I remember reading one or two other casting related essays by Tom Cobett, so far this is the only one could find.
now this perfectly jives with what I was taught and used in the Navy, alot of you describe SS and your cores totally different then what I remember , we bought SS from a foundry supplyer IFSCO to be exact, we added a very specific amount I believe 1.5 Cups to 100Lbs of sand , with 1% wood Flour (Which in our case was 1/2 the small scoop) , CO2ed the cores at 10 PSI, and threw them in the core oven at 250 overnight . and the Navy quotes Tom quite nicely " Only certain grades of Sodium silicate are suitable for making Co2 binders. Silicates having silica to soda ratios of 1.9 to 1 are satisfactory. common waterglass is not suitable as a binder because it has a silica to soda ratio of 3.25 to 1 high ratio silicates are not viscious or alkaline enough to react with Co2 and set(gel) during the gassing period" the Navy recommends sugar syrup for weakening cores, we never had it, probably because it would have attracted bugs, so we used wood flour one of those foundry mysteries all over our shop there wher written recipes, that included measurements like one large scoop, or 1/2 a small scoop that is some of that foundry mystery , someone did a bunch of weights and math, and wrote down the results, so no one would mess up the math... a few years down the road, we had people that had no idea how much of anything to use because all they knew was scoops, and did not know how much a scoop was or how much the material weighed. the weirdest measure ment we had was the "glug- glug" you know when you pour out of a bucket with a pouring top, liquad comes out in surges from breaking the vaccum, that is a Glug-Glug. we used one glug glug to 100 Lbs of sand to make petrobond for remulling it was one Glug glug to 300 lbs (size of the muller) V/r HT1
This part of it is incorrect, I've successful used common N-grade waterglass (3.22 ratio) with CO2 to make cores, it may be that other types of sodium silicate work better but the N-grade does work, here's a small demonstration.
Rocco, nice demo using N-type. For those who have not yet used sodium silicate, it is good to note how briefly Rocco gases the mix. Too much and the result is a weak core. Seems odd, but true. Simple table sugar is a pretty standardized product world-wide. I use it for a weakening agent and formally tested it at various percentages in the following linked thread. The amount of SS used, sand type and grade is clearly spelled out and may serve as a starting point for someone getting into SS cores. I use SS cores often and find them to be quick and convenient. http://forums.thehomefoundry.org/in...mal-baking-temperature-and-sugar-content.794/ Denis
One minor note about the N-grade SS, the mix in that demo was 5% by weight but I found my cores were a little too fragile, 6% seemed to be the sweet spot for for me. That's quite a bit more than Cobett recommends in his article perhaps that was necessary for me because I was not using the optimal type of SS.
Note: the person you have listed is one of the people I "do foundry" with, and I'm working to get oil running there.
Dennis, You are a lucky guy. Cobett has a huge fund of knowledge about metal melting. When you see him, please let him know how much I appreciate the help he has given me and this forum. Denis
No, Not Cobett. (I wish!) Jarrod Eells. One of the others was apprenticed as a pattern-maker, and worked in a foundry.
