in place - all done.  If, for any reason, you need it shaped a bit different, a couple of minutes with a utility knife will give you what you want.


Mud says

If you want to try to find this, search for “cast ceramic tube” or “molded ceramic fiber riser sleeve”.  Usually used in the foundry industry as a protective lining for pouring molten metal into forms.  

The following are some excerpts from the 4-movie set "Better Wood Heat" and you can see some of the molded ceramic fiber tube risers

Molded ceramic fiber tube images.

If anyone finds a source for this, I'd love to know about it.

Thanks!

So after several days of concentrated frustration trying to pin down some company, any company, that might make or supply these anywhere in the US, I have almost completely struck out. One brick wall after another. Most of them don't even seem willing to say what a minimum size order would be, let alone provide information about what exactly they make or offer.

The only exception to this stonewalling has been Carpenter Brothers in Wisconsin. They are offering "insulating riser sleeves" for metal casting. These are intended as disposable, single use ceramic fiber+sand forms to be poured full of molten metal. In 6" ID tubes, they are asking $5.20/lineal ft, minimum order a box of 18. This would be a fantastic price if they worked, but since the material this thread was started to discuss seems to cost about ten times that, they clearly cannot be the same thing, so I have no idea whether they do work.

This is the only firm result I have been able to reach by using the search keywords "insulating riser sleeve," “cast ceramic tube,” or “molded ceramic fiber riser sleeve,” Although dozens of other suppliers turn up, none of the others will allow themselves to be pinned down for ANY product, price, or even minimum order.

Does anyone have experience using disposable foundry sleeves?

Does anyone have much more specific search terms or descriptions to try to crack through all this stonewalling by the other companies? It would help a lot if, rather than describing what I am trying to do and trusting a sales rep to fill in the gaps, I could use their exact industry terms!

Does anyone have specific sources in the US for the kind of vacuum formed cast ceramic tubes previously discussed? Because I'm failing here.
Thanks all for all you do.

April,

You have discovered the other side of the reason i wanna drop this material.  The sellers are bizarre.

Hi April;
I also did the search you are attempting and I had the same frustrating results.
If you want the next best choices, then a High temp (2600F+) insulated firebrick is an awesome riser.
Next is the Morgan superwool five-minute riser, cheaper than insulated firebricks and every bit as efficient.
Lately, there has been some concern about the bio-soluble ceramic blanket.
In its unheated condition, it is completely safe to handle without personal protection equipment (PPE)
After Bio-soluble cfb is heated to riser temperatures, it changes form and becomes mildly hazardous,  PPE is recommended if handling a used bio-soluble riser.
Some folks have concerns that these fibers could somehow travel thru an RMH rise up the chimney and somehow become hazardous outdoors...
In my opinion that is not going to happen.   Yes if you are working inside the bell or inside your pipes in the mass you should wear PPE
The fact is, that if you are working with your head inside the bell/mass you would be foolish to not wear a dust mask/respirator regardless of any bio-soluble cfb used in the riser.

As a side note April, I investigated the company you found.  (Skyline)
Their bio-soluble CFB may supposedly meet Euro standards but it is made in China...
As much as I would like to offer lower prices on my products, I'll pass on offering any of their bio-soluble CFB.

Adding to my (short) list of sellers who will actually talk to you:
https://hightempinc.net/risers/

What they offer is also foundry sleeves for metal casting. They add that these are often used as permanent liners in kiln flues, which is close to what we're doing, so that's promising. So the product under discussion seems to be similar to what Carpenter Brothers has, although possibly a different formulation. They say, 6" tubes, 12" long, 1/2" thick, 30 per box, $12 each, which is at least sort of in the same price range. So apparently cartons of these things can be bought -- but only by the carton, and only in 1/2" thicknesses.

If you want something 2" thick and 4" long, it would apparently have to be custom formed. No wonder it costs $300.
OR. *Possibly* these people work in larger sizes: https://danserinc.com/capabilities-vacuduct/  
But we have yet to see whether they return contacts.

High Temp Inc did say they were willing to ship UPS but if so a few broken ones were inevitable so they'd really rather send things freight. But at least the boxes are light enough you don't need a pallet fork to unload.

The High Temp Inc salesman, like Thomas, was also a big fan of rigidized wool blankie. Which may be the simplest way to go.

"Skyline Components", for anyone who didn't catch the post in the other thread, was offering surprisingly cheap CFB, so I'm not surprised it's manufactured in China (then again, do we make anything at all in the US anymore?). They do not, however, offer risers, only board and blankets.

I looked into the feasibility of producing a molded ceramic fiber tube such as this.  It's perfectly doable, but the downside is the cost of the loose ceramic fibers and their availability.  Not to mention they are hard to handle without polluting the immediate vicinity with nasty fibers.  In my humble opinion, it might be a better option to attempt to spritz rigidizer on some Morgan Superwool and wrap it around a section of pvc or other pipe a few turns to give it form.  Wrap some chicken wire around it for additional support.  Whatever floats your boat.

10/11/2022 Edit.

It looks like I'm going to put my money where my mouth is.  With the way things are looking right now and energy supplies being used to wage war, I'm going to err on the side of caution and put off the RMH build I'd like to do (if I ever actually make up my mind what that is) and get everything ready that I will need to throw a decent J-Tube with barrel and bench together in a hurry if need be.  I've ordered some Morgan Superwool and  I'll be attempting the riser build that I outlined above in this post.  In addition to that, after withdrawing the pvc pipe form, I'll be smearing a hot fact of hi temp refractory mortar over the rigidized blanket, inside and over the chicken wire outside, protecting it from oxidation.  With a little doing I'll be able to set this upright and form the base into a nice stable pedestal that will sit securely over the core, eliminating any worries about it tipping over.  I'll keep you all informed as to how it works out.

So Carpenter Brothers did get back to me about their riser sleeves. They offer two, both intended as disposable forms for metal casting.
The LD Riser Sleeve in 6" interior diameter was $5.20 each, minimum order a carton of 18.
Its composition:
COMPONENT     WT%      CAS NO.
Aluminosilicate 20-30% 142844-00-6
Silica quartz      50-60%  14808-60-7
Free silica           0-0.1%  14808-60-7
Calcined kaolin    0-5 % mixture
Iron oxide             0-1 % 1317-61-9
hexamethylenetetramine 0-1% 1344-28-1

That seems like an awful lot of sand to do much insulating.
The materials SDS also did include a number of dire toxicity warnings, including cristabolite, but of which the most concerning was an order to "Keep away from heat/ sparks/ open flames/ hot surfaces" and further notes that it released all manner of dangerous gasses during combustion, including fluoride, generated extremely high temperatures, and could not be extinguished with water but only sand. This does not sound good for our application. When I asked the sales rep about this, his reply was:
" I don’t know why it says that. The only thing that would make sense to me is that they just copied the SDS from the exothermic riser sleeves for the insulating riser sleeves and didn’t realize it or no one ever mentioned it. "

Anyway, he then added that the higher quality, more insulating one would probably work better for our uses. Haven't got a price on that but I'm guessing it would be more in line with High Temp Inc.'s offering of $12 each/ minimum order of 30. The composition of these:
"Aluminosilicate Refractory Ceramic Fiber   61-71%
Crystalline Silica (Quartz)    12%
Colloidal Silica      4-7%
Modified Starch    4%
*Note: Rigidizing is a secondary operation that will ultimately affect the concentration of colloidal silica in the final product. The concentrations listed above reflect that of a product prior to rigidizing; post-rigidizing concentrations vary from product to product."

For this more insulating sleeve, he then sent me the SDS for Morgan Cerablanket, classification 2300*F, which we have probably all seen before. Plus the following note on temperature classification for both products:
"But riser sleeve manufacturers do not list these working temperatures because the riser sleeves are designed as a one-time use in a mold and will burn up, but the sand mold surrounding the riser sleeve prevents the metal from running out if the sleeve burns up."

So ... if I am understanding him correctly, it is essentially a 1/2" thickness 5 minute riser soaked in fumed silica, with a little bit of sand. Only you have to buy a whole carton at once.

I still feel like there have to be some kind of magic words I'm failing to say to get them to understand what I'm after: rigid, sturdy, insulating, long lasting, high temperature use without the binders giving way, resistant to flux and wood gas attack, not too poisonous. In other words, the aforementioned "sexy beast to beat!" But searching "Ceramic chimney liner," which seems to be what Peter calls it over in the EU, just gets me to terracotta, and adding "refractory" to the search terms only turns up an alumina cement coating for old terracotta, while "ceramic fiber chimney liner" gets me to the right product ... in China. The Vacuduct people, who do seem to be making exactly what we're after, when contacted pulled the same game most of the rest of these companies have done: I asked them what they had and what the minimum order might be, but they turned it around and said they just couldn't answer that until I told them what they had and what the minimum order would be. (??! So frustrating. Carpenter Brothers and High Temp Inc do at least get credit for not pulling that nonsense!)

... So that's as far as I've gotten.

Vitcas make ceramic fiber board  and mat rated to 2600f, they also sell a few different coatings.
All the bio soluble products like Morgans super wool seem to be rated  lower than pure ceramic fiber and therefore flux at lower temperatures!!  
I have gone right off using ceramic fibre but, if I really wanted to build a tube, then I would use 1” ceramic board cut accurately with a bench saw.
You could cut it into full length strips with the correct angle to make the Necessary  amount of .. say 1” strips.. to fit inside an 8” stainless steel tube.
The finished tube could be coated with Zircon or something similar but the main issue would be wearing full PPE and cutting the board outside with a hover attached to the saw!
https://shop.vitcas.com/products/insulation-materials.html
Re the glass distance, in my small vortex stove i have managed to crack ceramic glass set at 40mm from the flame path, it is now set at 60mm and holding up fine.
You can get false readings from a temperature gun while pointing at glass but the top box on mine seems to runs around 750c at max burn and that is about the same as ceramic glass will stand.

Quick note about Skyline Components CFB since it is mentioned in this thread: Avoid it!
I bought it to make a DSR2 core. It arrived with almost all broken/crumbling corners. It fell apart under flame. I was ONLY able to use it by treating it with a liberal amount of Sodium Silicate. I made this video at the time to demonstrate it's crappyness https://www.youtube.com/shorts/lwmUGAVHQtk

In the US, Ceramaterials will apparently fabricate vacuum formed ceramic fiber for individuals and small orders. Yay, found someone.
Less yay, for a 12" length of 6" ID tube, such as would be suitable for the DSR3, they quoted me:

1 PC - 2300F MD BOARD 8”OD X 6”ID X 12” LONG - NOT RIGIDIZED AND FIRED - $382.50/EA
1 PC - 2300F MD BOARD 8”OD X 6”ID X 12” LONG - RIGIDIZED AND FIRED - $466.00/EA
$175.00 Set Up Fee
LEAD TIME: 3-4 WEEKS ARO

plus shipping, plus 3% credit card or PayPal fees.

So, all told, $700 for a one foot, 6" interior diameter tube.

Wow!  That's outrageous!  I still have to obtain some 2x4 wire fencing, a little extra Sodium Silicate and something to make a hot face on the rigidized Morgan Superwool.  Any suggestions for the hot face material.  Would a basic masonry mortar be good for that?  I'd like to keep this experiment simple and executed with commonly available materials so most anyone can follow on if they'd like.

Thomas,
https://donkey32.proboards.com/thread/3676/disintegration-superwool-ceramic-fibre-board
This is a useful thread, once you skip over the macho squabble in the middle. The upshot seems to be that zirconia coatings help significantly. As for a mortar hot face, I'd think a refractory mortar would do you some good, if that's what you meant, but not a mortar based on portland cement, which would not stand up to the heat.

By the way, Ceramaterials did follow up about that quote when I didn't reply at first. They offered to drop it by 30%, which is still more than I'd pay for a single piece -- but it did leave me with the impression that they were sincere businesspeople, and if someone were wanting to get in bulk orders for, say, production of stove kits, it might be possible to negotiate with them into a more reasonable range. After weeks of frustration calling around to everyone I could find, they've been the most responsive company I've contacted. Also, the retail section of their website does bother to publish detailed data sheets without you having to chase them down. So credit where credit is due.

They may wind up with my retail order for the basics, but I still ain't paying that much for a single custom tube.

Thanks April.
Yes, I was referring to refractory brick type mortar.  I can find that at my local home store.  But there are a lot of possibilities.  Satanite comes to mind, but I believe that is cost prohibitive.  What do you think of this?

ITC-100HT is a versatile high temperature coating rated up to 5,000℉ proven to achieve outstanding energy savings and refractory protection. The coating is used as a covering for ceramic fiber insulation, castable, or brick refractory. The material works by reflecting radiant heat back into the furnace, kiln, or forge to achieve high temperatures quickly and efficiently. ITC-100HT improves the IR reflectivity of all furnace linings while improving fuel efficiency and overall throughput. Use the coating as a standalone product or a base coat for other ITC coatings. Applied by sprayer or brush after diluting with one part water to two parts ITC-100HT.

If you are in the US, small quantities of both satanite and ITC-100 are available repackaged from online sellers. This is more expensive per ounce, but saves you buying whole sacks or quarts. Poke around and see what you turn up.
If you are on the other side of the pond, check the brands Fox has recommended.

Got a response from Danser Inc.
__________________________________________________________________
We can make:
6” ID x 8” OD x 14” L
2300 DEGF VF Material, 16-18 PCF
Outside machined smooth
One (1), $225.00
2-3 weeks ARO
Price can be significantly lower for higher volume.
We use a colloidal silica for the binder, which maintains the structure once the “green” binder is burned out. 82.9% Aluminosilicate
https://danserinc.com/capabilities-vacuduct/
______________________________________________________________

I had this priced at 14 inches because that's close to the length of the horizontal afterburner needed in the 6" DSR3 core. Nice to know that someone out there is willing to even quote small orders such as this.

hello,

any thoughts on rigidising the ceramic blanket to make it safer to manipulate?
Do you think we could save ourselves the firing stage after the silica coating dries, and just place it as a riser once it´s dry and wait for the descomunal heat in the RMH to make it rigid?

I am attaching a link I found about this process

David.

I do think it would be just fine to use the ridgidizer as you say.  Once it dries, the item will be hardened and supposedly able to support it's own weight.  My plan is to follow on at that point with some sort of refractory hard face coating on the inside of the riser.  Thomas Fox has been experimenting with it on vermiculite board.  Here's a new one.  Just discovered that perlite come in board form now.  Low cost perlite insulation boards

In the Aslan Core thread, Solomon Parker reports that his ceramic fiber riser sleeve is melting down into glass. It is an 8" system with a ceramic fiber board burn tunnel. He has been burning well-dried lumber in it.

He also indicates where he bought the tube from in the Sates.