Hey everyone,

I have been infusing parts using a two mould method to reproduce a curved piece with smooth surfaces on both sides. Unfortunately, during my infusion, once the epoxy reaches the vacuum line side and it starts spurting bubbles into the catch pot (see the middle-right circle), small bubbles started to climb back up the resin line, which is connected to the resin feed pot (see bottom circle). I can't seem to get it to stop. During my first infusion of this part it did not have any adverse effects, but it still concerns me that air is:

a) apparently not all the air is moving towards the flow of vacuum - ie. towards the vacuum pump
b) there shouldn't be bubbles in there regardless. The only bubbles I could think of are ones that get mixed in with the epoxy and do not have a chance to off-gas out of the mixture before they are sucked into the part. I realized that a degassing chamber would help fix this, so I am going to build one.



And yes I just realized that you can't read the print so ignore that part of the picture haha.

Anyways, if anyone else has experience this, or knows what it may be, that would be a big help. It is unfortunate that it is a closed mould, as I cannot see the details of where these bubbles are coming from. Any help would be greatly appreciated.

-Mike-

I am afraid that you haven't included enough information to try and sort out your problem.

What is in your stack in the mold exactly.

Explain your procedure in detail. Temperatures and HG vacuum level?

Time it takes to infuse.

Show a part that came out of your mold.

Your desciption is too vague.

Fred

Sorry, for not including the details.

The stack is 2 layers of 200gsm carbon fiber, followed by soric 2mm core, with another 2 layers of 200gsm of carbon on top. There is infusion mesh at both the vacuum side and the resin inlet side, and the soric is roughly 20mm longer on both the vacuum side and resin inlet side so that it touches the infusion mesh (in hopes of getting a good spread of resin and good flow characteristics). The entire composite is 820mm by 650mm.

Vacuum levels are 28inhg (the most I have ever been able to pull in the shop). And the time to infuse is about 45 minutes. I am going to de-mould today so I can provide pictures of it once it comes out. The first piece that came out is already cut into its appropriate shapes.

I was reading elsewhere that when the resin reaches the vacuum tube, it temporarily clogs it, thus slowing the flow of air bubbles out of the laminate, which makes it easier for the other bubbles still in the resin to "float" back up the resin line. I know its a tough explanation and theory, but my camera cannot get good detail of the bubbles that I am talking about. I guess I should wait to see the results before I get worried, but I just have a bad gut feeling about this one.

-Mike-

as far as procedure goes:

a) pull 28inHg on closed mould
b) prepare epoxy in resin pot
c) unclamp and allow resin to flow through laminate
d) top up resin pot as required
e) wait 45 minutes for epoxy to reach vacuum side
f) AS SOON as resin burbles up vacuum line, close resin feed line
g) keep vacuum on laminate until cured.

It has seemed to work well for me so far, but if there are some crucial steps I am missing, please let me know.

-Mike-

g) is not needed if you have a sealed vacuum bag. if you have to keep the pump running then you have a sealing problem.

Hi Mike

Make sure your mold is warm and the resin is warm. If you have a perfectly sealed vacuum on your mold.(do the vac drop test before you infuse)

If so, let the resin flow out of your part to your catch pot. Let most of what ever you have left in your resin feed pot flow through. I believe this gives you a better chance of flushing out more air bubbles.  Now clamp off your vacuum line close to your mold. Wait 15 seconds before you clamp off your resin feed line. I believe this will allow your laminate resin pressure to equalize getting rid of vacuum voids or what are called pin holes. As you wait that 15 seconds you will see more resin being drawn into the mold then clamp it off close to the mold. Shut your pump off and let it cure.

This has worked for me. If you try this let me know how you make out.

Fred

Thanks for the tips guys. I like the idea of warming everything up for better flow characteristics, plus the workshop I work in can get a bit chilly (17 degrees celsius at times).

I have attached some photos of the piece out of the mould after being post cured. The pinholes appeared as I had thought they would, but oddly enough, there are two "fronts" of bubbles on the underside on both the vacuum side and resin feed side. Any ideas as to why this happened? Or has anyone experienced this kind of problem before? I think this may have been linked somehow to the bubbles I saw rising back up the resin feed line.

-Mike-

That is exactly how every piece I have ever done looked as far as pin holes.

Try again using my advice for sealing your bag, heating the mold. After you have infused  close off the vacuum side first then wait 15 seconds or so and then close off the resin feed. (also make sure your resin is up to temperature. and infuse with full vac)

This worked for me.

Hope it works for you. let us know.

Hey guys, an update with a new piece I pulled yesterday.

The piece is small and has a very deep contour to the mould (good for practicing on). There is some bridging on the small tip of the teardrop but that is another lesson I am learning to cope with. I have a couple pinholes, but more-so whole bubbles in the final part (especially on the tip of the teardrop where it bridged). However it is MUCH better than the last piece I tried. I followed Fred's steps as close as I could. I warmed everything up, and allowed extra resin to flow into the part after closing off the vacuum line (which I think helped a lot). Here are some of the notes I have made from this sample:

1. There is no need for infusion mesh on the vacuum side of the laminate. I had originally thought it might help distribute the vacuum across the part better, or aid bringing resin to the vacuum line. I had also wondered why the resin seemed to froth and create more bubbles right by the vacuum line. I now realize that the infusion mesh is what is creating this frothing, as there are a large amount of bubbles that are only contained where the infusion mesh is. I realize that this doesn't really effect the final part (as the vacuum line is far enough away from the part that it shouldn't matter) but I had always wondered why it seemed to make more bubbles at the vacuum line and I believe this is why. I know in the video "how to make a car bonnet", Matt places infusion mesh along the vacuum side, but I am going to try my next infusion without this. Also, he uses peelply, while I do not.

2. Once the resin reaches the vacuum hose, the resin in the middle of the part still contains air entrapped in itself. I have researched and it is due to one of three things. One, there is a leak somewhere (I did the vacuum drop test and it was sealed up). Two, the resin is off-gassing (I have heard that epoxy resin's do not tend to do this as much as vinylester or polyester resins, and it is quite dry in my shop so I do not think it is caused by this). Three, there is air entrapped in the resin from mixing that has not come out of the resin before infusing (this is where I think my problem is). How important is it to de-gas the resin before infusing it? I have found that even if warm it and let it sit for 10 minutes, there are still some bubbles in the resin. Also, the working time on some of my epoxy is only 30 minutes if mixed in large enough quantities, so letting it sit for a long time really is not the best for some applications.

3. Of the few pinholes I have, they appear more frequently the closer towards the vacuum hose I look. This may have something to do with letting even more resin travel through the part as Fred had stated. The real problem with this, is that I will end up with too much excess resin in the catch pot, and could have a potential fire hazard as the large mass of curing epoxy could overheat and catch fire. Is there someway to perhaps re-infuse the resin once it reaches the vacuum hose? Almost like a cycled system until all of the air is taken out? This seems complex, and maybe not possible while keeping vacuum on everything, but just at thought.

I will be making the exact same part once I clean up the mould, but this time I am going to get rid of the infusion mesh on the vacuum side, and try de-gassing the resin to see if that makes a difference. If anyone has any advice, tips, or arguments to what I have said above, please feel free to comment. I hope that this thread can help not only myself, but others as well.





-Mike-

thanks for sharing that information!

Matthieu Libeert
Founder MAT2 Composites X Sports
website: www.mat2composites.com