Voids in fibre gaps.

[TCook]

Hi I’ve been having issues with this infusion and can’t seem to get rid of these voids in the gaps in the fibres. I’ve read a lot about them and tried different methods but still get them. It’s two layers of 200g 3k carbon fibre using a perforated release film instead of peel ply. (I get the same results with the peel ply) I’ve ran 4 parts now all with the same issue. Im fairly new to infusion and am trying to learn and refine the process as best I can. Any advice or questions about this will be much appreciated. 
 

thanks 

[lo_0l]

23 hours ago, TCook said:

Hi I’ve been having issues with this infusion and can’t seem to get rid of these voids in the gaps in the fibres. I’ve read a lot about them and tried different methods but still get them. It’s two layers of 200g 3k carbon fibre using a perforated release film instead of peel ply. (I get the same results with the peel ply) I’ve ran 4 parts now all with the same issue. Im fairly new to infusion and am trying to learn and refine the process as best I can. Any advice or questions about this will be much appreciated. 
 

thanks 

How big is the part and how fast are you infusing it?

Looks like it might be a hood? Do you have pictures more pictures? Pictures of infusion?

[TCook]

Thanks for your reply. It is a hood and it is infused extremely slow. You can see the perforations allowing the resin through into the part I don’t know if this is bad or not it looks bad but the part is fine aside from the voids. It is off a classic mini so it’s no where near as big as modern hoods however I do plan on doing them in the future, will a bigger infusion create more issues with voids? 

[lo_0l]

1 hour ago, TCook said:

Thanks for your reply. It is a hood and it is infused extremely slow. You can see the perforations allowing the resin through into the part I don’t know if this is bad or not it looks bad but the part is fine aside from the voids. It is off a classic mini so it’s no where near as big as modern hoods however I do plan on doing them in the future, will a bigger infusion create more issues with voids? 

Someone like @Jeremy Senne might have some great input on this.

 

[Jeremy Senne]

There's a few typical causes for surface voids/porosity, but most of them boil (pun intended) down to trapped air or moisture.  A few questions with potential input based on the answers.

1. What is your tooling material?
   1. Is it a wet layup splash tool off of the original hood or a foam tool?
      1. If so there's a good chance that it has sat in a humid environment for a while and absorbed a bunch of moisture.  My suspicion is that you're infusing with warm to hot resin, which would encourage some of the trapped surface moisture to escape vapor pressure and get in the way of the cure as trapped vapor.  Thus every time you use the tool you refresh the problem.    
      2. The solution here would be to heat up your tool to bake it out for a few hours before you use it.  If you don't have an oven this could be as easy as building a small tent with vacuum bag around it and then putting a hair dryer on inside it.  Note that you'll want to stick around to make sure you don't start a fire...
   2. Is it a metallic tool?
      1. If it's a metallic tool it could be contamination from multiple uses or storage.
      2. I'd suggest a light resurfacing/polishing of the tool to take off any sealant/release compound and then reseal and rerelease.  Make sure that you cure the sealant and release long enough as these could also cause surface porosity.  This could also be the case for a fiberglass tool.
2. Are you pulling good vacuum during the infusion?
   1. You can check by verifying that if you pull vacuum and let it set for a few minutes the bag doesn't lose it's grab.  You'll probably want to pull at least 10-15 inHg for a good infusion.  If you have a gage you can verify directly, if not the bag should be difficult to shift at all at this vacuum range.  10-15 inHg is around 5-8psi so it should take around 5-8 lbs of force to lift a 1"x1" area of the bag off of the tool.  If you're low on vacuum you may either have:
      1. A few localized tool leaks that allow air to pull through the area that might be giving you porosity issues.  This could definitely be the case if your tool is an open cell foam or a wet layup splash that may have been damaged.
      2. An insufficient vacuum pump for the size of part you're trying to infuse.  This could be verified by doing a smaller part to see if that comes out good.
3. Are you degassing your resin before you infuse?
   1. A classic mistake with infusion is to mix up a batch of resin by hand, which instills a lot of air, and then go straight into pulling it into the infusion setup.  All of the bubbles induced in this process expand under vacuum so they're exacerbated.  This is the reason why autoclaves beat vacuum only cure most of the time because the pressure collapses the bubbles rather than encouraging them to expand.
      1. The easy fix is to buy a degas chamber and put your mixed resin into it for ~5-10 minutes before you use.  It will generally foam up then settle down.  An example degas chamber is linked below.  There's probably more cost effective ones if you're sensitive to that if you browse around.
      2. https://www.vevor.com/vacuum-pump-c_11109/vevor-2-gallon-vacuum-chamber-upgraded-multipurpose-acrylic-vacuum-degassing-chamber-transparent-vacuum-chamber-for-resin-degassing-silica-gel-degassing-gypsum-degassing-and-vacuum-extraction-p_010700464784?adp=gmc&utm_source=google&utm_medium=cpc&utm_id=20851263822&ad_group=160381533727&ad_id=684421397984&utm_term=&gad_source=1&gclid=Cj0KCQjwsuSzBhCLARIsAIcdLm4VMx12-IlomksllzZqPFhqjMGsOhg4YOCGFrlaSmrxVR8D54_40IsaAql-EALw_wcB
4. Are you holding vacuum on your setup for a sufficient amount of time to evacuate trapped air before infusion?
   1. Generally you want to hold vacuum a minimum of 1 hour before you infuse to encourage any air trapped on the surface to evacuate.  Bonus points if you also heat the tool either in an oven or via the hair dryer/tent described above while holding vacuum.  This adds energy to the system helping gas molecules vibrate and move around and escape the various forces that may be keeping them on the surface.  
5. Are you heating up your tool and resin during infusion?
   1. Lowering the viscosity of the resin to the minimum point you can will improve tool surface wet out and give you the best chance of a void free laminate.  Without any knowledge of the resin you're using a good rule of thumb is to heat the resin to ~100-150F shortly before infusing.  Note that this will reduce the work life of the resin so you may have to act quickly.  If it's a big part you may also have to do mix multiple batches as there are exotherm considerations.

All of the above said I'd suggest the following general process:

1. Ensure you're getting enough vacuum against your tool and that it's not itself leaking
2. Bake out your tool before layup
3. Do your dry layup and then bag and hold under vacuum and heat for an hour before you infuse, I'd aim for ~120-150F
4. Mix and degas your resin before use.  I'd also suggest preheating it.  120-150 is my experience, though double-check the cure temp of the resin you're using.  Even 100-110F would help a lot.  Degasing at temp would be better than cold.
5. Infuse at temperature then check your results

 

Good luck!

 

 

 

[TCook]

  

15 hours ago, Jeremy Senne said:

There's a few typical causes for surface voids/porosity, but most of them boil (pun intended) down to trapped air or moisture.  A few questions with potential input based on the answers.

1. What is your tooling material?
   1. Is it a wet layup splash tool off of the original hood or a foam tool?
      1. If so there's a good chance that it has sat in a humid environment for a while and absorbed a bunch of moisture.  My suspicion is that you're infusing with warm to hot resin, which would encourage some of the trapped surface moisture to escape vapor pressure and get in the way of the cure as trapped vapor.  Thus every time you use the tool you refresh the problem.    
      2. The solution here would be to heat up your tool to bake it out for a few hours before you use it.  If you don't have an oven this could be as easy as building a small tent with vacuum bag around it and then putting a hair dryer on inside it.  Note that you'll want to stick around to make sure you don't start a fire...
   2. Is it a metallic tool?
      1. If it's a metallic tool it could be contamination from multiple uses or storage.
      2. I'd suggest a light resurfacing/polishing of the tool to take off any sealant/release compound and then reseal and rerelease.  Make sure that you cure the sealant and release long enough as these could also cause surface porosity.  This could also be the case for a fiberglass tool.
2. Are you pulling good vacuum during the infusion?
   1. You can check by verifying that if you pull vacuum and let it set for a few minutes the bag doesn't lose it's grab.  You'll probably want to pull at least 10-15 inHg for a good infusion.  If you have a gage you can verify directly, if not the bag should be difficult to shift at all at this vacuum range.  10-15 inHg is around 5-8psi so it should take around 5-8 lbs of force to lift a 1"x1" area of the bag off of the tool.  If you're low on vacuum you may either have:
      1. A few localized tool leaks that allow air to pull through the area that might be giving you porosity issues.  This could definitely be the case if your tool is an open cell foam or a wet layup splash that may have been damaged.
      2. An insufficient vacuum pump for the size of part you're trying to infuse.  This could be verified by doing a smaller part to see if that comes out good.
3. Are you degassing your resin before you infuse?
   1. A classic mistake with infusion is to mix up a batch of resin by hand, which instills a lot of air, and then go straight into pulling it into the infusion setup.  All of the bubbles induced in this process expand under vacuum so they're exacerbated.  This is the reason why autoclaves beat vacuum only cure most of the time because the pressure collapses the bubbles rather than encouraging them to expand.
      1. The easy fix is to buy a degas chamber and put your mixed resin into it for ~5-10 minutes before you use.  It will generally foam up then settle down.  An example degas chamber is linked below.  There's probably more cost effective ones if you're sensitive to that if you browse around.
      2. https://www.vevor.com/vacuum-pump-c_11109/vevor-2-gallon-vacuum-chamber-upgraded-multipurpose-acrylic-vacuum-degassing-chamber-transparent-vacuum-chamber-for-resin-degassing-silica-gel-degassing-gypsum-degassing-and-vacuum-extraction-p_010700464784?adp=gmc&utm_source=google&utm_medium=cpc&utm_id=20851263822&ad_group=160381533727&ad_id=684421397984&utm_term=&gad_source=1&gclid=Cj0KCQjwsuSzBhCLARIsAIcdLm4VMx12-IlomksllzZqPFhqjMGsOhg4YOCGFrlaSmrxVR8D54_40IsaAql-EALw_wcB
4. Are you holding vacuum on your setup for a sufficient amount of time to evacuate trapped air before infusion?
   1. Generally you want to hold vacuum a minimum of 1 hour before you infuse to encourage any air trapped on the surface to evacuate.  Bonus points if you also heat the tool either in an oven or via the hair dryer/tent described above while holding vacuum.  This adds energy to the system helping gas molecules vibrate and move around and escape the various forces that may be keeping them on the surface.  
5. Are you heating up your tool and resin during infusion?
   1. Lowering the viscosity of the resin to the minimum point you can will improve tool surface wet out and give you the best chance of a void free laminate.  Without any knowledge of the resin you're using a good rule of thumb is to heat the resin to ~100-150F shortly before infusing.  Note that this will reduce the work life of the resin so you may have to act quickly.  If it's a big part you may also have to do mix multiple batches as there are exotherm considerations.

All of the above said I'd suggest the following general process:

1. Ensure you're getting enough vacuum against your tool and that it's not itself leaking
2. Bake out your tool before layup
3. Do your dry layup and then bag and hold under vacuum and heat for an hour before you infuse, I'd aim for ~120-150F
4. Mix and degas your resin before use.  I'd also suggest preheating it.  120-150 is my experience, though double-check the cure temp of the resin you're using.  Even 100-110F would help a lot.  Degasing at temp would be better than cold.
5. Infuse at temperature then check your results

 

Good luck!

 

 

 

 

Okay I’ll go through that as a check list before my next part. Would you say 26inHg for infusing is too high? I would normally infuse at that then dial it back to 15inHg once fully infused and left to cure. It’s cured in an oven but I have been infusing at 25°c waiting for potlife to end then putting it up. 

[Jeremy Senne]

10 hours ago, TCook said:

  

 

Okay I’ll go through that as a check list before my next part. Would you say 26inHg for infusing is too high? I would normally infuse at that then dial it back to 15inHg once fully infused and left to cure. It’s cured in an oven but I have been infusing at 25°c waiting for potlife to end then putting it up. 

Nope, 26inHg would be great for infusion.  Higher vacuum during the actual infusion process is usually better.  Also dialing it back is also perfectly fine and is one of the tricks the infusion guys use to control laminate thickness after cure (you essentially control how much you squeeze out into the infusion media out the sides).

I'd put it in the oven wet!  No need to wait for pot life IMO.  You might get a bit more springback doing this as it won't cure quite as evenly from a thermal gradient standpoint, but it will give the trapped air/vapor a better chance of getting out.

Knowing that you have an oven the best thing that you can do for yourself is baking out the tool shortly before you start the layup process, and after you're under bag but before you do the infusion.  1-2 hours at each stage will probably do it, I'd suggest 150F (apologies for english units... I don't think in metric well because America brainwashed me).

Good luck!

[TCook]

Would the look of this infusion concern you as I haven’t used the perforated film before and to me it doesn’t look like a good infusion with dry patches and areas looking like they’ve been cut off. It did fully wet out eventually but surely these isolated areas can’t be good. 

[lo_0l]

On 7/1/2024 at 1:16 AM, TCook said:

Would the look of this infusion concern you as I haven’t used the perforated film before and to me it doesn’t look like a good infusion with dry patches and areas looking like they’ve been cut off. It did fully wet out eventually but surely these isolated areas can’t be good. 

So, this picture was taken prior to it fully wetting?

Are you continuing to pull vacuum in the oven?

[TCook]

That picture is during infusion it did fully wet out, but didn’t fill me with confidence. And yes vacuum stays on until it is cured. 

[lo_0l]

On 7/2/2024 at 1:51 PM, TCook said:

That picture is during infusion it did fully wet out, but didn’t fill me with confidence. And yes vacuum stays on until it is cured. 

@Jeremy Senne might have some more input!

[Jeremy Senne]

Did the process changes get rid of the surface porosity?

Regarding the wet out... infusion is an artform almost more than it is a science.  A good infusion technician is hard to come by because there's so many idiosyncrasies.

It's possible the uneven wetout is related to the perforated release, but it's far more likely that it's related to one or more of the following:

 

• Inlet and outlet locations for the infusion
  • For infusion of parts larger than a few square feet or with curvature/buildups, you generally need to strategically locate inlet and outlet ports with valves to get a clean and controlled infusion that doesn't have spots that want to stay dry.  For a part your size I'd expect this to be 1-3 inlets along one edge of the part, and then 1-3 outlets along each edge and possibly even through the center of the part.  Typically you start with one inlet open and all outlets open, then close the outlets as they become fully infuse, then close a given inlet and move on to the next one until you're fully infused.  Every part is different and every infusion master has different preferences, but that's how I've done it in the past.  Here's a few pictures to show what a very large infusion looks like, and one to show that there are definitely sometimes localized dry spots.
  •  
  • 
• Infusion media
  • Typically some sort of infusion media or mesh is used to broaden the resin infusion inlet/outlets to ensure that the vacuum isn't choking vacuum completely and that the resin can move.  This helps broaden the resin flow and can encourage more even wet out.  I've seen this used over the entire surface of the part to essentially make it entirely one inlet so that the resin is mostly going in the Z-direction rather than primarily in the X and Y-directions.
    • Here's an example or two of the infusion media
    • https://www.freemansupply.com/products/fabrics-bagging/mia-vacuum-bagging-supplies/mia-flow-resin-infusion-media
    • https://www.carbonfiberglass.com/product/infusion-flow-media/
• Weave Type
  • Some weave types tightly bundle the fiber restricting the flow through them.  This can restrict resin wet out to capillary action only in which case you wait a lot longer as it's not pressure driven but rather surface tension driven.  You may have this periodically throughout your part as the weave might be too tight in some areas but not in other areas based on going around corners and such, hence the local dry spots that take longer to wet out.
    • Note that thinning the resin via heating it helps this too as it would lower surface tension by adding internal energy.  You could also heat the area around a dry spot locally with a heat gun or hair dryer to thin it in that area to encourage the wet out.

Hope this helps,

Jeremy

Edited July 4 by Jeremy Senne