Segmental Furnace Lid made from Plastic Refractory Blu-Ram HS

I take the lazy man’s approach to getting a seal between lid and furnace. I just use Satanite to glue a half inch of wool onto the top edge of the furnace. The weight of the lid mashed down the wool which acts as a gasket. It needs to be scraped off (easy to do) every few melts and replaced. Works well for me.

(Tank loaf is a new entity for me. Looks like yummy stuff. Thank you, I think. One thing I don’t really need is more food temptations! ;-). )

Denis

 

Well, the lid now has 10 hours and four melts on it in iron service. It looks just like it did after the first heat except for a slightly darker color. There are no cracks in the segments. Given my prior experience with refractories in monolithic applications, they have always cracked and as near as I can recall during the first heat. So, once again, I am encouraged by the results. I will continue to provide periodic updates.

I am getting three more boxes of Blu-Ram tomorrow or Thursday and plan to start making some vertical segments for my new furnace which will use my current lid. I am thinking of making the segments something like 5/8" thick except for the joints which I will make a little thicker to provide more strength for having them loosely key into each other. I have to play with the refractory a bit more before settling on a thickness. I think it will take only a little less than a box and one half for the vertical segments. I have found that a nice rule of thumb for Blu-Ram is that 1 cu inch of it weighs .1 pound. The segments will be wrapped in wool.

Denis

 

I got tired of waiting for more mizzou to come in the post, so made a 2 hr road trip to purchase a couple 50lb boxes of a phosphate bonded plastic refractory from Mt Savage refractories. Guys there were pretty cool. Didn’t mind my stopping by for a couple boxes when normal order is measured by the pallet, 60 boxes.

looks like this company’s version of BlueRam. Their name for it SAVAGE RAM 70-M Blue. At $38 per box, it was worth the trip!

 

I like your lid! The key is having it domed so it can grow upward as it heats. Great work.

 

Yes upward and outward seem to be key as does non-uniform growth. The non-uniform part may be more important in the burner-tube furnaces as opposed to resistance-wire-heated furnaces where heat application is much more uniform. In my mind segmentation accommodates uneven heating much better than monolithic designs since it allows different areas to move more or less depending on that area's conditions and does not require that adjoining segments stretch or shrink to match neighboring segments.

Denis

 

I wonder if an eccentric, oval or even cam lobe shape to the chamber would have any beneficial effect on the flame path? (Thinking out loud which is not usually a good thing)

 

Update:

The lid now has 15 hours of intense firing on it with no sign of deterioration or cracking.

Denis

 

Yes, between casting squares, getting them heat treated and building a new furnace, I have been pretty well occupied.

I have cast several squares 3 of which were keepers and 3 or 4 were "opportunities for learning." I put that in quotes, but it was quite literally true. It took me a while to figure out the right combo of gating, risers, and pouring temperature to come up with a reliable plan. I think I have got that figured out at this point.

Today I take the seemingly momentous step of tearing down my existing furnace so that I can install my new one on the base that carries the lid lifter and crucible hoist. I hate being without a proven furnace for a while. But that is the most pragmatic approach as rebuilding the base, axle, tow handle, and lifting attachments is more work than is justified. I just have to make the leap of faith that the new furnace will work. It will take a couple days to make the switch I think.

Denis

 

I mentioned earlier that a plinth I had made a year or more ago from castolite 30 had held up pretty well but was somewhat held together by melted-on crucible glaze and slag. I was able to remove from my decommissioned furnace last night. It had deeper cracks than I realized. But, indeed melted on slag and glaze made it still pretty solid. I was surprised how deeply and extensively cracked it was as discovered when I flipped it over.

The under surface


Views of upper surface:


Denis

 

The new plinth is designed to allow convection of flame/ hot gases under the crucible base. That is the reason for the ribs on top of it. I am hoping for better melt times also due to increased furnace volume and therefore dwell time and higher crucible placement. I expect that my optimal fuel flow rate will also increase some. Learning the new furnace’s optimal setting may take a few burns.

Denis

 

I put the furnace together today. Here are just a very few pics. I did not do a great job of documenting the assembly. But here is what I have.

This is what you get when you recycle the furnace base from a prior furnace. I had to add a base better suited for the current furnace resulting in a messy appearing but very solid base on which to build the furnace. I needed to make the add-on base since I changed my mind about wall height of the chamber after I had cut down the barrel. It was easier to make the add-on base than to trim an inch off the barrel height and tig on trim ring to reinforce its edge. The bottom of the barrel was cut out circumferentially so that the barrel walls can be lifted off the furnace without disturbing the base. That will allow for easier maintenance of the insulation should it shrink or burn out in an area.


You can see the segmented base is elevated by 3" feet allowing for space under the base for wool. That wool is wrapped and stuffed into place in this pic.


The first wrap of wool. Those wires are only there to hold the wool in place while I put on the second and then third layers of wool. They will likely fail related to heating when the furnace is in operation. But by then they will be unneded.


Before I wrapped that first wool layer on, I painted satanite on the areas that will overly seams in the hot face. Though I doubt leakage would actually harm the wool, the Satanite should seal the deal.



Here is the furnace wrapped in 3 layers of wool with the barrel tube slipped into place. I made sure the inside edges of the barrel were pretty smooth so it would slide over the wool easily. It was a snug fit, but slid on easily. On about 90 degrees or so of the furnace there was an almost 1" gap between the wool and the barrel tube. I stuffed fiber-glass wool into that area using a pushing stick. Once that was in place the wool seemed to be firmly held by the tube and the whole works was very solid feeling. Actually it was better than I expected. To trim out the stuffing I cut a 3.5" wide band of wool and pressed it into the 3" gap between the tube and the furnace segments. I placed about six wires on the outer layer of wool. Those I simply pulled taut by hand and spun a knot in the crossed wires. Those wires should not fail as I expect they will see temps on the order of 450 to 500 degrees F and likely lower than that if my insulation works as well as hoped.



Looking down into the furnace. The tuyere is near the upper center of the pic.
I crammed some Blu-Ram (not shown) into the cracks in the segmented base so that the 1/2" layer of play sand I pour onto the floor and then cover with a 1/2" thick loosely fitting disc of Blu-Ram won't trickle out through the cracks. The sand and its cover are going to be used as a sacrificial cover for the floor. I am hoping that once I get some build up of slag and iron on the sand cover, that I will be able to crack out the cover and scoop out the sand along with any residual slag and other junk that seems inevitably to want to coat the floor of a furnace. That cover (not shown) has a single slit to act as a control joint and a center hole that will, hopefully, limit additional cracking.


Today was supposed to be the day I would put some fire into the furnace, but family stuff (fun stuff) intervened and, so, the furnace waits another day.

I am definitely keeping my fingers crossed hoping that this work will not result in a smoking pile of rubble.

I am definitely liking the "modular" aspect of the furnace in that individual chamber panel can be replaced with the investment of only a couple hours forming and cooking time. Having the barrel tube removable also should simplify any needed maintenance.

To hold the burner tube in the tuyere I am reusing the strut made of angle iron and square tubing that I used on the prior furnace. The Blu-Ram tuyere simply wedges into place. So far, I have not secured with anything other than the restraint imposed by the burn tube wedged into the tuyere.

Denis

 

Denis, I have no doubt that you're new furnace is going to be a good performer. Although our furnaces are different, they are very similar built. Mine has 60 loose segments, and yours has 14.

Between the loose fit IFB's, hot gases escape (because of the positive pressure) into the ceramic wool, and a white smoke slowly makes its way out of the wool. My hot face is 2.5 inches thick and then I have 2 inches of wool. At three-quarter throttle after an hour of use, the outside of my drum is 60 to 70°C with 7 L of fuel burnt.

The stainless steel hose clamps expand a little bit and the brick gets a little bit loose after an hour burn. But, they seem to be tight again six or seven hours later.

 

Interesting, Matt. So you have raw IFB as your hotface? On my prior furnace I ran an IFB lid for about a year. But I had to keep it coated with Satanite as the 2600F bricks melted badly in a single run if the Satanite came off in an area.

Denis

 

So far there is no real damage to my bricks in the dozen or more melts of aluminum. I have had one boil over and one crucible failure and the aluminum just peeled off the floor. From my burner design I have problems with aluminum. My airspeed is very fast. My flame wraps the furnace almost to Times before it exits and then I have two torches 180° apart. When I was melting soda cans, I'd almost have to throw them in and then push them down with a stick. Any dross about 3/4 full on an A12 simply stirred it self with air movement. Sometimes dross just became airborne. And sticks everywhere on the inside of the furnace.
\
A little wire brush knocks this off easy.

This is the mess after the last aluminum melt. I haven't cleaned it yet.

 

Cans??? Come on man. The furnace looks good! I bet you are creating some kind of insulating boundary layer of air protecting your brick.