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Forges 101


Mikey98118

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1st test drive. 

Still needs the seal and some tuning. Overall pretty happy with the design. The nice even heat and low turn down will be handy to HT small knives when I eventually learn that skill.

These after about 5 min. Run time.

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On 3/14/2019 at 7:09 PM, Mikey98118 said:

It is a matter of one's place in life. Over a lifetime of steel work, I've used and owned many tools. For the last twenty years I have confined myself to the absolute minimum of hand tools needed that are cheap and safe enough for a beginner to buy and learn. What point would there be for me to explain to a newbie how easily a burner can be turned out with a lathe-drill-mill for instance. Mine has been still for nearly two decades. The first one of my younger friends who finds room in his shop for it, and out the door it goes. The machinist chest is already history. Last summer a box full of angle grinders hit the trail. This summer I will do my last ornamental iron project in the garden, and the fire feed and chop saw will go by by. Been working on the bucket list for these last three years. Soon my garage will contain one work bench and a few hand tools; that's all beginners are willing ol afford, so that is the game board I play on :D

This is when you have reached Jedi master level.

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On 4/6/2017 at 1:02 PM, Mikey98118 said:

Yes, it is possible to over saturate the blanket, but all that happens then is that the excess mixture coats the inner side of your forge shell; no harm done. I think most people don't get what a small amount of glass is actually contained in colloidal silica contents; in a gallon jug of fumed silica doesn't way as much as the plastic container it comes in.Yet, glass is HEAVY; to  swim in water without settling to a container bottom the silica particles have to be very small.

The magic of colloidal silica ( fumed silica in water) comes from capillary action. The silica and water mixture isn't running down the ceramic wool fibers due to gravity, but due to whetting action; each time some of it reaches an intersection, where two or more fibers meet, some of it stays in the intersection because surface tension balances the capillary force running along each fiber, allowing a tiny glob of silica to build up until no more of the material can be supported in the joint, and all further silica and water flow on by it.

Next, you dry out the water content, and the silica powder is melted to glass by the burner  before it can drop off the fiber. The build up of material is so small it would take a micrometer to measure the increase in the diameter of individual fibers, except at the intersections where much more silica collected...fortunately.

I recommend that people making their own rgidizer add food coloring (for a temporary dye), as most suppliers do, so that they can see how far into the ceramic wool the colloidal silica has penetrated. After firing, the food coloring is burned away, and the wool appears white again. Do you need the dye to due the work? No, but it goes a long way toward quieting anxiety:)

I recommend doing some reading about capillary action, whetting, and surface tension by doing a little research on the web; just input "brazing" to get a reasonably quick education on the subject.

Do you recommend making your own rigidizer  if so your recipe 

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Good morning all,

After making my way through this thread and burners 101 I think I'm ready to ask some questions.  I am working on building my second forge. My first proved too small for some of the decorative items I have been making.  Insulation is 2 - 1" layers of kaowool rigidized with the colloidal silica recipes from this thread.  Thanks for the food coloring tip!  That made it really easy to see where I had sprayed.  I plan to have high alumina kiln shelf for the flooring and now need to decide on a coating for the wool.  Right now I'm leaning towards the zircon/colloidal silica combination because I have easy access to both of those items.

@D.Rotblatt, have you used this coating in your forge or was it just the zircon/adbond coating?  Your post from just before Christmas is what has me leaning in this direction.  How thick did you make your slurry or better yet, what proportions of each did you use for the zircon/fumed silica?  Were both the zircon and the fumed silica in powder form?

Mikey, I'm following the recommendations from your book for the propane tank forge and wondered if the process for rigidizing the fiber board is like that for the blanket.  Butter, spritz rigidizer, bring to red heat, done.  Did I miss anything? 

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12 hours ago, Another FrankenBurner said:

He uses adbond II for the finish coating.

Adbond II only comes in 5 gallon amounts from Remet company - it's a colloidal silica used for ceramic shell molds. Pottery supplies have it for rigidizing, but I'm not sure that's the same stuff (since the adbond melted ceramic fiber in my tests). i'm looking into finding small amounts.  I'll let you know if I find them.

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On 11/1/2016 at 9:31 PM, Mikey98118 said:

Michael.

You place the pliable blanket where desired, push it into shape, and spritz the rigidizer into it. Then, you heat cure it in that same position; presto change-o, a stiff monolithic structure is created; either all at once, or area by area, as you see fit.

By silica based rigidizer, I mean fumed silica in water; better known as colloidal silica.

Sodium silicate (AKA water glass) melts at 1900 F and is expensive and heavy. Colloidal silica is use rated to 2300 F and doesn't melt below 3000 F; it is dirt cheap, costs very little to ship, and once the water is steamed off the blanket it adds almost no additional weight, because it flows over ceramic fibers in a very thin layer, do to its capillary action (wetting).

Why than would anyone use water glass? It makes a better binder for lite weight aggregates, like Perlite--not ceramic fiber blanket.

Where do I find Colloidal silica?

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Dan et al,

I talked with Bob at Remet yesterday and they sell gallons of Adbond II for around $40 plus shipping.  Considering that I will only use a small amount this may not be the best solution.  Is it within the realm of standard practice to just coat the rigidized wool with metrikote or equivalent?

Thanks again for all the help!

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9 hours ago, u_p_country said:

  Is it within the realm of standard practice to just coat the rigidized wool with metrikote or equivalent?

Yes it is. It was to support such thin protective coatings that I first started using silica based rigidizer. Once I realized how inexpensive and easy rigidizer was to employ, I started using, no matter what the final hot face layer was to be.

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19 hours ago, Rev. Mike said:

Where do I find Colloidal silica?

U-P_Country; Please note the difference between Colloidal Silica and Adbond II.  Both are called colloidal silica, but the Adbond II must have other binding agents in it which makes it unacceptable for a Rigidizer, but great to bond powders like zircon for a Hot Face.  I might have found a source for pints (around $16) and quarts of colloidal silica binder, but I have to buy some and test it to see if it works.  I'll report when I do.

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On 3/22/2019 at 8:28 PM, D.Rotblatt said:

note the difference between Colloidal Silica and Adbond II.

D.Rotblatt Thanks for the clarification.  I'll be looking forward to the results of your testing!

Mikey,  thank you for the idea about using just metrikote over rigidized wool. I may go that route for now.

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Matrikote seems to be a good product, which integrates well with the ceramic fiber. But I read somewhere that it was only rated to about 2500 F; that is okay in older forges--with older burner designs. But if you keep up with the Burners 101 thread, you would see that it just won't cut it anymore.

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Mikey98118  You got me there, I remember reading that as well.  It wouldn't do to line my forge with something that can't stand the heat!  I'll look into the Plistix and wait for more info from D.Rotblatt His methods are intriguing, especially his times to full heat!

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Glenn asked me to post my article on "Building a Furnace for the Home Foundry."  This article was written back in 2005 or earlier and is the result of a seminar I taught at a community college.  It is on my site RotblattSculpture.com along with other articles relating to casting. 

 

Safety Note:

This article was written over a decade ago, and omits concerns about silica fibers from the ceramic blanket.  The ceramic blanket needs to be rigidized and coated with a refractory to fix the blanket so fibers will not be blown into the air when in use.  Rigidize with a mix of fumed silica and water (Fused silica is available on amazon, and used for thickening epoxy).  Dampen the ceramic blanket with water from a spray bottle, the apply Rigidizer with a spray bottle.  A little food coloring in the mix will help you see how it is penetrating.  Heat to dull red to cure.  Coat with 1/4" of whatever refractory you used on the bottom and top by first buttering the ceramic fiber (wetting the ceramic fiber with a spray bottle) and then with gloved hands or trowel coat the blanket with refractory.  You can lay it on it's side and do 1/4 at a time.  Cover with a plastic bag and allow to cure 24-48 hours.  Then slowly heat by turning on the burner for a few seconds at a time until you no longer get steam.  Then heat to red to finish curing the refractory.  This coating will slow the heating time a bit, but I imagine only a few minutes.  Safety first.

 

Disclaimer

This article is an account of constructing a small bronze casting furnace. I am putting it here for educational purposes only. Should you attempt to build a furnace like this one, I am not responsible for ommissions, mistakes, or errors that may lead to injury or death. Building and operating a furnace without proper knowledge and a good dose of common sense can lead to injury or death! Read up on safety procedures before using this or any furnace. Dangers inculde propane explosions, severe burns, carbon monoxide poisoning to name a few. To start, take a look at my safety pageand Furnace Lighting Procedures.

 
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Also take a look at my Forge Page

I'm also a blade-smith and have made several forges using similar materials and techniques as this furnace. The main difference is a smaller sized freon tank rather then the 5 gal propane tank.

 
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I was invited to teach a seminar on furnace building for a foundry class at El Camino College. I took pictures during the seminar and combined it with pics of my own furnace to create this article with the intent of using it at other seminars. Thus it is written as a "How To" article, meant to be combined with the seminar, which includes discussions on safety and proper use of the furnace.

The furnace we built is a small helium tank furnace, capable of melting 30 lbs of bronze in about 40 minutes. This is exactly the same furnace I use in my own studio.

The features of this furnace are:

  1. Melts 30 lbs of bronze in 30-40 minutes
  2. Uses a party helium tank (the same size as a 5 gal propane tank)
  3. Inexpensive to make: under $150
  4. Lightweight and portable
  5. An easy weekend build
 
   
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Building a furnace for the Home Foundry: 
Capable fo melting up to 30 lbs of Bronze

 
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Introduction

This furnace is able to melt 25 lbs of bronze in about 30 minutes. It has a maximum capacity of 30 lb. of bronze or 10 lb. of aluminum (a #10 crucible just fits). The pictures here are from a class I did where we built 3 furnaces. Think of this as a recipe for building the furnace, there are many variations you may use depending on our skills, the tools in your shop and availability of materials. If you follow certain basic principles the furnace will work just fine. 

 

Basic Principles for Building a Furnace

1) A furnace body is mainly an enclosure to hold the heat that the burner puts out. The steel shell does not hold in any heat, it is the refractory that holds in the heat (the lining inside the furnace shell). The body could be made of screen and it will work the same, it’s only purpose is to hold the refractory in place.

2) The burner should come in at an angle (see diagram #1) so the flame forms a vortex or whirlwind around the crucible. This distributes the heat evenly and does not overheat the side of the crucible.

 
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3) The refractory you use must be able to take the heat within the furnace. Bronze is poured at around 2100 degrees F, but the furnace lining (especially where the flame is hitting it) gets much hotter. The lining on my furnace should take 2700 degrees. You cannot use plain concrete or substitutes, this can be dangerous. 2300°F ceramic blanket can be used, but expect a shorter life.

4) Every place there is a leak (i.e. flame shoots our from a hole or gap in the refractory) heat is lost. The less holes there are the better, but NOT from the point of view of melting the metal. The amount of heat lost from a small hole or two in the furnace is nothing compared to the amount of BTU's (heat energy) the burner puts out. The danger is that a flame shooting out the side will catch something on fire or worse, burn a hole in the propane line. Therefore, you should make the lining fit well - an easy thing to do, especially with ceramic fiber and castable refractory.

5) There must be a hole in the top of the furnace to prevent back-pressure from building up (especially important with a venturi burner). This hole also allows metal to be lowered into the furnace with a pair of tongs (not dropped!).

6) You must have a burner able to generate enough BTU’s (heat energy) to heat up the furnace to the temperature you want faster then the furnace looses heat to the outside. In an ideal world, a perfectly lined furnace (one that lets no heat out at all) could be heated to 2000 degrees F from a flame no bigger then a candle. In reality the flame must be a bit bigger to do this. The burner in this furnace puts out between 135-200,000 BTU’s.

That’s the basics.

The steel body is made from a party helium tank (it is the same size as a 5 gal. propane tank but helium is nonflammable). The bottom and top are lined with a castable refractory, and the sides are lined with Ins-wool or any ceramic fiber blanket that will take 2300°F.

The burner is based on Ron Reils EZ-burners - the plans are on the internet and highly recommended reading. They are updated frequently and should be looked at.

Tool and Part Lists

This list of tools and parts is off the top of my head, but should be fairly complete. There is always some latitude, since many of the parts can be made from scrap laying about the shop.

TOOL LIST

  • MIG/TIG/oxy-acetylene torch for welding.
  • Something to cut off the top of the tank and angle iron (oxy-acetylene torch or an angle grinder with cut-off wheel for the top and angle iron, and a jig saw with metal cutting blades for the smaller holes)
  • Hack Saw or angle grinder with cut-off wheel
  • Sharpie pen
  • Brick

PARTS LIST

The furnace body:

  • (1) A disposable helium tank or empty freon tank - the same size as a 5 gal propane tank (DO NOT use a propane tank) - [furnace body]
  • (1) About 5’ of angle iron 1” to 1-1/2” wide - [legs &burner holder]
  • (1) About 1' of 1/4" rod, rebar would do fine - [hook]
  • (1) hinge (about 2-3”) - [lid hinge]
  • (1) 2" hose clamp - [to attach burner to burner holder]
  • 15-20 roofing nails - [welded to lit to hold refractory]
  • (1) Bag castable refractory (Greenlit-45 (lighter, not as strong), Mizzou Castable)
  • 40" x 10" Ceramic fiber blanket (2700°F maximum temperature preferred, name brands are Inswool or Kaowool).

Burner

  • (1) 3/4” x 8” pipe nipple
  • (1) 1-1/2” x 3/4” reducer
  • (1) 1/8” nipple with pipe cap
  • (1) 1” x 5” pipe nipple
  • (1) #60 drill
  • (2) 3/16” bolts with a Drill and tap for that thread size
  • (1) propane hose with 1/4” fittings on either side
  • (1) Propane Regulator (0-30 lb. pressure)
  • (1) Propane fitting for attaching the regulator to the tank

 

 
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Cutting the Shell

1. Using a cutting torch, cut a hole in the top of the helium tank about 4 1/2” in diameter (the exact size is not crucial). 

2. Cut off the top of the tank just below the curve of the lid.

 
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Two views of the helium tank cut off around the rim. On the right you can see the hole cut in the center of the top. Note the placement of the legs, hole for the burner, and hinge.

 
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Attaching the Legs

1. On a flat surface, place the bottom of the tank on a brick and weld the 4 legs onto the bottom/side of the shell. Before welding sand off the paint where the welds will be using an angle grinder and sanding disc.

 
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A side view of the bottom half of the furnace showing the legs welded in place.

 
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Burner Attachment

1. An oval hole is then cut in the side of the shell about 4” above the very bottom of the shell. This can be done when cutting off the top since an oxy-acetylene torch is best for this. The hole should be about 1” tall and 2” wide - better too big then too small. Test it's size with a 3/4" pipe, view the plans above and diagram #1 for positioning.

2. A 4” long piece of angle iron is welded to the edge of the hole. It should be angled as shown in "diagram #1" at the top of the page. The burner will be attached with a hose clamp to the angle iron.

 
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Here's a view of the hole cut with an oxy-acetylene torch. The hole should be set about 1" above the curve of the bottom of the tank.

 

A 4" piece of angle iron has been welded to the side of the hole. The hole has been cleaned up with a grinder.

 
   
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A top view showing the angle of the burner. Look at Diagram #1 at the top of the page to see how the burner should be set.

 
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Preparing the Lid

1. Weld a number of roofing nails onto the inside of the top to hold the refractory. A hinge was welded to one side and the loop/latch to the other (a detail of making the loop is shown in below).

 
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A close-up showing the roofing nails welded in place. The loop is also shown to the right side.

 

A view of the lid with hinge, hook, and nails. It is ready for the refractory to be poured in.

 
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A close-up of the loops ready to be welded to the front of the lid. You only need one.

 
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Pouring the Lid & Bottom of the forge

1. Castable refractory is used to line the bottom and top of the shell. It should take at least 2600°F and should be about 2-1/2" to 3” thick on the bottom. 

2. Make a cardboard ring the size of the hole in the lid and tape it into place with duct tape. Also make a 2" thick ring of cardboard and set on a piece of wood. This is to make a base block to put the crucible on.

3. Mix enough castable for the lid and bottom, plus a little extra.

4. Fill the lid with refractory cement.

5. Pour the bottom of the furnace up to where the curve of the tank ends - this should be about 1" below the burner hole in the side

6. Use any extra to make a base block.

 

In Los Angeles, refractory can be purchased through:

Harbison Walker Refractories
7831 Paramount Blvd., Pico Rivera, CA 90660
(562) 942-2151

Independent Foundry Supply Co 
6463 Canning St, Los Angeles, CA 90040
(323) 725-1051

Harbison Walker should have outlets in all the major cities - they are a worldwide manufacturer. Look up refractories on the internet, or in a phone book for local dealers.

Inswool can be purchased by the linear foot from the following websites by the linear foot (it comes 24" wide). Also look on eBay - don't pay more then $6-8 per 2 cubic feet. I haven't purchased through the following, but the prices seem good.

5 foot lengths (10 square feet), about $3/sq foot. Enough to line 2-3 furnaces.
http://mywebpages.comcast.net/eellis2/EllisCustomKnifeworks/inswool.html

By the foot for $8 a linear foot (2 sq ft).  

https://www.iforgeiron.com/topic/61870-inswool-insulating-blanket/

 

 
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A piece of cardboard is bent into a circle and taped in place with duct tape. Castable is poured into the top and smoothed.

 

Here the bottom is poured. In this furnace I made an integral base block, but I recommend making it separate so it's easy to replace.

 
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Hinge, Lid Rest and Lid Ring

1. When the cement is dry, place the lid on the body and weld the hinge to the body.

2. The loop has a bar which will stick down along the body. Weld two small bars to the body on either side of the bar. This will align the lid when it is closed, while the loop can be used to lift the lid with a hook.

2. Cut a small piece of angle iron (about 4” long) and weld it to the shell so the top rests on it when open. Cut a disc of scrap sheet metal and weld it to the top of the angle iron rest (this helps prevent the angle iron from denting the top and eventually cracking the refractory).

 
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On the left side of the furnace is the lid rest welded below the hinge. 

 
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Lining the Shell

1. Cut a piece of 1" ceramic fiber blanket about 9" (measure the inside height of the furnace) by about 40". Make sure it is long enough to fit tightly inside the furnace body. Use a sharp knife or matte knife to cut it.

 
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The dark ring shows the Ceramic Blanket lining.

 

This shot shows the Ceramic Blanket lining. In this case I think I used 2" blanket (the inside measures 1-1/2", 1" is sufficient and leaves more room for a crucible.

 
   
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The Burner

I used the Ron Reil Burner shown below with the Bordeaux modification. Instead of a short flared pipe shown at the end of the burner in the plans, I used a 6” long pipe that is attached permanently to the furnace with a hose clamp to the angle iron that is welded to the shell. The end of this pipe is flared. The burner is held in the flared nozzle using a setscrew. Once the burner is set the right amount into the 6" flared end, mark the burner pipe or put a hose clamp around it to act as a stop. A #60 drill, taps, etc. can be purchased at OSH (Orchard Supply Warehouse).

Ron Reil’s website is: 

http://ronreil.abana.org/design1.shtml

The Reil EZ burner is shown below. Click on the schematic for a larger view:

A very good pictoral description of building this burner is available on Brian Boorman's website at: 

http://metalcast.boorman.us/reil_1.html

 
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Click on this schematic for a larger view.

 

The burner. Simple construction, and very efficient. In this burner I have a compressed air quick connect - I wouldn't recommend one so close to the burner since these are known to leak...

 
   
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Yup, it melts bronze. That's a #10 crucible in there. I've done dozens of pours over 20 lbs, and many smaller pours out of this furnace.

 

Here's the finished product.

 

Helium Furnace diagram 2.jpg

Helium Furnace diagram 1.jpg

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