Cast-Iron Furnace Build Using Partially 3D-Printed Molds

I am also concerned about this area, the original plan was to have another raised wall right around the exhaust hole (protecting the wool), but I couldn't figure out a good way to do this in terms of making the mold.

Actually, I was planning on doing a metal shell but it's not time nor skill that prevents it, rather a lack of raw material. My local metal supplier has been shut down for months now due to Covid. I could probably find another source, but that place had such good deals on material that I can hardly bear even looking through anyone else's inventory (it was a metal recycler that sold retail on the side). Hoping its all over soon so I can go ahead and load up on new stock.

Thanks for the suggestion on where to find sheet metal. That method probably makes for a very lightweight lid, and I like that idea for sealing the lid.

I'm going to definitely try integrating these ideas in my next lid; as I said this one is only a temporary one and really an experiment with how internal rebar will work.

Anyway, off to start making my crucible tongs!

 

Creating an airtight seal between the body and lid is something I have struggled with. I like this idea, but would hope to find a more permanent solution.

On my last furnace, I first cast the lid and let it dry. I then cast the body, placed plastic over it, then put the lid on with the hope that they would form a perfect bond. It turned out to be a very good fit, but not perfect.

I want to look deeper into the slanted/ cone shape mentioned above, but imagine the casting would be very difficult.

 

I cast my big furnace's lid like that, if I understand you correctly. The castable refractory lid has a raised 1" thick wall around the vent hole. And the same around the inside of the lid's outer shell, with a 2" deep ring-shaped recess between them where the insulation sits.

The way I went about it was to use a 2" thick donut of extruded styrofoam as a floating core to mold the cavity for the insulation, and clamp a couple boards across the slice of steel barrel that was used for the outer shell of the lid to keep the foam from floating any higher than that during the pour.

I don't think that was 1000 words, but I have pictures to make up for it. Everything to do with building the lid is all together in one post entitled "The Lid" in my oil furnace build thread (linked in my sig block). This way worked like a charm for me. I'm sure there are other ways to cast a recess in a refractory lid, but that was what I came up with. I realize this info comes a bit too late now to be helpful, but it's never too soon to start planning the next furnace!

Jeff

 

It probably wouldn't cause any great harm overall to proceed as-is until you find out what it's going to do. The prospect of the burnt fibers being blown skyward gets folks a little antsy though. A solution moving forward might be to cast a refractory sleeve to drop in from the top kind of like a flanged bushing. I haven't looked up your hole diameter but if you could keep it around 4" it should be fine.

Pete

 

Concerning the risk of outdoor use of ceramic fiber as a lid gasket material and it’s safety: I do think prudence concerning potential inhalation of fiber is appropriate. I also think it is useful to base decisions on science to the extent possible. I have reviewed numerous article published on the subject. To date no cancer or chronic obstructive pulmonary disease has been linked to industrial exposure to ceramic fiber manufacture or use. While I consider myself to be industrious (smile), my weekly melting of iron outdoors results in no perceptible fiber exposure and within the scope of risk exposure for ordinary daily activity (like driving a car for instance) to be essentially nil.

Here is one of many articles on the subject which is part of an ongoing monitoring program by the NIH, OSHA, and the CDC.:

https://pubmed.ncbi.nlm.nih.gov/20388033/

Denis

 

I've used rigidizer on all the exposed wool and coated the exhaust hole with ITC-100, hopefully that is good enough for the time being.

 

I will be interested to see how the ITC on wool behaves as I have no experience and I do not recall prior reports from anyone.

Denis

 

Did some work on a rolling base for the foundry. This is definitely a temporary base because it is extremely unstable when moving. I thought it would be a great idea to use 3 rotating casters positioned really close to each other, but really all it does it allow the very top heavy furnace to be basically right on the tipping point at all times. It still works decently when you lock all three wheels facing outward for the time being, I just need to be very careful until I figure out another solution.

I'm insulating the base with K-23 fire brick, which are so easy to work with it is crazy. I can't believe I haven't used these before. I think the bricks are going to be the way to go when I build my next furnace (just coat the inside with a layer of castable/satanite for the higher temps). They saw in half with no resistance at all, come in a standard size for replaceability, are actually rigid unlike ceramic wool and still have really good insulation properties. Also they aren't even that expensive for what you get.

Anyway, here are the pictures:

Aluminum plate I had lying around, just about the right size too. Sort of led me astray because it just seemed so easy to add those casters so close together...

Firebrick cut and shaped:

Used some refractory mortar between the bricks and a tiny bit to help hold the furnace onto the base, should be no problem to remove later if necessary (famous last words):

The astute among you may see the flaw by where the CG is vs the casters (aka, very close to the tipping point):

The most stable position for the casters:

Someday I'll get around to posting a video of my oil burner:
The start of the crucible picker (note the reason why the forge got unpacked; the flat bar turned into a rough U-shape for extra stiffness because I didn't have anything thicker):

 

I think you need to be careful with those wheels and maybe redesign them. Its going to be unstable and make the furnace very tall and difficult/more dangerous to remove the crucible.

A rocking design might work better where the wheels are off the side and you rock the furnace back to engage the wheels.

 

Looks tippy to me too, like it could trip over a pebble on your driveway while being moved into position, or worse, while it's hot as you roll it back into the garage or wherever. I might either use Zap's idea or build a wider cart for your furnace to roll out on. There are enough things to keep track of during a melt without adding "make sure the furnace isn't falling over" to the list. Aside from that it all looks great.

Oil fired forge, cool! Not sure I've ever seen one before.

+1 for the IFB subfloor. That has worked well for me too. A tiny bit of molten metal can cause a big hole to form in one of those bricks, but a bit of castable refractory on top or even just a thin layer of Satanite seems to be enough to protect the bricks from being eaten by those occasional drips.

Jeff

 

I seldom move my furnace as I just cover it with a 55 gallon drum, but this has been a pretty reliable setup. Of course it is worlds away from k.kuhn's furnace in terms of weight, but my main concern was stability when swinging the lid.

@k.kuhn. That's a pretty nice compact burner. I'll be interested to see what's inside.




Pete

 

Here's another option

 

You could just use a 2-wheel hand truck to move it. I agree with those who have suggested a wider base. That base could be as simple as 3 sockets on the base to slide 1-foot tubes in. Move the furnace on a hand truck out to your burn area. Rock it back a bit and slide in two base tubes. Slide it off the truck and rock it forward to put in the 3rd tube. It would be stable in use and compact to store. One of many, I am sure, possible solutions.

Denis

 

Here are some images of the lifting tongs that I've made for my #10 Procast crucible (which is what my furnace was designed around). I was worried about how much clearance I would have between the crucible and the wall of the furnace, so I made the tongs fairly lightweight and thin. There is plenty of room to fit the tongs around the crucible, so I can probably add reinforcements if necessary. Overall, the tongs feel like they are plenty strong enough to lift the crucible even while full.

Aligning the parts for welding:


The center/cross bars are high carbon steel in the form of an old flat pry bar, so should be plenty strong and durable. Also as explained previously, the backbone of the tongs have been bent into a U-shape for added strength:


After drilling and inserting the pivot:


Plenty of room to fit the tongs down around the crucible:


Easily holds the crucible under its own weight:


Not the prettiest welds, but it works:


There may be a weak point where the handles connect to the uprights, but that is easy to fix in the future with another brace:


Decided to add a pin to prevent overtravel and allow it to be hung:

 

Thanks for the tong-construction part. Pictures really help!

 

School and work have picked up recently, so I've haven't had as much time to be working on projects or uploading progress. But, I finally had a chance this weekend to work on the furnace and do the first pour!

The metal of choice was aluminum bronze. I managed to get together enough copper to make 20 pounds with 10% aluminum by weight. The application was casting a golf putter for a friend. I used Granta CES to select an alloy that was optimized for the application and that could make with materials I had on hand. The constraints were: high density, acceptable castability, resistance to corrosion in fresh water, and also apparently low hardness is desirable to give a "softer" feel (don't ask me, I'm not a golfer). It's also a nice gold color, and that sold it.



As it turned out, aluminum bronze C95200 (CuAl10Fe3) was ideal in these respects. This alloy is 10% by weight aluminum and 3% by weight iron with a balance of copper. As I don't really have any clue as to how to get iron into the melt, I decided to forego this alloying element and opt for a simple 10% by weight aluminum alloy. After a bit more research, the alloy I actually ended up creating is probably more similar to C95300.





This castability rating is really quite poor in comparison to other bronze alloys.





This aluminum bronze is actually a very interesting alloy, and if the ASM handbook is to be believed, has some pretty outstanding mechanical properties for a cast material. The tensile strength of this alloy is approximately 500 MPa, which is higher than an average mild steel. It is also a bit harder, with mild steel scoring an average of about ~120 on the Brinell scale, whereas this alloy is theoretically up around 140. I have a Rockwell hardness tester, so at some point I will do a comparison in the B or C scale between some steel and the alloy I ended up with. As far as durability goes, the literature seems to imply great corrosion resistance in both freshwater and saltwater applications, and interestingly is commonly used on boat propellers due to its ability to resist cavitation (perhaps a result of higher hardness?).

I would highly recommend picking up a copy of the ASM Handbook, if you can stomach the price. Otherwise there are some alternative sources where it may be available for a discount. Volume 15 - Casting has an entire chapter dedicated to sand mold making and provides recommendation for particular alloys from fluxes down to the recommended size and geometry of sprues.


There was some additional information which may be of interest:

“Other Alloys. Certain aluminum bronzes, most notably those containing more than about 9% Al, can be hardened by quenching from above a critical temperature. The hardening process is a martensitic-type process, similar to the martensitic hardening that occurs when iron-carbon alloys are quenched. Mechanical properties of aluminum bronzes can be varied somewhat by temper annealing after quenching or by using an interrupted quench instead of a standard quench. Aluminum bronzes alloyed with nickel or zinc use reversible martensitic transformations to provide shape memory effects (see the article "Shape Memory Alloys" in this Volume).”

“Aluminum bronze casting alloys containing more than 10% aluminum are heat treatable. These are alloys whose normal microstructures contain more than one phase to the extent that beneficial quench and temper treatments are possible. The copper aluminum alloys normally containing iron are heat treated by procedures somewhat similar to those used for heat treatment of steel, and have isothermal transformation diagrams that resemble those of carbon steels. For these alloys, the quench-hardening treatment is essentially a high-temperature soak intended to dissolve all of the α phase into the βphase. Quenching results in a hard room-temperature β martensite, and subsequent tempering reprecipitates fine α needles in the structure, forming a tempered β martensite. Table 9 shows typical heat treatments for three major aluminum bronze alloys. “



“A number of the copper alloys are susceptible to dross formation, and the normal precautions in pouring and gating are absolutely necessary to minimize exogenous inclusions. The drosses are usually complex oxides of copper, zinc, tin, lead, or aluminum in the aluminum bronze family. Iron is added as both a dispersion strengthener and as a grain refiner in aluminum and manganese bronzes. However, iron can become an undesirable inclusion in the other copper alloys.”

“Filtration of copper casting alloys is on the increase, using ceramic foam sections in the gating system. Oxide inclusions have been successfully removed from aluminum bronze alloys (Ref 153). Investment castings, both aluminum and copper base, can be successfully filtered using a filter section in the pouring cup or, in the case of larger castings, molded directly into the wax runner bars. Ceramic filters for copper alloys are usually alumina, mullite, or zirconia.”

 

I decided to separate the pictures related to the first pour into a separate post:

Soon after lighting the burner.

The burner setup, I also made a new base for the furnace. It's just a steel drum roller base and I simply drilled a few holes which lined up with the tapped holes I made for the previous casters.

It was my first time trying to pour this big of a crucible, so I get a pass. The aluminum handles on mold 2 are an experimental design which works pretty well. If the trapezoidal indexing tab doesn't align the halves well enough there is also a hole to put in a pin or a screw.

Very pretty surface oxides, liquid rainbow!

Not sure why these next few turned out so blurry, but these are the "ingots" left over after we did the various pours.

The one successful part we made. Still some surface imperfections, but good enough to finish up and put on a handle.

I may have tried changing too many variables on this run, since it was my first time using the new furnace and melting anything hotter than aluminum, and also trying out a new greensand mix (had previously only used petrobond). We were having many issues ranging from shrinkage cavities, porosity, mold shifting, and the list goes on. In terms of the melt, our first pour was way too hot and the greensand was probably too wet which caused a lot of issues.

Cooling down slowly with the crucible inside (empty) after the day was done. It took a full 24 hours to reach ambient inside. Everything held up well overall, but the two vertical cracks inside did get a little worse. The lid with the internal rebar held up really well, even the wool around the vent that was only coated in ITC-100. There was a very strange red/pink coating/oxide on the wool around the vent hole. I'm thinking it may have potentially been vaporized copper?