injection aided mold release

[JV_Comp]

I have a two part mold for a 15 rowing skiff. It is split along the centerline. The ends of the mold are very narrow and deep because the boat has a plumb stem forward and a narrow skeg aft. I can easily release parts by splitting the mold.

I want to modify this plug for infusion, however, by adding wider flanges and bonding the two halves together so there is no air leakage along the centerline. This means I will be unable to split the mold to release parts.

While there is no negative draft to the hull, I have tried pulling a hull without splitting the mold and it is pretty tough to do. The part doesn't want to release along the ends and keel. I tried pushing narrow wedges down into the mold but they just get stuck down there and the part stays put.

I would like to try air or water injection but I am not sure about the correct technique. Does anybody have any tips on air or water injection?

[SamSam]

Originally Posted by JV_Comp

I have a two part mold for a 15 rowing skiff. It is split along the centerline. The ends of the mold are very narrow and deep because the boat has a plumb stem forward and a narrow skeg aft. I can easily release parts by splitting the mold.

I want to modify this plug for infusion, however, by adding wider flanges and bonding the two halves together so there is no air leakage along the centerline. This means I will be unable to split the mold to release parts.

While there is no negative draft to the hull, I have tried pulling a hull without splitting the mold and it is pretty tough to do. The part doesn't want to release along the ends and keel. I tried pushing narrow wedges down into the mold but they just get stuck down there and the part stays put.

I would like to try air or water injection but I am not sure about the correct technique. Does anybody have any tips on air or water injection?

All I've ever used was just a 1/4" hole or two on the bottom of the mold, covered with a small piece of masking tape before gelcoating, that you hold an air nozzle against and blow air in until the part pops loose. To do that for a vacuum operation I think you would have to maybe tap it or something and put a plug in from the outside to make it airtight and then tape it or fill it with clay, or both, on the inside to keep it from filling with resin and to make it reasonably smooth.
You have to have some positive draft to make life easier, 1 or 2 % at the very minimum, 4 to 5 % to be minimum normal. I have never done any infusion and very little wet bagging (and that on a flat surface) but I think I've read that vacummed parts versus hand layup parts can be harder to remove, even though from the same mold, so if you're having a hard time removing a hand layup part you would have a good chance of wrecking your mold if your prep was not right.
If you are intent on making a one piece mold, I would try and introduce some draft to the mold by basically bolting it together solid on the bottom, putting a spacer (1/4"- 1/2" ?) thickness on the top of the stem and transom, and filling in the space with something like Bondo and then bonding the halves together. I wouldn't think that would alter the shape of your hull enough to bother.
Ignoring all of the above, I think the easiest and best thing to do would be to seal the flanges on the centerline with something compatible to the process before it was bolted together. That way you can pull it apart to easily prepare the mold for use, to easily remove the part and to easily repair the mold if needed.
I lived in Wisconsin from '70 to '84 on the Mississippi, in various places from Nelson to LaCrosse. The Coulee Region, God's Country. Beer, cheese, sausage and Polka Masses. Go Packers!

[JV_Comp]

Sam, thanks for the info.

I'll bond an an injection port in the each end of the mold near the keel, plug it with clay, lay up another hull by hand, and see if air injection helps.

I have been using Meguiar's Velocity 85 Low Emission mold release and it works fine. There is no transfer to the part and no odor to speak of.

I do get a little leakage of resin into the centerline flange. This leaves a few paper thin pieces of cured resin hanging down from hull centerline at various spots along the keel. They are so thin that they break off very easily but I still have to sand down a little ridge of resin that runs along the centerline of the hull.

I did try sealing the flange with various products but I still got air leakage when I tried to pull a vacuum. I'll work on it some more.

[wet feet]

I have known tacky tape,as used for vacuum bags work as a means of sealing moulds.A strip of it along the edges of the flanges and around all fastenings has worked on a good number of jobs that I am familiar with.Sometimes even at autoclave temperatures and pressures.

[SamSam]

Originally Posted by JV_Comp

Sam, thanks for the info.

I'll bond an an injection port in the each end of the mold near the keel, plug it with clay, lay up another hull by hand, and see if air injection helps.

I have been using Meguiar's Velocity 85 Low Emission mold release and it works fine. There is no transfer to the part and no odor to speak of.

I do get a little leakage of resin into the centerline flange. This leaves a few paper thin pieces of cured resin hanging down from hull centerline at various spots along the keel. They are so thin that they break off very easily but I still have to sand down a little ridge of resin that runs along the centerline of the hull.

I did try sealing the flange with various products but I still got air leakage when I tried to pull a vacuum. I'll work on it some more.

There is a similiar thread in the Materials Forum, titled Vacuum infusion+splitmold.
One person mentions the flange being specialized for vacuum by using a blow-up type of sealer and another talks about using tacky tape, which is what I would try.
You might try adding more bolts to the flange until you have them every 3-4" to help seal the split.
If you have trouble going through the gelcoat when you sand down the ridge in the keel, let the gelcoat set up enough to not alligator, then hand brush another layer down the centerline. Of course then you have to let that set up enough before laminating. Sam

[fiberglass jack]

when i have to do infussion with molds with many splits one mould has 8 parts what i do is use rubberbacked washers or make them with some rubber this seals the bolt holes good,then for the flange i paint the edge with some brushinf gel this takes a couple of minutes and tou got a airtight mould with many seams,to release the mold simplly quick sand away the gel and you can split the mold

[buckknekkid]

what part of Canada are you in Jack?