Author Topic: Foundry Furnace for the Tiny Shop  (Read 37835 times)

Offline vtsteam

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5421
  • Country: us
  • Republic of Vermont
    • www. sredmond.com
Re: Foundry Furnace for the Tiny Shop
« Reply #25 on: February 24, 2015, 06:02:04 PM »
4:22 PM :

2-1/4 lbs of molten aluminum (1kg).

Quite a fast melt from 5 oz muffin ingots especially considering that I hadn't half-filled the furnace with charcoal to start. Very pleased with that.

« Last Edit: April 30, 2018, 09:05:22 PM by vtsteam »
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline vtsteam

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5421
  • Country: us
  • Republic of Vermont
    • www. sredmond.com
Re: Foundry Furnace for the Tiny Shop
« Reply #26 on: February 24, 2015, 06:09:10 PM »
The pour. Sand was sub freezing, metal my worst aluminum, so not so pretty. And taking pictures of the melt with the furnace lid off didn't warm it up any!

« Last Edit: April 30, 2018, 09:06:04 PM by vtsteam »
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline vtsteam

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5421
  • Country: us
  • Republic of Vermont
    • www. sredmond.com
Re: Foundry Furnace for the Tiny Shop
« Reply #27 on: February 24, 2015, 06:14:21 PM »
And the not too surprising result -- the metal never reached the actual pattern -- the square sprue sections have nice detail though!  :lol:

« Last Edit: April 30, 2018, 09:06:35 PM by vtsteam »
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline vtsteam

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5421
  • Country: us
  • Republic of Vermont
    • www. sredmond.com
Re: Foundry Furnace for the Tiny Shop
« Reply #28 on: February 24, 2015, 06:25:08 PM »
And the various items cast with this pour:

A blob of aluminum that escaped when I accidentally knocked my ingot mold over  :wack:. And of course it escaped right into a small snow bank at the edge of the sand. No adverse effects though -- I was kind of wondering what would happen in such a case. But the snow is so cold and porous basically it just hissed slightly and solidified. I had to dig it out.

Then the "casting" aand finally a couple of small size muffins that escaped the upset. Not much to be proud of today as a metal caster except, IT WAS FUN ANYWAY!!!  And a big raspberry to winter.  :ddb:

« Last Edit: April 30, 2018, 09:07:05 PM by vtsteam »
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline vtsteam

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5421
  • Country: us
  • Republic of Vermont
    • www. sredmond.com
Re: Foundry Furnace for the Tiny Shop
« Reply #29 on: February 24, 2015, 06:41:42 PM »
I covered the tuyere and exhaust vent with a brick waited an hour. Then opened up the plaster and sand furnace for an inspection.

It looks the same inside as it had before the melt. The walls are completely intact the corners are sharp, and the furnace wall even still shows the molding lines from the cardboard form, and a shiny surface where it had before..

Well, the same, except for one thing......the furnace is a little cleaner -- most of the brown tarry stains from the slow burning charcoal of the first firing had burned off.  :med:

« Last Edit: April 30, 2018, 09:07:35 PM by vtsteam »
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline Manxmodder

  • Hero Member
  • *****
  • Posts: 743
  • Country: gb
Re: Foundry Furnace for the Tiny Shop
« Reply #30 on: February 24, 2015, 10:15:39 PM »
The mysterious tale of the invisible engine,perhaps it's changed it's quantum state :bugeye: ,how well it performs nobody will ever know for sure. :lol:

The furnace lining looks promising though.....OZ.
Helixes aren't always downward spirals,sometimes they're screwed up

Offline vtsteam

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5421
  • Country: us
  • Republic of Vermont
    • www. sredmond.com
Re: Foundry Furnace for the Tiny Shop
« Reply #31 on: February 24, 2015, 10:37:40 PM »
Oz, what it shoud have looked like:

[/URL]

[/URL]

But that was in zinc alloy during the summer, and after trial and error modification to the sprues, which this leftover uncast pattern didn't have. Which was why it was never cast.

It would have been surprising if it had actually come out well, especially in a frigid mold and with a cool pour. I left the furnace open, without blast so I could take pix. Not exactly good practice before a pour. Especially at -11C. But pix were more important, anyway. This was a furnace test.
« Last Edit: April 30, 2018, 09:11:11 PM by vtsteam »
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline Manxmodder

  • Hero Member
  • *****
  • Posts: 743
  • Country: gb
Re: Foundry Furnace for the Tiny Shop
« Reply #32 on: February 24, 2015, 11:27:27 PM »
Steve,yes I remember the V twin crankcase experiment and the different sprue configurations well,I was hoping you would get time to make a full engine from it some day.

I don't ever see plaster of paris in any of our builders merchants here,but there are a couple of local companies who make ornate fibrous plaster moldings and that's where I'll be making some initial enquiries.

There is another plaster compound that is use to fix plaster boards with the dot and dab method, I have a half bag of it left over. Maybe worth mixing some up and making a couple of test blocks,drying them out and seeing how well they survive in my wood burning stove.....OZ.
Helixes aren't always downward spirals,sometimes they're screwed up

Offline awemawson

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 6586
  • Country: gb
  • East Sussex, UK
Re: Foundry Furnace for the Tiny Shop
« Reply #33 on: February 25, 2015, 02:47:35 AM »
It's available quite economically on eBay. Had some delivered back in autum last year.
Andrew Mawson
East Sussex

Offline Will_D

  • Hero Member
  • *****
  • Posts: 579
  • Country: ie
    • National Homebrew Club of Ireland
Re: Foundry Furnace for the Tiny Shop
« Reply #34 on: February 25, 2015, 04:54:19 AM »
There are different grades of P-of-P available.

I have found a ceramics company in Ireland which has some good info:

http://rpmsupplies.com/index.php?route=product/category&path=50_105

They list 3 PoPs

Talking to them about use in a foundry lining (50/50 with sand) he recommended the Crstacal R

Engineer and Chemist to the NHC.ie
http://www.nationalhomebrewclub.ie/forum/

Offline MetalMagus

  • Jr. Member
  • **
  • Posts: 32
  • Country: gb
Re: Foundry Furnace for the Tiny Shop
« Reply #35 on: February 25, 2015, 07:28:34 AM »
Hi
While googling the plaster of paris. I came across this concrete designed for making furnaces.

http://www.specialplasters.co.uk/index.php?_a=product&product_id=244

Might be of some interest.

Cheers

Sean

Offline vtsteam

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5421
  • Country: us
  • Republic of Vermont
    • www. sredmond.com
Re: Foundry Furnace for the Tiny Shop
« Reply #36 on: February 25, 2015, 08:44:31 AM »
Thanks Oz, Andrew, Will, MM.

Oz, Plaster of paris is a different mineral compound than spackle or wallboard compound (which is what I think we call what you are referring to). Chalk vs Gypsum,   carbonate vs sulphate. And they have very different characteristics. The most valuable of which in poP is its ability to set without drying (water evaporation). Spackle will take very long to dry even if 1/4" thick on a wall, and if trapped between forms in a 2" thickness would never dry. It also shrinks on drying, unlike poP and would develop cracks in any thickness. The usual wallbord compound/spackle contains starch, as well as calcium carbonate.

poP cures, rather than dries -- it goes through a chemical change that liberates heat. And a thicker section will actually cure faster than a thinner section due to this heat. It doesn't shrink, which is why it is used for molding fine details.


MM, that castable refractory with that temp rating seems very reasonable in price, and if had been locally available here I might have used it. My guess is, you'd need 2 bags for a furnace this size.

Will I'm sure there are better grades of poP for the purpose. The problem for me is that there are NO castable refractories available cllose enough to me to be able to pick up. I would have to ship anything in that line, and the shipping costs can double the cost.

If I were going to pay big money for shipping a refractory my ultimate choice would be a fiber mat and zircon coating exactly as ironman uses -- as the highest insulating vaue, and a proven iron melting capability. And I do hope to some day do that if I can find the materials. But if it comes down to a castable with lesser temperatuure capabilities, I think this plaster and sand combo, available to me for $20 and local pickup at my hardware or builder's store makes good sense, and I'll be saving my pennies as a result for the ultmate refrac, some day.

I love it when a Plan B comes together!
Steve
www.sredmond.com

RobWilson

  • Guest
Re: Foundry Furnace for the Tiny Shop
« Reply #37 on: February 25, 2015, 01:19:55 PM »
Good to see you got the furnace fired up Steve  :thumbup:



Rob


Offline Will_D

  • Hero Member
  • *****
  • Posts: 579
  • Country: ie
    • National Homebrew Club of Ireland
Re: Foundry Furnace for the Tiny Shop
« Reply #38 on: February 25, 2015, 05:50:53 PM »
As this is the "goto" foundry thread at the moment:

The refractory: PoP+Sand seems to work well. So thats my furnace lining sorted.
I like the look of the gas bottle for the body and lid - we have a lot of these in Ireland
How much sand and PoP was needed/ 25 kg of each or more?

What would the max crucible size be: A4 or larger?

Next problem:
   Casting Sand:

Nowhere to buy it in Ireland! Talked to a few foundries and they all import from UK.

So yes I could drive 100K and 'try' to blag 25 or 50 kgs, however:

I can get 'play' sand in 25 kg bags (basically its a very clean, silica sand, for kiddies sand pits)

I need to add some 'clay' - I can get Koalin and Bentonite (both clays)

What is a recommended mix?

I know I can do it the old way (squeeze and shear the sausage [oops - off on a wrong thread  fantasie :bugeye:] ) but I need to know if its 100 parts sand to 1 part Clay additive or is it more like 10 to 1?

Its just I need to know how much to order!
Engineer and Chemist to the NHC.ie
http://www.nationalhomebrewclub.ie/forum/

Offline vtsteam

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5421
  • Country: us
  • Republic of Vermont
    • www. sredmond.com
Re: Foundry Furnace for the Tiny Shop
« Reply #39 on: February 25, 2015, 06:31:55 PM »
Rob, thanks!  :beer:

Will, I have only fired this furnace once, and it is experimental, so I can't say it is proven yet. I'd know better after ten melts how it will hold up.

The propane tank I used was larger than our usual BBQ tank here. The smaller ones are called 20 lb tanks. This one, I believe is a 30 lb tank. The cylinder body was approximately 18" tall (not including valve or sheet metal guard/handle), and 12" in OD.

I used up a 25 lb bag of poP, and nearly a bag of sand (50 lb, I believe)

Interior open space chamber is 12" high by 8" diameter.

It would definitely fit an A-6 crucible. I went with 8" diameter because I like to fit charcoal briquets on edge around the cast iron plumber's pot I use as a crucible. If a gas or oil furnace was contemplated, probably a larger crucible would be do-ablein my furnace -- however you do need space for tongs, so I don't want a smaller diameter. There are rules of thumb for bore size vs crucible sixe on other sites. I'm used to an 8" bore charcoal melter.

Seems like you could get sand from the foundries you mention if you are able to talk to them. I don't live  near any foundries. Ceramics suppliers/pottery supplies often have silica sand, and fire clay ( I've used fireclay and sand for both building furnaces and casting) In fac my greensand for aluminum today is still made from fireclay and sand, not Bentonite. My Gingery lathe and accessories were all made with that. I do have silica and Bentonite for my iron sand. The fireclay I've used is called Hawthorn.

I strongly recommend getting Dave Gingery's book on the Charcoal Foundry for all the info on foundry building, firing, greensand from clay and sand, moulding, etc.

Also I'd severely miss my two Terry Aspin foundry books if they were gone -- and they are published in the UK. All three are small but jam-packed paperbacks, and a tremendous bargain. I've read them all through several times over the years, and in my opinion they beat most online sources hands down -- but then I'm a reactionary when it comes to casting!

Don't be shy about opening a thread and asking lots of questions there -- you'll get a lot of differing opinion, this one isn't the go-to furnace thread or shouldn't be -- I'm a nutcase who generally does what you're not supposed to do and occasionally gets away with it, and this is an experiment that may  not work out -- just finding out if I can push an envelope for cheapness!  :beer:
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline Will_D

  • Hero Member
  • *****
  • Posts: 579
  • Country: ie
    • National Homebrew Club of Ireland
Re: Foundry Furnace for the Tiny Shop
« Reply #40 on: February 25, 2015, 06:40:55 PM »
Steve,

Thanks for all the info!

I will certainlt start a thread when I start to build!
Engineer and Chemist to the NHC.ie
http://www.nationalhomebrewclub.ie/forum/

Offline vtsteam

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5421
  • Country: us
  • Republic of Vermont
    • www. sredmond.com
Re: Foundry Furnace for the Tiny Shop
« Reply #41 on: February 25, 2015, 09:04:07 PM »
You're welcome Will!

Oops, forgot one thing, there is an online source of casting info that I keep going back to, because it is pure gold. Anything filmed or written by Ironman you can take to the bank!  :bow:
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline Eugene

  • Full Member
  • ***
  • Posts: 151
  • Country: gb
Re: Foundry Furnace for the Tiny Shop
« Reply #42 on: February 26, 2015, 08:55:36 AM »
Will,

In other threads Steve has shown some of the castings he's made using the lost foam method; they look very smart.

You don't need anything fancy for the mould medium, just dry sand. That's certainly the way I'll go to start with, as initially my requirements will be for relatively simple parts, and one off, so making really super duper wooden patterns isn't on. I've hammered a foam cutter together and had a play with it ... doddle.

Gas tank (Polish!) that's been full of water all winter,  a fire extinguisher body for a crucible, box section steel for a trolley, and some ally wheels and pistons are all to hand. I won't be starting for a couple of months yet, I've got other stuff to do, and it might have stopped raining by then.

Eugene

Offline vtsteam

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5421
  • Country: us
  • Republic of Vermont
    • www. sredmond.com
Re: Foundry Furnace for the Tiny Shop
« Reply #43 on: February 26, 2015, 09:24:21 AM »
Having done some lost foam casting, and shown it here, I have to admit, I don't like it, though, and I'd strongly recommend that anyone starting out just go with the basics -- greensand casting  from whatever source you can make it. The bottom line is it is sand and clay. Practically any type locally available will do. There are high tech and low tech versions of it, but I think for beginning aluminum casting at relatively low temperatures what you have most easily available will be fine. As I said above, bentonite is nice, but not required, and I've done all of my aluminum casting with fire clay and sand.

What I don't like about lost foam:

You need a new pattern for every part you make
It takes at least a day of prep -- coating, drying time
if you've gated wrong you can't just  repour in twenty minutes as you can with greensand.
the fumes are bad -- flaming polystyrene
it's very iffy -- tough to achieve consistency
you need very hot metal -- borderline oxidizing
it requires a greater head pressure, sprue extensions
sprue extensions pick up the loose un-bonded sand so re-melting sprues means sand in the melt.

the good:

Relatively thin sections are possible
surface finish can be great
no need for pattern draft

I don't think I'll be doing much more lost foam casting -- there may be an occasional reason to, but I'd say my success ratio with it is 25-30%. I do tend to use it for very thin sections, which is a challenge, but why bother with lost foam for a heavy sectioned part? My success rate for greensand aluminum is probably 90%. And it's quick to re-group, re-pour with different gating, and the results of a bad pour can be re-melted without sand contamination.

Anyway, that's just my own experience. Others may find otherwise... :beer:

I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline Will_D

  • Hero Member
  • *****
  • Posts: 579
  • Country: ie
    • National Homebrew Club of Ireland
Re: Foundry Furnace for the Tiny Shop
« Reply #44 on: February 27, 2015, 05:57:53 PM »
And yet another question:

Why does no-one melt and cast low carbon steel?
Engineer and Chemist to the NHC.ie
http://www.nationalhomebrewclub.ie/forum/

Offline awemawson

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 6586
  • Country: gb
  • East Sussex, UK
Re: Foundry Furnace for the Tiny Shop
« Reply #45 on: February 27, 2015, 06:07:30 PM »
In one word : Temperature

Hard to get furnace hot enough
Hard to get suitable crucibles

I've melted mild steel many a time inadvertently in my ceramic chip forge, that is propane and blown air powered, but just the ends of bars left in too long for forging. Different matter containing the stuff at a suitable heat for pouring.

Mild steel melts nicely in a coke fired cupola furnace, but although you may feed it with steel, it's cast iron that comes out due to the carbon in the coke.
Andrew Mawson
East Sussex

Offline vtsteam

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5421
  • Country: us
  • Republic of Vermont
    • www. sredmond.com
Re: Foundry Furnace for the Tiny Shop
« Reply #46 on: February 27, 2015, 06:51:55 PM »
Ironman has a video of converting steel into gray cast iron.

I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline vtsteam

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5421
  • Country: us
  • Republic of Vermont
    • www. sredmond.com
Re: Foundry Furnace for the Tiny Shop
« Reply #47 on: March 02, 2015, 11:43:00 AM »
Today it was gusty out, but I decided to test the tiny furnace out with propane instead of charcoal.

I also wanted to re-melt the aluminum from the last casting test to clean it up and get it back into ingots. The lost foam process necessarily gets loose sand mixed into the head discards of a pour, since the sand isn't moist and bonded with clay.  Also the failed pour left some of the pattern plaster coat mixed with the metal, and the escaped aluminum during the ingot spill was also dirty. I had nothing to lose remelting these remainders in a test, and I wanted to see how well they'd clean up -- or if they would melt at all with my propane burner and the new furnace.

The burner I had on hand was pretty small and the result of an atmospheric torch project that I detailed here:

http://madmodder.net/index.php/topic,8633.0.html

I wasn't sure this would do the job, and I do plan to build the larger fan pressurized propane burner ironman uses for his small furnace. But the little burner was available, already made up, and a propane tank nearby, so it was worth a try to see what would happen.
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline vtsteam

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5421
  • Country: us
  • Republic of Vermont
    • www. sredmond.com
Re: Foundry Furnace for the Tiny Shop
« Reply #48 on: March 02, 2015, 12:09:28 PM »
Well, it was a success all around. The small burner took some adjusting -- I found 8 psi was about right. The gusty wind did put it out a few times while I was trying to find the right settings of pressure, throttle valve, and flare position.

This is one clear drawback of an atmospheric torch -- it's definitely subject to wind gusts.

Eventually I found that if the furnace heated up sufficiently, it was less affected -- that took maybe the first five or ten minutess of heating -- it is still a small torch and there isn't the power to make the walls glow right away.

I also found that using my piece of stovepipe as a chimney on top of the furnace lessened the effect of the wind changes, and probably drew air around the torch, as well as keeping the torch drawing better.

Once the torch was drawing well and the walls starting to glow around the crucible, and I could see the crucible bottom starting to look dark red, I inched both the pressure and throttle up until I was at 10 psi and an open throttle. This sounded a little more ragged with the wind as it was. It almost blew out at one point, but reducing the throttle got it back on track.

When the aluminum appeared to start shifting and crumbling in the pot, I lifted the stovepipe off to give it a stir, but doing this allowed a gust to snuff out the flame. I closed the throttle, re lit the torch and inserted it back in the tuyere. The stovepipe stayed on after this. And the furnace was restored in a couple minutes to full throttle near 10 psi.

When the aluminum had melted and the pot and walls were glowing orange, I shut off the gas and skimmed the dross -- there was very little, and then poured small size muffin ingots. without incident.

Hard to say what the exact time to melt was because of the flame outs, re-starts and pressure adjustments, but it was roughly 15 to 20 minutes with this burner and furnace. As a comparison, the store bought charcoal took 12 minutes to melt the same amount aluminum in the same furnace with the same crucible. That was after it was lit, which takes maybe ten minutes, or so. So roughly similar total time.

One thing was obvious -- the furnace was unecessarily tall for propane melting -- charcoal takes up space, so needs a taller bore. I'd say a 20 lb cylinder would be plenty for a strictly propane furnace, though i still like an 8" dia. bore.

The ingots poured very clean, and look good. Since they are small, I'll probably use one at the bottom of other melts to start the molten pool in the crucible.

Here's what the setup looked like after the pour:

« Last Edit: April 30, 2018, 09:12:21 PM by vtsteam »
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline vtsteam

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5421
  • Country: us
  • Republic of Vermont
    • www. sredmond.com
Re: Foundry Furnace for the Tiny Shop
« Reply #49 on: March 02, 2015, 12:41:13 PM »
Since this is also a test of the plaster/sand furnace lining, here are photos of the furnace and lid after two pours and the original bake for a day. 

There is some hairline cracking in the lid near the exhaust opening, and the plaster there is softer -- I dug at it in a couple spots and it will crumble away if you do. However it isn't loose or flaking, and appears to be stable so far.

It's not dissimilar to insulating firebrick, which is also soft and can be dug away, and I have to say that my lids made of fireclay and sand also cracked and flaked eventually. Repairing them was part of maintenance over the years. Lids take a beating near the exhaust port. So far the plaster sand has not flaked, so there's no need to repair. We'll see how well it does over time.

The furnace body looks great. I do see a few small hairline cracks at the hottest part, near the tuyere  but again, no actual damage at all.

The lid:



The furnace body:

« Last Edit: April 30, 2018, 09:13:04 PM by vtsteam »
I love it when a Plan B comes together!
Steve
www.sredmond.com