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Overview of metal casting for beginners


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#1 Dan Manders

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Posted 15 December 2011 - 05:41 PM

Hi all, figured I'd make my first post something useful rather than a question. I know more about casting than blacksmithing, so I figured I’d help add to the casting section a little by providing a general overview of how to get started in casting, reference books, equipment needed, safety precautions, etc. Hopefully this will be something that can be referenced to give some direction to the people asking "how do I start casting metal" or "can I cast my own anvil", etc, since there seem to be a fair number of those posts. I just did a bronze pour and ended up repeatedly explaining the process to all of my neighbors in the building where I live and work, so all of this been in the front of my mind this week anyway. Before all the info I’ll show some pictures of the pour, since it always looks pretty cool.

View of my furnace running, with investment molds in the foreground: Attached File  DSC_0042.jpg   35.9KB   456 downloads
Me checking on or poking something: Attached File  DSC_0045.jpg   59.08KB   515 downloads


Taking the crucible out of the furnace: Attached File  DSC_0061.jpg   31.5KB   506 downloads
Pouring: Attached File  DSC_0114.jpg   12.58KB   463 downloads


Poured: Attached File  DSC_0190.jpg   33.17KB   470 downloads
This is what was inside (16 acorns + gating system): Attached File  DSC_0057 2.jpg   96.46KB   492 downloads
Acorn TIG welded to a steel stub (will be attached to a forged branch on a gate): Attached File  DSC_0065.jpg   18.73KB   481 downloads
A bunch of acorns, ready to be attached to the gate: Attached File  DSC_0071.jpg   46.72KB   439 downloads


SAFETY


Don’t do this unless you’ve done your due diligence. Ideally you would learn from someone in person, but if this isn’t possible you should read a few books (recommendations at the end of this post) and watch some videos of home metal pours on the internet. Molten metal in any quantity larger than a weld puddle is extremely dangerous, and not respecting it is for a serious accident. If you have questions, ask. Don’t blame me if you hurt yourself.

MOLTEN METAL
Once you have any quantity of molten metal, moisture becomes an extreme danger. A drop of molten metal on concrete (which holds moisture) will turn the water in the pores to steam, causing a small explosion which will propel liquid metal and chips of concrete into the air. Now think about what would happen if you spilled a whole crucible. ALWAYS CARRY AND POUR METAL OVER DRY SAND.


If you stick anything—a stirring rod, a skimmer, more pieces of metal to melt—into the crucible when there is molten metal in it, that object needs to be DRY. This is as simple as preheating metal on top of your furnace while it is running, and holding the end of any tools in the exhaust flame for a few seconds, but if you forget you will cause the molten metal to explode while you are standing there with your face over it. Likewise, your ingot molds (where you pour the leftover metal after filling your molds) need to be preheated on the furnace, or an explosion will occur. ASSUME THAT UNLESS SOMETHING IS TOO HOT TO TOUCH, THAT IT IS WET.

SAFETY EQUIPMENT
Goggles and a faceshield, not one or the other. Thick leather jacket, stick welding gloves, jeans, and heavy leather boots. That’s what I wear. Works fine to protect against the occasional bit of splatter, and at least won’t melt to your skin in a disaster scenario. Always keep a bucket of dry sand and a shovel on hand in case of a spill, and a chill bar (piece of heavy angle iron welded to the end of a three foot rod) to seize up the flow in case of a mold bursting or leaking.


HOMEMADE CRUCIBLES
Because of the serious dangers involved in working with molten metal, I strongly recommend NOT using a homemade crucible for anything hotter than aluminum (ie any copper alloys and cast iron). The proper crucibles will be discussed below with each individual metal, and a suitable homemade crucible for aluminum and other low-temp alloys will be explained.


Proper crucibles are essential, even if you make every other part of your setup: Attached File  DSC_0057.jpg   45.27KB   445 downloads

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First I’ll give a quick overview of some different metals you might want cast, and then I’ll give some details about the general equipment you’ll need to make for a small foundry.

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METALS

STEEL
Alright, so first off, you are probably never going to cast steel at home, and you are definitely never going to make a steel casting the size of an anvil. That’s just reality. Getting a crucible furnace to the temperature needed to pour steel is possible, but it will turn your furnace into a consumable. I’ll address this first, since it seems like a lot of people are interested in casting steel.


Here are approximate melting points of some various metals (all temperatures in F):

Mild Steel: 2750
Cast Iron: 2100
Silicon Bronze: 1800
Aluminum: 1200
Lead: 680


Keep in mind that you need the metal to be superheated a few hundred degrees above these temperatures to successfully pour them, so for example iron will be poured around 2300-2500 (hotter for thinner castings). The temperature in your furnace will need to be even hotter than this, meaning that your internal furnace temperature will be close to 3000. The refractory I used for my furnace is rated at 3000, and as mild steel melts at around 2750, you can see why melting it will rapidly destroy your furnace. Here is a picture of the refractory lining on my furnace where a drop of molten iron landed on it:

Attached File  DSC_0062.jpg   56.8KB   461 downloads

Bronze and aluminum will just stick to the surface, but molten iron literally eats right into it. The furnace gets so hot that you need one of the green oxy-acetylene faceshields just to view it with the lid open. It just can't handle the temperatures needed to melt steel.

CAST IRON
That said, with a properly constructed furnace melting cast iron is not at all difficult, however you need to use sand molds, as investment molds of the type you make at home (discussed below) cannot handle the temperature of molten iron (I’ve tried). Sand molding is an art form in itself, and getting it right will take a good bit of practice. There are a number of good books on this recommended at the end of the post. Finally, for cast iron, you need to purchase a clay-bonded graphite crucible. DO NOT MELT IRON IN SOMETHING YOU MADE YOURSELF. A crucible will run you $50-100. It’s an extremely cheap insurance policy, and is well worth every penny. Seriously. Not kidding. Virtually every piece of foundry equipment I have is homemade, except my crucibles for bronze and iron.


BRONZE
Ok, on to the nonferrous stuff. I personally only use silicon bronze for my copper-alloy castings, for a number of reasons. The first is it’s composition: Roundabouts 96% copper, 3% silicon, and 1% manganese. Here’s why that is important: brasses and other bronzes generally contain considerable amounts of zinc, tin, and/or lead in addition to the copper. To melt these alloys, you need to heat them above the temperature at which the alloying elements vaporize. This means that some zinc, lead, tin, etc will escape from the surface as a gas, especially when you stir or skim the melt. This means that besides exposing yourself to seriously toxic fumes, you are changing the composition of the metal every time you melt it. Silicon bronze does not change composition even after melting it dozens of time (as long as you keep a crucible only for that alloy), making it perfect for home use where we can’t test the composition of our alloys and where we want to immediately reuse the metal that makes up the gating system. Additionally, you can buy silicon bronze rods from most welding suppliers, meaning that you can weld it with an oxy-acetylene torch or a TIG welder and get a perfect color match (especially great for fixing small pits in castings, and welding two casting together and blending the weld in). For these reasons, I consider it worth the money to buy silicon bronze instead of using scrap bits of unknown composition.


For bronze, you really really really want to buy a crucible rather than making one. In particular, buy a silicon carbide crucible—again, around $50-100, and again, totally worth it. I’ve used a homemade crucible of the type described below for melting pure copper, since I didn’t want to contaminate my crucible for silicon bronze and I didn’t want to spend $100 on a one-time experiment. All was going well, the copper melted, I skimmed it, and then closed the lid of the furnace to heat it for another minute as the casting was going to be pretty thin and I wanted it really hot. When I reopened the lid to remove the crucible, it had failed and the bottom of the furnace was a lake of molten copper. If I hadn’t opted to put another minute of heat into it, it would have failed right as I was lifting it out of the furnace. That would have been about half a gallon of molten metal all over my legs and boots.

ALUMINUM
Aluminum works fine with scrap material, but for best results use cast (not extruded) aluminum. This means car wheels, bicycle parts, etc. are perfect, but tubing, sheet, beer cans, etc. not so much. Because aluminum melts at such a low temperature, you can safely use a PROPERLY CONSTRUCTED steel crucible, or better yet, a cast iron pot. To make the steel crucible, you can just weld a piece of thick-walled pipe to a thicker plate. I've used with much success a 1/4” wall, 4” pipe that was about 10” tall welded to a piece of 3/8” plate. I welded lugs on the side for tongs to grab. If you aren’t a competent welder please have someone else weld it for you, this isn’t the weld you want to fail. Also, as with any crucible, you need to purpose-make tongs that fit very well with no play.


LEAD
Lead melts at such a low temperature that you don’t even need a furnace, just a suitable steel or cast iron container and some torches. My neighbor recently cast an 1100 pound lead keel for a boat he’s building by putting the lead in a modified cast iron bathtub, melting it with a few roofing torches, and tapping it out of the bottom in to a sand-backed wooden mold. I don’t recommend wooden molds—the surface finish is not the best because of moisture in the mold, and the fire department was called because of the excessive smoking. Even without a furnace, all above safety precautions apply, and remember that lead is extremely toxic.


EQUIPMENT


Aside from your crucibles for bronze and/or iron, as well as a blower, you can easily make everything you need yourself. My entire foundry cost was easily under $1000, which includes a some good books (bought new, listed below), two crucibles, my furnace (cost about $300 in materials), a pottery kiln ($60 on craigslist, and only needed for lost wax casting), an electric blower ($25 on craigslist) and a slew of homemade equipment, mostly made from scrap steel. My furnace is overbuilt, and probably larger than many people on here would even need. You could spend much less on a simple setup. Here’s my entire foundry, packed away in a corner of my shop (it only comes out from time to time):

Attached File  DSC_0056.jpg   46.99KB   435 downloads

FURNACE
The central piece of equipment in a foundry is the furnace. For the scale we’re talking about, a crucible furnace is by far the most reasonable thing to build, so it’s all I’ll discuss. You can build a relatively furnace that run on propane or natural gas, which is basically just a vertical gas forge with a lid. However, these furnaces will have a hard time melting iron, if they can do it at all. I strongly recommend buying the manual from Colin Peck (in England) called “The Artful Bodger’s Iron Casting Waste Oil Furnace”. This is what I did, and would never build a different style of furnace. The design of the furnace body is simple and easily modified to use the scrap you have on hand, and he has perfected a burner design that uses a gravity feed to burn waste oil (used vegetable oil, used motor oil, and diesel all work well). There is no nozzle on the burner, so the fuel isn’t atomized, meaning you can use waste oil (free but contaminated with particulates) without clogging the burner. Also, since it is gravity fed there is no need for a pump, and oil at atmospheric pressure is MUCH safer than pressurized gas when you’re working with molten metal. Plus, it puts out much, much more heat than propane or natural gas—I can melt 30 pounds of bronze from a cold start in less than 45 minutes. Properly built, it burns very cleanly (zero smoking) and can easily melt cast iron. It could definitely melt steel if you wanted, but it will rapidly deteriorate the furnace lining. Using mostly scrap materials, I spent around $300 on my furnace. The cost is primarily the 3000 degree castable refractory (very highly recommended), which I believe cost $65 for a 50 pound bag (I used 3) about 5 years ago. I won’t give much detail about the furnace design since Colin is trying to sell his book, so you’ll have to buy it from him if you want the plans (please note, I in no way profit from this, nor do I even know Colin. It’s just such a good design that it’s all I care to recommend).


Attached File  DSC_0058.jpg   44.41KB   342 downloads Attached File  DSC_0059.jpg   50.28KB   299 downloads

HAND TOOLS

Attached File  DSC_0063.jpg   37.38KB   245 downloads

There are various, simple tools that you need, all of which you can easily make yourself. Pictured here are the pouring shank (long thing that holds the crucible while pouring), crucible tongs (to lift the crucible in and out of the furnace), skimmer (angle iron welded to a rod, curved on the end to fit my crucible, used for skimming slag prior to pouring), and an ingot mold (angle iron with the ends capped and a handle, for pouring off leftover metal after the molds are filled). Other tools not pictured include a 1/2” steel rod for stirring, a chill bar (described above in safety equipment), a pair of tongs for loading preheated metal into the crucible. Really simple stuff. Also note that you don’t need a pyrometer to measure the temperature. Just take your 1/2” rod that you use for stirring and stick it into the melt for a second and then pull it out. If the molten metal slides right off the end, you’re ready to pour. If it clumps up on it, it’s not hot enough. That method has never failed me, for aluminum, bronze, and iron.

MOLDING TOOLS
This varies depending on whether you are doing sand casting or lost wax casting. I haven’t done sand molds in a few years and no longer have my tools for that, so I won’t try to catalog what you need, but it’s just simple hand tools, and a muller if you're lucky enough to cross paths with one. I would recommend going with Petrobond (oil-bonded sand) over water-bonded sand for a beginner, as it’s easier to deal with and maintain.


I won’t go into much detail here on the actual investment casting process, but if you are interested you should buy the last book listed at the end of this post. I will say though that “microcrystalline wax” is what you want to buy if you are making sculptural pieces. It gets very soft when heated from your hands, and can then take any amount of twisting or bending without cracking, and it blends into itself very smoothly. Like silicon bronze, it is a product so superior that it is well worth the money. Investment molds can easily be made from 1 part water, 1 part pottery plaster, and 2 parts coarse sand.

For this process, you will need to burn the molds out in a kiln to melt out, burn off, and finally vaporize the wax, as well as calcining the molds. You need to run it for a few days and slowly ramp up the temperature, eventually keeping the molds at 1200 for a day and filling them with molten metal when they cool to around 800. A standard pottery kiln works fine, but be prepared to wake up once or twice each night to check on the temperature unless you have a digital controller. Also, you can burn out other organic objects (vegetables, sticks, etc.) instead of sculpting something with wax.

SUPPLIERS/MATERIAL RESOURCES

Budget Casting Supply is your best bet for online shopping, but if you live in or near a big city you should really look for local suppliers. If you don't know of one, try searching on ThomasNet. If you're not familiar, that website is a searchable database of manufacturers and suppliers for industry—extremely useful. Often, places that supply foundry equipment or refractory never have walk-in customers, and if you explain what you are doing they are often very intrigued and go out of there way to help you. I still have yet to pay for any ceramic fiber insulation, though I've gotten plenty of it between various forges and my furnace—a large refractory supplier can generally give you a "sample" that is more than enough for whatever you're working on.

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That’s about all I’ve got for you without writing a book on this. Hopefully this will be helpful to some of you who are interested in adding casting to your metalworking skills. I’m more than happy to answer any questions you have, and if anyone is in the Philadelphia area and wants to see a pour just let me know and I’ll invite you to the next one.

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RECOMMENDED READING

-“The Artful Bodger’s Iron Casting Waste Oil Furnace” by Colin Peck
...available from the author at http://www.artfulbod...alcasting.com/. This manual is what I used to build my furnace described above. I don't think I would ever build a crucible furnace that was not based on this design. Terribly written, never even proofread, but invaluable nonetheless.


-“The Metalcaster’s Bible” by C.W. Ammen

-“The Complete Handbook of Sand Casting” also by C.W. Ammen
...Ammen’s books are very readable and straightforward. Get these regardless of whether you are making sand or investment molds.


-“U.S. Navy Foundry Manual” reprinted by Lindsay Publications
...invaluable resource, but not the kind of book you read straight through (ie, boring technical manual). Again, though it is written for sand casting in particular, much of the information is very pertinent to investment casting as well.


-“Charcoal Foundry” by Dave Gingery
...great for starting out, it’s sand casting in its most pared-down form. Perfect for a super-low-cost setup to pour some aluminum to see if you like it.


-“Metal Casting: A Sand Casting Manual for the Small Foundry” by Steve Chastain
...there are two volumes. Good books, but not necessary if you are only interested in investment casting.


-“Studio Bronze Casting: Lost Wax Method” by John Mills & Michael Gillespie
...for investment casting.

Also check Lindsay Publications for other books on casting, including some of those listed above.


#2 MattBower

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Posted 15 December 2011 - 06:01 PM

Welcome aboard, Dan, and thanks for what looks like the most valuable first post that I have ever seen on this or any forum! There's also a good backyard foundry tutorial at AlloyAvenue.com (formerly the Backyardmetalcasting.com forums): http://www.alloyaven...y-Tutorial-Book I don't know if you've seen that one.

A source of reasonably priced crucibles is Legend, Inc.: http://www.lmine.com..._Code=crucibles

I have Colin Peck's book. I built a forge based on his burner design. It was waaay overpowered. :)

#3 Dan Manders

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Posted 15 December 2011 - 06:27 PM

I hadn't seen that, in fact I haven't looked at Lionel's site in over a year and didn't know it had moved. Thanks for linking to it, as well as that supplier (hadn't heard of them before).

#4 HWooldridge

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Posted 15 December 2011 - 08:56 PM

Great post - thank you - and I wish you lived closer to Texas. I was selected to cast some bronze hardware on two unrelated jobs and had to learn by reading books and web research because nobody does foundry around here. I was willing to trade out forge and power hammer time but found no takers (might be why I landed the job <LOL>). Some of the pieces were investment cast and the remaining parts were sand cast. I scrapped about 70% of everything I poured but it costs to learn. I did not use Petrobond, which probably would have worked better, but the water/sand mix did OK once I figured out its nuances. The investment worked much better than I expected but I didn't have a vacuum unit and there were bubbles on the castings. I built the wax models with silicone molds and that was pretty straightforward.

The entire exercise was definitely a learning experience and the customers were happy in the end but I really could have used some experienced hands in the shop.
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#5 Dan Manders

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Posted 15 December 2011 - 09:52 PM

If you ever find yourself doing any more investment castings in the future, you can make a slip coat by making your normal investment mix but using silica flour instead of course sand, and mixing it pretty wet. You just pour it over the wax pattern and use a brush to fully coat, and let it set up before investing the piece. It creates a thin layer of investment over the pattern with no bubbles, and then when you pour the mold the two layers bond. It virtually eliminates the problem of air bubbles, but you have to be careful not to make the slip coat too thin or it will crack when the bronze hits it.

And yeah, silicone molds are fabulous. That's how I did the acorns that I poured, a silicone mold of the real thing and then a zillion wax copies. I use Polytek PlatSil 71-20 and have always been very happy with it.

#6 OddDuck

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Posted 15 December 2011 - 10:40 PM

Welcome, and nice post! Thought that looked like Colin's setup, I use something very similar. They'd love to hear from you over at Alloy Ave., they are always looking for info on investment casting. And just think, a couple thousand more acorns, and twenty or thirty thousand more leaves, and you'll have a life-sized oak tree. ;)
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#7 ThomasPowers

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Posted 16 December 2011 - 11:47 AM

One extra tip: Generally you heat items to go into the crucible in the exhaust as mentioned above. However when you first put a cold piece of XYZ in the exhaust the first thing that will often happen is that moisture will condense out of the exhaust and onto the cold item. This is why you preheat *until* such moisture is boiled off and the item is hot too. Helps to keep the melt from getting chilled by a cold item being stuck in it too.

You will note that folks who have done casting make a big deal of the moisture danger---there is a reason for that!
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#8 Bentiron1946

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Posted 16 December 2011 - 06:00 PM

Welcome aboard! good to have another founder among us.

#9 president of pyromania

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Posted 30 December 2011 - 12:57 AM

great info, i have only done sand casting as it is much simpler. the materials are reusable, too! i just joined the site here, and am eager to learn another metalworking skill. looking for an anvil....

#10 philip in china

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Posted 30 April 2012 - 10:50 PM

I have been reading Stewart Marshall's book "Building Small Cupola Furnaces" and hope to try one out fairly soon. I am sure it can't be as easy as it seems!

I think anybody who asks the question "Can I cast a steel anvil at home?" answers the question "Do I have sufficient experience of dealing with heating and handling steel?" rather well.
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#11 Bentiron1946

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Posted 01 May 2012 - 05:01 PM

Philip, Building the Cupola is easy, it's the rest that is hard work! And you are more than correct about the rest of it being the hardest part. In the end it would be cheaper to buy a steel anvil than to cast your own but think of fun and grief you would miss out on.

#12 basher

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Posted 03 May 2012 - 11:15 AM

this is a very interesting thread.
I have just finished making an oil barrel sized furnace to take size 150 crucibles (92kg bronze capacity) for a (small) cannon poor later this year. I am running propane because its what I know, but find oil furnaces very interesting .
the furnace weighs in at over 500lb! .
Ill be doing a test melt next week just to check timing etc.
the casting will be done under the supervision of an experienced foundry man, I have some experience...............But.....
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#13 ianinsa

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Posted 03 May 2012 - 11:24 AM

this is a very interesting thread.
I have just finished making an oil barrel sized furnace to take size 150 crucibles (92kg bronze capacity) for a (small) cannon poor later this year. I am running propane because its what I know, but find oil furnaces very interesting .
the furnace weighs in at over 500lb! .
Ill be doing a test melt next week just to check timing etc.
the casting will be done under the supervision of an experienced foundry man, I have some experience...............But.....


Basher, Pity we did not meet when I was in your part of the world, umo(used motor oil) is my mantra we could have whiped a burner up in no time, Its the fuel of choise in our Abu Dhabi foundry.
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#14 chyancarrek

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Posted 03 May 2012 - 04:37 PM

Great post Dan.

I didn't read through the whole thing (I've been around a furnace or two) but your info looks pretty good.

Your building looks cool - You mention living and working there. What's the set up and are you pouring for a living?
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#15 Dan Manders

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Posted 04 May 2012 - 04:01 PM

Great post Dan.

I didn't read through the whole thing (I've been around a furnace or two) but your info looks pretty good.

Your building looks cool - You mention living and working there. What's the set up and are you pouring for a living?


Thanks, here's a link to the building I'm in: http://globedyeworks.com/.

Pouring is not my job, but neither is forging, yet. I'm in the process of transitioning it from a hobby into a job, and pouring bronze will probably figure into that somehow, I have to build a better burnout kiln first though. Using the electric pottery kiln was a cheap way to get started, but it requires constant monitoring as the temperature is difficult to stabilize, and it can only fit two or three molds at a time. It's terribly inefficient to go through the entire process for so few molds, considering the kiln has to run for over two days and my furnace can melt 30 pounds of bronze in 45 minutes from a cold start. In the next few months I'm going to build a gas kiln with modular walls so I can adjust its size up to around 20 cubic feet, and use a ramp/soak controller so I can just program a burnout schedule and leave it alone. Plus it'll double as a heat treating oven for hammer and press dies.

#16 Bill Keen

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Posted 18 October 2012 - 12:25 PM

Very nice tutorial. I've been doing casting for 40 years, everything from door hardware to 300 lb cast iron for restoration, plus sand and various investment processes for sculpture. Nothing you said would I change............other than, If I knew then what I know now, I'd be in computers. :) My in house furnace will melt 250 lbs bronze but I seldom have to. # 30 is what i used mostly. Out of the business end but retaining capability. Overhead cranes expedite handling. If by hand, always a aluminized apron. Nothing like having your pants zipper hit 200 degrees in the middle of a pour. Happy to share what I can still remember.

#17 Luke March

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Posted 06 April 2013 - 07:16 PM

So, I got Colin Peck's book, and I've been working on gathering the needed parts to build one of these furnaces.  The biggest issue, of course, is the refractory.  Because shipping would be killer to get three 50+ pound bags sent by mail, I've been checking my local suppliers, and came across a company that keeps this stuff in stock: http://www.sparref.c..._1214321489.pdf

 

Would this work for the furnace refractory?



#18 Bentiron1946

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Posted 11 April 2013 - 06:57 PM

In the past forty plus years I have made a half dozen melting furnaces using common fire brick as a furnace lining using fire clay as a mortar for the bricks. I cast a bottom in the water heater 4" to 6" thick of a 1/3-1/3-1/3 mix of fire clay, silica sand and portland cement, then start my courses of brick up the inside. A standard fire brick is 8-7/8" x 4-3/8" x2-3/8" or there abouts. I stand them on end with the narrow 2-3/8" face out, looking down you see a 4-3/8"x 2-3/8" rectangle with the 2-3/8" face toward the fire side. This will give you adequate insulation, still don't expect to be able to put you hand on the outside it will still be very hot. Now for the lid I so the same third/third/third mix as a monolithic pour. Sometimes the hardest part of building a melting furnace is finding and old water heater. Be sure and leave a hole near the bottom for the burner and place a half of fire brick for the crucible to rest on. Oh, nearly forgot, I make a plaster of fire clay and silica sand and coat the entire inside of the furnace. After a few firings this will take on a glassy appearance. Typically this lining will last about 6 to 8 years before you need to replace it, it will last longer if you replaster it yearly.

#19 Nobody Special

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Posted 16 April 2013 - 08:02 AM

Nice tutorial. Ever try "lost foam" method of sand casting. Make your forms out of insulating foam and leave in/burn out during the pour. Makes a kind of pebbly finish, but worked well when I tried it.



#20 Jammer

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Posted 16 April 2013 - 10:05 AM

Lost foam works great. The white pebble foam burns out the best and quickest. But, I like the blue and pink foams because they are much easier to carve and work.

The main trick to lost foam is to start your pour and don't stop... even when the flames come out at you, just keep pouring. Wear a face shield. If you stop the foam will melt out and the sand will collapse if there's no metal to fill the void.

FYI, the green floral foam doesn't burn out very well and the canned insulating foam doesn't either and it releases some gasses that are hazardous to breath. The blue pink and white foams release water vapor and black carbon threads like an acetylene torch does.






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