RTV for no-bake core sand core boxes?

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myrickmachine
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RTV for no-bake core sand core boxes?

Post by myrickmachine » Sat Dec 19, 2009 5:39 am

Am working on a core box for an engine cylinder head. It is a one-off affair, so I am trying to do this the easiest way. Am going to use the actual head from another engine as the outer pattern (adding material for shrinkage) and am making up a core pattern for the passages. The foundry I go to uses no-bake core sand. Question is can I make the core box mold from RTV? I can house the RTV in a wood box to give it rigidity. If so, making the parting lines for the core box would be real easy with a sharp knife. Comments/suggestions?? Tried to search this on the internet and found zip.

RONALD
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Post by RONALD » Sat Dec 19, 2009 9:46 am

Most core boxes are made of wood, as most patterns are, but I suppose it could be done in almost any material, even Paper Mache .

If I were doing it, and the core was not too big, I would first try a cheaper material called Water Putty. WP should be available at most hardware stores. It's a powder that you mix with water and pour/push into place, depending how much water you added. I have used this for small wax injection patterns for many years, and as a kid, I poured type metal into molds made out of it for small HO parts.

I use the CO2-Sand process for cores and also some molds.

jpfalt
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The RTV box should work OK

Post by jpfalt » Sat Dec 19, 2009 4:36 pm

I'm assuming you are making a core plug that is the shape of the core. The hard part will be making sure the silicon rubber doesn't stick to the core plug and that you can get the silicon off. I would also have the silicon removable from the outer box so that it can be peeled from the core if there is a little bit of sticking to the nobake sand binder.

Good luck with the casting.

myrickmachine
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RTV for no-bake Core sand core boxes?

Post by myrickmachine » Sun Dec 20, 2009 5:39 am

No problems with the release. I have a release spray I use all the time with this RTV. The wood core is going to be the pattern for the core box. I think the best thing is to visit the foundry this week and ask them what they think. If this works, the neat thing is I can pour the RTV around the core pattern in several layers then split each one with a knife. I need to know how the release will perform with the core sand they use. I'll report back....

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steamin10
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Post by steamin10 » Sun Dec 20, 2009 9:02 am

This doesnt sound like a one off affair.

By all means contact the foundry. They have their quirks about how they like to work.

A core can be carved from a block of resinated sand or linseed based core, and just worn away by hand to the principle dimensions. These gems can be carried to the foundry and used as is, with one for a backup. Many times I have used a core and added or subtracted material to get more or less metal in a place to change something.
Big Dave, former Millwright, Electrician, Environmental conditioning, and back yard Fixxit guy. Now retired, persuing boats, trains, and broken relics.
We have enough youth, how about a fountain of Smart. My computer beat me at chess, but not kickboxing
It is not getting caught in the rain, its learning to dance in it. People saying good morning, should have to prove it.

myrickmachine
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RTV for no bake sand cores- what I am making in pix

Post by myrickmachine » Fri Jan 01, 2010 8:20 pm

Here's pix of the head I am making to fit this old,old engine.
http://picasaweb.google.com/myrickmachi ... ionalModel#

The plan is to use wood blocking for the acreage of the core box then pour RTV close in to the core pattern to minimize the amount I need. Spent lots of prep time with the head and still more to go

myrickmachine
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Re: RTV for no-bake core sand core boxes? how it turned out

Post by myrickmachine » Sun May 16, 2010 5:49 pm

Got the casting back from the foundry. Minor core shift but very useable....
Now to match drill the holes for the head. Plenty of meat for the valve pockets.
pix at: http://picasaweb.google.com/myrickmachi ... ionalModel#

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steamin10
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Re: RTV for no-bake core sand core boxes?

Post by steamin10 » Wed May 19, 2010 1:42 pm

I have a Witte engine with a froze out head. I was going to try a bronze casting, but that is technically beyond me because of the valve seat. So it becomes a much worked over aluminum slab heat, or an iron piece from the foundry.

Nice work by the way.
Big Dave, former Millwright, Electrician, Environmental conditioning, and back yard Fixxit guy. Now retired, persuing boats, trains, and broken relics.
We have enough youth, how about a fountain of Smart. My computer beat me at chess, but not kickboxing
It is not getting caught in the rain, its learning to dance in it. People saying good morning, should have to prove it.

myrickmachine
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Re: RTV for no-bake core sand core boxes? Head now done!

Post by myrickmachine » Sun Jul 04, 2010 7:35 pm

http://picasaweb.google.com/myrickmachi ... ionalModel#
Posted some more pix of the engine head nearly complete- still some bits for the gas mixer to do.

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Re: RTV for no-bake core sand core boxes?

Post by Harold_V » Sun Jul 04, 2010 10:31 pm

Thanks for the pleasant trip through your pictures. Very nice looking project. Certainly not an easy task.

Harold
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myrickmachine
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Re: RTV for no-bake core sand core boxes? Head finished

Post by myrickmachine » Mon Sep 06, 2010 11:24 am

Well, the cylinder head is finished with the valves, hot tube support and fuel mixer. Pix at http://picasaweb.google.com/myrickmachi ... ionalModel#
Very rewarding albeit tedious at times.... Some of the most difficult machining I have done to date- got to learn to cut internal threads. I lapped in the valves in their seats and they seal nicely.

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