Oatey high heat (2500 degree) furnace cement bubbling

[smeeldog]

Howdy, 

[smeeldog]

Howdy, 
First, I am aware that furnace cement isn't the ideal (still unsure if what I have is a plausible) cement to use as refractory for a smelting furnace, though I learned this was not ideal after already having applied it the rigidized koawool. I do not understand what would make it not a usable material for smelting metals below 2500 degrees, I contacted the company and they told me it should be able to come in contact with fire without problem, I will attach links for the rigidizer and cement I used at the bottom. 
The rub is- at the cements thickest points of application it is around 1/4in, we stuck a 40 watt incandescent lightbulb inside the furnace, which has been in and on for about 3 days. Each day I have taken an oxy acetylene torch to the cement trying to get the heat up higher, at a low rate, keeping the flame half a foot or so off the cement. 
Yet I am am still getting bubbles when taking the heat up, some smaller than a penny, some larger than a half dollar. 
I did not change the consistency of the cement, and just applied one layer. 

Rigidizer- 
Cement-  

Thank you for your input

Edited February 8 by Mod30
Remove commercial links per TOS

[Buzzkill]

A few things:  Are you truly making a smelting furnace?  In other words are you taking raw ore and ending up with a consolidated metal ingot?   Or are you melting pieces of metal that are already mostly purified?  This is an important distinction.  First, it helps us understand what you are trying to do, and secondly different temperatures are usually required for smelting than melting. 

Next we need to know the metal that you are either melting or smelting.  2500 degrees F sounds really hot - and it is - but if you were smelting iron ore (or even melting iron for a pour) you would most likely exceed that temperature.  For copper or aluminum it might be a different story.

Next, regardless of what the manufacturer tells you, most of the refractory cements simply do not hold up for long under direct flame impingement circumstances. They are designed to stick pieces together rather than to take the brunt of hot, chemically active flames.  I wouldn't be comfortable using something rated for 2500 degrees in my forge, let alone something that would require higher temperatures.  The refractory I use is rated for 3000 degrees, and it's not uncommon to see people using something rated for 3200 degrees.  Again, that's for forging/forge welding, which can be accomplished at several hundred degrees cooler than melting or smelting iron or steel.

Depending on the type of refractory it is, removing the water more quickly doesn't necessarily give you the results you want.  A lot of us use a water setting refractory that cures best (most strength and minimal cracking) in a high humidity environment.  After a day or so of curing we do have to remove the excess water slowly by gradually raising the temperature.  If done too quickly it can create steam pockets which can reduce the effectiveness of the refractory and/or actually explode in extreme cases. 

O/A flames tend to be very hot and somewhat focused even if you are holding the torch back 6 to 8 inches.  It's really not the right tool for the job.    I don't know if you are seeing the results of rapid surface heating creating steam pockets or something else, but in my opinion you do not have the appropriate material for the job either.

[Frosty]

Welcome aboard, glad to have you. Pretty much ditto what Buzz said. You picked the wrong product for the job. It sounds like you "researched" by reading blogs instead of useful info. Not to blow our whistle but the forge and burner sections on Iforge have been pretty heavily vetted by the membership. So, you need to do more than just pick one and go with it, that post may be urban myth or other nonsense but it did get debunked in later posts.

Not knowing the difference between a melter and a smelter is a good indication of a blogucation.

As already said cement, mortar, etc. are just that cements they stick things together say bricks and are NOT intended as a flame face. The people answering your questions on the refractory cement site are selling their product and may not know diddly about furnaces of any kind. 

About what your flame face is doing. Cements take a long time to cure so you are probably boiling the water in it. Water that has NOT had time to form the molecular bonds required for cement to cure properly. Which means the flame face might not survive temps well lower than the rating.

I wish I had better news for you but afraid your finer is a write off.

Of course that's just my opinion, I could be wrong.

Frosty The Lucky.

[smeeldog]

Alright, this is good.
 
Thank you both, I'm glad it is obvious to you both I am fairly green when it comes to metal working. What I have is a melter, and my intention is to first melt brass in it. 
I had a hunch the oatey people did not know diddly, yet I listened to them, I know close to diddly. 
We have more wool on the way, it sounds like I should cut my losses with the product I have and order something with a higher heat rating, and in a different category of refractory in general. Any specific recommendations? Should I need the high humidity setting and curing stuff for southern NH, we have a propane burner heater in the shop which is bound to add a lil moisture. 
I understand my errors with heating the water in the cement too fast, without giving it enough time to escape out before applying higher heat. Like I said in my first post I think I could've applied this cement in a better way, though thats not here nor there considering what we are discussing. 

Also my dad is not convinced that we need to even use refractory and is teetering on the idea that koawool particulate is that dangerous to breath in, and once the initial dust gets blown out of the wool you dont need to worry much about getting poisoned. This can't be true right? It is a very bad idea to have untreated insulation being used in your furnace? 

Thanks again. 

[Goods]

If your ceramic wool is not encased, it will shed more fibers with each heat cycle, if not constantly. It needs to be covered with a good refractory! Safety first!

Keep it fun,

David

[Buzzkill]

Generally speaking it is a good idea to check with manufacturers regarding the uses of their products.  I don't want to discourage that.  However, as someone who personally tried to use one of the many refractory mortars/cements out there for my first propane forge, I can confirm that at least the brand I used did not hold up.

Kastolite 30 is a good choice for a water setting high alumina insulating refractory material.  It's rated up to 3000 degrees F and can be used as a flame face in addition to sealing in the ceramic wool fibers.   It benefits from nearly 100% humidity during the curing phase.  I usually enclose the casting in a plastic bag with a wet towel draped over the Kastolite material for a day or so to ensure that it stays as damp as needed for curing.  Ambient humidity should not be considered good enough.

Since you said you know close to diddly, it should be stressed that handling molten metal can be extremely dangerous - far more so than forging.   It requires a fair amount of PPE to minimize the chance of serious injury if when something goes wrong.  I have a limited amount of casting experience myself, but I would highly recommend trying to find a local college with a class or a local casting club/group that can assist you with all the particulars while you are getting started.  All this metal working stuff can be really cool and rewarding, but it's not worth being maimed or worse due to lack of knowledge or protective equipment.

[Frosty]

If your Dad still thinks it is OKAY to subject Kaowool to a flame in the same air you are breathing, have him ask ME I'll set him straight. Once heated to around a dull red the fibers begin to fuse into a hard ceramic and if they are not incased they break off and get blown out of the forge into YOUR BREATHABLE AIR! Think a nasty combination of silicosis and mesotheleoma. 

The current most liked castable refractory is "Kastolite-30-li." It is an insulating, 3,000f, high alumina, water setting, castable refractory.  As part of it's aggregate it has evacuated silica spherules that both lower it's physical weight AND provide insulation, slowing the conduction of heat energy through the flame face liner. High alumina refractories are more resistant to being dissolved by borax based forge welding fluxes. Once cured it remains concrete hard and tough up to 3,000f it's rated max working temp. Like everything it'll take more but you aren't likely to luck into an air propane forge burner that reaches 3,000f. Not impossible but very VERY unlikely.

I see Buzz beat me to the submit key. 

Minor difference, Kastolite sets by water forming molecular bonds with the calcite compounds that sticks the aggregates together in the refractory. A wet towel in a sealed plastic tote, etc. with the forge liner does it nicely. The product directions say 100% humidity, surface WET for 7 days after it is fully set for maximum strength and temperature rating. We're making home built hobby forges or melters, over night is plenty good enough for our purposes.

Double, TRIPLE, DITTO Buzz about taking a class or course in casting! There are too many nasty traps to step into to list in only a couple pages. Just a tiny bit of splatter from low melt aluminum will leave you on pain meds and hurting still and all it takes is ONE TINY mistake to have molten metal raining out of the sky. 1 cubic inch of 212f water converts to 1,200 cubic inches of steam under a couple conditions that can initiate phase conversion. So, ONE DROP of water in a mold can and WILL blow molten aluminum for 30'+ in every direction and lighting everything flammable in the garage on fire. Hmmm? And you want to cast brass? A drop of water at THAT temp will blow really REALLY HOT molten brass close to 2x as far.

One last bit of serious advice. I HIGHLY DISRECOMMEND casting BRASS! Even if you get the temp perfect it WILL outgas zinc oxide fumes which is a darned dangerous thing to breath. It does all sorts of awful things to your lungs, the molecule chains into little barbed sharp tendrils that pierce your aviola, (the little sacks in your lungs that fill with air and exchange oxy for co2 in your blood) Poking holes in your aviola is B A D enough but zinc oxide is soluble and being an invader your body calls out the chemicals to dissolve and flush it out. Why? Because the little barbed particles prevent mucus from flushing it so it's time for the big medicine. Unfortunately the by products are more toxic than the zinc oxide.

So, my sincere advice is to take a class or course in casting then learn to use YOUR set up with a relatively "safe" low melt metal. Aluminum is perfect, it's everywhere for salvaging, melts at a low temp, approx 1,100f and doesn't outgas dangerously toxic stuff. If you get a steam explosion good PPE will keep the worst off your hide. Molten brass or bronze require better PPE, on the order of proper fire suits. Once in a while I lend a hand at a local iron pour and I wear an aluminized fire suit over cotton pants, shirt and a Levi jean jacket. My least good PPE are my smooth toe, slip on leather boots but they're largely covered by my fire suit pants.

Brother I can NOT tell you how rewarding and just plain fun it is to work with really dangerous things but the flip side is living the rest of your life maimed and in pain. Even if the rest of your life is only a few days or weeks.

Frosty The Lucky.

[smeeldog]

This is all really good input, I really appreciate your time and effort into setting me on a good path, I will do what I can to find a course, invest in better PPE, change my material to aluminum, and get some kastolite. 

I will be sure to update you on this thread once I am there. 

thanks again me bruddas. 

excited to see where this goes.  

I forwarded your response to my dad frosty, thanks. 

[Frosty]

You're welcome, smeeldog one of the reasons I hang here is to maybe pass along some of what I've learned over the years. Hopefully you won't make the same mistakes I did and make some new ones to enhance my knowledge base.

Frosty The Lucky.

 

[smeeldog]

OKAY- so here is my update so far, I have decided on what I am going to get and use, and this will be my process if you feel like vetting it, I would appreciate it, there are also some questions i have, they will be bold-

In order- melter wall, (two layers) of 1 inch thiccc unitherm Ceramic Fiber Insulation blanket (8# Density, 2600°F), which I will butter and rigidize whatever insulation walls are exposed and will get coverd in satanite, and finally ITC-100 as the final protective coating. 

Can I cure rigidizer quicker by heat lamp after I apply it? Or is that too broad a question, if so how could I phrase it better. 

is a 20 pound bag of satanite enough to cover? I know I am going for a 1/4 layer, made up in multiple layers, letting cure and dry between each. 

My melter has a diameter of 11" a circumference of 3' 1'' and a height of 14'' (without the wool)  am I too slow and should figure this math out easily? 

finally, I'm confidant a half pint of ITC will cover that inside area of the melter, considering I am just painting on a layer, or am I wrong? 

I think I got through to my dad, I ripped out the old stuff from the melter outside with a particulate respirator on, gloves, glasses, and when I got home I washed all my clothes. 

Thanks for your help everyone. 

[Frosty]

Your ceramic blanket refractory in two 1" layers is "correct". Rigidize each layer.

Butter each layer of blanket by spritzing it with clean fresh water. A couple few drops of food coloring in the rigidizer will let you SEE how evenly it's covered. Buttering prevents the rigidizer from flash drying on contact with the blanket fibers so it flows to intersections and deeper. Once dry curing it will fuse the rigidizer making the blanket more rigid and encapsulating the fibers so they do NOT float in the air.

Once dry finish curing the rigidizer by lighting the burner and bringing the refractory to dull red or a LITTLE hotter and let it cool. This fuses the silica and refractory blanked fibers together.

 Figuring out how many sq' the inside surface of your melter is, is pretty basic math. I don't do math for folks. Same for figuring how much Satanite is required to cover, ? sq' 1/4" thick. Same same.

If you don't know how to calculate area, this is a good time to learn. Area= width x depth. Next multiply sq' x 144 or heck just calculate sq" from the start and divide by 4 to tell you how many cubic inches of Satanite you'll need. Do NOT forget to calculate the floor and lid. 

I've never used Satanite so I don't know if it's necessary or even a good idea to apply it in multiple thin coats. It isn't a kiln wash but I don't have experience with it so won't opine. Other than to say you might check the manufacturer's site for directions. 

My preference is Kastolite 30 but I don't know if you can buy small quantities right now though you might want to do a web search. Last I bought a 55lb. sack was around $100 but that's been years.

The melter will need a "Plinth" to set the crucible on so flame can circulate around and under the crucible.

ITC-100 is a "kiln Wash" that contains zirconium flour in a ceramic binder. Mix it to a consistency a little thicker than latex paint and brush or trowel it on evenly. Allow to dry COMPLETELY, an incandescent light bulb in the chamber works will. Once it is no longer chalky light the burner and cure it to red heat. That should set it well enough it can finish curing in use.

Don't forget the lid!

I believe most of this has been covered in "Forges 101". Forge and melter are the same basic propane furnace with small differences. Do some reading and get back if you have questions. The more you learn the better your questions will get and the more fun it'll be to answer, especially if we have to start looking things up. 

Frosty The Lucky.

 

[smeeldog]

I did not clarify that well enough, I knew how and why I needed the inside area for my forge, but I just couldn't find any info on square inch coverage for satanite online, and didn't know how to get that answer

 

[smeeldog]

And hey, will do, thanks again. 

[Latticino]

I have used Satanite for an inner liner (though Kastolite is much better in almost every way).  You definitely should apply Satanite in multiple thin layers.  Mixed correctly it can be troweled on.  I think I used at least (6) layers when I did it and barely got a 3/16" thick skin.  It will work to encapsulate the glass fibers from the blanket, but really not that much more.  It will be prone to cracking from thermal shock and will also be quite brittle (so watch yourself carefully when manipulating the crucible, and make sure you leave plenty of space for your crucible tongs).

Good luck and be careful.

[smeeldog]

loud and clear, is kiln wash then needed for kast o lite then, I understand one main reason to use ITC-100 is for its resistance to flux, and then there are the benefits of added efficiency.

[smeeldog]

I might as well add this here before it falls into obscurity since I wrote it on scrap paper.

The formula I followed was cubic inches of inside the melter, multiplied by intended thickness (.25") divided by 19.2 which JHCC has posted before is the number of cubic inches in a mixed pound of kastolite.

so 332.6 x .25/ 19.2= 4.3

Im just going to get 7 for when things get weird.

thanks everyone

[Buzzkill]

I'm not sure I understand what you did with your math there. The cubic inches of the inside of the melter may be helpful for determining your burner size, but what you really want to calculate the amount of refractory you need is the surface area of the chamber multiplied by the thickness you intend to use to get the volume of the refractory.  

 

You said the diameter is 11 inches.  After putting in 2 layers of wool your diameter is 7 inches.  The height is 14 inches. you should be able to take it from there.

After you apply .25" of refractory that will only leave you 6.5" of working space for your crucible and tongs.  You may want to go shorter and fatter.  I think starting with 14 inches in diameter and 11 inches tall would probably serve you better.

[smeeldog]

I do have a problem with reading and not thinking about what im reading makes sense, and assuming everyone knows something I don't, though this is still probably true. I didnt include the wool into the dimensions because I figured having extra powder couldn't hurt.

I agree shorter and fatter would be better, allas this was a prebuilt, though I know how to weld, I think my dad was itching to get goin, and well he can't take all the blame of course (or even most of it), but its funny where we have ended up, we do have a crucible that I think should fit.
 

so 3.5 being my radius, and taking out 2 inches for the floor and ceiling, 10 inches is height, comes out to 296 sq in, 296*.25 = 74

[Buzzkill]

Unless your floor and ceiling are going inside the cylinder, the length (height) won't change.  If you have a flat surface that you will set the cylinder on it won't take any additional space inside the chamber.  The same goes for the top. They will still need insulation and refractory, but they can be removed/replaced separate of the main body.  I suggest making it this way since it will be much easier to deal with if (when) a crucible fails inside your melter and you have to clean things up.  In the worst case you can just replace the flat floor that the cylinder sits on and not have to rebuild the entire thing.

I do agree with your math if we assume a 10 inch wall height though.

 

 

[smeeldog]

Yes the plan was to have the floor and ceiling inside the melter body itself, the ceiling is removeable due to the design of the prefab- it is just a top with handles and no hinge, but I dont see how I could do this with the floor. Though I understand the problem that causes for when crucible does fail.

When you say "you can just replace the flat floor the cylinder sits on" what are you referring too? The crucible is going to sit on a fire brick which will be on top off the floor of the melter, are you suggesting i come up with a way to make the floor separate from the walls of the melter body? (which is a cylinder)

I am sorry if I am missing something.

Also last thing (for now) that has to do with numbers, and I get it, I am dense, I am doing what I can to change that. But is 74 now cubic inches of kastolite i need to mix to get the correct amount of wall coverage?

[Buzzkill]

I probably wasn't as clear as I could have been.  You can cut a couple inches off the bottom in much the same way you intend to do at the top for your lid.  In fact they should both have a hole in the center, but a much smaller hole in the floor piece.

What I'm suggesting is 3 separate pieces that comprise your melter.  The bottom piece is the floor, which should have a drain hole in the center to allow molten metal to escape when there is a crucible failure. You can cast the floor with a small channel that runs to a hole that will be covered by the plinth that the crucible sits on.

The middle piece is just the the cylinder with the burner, and of course the removable lid (ceiling)  sits on top with a hole for exhaust gases to escape.  It may be a good idea to use some combination of latches, clasps, or hinges to hold everything together in use, but once it's cooled down you can separate the pieces and service them or replace them individually as needed without having to rebuild the entire thing.

I came up with the same number as you for the minimum amount of kastolite required for your build.  Experience has taught me to always get more than I need because the chance of me doing everything perfectly the first time I try it is quite low.

[smeeldog]

• Buzz, that is why I bought 20 pounds of the stuff, lololol. And gotcha, the channel leading to a hole in the bottom is a great idea, I will also be toying around with the idea of angle grinding the bottom off to make three separate parts, adding latches sounds like a good idea, for at least the middle connecting down to the bottom/ floor.
  
  Also I have too assume I'm right in imagining 74 is now cubic inches of kastolite coverage, mainly because you didn't say that unit is the wrong unit to go with, after having multiplied my square inches by the intended thickness of the kastolite wall.
  
  Anyways, thanks a bunch man, next time I'm your way I'll buy you dinner
  
  that goes for the rest of you too.

[Buzzkill]

Right.  You got the surface area in square inches and then multiplied that times the thickness to give you cubic inches of volume.   You can then use the density of Kastolite (lbs/cu in.) to calculate the minimum weight of kastolite needed for your build.  It seems to me that you have it right (assuming you used the right number for the density of kastolite.  I didn't check that).

When you get it completed and ready to use, the whole thing should be on a frame or something to elevate it a little bit so that you can put a bed of dry sand or something else to contain any molten metal that would exit your drain hole if the crucible fails.  You want nothing flammable or anything that could be holding moisture (like concrete) to come in contact with molten metal.  Always assume that there could be problems and prepare for them so you won't be surprised and you will limit the potential for injury.

Based on your postings on here I think you are moving in a generally good direction and speed on this.   I know when I get excited about a project it's hard to slow down and do things the safe/right way.  However, the success rate goes up and the injury rate goes down when I force myself to do that.

[smeeldog]

Greetings again everyone, or at least everyone that participated in this thread. Just would like to breathe one more breath of life in it and say that I just poured my first mold the other day and have spent the subsequent days polishing it up. It went pretty well, I had someone there with 911 on speed dial, wore pretty much all leather and did a lot of saying "well, we will see how this goes". The total time from start to finish was about two months, probably closer to two and a half, but you know, I wasn't really keeping track, maybe I should've been.

My mold which was made of around 65-70% plaster of paris and the rest fine sand, held up well enough to not destroy the outcome of the pour, and now my next task is to see how much less work I can get away with after pouring my next.

I am going to switch to greensand casting, though I am unsure about how I am going to make my own basic metal flask that uses a fine enough system to not cause any mold deviations when going to take my pattern out initially, as well as getting the cope and drag back together exactly where they were to start.

Anyways, I really just wanted to say thank you guys for the help, wouldn't have been able to do it without you. Or maybe I would have and it would've taken me a year, so thanks for sparing my life.

One last question, do any of you know of any graph or system that will tell me how smooth and polished I need my items face to be to allow for a cleaner cast with petrobonded sand and if different metals will pick up different details from the sand pattern negative? Id like to cast like 10 more of these things but want to obviously minimize clean up time.

 and if anyone is curious, I made an aluminum behelit from the manga Berserk by Kentaro Miura.