[WM] BlackEd's Warmaster Projects

[BlackEd]

A vacuum pump and a vacuum chamber:




The vacuum pump is a car tire inflator.  I put it inside an acrylic canister.  I added a tire valve so the pump can pump air out of the canister.  The second acrylic canister is the vacuum chamber.

I ran the pump for a few minutes -- it does suck air in.  This weekend I will test the pump with the vacuum chamber.

My RTV molds have had big air bubbles in them.  I'm hoping this device will suck the air right out of the RTV.  I also plan on using a bit less catalyst.  My guess is that I have been adding more than necessary, and that the RTV cures before any air bubbles can leave.

The only downside to this set up is that I do not have a vacuum pressure gauge, so I have no way to measure how well this set up works.

I also want to test this set up for getting air bubbles out of resin casting as well.

[Lex]

+1 for idea and execution !!

[azrael71]

Great work.
Always nice to see new sculpts:)

[Stormwind]

I am absolutely intrigued here.  I know very little about casting, great to see progress like this...

[BlackEd]

I tried out the vacuum pump and chamber this weekend.  The suction created in the vacuum chamber is enough to make it impossible to open the lid!  I snipped off one end of the hose to let the air back in. 

Realizing I needed a release valve, I drilled another hole in the vacuum chamber, and covered the new hole with a piece of tape.  Then, to amuse my 5 yr old son, I put a partially inflated ballon into the vacuum chamber.  It was fun to watch the ballon expand!

Then came the real test.   Would it suck the air out of the RTV?  I mixed up a batch of RTV, then placed it in the vacuum chamber and started the pump.  I didn't time how long I let the pump run (which at this point is the only measure I would have as to how much air was pumped out).   The results were not as dramtic as I saw on You Tube -- maybe because of the slower rate at which a vacuum was created, or even because I did not get anywhere close to a perfect vacuum.  However, I saw many bubbles appear and pop over several minutes.

Now I could watch the RTV bubble all day, but the pot life is 20 minutes.  After that, the RTV is too set-up to move.  So I poured the RTV.  It was noticeably thicker now, and I was getting concerned that I waited too long.  In the end, it seemed that there were only small air bubbles left in the RTV. 

I would have put the mold into the vacuum chamber but I put the frame on a tray that was too big for the chamber.  When I pour the second half, I will pour and then put the mold in the vacuum chamber.  This will allow the RTV to bubble all it wants while it cures.

Some notes:
I switched from using ounces to grams, as my digital scale can do either.  I made really sure that I have one-tenth weight of catalyst to weight of RTV.  The RTV seemed to cure just as fast as when I measured in ounces.  I may have to switch to another RTV, one with a longer pot life so that I can de-gas the RTV thoroughly.

I will post pictures tonight.

[BlackEd]

Here are some pictures of the balloon test that I did.  First, the partially inflate balloon.  Note that when the canister is unlatched, the lid is slightly open:



After running the pump for a minute or so:



I unlatched the cover of the chamber, but the vacuum held the lid down:



So there you have it friends.  One last picture:



I was very excited.  My son kept insisting that the release valve was so that we could let the vacuum out, and not, as I tried to explain, to let air in.

Here's a picture that proves he's my son:


Thanks!

[Stormwind]

Hee, you getting him to basecoat your Dreadfleet islands, there? =)

[BlackEd]

Stormwind:  Yeah, he's basecoating the Dreadfleet set for me.  It's what he wanted to do.  So I didn't argue!  I did teach him how to do drybrushing.  He isn't too bad at it.

The big news is that I finally had success in casting up copies of Capt Piett's pump wagons!  I've got 2 sprues of the goblin powered pump wagons and 3 sprues of the squig powered pump wagons!  I will post pictures tonight.

[BlackEd]

Here's a picture of the sprues I've cast for the pump wagons:



As you can see, all the parts of the model were cast!  As it turns out, I had to widen the channels that carried the resin.  I also widened the air vents.  As a result, itis much easier to get the resin into the mold.

I use a syringe to inject resin into the mold.  Previous to these attempts, there was resistance in getting the resin into the mold.  Some resin leaked out of the bottom of the mold.  Now the resin flows much more easily, and there is no resin leaking out of the bottom of the mold.

For this set of castings, I heated up my molds to 150 degrees F.  Prior to heating, I lightly coated the mold faces with silicone oil.  One the second (and third) castings, I used talcum powder.  I think all this helped reduce the amount of air bubbles in the cast parts.

I also found a new way to hold the two halves of the mold together.  I use two sets of wooden sticks (one stick on each side of the mold), with rubber bands providing the force to clamp the mold shut.  I use one set near the bottom of the mold, and the second set near the top.  This works very well, but I want to replace the rubber bands with screws and wingnuts to make it easier to use the clamps.

I found that I can cast the wagons with the tan resin, which is a bit stiffer when it is cured.

I suppose the next thing to do is to assemble one or two of these wagons to show you all the finished result.

Some notes for those of you who might want to try some resin casting.  Here are some things that do not work too well:  First, overheating the molds is bad.  Any trapped air bubbles will expand because of the heat.  Second, vacuuming resin can be problematic, and here's why:  The vacuum causes those trapped air bubbles to expand.  If the resin isn't completely liquid, the air bubbles will be trapped in their huge form.  Third (and last), if you have to bake the casting in the mold, make sure that you wait until the resin has cured.  Something about heat making the air bubbles expand.

The other thing I did for these casting was that I mixed 1/4 ounce of the A&B together to get 1/2 ounce of resin.  I think that smaller quantities than this make it hard to stay within the resin's tolerance of the ideal 1:1 ratio of the A to B.

[jchaos79]

Really interesting Black Ed. Congratulations for casting resin. Do you know the chemical name of the resin you are using?

and how rigid is the figure casted? can you bend it a little bit if the thickness is low? or it is totally rigid?

Great men! Thanks for sharing

[BlackEd]

I will have to find out the chemical name of the resins involved.

The tan resin is stiffer than the white resin.  The finished product is like a plastic miniature -- some very slight "give" or "bend" before you break or bend the piece permanently.

The white resin is more bendable -- it flexes more than the tan.  For some reason, I just like the look of the tan resin better than the white resin.  I have other casting in white resin, and the thinner parts (swords) bend more than I would like. 

[captPiett]

Nice - can't wait to see them assembled!

[Bel]

IIRC you can add some painting powder to the resin - just check the site of manufacturer.
To decrease the number of baubles - I usually put the mould with resin (vacuumated) in hermetically closed pot under the air pressure that I make with car-pump - 2,5-3 Bars is enough - for the whole time of curing.

[BlackEd]

Bel -- Do you mean that you vaccum the resin before you inject it into the mold?  How much time do you have before the resin starts to cure?  I've got 90 seconds with the tan resin and 180 seconds with the white resin, which isn't a lot of time.  I do want to try pressure casting -- I can re-use the car pump that I'm using for the vaccuum.  Thanks for your comments!  I was hoping I could get some advice from other people who have tried casting!

[Bel]

hmmm... I use a resin that stays liquid in 5-7 minutes before it starts to cure. Nevertheless the speed of work must be high. In general, you may miss the vaccuumisation stage - smooth-cast urethane plastic is low-viscosity and the most of air bubbles go out in the mixing process.

_____

But I have never get a casting absolutely free of bubbles (some little ones are always stay in)