Melting and casting metals...

MrCrankyface

H-M Supporter - Silver Member
H-M Supporter - Silver Member
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Nov 7, 2019
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FIRST THE BACKSTORY...
I needed to melt some silver to make a small jewelry piece for my wifes birthday.
My budget was absolutely 0 and I definitely did not have time to make a proper foundry/furnace.
Of course this also means I can't spend the money on buying one that already works(which in hindsight would've saved weeks of time, and money).
My first try was using just a propane torch, a bucket and some stonewool insulation.
I probably don't even need to mention that it did not work.
The insulation melted and the propane wasn't strong enough to reach high enough temps, fast enough. :rolleyes:

I realized I needed a better container that would keep more heat inside and wouldn't melt on me...
Having seen enough youtube videos, I started looking for those white firebricks, which turned out near-impossible to buy in Sweden.
What I ended up buying were these 50mm thick, 230x114mm, "fire-resistant bricks".
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From what I've gathered afterwards, whilst they are fire-resistant, they're also horrible as insulation compared to the white firebricks.
They're also crazy hard which makes them difficult to cut and shape, ruining my budget and project-time further.
Either way, managed to find a diamond blade($$$)that fit on my chopsaw, from previous experiments I knew I had to use watercooling, so that was made from a windshield washer pump.
Hastily folded up the metal sheet everything is sitting on to control the waterflow which drips into a second container on the side.

Many, many, many MANY hours later, I managed to get this together.
Each piece has been cut at an angle to get a smooth and even contact all around.
Further more, slots have been cut along the inside for kanthal wire(heating wire).
Initially I was still going to use propane but decided to go all in now that I've already wasted a bunch of money on bricks and mortar...
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Using special fire-resistant mortar I tried putting all of this together, excuse the mess, it's the first time I'm playing with stuff like this.:grin:
Put it on both between the joints and also on the outside(for unknown reasons, pretty sure I just got carried away like a child with ink markers. :rolleyes:)
A few hours into it as it started to solidify, I went around and smoothened it out with 80 grit sandpaper on a plank.
Still had some weird issues where the white areas are dead hard but the darker areas never became hard and are still kinda dusty to this day(several weeks later).
On the left you can probably see all the through-holes for both heater wires and temperature sensor.
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Really just shooting from the hip I made up a lid whilst I was at it, reinforced the mortar with some steel wire in a crosshatch pattern to hopefully help this hold together.
Made a hole in it since all furnaces you can buy seem to have it. Not sure if it's because you need airflow or if it's so you can feed in new material without lifting it.
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The amount of stress, wiring this up, and on the first startup, hoping it's not going to explode. :grin:
The SCR-dimmer was to control the amount of power on startup as I wasn't sure how much I would need to make the heater-wire glow.
Too little and you're not getting enough heat, too much and you'll burn it off.
First attempt was with 230 volt AC(1phase to ground, ~1800W input), this was enough for 200-300c, so far from what I need/want but at least let me slowly heat it up during first testing.
Second attempt was with 380 volt AC(2 phase, ~4900W input), this is the second heatup you can see in the video.
Luckily I got the length of the coil just right so I don't need the SCR-dimmer. It seems to get just hot enough with no limiter.

I've still only run it up to 200c or so since it's recommended to keep it at lower temps for a few hours to get trapped moisture out etc.
Thing is, even after this short run I could already tell the outer surface was heating up way too much, so going up to 1000c without modifications isn't going to be a good idea. :rolleyes:
Furthermore you can probably tell the mortar has cracked just from those heatups. Not sure if that's normal or I've done something wrong.

So next little experiment is to insulate the entire thing. I ordered some ceramic insulating stuff that never arrived and has since moved on to the idea of trying "perlite cement".
The idea is to have an outer case of sheet metal which contains the furnace and any volume inbetween will be filled with the cement.
I have a bunch of 1.2mm sheet pieces that used to cover some installations, they also already have a handy ledge at the bottom which I figured I could flatten out and shrink to create the curvature needed.
The bottom plate is a bit thicker thread plate aluminium hence why it's riveted and not welded. I'm just using scraps hence the possibly weird choices.
The picture doesn't do it full justice, but no matter what I did it was just insanely wonky all around and I couldn't get it to maintain a smooth/round curvature because the sheet itself was fighting against the shrunken lower ledge.
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This led to a complete rethink again.
I made a roller for rolling sheet stock ages ago, but it only takes 30cm wide strips, about half of the height of that thing.
Either way I ended up cutting the lower ledge off, splitting the sheet down the middle and extending it so it would be longer than the circumference of the bottom plate.
After rolling that a few times I cut out new bottom and top ledges to finish it off and give some structural stability before welding everything together.
Still not 100% but way better than it was, and good enough for this cause.
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So that's pretty much where I'm at currently.
3+ months behind on time and I'm not even going to count the money I've spent on this, trying to save money.
I'm currently printing these black pieces, to help me keep everything in the right placement as I start filling it with perlite-cement.
Most likely I will cast it in two stages, first fill the bottom cavity, within the bottom black piece.
Once that hardens a bit I can remove the 3d-print and put the furnace on it, then fill the rest of up to the brim.
The top black pieces makes sure I can get a layer of perlite-cement ontop of it as well, without spilling into the furnace.
Once it stiffens up a bit I will remove those pieces as well.
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So what's left on the todo list?
-I want feets on the bottom to distance it from the floor/table/whatever.
-Some kind of hinge is needed for the lid.
-I'm not sure if I'm even going to use the current lid or just cast a new one completely from perlite-cement.
-Electronics need a fail-safe so the coils turn off if anyone lifts the lid(both dangerous heat and electric power)
-Since this is turning out quite chonky I want it to have at least 2 carry-handles on the sides.
-All the electronics needs some kind of box to stay in
-I need a bigger crucible for later when I want to melt aluminium
-Definitely need special tongs to grip the small crucible I have for silver, can't afford any mistakes once that thing is hot as a spill might be disastrous.

So stay tuned, hopefully I'll get this working within a few weeks.
 
Mapp gas burns hotter than propane. I inject a airstream with the gas to the burner to get a hotter burn. Kaowool works great for insulation.
 
That is a very nice write up on your project. Thanks
 
Mapp gas burns hotter than propane. I inject a airstream with the gas to the burner to get a hotter burn. Kaowool works great for insulation.
Yeah I tried using a second mapp burner at the same time, but still didn't get the heat needed due to my bad setup.
I've heard of kaowool but seems impossible to get around here.
Going full electric now though and the perlite-cement seems promising.
That is a very nice write up on your project. Thanks
Thanks!

Further progress yesterday/today.

Sifted the perlite I had since there was a lot of fine dust in it, I think it will be much more efficient as an insulator if I get rid of that.
Then I measured up a 1:10 ratio of cement : perlite, in volume.
I've noted down what each weigh per liter, then I use the scale to quickly and accurately get the required volume.
First mixed up the cement then added in the perlite and tried to adjust the mixture by adding some water since the perlite will absorb a lot of it.
Ended up with a gravel-y slurry that seems to hold it's shape well, we'll see how strong it ends up..
The slurry weighs surprisingly little when you're used to "regular concrete". :grin:
For reference, that amoutn of cement is 515gram whilst the entire container of perlite is 427 grams.
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Here's the little 3D-printed mold to get a foot of sorts, for the foundry to sit on, before I pour in the rest.
I could probably have done a better job of compacting it after I filled the mold up..
I removed the mold after 24 hours and it seems to have stiffened up quite well and still holding a fair bit of moisture.
It also had a cover on top of the mold for those 24 hours to keep the moisture in, as I've read it helps the final strength if you let it harden real slowly.
Some pieces outside of this "containment" had turned white and seemed fully hardened, the strength wasn't impressive but should be enough even in that "quick harden" state.
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So about the todo-list and lifting handles.
This is probably going to weigh 50kg/110lbs when finished so why even bother lifting it.
Instead I started making a little cart with 2 wheels and a foot/pad.
Should make it easy to move yet stay still when you leave it.
The idea is to just put in a handle on the wheel-side so you can "angle it up" and roll it like a two wheel handcart, obviously when it's cooled down.
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Both of these furnaces look great! Each will have a good use. My first casting furnace was also dense firebrick (easy to get.) This works, but has high thermal mass. You might consider removing the wire and using it as an air/propane or oil furnace where the thermal mass is less of an issue. These larger crucible furnaces are more suited to larger volumes of aluminum or brass.
For silver jewelry, I would recommend a pouring ladle and an oxy/propane torch. You can just melt the silver (or small amounts of any alloy) in the ladle by direct heating with the torch and then pour it. Easy!
 
Both of these furnaces look great! Each will have a good use. My first casting furnace was also dense firebrick (easy to get.) This works, but has high thermal mass. You might consider removing the wire and using it as an air/propane or oil furnace where the thermal mass is less of an issue. These larger crucible furnaces are more suited to larger volumes of aluminum or brass.
For silver jewelry, I would recommend a pouring ladle and an oxy/propane torch. You can just melt the silver (or small amounts of any alloy) in the ladle by direct heating with the torch and then pour it. Easy!
Thanks! It's one and the same as you'll see soon, I'm just making things difficult for myself. :grin:
It is quite oversized for the initial job of melting silver, my reasoning is that if I was gonna build a foundry/furnace I might as well make it big and strong enough to also melt a lot of aluminium as that's something I want to do in the future.
I really want to invest in a oxy/prop or oxy/acet setup but just the oxygen bottle is almost twice the cost of this entire project(even at this current run-away stage).
The thermal mass is definitely one thing that annoys me, but we'll see how big of a factor that is once it's up and running, I think the power input is quite large compared to other "DIY electric ones" I've seen online.
Was your first furnace also electric or did you use some kind of fuel for it?

So todays work:
Finally went around the entire 'big bucket' and ground down the welds somewhat. Trying to remind myself that it's a bucket and not a show car, so I don't get carried away. :rolleyes:
I also riveted the bucket to the undercarriage so it can't slide around, but can be drilled out and removed if I need to for some reason.
The firebrick foundry then sits on top of the previously shown cement-perlite footing, which is then followed by a thick(8-10cm / 3.1-3.9") outer layer of more perlite-cement. I'm hoping the outer steel layer will be insulated enough to be touchable.
Two 3D-prints then slide into each other to make a tight seal on top, for two reasons:
1. Make sure I don't accidently fill the center with perlite-cement.
2. Get some support for the added layer of perlite-cement ontop of the hard bricks which will be roughly 3cm / 1.2".
Semi-funny side-note, I bought a HUGE bag of perlite, 100 liters. I figured this would last me a lifetime(and bulk is so much cheaper).
The second picture is how far I got with it, after my wife stole some of it and I sifted a lot of fine dust out, literally just missing a few centimeters. :rolleyes:
So off to the big-box store to buy smaller containers that are 10x as expensive just so I could finish up, I was missing around 10 liters of perlite..
Once poured in, I've tried to just compact it lightly, I don't want to smash it down but I also don't want voids/barely contacting cement.
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Cement definitely isn't my cup of tea, or something I'm remotely used to working with, but I've tried to get a decent finish on top...
From what I've read you're supposed to let it sit for a bit, and then you can try to improve the finish, gonna give that a try in an hour or so.
I was surprised by how much I needed to mix just to fill this thing, I must've made like 10 buckets at least, the volume was a bit deceiving.
To anyone trying something similar, get/borrow a proper cement mixer, doing all of this with bucket and drillmixer was horrible and I suspect it also damaged the perlite at times since it's such a rough process.
Also, the last pour/top layer is slightly more cement in the mix, around 1:5 instead of 1:10, the idea/guess here was to make smoothing easier and also have a stronger surface/top layer.
The 3D-print will probably be heated up and removed to be as gentle as possible to the perlite-cement, I'm guessing it's gonna stick quite hard since I forgot to add draft angles..
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I've covered it in plastic to keep the drying rate as slow as possible, so I'll be trying to not touch this thing at all for a week or so now..
There was some perlite-cement left over from the last mix so I made a little cupcake and another weird little shape so I can see how they hold up in a few days.

Regarding the whole gas/fuel/electric choice/discussion.
I know a lot of people really favor the gas/oil powered ones, and I'm sure they're both faster and more powerful, but they also scare the sh*t out of me. :grin:
I'm hoping this will be a more "fool-proof" design where I can just set it to 800c and chuck in my crucible with aluminium to be melted, and not have to worry so much about open flames, hot gases(obviously there will still be some, but less), whatever fuel I would be using etc.
I believe the one I saw melting copper(1085c melt temp) only had 1.5-2kW input whilst this has 5kW and the wire should be capable of 1200c, 1300c if I'm OK with a much shorter life span.
Time will tell if I've made the right choices and if my research is correct or just wishful thinking. :grin:
 
With todays fuel prices, unless you're burning waste oil, electric might cost less to operate. Looks great!
 
Watching your thread. I've thought about investing in one of these kits off Amazon in case I ever get into making engines and want to cast flywheels.

As mentioned by Firstram, you may look at the cost of electricity vs. gas. I made up some 1/2" diameter punches and 1 1/4" dies a while back and flame hardened them with an oxyacetylene torch. I noticed my acetylene tank dropped about 25 psi. The last fill to 300 psi cost about $100 or about $8 per 25 psi. I've gone to using a Thermolyne muffle furnace which draws about 2000 W. It takes the furnace about 30 minutes to get up to 1600 F (cherry red steel temp). Our electric rate is about $0.13 per kW/H. Difference for me was $0.13 for electric vs. $8 for acetylene. Of course, propane is a lot less than acetylene.

Bruce



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For jewelry casting you can use the bernzomatic disposable oxygen and propane cylinders. Not sure if they're available where you are though? You can get multiple melts of a jewelry size casting out of one oxygen tank like that. In the US I think those tanks are around 10 bucks.
 
28436_400x400.jpgnot trying to discourage your furnace build. I have several large crucible furnaces. It's just that I would never use them for jewelry..
 
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