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g'day Chris here and welcome back to clickspring Ian and Drew have requested a bit more detail
on the furnace that I built and tested over the last few months now to some extent it's
the typical furnace that you've probably seen before built around the Ron real burner design
but there are a few differences that might interest you that I'll point out along the
way starting with the regulator for the Prototype version of the Furnace I used a cheap no gauge
regulator and I immediately upgraded it to this one it does add a lot to the cost of
the Furnace but I think the gauge is definitely worth having because other than sound it's
all you've really got to indicate the energy input rate to the furnace the regulated gas
flow travels down to the burner which consists of a brass pipe with a hole in it surrounded
by a bell reducer Plumbing fitting as the gas exits the hole it draws in a flow of air
from outside the Bell reducer this airflow mixes with the gas travels down the tube to
the flame front and then ignites it's an incredibly successful and widely used design and for
a home shop furnace or a forge it's very hard to beat here are the components that I've
used to make it and you'll also find them listed in the text below this video foreign
ER jet is simply a brass pipe nipple drilled with a 1.1 millimeter hole the hole size controls
the rate of gas flow and I found this to be about the right size for this furnace
the Bell reducer is then drilled out to accept the brass pipe nipple [Music] foreign
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[Music] components are assembled threaded through the hole and a spot of JB Weld epoxy
holds them in place with an airtight seal [Music]
thank you and I've taken care to make sure that the jet aims straight down the middle
of the steel pipe nipple using the drill bit as a reference
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the epoxy needs a good 12 hours to cure and then once fully hard the drill bit can be
removed and the other parts of the burner assembled
now it's worth pointing out that at this stage the burner can't sustain a flame at the end
of the burner tube without a twee air to slow down the gas flow usually you'd see this as
a flared tube at the end of the burner but in this design the two-year is integral with
the base of the furnace and the burner connects to it using one of these couplings but more
on that in a moment for the base I had a sheet metal fabricator make a few of these hoops
from mild steel sheet this contains the refractory as it's poured and the dimensions are listed
below the molds for the cavity and plinth were made by using the cut off ends of these
plastic buckets I used hot glue to hold them together and a short section of PVC pipe for
the entry hole there does need to be a hole in the metal hoop to allow the coupling to
sit in place but I think you get the general idea add a good coating of silicon spray helps
the mold separate from the refractory once it's cured
set of screws at regular intervals ensures that the steel perimeter is retained on the
cast base and here's a closer look at the castable refractory
this particular Castle contains quite a high amount of silica and it's rated up to 1400
degrees Celsius
and finally here's a closer look at the finished item that I've been using for the last few
months showing everything in place [Music] now the key to the built-in twier is a small
lump of mortar in front of the opening and a slight flare at the mouth of that opening
both of which are easy to form using a bit of high temperature mortar once the base casting
has set
[Music] at low gas flow rates the slight flared to the opening is enough to keep the flame
attached but as the gas flow rate increases the flame detaches and moves forward to a
point just beyond the lump of mortar
now I'm not entirely sure about the fluid mechanics that work here but it appears to
be acting as a sort of parcel toy air in the channel of the base whatever the actual physics
the main thing is that it works these two features ensure that the flame is very well
controlled at all gas flow rates and it's a very simple approach that neatly solves
a number of issues first there's no need to forge a metal toy air so that's an immediate
time saving second the entry support and positioning of the burner are all taken care of by the
threaded coupling being cast directly into the refractory and finally there's no hole
for unwanted air to be drawn into the furnace as would be the case if the burner was sitting
free in an entry cavity
the body of the Furnace simply rests on top of the base and has an outer shell of sheet
metal construction again you can find the dimensions below I've sized it to accommodate
an A10 Crucible although at present I'm using A6 crucibles the lead is of similar construction
again mild steel sheet and in use it rests on top of the Furnace body
the body and lid have been lined with two layers of 25 millimeter high temperature ceramic
fiber which was bonded in place with sodium silicate and then rigidized with a thin spray
of colloidal silica
all of the hot surfaces were then given a thin coating of itc-100 it's a high performance
ceramic coating that significantly increases the thermal efficiency of a furnace now strictly
speaking you could probably get away without using the rigidizer but if the ITC 100 also
seals and rigidizes the wool but it's a whole lot easier to paint this stuff onto a rigid
surface than it is to paint it onto a soft wool surface so I'd still say use both after
firing it forms a hard heat reflective shell over the top of the ceramic fiber and whilst
it does work well there's a drawback to be aware of that I'll go through later and the
last little feature to point out are the simple tab handles that I've welded onto the sides
they're very easy to hold on to especially while wearing thick gloves
okay so now a few of the pros and cons that I've discovered so far a big positive to mention
first up is that it's very easy to set up and break down all of the components are light
and easy to move around and I also like that it's modular every furnace has a finite life
and will wear out eventually so it's good to note that I can simply swap out sections
of it once they become a liability without having to junk the whole thing
now the fact that it's very light means that it can be lifted up and stored on a bench
or shelf instead of taking up valuable floor space which leads to the other big plus and
the main reason that I went this way with the design having a low physical Mass also
means that it has a low thermal Mass so it heats up very quickly
compared to a furnace made entirely from castable refractory a much smaller proportion of the
energy is being stored in the body of the Furnace itself now this rather suits the way
that I intend to use it which is basically for ad hoc one-off castings I'll rarely need
to do multiple melts in a single day so I wouldn't really get the benefit of a heavy
Solid cast furnace that holds its heat between melts now on the con side the first thing
to mention is that this is definitely not a cheap furnace to make in my part of the
world it's impossible to buy the required materials in small quantities so I've ended
up with lifetime suppliers of a lot of this stuff even though I only needed a fraction
of what I had to order but just based on what I actually used for construction I'd estimate
material cost to be around 300 U.S which considering I've ended up with quite an efficient furnace
I'm pretty happy with
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now another drawback is the brittle nature of the ceramic coating I have to be much more
careful with this furnace than if it were all solid refractory and in fact I accidentally
chipped it while shooting this video for the other benefits it brings though it's a drawback
I'm happy to live with it's easy enough to patch it up with some spare coating and push
it straight back into service the repair fuses with the surrounding ceramic and it's basically
undetectable
and the final con to mention is that the low thermal Mass means that it cools down very
quickly there's no thermal Bank sitting around The Crucible like there would be with a full
castable refractory furnace but so far I haven't found this to be an issue at all it just means
that there can be no delay in pouring which is pretty much the case for any home furnace
where pouring occurs directly from The Crucible
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foreign
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[Music] now one thing I've noticed is that the higher temperature melts like copper are
a little more destructive on the hot face than say for example aluminum so I'm holding
off on pushing to find the top temperature of the Furnace just yet until I've done the
next few videos I don't want to risk wrecking it currently it's bringing a full A6 Crucible
of copper up to pouring temperature without issue so I think it's probably fair to say
there's a bit more Headroom to go and I'll find out where that limit is over the coming
months thanks for watching I'll see you later
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