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Compression Molded Foam - Max mold depth?

PostPosted: April 17th, 2017, 11:46 am
by Cameron
Hi all,

I'm exploring the compression molded process for a zipper case that houses a large product that is 10" tall, and 8" x 14" wide and deep). For functional reasons, I'd like the bottom part of the case below the zipper to be no more than 3-4" tall, and the top portion to be 6-7" tall. I know there is an upper limit to the depth you can get from a compression mold with good results, but not sure exactly what that limit is. Any tips? Thanks in advance.

Re: Compression Molded Foam - Max mold depth?

PostPosted: April 17th, 2017, 1:15 pm
by iab
It has been awhile, so before listening to my .02, consult an expert.

The material used in the draw is generally limited to the width of your draft. For example, you have 6 inches of draw, your draft is 5 degrees, the width of material used in making the vertical wall is a little over a half inch. In other words, you need that half inch to stretch to 6 inches (insert joke here), thinning out the overall material thickness. What will drive everything is the thickness of your foam and what is your minimum wall thickness in the vertical wall. This assumes fixing the position of your material's outside edges. But if you don't, I thought you could get material folding in on itself.

I'm a bit more sketchy on this, but I thought you could use a heat assist with compression molding, alleviating the thinning of the material.

Big radii also help.

But like I said, I basing this on a project a did nearly 2 decades ago. Memories fade. I could be entirely full of shit.

Re: Compression Molded Foam - Max mold depth?

PostPosted: April 18th, 2017, 3:10 am
by ralphzoontjens
Hi,

Since the material liquifies during the process typically these proportions can be reached from what I have seen.
You can consider low-pressure injection molding since mold costs are similar.

A unique property of compression molding is that if you work with a preform, you can vary the amount of blowing agent in the preform and together with a temperature gradient in the mold, you can create foams with different densities in different areas (functionally graded foams).

Re: Compression Molded Foam - Max mold depth?

PostPosted: April 19th, 2017, 10:56 am
by Cameron
Thanks for the tips guys. I've done a little more research on my own as well. One person I know has done 12" deep before. As usual, it seems finding the right vendor and/or being able to guide them to something you know is feasible is key.

Re: Compression Molded Foam - Max mold depth?

PostPosted: April 19th, 2017, 7:36 pm
by Kershaw
Whats the wall thickness? Foam laminated?

If you are laminating the sheet foam before press (I would assume its EVA or PE foam) than make sure you use a 4 way stretch knit, not a woven. Wovens and nonwovens (PUs) typically have a lot less stretch when compressed (some nonwovens can have a knit substrate or backer allowing more stretch). THis will cause your part to have less definition and easier delamination.

Keep in mind the part will be warm once its pressed - depending on the overall size and wall thickenss it may need to go into a form to keep shape while it cools.

If you are laminating sheet foam you can do a "cold" compression (laminated foam is still headed before being pressed) - typically less definition
If you are using raw foam in a substrate/pellet form you can do a "hot" compression ("injected") - typcially more definition