Green sand binder

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kelvin2164

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I'm having trouble with my moulds staying together.
I've made my sand according to guides on the web. Fine sand with about 10% bentonite. But the moulds are very delicate and fall apart easily. I can cast aluminium and brass in them but quality is not good.
I bought my bentonite on Ebay as a "beauty" treatment. Maybe it's not true bentonite?
Does a bit of oil help it stick together better?
 
No you probably just need more work. The amount of work to get sand truly ready is astounding. The more you yes it the better it gets. As I tell the kids, sand should be "fluffy". It doesn't really feel like sand. Lots of work. It's why everyone wants a muller
Dave
 
I bought a small cement mixer and keep my sand in it. I run the mixer about 20 min. befor using it. I also find that warm sand works much better than cold. Think about using clay when you were a kid, it needed to be warm and you needed to work it for a while befor it was usable. I use a sand with oil rather than water because it remains moist longer when not in use.

Mark T
 
+ 1 on the need for more work on the sand. Does it pass the squeeze test?
I've made sand by grinding up kitty litter that actually is too sticky!
I now use bentonite clay from a farm store.
I also use a home made Vontorne muller.

Chuck
 
I admit that I didn't spend much time mulling it. Just turned it over a few times by hand. I guess a cement mixer is something else to fill up the dwindling space in the shed.
Thanks for your help.
 
put your sand in a sealed container and set it out in the sun and let it sweat for a few days, then re mull...
 
OK, I still think the bonding is a bit weak, but I can do reasonable quality castings ok. But I now need to do a pump casting with a core. (I could probably do it without a core but I get terrible shrinkage problems). The sand is just too fragile for the core to hold together during handling. I've heard of plaster being added to help binding for this. Probably cook in the oven to get rid of all moisture. Any tips?
 
Traditional core often used sodium silicate as a core binder. this is sold at the local auto parts shop as radiator leak fix. Aka water glass. A tank filled with C O2 and a regulator will allow you to gas the core in the core box to cure it.
you can use a CO2 fire extinguisher with an added regulator for this purpose.
This method was demonstrated by Gary Martin of martin pattern and model.
For a one shot deal you could likey use a 12 gram co2 cartidge and a small dispenser sold for various uses. these small kits are sold in bike shops plumbing supplies and gun shops.
Tin
 
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Wow! Sounds complicated.
I was going to use pvc pipe to form the core. Ram in the sand, then extrude it out. It's only 30mm dia.
Will the water glass additive go off without the CO2?
Back in 'the old days" before all this internet knowledge was available, I used cement to strengthen the sand (not a lot, 15:1). Never worked very well. Gave off huge amounts of steam back up the sprue when casting aluminium (dangerous, but I didn't know any better). I suppose the cement sealed the pores to some extent and no where for the water to go. It did the job if the mold was left to dry for a few weeks.
Any other options?
 
I read somewhere that cornstarch added to the mix, and the core is baked before use....old school but it appeals to me..
 
I just tried a bit of corn starch in my sand. Added extra water to activate the starch, and cooked for an hour. Gave a very firm core that can still break up easily when needed. I will try it out when I'm ready to cast my cylinders.
The wetter mix with the starch in was very nice. A lot for stronger sand that doesn't fall apart as easily. I'm wondering how this would go as a regular addition to my sand. And would it be reusable or would the strarch not reactivate a second time.
 
Most green sands have some organic additive. Corn starch, wheat paste, fine sanding dust. They help with many things. Primarily they help with moderating the moisture content and give a more consistent green strength over a moisture range. They can help with "stickiness" but mainly thru moisture control. Just be careful not to add too much. Usually in the half percent range.
On a side note, I got my muller working yesterday and the increase in green strength with proper mulling is astounding!

Dave
 
I feel the main thing is left out and that is how much do you cast and just how much experience do you have? Casting has a learning time for how to and learning how to change the finished cast. Time is the only answer and the more you put into it, the more you will get out of it.

Happy New Years and make some chips.
Nelson Collar
 
Need to mull the sand
If you do not have Muller use your car and driveway
Driver over your sand and rake repeat 3 or 4 times.

Dave

I'm having trouble with my moulds staying together.
I've made my sand according to guides on the web. Fine sand with about 10% bentonite. But the moulds are very delicate and fall apart easily. I can cast aluminium and brass in them but quality is not good.
I bought my bentonite on Ebay as a "beauty" treatment. Maybe it's not true bentonite?
Does a bit of oil help it stick together better?
 
I did that too then I found out how good mulling was and built a Muller.
I think the best when found the soil I standing work ever better. We work on the ground and one some just keep digging and it work great.


I do not have a muller and my green sand work just fine. I do fluff it up from time to time, that and a little water.
Nelson
 

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