My First Furnace Design/Construction

That is definitely my preference.

The cracks don't concern me. Maintainability does. A Lego block type modular construction will allow me to make repairs and modifications without starting from ground zero.

Good advice.

At first scan, it looks promising. I will take me a few days to get through all his posts.

I have looked at the beer keg option. I can understand why they are so appealing for others but for me, it will be cheaper to get a skin custom made than to buy a used beer keg. Even used ones are not cheap here.

Dazz

 

Dazz,
Have you seen Ironsides furnace builds?
Well worth checking out. Just proves that it doesn't have to be complicated.

 

Hi
I consulted the supplier who can offer 1800 deg C rated castable. I will use that to make custom formed bricks backed with ceramic fibre insulation. Very close to what OldIronFarmer has done already. The only significant difference is that I will cast the bricks to shape rather than cutting them.

The plan is to start with the simple cheap things first, like tools, and leave the expensive items last. This includes the crucible and furnace.
The first things I will cast will be items for a modular aluminium flask system. An improved version of one I've seen somewhere on this forum.

I may have some questions during the detailed design, but otherwise I don't expect to be very active on the forum until I get to the furnace build. Probably several months away.

Thanks for all of the advice and feedback received. It has given me a clear roadmap to follow.

Dazz

 

Hi
A modular cast brick furnace on YT. Very similar to what I plan to do.

Dazz

 

Hi
I initial posts/design started with pre-made light insulating bricks. On the advice of forum members and my supplier, I have ended up with going with custom castable bricks. I don't see any problem with the idea of making bricks. Professional furnaces use them. Child labourers have been making them for eons.

I like the modular brick approach in the video but there are some points I don't like in the execution.

• There are no interlocking tabs between the layers. OK for temporary assembly but not OK for me.
• The bricks are too long, increasing the risk of cracking.
  
• The open surface of the mold forms a surface on the brick that is in direct contact with the adjacent brick. That surface needs to be formed by a mold face.
  
• The solid bricks will make the foundry very heavy and expensive, although I note a members furnace mentioned above weighed in a 250kg.

I plan to solve these problems with a semi-hollow brick, something like shown in the image. The image shows the rear of a brick and two sides. I just whipped this up in CAD so it is only for illustration.

• The bricks will be keyed together with half-round tongue and grooves on all sides.
• The rear surface of the brick will be the open side of the mold. The rear surface won't be in contact with the flame or another brick, so precise dimension and finish is not important.
  
• The hollows on the rear will be formed with vibrating male mold parts. I will be able to add/remove material to properly fill the mold.
  
• Relatively small bricks should reduce stress due to thermal gradients.

Dazz

 

It all depends on your goals: do you want to invent a new furnace with many modification cycles to iron out the issues or is your goal to make metal castings?. Ideally a furnace is cheap to build, run and maintain as well as simple and reliable with all other considerations secondary.

 

Hi
Accepting the inevitability of cracks doesn't mean they should be ignored. A brick based furnace effectively builds-in controlled cracks.

The castable I will be using requires 10% water to mix. I will definitely need vibration to get it into a mold. If I mess up casting a brick, I will learn something from my mistake(s) and move on to the next. If I mess up an attempt to make a single piece cast kiln, I will lose multiple bags of expensive castable that will take weeks to replace (not held in stock by the supplier). A brick based approach is for me a lower risk path to success. It is not radically different to other successful furnaces.

The planned construction method meets my design goals. Your design goals might be different. Different is not wrong, it is just different.


Dazz

 

Dazz, I do like your tongue and groove design. But, the hollowing of the back will allow for different amounts of expansion with in itself. IMO I think you’re going to have many hairline cracks within the brick at a very early stage. I just went with the light IFB,s and no mortar. So I literally have hundreds of cracks to start. I’m going to do an aluminum pour , then copper, then cast iron and evaluate the untreated IFB‘s after each firing. I built up my chimney exhaust mortar the bricks together and surface mortared. I’ll get to compare these two faces early on. When I was getting my IFB I had the choice between 28 and 35. The 35’s had aboat 25% more density/weight each. I was warned that the light IFB’s do not last as long under direct flame, but last longer under indirect flame. If this is the case, the rest of the inside of the furnace might get a 1/16”-1/8”coat. I’ve tested a scrap of my IFB‘s with direct propane and laser thermal sensing gun to get HI which is just over 1200°F. It was only glowing red-ish. Inside my furnace with diesel and WVO (the brick might react differently) the brick was glowing white.

There is a drawback to light weight/density IFB’s. They lose their hot face so fast, sometimes you just can’t reignite.

 

Yes, I agree that is definitely a risk. I think the brick would be most likely to crack either side of the central web. The rounded corners are an attempt to minimise stress risers that cracks could start at.

There are other things that might work to mitigate the risk:

• Minimising the thickness (front to back) to reduce the thermal gradient across the bricks and the associated stress.
• Back the bricks with good fibrous ceramic insulation to reduce the thermal gradient across the bricks,
• Make the bricks square instead of rectangular (in other words, pre-make the expected crack)
• Make the bricks smaller,
• Reduce the thermal mass to allow faster heating,
  
• Gently heat and cool the furnace.

A lot depends on the material properties and the quality of brick making. There is also a risk that I am just over thinking this. There are too many variables and uncertainties to make a reliable prediction of the effects of any mitigation. I am just going to have to give a go and accept the risk of failure.

Dazz

 

Hi Kelly
I am certain I will need a vibration table.
Nice furnaces. There are some complex shapes. More ambitious than I am aiming for. It does provide confidence in the feasibility of making bricks.

Dazz

 

Listen to what Kelly is trying to tell you.
Less mass is better. You don't have to use excess energy to bring a furnace to temp which equates to faster melt times.
Since the consensus is you folks down under can't get ahold of Satanite then Zircon W seems to be the goto hotface coating.
(one of you folks need to contact Harbison Walker and get a few bags to distribute down there)

Do you need more than 1/4" of hotface for emissivity? I don't think so, anything thicker than that is just a heatsink.

I'm a firm believer in this type of furnace and there are shortcomings for iron melting due to the fact that liquid iron is so hard on any refractory. The beauty of this furnace is, if the refractory gets compromised just use your fingers and peel the coating off and paint more on. If you have to do that every dozen iron melts, no big deal. It's easier than making more bricks and tearing your furnace apart to replace them.

You can build this furnace with an angle grinder and welder in a weekend. No computer, no Cad, just plain old 'getter done'.
Is it 'pretty' or look like it came out of a showroom? No.
Does it work? Hell yeah!

 

I think there is a lot of good information in the last 4-5 posts, but...
- if cast iron is the goal,
- and waste oil/diesel is the fuel of choice

A IFB design like he has shown would be way easier to replace non-mrotared brick. The slanted lid/ceiling would be a challenge. He could wrap the IFB’s with 2”(50mm) of ceramic wool like I did.

Dazz design;

 

There you go...compromising the KISS principle

 

Lol. Somebody had to . If he was goaling for only LP or NG 100%. But I think he’s looking for more.