furnace/forge ceramics/insulation/hotface questions

[julianf]

Basically a cupola furnace then?
Im going for insulated simply because perlite is cheaper than refractory.
Plus the rocket mass heater needs insulating.

I thought that cupola furnaces were something different? You fill the furnace wth the melt, and then knock out the stopper, or something?

The hotface is partially insulating. Be aware that perlite melts at the kind of temperatures we're on about. People mix it with stuff, and then, i assume, it makes a 'foam' type of insulation, but, if you just pour it in around the edge, it will decay to nothing in time. (or so ive read! ; )

 

[bigegg]

Cupola furnace:

Long cylinder. Fuel+ore/metal is fed at top, metal comes out at bottom. *usually* the melt is allowed to build up, then tapped - but that isn't what makes it a cupola.
The lack of a crucible, and the fuel mixed with the metal (ore) makes it a cupola. CUPola - literally, the furnace IS the crucible.

From what I can gather, if I make a laminated shell with hotface on the inside, (then a layer of ceramic wool possibly), then the perlite/refractory mix, the perlite should be OK.
I wasn't intending to just add perlite loose - but thanks for the warning!
according to http://www.hessperlite.com/siteGFX/perlitePDFs/Perlite-HighTempApplications.pdf
it softens between 870 and 1093c and melts at 1260-1343c, Held in a refractory matrix, I *think* (hope) it will be OK at the sorts of temperatures I'll be needing - mainly aluminium (750c) and a bit of brass (1050c)

I won't be doing any cast iron with this set up - although maybe later

 

[gaz1]

I would suggest using a 3 system insulation on outside hardcore/grog mix then the refractory mix on the inner coat

if using perlite mix your going to be using more of a one to one mix

its held up for over 2 years with 1600 refractory cement via a rocket stove of ppottys he used a one to one ratio mix on his riser

if you want to look at the 1 to 1 ratio riser of the rocket after one year usage

made 3 days before Published on Dec 11, 2014

1 year update

Published on Oct 17, 2015

not forgetting this is used in daily usage within cold weather / winter period

 

[bigegg]

Just found this:
http://lejpt.academicdirect.org/A11/071_080.htm

Nothing to do with refractories, just a scientific paper that says that aluminium is stronger when poured at a temperature nearer it's melting point, rather than at a higher temperature.

 

[bigegg]

I would suggest using a 3 system insulation on outside hardcore/grog mix then the refractory mix on the inner coat

if using perlite mix your going to be using more of a one to one mix

its held up for over 2 years with 1600 refractory cement via a rocket stove of ppottys he used a one to one ratio mix on his riser

if you want to look at the 1 to 1 ratio riser of the rocket after one year usage

"3 system insulation" ?


I would expect a 1:1 perlite mix - without a hotface as ppotty did (from what I can see in his videos) - to not last long.
I *think* that is a result of the hotface protecting the perlite from the corrosive atmosphere, though, rather than any inherent unsuitability of perlite as in insulator.

 

[gaz1]

its the refractory cement that protects the perlite the perlite is only an insulater for something thin in use with a rocket stove

heres my rocket stove core temps

ive used 1700 refractory cement but if you want a play with my core your more than welcome to come over fire it up and burn it hard to test it yourself before i put it into the wood burner

the firebox is only 5x5" but can be made much bigger

 

[gaz1]

@bigegg ive asked ppotty direct

Yes mix is still intact and shows no wear or damage I burn all winter 7 hours a day and sometimes in summer evenings too you could say its used solid for 7 months, doubt it would make any difference if i used it all the time though.
The mixture was by volume not weight obviously,not 50/50 but it was more 2 thirds refractory and 1 third perlite too much perlite would weaken it and make it soft.

id also like to ask @doubleboost on his furnace build as well

 

[Jim Davey]

Will subscribe to this thread, I've got a pizza oven in my garden to rebuild at some point and I'm sure the info on here will come in handy.

 

[julianf]

I gave my friend a load of night storage heater bricks.

I was round there today, and asked him if i could have one back, to see how it would break up.

Thing is, he had no idea where they had gone!

I mean, how can you just loose 20-off storage heater bricks!

(hes a good enough friend that, if he didnt want to give me one back, he would have just said as much)


Hes put up a new shed recently - my suspicion is that its sitting on small plies of storage heater bricks!

 

[julianf]

Ordered my crucible today - i did go for the salamander A20 in the end.

Ill probably use an a12 for most job, but i figure the A20 will be useful for some tasks, and id like it here now, so as i can be sure to make the furnace to fit.

I suspect the A20 will come in useful for the collection of brass taps etc. that ive got stacking up here.

Question -

Someone told me that its not a good idea to make brass ingots. That the alloy loose components in the melt, and therefore the fewer times melted, the better?
I know this is kind of true of any metal (will get losses / oxidation etc every time) but is brass really that bad? Scrap is so much easier to store once its been part processed.

 

[bigegg]

Ordered my crucible today - i did go for the salamander A20 in the end.

Ill probably use an a12 for most job, but i figure the A20 will be useful for some tasks, and id like it here now, so as i can be sure to make the furnace to fit.

I suspect the A20 will come in useful for the collection of brass taps etc. that ive got stacking up here.

Question -

Someone told me that its not a good idea to make brass ingots. That the alloy loose components in the melt, and therefore the fewer times melted, the better?
I know this is kind of true of any metal (will get losses / oxidation etc every time) but is brass really that bad? Scrap is so much easier to store once its been part processed.

The cw ammen sandcasting book states that 10-15% zinc should be added to a crucible just before pouring to replace zinc lost to evaporation.
Brass is *about* 50/50 zinc:copper so after two melts 20-30% of total equates to about half the total zinc content.

 

[julianf]

A20 has arrived.

As above, I suspected that it would be a touch excessive, however, thought it wise to have here to build the furnace around.

And, yes, it is somewhat excessive. Will be nice for things like casting barstock, or bulk ingot preparation, but i doubt ill ever need to cast anything that is that sort of volume, given that most castings are not spherical (ie once the volume is distributed, then the dimensions get larger quickly)


I dont much trust datasheets etc. and its easier to make somthing to fit when its in front of you.

Need to move my welder, and then ill start work.