Infusing in split moulds

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#1

A question from Tom in the MTI hose thread, which I repeat here, to maximise exposure:

Also reposted the picture which brought up the question:

My answer (others: feel free to add to this)

There are a couple of solutions, and it depends on the mould size and possibilities which solution can be used:

-envelope bag the mould. This is by far the simplest solution. Hardly needs explaining.

-bolt the (polyester) moulds together with sealant tape between the flanges. The disadvantage is that size tolerance is a bit off, and a seam may develop. But it can be enough to succesfully infuse. I would definately like to do a leak test before doing any work in the mould, but actually this is seldomly done.

-a further development on this is a recess in the flange, which is roughly 2/3th of the thickness of the sealant tape used. This makes it possible to mate the mould halves exactly, so the seam is closed.

-the same can be done with inflatable silicone profiles (D-shaped) by for instance Composite Integration. These are in general used for RTM-light. The disadvantage is the ends of the seam: You will need to stick sealant tape to silicone, which can be tough.

-a step ahead is a double seam construction. (with sealant tape or silicone profiles). Between the 2 seals a very high vacuum is applied, which acts as a protection for the product vacuum. This is a very safe way.

With high precision moulds even round silicone profiles can be used in square recesses.

I have also seen bagging film around the outside of the flange, to create a double seamed flange.

Another system is to apply a gelcoat and skincoat into the mould, then infuse in the (airtight) skincoat. It is highly advisable to apply a high vacuum on the perimeter, to prevent the skincoat from lifting.

#2

Regarding this topic i wonder how you handle babymolds. For example i have large upper and lower wing molds and have depending on the part babymolds i lay into the main molds. Examples are the leading edge flange and the leading edge of the flaps or the rear spar. All of them are layed into the mold and share infusion surfaces with the main mold. If there is a gap between baby mold and main mold would everyting fail or would the epoxy flow always along the shortest route to the mti hose passing smoothless from the main mold and then up the surface of the babymolds that are like L’s layed into the main mold?

#3

It is a bit puzzling. Do you happen to have a picture?

#4

babymold1.jpg
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Attached find a sketch of both baby molds. I would use them in two separate infusions.
The main wingskin infusion would require infusing in one step the wing skin on the main mold and also the leading edge flange on the baby mold. The flange is necessary to be able to glue both wingskins upper and lower together.
Similar the process for the flap in a separate infusion.

#5

Interested to see some pictures and also some methods of achieving some of the ways to get a 2 piece mould as good as the original.

#6

You should treat the mould + baby mould as one, so the MTI hose should “float” above the babymould. The seam between the mould and babymould should be (somewhat) airtight. The easiest way would be to envelop-bag the whole assembly.

#7

Main mold and babymolds will be infused together in the same bag.
So fixing the MTI hose on the upper edge of the babymold should be no problem? The resin will not flow into the seam between main mold and babymold and exert same unexpexted forces?

I am currently sanding the plug. Hope that in one month i will laminate the plug with polydur.
I am still lost on the fixtures i will use to screw the babymolds on the main mold to hold them in position and how to screw both molds together.
If I use the tipical pins or screws glued into the polydur, wont the resin always flow into the female screws and make them useless?

#8

Thanks for all to share experience on this thread.:slight_smile:

I’ve already thinking about some of solutions you writed Herman, just what do you mean by inflatable silicone profile?

Some pics of the multi parts(miss the third parts) mold I’m gonna need to seals for infusion:

#9

On smaller molds I have placed a very thin bead of silicone on one face of the flange and then mated the two flat flange surfaces together and let it cure. Careful not to put too much on because it squeezes out and can be a mess to clean up. Also it’s beneficial not to use a material that shrinks as it cures.

#10

See article RD-20-0010 in this PDF

http://www.composite-integration.co.uk/perch/resources/sm-0003-h-illustrated-price-list-no-prices.pdf

#11

Not sure how i should use that proposed D-seal I cannot inflate it because it could interfere with the vacuum. Would the vacuum press the seal against the mold? How should i bonb the seal to the baby mold?

#12

Having no prior knowledge of the correct way to make my 3 piece mold I did not plan for a seal and when the time came to bag my part I decided to use clay since it would compress and squeeze out when I bolted the mold together. and I was also going to use it to help blend the inside surface between the seperate pieces.

I am debating on cutting off some of the flange to lay up a channel for the tape. I believe I have seen a wax insert that is made to be laid up with the mold to provide the perfect channel for the tape.

my part was laid up wet and then bagged so I am very excited to try the MTI as it just arrived yesterday and I think infusing will make my parts even better but not only that they will allow me to work alone and take my time. it is a rather large part and takes 2 to 3 people 3 to 5 hours to complete. hmm better quality and easier to make- for the price its a bargain!