cast core idea

Disclaimer ...
I am new to this and the suggestion might be entirely bonkers, if nothing else have a good chuckle on me!

Thinking about design options, for me, I hit on the idea of casting rings that could be grouted together but may also work with dry joints, furnace rope in a rebate.
That would be shippable and modular so different height cores could be built from the same Segments, granted you would still need a burn tube.

The taper is exaggerated in the section and would be necessary to remove the centre core, mould core that is, the outer circumference could either be contained in a spring form or also slightly tapered to ease the release process.

Just a thought ! Am I bonkers or might this fly?

Al

Alistair Warburton wrote:
Just a thought ! Am I bonkers or might this fly?

I think you should try it.

Alistair Warburton : Every time I look at this I see something new, this is interesting ! I think that the Heat Riser / internal chimney is perhaps one of the easiest parts for D.I.Y.
homeowner fabrication. But, two bottom sections could be fitted together to make up the J-Bend, with gasket-ing to allow for expansion ! I Note that all the other cores have
their expansion strip at right angles to what I am talking about though !

For the Craft ! Think like Fire, Flo like Gas, Don't be the Marshmallow ! all comments , questions are solicited and welcome ! Big AL

Hay Al, I was thinking a similar thing, well the casting bit at least.

Shortly after I posted the sketch I realised that the bottom section would have been better if it was square, at least one side, so that either other cast sections, or bricks could but up against it.
I hadn't thought about using similar bits to build up the burn tube but it would probably make sense if the casting is hardy enough.

I would want to keep the concept similar though, basic bits in multiples I mean.
The sketch is what I think you meant, it would only take a single adaptable form with removable cores, to produce the parts.
It also occurs to me that mould making would be simplified by making the exterior hexagonal as opposed to round,
I have done a quick sketch of a form, with three removable cores, capable of making all four sections.


What is this "expansion strip" you refer to, it sounds like something I should know about?

I would be very interested in comments about suitable materials, commercial, home grown or a mix.

I like this modular concept for mass production purposes.
If somebody needs a taller version, they simply order extra 'rings'.

Perhaps if they were molded with one concave, and one convex surface, alignment/sealing would be simplified.

Keep the ideas coming.

A2A: Tis time,You really need to go to cobcottage.com to Download your PDF copies $15.oo, of Evans'and Jackson's Great Book Rocket Mass Heaters ,there is STILL
No other book in any language that Contains as much Rocket Stove / Rocket Mass Heater Family Information. (and I don't see a Ha' penny ! )

In the back of your mind you are still thinking about round plumbing parts, and the big difference in the smooth flow of either water, gas, or plasma,over using Square pipe, to
which I reply, I'll live with the noise, and heat is what I want, just like I want a nice super hot secondary Burn ! And accuse you of 'thinking inside the box' For the Craft!

Think like Fire, Flo like Gas, Don't be the Marshmallow ! All comments , questions are solicited and Welcome Big Al

concave and convex surface ....
Interesting I hadn't thought of that, although now I am I wonder if the whole thing might not be prone to bending like a giant spine.
It defiantly sounds like it is worth some thought though.

As I said earlier "I know nothing" but I think the benefits of this approach would be:-

Faster drying as sections will have a big surface area in comparison to their volume, much greater than a single massive part.
Less massive parts are likely to suffer less slump during casting so forms can be lighter and simpler, also filler and air pockets will not get compressed so the density of the casting should be similar for all parts.
(Don't actually know if this would be a problem in the first place)
Individual form cores can be slightly tapered so that taking them out is possible, again I doubt you could do this with a tube although I appreciate a tube could be burned out.
A poor casting is not a total loss.
Sections damaged during construction or even use can easily be replaced.
Riser height is adjustable during development.
Different section parts could be substituted, all be it with a new form, but still changing the dimensions of the burn tube during development would not require the whole casting to be scrapped.

Disadvantages:- (It seems only fair)
More complex and time consuming to build, cant do one big mix without multiple forms.
Might leak and need grouting.
Parts could crack into relatively small chunks and become unusable.

I expect I will not know if this is even viable, let alone worth while, until I try it.

We will see ... I am currently researching cast-able insulating refractory.

Al

I think you left out one big advantage: a potentially large difference in temperature from one section to the next is less likely to cause serious thermal stress and lead to crumbling.

"We will see ... I am currently researching cast-able insulating refractory. "

When doing your investigation into cast able refractory consider adding stainless reinforcement needles they will add significant strength and resistance to cracking.

A simple low cost refractory mortar can be made from 3-1-1-1 sand, fire clay, hydrated lime, and Portland cement, all measured by volume. Add water to get a creamy peanut butter consistency.

You may also want to consider stepped rings instead of flat that way you could avoid the need for seals as the laminar up-flowing nature of flue gases would create a self sealing labyrinth.

The rings could also be constructed with a tongue (T) top, and groove (G) bottom built into the casting to have the same effect.

Chip

Chip Friedline : I am making an assumption that you have some firsthand experience with early models of Ianto Evans' Early models of his J-Bend Rocket stove Mass Heater!

With todays improvements In using more insulating materials in the Heat Riser /Internal Chimney,or in wrapping the Heat Riser in insulating blankets the internal temperatures
have risen to the levels that will cause the failure of all portland cement and Lime mortars!

Further we are at the point that some of the cast-able core units are burning very close to the Theoretical limits for Wood fuels - Around 3500 F ! With new fire brick we can
literally Dip the fire brick in a clay slip before stacking the fire brick! This will achieve a nearly perfectly smooth internal wall on our Heat Riser minus all but the smallest pin hole
leaks between the interior of our heat riser and the exterior. This we can further cover/wrap in Perlite and Clay Slip or a fibre wool blanket !

I have a bias against the use of Portland Cement for nearly any other use than a slab floor with or without hydronic heating, but in this case I would save lime plasters for combination
tile and brick chimneys,limiting its use to the bricks only, and for waterproofing exterior Cob or Adobe Walls !

For the Craft ! Think like fire, Flow like a Gas, Don't be the Marshmallow ! As always your Questions / Comments are solicited and welcome ! Big Al !

Alistar Warburton : You can not keep a good idea from Surfacing again and again ! Come back and share some more ! Big AL

Any experience with using fired clay flue inside castable insulation mix? these are available in useful sizes. http://superiorclay.com/flue-liners.php

Okay, long time Lurker, first time poster. I was hoping to Lurk longer so I wouldn't make my first post sound stupid, but I suddenly realized I won't be alive long enough to sound intelligent!
Long story short, you don't need to use a solid tapered plug in the mold to remove the core: I cast foundry furnaces quite often, and have a 26 guage core that is a slip form. I have a vice grip welded (behind the hinge pin) to the ends of the slip form.
Using the slip form core means that I end up with an (almost) perfectly smooth joint between the "doughnuts" in my furnace to keep from causing turbulence in the flame path. I cast "doughnuts" almost exactly like V1 in Chip Friedline's drawing above (minus the taper, of course).
FWIW, and I have no idea if this will help on an RMH but it seems in my pea brain that this would be an advantage in the Rocket to create more draft in the combustion chimney, I wrap 3/8" vinyl tubing on the outside of the slip form after I expand it, barber pole style, to create a vortex effect around the crucible. I know that there is no crucible in an RMH, but a vortex is a vortex, and creating more draft creates more draft...

C.Ray Gill wrote:I cast foundry furnaces quite often, and have a 26 guage core that is a slip form. I have a vice grip welded (behind the hinge pin) to the ends of the slip form.
Using the slip form core means that I end up with an (almost) perfectly smooth joint between the "doughnuts" in my furnace to keep from causing turbulence in the flame path. I cast "doughnuts" almost exactly like V1 in Chip Friedline's drawing above (minus the taper, of course).
FWIW, and I have no idea if this will help on an RMH but it seems in my pea brain that this would be an advantage in the Rocket to create more draft in the combustion chimney, I wrap 3/8" vinyl tubing on the outside of the slip form after I expand it, barber pole style, to create a vortex effect around the crucible. I know that there is no crucible in an RMH, but a vortex is a vortex, and creating more draft creates more draft...

C.Ray, I've been wondering if a slip form is the way to go here. Any way you could post some pictures of your form set up?

C. Ray Gill : Yes! Pictures please ! For the Good of the Craft! Big AL !

Sorry, I just got home, I work weird hours. I'll try to get into my shop this week and get pics if I can. It's a REALLY simple slipform that works REALLY well for my application, I hope it helps you with yours!
Cross your fingers & be patient with me and I'll post pics asap.

When I get a chance, I'm going to build a small RMH to experiment with- just wondering if a "scale" model will work well enough to experiment with? I understand that the thermal mass & heat do not scale up & down proportionally, but will I at least be able to try a scale model to get a "feel" for RMHs? Thanks in advance!

C. Ray Gill : While it is possible to build a Rocket burner as small as 3 '' successfully , exiting immediately into a vertical chimney, with no attempt at running your
hot exhaust gases horizontally through a Cob Thermal Mass Bench, 4 '' is as small as it is practical to try to scale down to! Actually practical is to strong a word, it
would be much more ''practical'' to build a conventional 6" Rocket Mass Heater RMH, as proof of concept before trying to see if you are blessed with a location that
makes a marginal 4'' possible !

There is a state of still or stagnant air, right at the surface of all your ducting, this is usually referred to as a condition of Laminar Flow with the very hottest gases
being channeled down the very center of the ducting ! I wish the condition was referred to as laminar non-flow, it would make the explanation easier !

Two things, This is were I repeat my recommendation that you go to rocketstoves.com to download your PDF Copy of "Rocket Mass Heaters ", with
over 100,000 RMHs built word wide This is 'The Book' most used to create them, and allows you to come back here and know you are using the right words for the
right terms and conditions ! (and I do not make a nickel off of this !)

2nd, plan your project for good weather as you will want to do your 1st build of EVERY New RMH out of doors ! For the Good of The Crafts ! Big AL !

I used a 4" "rocket box" or "Justa" stove with a few (fairly) horizontal sections of exposed pipe for more heat exchange to heat my MH with last year. Depending on the wood and the weather it worked OK to frustrating, and took a lot of tending (every 15-20 min). I don't think it would be enough right now (6* outside, different place).

Before I moved I was working on a 5" system within an old cast iron stove, wish that had come to fruition. It still may as a shop heater.