A complete casting how to

[Tjark]

I know it’s back some time that I contributed to this forum.
I am still busy with my model two stroke cylinder patterns.
To generate some pocket money to get on with the cylinder pattern I was asked if I would cast some old motorcycle carburetor body’s.
So I took this challenge with both hands and got in the workshop.
For all off us hobby casters I have made a complete how to.
I hope you can do anything with this process, and please when I am not clear to you do not hesitate to put your questions on the forum.
I hope that I can answer them.
Well first I started with the float bowl’s.

The first picture is the float bowl core mold
This core is made by the SS proces,

[Tjark]

The SS process is a fast core making process.
You need for this process some fine sand, Sodium Silicate and a Co2 cylinder.
To get a good core you can start with a mixer off sand and sodium silicate by weight off 100 : 6%
So you need for every 100 grams off sand 6 grams off sodium silicate.
Then you mixed this very well, I do this with a old kitchen hand mixer.
When you shake the bowl where in you mix the two components and you see no lose sand around it shut be fine.
Then you fill the core mold with this mixer and press it tight in the core mold.
Depending on the core depth and wide it could be that you have to make thin holes in the core to let the Co2 gas thru the sand.
The recipe I use for the core sand is some different then the standard mentioned formula u find on the internet.
My recipe for the mixer is as follow 100 grams off sand with 10 grams off SS.
I found that the sand type has a lot off influence to the amount of SS you have to use.
How finer the sand the more SS you have to use.
I use Dansand ( a sand type delivered by Bemix).

The time for gassing  I do this in two stages.
First I gas the top with a rubber bowl.
Then I unscrew the bowl en gas every hole I made in the core so long that the gas is blowing  out.
At first you will notice that all the gas is adsorbed in the core.
When the reaction is complete you will see the gas is flowing over the core.
This is the point that the core is ready.
P.S. You have to gas all the holes you have made this way.

   Tjark.

[ths]

Hi Tjark,

Is that a sink or drain plunger you are using to deliver the CO2? Looking forward to more.

Cheers, Hugh.

[Tjark]

Hugh, your spot on, it’s a sink plunger bowl, very sheep only € 2,00 over here.
Forgot to post the picture off the holes made in the core sand.
Here it is;

     Tjark.

[Tjark]

This is the result off a short time off work.
Now it’s time to make the sand molds.
 
 Tjark.

[Tjark]

Now I going to make the sand mold.
I use oil bounded sand, this gives the most detail to the casting.
First I put the bowl pattern in the sand box.
Because this is a very simple pattern I use only one box.
The core is will close the base off the sand mold so there is no need for a second box.
I have forgotten to take a picture from the base with the core in place but I think it will speak for it self.

[Tjark]

Made today some core’s for the carb body’s
This with the same method as the float bowls.

  Tjark.

[Tjark]

Started today with the sand mold for the carb body.
First pictures are the pattern’s off the body.
Then the first and second sand mold’s.
The last picture shows the core inserted.

     Tjark.

[stevehuckss396]

What do you coat your patterns with to keep the sand from sticking to them?

[Tjark]

Steve, I use baby powder and a very soft brush.
I also use it on the oil bounded sand to separate the two sand molds.
This works great.
You  can get special powder but for a hobby foundry its to expensive because I have to buy it in packages off at least 100Kg.
 
  Tjark.

[stevehuckss396]

I meant the paint. I have a few patterns and they were sprayed with enamel. The sand sticks to them and I was told the enamel paint and the oil in the sand dont like each other.

[Tjark]

Steve the pattern’s are coated with Polyurethane.
The carb body’s are quit some years old and have an old type off urethane coating.
The pattern for the float bowls are coated with a new type off urethane coating.
You can find some more information at http://www.scabro.com/
And at this page https://toolingandcomposites.sika.com/en/solutions_products/04/04a008/04a002sa02ssa01/04a002sa02ssa01100/04a002sa02ssa01101.html

This is the page with type’s  off coating :
https://toolingandcomposites.sika.com/en/solutions_products/04/04a008/04a002sa02ssa05/04a002sa02ssa05100/04a002sa02ssa05104.html

There are complete block in where you can mill your pattern and coatings for your pattern.
If you need more information let me know.

   Tjark.

[ths]

Looking forward to the pour. Hugh.

[Bezalel]

Nice Work Tjark
 
I think I'm going to enjoy this thread 
 

What do you coat your patterns with to keep the sand from sticking to them?

Steve, I would have to agree with Tjark,  talc powder works pretty well with most pattern coatings, to stop the sand sticking to them.
 
My prefered coating is a good quick drying sanding sealer that also has talc in it as a filler, seems to work quite well, even when I forget to talk the pattern before adding the facing sand.
 
Bez
 
edit: dumb spell ckecker.... can't know the difference between talcing and talking

[stevehuckss396]

My prefered coating is a good quick drying sanding sealer
 
Bez

So are you talking about a sandable automotive primer?