Glove Box for bubble free casting??

[Anvils Hammer]

sand???? I thought of that but instantly dismissed it as horrifying.. the small amount of air in the sand would surely explosively exit, lifting sand into the air and then into the pump?? but you guys have tried it and it works ok?

Ive accuratly measured my pot... it says 10L but is actually 12.5L air volume.

My current pump gets that down to-

100 mbar in 25 seconds
25 mbar in 45 seconds
<10 mbar in around 70 seconds

The gauge is not accurate enough to measure less than 10mbar, but when the needle stops moving I guess the pot is empty.. around 80 seconds probably.. but I know the pot leaks.. so the ultimate vacuum is affected by that.

The new pot is tested to 0.02 mbar before it gets shipped to me.. so no leaks here! Its volume is 16.7 L, but with the foam inserts, Im going to reduce that to around 10.5L, so actually smaller than the current pot, this means that the times listed above should be achieved on the new pot, which means the current vacuum pump will do the job for now. I could also potentially get and cut even more foam, to lower the volume even further. I only need about 6L to cast with most molds.

I resealed up the pot connections last night and did another test with my lego rig that pours in the vacuum. I waited till about 2.5 mins after I mixed and 2 mins after the vacuum pump started.. so definatly the lowest vacuum I can get.

The parts came out riddled with air bubbles.

My suspicion is that the resin was opened a week or so ago, and in that time has absorbed some moisture, which boils in the vacuum.. at least thats what Im hoping, its hard to tell when I cant see whats going on in the chamber.

Logically, If I pour in a vacuum, bubbles are impossible, but in my experiments so far Ive not been able to avoid them, it would be a tragic waste if I get the £££ chamber and still get air bubbles.. Im bricking it a bit at the moment.

Fingers crossed it works perfectly first time!

AH

[blind pig]

Sand works just fine.

I'd think foam would expand under vacuum if it wasn't sealed 100%?

[mangozac]

I've noticed that when recompressing if its done too fast the sand does have a tendency to jump up onto the mould, but I've never noticed any coming out. Your vacuum pump would have to be really fast to suck any sand up into it. Bottom line is that the sand works, but if you want to be nice and professional about it the resin covered foam would be pretty cool. You've probably want to either give it a really thick resin coating or add some fibreglass to it though.

I'm surprised that a week's worth of moisture can have that much effect. You might need to look at displacing the humid air with canned air designed for this kind of thing before replacing the caps on the big bottles of resin.

[blind pig]

When I do use sand, I have a 12mm plate of MDF cut out to the same diameter of the chamber and sitting on the sand. It allows me to be sure of a level surface and stops the sand from moving.

[Anvils Hammer]

Well the pot has arrived!

First impressions.. its awesome.. very well made and high quality.. which I would expect for somthing so expensive!! I will upload a photo later.

Firstly the vacuum performance. My old pot (12L) got to 100mbar in 25 seconds. The new chamber pulls down to that in 28 seconds, despite being 5L bigger!

It takes around 85 seconds to pull down to 30" of mercury (probably more like 29.9 but the dial is only an indicator). I plan on getting a digital vacuum gauge soon so I know down to the micron..

The blue foam is fine in a vacuum within being sealed.. I assume each air bubble is so small that the pressure created is unable to burst it.

I used foam with a density of 30kg per square meter. The volume of the pot is then about 10L.

This 10L volume pulls down to 100mbar is 17 seconds, and right to the bottom of the dial in less than a minute. Result!!

So the vacuum is perfect. Thats step one achieved.

Now for the experimentation. Obviously I boiled water at room temp.. but the resin.. the resin!!

First test- my previous "experiment mold"

The resin degasses a bit in the pot.. but when I pour it over the mold, it goes completely crazy with bubbles- full on boiling.. Know Idea why...
Atmosphere makes all the bubbles vanish.
When I demolded there were still some bubbles present.. similar to the previous experiments with the old pot, but the bubbles were smaller.

Second test- some random split molds.

Same again with the crazy bubbling as soon as I poured it over the molds.

Result- better, some air bubbles still, but none larger than 0.5mm.

I then put the resin and hardener separately in the chamber and vacuumed them for 10 minutes. the two separate parts continued to bubbled the whole time.. when I poured the third test the molds still bubbled like crazy.

I guess that the resins have components in them which evaporate under vacuum..

The small bubbles im finding in the parts are caused not by air, but by the vapours released by the resin. Atmospheric pressure crushed almost all of them out (as they are at almost zero pressure) but there is still enough vapour to form and trap the remaining tiny air bubbles

My Quality control means Im not happy to send out parts knowing they have bubbles, even really tiny ones that would fill with paint easily..

but I dont want to have to pressure the parts either, as that is a whole second process, which slows down the mold turn over drastically.. not a problem at the moment, but if I grow the company to where I want it to be, Ill be casting all day every day with no time to make new products!

Stay tuned for more results and photos...

[paulson games]

Resin gives off vapor and heat as it cures. The "Resin shrink" that occurs as it converts from liquid to solid is the material that is lost as vapors, it may only be less than 1% of the resin's solid volume, but converted into gas it's a lot of volume.

If you turn off your normal overhead light and use a flat spectrum light, florescent latern, black light or refracted laser you can use it to see fine particles and dust in the air and it'll make the vapors quite visable. Whoever knew that CSI techniques aren't just for solving murders?

One night I was in the middle of running off some casts when our power cut off, as I still had a couple pots worth of air in the compressor so I was using a florescent latern which flickers with a very faint strobe like effect which was placed on a shelf behind my work area I was amazed at how much dust was hanging in the air from using the talc for the molds but I was even more shocked when I saw the vapor coming off the resin I'd mixed, it looked like a fog effect generated from dry ice. (Besides the flicker I think the latern has a polarized element in it's covering as the light it emits seems very flat)

Normally it's nearly invisable, but if you get down low so the cup is at eye level you can actually see faint wisps of vapor even in normal lighting. It looks a bit like the waves in heated air. I've also noticed that after a day of casting I get a sort of resin frost on my hands sometimes from trace amounts of built up vapor.

Of course being the hard headed idiot I am I still don't bother with gloves or a mask even though I've seen the stuff actually floating in the air. Fans help vent the room out but under alternate lighting it looks like a crazy horizontal tornado and even with the mix of fresh air you are breathing in a lot of crud, probably why I feel cruddy after a whole day of casting.

More than likely the curing vapor is messing with your casts, baby powder will help even if you are achieving a good vacum it'd help guard against the internal gasses that released from the resin. It wicks the resin to the silicon and really helps.

[mangozac]

I've been giving this a bit of thought today and I can't say I've got any advice left. This is well beyond my expertise and experience! Have you spoken to the resin supplier or even the vacuum chamber manufacturer about it? The technique must work since we've seen it in use...

I certainly expect there to be components of the resin that will boil at complete vacuum like that, but would hope that the effect is minimised once the reaction starts taking place after the two parts have been mixed.

[Anvils Hammer]

Paulson, seriously you dont use a mask?? you are crazy and risking serious lung damage.. Im a bit haphazard with gloves but I always use a full respirator with replacable cartridged rated for organic vapours... cost me £30 but new lungs are totally out of my price range/current medical tech..

Im not sure how I get baby power in the molds.. Ill give it a go..

Thinking about it, Im also going to try banging the molds, like I used to when I was gravity casting.. this might knock the tiny bubbles off the mold walls.. worth a go..

The bubbles which are forming are mostly this size, some slightly larger.-



I want to send parts out which are 99% bubble free.. one small bubble in almost every part is just not on..

If I put them in a pressure pot after vacuum pouring, I can get perfect parts EVERY time.

my gut feeling is that the extra effort to put them in a pressure pot is LESS than the effort required to check the parts for bubbles and recast dud components.

If I vacuum and pressure, I can garantee there will be no bubbles without having to look.

Zac, yep the technique should work.. Im going to chat to the resin company.. the vacuum guys have supplied what I asked for.. a chamber which will hold a perfect vacuum.

I mix the components and vacuum.. and a few bubbles are given off.. but not that many.. as soon as I pour into the molds, the resin goes crazy and bubbles much much more.. literally looks like boiling.. then atmospheric pressure makes all the bubbles go away instantly..

Ill also try leaving the resin bubbling in the molds a little longer.. might help..

Got my son staying with me for the weekend so will resume experimentation on monday!

I have about a dozen molds to make urgently and two dozen more to do in the next week or two.. gonna be crazy busy but thats how I like it!

AH

[paulson games]

[Anvils Hammer]

A quick update but not photos..

Zac, I've spoken to a few companies about vacuum casting now, it looks like the difference is tempreature. All the Rapid prototyping machi9ens which get perfect vacuum poured parts are using specidally designed resins, which are poured at tempreatures of 70c or more, into pre heated molds, then left at that tempreature to cure for a few hours. So its wonder with my kit I cant match it!!

I linked to a vacuum casting resin in the other thread which Im going to get more info about, as 70C for the molds/curing oven is achievable at home..

Yesterday I "upgraded" my vacuum pot with a new clamp for the resin cup, made of lego to allow for quick release, Im pretty pleased with it.

The new pot holder is centralised, meaning I can pour resin on both left and right sides of the cup, allowing for two lines of molds and greatly increased capacity.

Im currently pouring about 90g of resin per plate, which is double what Ive previously managed and all helps speed up manufacture.

Ill try and get some photos of the vacuum pot in use.

AH

[unobarramodels]

Hello everyone
Very interesting post. Any news on these machines for mix and pour resin in vacuum? Some time ago I'm looking for informations to build a machine of this type.
Kind Regards,
Luis