Portable Compact 6" RMH Hybrid w/ internal mass and all cast internals

Progress?
I made two sacrificial wooden burn chamber moulds and I'm happy with this 2nd one, I made a slight upward angle on the roof of the burn chamber increasing slightly toward the riser, which helps with fast start-ups and immediate draw pull because heat rises. I will probly wrap this internal wooden core in wax paper or something when it's time to cast the refractory and perlite main core

Might have to fire up the cement mixer soon boyz

looks beautiful! are you planning to use any loose perlite for increased insulation value? maybe you could do a little of both. do a thin refractory cement riser made from two sets of tubes one 6" and one 7 or 8" and fill that gap up with refractory perlite mix and then a 10" tube with loose perlite for maximum insulation value and increased temps in the heat riser?

keep up the good work, looking great. this will turn out to be an amazing proper rocket stove my friend?

any secondary last minute plans for the expanded feed magazine a propane tank would fit in there i see the space it will fit? if you do use a propane tank you can bolt it to the front metal and pour the cement around the propane tank and wood mold core and boom... a mega feed magazine! it would be an easy mega upgrade.

i want the core to be strong and ive designed the casting to be no thinner than 5-6" at its weakest/thinnest point and with my 6" square feed i can still do my usual pellet burning if need be. I could possibly go 6"x8" and use a lid if need be , without making any weak spots in the cast core...

my last model had a 5" OD feed tube so this 6" one will be at least 11 cubic inches more for CSA- so it is going to be slightly oversized. I like the external oversized feed mag you use- but i cant use it on this model without risking thin/weak casting areas in the core and i want the square pellet feeder possibility to remain.

I have bought 75.oo worth of perlite so it should be well insulated- we will soon see what i have room for. I'd like to save room to fit a vaccum hose down inbetween the outside of the riser and the barrel , for ez 2ndary clean-outs by removing the lid and sticking the vacuum wand in the bottom of the barrel . The primary clean out is in the front access port

my system is larger than yours and i have no problems using a stick with a piece of sheet metal in the shape of my burn tunnel kinda like a garden hoe to drag out the ash and it works very well and very easy for me and im sure it will be easy for you since you are constructing a front port.

Using a propane tank will strengthen your core not make it weaker. remember you are pouring it into a metal shell and the tank would be bolted to the metal shell frame and it seriously is stronger. my outer shell is smaller than yours. i use a half 55gal drum for my shell frame. believe me the tank provides more strength not less. it would be a strong upgrade and is a bolt on. you can design an insert to plug into your tank to use pellets. i know i could totally use pellets in my system with ease and you are one of the smartest tinkerers ive seen and are very capable of building a tank pellet upgrade add on.

also another thing to strengthen your concrete shell is to use rebar, chicken wire, field fencing, or also pink fiberglass fibers mixed into your concrete mix before you pour it into your metal shell. that way you will feel comfortable upgrading to the tank.

a little off subject but when a person builds a cast of the burn tunnel and riser why not add rebar or something to help everything hold together better???
thanks

Anthony Donner wrote:a little off subject but when a person builds a cast of the burn tunnel and riser why not add rebar or something to help everything hold together better???
thanks

yes it would

i have a few different types of rebar and mesh made for that- its possible i may use heavy mesh near the top.

i have to see if this cement mixer works next- and i will cast it likely after the last frost which should be done soon

John McDoodle wrote:i have a few different types of rebar and mesh made for that- its possible i may use heavy mesh near the top.

i have to see if this cement mixer works next- and i will cast it likely after the last frost which should be done soon

i would use the rebar along each of the sides of the propane tank and the mesh along the top near the tank on both sides.

i wont be using a propane tank fuel magazine on this unit - however you did inspire me to oversize my feed tube -

but we will likely build a large mag unit next, for my stepfather. he wants a rocket now after seeing mine smoke free and efficient - and he wants large capacity for long unattended burns. he currently has a smoky stinky wood stove which is not efficient

Rebar doesn't work on cast refractories, because of the different rate in expansion between metal and the cast refractory.

In foundries, they use stainless "mesh" or needles.

http://www.ebay.com/itm/Refractory-Reinforcing-1-430-Stainless-Steel-Needles-10-/130337734449#ht_76wt_1108

good point max

my last cast is okay and it has no rebar at all. (but it has some of that 6000psi fiber enforced stuff)

maybe this one will be fine without fiber or mesh... ? even if it cracks the steel tub should hold it all together, right?

It should hold it.

Most of the refractories crack at some point in their life.

im pretty excited now- today i located our cement mixer and its clean inside and it works still ! its been sitting outside for a decade and it still works great somehow ! its going to make my life much easier this time hopefully

do i need the 6000 psi enforced fiber concrete mix like i used last time? this time i planned on using this rutland refractory cement instead. my last compact RMH hybrid casting i made is really strong and i want this one to be also

stay away from using the 6000 psi enforced fiber concrete mix in your burn core and riser. you may use it after you pour your core on the exterior of it. 6000 psi enforced fiber concrete mix is NOT refractory and will eventually break apart. you may use the refractory with the other high temp materials for the core then fit the propane tank in bolt it to the outer shell then pour the 6000 psi enforced fiber concrete mix on the out side of it all between the core and the outer metal shell.

Slowly making progress in my lack of free time.

Sand is okay to use in the cast cob mix right? I think I've also found some backyard clay so I might throw some earth from home in the mix , more than last time

Here I've notched the angled ceiling of the burn chamber in order to mate up the moulds as best as possible. I have a good feeling about the angled roof of the burn chamber, and this project in general

These photos are all temporary mock-up just to get a better idea of what it's going to be like in looks and size

i need a personal opinion

doors facing frontward for a simulated appearance of operatable doors and accents? or use doors as the (hidden) back-side facing the wall? if i use the plain back as my front i can install a temp guage in that round lower hole in the lower side

have you thought about using the doors to view the fire somehow?

not really. i had considered moving one door to the inspection cover front area- but changed my mind. the doors had plastic/fiber window pannels but i removed them and put a big sheet of recycled stainless in there. there could be a window at the inspection door / primary ash clean out area- like a small woodstove front door with adjustable/close-able air intake for pellet burning occasions


Update :
New YouTube video went live today on updates and progress on this cast core permenant mould
https://www.youtube.com/watch?v=Tf4IEOY38EE

I did so many rivets today that I don't want to do any more for at least a week lol. I gotta say tho, it's really getting nice and purdy and sturdy. I chose to use the doors as the front facing side and I cut my ash clean out inspection door hole accordingly because I want the bell barrel heat exchanger to be on the right side of the unit , looking from the front which is now the doors

new video went live today
its not very "compact" or "portable", she's a brick house, but it does have a heavy base and caster wheels if that counts LOL

heres a link!

Rocket Stoves Ep#18! Cast Core Model - Finishing

today i test fired the core and burned out the wooden mold/core!

here is a few videos, but there will be more uploaded later also.

heres 3 video links from todays test-fire!

Rocket Stoves Episode 20! cast core model first fire


Rocket Stoves Episode 21 cast core fire & curing


Rocket Stoves Episode 22 cast core burning clean


have a nice day

I'm at a brain fart for riser ideas.   I've seen people online build them with cob which is something I'd like to try, but it seems they all have metal in the inside, which is kind of the opposite of what I want to do on this project, to keep the metal critics happy, and for myself as an experiment.  I'm also sick of buying stuff, and cob seems like cheap and easy and proven and easily available.  I also like earthen soil cement, and firebricks.  I'd build a firebrick riser if they weren't so expensive around here.   So should i make a con riser?   Earthen soil cement?   I still have perlite left.  Can it be done without steel inside?    Do most cob risers all have a steel inner pipe?  

Thanks

I wouldn't use solid cob, but if you have perlite and clay, you can cast a riser that is a mix of perlite with just enough clay to stick it together, and no more water than necessary. You have probably seen the test - make a "snowball" of the mix that holds its shape, but with firm finger pressure pops into fragments.

You can make an outer shell of stovepipe. If you want a 12" diameter shell, take two 6" stovepipe sections, "unroll" them a bit so they each form a half-circle, and snap them together normally. The way circular geometry works, two 6" diameter circles have the same circumference as one 12" circle, and a 6" and a 4" equal one 10".

You can use heavy-duty cardboard for a sacrificial inner form. Sonotube concrete forms if you can find it in the right size works fine.

thanks glenn for the help.

  i dont have pure clay, but i do have perlite and pipe sections, and the earth around here is very clay rich and "sticky".  can i use found earth harvested from here?  i dont really want to take too many chances but ive already conducted 99 experiments lol.  maybe i should just go buy some "fire clay".

i wonder if only a small amount is required to hold the perlite together, if earthen/clay and refractory cement would make a good refractory adhesive?  i know i can buy small tubs of refractory locally, but found clay is cheaper lol.  

i have no problem burning out a cardboard tube, similar to how i did my core with sacrificial wood.  are 6" tubes available?  i figure the outside diameter of the riser should be no more than 10" max.  inside diameter will be around 6".  i would prefer 6"I.D. and 8"O.D. but would 1" be thick enough for the permenant riser?  it could be made replaceable if need be.

heres a recent 4hr torture test video series i posted today, testing the core mostly.

episode 28


episode 29


episode 30


ep 31


ep 32

If your clay soil is good and sticky, it would probably work as the binder for perlite. The clay on the inner face of the riser will be fired to pottery, and if it is low-temperature earthenware clay, it might not hold up too well. The worst likely result would be that the inner face shrinks and cracks some, but the outer layers would still be good. The hotter your core gets, the more important it would be to have high-heat-tolerant fireclay. A 6" core might or might not get that hot.

I would make a sample of perlite-clay as you expect to use it, and dry it and put it in your burn tunnel under the riser. If it is still okay after a few good hot burns, I think it will be fine for your riser.

I have not seen sonotubes smaller than 8" nominal (as little as 7 5/8" o.d. actual), but cannot say they don't exist. Carpet tubes might possibly exist in the right size, or could back up several layers of corrugated cardboard wrapped around to get 6" o.d.

Perlite-clay is recommended to be at least 2" thick to get the insulation, and the structural integrity, to work as a riser.

Greased sewage pipe can be used to form the riser inner surface. Tho, be very careful when pulling it. You can use clingfilm to further enhance the ability for pulling the tube, or waxed paper.

And about clay testing.





http://collections.infocollections.org/ukedu/en/d/Jh2385e/4.3.html

Thanks guys
I was going to take Glenn's advice and make the riser 2" thick, and it's going to 6" I.D. so the Outside diameter should be 10" right?   I cannot seem to find a 10" diameter pipe here locally...   Every local store has 6,7,8" but not 10"    
I could get DUCT pipe at 4" and 6" and put them together but they are galvanized so that might off gas toxic fumes right?  
Ugh.

I've decided I might have to use galvanized DUCT for the permenant outside mold of the riser.  I don't want to but I cannot get 10" stove pipe, or any combination to make 10".   I've also posted some more videos on my YouTube of the core and testing and post test inspection on the core.   Links will be posted later.

If you heat the galvanized duct in a fire outdoors (stay upwind of the smoke), the zinc will convert to a stable and safe form, and you can then use it indoors. The fire will also anneal the metal and make it easy to bend to the right radius.

Another possibility is to use two sections of 6" black stovepipe, snap one joint together normally, and screw the other together with a 2" or so overlap. It wouldn't work as duct, but it would work fine as a shell to hold perlite-clay.

Thanks for our help and advice Glenn.

I knew the stovepipe wouldn't work smoothly at 10", and I decided to grab the duct/vent pipe.  It's against my religion to use galvanized normally but I'm sure I'm not the first, and after the riser isn't that hot anyway.  
I will likely burn it off first if I can, and or paint the duct with hi temp stove paint.  
 I got a 4" and a 6" pipe and put them together after cutting them to length individually.
Maybe tomorrow I can do some more

So what is your formula for the riser?

William that is a good question.

I can't tell you an exact recipie but I can tell you it's a recipie for a DIY small forge insulation.  Clay cat litter, plaster of Paris, perlite, water.   Probly 1 part clay littler, 1 part plaster, 1.5 parts perlite, and a shovel full of earth.    I plan on trying that for my first riser cast attempt (without any permenant steel inside).  I will burn out or remove the inside riser mold pipe, but the outer 10" mold pipe will stay as part of the new riser.

Thanks for easing my mind about using galvanized pipes.   I know people who have gotten deathly ill from welding it, but I'm sure the outside of the riser won't get to welding or melting temperatures.

Gypsum plaster will disintegrate at the temperatures inside the riser. You may see the riser interior surface slowly eroding with use.

I googled "plaster of Paris temperature rating"
This big top paragraph came up

I've already done the new riser today.   It may require days of curing and extensive testing, but the riser should be easily replaceable if need be.   Hopefully I won't need to but if the plaster will hold up in a metal FORGE, I'm sure it should also hold up against a little 6" rocket, post-mass

My bad - I read a reference to gypsum calcining temperature (which apparently can vary from ~100 to 400 degrees C) and assumed that calcining entailed disintegration. It actually does entail some weakening, not sure how much:
"the chemical composition of gypsum. It is hydrous calcium sulfate, with the chemical formula CaSO4-2H2O. This means that it is calcium sulfate (plaster of paris) combined at the molecular level with water of crystallization. This water makes up about 20 percent of the gypsum by weight. Although gypsum does not burn, it does change its chemical formula and structure when raised to high temperatures: the water molecules are detached from the calcium sulfate, weakening it and reducing its fire resistance."

I was thinking the same thing about the plaster.
I hope to see a great outcome,plaster of Paris is cheap and readily available.
The little litter clay has also been dismissed as being prone to cracking.
I am hoping this concern is overblown.
Besides, the inner surface of the riser may be fused together from the heat by the time the metal fails.

william, i am also hoping for a good outcome, but its purely experimental.  i guess its already been experimented with by DIY forge guys forging knives and melting alum cans, but who knows.  one way to find out lol.

also, the metal insert wont burn out because i will remove the inside pipe before i fire it, well thats the plan anyway.  no steel inside is my only mission on this experimental stove.  if i build a 3rd stove, it would likely be more like my original stove, but with a 6" feed and burn tube, lined with firebrick, ive already drew that type of design and posted it here on one of my rocket threads.   i just feel like steel and bricks would be easier to work with.  however easier isnt always better either.  but i digress, so i march onward.  i want to use firebricks someday but they are like 6$ each around here! :O

heres the latest video links on this project.

episode 33 Inspection after torture test part1


episode 34 Post-test inspection part2


episode 35 Perlite, Kitty-Litter & Plaster Riser?


episode 36 Experimental riser curing