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tsombnik
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Hello friends, i am currently working on a project where we are manufacturing CFRP Parts with vacuum assisted RTM process. We are using infusion resin with infusion hardener (HP Textiles (HP-HE3000RI-30) / HP Textiles (HP-HTE300RI-9)) and Semiperm Monofilm R&G Release Agent. We are experiencing weird white spots inside of the part after curing of the resin and arent able to fix them. The wierd thing is, that we have these white spots very concentrated at a few positions of the part. The rest of the resin inside the resin pot is clear! What could be the problem? This is how the process looks like: 1) Inserting preform into the tool 2) Closing of the tool 3) Vacuuming of the tool 4) Injecting of the resin with 0,7 bar injection pressure 5) Wait 2 days until resin is cured 6) Open the tool I have added a picture inside of my post. I hope you can help. Thank you very much for your potential help, All the best, Nik 
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Warren (Staff)
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From the picture it is hard to tell exactly but it looks a bit like some form of bridging in those areas meaning thicker resin. The reason it appears white could be simply a moisture reaction or maybe some reaction with the sizing and because the resin is thicker, it shows up more there.
What kind of tooling are you using? What sort of curing environment.? The surface of the part seems to have quite a poor quality generally.
Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant
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tsombnik
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Group: Forum Members
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+xFrom the picture it is hard to tell exactly but it looks a bit like some form of bridging in those areas meaning thicker resin. The reason it appears white could be simply a moisture reaction or maybe some reaction with the sizing and because the resin is thicker, it shows up more there. What kind of tooling are you using? What sort of curing environment.? The surface of the part seems to have quite a poor quality generally. Hi Warren, thank you very much for your fast reply! Indeed you are right, the resin is thicker in the white areas, since the fibers can't really adapt to the honeycombs. I like the idea about the sizing. So you are saying, because the resin is thicker at these spots, the reaction is stronger and therefore somehow the white colour appears? Our Hardener is a 300 Minute hardener. I guess there shouldnt be a reaction heat problem or something like that. Although, it could be possible. As tooling we use SikaBlock M600. This was actually a bad decision, since the material is way too soft. It was a decision, made by low costs... next time we use SikaBlock M1000 or something like that. This is also the reason for the surface quality. We milled the tool, cleaned everything, grind the surface to make it smooth, cleaned everything again, and then applied epoxy resin for sealing. The surface of the tool seems to be okay if you look at it only with your eyes. What do you mean by curing environment? The part stays inside of the tool for 2 days, until the resin is cured. Then we take the part out of the mould. I dont know if the humidity is high or low inside of the room. We have temperatures around 20-23°C. All the best, Nik
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fibernoob
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Im not sure its your case... but I have had similar problems when I used too much (wax based) release agent and did not polish it into the mold.
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tsombnik
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Group: Forum Members
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+xIm not sure its your case... but I have had similar problems when I used too much (wax based) release agent and did not polish it into the mold. Hello fibernoob, we also used wax based release agent in the area of the sealing cord, so that we can use it again if resin reaches the sealing areas of the tool. So yeah, im pretty sure this can be the reason. We are going to clean the tool again and wont use the wax release agent anymore. If somebody has another idea though, please tell me  Maybe it can help. Thank you for your help! Nik
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oekmont
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I've had similar effects caused by moisture. the storage of the resin might be too cold, so that water condense on the resin, once it's in the mixing pot.
Do you degas your resin before the process? This can be a countermeasure against moisture. Additionally the degassing foam wich occurs without pre-degassing might cumulate in bridging areas, and produces this opaque resin after the compression. Do you have the access to a microscope for a mircosection?
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tsombnik
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Group: Forum Members
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+xI've had similar effects caused by moisture. the storage of the resin might be too cold, so that water condense on the resin, once it's in the mixing pot. Do you degas your resin before the process? This can be a countermeasure against moisture. Additionally the degassing foam wich occurs without pre-degassing might cumulate in bridging areas, and produces this opaque resin after the compression. Do you have the access to a microscope for a mircosection? Hi oekmont, yes, we use an Exicator for degasing. Something like this: ( https://goo.gl/images/W822mS)So i guess the degasing foam cant be the reason? For future experiments we will degas way longer to be sure! Nowadays we only degas for around 5 minutes. But if you would be right, wouldnt all the resin be opaque, not only in the bridging areas? If you look closely at the bottom of the picture, just below the fibers, you can see the resin of the ring gate being clear. I dont have access to a microscope. And even if i had, i dont have the skills to see anything 
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oekmont
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during infusion, the outgassing happens where the pressure is the lowest, which is at the flow front. At bridging areas, this gas can accumulate, and stay there during the solidification. This gas consists of trapped air and physically soluted gasses, wich contains h2o. After the impregnation this moisture diffuses back into the resin, but can't get very far.
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tsombnik
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We are not directly doing an infusion. We close the tool, pump out all the air and therefore create a vacuum. Then we have a resin storage which is set under a pressure of 0,7 bar. After the vacuum is created inside the mould, we open the vents and the resin gets pumped into the tool. So we have both, vacuum inside of the mould and the resin gets pumped inside with a pressure of 0,7 bar.
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oekmont
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still, there is a vacuum inside the mold, and the resin front is under vacuum. What kind of pump are you using? Are you using the same pump for the evacuation as for the degassing? What negative pressure do you reach?
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