MadModder

The Shop => Metal Stuff => Topic started by: vtsteam on February 21, 2015, 01:14:49 PM

Title: Foundry Furnace for the Tiny Shop
Post by: vtsteam on February 21, 2015, 01:14:49 PM
I hadn't planned on doing a thread on this little furnace, because it's not much different than many others online. But it's come up a couple times, so I'll just show what I'm trying.

I've run a charcoal briquet aluminum furnace since 2002 using the recipe set out by Dave Gingery in his book (highly recommended) and built my lathe with it back then, a complex milling attachment, many accessories, and a disk turbine (whose blades were actually cast from aluminum melted in a ordinary campfire -- no furnace at all). The furnace was of sand and fireclay construction, but finally deteriorated after ten years when rain leaked through a metal cover over a winter and the shell rusted out.

Then a couple years ago I tired building a sawed off single charge cupola as an experiment. That failed (with wood charcoal, at least -- didn't have coke, which might have worked). That was re-fitted with an oil burner and I was able to successfully cast with iron after much trial and error.

So now with my new tiny shop, I find i need to cast an aluminum pulley to upgrade my Gingery lathe spindle to 1" dia. And I want something less massive and involved than the oil burner -- which is overkill for that purpose. Also located by my distant and unheated big shop, and outside, under snow.

Anyway, those were the reasons for a new furnace. I also hoped to have alternate metal capability -- small capacity iron would have even been possible if I was able to follow Ironman's small furnace design. But I wasn't able to find the very expensive rigidizer he uses, here in the States. So I dropped back in my expectations to maybe being able to melt the red metals.

Instead of fireclay and sand, this time, I wanted to try Plaster of Paris and sand. A recent video post here showed another furnace made from a galvanized bucket using the same refractory, but I'd been thinking about poP for a long time before that. Steve Chastain's books refer to commercil pouring liners of that material, and show data that it has a high insulative ability as well as refractory qualities. Bronze statuary casters have long used it for lost wax molds, flinging it onto the armature to prevent bubbles.

Anyway, wanted to try it and see how refractory, insulative, and long lasting it was. I still want to make Ironman's furnace some day, and will when I can find the right materials. If the plaster doesn't last long, I can always replace it with blanket and rigidizer. So this is a pure experiment, with little to lose.

Materials were sand, a bag of plaster of Paris ($14.95 at the local hardware store), and an expired 30 lb propane tank (a little taller than the 20 lb size) for a  casing.

I had some left over 8" dia. Sonotube (cardboard form used for casting concrete pillars) and I used that for a form inside the furnace. It actually measured 8-5/8" wide so I cut a 1" strip out of it and taped it back together to reach 8".
The seam made it easier to remove when the plaster was cured, too.

The mix was equal parts of sand, plaster, and cold water, and I mixed about 2 quarts at a time. Actually, the first pour was about half that in size, and used a little less water to make a heavier pasty mix which I used to "glue" the outside of the form to the propane cylinder.

This stuff sets off in literally 3 minutes, even with cold water and cold materials (very -- they were stored in a cold shop) so you have to work very fast. DO NOT use warm water!

As soon as that kicked, I ddn't have to hold the cardboard form any more, and could pour the rest of the refractory with no leaks. The proportions I used makes a good pourable mixture that self levels. Within an hour, I peeled out the cardboard form to a nice clean interior. Then I poured the bottom inside the furnace cavity -- about 2" deep.

Finally I found a cardboard mailing tube of exactly 3" diameter and used that to form the lid hole form. in a similar way to the furnace cavity. And then poured the lid.

Today, after 3 days of drying, I brought the furnace outside, and put a double layer of charcoa briquets in and lit it off. This applies gentle heat, and will help me drive off the water from the plaster -- it will probably take all day, and I'll be adding charcoal as needed. Moisture is obvious as steam this time of year!
Title: Re: Foundry Furnace for the Tiny Shop
Post by: dsquire on February 21, 2015, 01:25:53 PM
Good to see you underway with this one Steve. I'll be watching over your shoulder.  :D

Cheers  :beer:

Don
Title: Re: Foundry Furnace for the Tiny Shop
Post by: awemawson on February 21, 2015, 01:27:44 PM
Good stuff Steve BUT

 :worthless:

Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on February 21, 2015, 02:13:19 PM
Sorry, I didn't take any pix of the construction. Here it is after running an hour with charcoal. Sorry also -- I couldn't paint the furnace this time of year -- too cold, but plan to make it nicer when things warm -- if they ever do.

(http://www.vtsteam.com/TinyFurnace/TinyFurnce2.jpg)



(http://www.vtsteam.com/TinyFurnace/TinyFurnce1.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on February 21, 2015, 02:55:51 PM
I added more charcoal to about 3 layers deep after three hours and a piece of old stovepipe on top to increase the draft a little. Still way to early to get out the blower. The brown residue inside the barrel and under the cover will burn off once the furnace is in use at high temps. For now, sorry about the Grapes of Wrath appearance here! You can tell I'm suffering from cabin fever to be doing this at this time of year.....

(http://www.vtsteam.com/TinyFurnace/TinyFurnce3.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on February 21, 2015, 03:44:14 PM
I've debated whether to explain my procedure for cutting up a propane tank. I'll put it down here, but this isn't a recommendation to anyone, just an explanation of what I did, and why I did it that way.

I used to build pulse jet engines, and some of the principles apply, to my way of thinking.

The first principle in avoiding a detonation in a container is to remove all fuel. No fuel, no detonation.

The second is to reduce the volume of potentially combustible mix as much as possible. Reduced volume, reduced energy available.

The third is to provide a relatively large opening in the container. The less containment/restriction the more likely conflagration (rapid combustion) vs detonation (explosion).

Taken all together:

1.) I opened the gas valve on this propane tank and left it outside for 3 years. That still doesn't guarantee no "fuel" since these tanks typically have a tarry residue internally, which if heated will boil and offgas under torch cutting heat and even though it isn't propane itself, it is flammable (and explosive if contained).

2.) Removed the valve entirely with a pipe wrench. This increases the size of the orifice greatly compared to leaving the valve on. This alone reduces the chance of a detonation.

3.) Washed the tank out with hot soap and water. This won't remove most of the tarry residue. So it would be foolish to depend on it. It will remove lighter oils, to some degree.

4.) Filled the tank with water to an inch under the top. This drastically reduces the volume of potential air and fuel mix. The ratio of the current orifice size (about 3/4" diameter) to the contained gas volume (about a pint) has now been increased maybe 1000 times what it was with the open valve attached and the tank empty. There is little volume to burn, and an easy way for hot gasses to exhaust if it does.

5.) With the tank full of water I lit a match and held it over the orifice. No reaction. no pop. Nothing. (Again, I'm not reccomending this to anyone, I'm just repeating what I did and why I did it this way. What I did applies only to this tank, this type of fuel, and this lead-up procedure, not every situation. Make no assumptions about different situations based on this.)

6.) I drained out about a quart of water and repeated. No ignition.

7.) I drained out enough water to lie a little below my cutting line, and repeated. No ignition.

8.) I used a 4-1/2" grinder with a cutting disk in it to score around the tank, still filled with water, and then cut through. The water level was low enough not to wet the disk or grinder, and I wore rubber gloves.

I did NOT use a cutting torch. A cutting torch raises the temperature of the surrounding metal tremendously, and I did not want to vaporize any possible tarry residue in the tank. A torch is in my opinion a bad tool for this kind of thing, and procedures which use inert gasses in the tank are less safe (http://in my opinion)than using water. If the gas isn't right, you can't tell, and the contained volume is way too big for safety. Leaving the valve on the tank really increases the danger.

That's my personal opinion. Many tanks have been cut with torches, and many swear by inert gas fills to do it with. I prefer my way. It makes sense to me, and results are apparent at every step.

Sorry to go on at length here, but I haven't ever seen this explained this way before and thought it might be useful. Nothing in this guarantees safety, and every person must assume personal responsibility if they try to use a propane tank. Other substances and tanks can behave completely differently.

Title: Re: Foundry Furnace for the Tiny Shop
Post by: RobWilson on February 21, 2015, 03:48:27 PM
 :clap: :clap: Nice one Steve , I do like a good foundry/furnace build  :thumbup:

Rob

PS ,That white stuff looks cold  :(
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on February 21, 2015, 05:14:54 PM
Thanks Rob, Andrew, Don!  :beer:

Maybe also a word on cutting the exhaust hole in the tank top:

I took a piece of hardwood and whittled it into a tapered plug, then hammered it into the threaded valve hole. Then sawed it off flush. Marked the center, punched it. Then used that as a guide for the pilot of a 3" bi-metal hole saw in an electric hand drill. Low speed and light pressure cut a perfectly clean hole, centered on the top. I did this before filling with the plaster mix.

The tuyere hole was also cut with a hole saw sized to fit U.S. 1-1/4" steel water pipe (1-38" ID actual, and about 1-5/8" OD) started square radial but after cutting through the outer metal and into the plaster angled to be more or less tangential to the furnace chamber. The bottom of the tuyere is about 1" above the furnace chamber bottom.

The tank and top were wire-brushed to remove the tarry residue in the tank before pouring with plaster, as well.
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on February 21, 2015, 06:01:41 PM
It's started to snow, and get dark out and the furnace has been cooking for 6 hours now, so I added more charcoal and about a minute of soft blast to get the coals all lit. They're carrying on well, now and the heat is definitely up a notch:

(http://www.vtsteam.com/TinyFurnace/TinyFurnce4.jpg)

(http://www.vtsteam.com/TinyFurnace/TinyFurnce5.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: mattinker on February 21, 2015, 06:57:13 PM
Steve,

I see where you're going, plaster does have good refractory characteristics. My only fear is that it may not stand up to repeated heat cycles. It is relatively soft. It is used to make moulds for lost way casting which are only used once and are then broken open. I've never seen any references to it in kiln or foundry construction. I would think that something like ITC100 painted on as a surface protection might be useful to increase usable life. This is an interesting experiment!


All the best, Matthew
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on February 21, 2015, 07:03:05 PM
Matthew, I'm hoping the sand will give it toughness.

If I got ITC100, I'd be thinking kaowool blanket/iron melting -- it may come to that if this doesn't work.
Title: Re: Foundry Furnace for the Tiny Shop
Post by: mattinker on February 21, 2015, 08:13:14 PM
It's only as tough as the binder. ITC gives a surface protection and reflects heat. It's uses are not limited to Ceramic fibres.

Regards, Matthew
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on February 21, 2015, 09:49:50 PM
I don't agree about the toughness of a binder, Matt, but let's see what actually happens first before pre-judging the results of an experiment just starting out.

And Matt, I know what the ITC product is used for and what it is. My point is, if I'm going to spend more than five times what the plaster costs on a coating to protect it, that's kind of silly!

As I said if I wanted to plunk down serious money for a coating, I might as well go whole hog with a fiber blanket refractory under it -- a refractory itself which costs only about half of the price of that expensive coating. And hopefully gain the capability to melt iron.

And actually, if I were going to spend $100+ a pint for a coating specifically to melt iron, I'd prefer to use a zircon based coating, that ironman uses.

Which brings us back to the very reason for starting this thread....I can't source that zircon coating for the present here in the US. So I'm giving up on iron, and high tech solutions in this furnace and focusing on melting lower temp metals using low tech refractory. And plaster of Paris is what I 've wanted to try for a long time.

Now, preliminary impressions -- the sand and plaster are much tougher than plaster alone. It was obvious even molding it and cleaning off drips.

Current status of the furnace -- I shut it down after 9 hours of baking the lining, and put it away for the night. We'll do a post mortem in the morning.
Title: Re: Foundry Furnace for the Tiny Shop
Post by: Manxmodder on February 22, 2015, 12:04:10 AM
Steve,very interesting thread I'll be following this experimental build closely as I have an old scrap propane cylinder that I took the top off a couple of months ago(pillar valve removed and filled with water and surgery performed with small angle grinder, just as you did :thumbup:)

I agree with you on the water vs inert gas option as a more certain safety measure when cutting the top off though I have seen a couple of other guys cut them open after filling with dry sand,which does the job of reducing the free internal volume.

Watching with interest,I hope this works out well.....OZ.
Title: Re: Foundry Furnace for the Tiny Shop
Post by: SwarfnStuff on February 22, 2015, 01:33:36 AM
Thanks for posting Steve.
   For what it's worth, if you need to extend the set time of plaster of Paris a trick I have used often when patching up the dings on the plaster walls is to add a little repeat little, milk, you know, the white stuff from cows?
   Don't know the chemistry but it does work. Too much milk and you will wait hours. I got this tip from a plasterer friend many years back.
  Now I will watch along with the others to see how you furnace performs.
John B
Title: Re: Foundry Furnace for the Tiny Shop
Post by: bertie_bassett on February 22, 2015, 05:40:40 AM
looking good  :thumbup:

will be watching as this progresses and stealing all the good ideas when I get round to making one myself.

have started saving up ally heatsinks, but that's as far as iv got.
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on February 22, 2015, 12:22:36 PM
Thanks Oz, John, Bertie!  :beer:

I emptied the ash out of the furnace this morning, and the lining is in fine shape. No deterioration. In fact the impressions of the cardboard tube seams are preserved as is the "shiny" areas where I'd used plastic tape on the form. The lining rings when I tap it, so it seems reasonably dry. The lid however still seems slightly soft when scratched -- most of the lid surface is blocked from the heat by the shell, so that will take some more time to fully dry out. There's also probably still bound water in all of the lining --  this bake isn't really a test yet -- that will come with full melting heat. But I should be able to leave the furnace in the shop now -- freezing temps shouldn't hurt it. I did bring the lid back indoors to dry further.

Title: Re: Foundry Furnace for the Tiny Shop
Post by: mattinker on February 22, 2015, 04:24:15 PM
I hope it survives the first firing! The sand should allow the plaster to bind at it's maximum a minimum of plaster between the grains of sand, but it is still that plaster that holds the sand together! The results will be interesting!Something cropped up on the Hobycast forum today, ITC 100 in 1/4pint bottles for $25! I know it's not in the budget, just thought I'd let you know!

Regards, Matthew
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on February 22, 2015, 09:06:12 PM
John B, thanks for the milk tip. It's interesting, I think the sand acted in the opposite way, as a catalyst for the Plaster of Paris. The reason I think that is, my wife decided she wanted to cast about a cup of Plaster of Paris (without sand) today for a project she had. We mixed it up and I expected the near instant cure I was getting with the refractory mix. But it ended up taking a LOT longer -- at least 20 minutes. So I think the sand must really accelerate that stuff.

Thanks for the tip about milk. If I ever have to do this again, I'll probably try it to slow things down a little.
Title: Re: Foundry Furnace for the Tiny Shop
Post by: Eugene on February 23, 2015, 04:15:19 AM
Meanwhile even further off the main topic ...... I'm a bit leery of using a steel crucible for melting ally. Is there a coating or liner that could be applied to the steel interior to prevent the iron dissolving into the charge? I ask this from the safety point of view as much as anything else.

I had thought of just using a loose-ish liner of potters clay; if some means could be found of retaining it during the pour, that would seem on the face of it to be workable. Is it? Or what?

Eug

Title: Re: Foundry Furnace for the Tiny Shop
Post by: awemawson on February 23, 2015, 05:02:11 AM
I used to use a Zircon wash on ladles I used for aluminium. Warm the ladle over the furnace and paint it on with an old broad paint brush - it flash dries. Same for stirring pokers etc.

This was to prevent iron dissolving into the melt. I've never been happy with the multitude of ferrous 'pipe crucibles' that you see on the web from a metallurgical point of view. I've always used clay / graphite conventional crucibles.
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on February 23, 2015, 07:44:24 AM
This is one of those perennial user purpose and style disagreements. I've used a cast iron plumber's pot for all of my aluminum melting career, other than some bigger pours which used a 4" pipe nipple and welded plate bottom.

Here's the deal -- I mainly melt pistons for stock metal. Those pistons were cast with steel clips right in them. So no way are you going to avoid "iron contamination" by using a ceramic crucible or a ladle wash with these. Nor do most of the world's engine makers for what is obviously an extremely demanding application. Melted pistons, despite the steel clips make great castings -- naturally. That's what they are! My castings for my lathe, accessories turbine, etc were fine castings, the lathe hasn't fallen apart after a dozen years, and I expect it to last a lifetime.

Now there is nothng wrong in my opinion with using virgin alloys, a non-ferrous crucible or wash to control a melt and get single named alloy results. If that's what you enjoy doing, and/or you have a demanding application, I don't say no. It suits the application and the style of the caster. And vise versa. If you're melting scrap, and casting heavy sections for non-NASA parts, as most of us do a ferrous crucible isn't a problem and shouldn't be disdained.

What IS a problem is too thin a crucible if steel. It should be at least 1/8" thick and preferably double that to last any time at all. Thin stainless steel canisters burn through in only a couple pours, too. Using a steel soup can is asking for trouble -- not to mention the coatings inhalation problem. The recent video elsewhere on the site using a fire extinguisher bottom, seems both hard to obtain and too thin. Why bother? A pipe nipple is much thicker and readily available. To me the best iron crucible is a cast plumber's pot. It doesn't waste in the flame as steel does -- I've used one for 12 years.

 If you are worried about iron, you can line any ferrous crucible on the inside with fireclay and sand if you don't have the bucks for an expensive ladle wash. It will then be a ceramic crucible to all intents and purposes.
Title: Arctic Pour
Post by: vtsteam on February 24, 2015, 05:38:07 PM
I shoveled snow and chipped away ice until I saw frozen ground then covered with some coarse sand and set-up the furnace. As I mentioned in the Tiny Shop thread temps last night were the lowest of the winter -26C and today it only warmed to 11C and it was windy too. I still wanted to try the furnace out and I used some of my poor grade aluminum and an old lost foam pattern which I'd made last summer for an engine casing. It was only 6mm thick and I'd had some difficulties back then with this gated version of it. But it was something to try with the furnace -- any excuse!

(http://www.vtsteam.com/TinyFurnace/TinyFurnce6.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on February 24, 2015, 05:42:10 PM
Gear set out, charcoal lit ready to go. No blast yet Lost foam mold setup in the small orange child's bucket lower left :

(http://www.vtsteam.com/TinyFurnace/TinyFurnce7.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on February 24, 2015, 05:50:53 PM
Blast on, coals coming up to heat....4:10 PM :

(http://www.vtsteam.com/TinyFurnace/TinyFurnce8.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam 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.

(http://www.vtsteam.com/TinyFurnace/TinyFurnce9.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam 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!

(http://www.vtsteam.com/TinyFurnace/TinyFurnce10.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam 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:

(http://www.vtsteam.com/TinyFurnace/TinyFurnce11.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam 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:

(http://www.vtsteam.com/TinyFurnace/TinyFurnce12.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam 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:

(http://www.vtsteam.com/TinyFurnace/TinyFurnce13.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: Manxmodder 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.
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on February 24, 2015, 10:37:40 PM
Oz, what it shoud have looked like:

(http://www.vtsteam.com/LostFoamCasting/TwinCase11a.jpg)[/URL]

(http://www.vtsteam.com/LostFoamCasting/TwinCase9.jpg)[/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.
Title: Re: Foundry Furnace for the Tiny Shop
Post by: Manxmodder 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.
Title: Re: Foundry Furnace for the Tiny Shop
Post by: awemawson on February 25, 2015, 02:47:35 AM
It's available quite economically on eBay. Had some delivered back in autum last year.
Title: Re: Foundry Furnace for the Tiny Shop
Post by: Will_D 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 (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

Title: Re: Foundry Furnace for the Tiny Shop
Post by: MetalMagus 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
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam 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.

Title: Re: Foundry Furnace for the Tiny Shop
Post by: RobWilson on February 25, 2015, 01:19:55 PM
Good to see you got the furnace fired up Steve  :thumbup:



Rob

Title: Re: Foundry Furnace for the Tiny Shop
Post by: Will_D 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!
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam 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:
Title: Re: Foundry Furnace for the Tiny Shop
Post by: Will_D 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!
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam 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:
Title: Re: Foundry Furnace for the Tiny Shop
Post by: Eugene 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
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam 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:

Title: Re: Foundry Furnace for the Tiny Shop
Post by: Will_D on February 27, 2015, 05:57:53 PM
And yet another question:

Why does no-one melt and cast low carbon steel?
Title: Re: Foundry Furnace for the Tiny Shop
Post by: awemawson 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.
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on February 27, 2015, 06:51:55 PM
Ironman has a video of converting steel into gray cast iron.

Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam 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.
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam 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:

(http://www.vtsteam.com/TinyFurnace/TinyFurnce14.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam 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:

(http://www.vtsteam.com/TinyFurnace/TinyFurnce16.jpg)

The furnace body:

(http://www.vtsteam.com/TinyFurnace/TinyFurnce15.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: DavidA on March 02, 2015, 01:30:38 PM
VT,

Am I correct in saying that you have no insulation between the refractory and the outer steel wall ?

I'm thinking about making something similar for aluminium,  just to get some practice at casting.

I have insulation that I got from Norman,  but don't want to use it on the aluminium furnace if it isn't necessary .

Dave.
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on March 02, 2015, 01:44:18 PM
No David, it isn't necessary. The 2" of refractory acts as insulation for the relatively short heating times of aluminum in a furnace this size.

The outside near the bottom was "hottish" after a full day of baking the shell when I first built it, but not hot enough to even bother the paint, and I could touch it briefly.  Wouldn't want to hold my hand for long on it, but that's about how hot it was. Higher up it was just warm.

A twenty mnute to half hour aluminum melt barely warms the outside.
Title: Re: Foundry Furnace for the Tiny Shop
Post by: DavidA on March 02, 2015, 01:54:02 PM
VT,

Thanks,

 Something else to add to my 'to - do' list.

Dave.
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on March 02, 2015, 08:49:05 PM
With the morning's pour having worked with propane, I thought about it for awhile and then decied late in the day to go for a pulley pour. This meant clearing enough bench space to do the moulding, estimating the amount of aluminum needed, locating the baked sand cores I'd made and re-conditioning the sand.

I weighed out 56 oz of aluminum, which seemed like it would be enough, though this particular mould would have a very long sprue (for me) in a 3 part flask, and a riser. Moulding took quite awhile, I haven't cast anything in a year and a half, and this one had a bked core and a hanging greensand core in the cope, and a sprue running through cope and cheek. I didn't want to mess up, and with darkness coming I wouldn't have a chance to remake the flaask.

Everything worked while moulding, nothing dropped out even though I did a couple of rolls, and the core fit the prints holes when put together. The wind had picked up worse than it was this morning, it was really whipping. Temp was -7C. I re-oriented the furnace to take advantage of the wind direction, and piled up bricks to shield it from low pressure. I started the furnace at 4:05, and had 56 oz of molten aluminum a half hour later.

I gave it a little extra time in the furnace to pour hot with the chilled mold, skimmed and poured. Well unfortunately, I had underestimeated by probably 4 oz, and the sprue and riser didn't top out. Ahhhh, well! There's alway still hope til you open these things.

(http://www.vtsteam.com/Gingery/pulleypour1.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on March 02, 2015, 09:02:09 PM
I kinda peeled off the layers one at a time, hoping all went well. The first one showed the inverted greensand core had stayed in place, and the baked core looked crumbly. No shrink cavities, the shorted riser had been just enough:

(http://www.vtsteam.com/Gingery/pulleypour2.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on March 02, 2015, 09:09:53 PM
And pulling off the drag showed the bottom pulley looked good. not tears around the baked core, and it was still positioned okay:

(http://www.vtsteam.com/Gingery/pulleypour3.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on March 02, 2015, 09:13:30 PM
The core was soft and easily dug out. the pips are from the vent wire:

(http://www.vtsteam.com/Gingery/pulleypour4.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on March 02, 2015, 09:41:42 PM
Finally, the break-out. Everything looks good!

(http://www.vtsteam.com/Gingery/pulleypour5.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on March 02, 2015, 09:53:25 PM
Ready to machine, I couldn't have asked for a better result, particularly under the circumstances. With all the changes in thickness, I figured this one for a bear, but everything worked first time out. Really happy with it!!

You can see the double sprue here. Final weight of pulley casting, 42 oz. One more to go.

(http://www.vtsteam.com/Gingery/pulleypour6.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: awemawson on March 03, 2015, 02:33:32 AM
Excellent Steve

It must be rather nice to be back casting after a year or so.. It's now over seven years since I had mine set up, something else always is crops up!
Title: Re: Foundry Furnace for the Tiny Shop
Post by: PekkaNF on March 03, 2015, 03:47:54 AM
Wow, all that looks like magic! I tired "green sand" like 20 years ago. Never worked out for me, none of it! I did have some success with oil-sand. Paid something ridiculous of few kilos. That was pre internet....

Thanks for showing - really inspirational.

Pekka
Title: Re: Foundry Furnace for the Tiny Shop
Post by: Manxmodder on March 03, 2015, 04:01:03 AM
Happy days,looks a right good casting does that  :clap: :clap:

The wire vents you mention,are they serving pretty much the same purpose as piercing with a hacksaw blade,as I have seen others do?......OZ.
Title: Re: Foundry Furnace for the Tiny Shop
Post by: awemawson on March 03, 2015, 06:44:44 AM
Happy days,looks a right good casting does that  :clap: :clap:

The wire vents you mention,are they serving pretty much the same purpose as piercing with a hacksaw blade,as I have seen others do?......OZ.

I made up a set of 'prickers' - just  bits of oxy-acetylene welding wire about 9" long with a loop bent in one end (so it looked like a kids bubble blower) to hold it by. Gently feel it down to the pattern in several places to let the gases escape freely.
Title: Re: Foundry Furnace for the Tiny Shop
Post by: RobWilson on March 03, 2015, 10:01:36 AM
 :clap: :clap: :clap: :clap: :clap: very nice Steve  :thumbup:

Bottom gating worked well .

Is it one of a pair of pulleys   or do you just need the one  ?


Hopefully I may get a wee  bit of casting done this year , some new foundry toys arrived today  :)


Oh yes , did you do the  :ddb: dance  :lol: :lol:


Cheers Rob 
Title: Re: Foundry Furnace for the Tiny Shop
Post by: mattinker on March 03, 2015, 11:07:38 AM
Interesting, you cut a very small gate! I'm glad it worked out!

Regards, Matthew
Title: Re: Foundry Furnace for the Tiny Shop
Post by: tom osselton on March 03, 2015, 11:24:08 AM
Casting looks good!
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on March 03, 2015, 08:22:41 PM
Andrew thanks so much! You must get back into casting. I forgot about the sheer fun of it (when it works!) -- breaking away some dirt to see what you've got -- and the playing with fire.... you know what I mean!

Pekka, thanks kindly! it's probably just being familiar with whatever materials you've got, through trial and error. Every sand is different, but I believe most are workable for aluminum at least. It's just doing it enough with your particular ingredients. The feel of the sand - tempering is very important, and the proportion of clay to sand also. But not necessrily the pedigree or cost.

This casting was made with 13 year old greensand made from fireclay and sand, not even Bentonite. The very same sand I cast my lathe, accessories, and everything else aluminum with.

I'm used to it, I know how it should feel, and how hard to ram it and how to vent it, etc. And I'm sure that would all be different if I changed to a different sand.

In fact casting was all brand new again the other summer when I did so with iron. Everything was different, and I had to re-learn it. Coming back to this stuff, wth aluminum in a foundry the size of my original, with my old sand, everything was familiar, and second nature.

Oz thanks! re. using a venting wire to poke holes. Everybody is different, but I would never vent with a hacksaw blade. I prefer just the opposite -- a fine straight wire, 1 mm (.040"), stainless steel spring wire.

I started out with coarser wire -- bare house electrical copper wire -- it was too thick, not straight enough, and dug out divots and tended to crumble the mold surface if poked through from the inside (I frequently do this -- not just venting from the outsode toward the pattern).

I later went to aircraft SS tie-wire -- still not stiff and straight enough, and too coarse, though better. Finally I found a a kitchen baking tool for poking pastry just perfect for the job. It had a coin sized flat plastic handle, 1 mm stainless spring wire, perfectly straight (so it didn't tend to disturb the sand when pulled out) and very thin. I think it cost $3. That's what I use. It really helps make a clean mold.

Seems a small point -- but it what works best for me.

Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on March 03, 2015, 09:06:52 PM
Thanks Rob!!!! Oooh, I forgot!

             :ddb:

My daughter loves that one! Always wants me to put them in posts if she sees me typing.

I do have to make a matching pulley -- except for the hole -- it goes on a 5/8" arbor.

I'm not sure it's worth coring 1/2" -- might just make it solid. Probably better if I core it, though -- I didn't get shrinkage at the top this time -- that might not hold with an even thicker center. I think I might have some old 1/2 cores stashed away.....

New foundry toys????? Whadidjaget??  Huh? Huh? Huh?  :drool:

Thank you Matt. (I think it was the right size!)  :beer:

Thank you Tom! Your own castings looked great, out of the starting gate!  :beer:

No further progress today guys.....it was Town Meeting Day in Vermont -- our once a year indulgence in local participatory democracy. Townspeople propose, debate, modify and vote every aspect of the budget for the upcoming year.
Title: Re: Foundry Furnace for the Tiny Shop
Post by: RobWilson on March 04, 2015, 03:53:07 PM


New foundry toys????? Whadidjaget??  Huh? Huh? Huh?  :drool:


Hi Steve ,

I bought myself , a few of each /different sizes  ;  Scotch cleaner ,English cleaner , Scotch club cleaner ,flange cleaner ,girder tool ,flange bead  upset ,boss tool ,straight bead ,spoon tool , and a few I have not found the names of yet  :lol: :lol: :lol: you did ask  :) all moulding tools  :dremel: 

Rob

Ill take a bonny photo of them at the weekend .
Title: Re: Foundry Furnace for the Tiny Shop
Post by: Will_D on March 04, 2015, 04:03:09 PM
Talking of foundry tools - does anyone have any recommended designs for the more common crucible tools we use for these:

A2, A4, A6

In particular lifting out the furnace tongs either straight or with a 90 degree offset.

Pouring handles

Its not so much the diameters to match the crucibles its more about the length and strength of the sections needed. Also safety features that are not always shown in the basic undimensioned drawings.

I don't want to buy stock lengths of the wrong sized steel
Title: Re: Foundry Furnace for the Tiny Shop
Post by: RobWilson on March 04, 2015, 04:12:24 PM
Hi Will

If you can hang fire untill the weekend I will measure up my crucible gear , easy to make , simple ,been using them  for years   :thumbup:

Re bar makes for good poring shanks and the likes (nice and grippy)  cheap to .


Rob
 
Title: Re: Foundry Furnace for the Tiny Shop
Post by: Will_D on March 04, 2015, 04:19:23 PM
Cheers Rob,

No rush! Waiting for the weather to improve before cutting down the gas bottle etc.

Yet another question:

Using a butane/Propane tank as the basic for a charcoal/coke furnace do people build in a dump grate to empty the ashes or leave as is (much safer if a crucible breaks)?
Title: Re: Foundry Furnace for the Tiny Shop
Post by: RobWilson on March 04, 2015, 04:30:33 PM
Never Charcoal fired Will , thats one for Steve .

As to the safety hole ,mmm  personally I  think its safer that the molten metal stays in the furnace ,let it cool, break out solidified metal and repair/patch furnace lining ,so I have never had a safety hole in the bottom of any of my furnaces .


Rob

 
Title: Re: Foundry Furnace for the Tiny Shop
Post by: Will_D on March 04, 2015, 04:56:20 PM
Rob,

I didn't mean a safety hole.

Some solid fuel furnace designs I have seen incorporate a "Dump Flap" that allows you to drop the coals out of the cold furnace.
(In paricular cupola designs).

Otherwise you have to turn it upside down to empty it out!
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on March 04, 2015, 04:57:45 PM
Mmmmmmmmmm, rebar!  :drool:

1/2" dia, here. Actually these are mostly cupola tools....... but you get the idea!

(http://www.vtsteam.com/SawedOffCupola/Cupolaconst59.jpg)

(http://www.vtsteam.com/SawedOffCupola/Cupolaconst51-1.jpg)

(http://www.vtsteam.com/SawedOffCupola/Cupolaconst53.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on March 04, 2015, 05:00:34 PM
Rob,

I didn't mean a safety hole.

Some solid fuel furnace designs I have seen incorporate a "Dump Flap" that allows you to drop the coals out of the cold furnace.
(In paricular cupola designs).

Otherwise you have to turn it upside down to empty it out!

I have a dump gate at the bottom of the cupola I built, but the smaller aluminum charcoal melters get dumped by hand. Usually at the end of a pour, I cover the exhaust port and tuyere with a brick. This extinguishes the charcoal, saving quite a lot of it for starting the next time. It also slows the cooling of the furnace interior, so reduces cracking. I also leave the hot but empty crucible in there for the same reason. It's easier on crucibles (I believe.......warning, personal opinion!)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: Joe d on March 04, 2015, 05:02:22 PM
VT Steam

Completely O/T here, but I really like your dog!  Looks remarkably like
my late and still lamented friend Max who enlivened my life for 16 1/2 years.

Give him/her a milk-bone on my behalf!

Joe
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on March 04, 2015, 05:05:14 PM
Certainly will, Joe.

He's a long legged dachshund. Half border collie, half long hair dachshund.

I don't know which half is which, though.
Title: Re: Foundry Furnace for the Tiny Shop
Post by: RobWilson on March 04, 2015, 05:44:41 PM
Rob,

I didn't mean a safety hole.

Some solid fuel furnace designs I have seen incorporate a "Dump Flap" that allows you to drop the coals out of the cold furnace.
(In paricular cupola designs).

Otherwise you have to turn it upside down to empty it out!

Aarh you mean a drop bottom Will , I have one on my cupola  :)

(http://i1066.photobucket.com/albums/u410/RobWilson100/Cupola/P1070688_zpscfbb33e3.jpg) (http://s1066.photobucket.com/user/RobWilson100/media/Cupola/P1070688_zpscfbb33e3.jpg.html)

When I was a young lad doing cast iron coke fired there was never much left in the bottom of the furnace .

(http://i1066.photobucket.com/albums/u410/RobWilson100/Foundry/Scan10005_zpsk9bxtkyq.jpg) (http://s1066.photobucket.com/user/RobWilson100/media/Foundry/Scan10005_zpsk9bxtkyq.jpg.html)
(http://i1066.photobucket.com/albums/u410/RobWilson100/Foundry/Scan10001_zpskajznhci.jpg) (http://s1066.photobucket.com/user/RobWilson100/media/Foundry/Scan10001_zpskajznhci.jpg.html)

20 odd years on and I am still making blowers and furnaces ,,,,,,,,,,,,,,,,,, me thinks I could have a problem  :loco:


Any way enough  :offtopic:



Cheers Rob
 

Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on March 04, 2015, 09:13:13 PM


New foundry toys????? Whadidjaget??  Huh? Huh? Huh?  :drool:


Hi Steve ,

I bought myself , a few of each /different sizes  ;  Scotch cleaner ,English cleaner , Scotch club cleaner ,flange cleaner ,girder tool ,flange bead  upset ,boss tool ,straight bead ,spoon tool

Huh????

Could you repeat that in English, Rob? :lol:

(me gazing down at a clementine crate with a stolen bent kitchen spoon, a rusty artist's pallette knife, and a baking poker thingy, a clothes pin, a candle, some bits of dowel, pieces of round bar and tubing, a sawed off table leg, a clothes pin, and a piece of galvanized tin bent into a "U".) Ahhh, me I can see jealousy in my future. No longer, how you say.......a nice bit o kit?

And I thought I was stylin'  :lol: :lol: :lol: :lol: :lol:

You know......havng it all organized like that in one crate?   :lol: :lol:
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on March 04, 2015, 09:20:03 PM
Joe, Fletcher said, "Thanks for the cookie!"

I told him it was from joe, overseas. He said he owes you one......  :beer:
Title: Re: Foundry Furnace for the Tiny Shop
Post by: Joe d on March 04, 2015, 10:25:35 PM
Tell Fletcher he's welcome.  Curious though, when did Quebec get to be overseas from Vermont?

Lake Champlain getting salty?  :clap:

Cheers, Joe

Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on March 04, 2015, 10:40:18 PM
Ooops! Didn't look at the flag before posting!  :Doh:

Well the official name on some maps is Lake Champlain Inland Sea, so maybe I can get away with that.......

nah.... apologies neighbor!  :wave:
Title: Re: Foundry Furnace for the Tiny Shop
Post by: Joe d on March 04, 2015, 11:05:44 PM
It's all good Steve, the rest of Canada often wishes Quebec WAS overseas too!

One of these years we'll get together for a cup of coffee at the show in Windsor. :beer:

Joe
Title: Re: Foundry Furnace for the Tiny Shop
Post by: Will_D on March 05, 2015, 05:21:06 PM
Mmmmmmmmmm, rebar!  :drool:

1/2" dia, here. Actually these are mostly cupola tools....... but you get the idea!

Thanks VT,
Nice pictures

Colour coded as well!
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on March 05, 2015, 06:10:36 PM
Joe that would be really great!

Thanks Will! :beer:

I took a break from casting today and drilled and tapped two 5/16" holes in the back of the cone pulley casting and bolted it directly to the lathe faceplate. Then I slowly worked off the machining allowance in this small lathe -- about 1/4" on the diameters of the sheaves. I couldn't dig too deep without chatter on something ths large -- I'm looking forward to a bigger spindle and bearings when the pulleys are finished!

When supper time came around I had it roughed out to 5",4",3" and 2" diameters. I haven't bored it yet, and I haven't started cutting the grooves for the J type Poly-Vee belt. I did make up a 40 degree gauge from some galvanized tin, and then sharpened a lathe tool using that to compare it with.

Here's the pulley on the faceplate:

(http://www.vtsteam.com/Gingery/PulleyBlank2.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on March 06, 2015, 10:56:13 AM
Hmmm, thinking about this in the morning here. I am going to have to come straight in 90 degrees with the lathe tool to cut the grooves, but I have to work up to very near the left edge of each sheave because the lands aren't much wider than the belt. In other words, groove right close to the base of the next larger sheave. So the tool I made with the cutting point at center was no good. I need to put the point as close as possible to the left side of the tool.  :doh:


Rob, you okay? I don't know what A&E is, but guessing it isn't a good thing.....

I do want to see those tools (kidding of course, earlier)!  :beer:

ps your foundry photos above are crude enough to make me think that, following your lead and calculating from an equivalent skill level, that in 20 odd years I'll be turning out tooling as beautiful as the stuff you do now. Which fills me with hope! Assuming the underworld has a furnace......  :dremel:
Title: Re: Foundry Furnace for the Tiny Shop
Post by: Manxmodder on March 06, 2015, 11:11:33 AM
A&E usually abbreviate for accident and emergency,though ass & elbow seems more apt on some occasions. :lol: :lol: 

Edit to add: A & E could also stand for awkward and eccentric,like all good MadModders should be.
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on March 06, 2015, 11:36:25 AM
Not the Arts and Entertainment channel then?  :scratch:
Title: Re: Foundry Furnace for the Tiny Shop
Post by: RobWilson on March 06, 2015, 01:11:36 PM
[

Huh????

Could you repeat that in English, Rob? :lol:

(me gazing down at a clementine crate with a stolen bent kitchen spoon, a rusty artist's pallette knife, and a baking poker thingy, a clothes pin, a candle, some bits of dowel, pieces of round bar and tubing, a sawed off table leg, a clothes pin, and a piece of galvanized tin bent into a "U".) Ahhh, me I can see jealousy in my future. No longer, how you say.......a nice bit o kit?

And I thought I was stylin'  :lol: :lol: :lol: :lol: :lol:

You know......havng it all organized like that in one crate?   :lol: :lol:


 :lol: :lol: :lol: :lol: I have just gone up market Steve , moved on to a Dows port wooden box  :)



Rob, you okay? I don't know what A&E is, but guessing it isn't a good thing.....

I do want to see those tools (kidding of course, earlier)!  :beer:

ps your foundry photos above are crude enough to make me think that, following your lead and calculating from an equivalent skill level, that in 20 odd years I'll be turning out tooling as beautiful as the stuff you do now. Which fills me with hope! Assuming the underworld has a furnace......  :dremel:

Yer I am fine , just had a few chest pains and decided to get get back some of the national insurance money I have payed for years , ended up doing a bit "Train spotting " on the NHS  and they gave me a canny bottle off easy start too  :med:



Aye my foundry/crucible  tools were  a bit ruff back then , that blower was canny though ,cast iron did not stand a chance  ,,,,,,,,,,,,aaaarh happy days  :)


Rob





Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on March 06, 2015, 10:00:51 PM

 :lol: :lol: :lol: :lol: I have just gone up market Steve , moved on to a Dows port wooden box  :)

Gee, Rob, does sound like an improvement, how do you get one of those?  :) :)

Quote
Yer I am fine , just had a few chest pains and decided to get get back some of the national insurance money I have payed for years , ended up doing a bit "Train spotting " on the NHS  and they gave me a canny bottle off easy start too  :med:

Hey, don't downplay it. Take it easy, man, we really need you! :bow: :bow: :bow: :bow:  :bow: :bow: :bow: :bow:

Quote
Aye my foundry/crucible  tools were  a bit ruff back then , that blower was canny though ,cast iron did not stand a chance  ,,,,,,,,,,,,aaaarh happy days  :)

Those days are still here. Rob I watch you grab a handful of cast off junk, see the potential, and turn it into some graceful celebration of skill and utility. That's so amazing! Some say what differentiated human beings from other animals in evolution was the ability to make and use tools. It created a different form of life. But then Jane Goodall discovered a chimpanzee that fished termites out of a mound with a grass stem -- so tool making wasn't totally unique. Which kind of explains my own background.....
:lol:)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on March 06, 2015, 10:22:57 PM
I started turning the grooves in the smallest sheave -- getting chatter even though this is a single point tool, and I took apart and cleaned and adjusted all of the lathe slides, and tightened down on the split spindle bearings. It just won't behave. Basically I need what I'm trying to make -- a more robust spindle and bearings.

Though the speed is the slowest, and the sheave the smallest, I think the chatter is a result of the distance from the faceplate, and it may be less of a problem with the other sheaves which are closer.

I dunno, I was thinking of boring it insted, and then putting the pulley on an arbor and then doing the grooving between centers. But I don't know if that would help or make things worse for this particular piece. :scratch:

I guess I could wait a few weeks for warmer weather and then just turn it on the Craftsman 12". But a Gingery should build itself, without help, seems like.
Title: Re: Foundry Furnace for the Tiny Shop
Post by: RobWilson on March 07, 2015, 03:30:17 AM
Morning Steve


Animals with tools   :dremel: , My favourite is the Sea otter using a stone as an anvil  :med: .

Could you bring your tail stock up to give the outer end a bit support  . Also mounting the tool upside down and running in reverse can do the trick . or make a spring tool  :dremel:  :)

(http://i1066.photobucket.com/albums/u410/RobWilson100/Spring%20tool/P1020976_zpsv9liwodl.jpg) (http://s1066.photobucket.com/user/RobWilson100/media/Spring%20tool/P1020976_zpsv9liwodl.jpg.html)
(http://i1066.photobucket.com/albums/u410/RobWilson100/Spring%20tool/P1020975_zpsikoopsqb.jpg) (http://s1066.photobucket.com/user/RobWilson100/media/Spring%20tool/P1020975_zpsikoopsqb.jpg.html)
(http://i1066.photobucket.com/albums/u410/RobWilson100/Spring%20tool/P1020974_zpsvdccil9i.jpg) (http://s1066.photobucket.com/user/RobWilson100/media/Spring%20tool/P1020974_zpsvdccil9i.jpg.html)

Just the job for what your doing , Excellent  for screw cutting , and you get to make use of snapped centre drills/milling cutters   :med:


Rob

   
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on March 07, 2015, 11:00:14 AM
Rob, that's a very nice holder!

re. bringing up tailstock center -- the bore is still just the raw cored hole not centered, I could bore it out now, but the hole would be bigger than my tailstock center (MT1).

Maybe I should make a pipe center. Or maybe plug the hole with hardwood -- that might work and I wouldn't need to bore yet.

re. boring -- I should have put spacers behind the pulley -- the spindle is solid, so boring will mean removing the pulley, and re-centering it to get the spacers in. Otherwise everything could have been turned at one go.

I could try to make a spring tool like yours (I'd like to), but there are some complications -- I'm at the limit of my cross carriage back travel on the larger sheave. Maybe I can do it though if I substitute my boring table and make a tool holder to fit on that, since it is much longer and has more travel.

Running in reverse with upside down tool -- I don't think I have reversing capability with this washing machine motor -- haven't tried figuring out if the wiring would allow it -- I'm still confused on that subject for mystery motors. One thing that would work well though: no worries about chuck or faceplte unscrewing in reverse -- all fixtures/backplates are cast on their arbors. I change arbors to change fixtures.

But I might be able to make a rear toolpost for the boring table. So maybe I wouldn't need reverse to do that, and gain  parting ability, too?
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on March 10, 2015, 07:43:44 PM
I ended up plugging the hole in the pulley with a tapered hardwood plug, cutting it off and drilling with a center drill, and then bringing up the tailstock center as you suggested, Rob. That worked well enough for the first couple of sheaves. It got progressively better as I moved toward the headstock, and for the third sheave on, so I stopped using the tailstock -- it was getting in the way of measuring the groove spacing.

(http://www.vtsteam.com/Gingery/PulleyTurn.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on March 24, 2015, 01:08:21 PM
Today I cast a base for the new lathe I'm building in the furnace, and after 10 heats in winter, no functional problems with the plaster lining so far, despite the extreme cooling after a melt. There is some cracking, due to expansion and contraction of the lining -- but they seem quite stable. I've noticed that they disappear when the furnace is hot, and reappear when it cools down. Basically expansion joints. And no worse than my old fireclay and sand furnace refractory, which lasted ten years. In fact, better so far -- no patching has been necessary with the plaster furnace.

There are a few small chunks broken off around the top of the lining, but these occurred when the furnace fell over (long after a melt) because the warmth gradually metled a layer of ice under the soil. The furnace gradually leaned over and toppled with the lid on and an empty crucible inside. I was eating dinner at the time. A few linilng dings were the result, but nothing needing repair.

After the melt today, the furnace was hot. Spying on a shelf the old brass POV valve removed from the propane tank I had made the furnace from, I thought maybe I should try to melt that. If the lining is going to fail, that should do it -- temps are a lot higher and a lot longer heats needed for brass.

And curious to see whether my small atmospheric propane torch was man enough to melt brass, and if it did, what kind of brass would I get out of an old valve? Lots of interesting questions to explore! If the lining gave out, it wouldn't owe me anything -- the whole furnace cost me $22, I think, and I'd had a good number of heats already.

So I popped the valve into a small clay lined crucible and turned on the propane at partial throttle and 10 psi.

(http://www.vtsteam.com/Shop/MeltingValve.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on March 24, 2015, 01:28:36 PM
And the results after about 20 minutes:

Yes indeed, an atmospheric burner made from 1/2" EMT can melt brass in this furnace.  :thumbup:

Nope, the lining showed no change after melting brass.  :thumbup:

Yup, the brass looks halfway decent (Vermont expression, meaning "good")  :thumbup:

Guess the furnace owes me even less than it did.....

Brass muffin:

(http://www.vtsteam.com/Shop/brassmuffin.jpg)

The furnace lining, 11 heats incl. 1 brass melt:

(http://www.vtsteam.com/Shop/FurnaceAfterBrass.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: awemawson on March 24, 2015, 04:13:08 PM
Looks like you've hit on a useful formulation there Steve with your Plaster of Paris and sand - certainly seems to hold up well. Realistically it's only the first few mm that take the full heat I suppose. The temperature gradient from 'flame facing' outwards must be quite steep I expect.
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on March 24, 2015, 08:15:59 PM
Well I'd been thinking about using plaster for quite some time Andrew, after some references to sprue pouring liners (for insulation), and a reference to using gypsum blocks in a bronze furnace, and plaster in statuary practice. The sand part was in a video posted on the forum, and I used a sand and clay liner before, so it seemed reasonable -- I just wasn't sure how well it would hold up and if calcining would be a problem. It's working so far. And the insulation value seems very good. 2" is fairly thin, but the outside of the furnace doesn't get very warm after an aluminum pour.

Another point of interest -- melting crucible of aluminum in the furnace took 20 minutes with propane and 15 minutes with charcoal briquettes. Propane is neater, and faster to light, but more expensive and slower to melt.

Charcoal is easier to do other things around -- I don't like straying from the furnace when using propane in case of a flame out.

While charcoal is starting (no blast) i can ram up a mold, and have a hot furnace ready to melt metal when the mold is set down. In fact, I've had aluminum in the crucible begining to melt a little if I took longer than usual making up a mould, even without a blast in my old furnace. That was quite a surprise the first time it happened! And a very fast melt afterwards. My usual procedure building the first lathe was, a little lighter fluid in a furnace 1/4 full of charcoal, light off, and when the embers had just started, add the crucible with initial charge of alumnum. Cover the furnace, and go make up the mould(s). When finished, things were already hot, and the blast made short work of the melt.

I can see using both fuels on different occasions for different purposes. It would be interesting to see how well charcoal melts brass. Might try that soon.
Title: Re: Foundry Furnace for the Tiny Shop
Post by: mattinker on March 24, 2015, 08:59:43 PM
Hi Steve,

This is looking really good so far! definitely worth a try. Just a thought, any sign of glazing from the silica sand melting, the silica sand with the calcium from the plaster (if there's enough in the plaster present) should glaze over, if there isn't enough calcium, it should form water glass.

Time will tell, regards, Matthew

Edited to include glazing thoughts.
Title: Re: Foundry Furnace for the Tiny Shop
Post by: Manxmodder on March 24, 2015, 11:41:48 PM
Great results for little outlay,can't ask for better than that  :clap: :clap: well done.

I'll be really interested to see how well it melts brass on a charcoal firing  :thumbup:....OZ.
Title: Re: Foundry Furnace for the Tiny Shop
Post by: RobWilson on March 25, 2015, 01:59:16 PM
I would say well done that man  :thumbup: , dam fine result  for $20  :ddb: :ddb: :ddb:   


 only a Yorkshire man would want it done for 10 cents cheaper  :lol: :lol: :lol:


Rob ( running away )  :ddb:
Title: Re: Foundry Furnace for the Tiny Shop
Post by: awemawson on March 25, 2015, 02:07:20 PM
I would say well done that man  :thumbup: , dam fine result  for $20  :ddb: :ddb: :ddb:   


 only a Yorkshire man would want it done for 10 cents cheaper  :lol: :lol: :lol:


Rob ( running away )  :ddb:

Oi !

Andrew (Yorkshireman :)  )

Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on March 25, 2015, 03:22:27 PM
$20? Wasteful luxury! Why, when we were kids we used to melt titanium in a carboard box lined with horse manure and consider ourselves-ill used to escape ten cents the poorer........
Title: Re: Foundry Furnace for the Tiny Shop
Post by: awemawson on March 25, 2015, 03:30:02 PM
Steve, I do believe we've converted you to British humour  :lol:
Title: Re: Foundry Furnace for the Tiny Shop
Post by: tom osselton on March 25, 2015, 04:44:45 PM
Lucky ba**ard we never had a box!   :)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: Will_D on March 25, 2015, 06:02:47 PM
Ehh! you were lucky:

Titanium:

We had to scrounge the wires from the young ladies bras' to aquire enough "Tit-ane-er-ium" to melt down to cast 'owt useful from that imaginatively named metal  :bugeye:
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on April 30, 2018, 10:16:05 PM
Looked up this old thread because I'm finally rebuilding -- or relining the tiny furnace. Not because of any defect from heats, but because the lining got wet and stayed that way all winter this year -- I hadn't noticed, since the lid was on. The lining went soft and crumbly -- maybe the multiple freezes and thaws had a hand. Anyway, the price of plaster of paris is now up $2 I noticed. Bought one for the refurb.

This evening before dinner, I chopped and scraped out all the old lining, ready for renewal. Read this thread over to see what I'd done 3 years ago...oh, also restored all my photos in it after, you know, the Photobucket fiasco.

I'll try to get pix of the relining process.

(all this is in preparation to resuming casting for the headstock cap on my uhhhhh "new" lathe build).
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on May 01, 2018, 10:15:09 PM
After work today, I took a wire brush to the inside of the old furnace shell:

(http://www.vtsteam.com/TinyFurnace/TinyFurnaceShell.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on May 01, 2018, 10:19:46 PM
Nice to be working on grass again instead of snow, or later, mud. The bit of lawn above wasn't green three days ago. Spring happens fast here when it decides to!

I found a piece of Sonotube (cardboard concrete form) in the big shed that was close to the ~8" OD I wanted. It was 8-5/8", so I cut a strip out 1-1/2" wide.

(http://www.vtsteam.com/TinyFurnace/CutSonotube.jpg)

Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on May 01, 2018, 10:22:27 PM
And then taped it back together.

(http://www.vtsteam.com/TinyFurnace/TapedSonotube.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on May 01, 2018, 10:25:52 PM
These are the ingredients for the lining renewal: some water, sand, and plaster of Paris, plus the Sonotube and shell.

I taped a bit of PVC pipe in the Tuyere opening to serve as a plug. I stuffed both ends of the pipe with paper towels to prevent the liquid lining pouring out before it set.

(http://www.vtsteam.com/TinyFurnace/Ingredients.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on May 01, 2018, 10:30:12 PM
You can see the Tuyere plug here, set at an angle to give a tangential flow for the blower (charcoal) or burner (propane).

I taped around the outside of the plug also, to prevent leaks.

(http://www.vtsteam.com/TinyFurnace/TuyerePlug.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on May 01, 2018, 10:40:24 PM
The shell is 12" in diameter, and with an 8" form, I should end up with 2" of lining.

Plaster of Paris is quite a good insulator. It's used as sprue and riser liners in big time iron casting for this reason. My guess is that the insulative quality is partly a result it being quite porous when cured. To be honest I was surprised to first learn that plaster was used in iron work at all. Bronze statuary, yes. Anyway reading that was one of the reasons I thought it might work out long term for this non-iron melter.

This originally experimental furnace really did live up to the hope -- and if I hadn't let it sit wet over this last winter, the first lining would still be giving good use. I've easily melted brass in it, as well as the lower temp aluminum and zinc castings for my "new" lathe.

Anyway, here's the first pour of plaster and sand mix. This forms the bottom, and I waited for it to set up before putting the Sonotube form in.

(http://www.vtsteam.com/TinyFurnace/BottomPour.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on May 01, 2018, 10:54:04 PM
I mixed plaster of Paris by filling half a gallon bucket with cold (not warm) water. Then I poured plaster in to the center slowly until it took no more and formed a lasting "island" in the middle of the water, without collapsing. Like in the photo below. That's the normal mix rate.

Then I mix by hand. Literally. You put your hand in and stir and squeeze out all the lumps. Trust me, a spoon or any other utensil will not work as well, and you will get lumps.

Then sand is added. I just added hand fulls to roughly what felt right. I'd guess about the same amount as I'd added plaster. Again, the hand stirring and lump dispersal method is best.

Then just pour.

Plaster of Paris will take anywhere from 3 to 20 minutes to begin setting up, depending on temperature, quantity mixed, and what it's mixed with. Sand, temperature, and volume of mix all accelerate it. So cool temps, mixing no more than 2 quarts (liters) of water, and stirring and pouring quickly all help.

I've had it go off in summer in 3 minutes, which isn't even enough time to clean out your container. It cures by exothermic reaction -- in other words it generates heat in curing -- a bigger volume generates more heat more quickly.

(http://www.vtsteam.com/TinyFurnace/MixingPlaster.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on May 01, 2018, 10:55:43 PM
Second pour, with the form in place:

(http://www.vtsteam.com/TinyFurnace/SecondPour.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on May 01, 2018, 10:57:54 PM
Again I waited until the plaster started to feel firm. And then made the third pour.  I'd done that before placing the Sonotube, too. Otherwise it would have embedded into the bottom, and been hard to remove.


(http://www.vtsteam.com/TinyFurnace/ThirdPour.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on May 01, 2018, 11:02:15 PM
Lasxt pour. This time I added extra sand to make it a bit firmer so it wouldn't overflow the lip of the shell. I wanted to build the height up a small amount towards the cardboard form. That can be abraded back down to fit the lid -- but if the top is left with hollows, then it will leak rather than forcing the exhaust through the flue hole. A slightly thickened mixture allows that little bit of slope from the tube down to the shell edge, without runoff.

(http://www.vtsteam.com/TinyFurnace/LastPour.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on May 01, 2018, 11:06:38 PM
Letting it cure for about an hour, I stripped out the cardboard form by collapsing the seam edge inwards.

It probably only took 2 hours total to renew the lining, and the cost was $16 worth of plaster of Paris -- the sand water and Sonotube, were already on hand.

I didn't have time to do the lid -- have to leave something for tomorrow.....  :dremel:

(http://www.vtsteam.com/TinyFurnace/Unmolded.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: awemawson on May 02, 2018, 02:58:36 AM
Great work Steve, and also great to see you back doing things :thumbup:

I'm amazed that the P.O.P. lining stands up to iron temperatures even with the addition of the sand. When I was doing lost wax casting it was OK for aluminium but brass, bronze and copper needed a special high temperature version. For iron I used a hybrid of lost wax to form the cavity, and sodium silicate for the bond with dry silver sand - worked pretty well.

I'm no chemist, but as I understand it, the high temperatures decompose the P.O.P. by reversing the hydration reaction.  :med:
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on May 02, 2018, 07:31:34 AM
Andrew thanks!  :beer:

also, re poP and iron, according to Steve Chastain, plaster of Paris is used commercially for insulative sprue and riser liners for iron, not iron foundry furnace linings. I wasn't suggesting that. I assume those are single use applications.

Iron melting wasn't the intention from the start with this furnace -- non ferrous melting was the spec. Worked fine for that. I have my other furnace for iron.
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on May 02, 2018, 09:29:43 AM
And Andrew, as for melting brass, see here and next few posts in this same poP furnace lining thread:

https://madmodder.net/index.php/topic,10482.msg121017.html#msg121017 (https://madmodder.net/index.php/topic,10482.msg121017.html#msg121017)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on May 02, 2018, 08:38:33 PM
I poured the lid today the same way. I used a 3" shampoo bottle to make the vent hole form. It fit the metal lid perfectly.

(http://www.vtsteam.com/TinyFurnace/LidPour.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on May 03, 2018, 09:37:09 PM
Form removed, lid is done.

(http://www.vtsteam.com/TinyFurnace/LidFinished.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on May 03, 2018, 09:38:20 PM
And the shell given a new coat of paint:

(http://www.vtsteam.com/TinyFurnace/Painted.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: sparky961 on May 03, 2018, 09:47:53 PM
Looking good.

Not that it helps you now, but pearlite (slightly crushed) is another good addition to DIY refractory. Available at garden centres.
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on May 03, 2018, 10:11:00 PM
Sparky I've got plenty of it on hand, and used it 17 years ago in the lid of my first furnace (see my Gingery lathe thread), but found it eroded pretty easily compared to the current lid lining, and was difficult to patch after.

The plaster of Paris mix I'm using now is, in my experience even more insulative than the perlite mix I used before. The furnace shell stays noticeably cooler after a similar melt.

If you've ever felt plaster of Paris once it's dry, it is surprisingly light in weight. That's because it is highly porous -- and therein lies the insulative quality.

There's a million ways to skin a cat -- I've worked through a few of them ...enough to know what works best for me -- others will certainly vary.  :beer:
Title: Re: Foundry Furnace for the Tiny Shop
Post by: awemawson on May 04, 2018, 02:14:50 AM
. . . Ah all very well BUT

. . . How did they cast the ancient Pillar of Dehli . . .?

Google it  :clap:
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on May 04, 2018, 04:12:11 PM
Forge welded wrought iron, not cast iron, according to Wikipedia.......when I Startpaged it.   :poke:
Title: Re: Foundry Furnace for the Tiny Shop
Post by: awemawson on May 04, 2018, 05:04:09 PM
Well done Steve - you are the  only one to find out  :clap: :clap:

It's a myth that it is cast stemming from the Victorian era of the Raj when of course a lot WAS cast !
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on May 04, 2018, 07:58:16 PM
It always seemed confusing to me that wrought iron and cast iron were completely different animals. Wrought iron having less carbon than steel makes sense, "iron" being the element name. But cast "iron" having  more carbon than high carbon steel doesn't. Why call it iron then? Or why steel at all? Just call it all iron, and modify the name by how much carbon it has. Aluminium alloys are always aluminium. I dunno.... there was a time, before I was casting when I thought cast iron was really just pure iron.

Uhhhhhh no.  :wack:
Title: Re: Foundry Furnace for the Tiny Shop
Post by: hermetic on May 05, 2018, 09:26:08 AM
Hi VTsteam, When you put iron ore in a blast furnace with coke and limestone, what you get running out of the bottom, is pure iron, but because it has been smelted with coke, it has picked up a high content of carbon. When the run off is allowed to cool it is known as cast iron. Cast iron is very strong under compression, but also very brittle. The process for producing wrought iron from cast was to remelt the cast iron in a reverbatory furnace (where the iron is heated by indirect heat, so it cannot absorb any more carbon) the furnace, known as a puddlers hearth is also charged with iron oxide, and when the iron melts the carbon reacts with the oxygen in the oxide, and boils out of the iron as carbon dioxide. This reduces the carbon content, and after a process of removing from the furnace and power hammering (and repeating) it becomes almost pure iron with fibres of slag running through it, which can be seen on a piece of fractured wrought iron. Take pure iron, minus the slag, and add to it a small amount of carbon, and you have mild steel, useful, but not hardenable other than case hardening. Add slightly more carbon, and you have a tool steel that can be worked and shaped hot in its soft state, and then hardened through and tempered so it is tough, and will also hold a sharp edge. All these metals are Iron/carbon alloys, and this is a gross simplification of metallurgy as learned in the school metalwork shop and from the excellent Hardening, tempering and heat treating by Tubal Cain, No1 in the workshop practice series. hope this helps,
Phil
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on May 05, 2018, 10:10:40 AM
Yup.  I've cast iron. Terry Aspin's books in that same series are some of my favorites.

I'll be tempering the furnace lining today (different kind of tempering) and I hope even casting something, if I can get my old greensand into condition, and the pattern finished.....  :beer:
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on May 05, 2018, 09:51:51 PM
Today I made first heat in the Tiny furnace -- working up gradually to drive the moisture out of the lining. I started out with some wood kindling:

(http://www.vtsteam.com/TinyFurnace/WoodFiring.jpg)
Title: Re: Foundry Furnace for the Tiny Shop
Post by: vtsteam on May 05, 2018, 09:57:51 PM
I set a piece of stovepipe on top of the furnace lid for a gentle draw -- a blower would have been too much.

When the wood had burned down, I added a layer of charcoal briquettes, about 2 deep. After half an hour again, I filled the furnace up half way with charcoal, and then let it cook for most of the day.

I also conditioned my greensand, which was dry as the Sahara. All in all a rewarding Spring Saturday, with daffodils in full bloom, and my casting gear coming back into some semblance of working order.  :ddb:

(http://www.vtsteam.com/TinyFurnace/ChimneyDraw.jpg)