Pressure Casting Resin Questions

DMS General
#1

I’m working on a project with Smooth-On two-part urethane resin and silicone molds, reproducing dashboard vents for the silver car that spent the last week in the automotive square. Initial results tell me I won’t have much success with passive casting and venting of the molds. I think I’m going to have to do the castings under pressure to achieve acceptable results.

The urethane I’m using for this project is TASK-4, which is a slow-curing resin with a demold time of 16 hours at 75 degrees. I tried Smooth-Cast 327 (40 minute demold) previously, with even worse results.

What I want to know is, if anyone has any suggestions to achieve good results without getting huge surface bubbles in a portion of the mold which is impractical to try venting. Also, as far as pressure casting goes, what kinds of solutions are there at relatively low budgets?

Structurally, the trial pulls have pretty much been solid, except in areas where bubbles have removed structural features like pins. However, aesthetically, all of the castings have been trash due to heavy surface bubbling.

Any suggestions are appreciated.

-Kris

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#2

If you can do some kind of vibration on the mold as you’re pouring the material in you can help get rid of the bubbles.

#3

I’ll try hooking up my broken dremel to the mold box, for science. I don’t know if I’ll be able to get all the bubbles out with vibration alone, though. There are a lot of awkward areas in these vent molds where air can get trapped.

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#4

Hmmm… May require some additional paths for the material to flow through into the mold.

Or, rotation. :slight_smile:

#5

There is a vibration brass polisher on the shelves in the shop area I think. That might be better for vibrating your mold. it has a big opening in the top with a screw sticking up in the middle of it. You might be able to rig a board held on with the screw that you could attach your molds to.

Russell Ward

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#6

A potentially interesting article:

http://hapcoweb.com/wordpress/vacuum-vs-pressure-when-resin-casting/

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#7

I cast pen blanks but they are relatively small parts, 1" square x 6" long. My experience is pouring it very slowly to avoid bubbles. Then use a pin or toothpick to poke at bubbles as they surface. I use Harbor Freight pressure paint pot for pressurizing. You just have to make sure pressure both at the compressor and at the pot is set for 15 psi maximum.

Good luck. Would love to see the silicone mold and how you made it.

Manny

#8

@Raymond, the majority of the bubbling has been on the surface that will ultimately face outward on the finished part, across a wide section. Venting it completely is impractical. Rotation is probably a valid idea.

@Gimli, I’ll put that into consideration. It probably would be more suitable than taping a broken dremel to a mold.

@munawar, that sounds like a good idea. The molds are probably too complex to try and coax bubbles out with a toothpick, but they’re fairly small and should fit several into that pressure pot.

#9

Hello all, I am wanting to get into resin casting and so far have learned that there’s a decent bit of specialized equipment needed. Before dropping that kind of cash I figured this would be a good place to try it out. Does anyone know if the space has a vacuum chamber and pressure pot for member use? And is there anyone who wouldn’t mind answering some questions about the process? Thanks!

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#10

@Val_Curry is a very valuable resource here at Makerspace- plus he teaches several casting classes a month. He might know.

#11

New to the space, but have done some work with both products from Smooth-On and Brick in the Yard. Depending on your castings, there really isn’t much specialized equipment needed. Take your time and most castings won’t have issues with surface bubbles. As far as a vacuum chamber, one can be crafted for relatively little funds. Here is a simple chamber for $90. http://www.instructables.com/id/Simple-DIY-Vacuum-Chamber-and-Pump/ Would be happy to answer any other questions you have.

#12

Hi, and thank you! The more I’ve read it seems like just doing the degassing prior to casting and just pouring slowly is the key to a relatively bubble free pour. Thanks for confirming!

I’m planning on making sheets that are 1/4 thick that have swirls of 2 different color resins, with a layer of water clear added later to the top. Do you have any tips or experience with that?

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#13

Clear has been my hardest to work with for the bubbles. Degass prior will definitely help. Also, pour a small amount in first and roll it around to push out any surface air bubbles. From there, simply slow pour starting at the lowest point.

#14

Hi,
On the water clear resins it is definitely good to vacuum degas them first to get a good bubble free interior.

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#15

Another technique is to spray mold release on the surface. This breaks the surface tension helping to break up bubbles. Of course only do this on the last pour because the layers won’t fuse if you do it in between layers.

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#16

Just saw their site.
Great info and resources.

#17

Did you get this project worked out?

What was the size of the mold?

I am trying to acquire vacuum degassing and pressure casting equipment for the space.