Help in pattern separation from the sand

Paste wax will fill those layer lines.

 

Here's a readily available alternative, use a small open end wrench to tap up on them.

 

As was alluded to before, tilt your pattern a spray paint it with any glossy paint. Then use lots of parting compound. Baby powder. If you get clumps in the pattern you won't mind, it will be so much better than what you're getting. However you will find when you get baby powder on your hands you can't brush it off. Same with the pattern.

One point, the sand will eagerly grab even 1/5 mm printed layers. I paint mine with thin water based wood putty then sand it back to where I can see plastic. Wood putty dries fast and is super easy to sand. Then a spray paint layer gives you a slick finish.

You need a slick finish. The itty bitty corners of sharp sand pack into horizontal grooves will grab like velcro.

 

Yep - 1/5mm layers are what and FDM printer typically spits out, and that truly is grabby. That's what V1.0 of this pattern was like, haha.
I actually dropped the layer height further down to 1/50th mm which, maybe combined with a tiny bit of sanding or a spray lacquer should do well. And everything, EVERYTHING, is now generously radiused. It looks like a kids' sand castle mold, which.... under the circumstances.... is probably a good thing actually.

I am a little hesitant about spraying stuff onto SLA prints specifically because what you get right out of the printer is good enough that I'm a little worried a sloppy paintjob would be highly likely to make things worse. I might start out trying the lacquer on these earlier patterns to get a bit of an idea of how it works.

I will also consider baby powder proper, at least for these tougher jobs. I've heard talc isn't great for your lungs, so I've stuck with plain old chalk powder that I have bags of to begin with. Some commercial parting compounds use the stuff, so I figured it might do the job. And certainly it is proving to be a heluvalot better than nothing!

 

If what you got from the printer was good enough why did you start this thread?

Any dust is bad for your lungs. You should be wearing a respirator. Where did you hear talc is bad for your lungs? Baby powder is now corn starch. However if you have bags of chalk dust use it if it works. I guess you started out not using it but if it doesn't work you might try corn starch.

Sounds like your experience is a little better than mine so we're looking forward to some fine castings.

What draft are you using, by the way. For small parts like that 10 degrees is not too much.

Also, with that pattern and my green sand I would never vent it. Good green sand is very porous to air and seldom needs venting. What looks like poor venting is usually early solidification. Your green sand my not be porous, however. Here's a video that demonstrates an unvented cavity with aluminum.

 

For talc, something olfoundryman said in one of his videos I think.

As for starting this thread - it is obvious that the pattern pullout isn't working. However, there are many factors to this, of which pattern surface finish is one. I'm sure glossy paint is great for a lot of things and I might also try it here, just expressing some fears regarding dripping etc. in such a small part outweighing the added slickness.

I'll give corn starch a go if the newest redesign doesn't deliver the goods. Heck, I'll at some point try it in any case.

Might be that the fact that my first attempt adding vents was dramatically better than the one before has set me on the wrong path with that - maybe it was simply to do with the pour having been less incomplete than the other ones due to the web structure being less imperfect. (important to note here that with my 60ml crucible, and this part itself being about 35ml, the reliefs filling in very significantly eats away at my margins for sprue and feeder). I'll skip them on my next attempt and see if I miss them!

As for draft, I don't have the CAD design right in front of me so I can't be sure. My gut instinct is that it was perhaps 5 degrees. If I have to go for yet another reprint, I'll consider upping this further, owing to your suggestion!

 

I was out of baby powder and got corn starch at the drug store, it didn't work very good for parting.
The grocery store had the J&J talc. Back in business.

 

Umm, shouldn't that be the other way around?

 

Perhaps two parts Talc to one part graphite, then "rumble" in a ball mill for an hour?

(What I hope/plan to do here, anyway.)

 

Makes sense as talc is hydrophobic. Corn starc not so much. Graphite is also hydrophobic and I am beginning to be more confident is a more effective parting compound than talc. Brushing them onto the pattern AND sand seems to help fill mini-crevices and provide better parting. Still working on trying to be sure of the above.

Denis

 

After the talcum powder lawsuits all our baby powder is corn starch. I've never tried the grocery store variety. I wonder if it is coarser than baby powder. I can't tell it from talcum powder.

Mine is kept sealed to avoid absorbing moisture.

 

I had found talc as an "After Shower Powder" in a local Dollar store. It was real and about 2 bucks a pound. But the source dried up a year ago. I had heard potters use talc in glazes etc. So, I went to the local pottery place. Yup. They buy in 50 pound lots for less than a dollar a pound. I bought five pounds for 5 bucks. Don't be put off if it is not snow white. It can be white or commonly grey.

I had bought some parting from Teton on Amazon.
Teton-Part Foundry Parting Powder Dust, Non-Silica (5LB)
I do not know for sure what it was, but I did not like it and it was 10 times more expensive than talc.

Bottom line: get talc from a potter.

Denis

 

Alright. I read into it and determined that the pure swiss talc sold by my nearby supermarket was probably sufficiently asbestos-free for me to trust my respirator on.
And man what a difference it makes! The stuff is lubricious as anything, just beautiful. Pattern pull-out is now only the 2nd of my concerns.
The first is a parting line. I do not know what I am doing wrong, but I have not once in my life managed to separate the cope and the drag without on of the pieces grabbing a healthy amount of sand from the other. Picture attached of a middle-of-the-road separation. And trust me there is some talcum in there - you can see a bit on the bottom right corner where my two boxed do not mate perfectly. This seems to keep happening regardless of sand moisture (though wetter seems like it might be worse), nor have my new fancy alignment pins that suck much less resolved it. Is there something special to lifting technique or ramming that I could be missing here?

Thanks so much for all the help by the way. I've definitely worked through this faster thanks to you lot!

 

If that is after dusting, you're not using enough.
This is what mine look like.

 

What he said^^

Also, using a a soft brush to brush the talc on the sand and pattern surface seems to help. I use an inexpensive brush similar to this for brushing. The brushing seems to help fill the tiny crevices between sand granules.

Additionally, I often use agricultural graphite (Seed Slik) as a parting compound. Sometimes I sprinkle over the talced surface and give it a gentle brush too or I use it as the sole parting compound. I think it is even better than talc.

I agree that too wet sand is a contributing factor to incomplete separation.

Denis

 

It looks to me like you are not dusting the parting line. when you flip the drag to ram the cope be sure to give it all a liberal dusting.

Otherwise, if you have been dusting, your sand is too wet like Denis said.

 

As others said, talc is a good parting compound for green sand. I use the Johnson & Johnson talcum powder for many many years with out issues. My brush is a rug cut in stripes (the softest brush I could find/make up). I sprinkle some talk and then gently spread it over. You seem to have very wet sand and not so good strength.

 

Hmm.... I wonder if I could be low on clay content. Because that's the behaviour you'd expect with too little clay, no? Little binding strength, and therefore to get it to even close to acceptable levels one must push moisture up rather high.
I've not considered that at all given all this talk about natural sand being too high on clay, and therefore the way I went about processing my sand paid little attention to clay retention - I simply dried it up and sifted it down, separating all the hard clumps into another bucket. This clumpy mass is rather high on clay - I've successfully extracted a lot of fine particulate from it that sure seems to fire like it was clay when concentrated.
I'll run a little experiment mixing that powder with my sand in varying proportions, and see how the properties change.

 

Okay. Preliminary results are in. More clay definitely has the potential to help. Did a lot of blind testing with little 100 gram samples of sand mixed with 0g, 2.5g, 5g, 7.5g and finally 10g additional clay - each sample wetted with 15ml of water, and tested both immediately and after a couple hours of moisture evening out and evaporating a little. Distinct difference in green strength for the extra-clay samples.

 

One word of caution, be careful not to add too much clay, try small additions at a time or you could find you have perfect moulds that are not permiable and venting becomes an issue. (I know, it's half a dozen of one and 6 of the other with greensand, you fix one thing and the other gets in the way!)