Tilting Kettle Furnace Under Construction

[lazersteve]

I've been working on a new propane fired furnace, not a really big one, just something for melting around the house.

Today a friend of mine and I worked for six and a half hours to construct a tilting kettle furnace I designed from a mixture of ideas I've seen here and elsewhere. Here's what we got done today:

[youtube]http://www.youtube.com/watch?v=ce1Q4VfglxI[/youtube]

It's still in need of a lot of things ( lid needs refractory, propane plumbing, nozzle is in the mail, inlet on furnace, casters, etc.) but the bulk of the work is done.

My friend did all of the welding and I did most of the fab work and all of the design work. We worked our buts off in his metal shop. He taught me how to use six of his machines to speed things up.

The core of the furnace is an 8" x 10" x 1/4" steel tube with a welded flat bottom. The base is a 18" x 18" square with a cross member, all made of 1-1/4" square tubing x 1/8" thick. The uprights are 10" x 3" x 1/4" steel c-channels with a 1" steel pipe split in two on top for the furnace pivot and supported by some 1-1/4" angle irons. The support rods were made of 3/4" all thread recess welded into the furnace pipe wall at 5-1/2" from the bottom of the furnace. The lid is an 1-1/2" ring of the 8" pipe and a two piece cone with a 3-1/4" vent hole welded together, hinged in the back with a 3/8" pull pin for easy removal and a large round 3/8" steel loop for a handle. The burner support arm is 2" x 1/4" steel bar bent to the curvature of the furnace and welded in place along with supports. A split 1-1/4" pipe serves as an adjustable tie point for the burner tube. The kettle tilt handle is a 12" x 3/4" rod with a decorative ball on the end. There is a small 3/4" x 3" piece of steel welded to the lower left side of the furnace as a stop to keep the furnace from tilting backwards when the lid is opened. On either side of the rim of the furnace is welded a 30 degree angled 1-1/4" x 1/2" x 3/4" steel stock as a lid guide.

This furnace will hold up to a 5" OD x 7-1/2" height fire clay crucible as seen in the slide show. It will of course hold smaller ones as required.

I designed this furnace several years ago and have been taking ideas from various places to get the design just how I wanted it. I was in the post office the other day and saw my welder friend and asked if he would mind welding it up for me. As you can see, we had one hell of a fun day today. I had to work one handed as I'm still not able to use power tools with my right hand, so it was a labor of painful love for me.

I want to thank Harold for posting the photos of his furnace years ago, which inspired me with the basic idea of a tilting furnace. My tilting furnace is not as large as yours Harold, but I don't see myself ever needing one that big. If I do, now I feel confident enough to tackle the job.

Steve

 

[4metals]

Steve,

You do very nice work, my only question is why do you need to have a tipping furnace for such a small capacity crucible? I'm sure the unit will work fine but to tilt you will have to either cement in the crucible or support it in a way that the flames can still spin around the crucible. With induction you can pack in a ram mix and it is pretty quick, but with a flame that has to spin about the crucible it is more difficult.

For a crucible the size you're talking a push up device would allow quick interchange of crucibles and raise the crucible to the top of the melter so all you have to do is grab it with tongs, walk it to the edge (a few inches) and tip it into a mold.

 

[lazersteve]

You do very nice work, my only question is why do you need to have a tipping furnace for such a small capacity crucible? I'm sure the unit will work fine but to tilt you will have to either cement in the crucible or support it in a way that the flames can still spin around the crucible. With induction you can pack in a ram mix and it is pretty quick, but with a flame that has to spin about the crucible it is more difficult.

For a crucible the size you're talking a push up device would allow quick interchange of crucibles and raise the crucible to the top of the melter so all you have to do is grab it with tongs, walk it to the edge (a few inches) and tip it into a mold.

4Metals,

Thank you for the reply.

The main reason I built it like this was to see if I could do it and to get away from my electric kilns. I'm thinking I'll use it upright for everyday tasks like melting gold, silver, and such, and eventually line it with a new refractory configuration and other mods that that allows the furnace to be used with the lid closed. One of the things I have not added to the current design is the locking mechanism for the pivot. This was already in my design, but we ran out of time today and I have not hammered out all of, or even the exact details to construct it yet. I want the latching mechanism easy to operate with gloved hands, yet safe and reliable enough not to fail when the unit has a hot charge in it.

I already have some refractory pucks cast to boost the large crucible up for easy tong access and to allow the flame room to circulate around the larger crucible. I also have designed the lid with enough extra space to allow the taller crucibles to stick up into the lid area for access as you have mentioned. This is why the lid refractory is not in place yet. I waited to get the refractory placement right with the actual boosted crucible height. This also leaves me room to play with adding a spouted crucible and have the crucible top supported but the pressure from the closed lid to keep it from tipping out when pouring. Even when the large crucible is fully recessed it allows for plenty of flames to spin around it since the inner walls of the furnace are parallel to the walls of the furnace and the crucible tapers.

One other use I have for the tilt is to turn it 90 degrees, lock it in that position and do small scorifications and cupellations with it like an oven.

Do you have any details on the 'push up' device you mentioned? Is it a pivoting lever that elevates the crucible out of the furnace? How does the refractory seal properly around the mechanism and how do the mechanisms stay protected from the heat of the furnace?

I'll post videos of the furnace in operation once it's fully constructed.

Steve

 

[Harold_V]

My tilting furnace is not as large as yours Harold, but I don't see myself ever needing one that big. If I do, now I feel confident enough to tackle the job.

Steve

You're making the right decision, Steve. (Nice, by the way!)

My first melting furnace accommodated only a #1 crucible. Like you, I couldn't see the need for anything large. With time and progress, I came to understand how wrong I was, but building the first furnace was an exceptional learning experience. From it, I knew what to do, and what not to do, for future builds. Without that experience, the tilting furnace I built most likely wouldn't have worked well. Yours, too, is likely to be a good learning experience, better preparing you for a future design. It's all good, Steve.

As far as volume is concerned, there will always be a time when something larger would be to advantage. However, as crucibles get larger, you must use proper handling tools, to avoid the risk of breakage. They are not inexpensive. For that reason, you will likely settle on a size that will suit your needs. If silver is in your future, it may demand something in the #6 or #8 size. Only you can tell. I got by adequately with a #8.

The most valuable lesson I have learned in my many years is to take it slow. I have never enjoyed exceptional success, but I have also never been at risk. Had my refining venture not turned out to be a business, it would have been a complete success anyway. After all, it was intended to be a hobby only---nothing more. By allowing it to grow as required, I was assured of success. I acquired equipment only when it was a necessity. As they say, a bird in the hand---

Harold

 

[4metals]

Most push up furnaces I have seen use a hydraulic cylinder beneath the unit. The top of the cylinder is actually the crucible rest puck made of refractory and it is as tall as the length of the push up so no mechanical seals of the piston are exposed to the heat zone.

Inductotherm uses a removable (threaded) head for the piston and a catch tray fits over the extended shaft before the head is screwed on. This functions as a spill tray and protects the piston. For larger units these pistons fit into a hole in the floor because they are long. There are push up furnaces made for most crucible sizes up to #20.

As I said the main benefit of a push up is the quick interchangeability of the crucible.

Operating the furnace while tilted 90 degrees for scorification in an interesting idea.

 

[HAuCl4]

Better tilt it a little less than 90 degrees, or the crucible will empty!. :lol:

 

[lazersteve]

Better tilt it a little less than 90 degrees, or the crucible will empty!. :lol:

When operating at 90 degree tilt as a muffle furnace the crucible would not be used. The cupels or dishes would be placed on a bed of bone ash instead inside the furnace.

I had even considered using a refractory insert to make the 'floor' of the 90 degree tilted furnace flat when operating in this position. This would provide me with a flat work surface and would serve to protect the lining of the furnace at the same time.

Steve

 

[Barren Realms 007]

I have a small question, on your burner it looks like it goes straight into the side of the unit and will blow the flame directly at the crucible. Most of the desighns I have seen show the burner going in at and angle so that the flame creates more of a swirling motion. Any personal reason you decided to do this?

And I like the idea of a shelf in the post above.

 

[lazersteve]

I have a small question, on your burner it looks like it goes straight into the side of the unit and will blow the flame directly at the crucible. Most of the desighns I have seen show the burner going in at and angle so that the flame creates more of a swirling motion. Any personal reason you decided to do this?

And I like the idea of a shelf in the post above.

You may notice the inlet hole for the burner is not yet cut so the burner entry angle is not determined yet. The mounting bracket for the burner will be fine tuned with a few hammer taps to position the flame exactly where I want it once the 1:12 flared nozzle arrives and I see all the parts aligned together.

The burner mounting bracket was fabricated so that it's angle would be tangential to the perimeter of the crucible base and offset from the center line of the furnace.

Steve

 

[Barren Realms 007]

I have a small question, on your burner it looks like it goes straight into the side of the unit and will blow the flame directly at the crucible. Most of the desighns I have seen show the burner going in at and angle so that the flame creates more of a swirling motion. Any personal reason you decided to do this?

And I like the idea of a shelf in the post above.

You may notice the inlet hole for the burner is not yet cut so the burner entry angel is not determined yet. The mounting bracket for the burner will be fine tuned with a few hammer taps to position the flame exactly where I want it once the 1:12 flared nozzle arrives and I see all the parts aligned together.

The burner mounting bracket was fabricated so that it's angle would be tangential to the perimeter of the crucible base and offset from the center line of the furnace.

Steve

Makes good sense.

Fine tune with a hammer....

I am leaning towards a desighn like this and want to see how your turns out. I have from a 5 gal to a 100 gal contaiers available.

Can I ask where you ordered your crucible from or if you have more you can get. That looks like a nice convinent size to work with.

 

[lazersteve]

The crucible is a 'K' size type.

I can source them for you if you like.

Steve

 

[Barren Realms 007]

That would be excellent, when I get ready for one I will let you know.

What is the round about cost on one of that size?

Any reason you chose that over a graphite? Or is it just your preferance?

 

[lazersteve]

What is the round about cost on one of that size?

Depending on the material it's made of between $10 to $20 dollars ballpark.

Any reason you chose that over a graphite?

Graphite takes longer to heat and decays with use. I have some salamander type crucibles that I plan on trying in the furnace, but I don't know any of the pros and cons of them yet as I have not worked with them to date.


Steve

 

[HAuCl4]

Better tilt it a little less than 90 degrees, or the crucible will empty!. :lol:

When operating at 90 degree tilt as a muffle furnace the crucible would not be used. The cupels or dishes would be placed on a bed of bone ash instead inside the furnace.

I had even considered using a refractory insert to make the 'floor' of the 90 degree tilted furnace flat when operating in this position. This would provide me with a flat work surface and would serve to protect the lining of the furnace at the same time.

Steve

IMHO the "revolving circular flue" of this type of furnace is very violent. I doubt the flue swirling around the crucible will be the same with the furnace tilted or without crucible. Be prepared for a lot of "experiments". I never tried tilting a gas-fired furnace with the gas on!. Tilting electric furnaces with electricity on is easily done and relatively trouble free if the crucible is well supported, but here you can even cause the furnace to "smother" and then you'd quickly build up a pocket of unburned gas, a recipe for explosion as soon as oxygen contacts re-establishes. Be very cautious!.

 

[lazersteve]

I can see how the gas may form a pocket and lead to a burst of flames and hot gases. The propane regulator has an adjustable pressure flow control on it and the propane flow will have a cut off valve as well.

I will be sure to cut the gas flow when tipping the furnace for a pour.

When using the furnace as a muffle I'll be running the gas at a much lower pressure to keep the temperature in check so I'll have to experiment to see if reverse gas pressure build up inside the titled furnace is an issue. I've been toying with the idea of a removable refractory plug along the side of the furnace (the top when tilted) to allow any reverse pressure and off gasses to escape.

Thank you for the extra advice as all input is crucial to the successful and safe operation of this unit. I'm sure the design will go through several stages of evolution before it's safe and just how I want it to boot.

Steve

 

[HAuCl4]

Also an alternative to 4metals "push-up" is a "lift-off", where the furnace walls lift with a lever or crank and the crucible and rest are stationary. This design loses heat fast though when the furnace walls are lifted, and IMHO is good only for medium to small crucibles. (That can be lifted by 1-2 persons).

A design of this type is clearly described in this booklet:

http://www.amazon.com/Building-Gas-Fired-Crucible-Furnace/dp/1878087088/ref=pd_bxgy_b_img_b#_

 

[4metals]

I agree with Mr. Aurochloric acid, without a crucible to define the circular flame path the alternate use as a kiln may have problems. When the furnace is upright and the flame enters at an angle the flame swirls clockwise and hugs the wall without a crucible. But the flame is always spiraling upward towards the top of the furnace.

If the furnace is tilted 90 degrees, the flame will be forced to travel horizontally while hopefully continuing to spiral. Without a crucible in place to give the flame a defined path to follow the flame may have a mind of its own.

As far as forming gas pockets I think if the furnace is glowing red before you tip it, the gas will combust completely and not form pockets of gas.

Are you using just propane or propane and forced air?

 

[lazersteve]

The plan is just propane for now.

What about my idea for a custom cast muffle insert into the tilted furnace cavity that allows the gas to flow around it?

Steve

 

[HAuCl4]

Steve: Those gas-fired furnaces have to have an exhaust near the top. The gases heat the charge by convection and move from the bottom up. Any attempts to make the hot gases to flow downwards are doomed to create cross-currents and possibly a "smother" (Think plugged-out chimney), where the burnt-out gases kill the flame due to lack of oxygen. (Like a CO2 extinguisher). Then gas accumulates, heats up and when oxygen gets in (because you open the lid to look. :shock: )==> boom.

Here attached is a design for operating the furnace tilted 90 degrees, you simply put the inlets and outlets as removable inserts, then the gases encircle the crucible and exit on the top (several outlets on the top, inlets 1 is OK, 2 better).

You can use a large clay crucible as the muffle, filled with some refractory cast to make it have an horizontal surface inside.

When you want to operate the furnace upright, you simply, plug in the refractory inserts in the holes and use the holes of your original design.

I hope it helps.

 

[lazersteve]

That's exactly what I was thinking.

Steve