Mold Seal Design

[ClarkT]

I've got a three part mold to design, and the mold must be vacuum tight. I've no problem designing the O-ring seal down the centerline flange, but when I get to the intersection of the transom flange with the centerline flange I've got a problem.

One option is to glue the O-ring into a single part, with a union at the transom/flange intersection. Another is to have the centerline O-ring seal to the transom O-ring. Both seem like terrible ideas to me, and there must be an elegant solution to this.

Anyone have a suggestion for how to handle this in a tidy sort of way?

Rgds,

[marshmat]

elegant? there probably is, somewhere, somehow. When using multi-part vacuum-tight molds, I've always just used high-grade flash tape; looks horrible but it works.

[wet feet]

You may have no problem designing a groove for an O-ring,you may find it a challenge to manufacture the groove without voids occurring.You give no clues about the type of boat or the production rate so I will advance the following suggestion which works with modest numbers quite well.Just use tacky tape along the outer edge of the flanges and press a good dollop over the bolt heads to seal them.If you are not using blind threaded inserts in the adjacent flange,you may have to use a blob on the other end of the bolt as well.It may be a crude solution but it works.

[IHeartFRP]

We had to convert traditional hand lay-up molds to air-tight infusion molds and boy was it a challenge with the first one (well we didn't bother to convert it, we just threw the material in praying for the best and wasted two days sealing leaks). We did learn that a layer or two of sealant (tacky) tape on the inboard side of the flange bolts does a world of good. Make sure the mold flanges are nicely finished and the flange bolts shouldn't be spaced more than a foot apart. The more evenly spaced and frequent the clamping force, the better.

Also, we had a big problem with air being pulled through the mold itself into the part. Some of the molds were old and had hairline cracks in the tooling gel coat. Believe me when I say that air WILL find a way in... somehow. To remedy this problem we bought some high-build epoxy primer and coated the outside of the molds. It did a great job sealing them off and makes the molds look a lot nicer too!
Good luck.