Resin Infusion Voids
Resin Infusion Voids
(OP)
Hello all,
I am new to this forum and am excited to learn from the wealth of knowledge and experience from all of the members. I did some searching and found some similar issues regarding voids in my laminates while using VARTM methods.
I am using a sizeable aluminum mold that has a computer controlled heating element to control the curing process. My layup schedule is three layers of type 7781 fiberglass and a resin system designed for RTM. I have my fiberglass against my mold surface with a layer of peel ply on top of that, followed by one layer of flow media and then my vacuum bag. The mold is single sided at this point and has two vacuum ports and one point of infusion.
I am degassing my resin for about 15 minutes while preheating both it and the mold. The preheating of the resin is minimal via a hot plate but the mold itself is brought up to 50 C. I am pulling my resin through the two vacuum ports selectively to promote full saturation. Once the part is fully wetted out, I am switching my inlet port over to the vacuum side and pulling out excess resin/air from all three ports. At this point, the mold is then raised to 100C for four hours, per the resin's cure cycle recommendation.
I have vacuum gauges at my resin trap as well at my pump and they are reading identically without any drop.
The problem occurs once most of the excess resin is expelled, and voids show up in the form of very small air bubbles as well as leaving large areas of the fabric appearing to be dry, as seen through the vacuum bagging.
Am I promoting further degassing by heating up the mold in my later stages? Is it possible to be applying too much vacuum (I have read in another thread to lower the vacuum to 10 in/hg once the infusion is complete) which would result in creating voids?
If I had any types of small leaks would it be introducing the air back into the laminate in large volumes?
Any help is appreciated, thank you very much!
I am new to this forum and am excited to learn from the wealth of knowledge and experience from all of the members. I did some searching and found some similar issues regarding voids in my laminates while using VARTM methods.
I am using a sizeable aluminum mold that has a computer controlled heating element to control the curing process. My layup schedule is three layers of type 7781 fiberglass and a resin system designed for RTM. I have my fiberglass against my mold surface with a layer of peel ply on top of that, followed by one layer of flow media and then my vacuum bag. The mold is single sided at this point and has two vacuum ports and one point of infusion.
I am degassing my resin for about 15 minutes while preheating both it and the mold. The preheating of the resin is minimal via a hot plate but the mold itself is brought up to 50 C. I am pulling my resin through the two vacuum ports selectively to promote full saturation. Once the part is fully wetted out, I am switching my inlet port over to the vacuum side and pulling out excess resin/air from all three ports. At this point, the mold is then raised to 100C for four hours, per the resin's cure cycle recommendation.
I have vacuum gauges at my resin trap as well at my pump and they are reading identically without any drop.
The problem occurs once most of the excess resin is expelled, and voids show up in the form of very small air bubbles as well as leaving large areas of the fabric appearing to be dry, as seen through the vacuum bagging.
Am I promoting further degassing by heating up the mold in my later stages? Is it possible to be applying too much vacuum (I have read in another thread to lower the vacuum to 10 in/hg once the infusion is complete) which would result in creating voids?
If I had any types of small leaks would it be introducing the air back into the laminate in large volumes?
Any help is appreciated, thank you very much!





RE: Resin Infusion Voids
Chris DeArmitt PhD
President - Phantom Plastics LLC
Consulting, ideas and training on plastic materials
www.phantomplastics.com
RE: Resin Infusion Voids
RE: Resin Infusion Voids
Chris DeArmitt PhD
President - Phantom Plastics LLC
Consulting, ideas and training on plastic materials
www.phantomplastics.com
RE: Resin Infusion Voids
The heat is then ramped up to 100c from 50 at this point. With the heat still at 100, we should try lowering the vacuum?
Just wanted to clarify, wasn't sure if you meant that the heat and vacuum were a problematic combo or if both were troublesome.
Thank you!
RE: Resin Infusion Voids
Here are some basic principles. Total pressure on the bag is equal to fiber compaction pressure plus resin hydrostatic pressure. This relationship always holds at any point. The lower the resin hydrostatic pressure, the more likely that a bubble will grow or form. The less the fiber compaction pressure, the thicker the fabric ply will be. Vacuum cannot remove air or volatiles unless there is an open channel for the volatile to flow through.
RE: Resin Infusion Voids
Slow down the resin flow close to vacuum line placing the vacuum tubing at 50-60 mm from the laminate edge ( dont' place it on the laminate !! ) and use some flow stopper/retarder below the vacuum tubes ( peel ply, dry fabric work fine)
Make proper use of resin trap that must be sized according to the volume of resin involved. Let the resin flow from resin tank to the trap without interruption of resin feeding from tank. Let the resin gel and only then decrease slightly the vacuum.
I hope it helps