Crucible furnace construction, with or without refractory cement?

[cds333]

From my research I have learned that the difference between making a forge out of ceramic fiber as opposed to castable refractory is that the former heats up quicker and is a more delicate structure, and the latter takes longer to heat up and uses more fuel but stays hot much longer.

My goal it to make a small furnace capable of melting aluminum at first, and other metals eventually, that can double as a small forge to heat metal for the occasional blacksmithing project.

If anyone is familiar with Micheal porter's book, he describes a propane-tank forge that is made from only ceramic blanket and ITC-100., however later in the book he describes a furnace that is only refractory cement and ITC. I have also heard that it is recommended to add a layer of ceramic blanket outside the layer of castable refractory if you are using it, to keep heat from escaping, (i guess heat likes to travel right through the hard layer?!?)

I have seen many different furnace designs, all the way from cheapo homemade portland cement up to the ceramic blanket/kast-o-lite type, and have no idea which is best and for what reasons. Would it be possible to make a crucible furnace out of ceramic blanket and ITC-100 only? Or do I definitely need the layer of kast-o-lite or mizzou for example?

What are your thoughts guys?

Thanks!

 

[Buzzkill]

First off, welcome to the forum.  There's lots of good info on here for you, but you have to dig for some of it.  The search feature on here is less than ideal, so you're usually better off doing a web search and including "iforgeiron" as part of your key phrase to find things here.

Secondly, Michael Porter is a member here, so you can ask him for clarification directly if needed.

In general, multi-purpose tools don't perform any of their tasks as well as you'd like.  The typical advice on here is build a forge for forging and build a furnace for melting.  They do have a lot of similar components, but they are not identical in construction or in function so trying to use one for the other purpose will often result in frustration and limited success.

Some of your questions will have potentially different answers depending on where you are in the world and what is most important to you.  Since this is a world-wide forum it's best if you include your general location in your profile so that any answers which are location dependent can be addressed properly. 

I highly recommend getting a comfy chair, something to eat, a cold beverage and spending some time reading through the copious quantities of information available.  For your interests I would start with the gas forge section of the forum.  Read through Burners 101 and Forges 101 for starters.  Both are authored by Michael Porter and have lots of good info and discussions contained within.   There is also a section for foundries and casting that you will probably find interesting.

I will say that you are on the right track with the ceramic blanket, a castable refractory for a liner, and ITC-100 (or comparable kiln wash).  Forget about the portland cement or plaster of paris "refractories" you may have seen on YouTube or other places on the internet.  They are not suitable materials for high temperatures, they will cost more money in the long run through fuel use, and may even be dangerous in certain circumstances.

[cds333]

Thanks for the welcome! Great to be here.

To clarify, it will primarily be used as a furnace. I will eventually be building a dedicated forge as well, probably like the one in the book. I don't do enough blacksmithing at present to justify a dedicated forge, however once I build my belt grinder I will have more use for that. I mainly want to cast aluminum into custom shapes that I can then turn and mill.

For the furnace I am thinking about using the cheapest stuff i can find, so I can build a prototype and iron out all the bugs before spending a few hundred on all the best materials. If I can get my burner to work in the geometry of whatever I build then I'll know I have a good design. I don't care if it only works for a few weeks or whatever.

My searches have not turned up anything about my question specifically however, if there is anyone out there who has built a furnace out of ceramic wool alone I couldn't find it. (Possibly due to the fact that it has so many different names)

So my question is: why does the foundry in the book not need insulation and why does the forge not need refractory?

Thanks so much!