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Pinholes in surface after resin infusion
2

Pinholes in surface after resin infusion

Pinholes in surface after resin infusion

(OP)
Please help me before i go insane... After every infusion i do (practcing on glass using carbon fibre and plain weave e glass) There are small gaps between every tow in the weave. I have tried everything i can think of to stop this. I am using carbon that is stored in bubble wrap, epoxy infusion resin, i acheive full vac and no loss of vacuum. As i do it on glass i can see where the problem lies.... During infusion it works perfectly, but as soon as i clamp the feed line small voids form in the weave. I also de gas the resin for 10 minutes first. Any help would be very much appreciated.

RE: Pinholes in surface after resin infusion

How do you define full vacuum? The only meaningful definition, in this case, is absolute pressure - not gauge pressure. Absolute pressure is measured relative to a perfect vacuum (zero is a perfect vacuum), and requires a special gauge like a U-tube manometer. Gauge pressure is measured relative to ambient atmospheric pressure (zero means no vacuum), and is what most gauges measure.

There are two reasons for your pin holes.
1. Residual air in fibers tows that were encapsulated by resin flowing through the weave openings. After resin plugs the vacuum port, no more air can be removed. Capillary action causes resin in the weave to wick into the tows, displacing the air into the weave openings. The solutions are use a better vacuum (so there is no residual air to trap), or to slow down the infusion so that the wicking of resin into the tows closely follows the flow front through the weave (so the resin can push the residual air out the vacuum port).
2. You may be boiling the resin by applying too much vacuum after you close the resin inlet. Resins will always have some volatiles (including the resin itself). After closing the resin inlet and the vacuum line is full of resin the vacuum should be reduced to 10 inHg. This provides 10 inHg of compaction pressure on the fibers while maintaining 20 inHg on the resin during cure.
 

RE: Pinholes in surface after resin infusion

(OP)
Thank you for helping compositepro. Your the first person to give me something to go on. I have tried infusing at 'full' vac then dropping to 15inHG, in this case the void content was dramatically reduced however the resin was so thin over the finished part that some fibre was visible outside the resin (i am not using any gel coat). So i did it again but reduced the vacuum after infusion to 20inHG, in this case i got almost perfect results. But again there was a very slight show of fabric but the resin skin seemed much thicker. On the third attempt i reduced to 25inHG... this is where it gets interesting, There was no 'print through' of fabric but the voids had returned in the tows. Also bubbles had formed on the top of the laminate and in the infusion mesh. It seems as if the resin is still emitting volatiles even though i had spent a long time de gassing. (i am only using around 70 grams of resin for my test pieces).

To go back to your suggestion. If i reduce to 10inHG would i see more 'fabric print through'?

Oddly the guys i bought my pump and gear from say i should always infuse at 'full' vac from beggining to end. I am also using their own resin which they say they use themselves.

I am seeing 'full' vac only using the supplied vacuum guage fitted to the catch pot. Also the pump goes quiet on full vac.

In all cases i reduced the vac before clamping the feed line.

I wonder what your thoughts might be on this?

Regards, Chris.

RE: Pinholes in surface after resin infusion

Crud,
stub in another vacuum gauge near your inlet port, so you can see what the vacuum on your layup/infusion really is away from the pump. However be aware that residual air from the gauge hose can enter your layup.
 As Composite Pro says slowing down the rate of resin transfer to get better wet out may help.
B.E.

RE: Pinholes in surface after resin infusion

(OP)
I dont know whether this would be the same thing but i tend to only have a small amount of infusion mesh (flow media) then just the laminate/ peel ply. As soon as the resin hits the laminate without the mesh it slows down(i am only making pieces around 6 inch's by 8 inch's).

I have also tried infusion mesh under both inlet and vacuum ends. But i think my parts are too small and thin for that.

Or would you still recommend controling the speed of the infusion using the clamp?

Thanks, Chris.  

RE: Pinholes in surface after resin infusion

Yes if you are using a vice grip type clamp where you can throttle the resin flow.
  The other thing to look at is the viscosity of your resin.
You can alter this a little by warming or cooling the mixed resin. Cooler resin, higher viscosity, slower wet out rate.
Warmer resin, lower viscosity, faster wet out rate.This comes with the penalty of faster gel time if you over do it. However with a small piece like yours, a lower viscosity may get you better wet out and push the air to the outlet of your mold faster.
B.E.

RE: Pinholes in surface after resin infusion

When you reduced the vacuum you apparently allowed air to flow back through the vacuum line into your laminate. The vacuum line needs to be full of resin and remain full when you reduce vacuum. You should be able to see this through a transparent plastic line. With VARTM the big problem is that during infusion the area around the resin inlet will become very resin rich and thick because of high resin pressure relative to the area around the vacuum line. When the inlet line is closed the expectation is that the thickness will equilibrate throughout the panel. It is the "sponginess" or compressibility of the fabric that controls the panel thickness in concert with resin content and viscosity. Viscosity resist flow and therefore resin pressure can vary from one area to another. Resin pressure plus fiber compaction pressure is always equal to bag pressure (which is ambient air pressure). And thickness is directly related to fiber compaction pressure.

RE: Pinholes in surface after resin infusion

(OP)
Thank you very much to you both for your support. I will put some of your points together tonight when i carry out another test piece ( then i will be out of resin untill saturday). I will let you know how i get on. I will try infusing at full vac (or as full as i can achieve with no proper guage). Then when the vacuum line becomes full of resin with no air i will drop the vacuum to 21-22 hg's and clamp. I have tried at less but it didnt seem to have quite as good results. I think the big thing is that i didnt wait for the vacuum line to be properly full on my other test pieces.

Chris.  

RE: Pinholes in surface after resin infusion

(OP)
ok, test done and out of resin untill the weekend. The results were average. Roughly the same as last time.

If i am acheiving full vacuum (lets say i am for the purpose of this question), even on a part as small as 8x6 inch's, should i leave the stack for any longer than a couple of minutes to ensure all the air is removed?

As i mentioned in my other post the part appears to infuse perfectly (looking from the under side on a piece of glass) it is only when the feed line is clamped that the problem occurs. I will post a picture of a typical layup of mine for some scrutiny, infused with peel ply etc still in place.

Could any one here tell me if it is possible to infuse a single layer of carbon fibre? (not that anyone might want to) just a question.

Chris

RE: Pinholes in surface after resin infusion

It takes a while to remove the last vestiges of air, a couple of minutes may not be enough.
Also with the second gauge I mentioned, after you have pulled "full Vacuum", turn off the line from the pump to your layup and observe the gauge on the layup stack for at least 10 minutes, it should not move. If you do see movement
this will indicate a minuscule leak that can create some of the problems you are having. Your pot clamps and spigot valves should be capable of supporting full vacuum or at least 29"Hg.
 B.E.  

RE: Pinholes in surface after resin infusion

I just re read your original post where you said you had no loss of vacuum.
 Did you determine that by the method I just mentioned, or were you using another method?
B.E.

RE: Pinholes in surface after resin infusion

(OP)
The method was probably not sufficient really. I pulled as much vac as possible and closed the 1/4 turn valve. Then turned the pump off. I left it for about 3 hours and when i returned the bag was as tight as it was when i left it. But i guess i should probably stick a guage on it so i can see if it drops at all.

RE: Pinholes in surface after resin infusion

(OP)
Got a question.... i read a post on the net saying that some bagging plastic can be too stretchy for infusion, therefore filling the flow media/ laminate with 'bag' where the air would normally flow through thus restricting air flow. Does this sound like it could happen??

Regards, chris.

RE: Pinholes in surface after resin infusion

It may be possible but it would pinch-off resin flow long before pinching-off airflow. It isn't really a good practice to have the vacuum bag directly in contact with the resin. Any permeability or pinhole in the bagging film will leak air into your part. There should be release film and breather between the part and the bag. That way all leaks (resin or air will be into the breather. The breather should be connected to full vacuum all the time. All films should be assumed to have pinholes.  

RE: Pinholes in surface after resin infusion

Crud,

I've spent the past 8 months doing a lot of trial and error to learn VARTM.  At one point I think I was having the same problem as you.  Are you using a vacuum bag around the sheet of glass?  When you clamp off the inlet do you have epoxy in the vacuum tube going to your pump?  I am wondering if your epoxy is going up the creases of your bag and right into the pump line.  At that point any air leaks causes the epoxy to percolate in your part and causes pin holes and voids.  If you have any creases in your vacuum bag the same thing will happen, the epoxy will follow the path of least resistance and go right to the outlet.  This may cause voids because the epoxy does not flow through the fabric.  Rather than using resin flow, make your part a little oversize and surround it with a perimeter of breather material on peel ply.  Pull the vacuum on the breather material and infuse from the lowest point or the center.  You can also do some fabric flow tests to see which point is the best to pull from and to infuse from using fiberglass and some other liquid - I've used coffee before so I can see the flow pattern.  Another thing to consider is that if you see the epoxy percolating in your exit tube - there is a leak. Also, look at the geometry of your part.  I like to set things up so that I use the vacuum to pull a void in the fabric and let gravity fill things up.  If you keep your exit end higher and keep enough epoxy in your feed tube you'll usually be okay.  

Good Luck!

Mike

RE: Pinholes in surface after resin infusion

(OP)
Thank you moto mike, i think i am having the same problems as you were having. I have been trying for about four months now too. I have never tried a breather layer around the perimiter so i will definety try that. (what would the purpose for this be though)?

I do indeed butyl tape the bag to the glass.

I have done tests where the resin flowed into the vacuum line and tests without it flowing into the vacuum line. Neither seemed to make much difference.

On full vacuum bubbles appear as if the resin is out gassing but i degas the resin first so i can only assume they are trapped air? but they dont seem to want to make their way to the vacuum line they just sit in the mesh or peel ply.

RE: Pinholes in surface after resin infusion

I suggest that your problem may be moisture related. If your resin was exposed during high humidity, then the moisture absorbed by the resin is outgassed as steam during the cure cycle. Was it raining the day you did the process viz. high humidity?
High vacuum levels exacerbate the problem by expanding the voids. Despite the common perception that vacuum removes voids, it can make them worse by the low pressure expanding the voids. The resin flows away, not the voids.  

RE: Pinholes in surface after resin infusion

Crud,

Can you upload a picture of your layup? Also what type of epoxy are you using?

You shouln't have to degas the epoxy because you do that with the vacuum pulling while it cures.  Get yourself a resin trap with a guage. Hook it up tp your pump and then clamp off all the lines to see how long it holds vacuum. If that holds then put it in line to your layup. After pulling it down clamp off from the pump and see how tight the layup is. If that is all okay then I think the problem is some thing that I also ran into.

You are getting air in the system when you infuse. Because you are not using breather, the air in the inlet tube goes into the fabric. The epoxy takes the path of least resistence and goes around the air and hits the outlet tube which encapsulates the air. The air just percolates in the part. Have you seen in the outlet tube when you get a little resin in and it moves up and down but doesn't travel too far? The same thing happens in the part.

Make sure you wrap the vacuum tube in the bag with breather, otherwise it stops pulling once the epoxy gets there. You use the breather to pull air and excess resin through the part. This keeps an open path to the vacuum pump. Also, you can put breather strips to pull the epoxy in specific directions if the geometry of the part moves it away and you get a void.  Remember that even with vacuum, gravity will affect the epoxy flow.

Hope this helps. I've read a lot of textbooks, whitepapers, etc. On this and set up several hundred parts in the last few months using many different epoxies and resins. I'm still learning everyday. This stuff is not all that easy. Good luck.

Mike

RE: Pinholes in surface after resin infusion

(OP)
Motomike,

Yes thats exactly what happened yesterday the resin creeped into the vacuum line (i have a catch pot with a guage), i thought it was odd when i saw the resin fall back down the vacuum tube then rise again then as soon as a drip went into the pot it fell again. I have set another one up today using some breather around the vacuum line and i timed it just right so the part infused without hardly any going into the breather and so far none in the tube. Ill let you know how i get on.

Thanks again mike. Regards, chris.

RE: Pinholes in surface after resin infusion

Moto mike said "You shouldn't have to degas the epoxy because you do that with the vacuum pulling while it cures."
 
The problem with doing that is that your resin is now degassing inside your mold producing bubbles in your part.

I will reiterate what Composite Pro said " 2. You may be boiling the resin by applying too much vacuum after you close the resin inlet. Resins will always have some volatiles (including the resin itself). After closing the resin inlet and the vacuum line is full of resin the vacuum should be reduced to 10 in Hg. This provides 10 in Hg of compaction pressure on the fibers while maintaining 20 in Hg on the resin during cure."  

 

 Reducing the vacuum pressure allows the the gas bubbles to collapse on themselves.
B.E.

RE: Pinholes in surface after resin infusion

Chris and B.E.,

First, good luck Chris with the new setup. Make sure you keep some resin on the backside of the feed tube clamp after infusing. It helps seal off air. Timing the clamp off is important. With practice you will learn to clamp a little early to let the resin wetout and the vacuum migrate it. This will give you a thinner and lighter part. What is the gel time of your epoxy?

Second,  B.E. I guess it depends on your resin system. I have pulled 29 in Hg on parts for hours without degassing and have not found a problem with boiling off the volatiles in my system. Hopefully I won't run into that. I was wondering how decreasing the vacuum would give you 10 in Hg in the tube but still maintain 20 in the bag? I would think it would be the same, 10 throughout the system. As I said I'm still learning and can use any advice on this stuff.

Thanks

Mike

RE: Pinholes in surface after resin infusion

Moto Mike
Here is how you get 10" Hg in the tube and 20" Hg on the bag. Its called double bagging.
 With redundant vacuum chambers about the perform comprising:a mold;a preform located on the mold;an inner bag sealed to the mold and enclosing the preform and forming a first vacuum chamber,an outer bag sealed to the mold and enclosing the inner bag and forming a second vacuum chamber,at least one vacuum pump coupled to the first vacuum chamber and the second vacuum chamber to evacuate the second vacuum chamber to a pressure greater than the pressure in the first vacuum chamber; and a resin source coupled to the first vacuum chamber to infuse resin into the preform while maintaining the pressure in the first and the second vacuum chambers.
Be aware that some, of this stuff is patented by various people. and goes under various trade names such as: Scrimp,Vartim, Vec.
B.E.




 

RE: Pinholes in surface after resin infusion

B.E.,
I was wondering right after I submitted the post if you were referring to using two layers of vacuum bags. Neat idea. I wonder if it wouldn't be easier to vacuum the outer bag and use positive pressure to infuse. Probably a whole different set of problems with that as well.  Thanks for the info.

Mike

RE: Pinholes in surface after resin infusion

Th double vacuum-bag process is a very effective process for making void-free, non-autoclave parts but it is not relevant to this discussion. "Double vacuum-bag" is a confusing misnomer. One of the "bags" must be a hard, structural shell which would more appropriately called a vacuum chamber or vacuum-oven. One iteration is a vacuum-bag over a steel pot. In this case, the vacuum-bag is used as a gas seal but the steel pot is used to keep the outer bag from applying any force to the inner bag. This is essential to making the process work.

A vacuum-bag in ambient air is under 30 inHg at all times, whether or not you are pulling vacuum. 30 inHg is the barometric pressure and is equivalent to 15 psi. It exists because the column of air over every square inch of the earth's surface weighs 15 pounds. Pulling vacuum under the bag will only reduce the fluid pressure. That fluid is resin or perhaps air. So if the fluid pressure under the bag is 10 inHg of vacuum (20 inHg absolute pressure) and the fluid pressure above the bag is zero gage pressure (30 inHg absolute pressure) what is keeping the forces in balance on both sides of this thin plastic film? It is 10 inHg of compaction pressure on the fibers.
 

RE: Pinholes in surface after resin infusion

(OP)
Moto mike.

The pot life is around 90 mins.

Gel time is around 5-6 hours at roughly 20-25 Degrees c.

It is epoxy resin specifically designed for infusion.

I'm sure we will get it sorted soon. I think there is much more to it than i thought. But i never quit...so ill keep trying untill i get it sorted.

It seems when i have been doing this that as soon as the resin blocks the path of air near to the vacuum port, that the vacuum reduces from the vacuum side back towards the feed pot. I think this happens because as soon as the resin blocks the path of air the fibre glass appears too lighten in colour very gradually as if its loosing its compression. When the part comes out, it then looks dry and suffers from the problem of voids inbetween all the tows.

RE: Pinholes in surface after resin infusion

Chris,

I would suggest going back to basics to determine a few things first. 1) Figure out if you are vacuum boiling the resin.  To test this I suggest doing a traditional wet layup.

Try This.

1) Layout your tacky tape perimeter and cut the appropriate vacuum bag to fit.
2) Cut a few layers of fabric, one layer of peel ply, and three layers of breather to fit inside the perimeter of the tacky tape.
3) Mix up your epoxy and with a brush wet out the layers of fabric on your glass mould.
4) Put the peel ply on top of the fabric and resin followed by the tree layers of breather.
5)Place your vacuum tube wrapped in breather on top of the layers of breather.
6) Place your bag on top of all this and pull vacuum until it cures.
7) See what you have and if you have bubbles in the fabric.

2)Now if the test shows that the epoxy didn't vacuum boil then try this.

Do the setup with the breather and peel ply just like you did above but don't wet out the fabric.  Add your infusion tube at one end and your vacuum tube at the other end - right on top of the breather.  Now for geometry - orient the part so that the inlet is lower than the outlet and let the filling pull against gravity.  This should help avoid any air bubbles.

You can add a little heat with heat lamps to speed up the cure.

Let me know how it goes.

Mike

RE: Pinholes in surface after resin infusion

Is it possible that it is due to a gel time too long?
After infusion of the fibers the inlet is clamped; then the vacuum is still pulling the resin out of the fibers  and thus creating little dry spots or void bubbles?

RE: Pinholes in surface after resin infusion

Gregoire, it is possible to look at it that way but it is not very helpful for solving the problem. It is not practical to vary the gel time for every different size of part. But you are correct in that this small part is more difficult because the gel time is so much longer than the infusion time. If the part were much larger this problem may not occur. But that depends on what the actual problem is. And that has not been determined yet.

One factor that should be measured is the final part weight and initial preform weight. That will give the resin content, which will give some indication if there is too much resin bleed out of the part(causing boiling). If the resin content is not low (less than  about 35%) then the problem is trapped air. But as I said earlier, both issues are involved to some degree. This is what can make solving the problem difficult, and requires an understanding of what is going on.
 

RE: Pinholes in surface after resin infusion

Chris,

I believe I have the answer for you. I use a similar epoxy to the one you described. I have made hundreds of parts without experiencing the problem you are having...guess what...I don't degas the epoxy.

I tried a test today and degased the epoxy..and guess what happened? The epoxy was filled with tiny little bubbles. I let the epoxy sit to cure and did not shoot a part. I checked it repeatedly and even though it looked like the bubbles were gone, if I put a stir stick in and just pulled it back out it was covered in a thin layer of epoxy that was filled with tiny bubbles.

Take care in mixing your epoxy by hand and do not degass. I believe that the viscosity or surface tension of the epoxy may prevent it from collapsing the bubbles.

Good Luck!

Mike

RE: Pinholes in surface after resin infusion

(OP)
moto mike.

What size was the part you did the test on? And how many layers did you use?

I think it has something to do with the size of the part. And pulling full vac.

I have just set a piece going, and infused at full vac but just as it has infused i reduced the vacuum to 21hg in's.

I have noticed that all the air appears to be removed from the part but there are no bubbles at all in the part (it wont cure untill tomorrow).

I have done this before and the part came out perfect. I think that if the part was maybe 1m2 that it would cope with full vac. Although i dont understand why this happens it seems to work.

Dropping the vacuum tho 21hg in's doesnt seem to drop much compaction pressure either so should be ok on a contoured mold. Ill post tomorrow after i remove it and see what it looks like. But i have a feeling it will come out perfect.

RE: Pinholes in surface after resin infusion

(OP)
moto mike.

To answer to your prevoius post, i have tried degassing and not degassing and it always comes out the same.

Its not so much tiny bubbles but voids inbetween the tows in the weave as if the resin is being sucked from the gaps. Hence the reason i am testing dropping the pressure again.

Chris.

RE: Pinholes in surface after resin infusion

Chris,

Glad you figured it out.  It may just be a problem with vacuum vs mass of the epoxy in your part.  Trying to relate this to some avenue of science to explain what you are seeing would be nice but beyond the scope of this forum.  I did not shoot my part with the degassed epoxy as it took took long to clear.  It did start to clear up as it reached cure temp but it still had air bubbles around the stir sticks that I left in the cup.  My parts range in size and layers.  Usually 3 to 5 layers and up to 14" by 16".  I can't say too much more about my system as I have been developing it for 8 months and I use a pretty unique way to infuse and then cure with elevated temp and pressure without an autoclave.  I can turn parts out every three hours.  Its been a lot of work and many 24/7 days, but it works really well.  I don't let anyone into the shop to see the system, not even family or friends and definitely no cameras.

At this point I'll leave you to experiment on your own.  I apologize if I didn't help you as much as I hoped.

Good Luck with your projects.

Mike

RE: Pinholes in surface after resin infusion

I have the same problem, little tiny pinholes evenly spread in my test part. I have done tests for months and have no ideas any more. I am using a two sided rigid mold whith th VARTM technique. My injection pressure is curently 0.16 bar (0.16 kPa). The injection goes well, however the pinholes only come after some 45 minutes after infusion. I clamped the resin inlet off and put the vacuum of on the vent so that ambient pressure is everythere. What can be the reason why the bubbles occure? I used degased low viscosity resin and non-degased low viscosity resin.

RE: Pinholes in surface after resin infusion

A good resource to these problems is Resin Transfer Moulding for Aerospace Structures by T. Kruckenberg and R. Paton, ISBN 0 412 731509, Chapter 13 page 438 "Defect Formation"

RE: Pinholes in surface after resin infusion

(OP)
I found another thing that makes my test parts perfect quality... If i squeegee the part (flat test panel) i can see the air being removed from the part. Then it comes out perfect. However if i leave it to do it on its own the air seems to get trapped by the resin and will not move out the part unlesss it is helped.

So i think i must be getting air trapped in the part, but my next step is to find how to stop the air getting trapped in the first place.

RE: Pinholes in surface after resin infusion

Hey MotoMike, I read the section and could not find any mistake I have done. What I tried is a test with different kinds of glass fibres in one part, the result was that there was still an even distribution of the tiny bubbles in the test panel. I think the bubbles come from the resin system. I don't know what I did wrong. Does anyone have an idea?

RE: Pinholes in surface after resin infusion

We seem to have a problem. That everyone is facing so it might be best to try to apply some scientific testing to this. I would propose some systematic testing to try to pinpoint the problem. Here is a rough idea of what I am thinking:

Bubbles caused in the resin/epoxy matrix could be caused by three things:
1.trapped air
2.trapped gas or volatile
3. Vacuum bubble

From these I would tend to believe that trapped air would be the best choice followed by a trapped gas or volatile.

To test your system look for air leaks. I did a test with a layup of breather fabric and water colored with different food coloring to look for leaks. I even submerged the whole system in water to test. The results were interesting but not totally conclusive because the surface tension of the water can plug small leaks. The use of smoke or some other aerosol would be better.

Another thing is to look at the basics of moving a liquid through a media with vacuum or pressure. Is there an even resin/epoxy front through the system? Use peelply, flow media, and breather to maintain even flow of resin/epoxy and distribution of vacuum through the system. Try different viscosity resin/epoxy and different temperatures. Practice releasing and closing the infusion tube to eliminate air. Try different fabric suppliers but be careful when testing with glass and then going to carbon as they most likely have different sizing and wet out characteristics.  Also don't assume that because your system works with polyester/vinyl ester that it is an easy switch to epoxy. The polyester/vinyl ester matrix has a relatively low viscosity and surface tension which allows it to wet out quickly and then it gels relatively fast. Epoxies take a bit more R&D to get just right and you may have to work with different temps to reduce the viscosity and/or improve the gel time. Be cautious of your mould release and mould material max temps.

Also look at chemical interactions. Are dust, dirt, oils from your skin, release chemicals getting on your fabric and causing a problem? Fabrics are coated to work with different resin systems (I believe its called sizing) is your fabric sizing suitable for your resin/epoxy matrix?

My advice, start with vacuum and leak tests. Then work on resin/epoxy tests. Try different ones and at different temperatures. Be careful with polyester/vinyl esters when trying different temps as they can set up fast. Also be aware of your gel time and try to match it with the size of your part and rate of infusion. If your part is small and you can infuse in seconds but have to wait hours for it to gel you have a higher probabilty of getting a leak and pulling in a bubble.

So a few more basics. If you have bubbles in one area of the part, trace the bubbles and look for a leak or an area that does not have good vacuum. If it is evenly distributed throughout the part then you may have a major leak or more likely the resin/epoxy has dissolved gases, you have impurities in your components or chemical interactions.

Try a wet layup with a brush but pull vacuum as if you infused to see if the resin/epoxy is degassing or there are chemical interactions not related to infusing, this assumes that you can get a tight vacuum without the infusion tube.


Keep your system tight, keep everything clean, try different components, keep good notes, and good luck with your projects.

Mike

RE: Pinholes in surface after resin infusion

I had one more insight to try. After infusing and clamping off the infusion tube try elevating the tube so that it is higher than the part.  If you clamp so that some resin is in the tube after clamping and you don't have an air leak the bubbles will migrate to the top of the resin in the tube. Although, if you are pulling the resin through peel ply it may not let the bubbles back through. Its something that I tried awhile ago and it seemed to work.

Mike

RE: Pinholes in surface after resin infusion

I would like to thank Chris for starting this thread and everyone that contributed because you led me on a path to some discoveries about my techniques.  My setup is very similar to the one that Chris initially described with the exception that I use a 12 CFM pump connected to a resin trap with gauge that connects to a manifold that lets me pull 6 parts at once.  I was not having any problems with the surface quality on my parts and thought initially that I had some answers for Chris.  It turns out that the contributors that focused on vacuum pressure were on the right track.

In trying to figure out why I wasn't having the problem I connected vacuum gauges and small resin traps (made with pvc pipe) to each of my bags.  Initially the vacuum for each part was 27 to 28.5 in Hg. Not the 29.5 that I had near the pump but I thought it was acceptable.  After infusing the parts I was shocked to see that the vacuum dropped in each part to less than 15 in Hg.  I was developing leaks after infusion which explains my surface quality versus Chris's.  I sprayed some water around the setups and found that the corners of my bags were leaking as the resin flowed through the parts.  I did some testing and redesigned the way the corners were taped and got the vacuum to stay consistent.  When I demolded the parts I now had the pinholes that everyone has been speaking about.

My setup was fabric on the mould, peelply on top followed by breather fabric and vacuum bag.  The infusion tube with spiral wrap at one end and the vacuum tube wrapped in more breather at the opposite end.  I noticed that I was infusing and pulling vacuum from the backside of the part.  I made up larger moulds and cut my fabric an inch bigger all the way around.  I then placed a perimeter of breather fabric on the mould so that it would be directly under the extra inch of fabric.  I left the breather off the back of the entire part and only used peelply under the infusion tube placed as close to the edge as I could place it.  I put the vacuum tube on breather fabric at the opposite end that I stuck under the fabric and on top of the perimeter breather fabric.  In this way the vacuum tube was off the part and connected only through extra breather fabric to the part (the vacuum bag was cut several inches bigger to fit all the extra fabric and breather.  My goal was to use the extra breather around the perimeter to pull vacuum to the face of the part instead of the back.  I trimmed off the oversize part and extra breather later.  I did this for one part and under the maximum vacuum that I could get at the part 28.5, the part was perfect with no pinholes or voids.  I made up 5 more moulds and have been running all six daily and the results have been superior, no pinholes, voids, or bubbles on the surface of any part.

Can Chris or someone else who has been having pinholes try this and let me know if it solves the problem for them as well?

Thank you!

Mike

RE: Pinholes in surface after resin infusion

(OP)
Thanks for this mike. I thought i had got the process sorted untill i tried to make a carbon bonnet vent in my new mould. It came out sub standard. But when i was doing the flat sheet i was sort of doing what you had just described. On my new mould i have about a 5 inch flange around the part for the bag. But even this seems to be too small. I think 10 inchs would have given me the space i need to do it properly. However i am going to try again today doing the set up exactly as you have just described but but my layup in the vacuum bag instead of sealing to the flange. This should give me enough room to put a breather around the perimiter. I will let you know tomorrow how this comes out.

I do agree that without a breathable perimiter as soon as the resin has passed over the fabric and goes to the edges that vacuum is reduced due to the resin blocking the vacuum from the back to the front. So what i think happens is when the part is infused or nearly infused the vacuum pressure drops from the back of the part towards the front.

I could be wrong but ill give it a go anyway.

Cheers, Chris.

RE: Pinholes in surface after resin infusion

(OP)
I have a question for you mike if thats ok? When you have a perfect infusion do you see any bubbles that appear to get trapped in the weave of the cloth? I have found on mine that when i get a really good one i hardley see any bubbles in the back but.... if i get any bubbles that appear in the weave that i can see throught the bag, when i de-mould the part this is where any imperfections seem to be. If i squeegee the bag with my finger nail i can see as if there is trapped air that moves when physically pushed. I have never put a guage on my bagged layup and think this may be a good idea to see whats going on with the pressure.

Regards, Chris.

RE: Pinholes in surface after resin infusion

Chris,

I have a couple of countersinks in my mould where I put screws to mount the part.  I will sometimes get a few bubbles at the top of those, but fortunately I drill those out.  I figure it may be bubbles from not degassing the resin and since the countersinks are the high points they end up there.  I have always thought that if I see a bubble like you describe I have a leak and can track it to there.

Put your resin trap and gauge as close to the part as possible.

I will give you a little hint on infusing and limiting the air you introduce to the part.  Get yourself a funnel or a soda bottle and modify the cap so it fits your tubing.  I modify soda bottles by cutting the bottoms off.  Mount them in something upside down.  Pour your epoxy into them and let the epoxy run down into the part rather than letting vacuum pull it up while trying to keep the tube under the fluid.  Don't do this with polyester or vinyl ester resin as it will go right through the plastic and make a mess (from experience).  It seems to work well with most epoxies though.  I just find this easier to eliminate air when infusing and most of the bubbles in the epoxy will migrate to the top of the soda (the bottom actually) bottle and never make it into the part.

Give it a try and let me know how you make out.

Mike

RE: Pinholes in surface after resin infusion

A little different tack.

I suspect that the bubbles you are experiencing are caused during resin exotherm.  Temperature increases and flashes volatiles or dissolved air in the resin.  starting point will always be an inclusion or fiber tip.  It will be worse in areas of thicker laminate.

Reformulate your resin so it has a gentle gel formation prior to exotherm.  You should much fewer voids.

Chris

RE: Pinholes in surface after resin infusion

It sounds like your draining your part because either your laminate or infusion mesh is connected to your vacuum source. You should have at least 3-6" of space between where your laminate ends and your vacuum source is, the only thing connected the two should be peel ply. You also want to keep full vacuum the entire time, theres no reason to lower your vacuum if you do it right. Depending on your laminate and size, clamp the resin source off either a couple inches short of your laminate or at the end of your laminate depending on the excess resin in your flow medium. Experience will help you determine when. I also find that the red mesh has the best cosmetics, and the green has been RC with a very slight compromise in surface quality but absoultly no pinholes in either. You should be able to get a perfect pinhole free surface out of mold with no surface coats/gel coats required.

RE: Pinholes in surface after resin infusion

*better RC* ment to say above.

RE: Pinholes in surface after resin infusion

another point to add is you must have a perfect vacuum with absolutly no leaks. You ahould be able to cut your vacuum source off before in infusing for atleast 15-30 minutes and see absolutly no drop in vac. level. One peelply strand can ruin this. Do not attempt to infuse unless you have no drop!

RE: Pinholes in surface after resin infusion

Exactly what Hojo said. One peel ply strand ruined one of my infusions so take the time to check your seal carefully.

www.compositescentral.net

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