Hi guys what role does infusion speed play on the final outcome of the part and what’s normally recommended, fast or slow.
In my experience, as slow as your pot life can allow. I haven’t noticed any negative side effects of infusing slowly, while infusing too fast can leave pin holes.
Infusing too quickly can leave pinholes. So as Hanaldo said, the slower the better.
My problem with infusing too slowly by means of clamping the resin intake line is that this clamp ends up speeding up the resin at that segment, sometimes leading to air bubbles dissolving out (lower pressure where it’s moving faster at the clamp). If you’re not using MTI hose those air bubbles can easily cause problems. Using smaller intake tube diameters can cause similar problems.
Best way to moderate infusion speed, IMO, is by the temperature of your resin. Get it to the correct thickness that yields that right resin front speed. This is really only a problem if you live in hot environments (Texas…) and mix your resin outside. Any of the typical resins meant for VIP below RT are usually thick enough to yield a slow enough infusion.
thanks for the response. I’m using MTI hose all the time but never clamped the inlet to slow down the resin but 2 days ago i infused a part and slowed down the resin by clamping the inlet on and of, so when i demolded i noticed that i had pin holes which was a bit strange coz ever since i started using MTI hose i never has pin hole issues, the only issue which i had was that i wasnt quite satisfied with the amount of resin on side facing the mold (sort of didn’t have enough resin though the surface was not dry) but this time around after clamping on/off the inlet i was very much satisfied with the amount of resin on top of the laminate apart from the PIN HOLES on the part. note that there was no pressure drop from the 30min pressure drop test i did.
Infusing too slow will cause more problems than infusing too fast. Very important is the vac level. Than better the vacuum is, than less critical is a fast infusion.
If you infuse slow you have a longer pressure drop area at the flow front which can end in expanding bubbles or outgassing the resin.
And bith things will cause pinholes. Too fast can only be critical if you overrun dry areas, but this will only cause problems if you have too many differences in thicknes.
Very interesting, any idea why this time around i was able to get more resin on the surface of the part which is facing the mold coz i’ve been struggling to get that same finish when infusing at high speed. lastly note that i had 2 layers of 200g 2x2 twill
I don’t know why you now got a more resin rich part. Have you tried to place the resin pot above the part and wait a few minutes after the resin hit the MTI hose everywhere before you clamp it? Than you should get the same result.
Can you elaborate on that DDcompound? I too have noticed these expanding air bubbles, which seem to be exacerbated by trying to slow infusions down through clamping the line - and I can’t tell if it’s because clamping the line helps dissolve out air at the clamp or if it’s because the reason you just stated. As far as I know, nearly all infusions have some amount of air bubbles at the infusion front, right? Are those bubbles just small enough to collapse into something that doesn’t produce pinholes once the vacuum is relieved?
Most times when I degas the resin there are at least no or only very few airbubbles at the flow front or in the resin.
As long as the resin line is open the ambient pressure is pushing the resin in the part. So there is only at the flow front a vacuum working. The ambient pressure keeps the bubbles in the resin very small so that you can not se them.
If you slow down the infusion speed than bigger the pressure difference becomes because the vacuum is working at the resin because it is not pushed in fast enough.
This will end up in a laminate with lots of voids. If you clamp too long the resin can start degassing so that some gas will stay in the laminate.
You can test this effect by infusing glas with undegassed resin on a glas plate.
Let the infusion run and you will only see few bubbles at the flow front. If you now clamp the feedline you will see that there will suddenly be lots of bubbles everywhere in the laminate. If you only close it short and than open the feedline again the bubbles will become small again.
If you keep it clamped for a longer time and than open it again the resin might have started degassing, and than most of the bubbles will not become small again.
Also nice to test the effect of the MTI hose. Infuse one panel with MTI and one with spiral.
When the resin hits the MTI hose and you close the feedline the resin will become and stay clear.
If you clamp the feedline with the spiral you will see that the vacuum is still working and the resin will become milky because of thousands of tiny airbubbles.
Nice, thanks for the response DD. I have never been able to do an infusion without having some sort of bubbles appear at my resin front, even after large amounts of degassing (15+miniutes). I guess they are introduced from unclamping the resin feed line too quickly. I’ll have to work on getting rid of those. However I know I’ve seen other people on the boards comment before on how they too have a couple of bubbles at the resin front, and that it is a fairly normal thing…but ya I can see why it would be a problem.
Bubbles at the flow front are not a problem. But it is better if there are none. With some resins you will never be able to get rid all of them.
You should never clamp a feedline during infusion, that will always cause voids and/or pinholes.
Ok, but as you know is common practice to clamp feedlines at the end of the infusion while the resin front has not arrived yet to the limits of the piece, how come that clamping then does not produce the voids/pinholes that you mention ??
There will only not be any yoids or pinholes if you do not clamp too early. You normally have resin pooling or a resin rich area around the inlet. You clamp a little before the resin reaches the end of the part to suck resin from the resin rich area into the dry fabrics.
If you clamp to early you will have voids and pinholes, if you clamp to late you will have a more resin rich laminate.
To prevent this we made the MTI valve.
So, to control the resin richness of the laminate, reducing the vacuum levels is not necessary ??
I would also like to hear what would be your advise in another thread I initiated here
bubbles at the flow front is common just ffrom the resin flowing in a turbid manner simply from the fibers of the reinforcement that it’s wetting. as long as you are at a steady state that the front isnt racing way ahead of these bubbles clearing you are ok and they will be pulled thru the part clean (unless you have a bridging site and they will collect here)
Also, if you infuse too fast, resin will leave voids in the tows, racetrack, and leave a very weak part in your hands. Slower infusion will allow the resin to fill the tow more, and stop bubble voids due to racetracking. Talking micro and macro scale here, not really things you can see.
I am having inconsistent results when infusing and never know how the results will be (pinholes on the surface or microvoids within the laminate) even though I keep the whole process and set up consistent. Sometimes there are bubbles at the front, others none. I’ve noticed the bubbles at the resin front in my infusions are caused by gas rising to the flow mesh escaping from the laminate while being wet out. In the past I have performed 10 minute degassing then raised it to 30 minute to see if there is a difference. No different in results. 
With all factors being the same I am coming to the conclusion that I have to focus mainly on infusion speed. Can anyone be more specific in infusion speed. Fast and slow is a relative term depending on a number of factors.
Can anyone supply some info about composite thickness that is being infused and rate of speed (mm/minute or inches/minute) in comparison to “fast” and “slow” infusions? I understand that infusion start out fast then slow down as the resin must pass through more material but if I can get some flow rate numbers as a comparison I can see if I’m infusing too fast or too slow and make adjustments.
Also what diameter feed hoses are being used?