Oscillator Cylinder Pattern

[vtsteam]

I pulled the cover off of the furnace. There's a mound of sand in front of it, frozen solid. Going to have to clear snow and level out a bigger area if I'm going to melt iron. This should be interesting.

[CI]

I was working on a project where we were trying to get some motors started that had 10 foot diameter rotors.
They hung a canvas tent over the entire motor, and used a heater under one edge.
Worked very well, and they got the windings dry enough to get the motor started.

I am sure you can figure out a way to do it.
We are rooting for you !
Be safe.
 

[vtsteam]

Thanks CI! 

I've got tarps, but unfortunately (or fortunately, perhaps) we have 3000+ F high speed blown exhaust to contend with, re. tenting. But the positive side of that is lot's of radiated heat around the furnace. I'm thinking a dry run in advance of pour day would both test out the burner and put a thaw on the imediate area. Probably dry the sand as well. I think I'll do that. Be good to know the furnace is running well. Wish I had some other purpose for the wasted firing, but plenty to do, and too many irons in the fire, so to speak, is not smart.

In other news, I found some very thin aluminum tubing just slightly oversize for the core. It is thin enough to get away with a single slit -- springs outwards easily. NOT easy to cut with a hacksaw -- kind of a wonky cut down the length, but I'll insert a file between the edges, and cleaning them up will bring it down to a close fit to the core prints, which would be ideal.

Unfortunately it's painted -- hope that doesn't smell when baked. Usually baked sand cores with molasses water and cornstarch (or flour) binders is welcome in the house. Guess we'll find out......

[vtsteam]

I taped off the flanges and added some Bondo fairings to the valve block.

[airmodel]

I have never used portland binded cores that small. So that answers my question, there is limit as to how small you can go.

[vtsteam]

Well, airmodel, I can't say for sure -- it just didn't work for me when I tried in the past, but everyone is different, and has different materials. The sand for one. I think small cores may yet be possible w/ Portland, depending on how much cement, and how coarse and uniform the sand, and whether they add a wire, and then again how long the core is. The longer and narrower the more fragile.

I have had good luck with 3/4" and smaller cores using the baked sand method. I think Portland becomes good from 1" on up, again depending on length. The disadvantage is the 3 day wait. But they probably can be stored indefinitely. Baked sand on the other hand if using kitchen type binders are subject to moisture absorption, just like cookies (biscuits). Although you can store them in a sealed container, and/or dry them again by reheating.

Anyway, because of the time crunch, I've started on baked sand cores today. I'm trying a new recipe, altered from the Gingery Lathe Book cores I once made, and we'll see how well it works out.

For that I used (apologies for the non-metric measurements, but that's what my kitchen utensils are) :

All measures (uncharacteristically) in volume:

5 fl. ounces dry medium grain silica sand
2 teaspoons corn starch
Mix well, set aside.

Combine 1 teaspoon molasses with 3 tablespoons warm water.
Add a little of the liquid to the sand mix at a time and stir, adding just until the sand clumps together.
Pack into core mold a little at a time, ramming lightly with a dowel.
Push a wire through if desired to vent.

I didn't leave the wire in place, since at 1-1/4" dia. and 5" overall, I hope the core will be strong enough without. But that might prove to be a mistake.

Bake at 350 until brown but not black, about an hour.
Cool and release.
Fingers crossed!

[vtsteam]

I checked the baking at an hour, and decided it needed a little more to brown thoroughly so gave it another ten. The I left it in the toaster oven to cool gradually.

Later, unmolding, I ran into trouble -- the core had stuck to the aluminum corebox. I eventually got it out with a struggle -- leaving some unevenness. That will mean a few more clean-up passes when boring the cylinder. Better to have a clean release, so next time, I might try wiping some vegetable oil on the inside of the tube before ramming. Plastic pipe with the Portland cement binder always releases, but baking kitchen ingredients in aluminum is another matter.

The core is very strong. I accidentally dropped the tube with core one time onto the concrete floor while struggling to unmold it. I fully expected it to emerge in pieces. But nope, it was intact. Now if it will act right in an iron pour, I'll keep this recipe.

[crueby]

Fascinating stuff - never knew there was so much to these processes!

[CI]

Perhaps you have address the question already, but what about using linseed oil ?
Isn't that what the old foundries used ?
I guess it could have a lot of odor.
.

[vtsteam]

Yes they did, but I've had good results without it, and yes it does have odor when baked, is harder to mix in (oil and water are both present). And it's toxic stuff -- not necessarily the linseed oil itself, but the drier compounds they put into so-called "boiled linseed oil". Raw linseed oil is a non-drying oil. Boiled is the drying version, and at one time was actually boiled to make it that way. But not anymore. They use drier compounds.

But anyway if just the two kitchen ingredients work (and smell like cookies baking) there is no, ahem, family objection, costs less, etc. I think it's the ideal, at least for me.

But lets see how this one performs. This is an experiment.

[vtsteam]

I finished the pattern tody. I had added trunnion bosses (removable), then hit the whole thing with two coats of sanding sealer, sanding between coats. Then rattle-canned it with an old can of Krylon red.

The trunnion on the valve face might not be a good idea to cast in place. After all, I'll probably put a runner there anyway, and also there might be a shrink depression around that boss. Well, the valve face is thick so there's a good machining allowance, but that's the area I would expect trouble from, if i do have some. Other than gas problems if the core doesn't work out.

Ah well we'll soon find out..... if weather holds and I get everything ready. Fingers crossed.....

I did some figuring: I think the cylinder casting will run to about 5-1/2 lbs. Sprue gates and riser maybe 2-1/4 lbs. Nine and a quarter pounds of iron would probably be comfortable, but I'm rounding up to ten anyway.
So an A6 crucible and 16 grams of ferrosilicon for the brake rotor metal I've tried in the past. Unfortunately, I have different rotors, this time. Also unfortunately, I have none broken up. Not my favorite chore, particularly in snow.

I got the greensand in the house to warm overnight. So we're looking good for tomorrow if the weather is as predicted.

[CI]

Looks nice !
.

[airmodel]

I checked the baking at an hour, and decided it needed a little more to brown thoroughly

I used an epoxy core years ago so in the cold weather I put the core on my wood heater. I forgot to check it so it was a dark brown. I thought I had to scrap it but used my finger nail to see if it was hard and I could not scratch it. I used it in the next days pour of iron and worked perfectly. Epoxy cores seem to take some abuse.

[Jasonb]

That sounds a very heavy cylinder, I would have expected a lot less for the bore size.

I just scaled up the CAD for that fabricated one I showed earlier and added 3mm machining allowance to faces and the bore and it came out at just over 1lbs. Even if I fill it solid it is still under 2lbs.

[vtsteam]

Jason, I just did a rough estimate. But maybe I was too generous. For a little better estimate, I'm just considering it roughly a cast iron tube averaging OD 2.5" ID 1.25" and length 3.5"

I make that out to be volume 12.9 cu/in, density 4.55 oz/cu in (apologies for the units), so 3lb 11 oz. Please correct if more foolishness involved on my brain's part. I could probably get away with 7 lbs melt to include all of the other mold cavities plus skimming and stupidity allowance. But again, it isn't a big deal to get too fine an estimate on it.

And a short pour is a cause for much strange language, involving self recrimination.