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Semi-hollow, saline filled, Kraton part

Semi-hollow, saline filled, Kraton part

(OP)
I have a client that wants to manufacture a flexible plastic part with two hollow sections that will be filled with saline and sealed. Imagine an oblong oval shaped tube where the ends are solid and the long sections hollow. I know there are various ways to accomplish this via multi-piece assembly. However, this presents some sealing and reliability issues. I'd like to locate a means to mold the part as one piece that can be filled via injected saline and thermosealed afterward. The hollow section is .030-.040in thick, and the overall tube OD is about .25in.

I'm not an injection molding expert, but I've designed a handful of molded parts, and I can't wrap my brain around how to accomplish this. The closest I've come is maybe gas assist? Any thoughts? Thanks in advance.

RE: Semi-hollow, saline filled, Kraton part

Is it possible to have the saline fill the full oval instead of having solid ends? If so you could rotomold to get your hollow part and then inject the saline in while pulling out the air.

If you need to have the solid sections could you deal with a bow in the part? Then you could rotomold as before to get a uniform wall on your hollow part but in this case you would have much more material in the mold which would settle at the low ends after rotation was stopped (hence the bow) and create your solid sections.

Another option if you need a flat part is to rotomold normally to build up the wall and then increase rotation of the mold to keep the remaining material out at the ends until it is set.

Can you give us a little more detail about the use case?

RE: Semi-hollow, saline filled, Kraton part

If you were careful about how you inject the polymer (to prevent erosion), you might get a dissolvable core (soluble core, salt cake core) to work, then you'd just inject water to create the saline solution...

You could lay up the tube section on a collapsible mandrel (or extrude it), then glue in the end sections with a vulcanizing adhesive, possibly before fully curing the extrusion to promote good adhesion...

Or layup the part with strips of uncured rubber (like making industrial rubber hose) over an inflated latex mandrel or a rigid soluble core.

I like the rotomold idea, and using a thermoplastic resin means you are more likely to be able to heat-seal the product after saline fill, that will be more problematic with a thermoset cure rubber.

RE: Semi-hollow, saline filled, Kraton part

(OP)
Thanks for the input, guys. The design at the left/right ends isn't exactly as pictured, but there is some bending that will happen there. I'll check with my client, but I don't believe having saline throughout would be an issue in and of itself. However, not being solid might make the tube collapse on itself because during use there would be some bending at the ends. I don't know much about rotomolding, but I'll look into it. I was thinking gas assist, but that seems like something that would require a lot of fine tuning.

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