Powderizing Perlite for Refractory
(& Bentonite Clay)
One Saturday (which started this whole metal casting endeavor) I was working on modifying my Delta 14" bandsaw to incorporate a quick release for the band tension. In order to do this I need to fabricate a piece to fit in between the ribs of the upper support casting. At first I was going to machine it on my milling machine but after making a triangular pattern out of wood that tapered and was filleted to match the casting I realized that would be too labor intensive and inaccurate.
So, a casting came to mind, but where to get one made? I've heard of people taking a class at the local technical vocational college just to make something they needed, but that would not be timely. So, I Google'd on the off chance that people actually do this sort of thing at home. Wow. To my surprise, a lot of people do this at home!
So I read through a lot of the information posted on the web and am in the process of (preparing to) build a furnace. Getting the material to make the refractory is my first obstacle. I only say obstacle because I don't (or didn't at first) know where to get fire clay (ground fine enough), Perlite, and silica sand.
Well, Ace Hardware had Schultz's Perlite and Home Depot had Scott's Perlite so I bought a bag of each, and a sifter from Ace, my idea being to sift so I'd get the finest particles. Well, it didn't take but a couple minutes to realize not only did I not have the patience for sifting, The Perlite was in such large chunks I'd be lucky to get a cup out of the 8 quart bag. There's got to be a faster way and there's got to be a way to grind it up so I have no waste (i.e. can use it all).
The food processor? Although it might do the job, the hole down the center where the shaft sticks up means a lot of powder down through it. Messy. The Osterizer? Hmmmmm.... Mine has seen it day.... 20-30 years old. Been looking at new models for years. Hmmmm.... Good excuse to get a new one. Hmmmm..... Sold.
Down to the basement it goes (and luckily being single I didn't have to sneak it down). So, I fill it half way with Schultz's Perlite. Mix... Not bad... Frappe'. Even better! Wow. This is working. Talcum powder consistency in no time. Ok, fill it to the top. (The patience thing.) Tends to not mix up well. Ok, so while it's running firmly hold the container onto the base and tip it to about a 45 degree angle and rotate it 360 while doing so. Even tip it 90 degrees on it's side, that makes it work, but... In business though.
Results, starting half full in 15 to 30 seconds it flows real well, like a liquid without any tipping. In no time that 8 quart bag of Schultz's Perlite was powderized. On to the Scott's. Oh-oh, a no go. Half full, just like with the Schultz's but it wouldn't mix. Even coaxing it by tipping it. Up what's? ;) I feel the Scott's Perlite. Seems to have a high moisture content. Do I now enlist the oven also? Can't take that to the basement though, and don't want to wait that long (there's the patience thing again). Ok, the microwave.
Taking a 8x8 glass baking dish, and experimenting a little, 15 minutes on high seems to be the proper recipe. Now the Scott's powderized just like the Schultz's. Then I get to thinking about the fire clay and what I heard about kitty liter being Bentonite clay but too coarse to be of use in it's normal state. Hmmmmm..... Waiting while my next batch of Perlite is nukin'... Vader won't mind if I abscond with a little of his kitty liter, well, especially if he don't know.
Fill the blender up half way with kitty liter and in 30 seconds or less, powderized Bentonite clay. Although Vader's lucky I can't use his remaining kitty liter because of the deodorizing crystals, I think I solved the fire clay issue. Now to find some silica sand tomorrow.
Although powderizing the Perlite in the blender sounds like a time consuming process, it's really not that bad. What's time consuming at the moment is nukin' the Scott's Perlite and having to wait. I think the problem with the Scott's Perlite is the fact it is stored in Home Depot's outside garden area and it's been raining around here, and who knows, maybe it was stored in an area where it was hit directly by rain before I got it or that shelf I got it off of gets rained on too. The Schultz's Perlite from Ace was in the store.
I think I still might opt for the Scott's verses Schultz's even with the high moisture content because the Scott's was purer. The Schultz's had a lot of dirt mixed in with it (not an issue if your using it for it's intended purpose) and the resulting powder is slightly brown, and the Scott's was pretty close to 100% pure white. Also, the 8 quart bag of Scott's Perlite seemed to contain quite a bit more Perlite then the Schultz's but that could be due to it's coarseness, price was relatively the same. I know volume can be deceiving so next time I'll weigh them to see.
Although I doubt I'd want to use this method to make enough refractory for a 32 gallon garbage can sized furnace, The "2 Bucks" furnace at Backyard Metal Casting or the 6 gallon garbage can sized furnace I'm leaning towards building won't be too bad. And one can always pick up a cheap dedicated blender at Goodwill or on eBay. When all was said and done the two 8 quart bags of Perlite yielded about a gallon and a half in powder form.
I shot a 15 second video of the powderizing process showing how fast is actually goes. You can see it here: Perlite Powderizing. You can see it gets ground up so fine that puffs of Perlite are blowing out the top and there aren't any real gaps in the cover fit.
I also noticed the smell of the Perlite while nukin' it and it reminded me of a smell of something I used for my aquariums, when I had them, but I can't place it as to what it was.