Sealing demoulding points in mould

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#1

Hi all,

Ive got a couple of moulds which I need to put in some access point on the back to assist with demoulding. Just parts with some tight radius and angles that don’t lock the part in but do make it impossible to get anything between the part and the mould to break the surface tension.

I toyed with the idea of bonding in a fitting to inject water or air in, but I think the simplest way is to just drill a hole and then bond a nut to the back so I can use a bolt to push against the part. There’s a few sections on these moulds that get cut out of the final part, so I should be able to get away without any cosmetic defects.

My question though, is how do I seal these holes on the mould surface? I will be infusing these parts, so I need a 100% seal. The easiest way that I have thought of is to make a ring of bagging tape around the hole and then put a piece of bagging film over it. Is there an easier/better solution?

#2

short bolt with rubber washer or o-ring ? cover the bolt end in the mould surface with wax ?

#3

That’s an option, but it doesn’t seem hugely reliable to me. Fair bit to go wrong with that.

#4

I would use some type of caulk on the threads then just put bagging tape over the bolt itself. No need to bag the entire bolt head with a ring of tape. If you are envelope bagging things masking tape works on bolt heads and washers to protect from bag puncture.

But that’s probably what I would do. Caulk and bagging tape. Also you can buy plastic bolts as well to make your life easier encase you are worried with sticking.

#5

I’ve done this before. I set weld nuts on the pattern before spraying the tooling gelcoat. Built up the laminate to cover the nuts completely. I smoothed the back of the mold about 3-4 inches around the nut and polished it. I put a piece of 2" Airtech flash breaker tape on the mold surface over the nut to keep gelcoat and resin out of the threads and then a piece on the back of the mold for vacuum integrity.

When you’ve finished molding, pull the tape off the back of the mold and run the bolt in to push on the part.

More often than not I will just put a blow hole in the mold but, of course, you could blow air through the nut as well.