How high a vacuum do I need ?

General Composites Discussions Equipment Talk
#1

I am looking at moving into the world of resin infusion from wet layup and I am considering my vacuum pump purchase. I have a good idea of brands, types and performance and I will be buying something decent second hand off eBay. However one question I haven’t found a solid answer to is how high a vacuum will I need?

Is 25" HgV enough or do I need 29" HgV or greater? Does the strength of the vacuum improve the fibre to resin ratio as long as you don’t get so far that the resin gets to a point when some of the components change phase?

#2

Well you don’t HAVE to reach 29", I started learning infusions on a pump that only reached 24" and I think Canyon has experimented as low as 18" maybe I read his thread wrong tho. Twodollardoug recently did a build on a pump that reaches 26" and he spits out good parts. So in a nut shell try to get the highest vacuum you can, but don’t be worried if it doesn’t reach 29".

#3

The reason I ask is I have seen some nice second hand pumps with 25 HgV for sensible prices but the cheap HVAC pumps offer 29 HgV. I didn’t want to sell my self short and get something un-suitable.

#4

Well “suitable” depends on what size of parts you are trying to infuse and how often you are going to use the pump. All day and night everyday for full production in a professional composite shop then go with the large pump. If this is something that is for at home then the HVAC pump is fine, properly maintained they will last for years. I’ve only seen problems with them when people didn’t have filters or wouldn’t change the oil.

#5

the higher the better. higher vac gets you less voids, but voids present would be larger. lower vac makes it very difficult to remove moisture from the laminate unless you increase temp. at 25HG you would need to get the laminate above 100F to remove moisture, where as if you can pull 29.9hg you can remove it around 14F. also with lower vac you have less compaction.

#6

I’ve been told viylester infusion resins will boil off styrene if pulling more than 17" vac causing bubbles in the resin front and the fnished laminate. Is there any truth to this or should I pull as deep a vacuum as possible regardless of the type of resin (vinylester / epxy) I will be infusing?

#7

there is, thats why you get a resin system designed for infusion.

#8

This has been the experience in my research. I went down to 17 in Hg and the infusions came out riddled with voids. ~25 was about the lowest I could go with clean surfaces. Pressure did affect how fast the infusion went though and from simple fluids mechanics a lower pressure means you’re limited to shorter infusion distances.

#9

what type of resin? how high of a vac is your pump capable of? how long of a vac soak did you do before infusing?

#10

700 Cps infusion epoxy resin, I let the vac sit for 2 hours before infusing, ambient temperature was about 70F. The pump is capable of 27 in Hg.

#11

without seeing the setup and laminate stack its tuff to say. I would imagine we are talking about surface defects though correct? I think you would have much better luck at higher vac, longer vac soak time, and lower viscosity epoxy. your infusion media could be flowing too fast for that high of viscosity resin. prolly the lower vac resulted in less fiber compaction which added resin flow through the fabric better. Just guessing based on limited info.

#12

Thanks for the pointers. I was looking at this VT4.40 pump http://www.remequip.com/downloads/picker/Becker/Vacuum%20Pumps/Rotary%20Vane%20Oil-Less/VT%204.10/VT4.10%20Data%20Sheet.pdf

#13

The lower vacuum infusions had a lot of surfaces voids near tow intersections. There weren’t too many more defects inside the composite itself. All my high vacuum level infusions came out with perfect or near perfect surfaces, especially when I let them sit to remove all the moisture like you said.

#14

oh ok, I misunderstood what you were saying.

#15

An update to the thread. I picked up an Edwards E1M8 off eBay which should be capable of 9.5m3/hour and 3 x 10-2 mbar.

Just need to make some space in my garage and I can start using it.

#16

yes vinylester boils if vac is too high even infusion types, boil point depends on styrene levels and here in RSA differs from manufacturer to manufacturer.

#17

I decided to research the myth of styrene boiling over -0,6 bar. (60% vacuum).

I took a vacuum chamber with transparent lid, a mixing cup with styrene, and a vacuum pump capable of creating a deep vacuum.

I placed the styrene (100% pure) in the vacuum chamber, and pulled a vacuum. At -0,6 I started to watch closely: nothing
-0,7: nothing
-0,9: nothing
-0,98: nothing
actually with that pump I could not get it to boil.

Then I repeated the same with a cup of styrene, and a cup of water. As expected, the water boiled at -0,98 or so. The styrene was still sitting still. Then the water vapour condensed on the glass, and I quit the experiment. (I was doing this in my house, and the styrene started to smell)

About vinylester boiling off: Peroxides that contain H2O2 react with certain ingredients, and make the vinylester boil. Especially when pressure is dropped, the bubbles can form. This might be the foaming that VE is notirious for.

Either wait some time after mixing, and before shooting, or degass the resin before shooting. Use peroxides that are low on H2O2.

#18

yes, the wrong hardener can really make the VE foam. you’ll get loads of air formed, and a lot going along the channels. The laminate you end up with looks like one wich is hand-layup without degassing.

(I was doing this in my house, and the styrene started to smell)

The things people do in their houses. experiment with styrene, postcure epoxy in their kitchen oven, or like me, polyester filler, and the sanding of it, on the kitchen table…

#19

The neighbours once called the fire brigade, as they smelled a gas leak. I was laminating with polyester in the garage…

I know of a guy spraying PU paint (DD lak, for Sushos information) in his bedroom. Sleep well…

#20

truth as in it will cause bubbles. However, they are present due to the chemical reaction happening in the first place. I have done TONS of VER parts, and never had issues with the resin itself causing bubbles.voids