Plaster-sand mix forge concept

[Micah Burgin]

So, kicking around some ideas lately has led me to try and figure out a way to use an easy and cheap refractory-ish material that can be obtained for relatively little in the way of both time, and money.

 

First off, the 3D model concept included here is in no way final. If you want, I can upload it, but the dimensional breakdown is as follows anyhow:

base: this is essentially totally scale-able. anything from a general use forge effective from rivets and nails to axes and tongs to a charcoal fired sword forge. basically, what you want to do is line up bricks from 3-wide to 5-wide and 5-long to whatever you want, for the base of it. then, make a second layer of bricks on top of that one with the row in the middle missing, and one or more side bricks missing in order to allow the air porting. (Either one in the middle, or two with one brick in between)

 

Next, you'll need to add the plaster sand mix to the fire pot. place some cinder blocks or bricks to block off the ends of the trough and then lay a PVC pipe of any thickness into the air trough (1/2 inch would be best) and either cut it so that it ends in the middle or at the end of the air trough. now, you'll need to mix 1 part sand, 1 part plaster, and 1 part water together. try not to make too much, but if you think you have, use it as mortar for the bricks in the assembly. Once the mixture is partially solid (The consistency of mud, almost) pour it into the trough over the PVC pipe and cut a V into the center. Make sure that the PVC segment is covered with the mixture (At least 1/4 inch worth) so that it's somewhat shielded from the heat (Don't worry if it melts or burns though, the plaster mix will hold its shape perfectly even if the stiffener is gone.) and leave to dry.Once dried, you'll need to start work on the cover.

 

There are many options for the cover, but here's the basics: you need some form of U shape with the back enclosed. You can close off the back with steel, so don't worry too much about that. it'll also need a hole in the back to vent out hot gasses somewhere other than your face. 

 

It can be made with a mold, or with something to prop it up (A bucket, piece of sheet metal, etc., will work great) and you can make it on top of the base this way.

 

The 3D model has my approximation of the location of the fireball (Just guessing) and most of the concept for you, but the above information should help you make one. I'm going to be making one soon, but the basic cost for the normal size one would be about 10 bucks for the bricks if you use the 2x4x8 ones that come anywhere around 40 Cents each., plus a bag of plaster and a bag of sand ends up at about 40 bucks (Assuming you're getting 50 pound bags of plaster and sand) total, with enough left over to make a Re-bar grid for the air outlets, which you can just build into the plaster to anchor. Not too bad as far as costs go!

If you are not a fan of stooping down to your forge, make sure that it's on a table when you're making it where it can have a permanent residence, or use bricks to build up a base and then place some plywood or other sheet material on top of it.

 

This is the concept for the forge. Orange ball = approximate location of the fireball. Air in and out ports as well as the air inlet are visible. This is intended to have a metal sheet or baking tin used as a front cover to hold in heat, but can just as easily be used without. you may also want to add in a hole over the air outlet so charcoal can be dropped in from above, but be sure to make something to block it up if you do.

[Charles R. Stevens]

Plaster of paris makes a poor refractory and a worse insulator. It's used for low temp casting of jewelry. 

[Micah Burgin]

15 minutes ago, Charles R. Stevens said:

Plaster of paris makes a poor refractory and a worse insulator. It's used for low temp casting of jewelry. 

Yes, it is, but mixing it with sand actually fixes that problem.

Here's a video of someone using it with charcoal to melt aluminum, and he gets steel yellow hot in there, without even positioning it well: https://www.youtube.com/watch?v=hHD10DjxM1g

I've worked with it and it's both a good insulator and a decent refractory material. Cures fast, too.

 

Just to be clear, it's a fifty-fifty mix of plaster and sand where the plaster acts as a binding agent and takes on the properties of sand for the most part, and is capable of both insulating and taking a beating.

Edited November 16, 2015 by Micah Burgin
Wrong 's.

[Smoggy]

[Latticino]

Mixing it with sand will certainly help with it's refractory properties, but I doubt greatly it does anything for it's insulating capabilities.  Two things to remember from that DIY video.  First, there is no indication of how much fuel needs to get dumped into the melting furnace, so efficiency (which is pretty directly related to insulating capacity) is not spelled out.  The other is that aluminum melts at around 1,250 deg. F and forging temperatures can reach twice that.  I'd be really careful to put some kind of non-flammable and preferably insulating material between this proposed enclosure and any table support (unless that table is itself quite heat resistant).  Of course your bricks will help with this, but be aware that normal bricks and concrete block are not rated for this kind of temperature either. 

It might be prudent to actually build one of these before recommending a design to all and sundry. 

I'd say this material would be fine for the basin of a solid fuel forge.  After all, folks use raw clay mixed with a variety of additives (including sand) for that as well.  If it burns thru you can just break it out and replace it cheaply.  Not sure how this mix will resist flux, of course, but that may not be a big concern for you.

Finally, here is some additional information that may help you in your cheap refractory formula search.  Admittedly it isn't on You Tube, but Anvilfire has some very reputable contributors, and this one appears to have actual forge building experience: 

Good luck

 

Anvilfire does not allow hotlinks from it's site

[Charles R. Stevens]

I'm with you Smoggy, 

[the iron dwarf]

burning pvc pipe will produce toxic fumes

[Micah Burgin]

19 hours ago, latticino said:

Mixing it with sand will certainly help with it's refractory properties, but I doubt greatly it does anything for it's insulating capabilities.  Two things to remember from that DIY video.  First, there is no indication of how much fuel needs to get dumped into the melting furnace, so efficiency (which is pretty directly related to insulating capacity) is not spelled out.  The other is that aluminum melts at around 1,250 deg. F and forging temperatures can reach twice that.  I'd be really careful to put some kind of non-flammable and preferably insulating material between this proposed enclosure and any table support (unless that table is itself quite heat resistant).  Of course your bricks will help with this, but be aware that normal bricks and concrete block are not rated for this kind of temperature either. 

It might be prudent to actually build one of these before recommending a design to all and sundry. 

I'd say this material would be fine for the basin of a solid fuel forge.  After all, folks use raw clay mixed with a variety of additives (including sand) for that as well.  If it burns thru you can just break it out and replace it cheaply.  Not sure how this mix will resist flux, of course, but that may not be a big concern for you.

Finally, here is some additional information that may help you in your cheap refractory formula search.  Admittedly it isn't on You Tube, but Anvilfire has some very reputable contributors, and this one appears to

have actual forge building experience: 

Good luck

Yeah, this will obviously be revised post build. If nothing else, the mixture would serve very well as a structural concrete-like substance, and essentially make a good base to put refractory on. As far as flux goes, yes, that's not really an issue for me. and if you look at his steel crucible, it's reached yellow, and my aluminum casting expirience (Which is not vast, but I'm pretty well-versed) has shown that to get aluminum to flow properly and expel impurities, it needs to be at or above iron forging temperatures. You can tell when it's reached them because the molten metal will glow like solid iron does, and as you can see from the video, his does. Note that aluminum hits dull red when steel hits orange or yellow (Depending on the distance from the fire, obviously, with such a large crucible worth) so that should be fine.

 

I'm going to put a little disclaimer at the end of the post, :3

 

13 hours ago, the iron dwarf said:

burning pvc pipe will produce toxic fumes

Yeah, it can, but if you're running it in a curing burn, I'd highly recommend just blocking off the front and standing away from the back outlet port, should dispel any toxic fumes. Also, remember, it's only going to be about a cubic inch worth of PVC burning at most, so you should be fine.

 

Anyways, I'll quickly revise the post to include info on pre-coating with refractory or using refractory bricks as the arch for the top. I think I'll try both (Got plenty of plaster and sand, and bricks are really cheap anyhow) to see what's best. 

 

Thanks so much for the help guys! The info is very useful!

 

(BTW, I think I'm going to do a test on the insulating properties of the stuff. Any recommendations on how? I'm thinking a calorimeter and trying to measure it's specific heat capacity but that's tricky because of the water involved....)

[Charles R. Stevens]

Partner, your doing folks a disservice. Tho it will probably work for a wile, it certainly isn't the best or cheapest way to do this. Adobe mud is cheaper, better insulating and tends to partially vitrify. We have descused plaster of Paris more than once, and many of the folks here have been forging longer than you. Now as a personal experiment great, but as this is an Internet document that many folks will read, and some will take as gospel, please differentiate between you opinion and experience.

by the way, YouTube has some real gems, but more trash, vet it carefully.

[Micah Burgin]

42 minutes ago, Charles R. Stevens said:

Partner, your doing folks a disservice. Tho it will probably work for a wile, it certainly isn't the best or cheapest way to do this. Adobe mud is cheaper, better insulating and tends to partially vitrify. We have descused plaster of Paris more than once, and many of the folks here have been forging longer than you. Now as a personal experiment great, but as this is an Internet document that many folks will read, and some will take as gospel, please differentiate between you opinion and experience.

by the way, YouTube has some real gems, but more trash, vet it carefully.

I know that youtube is full of trash, but this guy is good.

 

And yeah, you guys do have more expirience, I'll never deny that.

 

As far as this post is concerned, I tried (Possibly failed, but I did try) to frame it as a concept, not as an end all be all guide to the perfect enclosed charcoal forge, and hopefully people will pick up on that. And of course, the golden rule of internet forums, if there are comments, read them first!

 

I think that there are many people who would realize that this is purely conceptual, especially from the title of the topic, and I think you might be overlooking that. Then again, this is the internet, where assuming the stupidity of some is not just safe but recommended.

[Smoggy]

14 hours ago, Smoggy said:

I hate to say it, but I told you so.......

[Charles R. Stevens]

smoggy, whats the quoat about "wise men not arguing..."

I'll leave this one for some one with less tact and more tolerence. 

[Micah Burgin]

5 minutes ago, Smoggy said:

I hate to say it, but I told you so.......

What is the smiley supposed to mean exactly? Is this some odd forum tradition I am not familiar with?

[Latticino]

1 hour ago, Micah Burgin said:

 if you look at his steel crucible, it's reached yellow, and my aluminum casting expirience (Which is not vast, but I'm pretty well-versed) has shown that to get aluminum to flow

 

(BTW, I think I'm going to do a test on the insulating properties of the stuff. Any recommendations on how? I'm thinking a calorimeter and trying to measure it's specific heat capacity but that's tricky because of the water involved....)

Please remember that digital pictures and video don't give anything like accurate colors for heated steel.  If you look carefully, or even experiment yourself, you will notice that the steel being forged in most amateur videos looks like it is much hotter than required (often white hot).  This is due to the camera sensing elements, not the actual heat of the material. 

As this is only the basin for holding solid fuel, insulating characteristics are not necessarily critical as regards potential for forging, just for keeping the body of your forge from burning the surroundings and the rest of your assembly (including the PVC, whose vapors on burning are nasty).

Insulating properties for materials can be calculated for known material thickness, enclosure geometry and interior and exterior temperatures.  Of course losses from various types of heat sources must also be taken into account (i.e. radiant losses from doors and convective heat losses from transfer of products of combustion).  Probably the best way to test materials would be using electric heating coils (where an enclosure can be fully sealed).  I'll bet ASTM has a standard for this (ASTM C177 or C518).

Please note that the thermal conductivities of some of the products you have been discussing are as follows:

Plaster/sand mix:  0.71 W/(m deg K)  per the Engineer's Toolbox (which I have found to be rather accurate),

Insulating fiber blanket:  0.07 W/(m deg K) per manufacturers data.

Note that the latter is 10 times better insulator at a more elevated temperature

[Charles R. Stevens]

Smoggy is laughing at me aguing with a young know it all new guy. 

Now, after picking on said new guy, mind a bit of advice? 

[Micah Burgin]

1 minute ago, latticino said:

Please remember that digital pictures and video don't give anything like accurate colors for heated steel.  If you look carefully, or even experiment yourself, you will notice that the steel being forged in most amateur videos looks like it is much hotter than required (often white hot).  This is due to the camera sensing elements, not the actual heat of the material. 

As this is only the basin for holding solid fuel, insulating characteristics are not necessarily critical as regards potential for forging, just for keeping the body of your forge from burning the surroundings and the rest of your assembly (including the PVC, whose vapors on burning are nasty).

Insulating properties for materials can be calculated for known material thickness, enclosure geometry and interior and exterior temperatures.  Of course losses from various types of heat sources must also be taken into account (i.e. radiant losses from doors and convective heat losses from transfer of products of combustion).  Probably the best way to test materials would be using electric heating coils (where an enclosure can be fully sealed).  I'll bet ASTM has a standard for this (ASTM C177 or C518).

Please note that the thermal conductivities of some of the products you have been discussing are as follows:

Plaster/sand mix:  0.71 W/(m deg K)  per the Engineer's Toolbox (which I have found to be rather accurate),

Insulating fiber blanket:  0.07 W/(m deg K) per manufacturers data.

Note that the latter is 10 times better insulator at a more elevated temperature

Okay, thanks for the info. I think that this is mainly just going to be acting as an enclosure. Any info on common refractory cement? 

And of course, specific heat capacity (the metric one, forget it exactly sorry) is what I'd be getting out using a normal calorimeter.

2 minutes ago, Charles R. Stevens said:

Smoggy is laughing at me aguing with a young know it all new guy. 

Now, after picking on said new guy, mind a bit of advice? 

Anything is useful, sorry if I come across as the aggravating newbie, always did suck at first impressions.

Please realize that if I come across as against constructive criticism it's just me being defensive, feel free to bust my head in if need be. I usually do better with CC, don't know what was wrong at the time, must've been tired or out of whack or something.

[ThomasPowers]

Well a few questions---How many of these have you built?  How many hundreds of hours have you used them to check out their efficiency and longevity?

Or are you telling folks how great it will be with NO personal experience?   Do you have the experience to be able to rate the accuracy of what you see on the screen or even with what you may build and test?  (Avoiding the "I've never used a different one but I can say this one is best")

 I've used clay and wood ash for  forge liners before for several years each one; FREE, long history of use. I have friends who have used just an ash bed as a forge base; FREE long history of use...got more than a decade of using various adobe based forges for historical demos out here in adobe land.

[Micah Burgin]

1 minute ago, ThomasPowers said:

Well a few questions---How many of these have you built?  How many hundreds of hours have you used them to check out their efficiency and longevity?

Or are you telling folks how great it will be with NO personal experience?   Do you have the experience to be able to rate the accuracy of what you see on the screen or even with what you may build and test?  (Avoiding the "I've never used a different one but I can say this one is best")

 I've used clay and wood ash for  forge liners before for several years each one; FREE, long history of use. I have friends who have used just an ash bed as a forge base; FREE long history of use...got more than a decade of using various adobe based forges for historical demos out here in adobe land.

I've never made one, hence why it says CONCEPT in the title and SHOULD work like I said, not WILL.

 

Hopefully it shouldnt've (Not a real contraction sorry) come across as from expirience?

[Latticino]

I don't have a tremendous amount of experience building solid fuel forges.  In my experience of using same they don't need a lot in terms of "enclosures", just something to consolidate the fuel in a location where the forced air can be directed to burn it as required (not to mention drain away the ash produced).  I would certainly experiment, but believe that you are overthinking your forge design, and possibly combining it with flue design (which is a whole different kettle of worms).  Might want to try building a successful design before you set out to reinvent the wheel.

[Micah Burgin]

Just now, latticino said:

I don't have a tremendous amount of experience building solid fuel forges.  In my experience of using same they don't need a lot in terms of "enclosures", just something to consolidate the fuel in a location where the forced air can be directed to burn it as required (not to mention drain away the ash produced).  I would certainly experiment, but believe that you are overthinking your forge design, and possibly combining it with flue design (which is a whole different kettle of worms).  Might want to try building a successful design before you set out to reinvent the wheel.

Yeah I think I'll try using the stuff as a base packed with ash (Since ash is a proven material) in order to explore a possible usage for it as (With no proper technical term in my vocabulary) "Hogging" or general forming material  in order to make a shelf and fire bowl... That way, no insulation is required and since it's just the base it could technically be done with a hole in the ground...

 

SORRY! I'm a huge over-thinker. The blessing and curse of a STEM-oriented mind, eh?

[ThomasPowers]

I have a pair of BS degrees myself and while you don't have to be a rocket scientist to be a good smith I know several good smiths that were rocket scientists...

[Charles R. Stevens]

Lol, with that attiude you'll do fine.

first hint that you where a young new guy, first post is about a sword forge, and the self assuredness that your idea was new and great. Second that you needed a 5' long forge to do the job. 

Most newbies want to forge swords off the bat, most of us have been there. 

Swords, axes and most everything else ( thick sections and powerhammers are exeptions) is forged 6" at a time, swords are a high order skill set, reguiring basic, Intermidiat and advances forging skills. Not to mention basic, intermidiate knife making skills. 

We have seen that so often its an inside joke, we all role our eyes when we see it, then we wait to see who is dumb enugh to wade in and "help" usualy ends badly, hurt feelings all around and the new guy quits in a huff. 

How about we start with a nice viking erra inspired side blast that will go nicely with your 8# sledge anvil? Then from there we can forge some tools to get you started on your way?

 

BS, wat did Frosty say about sharing inisuals with Black smith?! Lol

[Micah Burgin]

Sounds great to me! Just to be clear I suggested that the design was scalable, not that it needed to be 5', haha!

 

I honestly don't want to make swords that much, so anything works as far as a forge for me.

 

And side blast sounds good. I have an old fire pit lid, I'll post some pics so we can plan something based on that as its center. 

[Charles R. Stevens]

TP, we might be aboe to do somthing with this kid!

colledge hasent ruint him yet...

Dosnt take much

[Micah Burgin]

11 minutes ago, Charles R. Stevens said:

TP, we might be aboe to do somthing with this kid!

colledge hasent ruint him yet...

I feel like you'd love my work bench, hahaha! 

 

And that's all I need for the info, I have some ash-y mud from making charcoal that'd go great with that design. I'll try it out today, hopefully I can run it by wednesday and show you guys my results.

 

Just for clarification, about how deep is the fire pot in your design? Kind of hard to tell from the angle.