- Joined
- Nov 7, 2019
- Messages
- 434
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.
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".
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...
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.
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. )
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.
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.
The amount of stress, wiring this up, and on the first startup, hoping it's not going to explode.
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.
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.
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.
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.
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.
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.
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".
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...
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.
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. )
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.
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.
The amount of stress, wiring this up, and on the first startup, hoping it's not going to explode.
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.
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.
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.
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.
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.