Author Topic: Surface fines  (Read 5117 times)

Offline Tjark

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Surface fines
« on: November 08, 2013, 07:47:05 PM »
Is there someone who knows how to get a good surface fines when using a sand core made with a mix off sand and SS?
I having only this problem  with one balanced core as on the picture.
Maybe someone knows if there is some kind off coating to get a smother finish.
The casting temp is good and I have no gas inclusions, see picture off the base site, turned with a diamond tip.

Offline ths

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Re: Surface fines
« Reply #1 on: November 09, 2013, 02:13:30 AM »
Are you using baked cores, or CO2 setting cores? When I was doing foundry at tech, I always got great results with the CO2 process. Core sand was generally finer than the regular casting sand, but not as fine as facing sand.

How well was the core sand mixed with the binder? It looks from the photo that a bit has broken off, perhaps washed away during the pour.

Cheers, Hugh.

PS: I don't know what SS is.

Offline tel

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Re: Surface fines
« Reply #2 on: November 09, 2013, 08:25:02 AM »
sodium silicate I suspect
The older I get, the better I was.
Lacerta es reptiles quisnam mos non exsisto accuso nusquam

Offline Tjark

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Re: Surface fines
« Reply #3 on: November 09, 2013, 09:25:29 AM »
Ths, as Tell said SS is sodium silicate, this is the Co2 process as you mentioned.

The casting is a old type Amal carburetor what is not for seal anymore.
The inner core for the carb bore and slide I am quite satisfied with.
It could be a little better but so far its oke.

The bottom off the carb (here will fit the needle yet and main yet) is very rough.
I have used the same method for the carb bore and slide as for the bottom core.
Yet the bottom core was not oke, after casting.
Maybe I did not compressed the sandmix for the bottom core enough.
Will give it a next try when the whether is clearing up.

Offline ths

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Re: Surface fines
« Reply #4 on: November 09, 2013, 10:24:02 AM »
Yes, sodium silicate. That's what we used. Good luck with the next pour.

Offline Tjark

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Re: Surface fines
« Reply #5 on: November 14, 2013, 08:04:17 PM »
On the metal casting forum (alloy Avenue) I have put the question how to get a nice clean surface finish and two people came with a solution.

The first solution,  rub the core with graphite powder.

The second, make a mix from bentonite, graphite powder and a bit of  maltodextrin and water.
The proportions for the mix are by weight; 8 parts bentonite
                                                              8 parts of graphite
                                                              1 part of maltodextrin
Add water to make a gravy like concstency.
Then paint it on quickly , so the core remains intact  and let it dry well before use.

The second option I will try in one off the next day’s.
Been busy now with making some new core’s.
I think I start painting the core’s around Friday or Saturday.
Then I have to see when the mix is dry and will make some castings to see the result.

    Tjark.

Offline Tjark

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Re: Surface fines
« Reply #6 on: November 29, 2013, 05:06:45 PM »
Because the weather is to bad over here to cast you can aways talk about it.
Had a talk about the core finish this week with a professional.
He has given me some off the past they use now days,
It is called alkoholschlichte.
So now I have two solutions for the problem to try.


  Tjark.

Offline Tjark

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Re: Surface fines
« Reply #7 on: December 28, 2013, 02:51:36 PM »
Have been making some new core’s.
Have also tried  to make the core’s more smooth.
The best way I found is the next formula;
The second, make a mix from bentonite, graphite powder and a bit of  maltodextrin and water.
The proportions for the mix are by weight; 8 parts bentonite
                                                              8 parts of graphite
                                                              1 part of maltodextrin

The Alkoholslichte was not working very well.
It was not fluid enough I think.
You can see the result in the picture.
The black one is with the above formula, the purple one is with the alcoholslichte.


  Tjark.




Offline jirvin_4505

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Re: Surface fines
« Reply #8 on: May 22, 2022, 10:47:21 AM »
Very late to party.  Just wondering was the problem solved?