Tilting Kettle Furnace Under Construction

[Barren Realms 007]

How thick did you pour your refractory?

The ones I have seen operate the main damage to the inside comes from where the flame attacks the refractory at the point of cntact with the flame.

A layer of tile similar to what is used on the space shuttle.

A replaceable piece of fire resistant sheetrock(not much of a good idea but it works as a barrier to an extent).

A ring of stainless at the bottom where most of the flame is.

Fluxes used seem to cause more damage than the heating itself.

 

[lazersteve]

Here are the specifications of the insulating refractory that I'm using:

Kast-O-lite 30 LI Insulating Castable Refractory:

This is a 3000 degree F (3000°F = 1649°C), High Alumina Insulating Castable Refractory for making forges. You can cast the entire refractory liner for a forge or just the floor using this material! This material has a very high resistance to flux, if you're doing a lot of forge welding and have a dedicated forge for forge welding in, this is a great material to use!

This material has a much better thermal conductivity rating than Mizzou castable...a castable forge doesn't have to be expensive to operate!

- 3000F degree temperature rating
- Highly flux resistant
- Low thermal conductivity = highly insulating compared to Mizzou
- Density = 90 lb/ft^3

- This material has a thermal conductivity of 4.54 BTU-in/hr-F-ft^2 at 2000 degrees F and conducts almost 40% less heat through the forge shell at 2000 degrees F!

The floor of my furnace is 2.5" thick and the walls are 1.5" thick.

As you can see from the specifications above the refractory has a low thermal conductivity and a high temperature rating, so the lining should not be degraded at the temperatures I'm operating it at 0 to 2012 F (0 to 1100C ).

I'm thinking that the steel shell is getting heated via two possible routes:

1. The nozzle inlet. The nozzle glows a dull red color during operation and is in close proximity to the steel shell (~1/8"). This may be causing heat to migrate around the lower section of the steel shell and could be resolved by repositioning the nozzle at the inlet.

2. The lid is getting heated almost directly from the flame that exists the top of the furnace. I feel that cutting the steel about 3/4" back around the top lip of the lid will reduce the amount of heat being conducted to the steel shell of the lid. This would also reduce the amount of heat that migrates down to the lower section of the bucket via the steel of the lid in contact with the steel from the lower shell.

The second problem could also be resolved with a refractory 'bung' inserted into the exit hole that reduces the exit hole diameter and elevates the flame exiting to above the steel of the lid. The bung would be shaped like and inverted top hat with a hole in the center and inserted into the exit hole where the flame escapes. This would provide a layer of insulation between the exiting flame and the outer steel skin of the lid.

Here's a quick sketch:

An outer layer of additional outer insulation may still be required even after the above modifications.

Steve

 

[Barren Realms 007]

Your refactory is too thin.

 

[Noxx]

I have to disagree, commercial refractories do not need to be very thick. Why are you suggesting thicker refractory walls ?

 

[Barren Realms 007]

I have to disagree, commercial refractories do not need to be very thick. Why are you suggesting thicker refractory walls ?

Why would you disagree with that NOXX?

Now I will be the first to admit that I have not been around a foundry of the same nature that most here have been around. Running the high temps that are being delt with.

But I have been around many similar items in my line of work.

I worked daily with 3 systems that were 1.5 mbtu burners set in a SS ring (wraped in rock wool with SS cover barrier) that blew the flame into of all things a fiberglass stack where water was sprayed in to evaporate the water, we replaced the stacks every 4-6 months, and the spry nozzels lasted 1-2 months. There was a lot of heat transfer thru this setup.

I maintained a 300' tunnel furnace where they took cotton and treated it with chemical to make it fire resistant for use in furnature, this system had a layer of rock wool to keep heat tranfer down.

Boilers, I don't even want to count!

Pool heater's, even these have a layer of rock wool for protection 1" to 1-1/2" thick if memory serves me right.

Fire resistant sheetrock 3/4" is desighned to last 1 hour at 2,000 F if memory serves me right. 2 laters for a 2 hour protection.

A firwall of brick is minimum 4" thick.

Have you ever seen a chimney stack built of brick? You see the outside brick, but did you know there is another inner chamber with 3 courses of acid resistant brick if I remember right. This is for protection from the acid not the heat. And the mortor joints are super thin.

If I am correct I don't think you will find a furnace running these temps with only an 1-1/2" wall. A brick layed on it's side is 2-1/4"" thick. And I think you will find that a furnace of this type built of brick is going to have a minimum of 3 courses of brick but I would say closer to 4 or 6 courses of brick layed.

These figures are probably a little off and there are others here in construction that can correct them for me. I have been out of this aspect of construction for some time so I don't have to keep the figures in my head. And besides I didn't have to keep up with this information because in my line of work it was not my job, it was the general contractors responsability to keep up with this info.

I was not trying to imply that Steves desighn was wrong. I don't think it is! I love the desighn of it.

His concern was the 220 F temp of the outer surface of his furnace. As stated in the post below.

This material has a thermal conductivity of 4.54 BTU-in/hr-F-ft^2 at 2000 degrees F

When you desighn for something like this you desighn for thermal conductivity. Common sense will tell you that if you have too much heat transfer your barrier is too thin.

I don't recall a furnace that I have seen constructed like this with less than 4" walls maybe 3". And all of them degrade with time and use. So your desighn should accomodate for this factor as well.

Check on this web site for info and desighns.
http://www.backyardmetalcasting.com/index.html

HAuCl4 wrote:
May I suggest adding a layer of heat insulation to that furnace?. Having something so hot exposed is an accident waiting to happen. Just my opinon, and a layer "sleeve" made of refractory wool would not be heavy or expensive. Maybe too many modifications are impractical, you be the judge.


I have actually already considered this and I'm on the fence as to whether or not insulating the exterior would cause the steel to retain more heat and begin to get red hot creating a possible failure condition. After that thought I also considered adding cooling fins to the exterior to provide extra cooling to the casing, but this would also sap heat away from the interior of the furnace. Like I said, I'm still working out the pros and cons ofeach hoping to find a happy medium.

I'm open to suggestions on both fronts and will incorporate any ideas that prove to be useful and practical, now and in the future.

The furnace project is an experiment that is still in process and is by no means completed. I've already considered replacing the bucket with a 10" version for a thicker interior refractory wall. I've also considered a heat reflective coating inside the bucket walls between the refractory lining and the steel.

Steve

The fastest and easiest fix for his problem would be to weld some small tabs on the bottom side sticking out, or a bottom support ring. Take a piece of 1" fire rated sheetrock, cut it to size, wet it so it will be flexible and put it on the side of the furnace and hold it in place with long SS pipe clamp's. I would assume this would cut his heat transfer down to 120-140F on the outside of his furnace.

But to be honest a 220F temp is not that bad IMHO, just operate the thing outside and watch your clothing.

This is an uneducated guess on my part:
The refractory will possibly last 18 months depending on how much he uses it and how it is stored.
The thinner the refractory the more prone it is to absorb moisture into the interrior of the refractory.
Thus each time it is cranked up there is a possability of damage from expanding moisture..Steam!
The thinner the refractory the more prone it is to crackes and hairline fractures.
The thinner it is makes it more likely for the refactory to crack apart and break up when these fractures appear.


EDIT: You want to think about heat transfer? I have seen on HVAC system's on a run of ductwork less than 15' in an attic change the temp of the air leaving the air handler and coming out of the vent by over 10 deg F.

 

[lazersteve]

When you desighn for something like this you desighn for thermal conductivity. Common sense will tell you that if you have too much heat transfer your barrier is too thin.

Not necessarily, I've already pointed out two sources of heat exchange where the energy can migrate around the insulating barrier. I've now begun the mods on the unit to circumnavigate these sources of heat migrating to the shell.

I have a feeling that once I control the exposure of the steel casing to direct heating from the nozzle and the lid's exposure to the exit flame that the casing temperature will decrease. I've ordered some paint on refractory surface coatings for the inner side of the refractory lining and the inner side of the steel casing and nozzle as well. I think the exterior of the unit will cool down considerably once these changes are all in place.

I'll post my updated design changes as they are completed and testing is run. I will take new temperature readings when I fire it up after the mods.

If anyone else has made a similar sized furnace please post the temperature readings of the exterior of the furnace after one hour of operation. If possible post the specifications of the refractory you used and it's dimensions.

Steve

 

[qst42know]

Is it possible there is still moisture trapped within your cast-able? It wouldn't take much to efficiently transfer heat.

Does your shell temperature improve with each firing?

 

[Barren Realms 007]

When you desighn for something like this you desighn for thermal conductivity. Common sense will tell you that if you have too much heat transfer your barrier is too thin.

No necessarily, I've already pointed out two sources of heat exchange where the energy can migrate around the insulating barrier. I've now begun the mods on the unit to circumnavigate these sources of heat migrating to the shell.

I have a feeling that once I control the exposure of the steel casing to direct heating from the nozzle and the lid's exposure to the exit flame that the casing temperature will decrease. I've ordered some paint on refractory surface coatings for the inner side of the refractory lining and the inner side of the steel casing and nozzle as well. I think the exterior of the unit will cool down considerably once these changes are all in place.

I'll post my updated design changes as they are completed and testing is run. I will take new temperature readings when I fire it up after the mods.

If anyone else has made a similar sized furnace please post the temperature readings of the exterior of the furnace after one hour of operation. If possible post the specifications of the refractory you used and it's dimensions.

Steve

On the top part it has been suggested to recess the steel at the opening 1-1/2"-2" to stop the heat transfer that you are having. But I like your desighn better and would keep it the way you have it.

On the nozzel do you still have it desighned to point straight in? And if so are you having a blow back at the opening? That was the reason for the suggestion on my part for the angled inlet to create a vortx effect of the flame rather than a streight in efffect that can cause blow back.

I am interested in knowing what kind of paint on refractory you have found and what thickes does it say will stop how much heat transfer?

 

[qst42know]

These come up often on the blacksmith sites.

http://www.budgetcastingsupply.com/ITC.php

 

[lazersteve]

Is it possible there is still moisture trapped within your cast-able? It wouldn't take much to efficiently transfer heat.

Does your shell temperature improve with each firing?

This is actually the first time the refractory was fired up to operating temperature, so yes that could also contribute to the problem witnessed.

Steve

 

[lazersteve]

These come up often on the blacksmith sites.

http://www.budgetcastingsupply.com/ITC.php

I purchased two of the ITC line a few days ago. The 100 for the inner surface of the refractory and the 213 for the nozzle and steel casing inner walls.

Steve

 

[lazersteve]

On the nozzel do you still have it desighned to point straight in? And if so are you having a blow back at the opening?

The nozzle has never been aligned straight in, it's always been aligned at a tangent since before the project was fabricated. The flame swirls around the inner wall of the furnace up and out as planned. There is zero blow back at the opening when operating.

I am interested in knowing what kind of paint on refractory you have found and what thickes does it say will stop how much heat transfer?

See post above and specifications for ITC-100 and ITC-213.

ITC-100 is a paint on, highly IR reflective, flux resistant, refractory coating for furnace linings.

ITC-213 is a paint on coating for furnace nozzles, parts, tools, and crucibles to extend the components life at high furnace temperatures.

Steve

 

[Barren Realms 007]

Cool, I'm looking forward to see how well it works.

 

[butcher]

Steve, in boilers we use a castable refactory (thick layer) (also the castables are usually a softer more easily damaged refactory) this refactory has air space (pockets) when dried, and then a wash coat refactory like sairset as a thin layer it bakes on to form a silica glass like coating, this coating is stronger and helps protect the softer castable refactory.
I believe the castable refactory with air pockets in its structure actually helps as an insulator, as it will not conduct as well as a solid like firebrick will conduct heat to the metal surface covering, I do not know if I explained this so you might even know what I am saying, I do not know what type of refactory you are using, the castables are usually covered with a mortor wash coat, it would be kind of like using the two types of firebrick furnace, the white easily cut brick will not absorb the heat well and the air pockets will keep conduction of the heat transfer to a minimum, while if you used the heavier clay type firebrick it would absorb and transfer the heat easier through conduction, hope this helps and is not just another of my rambling's on

 

[Noxx]

Steve, any ITC-100 remaining you wish to sell ?

On the other hand, Barren, I though you was saying that the refractory is too thin and risk cracking. Thermal conductivity of the refractory layer is not critical, as long as you have many layers of ceramic blanket or equivalent.

Commercial refractory might crack a littler over time, but there's nothing to worry about...

HAuCl4 and others, here is another similar type of burner:

The tip is a MIG welding tip, 0.035'' dia.

 

[Barren Realms 007]

I agree 100% with you NOXX. I was just stateing there is more of a possability of it with thinner refractory. But I think the coating he is going to put on it will stop this and he will be fine and have many years of service out of the furnace.

 

[lazersteve]

Steve, any ITC-100 remaining you wish to sell ?

I'll make sure you get some Noxx, send me a PM and we will work out the details.

Steve

 

[HAuCl4]

I'm eagerly awaiting to see if these reflecting paints, modifications, etc, would prove satisfactory. My intuition tells me the walls are too thin. This stuff can be properly calculated for a k and a thickness for a given drop of temperature between the inner and outer furnace. I'll try to find the formulas.

 

[lazersteve]

I'm eagerly awaiting to see if these reflecting paints, modifications, etc, would prove satisfactory. My intuition tells me the walls are too thin. This stuff can be properly calculated for a k and a thickness for a given drop of temperature between the inner and outer furnace. I'll try to find the formulas.

I did some looking, but I couldn't find any formulas except for houses. If you can post one that would be awesome.

I'd like to type in the operating furnace temperature, the desired shell temperature, and refractory type then have a resulting thickness provided from the formula.

The ITC-100 is reported to be very good at reflecting IR. A lot of folks are using it directly over koawool in miniature forges from my reading elsewhere.

I'll put it to the test once it arrives. If all else fails I'll work on a larger 10" diameter kettle and make the liner a two layer system instead of one.

I'm very happy to see people getting involved in this as two heads are always better than one. I'm still curious what other peoples casing temperatures are on coffee can furnaces and the like. Of course the refractory specifications on the furnace would also be great.

Steve

 

[lazersteve]

I did a little more looking and found these:

Thickness Calculations Example

and

Insulating Refractories

Now I need to do some math.

Steve