Core mix

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jscarmozza
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Joined: Mon Mar 03, 2014 5:09 pm

Core mix

Post by jscarmozza » Tue May 17, 2016 6:32 pm

I'm trying to make a core using CW Ammen's recipe (sharp sand, molding sand and wheat flour tempered with molasses water) but it won't release from the core box. The core box is well made but contains a lot of fine details, I varied the compaction and moisture content of the core mix and tried Pam as a release agent, but nothing worked. The recipe has good green strength and bakes hard but it will not release from the nooks and crannies in the box. I usually use Ammen's linseed oil recipe but decided not to use it this time because of its low green strength. I hope the picture of the core box uploaded, if anyone has any thoughts on this I'd like to hear them. Thanks.
John
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steamin10
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Re: Core mix

Post by steamin10 » Tue May 17, 2016 10:37 pm

As I know them, cores are to describe major voids in the casting, like a cylinder bore, and do not carry fine detail. Your part, if you want to catch all the bolts and levels, should be broken down to smaller blocks, that carry less detail, so they can be thrown onto a baking board with less flaws, since every detail has the potential for lifting and failure.

In methodology, I use siilicate, or oil based sands, that are thrown on a cookie sheet, to be baked off. The core is packed, and lightly but quickly tapped on the sheet, and it stays where I put it..

cores that are tough to strip, I usually use auto wax to slick the core box, and then use wheat flour, or cheep baby powder to dust the box from a double nylon or cotton sock. This aids the release. If your core sand is too sticky, it can cause headaches by sticking to everything, and the vacuum produced, can hold it like a jello mold, making it rip apart, instead of cleanly falling free.

This is where your experience comes in. Is it tomato, or potato? Get the toes out and you are ready.
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.

jscarmozza
Posts: 250
Joined: Mon Mar 03, 2014 5:09 pm

Re: Core mix

Post by jscarmozza » Wed May 18, 2016 6:50 pm

Big Dave, thanks for the tips. I tried them and got about 80 percent of the core, a lot better than I was getting. I also switched back to the linseed oil mix and I think that also helped. I baked the core and it turned out to be very firm, including the fine details. However, it was very porous since I didn't pack the mix into the box, I just left it about 1/4 inch high and pressed it down with a board; if I packed it tight none of the fine details released.

Somewhere along the line someone got this to work, the core box is for my GG1 wheels and I have 12 of them, I guess an experienced foundry can get this done. I was planning to do a brass pour in the near future and I needed a few more things to pour so I thought I'd give the wheels a try...maybe not. Thanks for replying, your tips are always helpful.
John

jscarmozza
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Re: Core mix

Post by jscarmozza » Thu May 19, 2016 10:37 am

I got it Big Dave!

I tried again this morning and each try was worse than the previous one, so back to the book I went. What I learned was your tips were on the mark, my mixes were way too wet and my core box was way too dirty with all the crap that I had been applying to the inside. So I cleaned the box with kerosene, dried it well, dusted it lightly with wheat flour, made a new core mix of 40 parts clean sharp sand and 1 part linseed oil, a sprinkle of water and a squirt of kerosene, it felt barely damp to the touch. I rammed it into the box, turned it over, gave it three sharp raps and out it came...nearly flawless. I'm baking it right now, I'll post a picture when it's done. Thanks again Dave you put me on the right track.
John

jscarmozza
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Re: Core mix

Post by jscarmozza » Thu May 19, 2016 11:45 am

Here is a photo of the core, it has a nice dense texture, no porosity and it picked up all of the details in the core box.
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Harold_V
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Re: Core mix

Post by Harold_V » Thu May 19, 2016 4:22 pm

Thanks to both of you. I've followed this with considerable interest, as foundry work is, and has always been, of interest to me.
Very nice core, by the way!

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.

jscarmozza
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Joined: Mon Mar 03, 2014 5:09 pm

Re: Core mix

Post by jscarmozza » Fri May 20, 2016 7:40 am

You're welcome Harold, and thanks to all the guys that take the time to answer questions, they're a good bunch. I made 5 good cores and 3 failures due to too much moisture, I plan to pour sometime next week, I'll post a picture of the results.
John

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steamin10
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Re: Core mix

Post by steamin10 » Fri May 20, 2016 2:43 pm

For my part, I have gone through the agony of fiddling all day, and not getting any usable castings for whatever reason. Only to come back and get it all right the next day with a minor tweak, or sand dryer than yesterday. ( It is a common failing in making cores to get the mix too wet). It tends to tighten the cores to where they will pass less gas, and you can get blows in the casting from lack of venting. On making one piece cylinder cores form two part mold cavity, a plastic soda straw rammed in and then pulled before you strip the core, makes a big gas channel right where it is needed most.

It is most rewarding to hear of solving the problem, and that is all you. I cannot do it for you, just try to outline a better trail. The effort, that gains the experience, is all you. Kudos for getting a difficult and complex core to make the grade. i am sure you have added to your learning curve.
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.

jscarmozza
Posts: 250
Joined: Mon Mar 03, 2014 5:09 pm

Re: Core mix

Post by jscarmozza » Thu May 26, 2016 1:50 pm

I cast the wheels yesterday, attached is a photo of one of them which is pretty much representative of the other three. The core worked fine, but the wheel pattern was a mounted gang form of four wheels and gates on one side, with the runner mounted on the other side. I estimated that the flask full of sand weighed over 200 pounds, too much for me to handle by myself, as a result I jostled it around quite a bit. All the rough handling cracked and loosened parts of the mold, so the very fine cores were placed in a very rough green sand mold. This was the first time I used a professionally made pattern, it was very well thought out and constructed, my only reservation was the size of the in gates, I believe they were sized for grey iron and I was using red brass; to make the metal more fluid I added a half spoon of phosphor copper shot to the melt. The pour went well and although the wheels aren't perfect, they're the best castings I've turned out so far. The detail on the wheels is pretty good, most of the little hex nuts turned out sharp and clean. All in all the the use of a core to get fine detail in a casting is a good alternative to green sand alone which would not likely hold the fine details during the pour. The problem with using a core is having the skill level to produce the core box, this core box and the pattern are about 50 years old, the man who made it was a true craftsman.
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