I only have a small vacuum pump for infusing that pulls about 27.5hg MAX. I seen to get voids on everything i make so far would a bigger pump help this?
No, as long as you’re getting to full vacuum on your actual layup. An infusion at 27.5 in hg with a 3 cfm pump is the same as 27.5 in hg with a 1/2 cfm pump.
thanks for this.
but the 3 cfm pump would start the vacuum process faster, correct? (with the initial evacuation of air)
hopefully that made sense.
Not speaking from experience, but the larger CFM pump would draw the vacuum faster and make up for any leaks better, but 27.5 in Hg is the same regardless of pump cfm.
thanks - that is exactly what i was looking for.
-Andrew
Exactly as romoman said, the CFM is how much air it will move over a specified amount of time, in this case Cubic Feet per Minuite.
Vacuum pressure is exactly that, pressure.
An example of this would be, if you have two different pumps acting on two identical sized bags both of which were leak free.
a) 6CFM that will pull vac to 29Hg
b) 3CFM that will pull vac to 29Hg
In this case both will end up pulling down to the same amount of vacuum, However pump ‘a’ will pull that vacuum(29Hg) in half the amount of time that pump ‘b’ will take to get down to full vacuum (29Hg).
I hope that this helps.
I just see a lot of people saying they pull 29HG plus and on a good day mine pulls 27.5HG. Am I right in saying that the higher the HG the more pressure is placed on the part and making less voids?
More HG does mean more pressure on the part and reduced likelihood of creating voids. It may not mean complete removal of voids though.
How can i pull 29HG?
Higher pressure means more consolidation of fibers and less resin needed in part. That’s why autoclaves are so nice, with vacuum pumps you can only hit pressures of 1 atm. With autoclaves 2 or 3 atms are easily attained. And all that extra pressure means you’re packing in as much high strength carbon fiber in as little volume as possible which is the end goal.
Higher pressure also it means less likelihood of voids, but voids (in infusion) also depend on your layup, how fast you infuse, how thick your resin is, how fast it sets, outgassing of your resin, and probably another two or three factors I don’t even know about.
However try infusing at 8 in of hg and you’ll see how bad the part turns out.
I’m currently doing studying the effects of infusing parts at different vacuum levels. So far I haven’t tested the resin content but measuring the thickness it is easily noted that less pressure means a thicker part even though the layup schedule is the same everytime. I’ll post all my results once I’ve completed the study!
Sorry for the late reply but I had to run out this morning.
You can pull 29 in hg but buying a better pump but as you start getting into 28-29 range things start getting pretty expensive. At some point it’s impossible to remove air with the vacuum pumps that you see on this forum and to reach a perfect vacuum you have to also use a diffusion pump in series with a standard vacuum pump.
Thanks its becoming a little clearer. I know a little about vacuums because we have electron beam welders at work (one of the biggest in europe) but its a lot more high tech than i am dealing with. diff pumps chillers and stuff like that. I just think in my case a little more pressure would do the job or help anyway!
drtcmm who do you work for up in lancashire?
Rolls Royce :):)
I am a welder! Where you from?
ahh ok I was thinking of another company that I know up there!!!