Steve W. wrote:
Ed Huntress wrote:
On Tue, 20 Mar 2012 16:50:11 -0400, "Steve W."
wrote:
Ed Huntress wrote:
I use the oddball stuff for items where the strength isn't a real
issue, Decorative stuff or covers and such.
The high silicon gets used for wear related items. I like using it
for castings that will end up handling abrasive abuse or in
locations where it will be the wear surface. Yes it can be a real
PIA to machine but it wears real well once finished.
It makes REALLY nice bullet molds.
I use various molds, sand, metal, lost wax/plaster. Two home built
furnaces. One is electric and one gas. The electric is NICE for
temp control and even heating. The gas is much faster to full heat
but hard on alloys.
I'd like to get into it some more, and I'm half-equipped, thanks to
the generosity of onr of our regulars here. Now I have to build a
furnace. I built one of those little Gingery charcoal furnaces around
20 years ago, and it was enough to get me interested, but it
deteriorated and I haven't replaced it yet with something better.
Soon...
I started with a charcoal unit. They work BUT the temperature
control is REALLY difficult to do with repeatable results.
The gas units work pretty well IF you have a source of low priced
gas to feed them. These days that can be difficult if you don't have
a NG line already.
This was the basic idea I used for my electric.
http://www.dansworkshop.com/2008/03/...ing-furnace-2/
Mine is larger than this and has better temperature controls (from
an industrial oven with three temperature sensors)
From a cold start I can have a batch ready to pour in about an 1.5
hours. The batches after that take about 30-45 minutes after loading.
The gas unit takes about 45 minutes from a cold start and 20 or so
for each additional batch. But you don't have the thermal control
over the melt.
I'd like to see one run. Did you use Kastolite, or what?
First one I used a home mix: 1 1/2 parts Portland cement, 2 parts
silica sand, 1 3/4 parts perlite and 2 parts fine fireclay Has held up
very well so far.
The newer one uses Mincast and firebrick.
If I do another it will be the home mix again, easier, cheaper and it
seems to hold up better.
I built the new one with a double wall as well. If you look at dans
unit just add a second housing with simple fiberglass insulation
around it inside a stainless cover. It reduced the radiated heat a LOT...
What's your opinion on this, Steve: Gas or electric? I won't do a lot
of melting. It will be pretty basic stuff. I can handle the electicals
or a gas burner. I have natural gas but I'm not in a hurry for melts,
so I don't care about that.
Hands down the electric. No dealing with gas plumbing or possible
leaks, no cleaning of jets or playing with the air mix to get it
right, no worries about what/if the gas is an odd mix that might add
something to the blend, MUCH more portable due to easier power access,
and it is MUCH, MUCH quieter than gas. Most of the gas units sound
like let engines which gets old really quick. With the electric you
hear the click of the contactors and the occasional sound of shifting
metal in the crucible.
Interesting the portability comment, I presume you mean mains gas. The
reason I made the glass annealing oven, I mentioned in another comment.
gas fired was due to portability. It had to be operated in a field with
no electric power unless you brought you own. The controller was powered
by an old 12V car battery and lasted the 5 days of the event. The burner
was run on bottled propane. I agree on the noise of gas fired furnaces
but a lot of that is due to burner design, they'll never be as quiet as
electric but multi hole burners can be much quieter than a single big
burner like many use.
What's the voltage and current draw on those things?
220-240 volts
My small electric has an inrush of around 18 amps on initial start and
that drops to about 15 once it is warmed up.
The big one takes about 40 on initial start and drops to 32-34 once warm.
Which do you think is easier to build?
Electric. BUT getting the room for the coil can be interesting. The
new one was easier sinse I knew what to expect. I used a sonotube
section with a thin sheet of foil around it. Then a coil of 1/2" black
poly around that secured with hot glue.
Thanks for your thoughts. I do know about the many online sources of
info, which I'll wade through when I'm ready for this. But since you
have both electric and gas, I'd really like your opinion.