Introduction

That degrees Fahrenheit, Pedro's in Portugal, I'm pretty sure he's talking about degrees Celsius

I highest I think I've seen is 3400°F (1871°C)

 

Too low, look what I found
https://www.americanelements.com/hafnium-carbide-foam-12069-85-1

I wonder if I could make a furnace with this as a refractory, 3900° C (7052° F) melting point.

 

It's going to come down to what you can get your hands on. You'll be lucky if you can get Mizzou or kastolite.

 

The rule of thumb with an oil furnace is 50mm space between the crucible and the bore wall. That allows for adequate combustion and also allows for lifting tools to fit without scraping the walls. I think the clearance with my #18 is about 40mm (look at me speaking metric.lol. It's helpful when you give measurements or temperatures to use C, F, mm, inches, etc as appropriate. Imperial is alive and well over here.)
There are a lot of different furnace types that we can build but I will mention 3 for the sake of my own limited experience and to give you some reasonable options to research so you can make some informed decisions.
1) Refractory hot face wrapped in ceramic wool in a barrel or keg.
2) Ceramic wool (kaowool) only with a face coating of high-temp mortar in a barrel . Satanite is available here in America. (not the stuff you can get at home centers).
3) stacked firebricks. Either insulating type or hard bricks.

For 1&2 look to member Tobho Mott among others. He has excellent build threads for both.
For 3 look at members OMM and Oldironfarmer. There is a building block material common in Europe but not common here. The name escapes me at the moment-Yupo, yugo? It is amazingly refractory and well suited for this.

There are many other member builds as well, but those are the ones that come to mind. Once you really consider what your casting goals are at least in the short term, you can make decisions about type and size of crucibles and furnace as well as needed materials to get it done. Notice I didn't mention skillset. Obviously more is better, but if I can do this so can you!
So study up on what these guys have done and have at it. You will probably be hearing from them anyway. If this bug really bites you, you'll probably be building another furnace anyway!

Pete

 

Yes, ytong. Forgive my goofy memory lol. It seemed to me that the guys using it were getting pretty darned good service from it but that maybe wishful remembering too.

 

Thanks guys, but it says is can't go over 1450 because the ytong will fail. How will I melt iron in the future? I would rather build a long lasting proper furnace, that I barely have to worry about it overheating, to melt whatever, rather then building something just for aluminum or bronze.
I did mail that company asking if that hafnium carbide foam would be suitable for the interior of a furnace.
And also found a local company that makes and develops refractory since 1843
http://www.abrigada.com/index.php/en/
Aldo I have spoken to them, and mailed them already last week, no reply still.

I assume the refractory needs to be able to withstand at least 100 or even 200° C more than the melting point of whatever I am melting?

 

Yes. I was just presenting some options in my post above. Your refractory will have to exceed your melting/ pouring temperature by quite a bit. The furnace needs to be at a higher temperature than the metal for obvious reasons. My furnace refractory is mizzou as mentioned above. It's max rated temperature is actually 3000F which is adequate for cast iron.

Pete

 

I don’t know how it works in Portugal, but as a hobby foundry guy, my writing to refractory production companies to inquire about products almost never nets a reply. They are not interested in a 50 or 100 dollar transaction.

On the other hand, if I show up at a small or medium commercial foundry and talk to a foreman or secretary explaining my plight, there is a chance someone will take me aside and show some interest in helping me out. I buy a few pounds of thing like ferrosilicon that they buy in 500 pound drums. And that is where I learned about and bought my first box of Blu-Ram HS plastic refractory. And that is where I got to see magnesium dumped into molten grey iron to convert it to ductile. That was a light show!

It looks like there are quite a few foundries in the Lisbon area.... I’ll bet 4 or 5 will turn you away, but one of them will let you in the door.

Denis

 

I did this way back in the day and not only did I get the sand I was looking for, but a few months later they offered me a job because I showed interest in the craft

 

I have a company email, the company is quite large and well established in the portuguese construction industry, my surname present in the company's name (my grandfather founded it). So luckily, that opens a lot of doors. I always write has : we (the company ) are interested in your products.
A few companies are covid crazy, and are working half steam only, I of course take the recommended precautions, but refuse to act like this is an outbreak of the ebola.

I have spoken to one of our compressors and air systems specialists (in the company) , and can quite easily a vacuum a furnace (build with proper seals and 2 valves) , and remove oxygen, and replace it with argon. Now, is there a way to use an oil burner to fire one of those? (it would have to be from the outside I think) or, I was looking at the electric powered ones, and we have a few hundred generators all the way up to 300 kva, and all need, every now and then, to be put in heavy charge, we have a machine with a propeller to consume the needed 456 Amps, but it pretty much goes to waste, the huge fan spins and there goes all that energy. (this already thinking ahead regarding stainless )
How do you get an accurate measure of the temperature inside the furnace? I now have a laser gun but it only goes up to 600° C, are there probes or thermometers/pyrometers that can withstand 1600/1800?

 

I used ytong years ago to hold up my 300gallon aquarium off the floor. It's a fine building material, but it's not refractory cement. Don't putz around, get the real stuff or do the kaowool covered in satan shit.