How can I prevent resin absorption in open-cell foam blocks?

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#1

Hey all, new here, I’ve gotta say this place rocks!

Just like the title says, I’m making some small speaker isolation pods, and will be using a male mold which has been constructed from a styrofoam hemi-sphere which I got from a craft store. Anyhow, the styrofoam is open-celled, and I don’t want any resin to be permeating it.

Now, I could just cover the mold with a plastic release film…but here’s the kicker. I’m going to be using vacuum bagging. Will the air pulled out of the open-cell styrofoam cause bubbles under the release film?

Thanks, and once again, this place is great!

#2

Well, where do I start: Welcome to our Composites forum!

First off, Polyester resin (PER) WILL MELT Polystyrene foam to nothing…I learned that the hard way one 2 am working on a “rush” project at my classroom…

Most of those speakers are done with a small wood ring glued to a base and Polyester fleece pulled over and glued or tacked down on the backside. They coat the fleece with PER, fiberglass & body filler (PER with thickeners).

Do you have any pictures to show us what you are trying to do as that would greatly help us to help you?

#3

Id say if your making a male mold…you could cover the sphere in elmers glue until it has a small surface of glue. Sand it down a bit and maybe paint with flat laytex?

Why not just use a rubber ball?

#4

Did someone ask for a Male Model? (Hand in the air…lol!)

Oh, male mold…opps…

We are making one in the classroom out of PUR foam that when finished, the part will look like a bath tub, but you cut an oval out of the floor of your closet, place & seal this tub down and fab a hinged new flooring for a hidden storage area for off season clothes, extra blankets, pillows or in my wife’s case…for more clothes period!

#5

I’ll be a bit more specific about the speaker application…

These are two 6" midrange drivers mounted in the backseat of the car, on the partition between the trunk and passenger area.

The problem is that whenever the subwoofer hits hard, the smaller cones of the 6" drivers are rattling. The purpose of these parts is to isolate the back of the speaker from the area in which the subwoofers move the most air, preventing the rattling problem.

I could go wooden ring approach…but instead, I’m going to use a half-sphere, put an inch or so of disc onto the flat side of that hemi-sphere, to give it a bit more depth, then make the part with a 1" flange for easy mounting.

And bingo on the polyester resin dissolving bit…I definitely want to avoid that problem!

#6

Why not find a ceramic bowl or tuperware piece to make the mold off?

Glue some carboard in a circle around the lip of it and BINGO you have your mini cabinet to protect the smaller driver.

Much easier than using a piece of foam. Plastic tupperware or what not can be had for next to nothing in a dollar stor.

Hell I made a tray mold from one of the disposable lunch box tupperware things. If it can stand a dishwasher, you wont hurt it.

#7

Plus it is made from PE and does not need any release agents too!