stumped by vac leak after infusion starts

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#1

Hi, I’m completely new to infusion and making a few test panels before an attempt at infusing a hood for my racecar. My test panels are 12x30 inches, with a total of 3 layers of 2x2 5.7oz twill, and one layer of lantor soric XF (2mm). I’m using a plate of steel as my mold, grey mastic tape and nylon bag material. I have about 3 inches of sacrificial laminate on each end of the part. I have a single layer of peel ply and about 6 inches of green mesh on each end. The green mesh overlaps the section of material containing the soric by 3 inches or so. The spiral material is on top of the mesh, and I have another layer of peel ply covering the mesh, to prevent the bag from being pulled down into it.

I’ve done 3 test panels and each one has failed in the same way. With each one, about 5-8 minutes into the infusion, the bag starts to get slack on the resin side – especially near the feed spiral, and the resin pools inside the bag instead of proceeding through the part. Once this occurs, flow from the resin cup stops. The bag stays tight on the dry side of the part, and my gauge continues to read 29in Hg. I tested last night’s bag before starting, and it held vacuum with no measurable drop for 90 minutes before the infusion started. I assume I have a vacuum leak causing this, but I cannot find it. I’ve used a stethoscope, and clamped the feed line in the hopes of finding the leak once the bag goes slack, but I haven’t been successful. It seems strange that the bag would be fine for an hour and a half, then only leak once I introduce the resin, but that’s what has happened 3 times now.

I’m stumped, and could use some suggestions on how to troubleshoot and what to change for my 4th attempt at a test part.

Thanks!

#2

What type of resin are you using? Is the resin designed for infusion? Infusion resins typically have low viscosity (100 - 300 cP) and no thixotropes like in a laminating resin. If the resin is too viscous it may flow a few inches and stop even though you are still pulling 20 "Hg. Once the flow stops the material that has already been wet out may spring back like you mention especially is the resin supply is elevated above the part.

#3

What type of resin are you using? Is the resin designed for infusion? Infusion resins typically have low viscosity (100 - 300 cP) and no thixotropes like in a laminating resin. If the resin is too viscous it may flow a few inches and stop. Once the flow stops the material that has already been wet out may spring back like you mention especially if the resin supply is elevated above the part.

#4

Indeed it sound like you are using hand laminating polyester or vinylester.

Another option is that the 3 inch overlap is not enough to let resin pass through efficiently. however, this should show directly in the beginning. (slow infusion)

lso with Soric (but totally unrelated) it needs about 30 minutes of vacuum to equalise pressure.

#5

I’m using MAS low viscosity epoxy: http://www.jamestowndistributors.com/userportal/show_product.do?pid=3440&familyName=MAS+Low+Viscosity+Epoxy+Resin

I have the resin cup and the part both sitting on the same workbench.

#6

MAS low viscosity epoxy isn’t very low in viscosity…at least compare to infusion specific resins.

#7

If mixed with their own MAS hardeners, the viscosity is relatively high: 550-650 cps. (mixed)

For infusion you are targeting for some 100-200 cps.

This might be the reason for the “stall”. Anyhow, it is advisable to look for a lower viscosity epoxy, and also when the infusion gets slower, take a marker and mark the resin front. This at least shows the progress when things get slow.

#8

Thanks for the suggestions. I switched to MAS Infures for a couple of test parts, which seemed to work ok. I prepped the mold for my hood and after chasing a couple of leaks, the bag held vacuum with no measurable loss for over 2 hours. The reinforcement was 4 layers of 5.7oz and a single layer of 2mm soric. Total infusion time was 84 minutes to feed clamp, and the bag held great the whole time. Unfortunately, it was only around 10in Hg on the gauge this morning. We’ll see what the part looks like tomorrow night.