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Monday, March 10, 2014

Venturi Forge Build Part IV - Lining

Continued from Part I here
                from Part II here
         and from Part III here

After a little bit of a hiatus, I finally found the time to finish this project (although I suppose it has technically been done for a few weeks now). I will preface this with the following: I am showing only the simplified version of what I did with the lining, because I went about it in a very backwards, roundabout way. Had I a little more foresight, I would have done it as I am writing about it.

First, a warning. Kaowool is a ceramic fibre insulation that SHOULD NOT BE BREATHED. When cutting, it is critical that you wear a dust mask at the least.

That being said, the majority of the insulation in the lining comes from the kaowool. I used two layers of 1" blanket for a total of- difficult math here- 2".

Measuring the width and guessing the length (circumference, didn't have a flexible tapemeasure) worked just about perfectly. For the second layer, I left out enough room for the firebrick that I will use as the floor. This is for two reasons. First, it is more wear resistant, and second, flux tends to annihilate kaowool.

Notice that the forge housing is a little longer than the length of the two firebricks placed end to end. That would have been easily avoidable had I thought of that before cutting the housing. It still would have been fixable, but that would have meant cutting half that length off both sides, which with only a pair of tin snips, I was not about to do.

Next came the door. This is where the problems began. I should have, and I realized this far too late, cut the door like a trapezoid with the taper narrowing the hole the farther it went in. That would have prevented many of the sealing issues later on, but the best solution would to just not have a door at all. At least, not for a welding forge.

This is an in progress shot of the door to show how I attached the kaowool to the metal. There are wires pierced through the pieces of insulation, then fitted in the cracks between the door and the flange I riveted to it. Although not the best solution, it was all I could come up with after some deliberation. I also considered using furnace cement, but I do not think that would have worked well as the curing process would likely have lifted it apart (and it does not bond well to the raw kaowool).

The first covering over the kaowool is satanite. The purpose of this is to seal the kaowool, better the insulation, and serve as a base for the subsequent treatments. Below are the directions from the distributor-

Mix the Satanite to a thick paste...just keep adding water slowly until you get a pasty consistency that you can paint on with a paintbrush....roughly the consistency of sour cream. Spray the ceramic fibre insulation down using water with a hand sprayer to wet it lightly. Next, apply the Satanite to the wool using a paintbrush, covering all exposed wool surfaces. To cure it, you want to dry it slowly. First, let the forge sit for a few hours minimum to air dry a little, then fire up the forge just briefly and shut it down. Do this several times, allowing it to cool down in between and increasing the on-time with each subsequent cycle. You'll see water vapour evaporating the first few times you do this. Finally, fire it up and bring it up to full temp to fully cure it. You will probably want to apply at least two coats of Satanite in this's a little time consuming (do it over a couple of day period) but makes for a more robust coating. a 1/4" layer is a good thickness to shoot for. If you are going to apply ITC-100 over top of the Satanite, be sure to fully cure the Satanite first.

Above is only the first coat of several.

Over the satanite I used ITC-100. This is an infared refractory which supposedly increases the thermal efficiency of the forge by a significant amount (upwards of 30%). Again, below is the recommended application-

How do I mix and apply ITC-100?
For ITC-100, the manufacturer recommends to mix it 2:1, so if you have a pint, mix it with a half pint of water. My experience, indicates that mixing it a little thinner is just as good if you are using Satanite as a basecoat first. Since you're using the Satanite as a protective coating, the ITC-100 doesn't need to serve this function. Mix it thin, and apply the coats evenly. Applying several thin coats is better than applying a single thick coat. You'll likely have some left over for future patching. Apply the ITC-100 over the Satanite only after the Satanite is fully cured. You can use ITC-100 alone without first applying Satanite, you will just need to use more of this material.
How much area will ITC-100 cover in a forge?
ITC-100 will cover 6 to 12 square feet per pint, or 3 to 6 square feet per half pint. If you apply a basecoat of Satanite to your forge first, you can get by with the larger number for square feet coverage. An additional benefit to doing this with Satanite first, is that Satanite is cheap and by building up a 1/4" layer of Satanite over you Inswool liner before applying the ITC-100 your forge will be more robust.

All the steps in this process require the coatings to be cured, by gently heating the forge over several hours (which quickly turns into days). This is after the ITC-100 has been fully cured.

Finally I mixed some bubbble alumina to serve as a flux resistor on the edges where lining meets firebrick and around the door opening. I did not think the stuff would actually have bubbles in it, but it does. They are the rigid sort of bubble almost like an empty eggshell.
Mix the Bubble alumina to a troweling consistency and trowel it in place onto dampened Inswool ceramic fibre blanket Let it dry for a few hours and then slowly fire up your forge to fully cure it. This is one of the most flux resistant coatings we have found.
I originally intended to use this on the firebrick too, but later decided against it due to the difficulty in making the surface flat, which is important (to me) while heat treating thin blades.

To keep the alumina from seeping over the edges of the firebrick, I folded some paper and made a barrier to keep it in place while it set.

And what it looked like after. As I said, it was very difficult to keep neat.

Finally, it was time to seal off the ends, the back one here. While planning the design, I intended to forge a rim around the edges of the doors, but abandoned that after cutting the sheets with the tin snips again. To keep the kaowool in place, I bent the material from the opening upward. That flange will slide inside a layer of the wool.

In the front (and back, later), I used the 1/8"x2" rectangular bar I intended to reinforce the burners, but did not need, to guide the flame out of the forge body so it would not creep up the flat surface. I bound it with rutland's furnace cement, but some sort of mechanical reinforcement is recommended (rivets, bolts, etc.)

After the two ends were screwed in place, which was a trial not having a drill to use, I filled finished the last of the insulation. With the scraps from the initial lining, I cut strips and fit them in place, finally sealing it using the same process as the main body. (This one is an in progress picture and is not actually that sloppy).

That's it! After doing a stress test, it easily reached 2200 degrees (F) at 10psi. I had to take out the thermocouple before melting it, but since I have done a little welding and it runs great. I did make a few buffers to reduce the chamber volume, but no pictures of those at the moment. For use with the door, however, they need to be removed.

Feel free to ask any questions in the comments.


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