Is is possible to use silicone as an insert to an aluminium frame?

[cottontail]

Hello,

This question might be completely daft, so forgive me in advance. :p

I have seven years experience making silicone molds (degassed/vacuumed) and resin casting (under pressure) using a 2-component rigid urethane casting compound that cures at room temperature.

I make silly little action figures.

I have been thinking about getting a bench top plastic injection machine (like the LNS Technologies one or similar).

Is is possible to use silicone as an insert to an aluminium frame, like epoxy is used in this example?
217

http://www.instructables.com/id/Home-Plastic-Injection-Molding-with-an-Epoxy-Mold/

I know that many silicons can withstand temperature, so would the chief issue be deformation? I.e. the worst you'd see is some extra flashing?

Or perhaps it wouldn't take long for the mold details to tear away given the heat exposure?

I would think to use maybe recycled polypropylene (flow temp of 90-150 °F) for casting.

The silicone I have the most experience using is ELASTOSIL® VARIO 40

https://www.wacker.com/cms/media/documents/markets_brands/plastics_download/Infosheet_Elastosil-Vario.pdf

The other silicones I have access to here in my home town are:
ELASTOSIL® VARIO 15
ELASTOSIL® M 4470
ELASTOSIL® C 1200 A
ELASTOSIL® M 4503
ELASTOSIL® M 4642
ELASTOSIL® M 4644
ELASTOSIL® M 4670

Any thoughts?

Thanks so much!

REgards
John

[JayDub]

Just a couple of points to ponder:

Polypropylene isn't cast, it's injection molded. Even a basic bench top unit will generate a few thousand psi, so deformation of a flexible silicone may be more significant than just a little extra flash. Also the 90 to 150 F you quote is a typical recommended mold temp, not melt temp. The polypropylene itself will be at around 400 F when it hits the silicone. And cooling time might be excessive with no cooling channels and poor heat transfer through the silicone.

[cottontail]

Just a couple of points to ponder:

Polypropylene isn't cast, it's injection molded. Even a basic bench top unit will generate a few thousand psi, so deformation of a flexible silicone may be more significant than just a little extra flash. Also the 90 to 150 F you quote is a typical recommended mold temp, not melt temp. The polypropylene itself will be at around 400 F when it hits the silicone. And cooling time might be excessive with no cooling channels and poor heat transfer through the silicone.

Thanks for the reply JayDub.

Yes, I mean, I would aim to injection mold the polypropylene.

Ok, noted with the melt temp.

I was just wondering if anyone had tried using a silicon insert. Maybe there is a reason no-one has tried it. :D

[techkits]

Hi,

I did a test with my LNS Model 150A benchtop machine with a rubber mold in an aluminum frame (see photo).

433

It is possible, but as others have noted, the injection pressure causes the mold to compress.
The frame helps lessen the compression, but this means that it is not feasible for making parts with specific dimensions.
It is less of a problem if you are molding something that does not need to be an exact size (like the animal in the photo)

I only tried 1 shot, so I do not know how long the mold will be able to withstand the heat from the injected plastic...

-DW