edges of panel under vac

I think rx is trying to get away from my artsy comments being valid. I appreciate both of you responding to my difficulties and offering advice on infusion.

As for the 60% vac; I'd like to try it again, but I think the bleeder valve is not allowing any introduced bubbles to pull through the epoxy; perfs; and top lamination, so I need a pump that can set itself. A vac pressure switch in my system would never work because the air bleeder would always bleed down. The only way a pressure switch would work is full vac.

I would degas if I try infusing.

Thank you both.

 

Can someone explain the physics of this, please? Or reference a layman's explanation.
Is the gas in solution a result of mixing the resin and hardner? If not, then surely the best time to remove it is before they are mixed?
Why would the air that is entrapped from mixing (and any gas in solution) be easier to remove in a bucket with a small surface area vs on the job with a colossal surface area? Assuming that both are under full vacuum.
Why is Scotchbrite in the bottom of the bucket a better bubble nucleator than the reinforcement, peel ply or infusion mesh? If Scotchbrite is better, why not position it at the end of the resin inlet pipe so all the resin passes through it during the infusion?
I appreciate that resin at 35C is going to be less viscous than at 25C, so the bubbles will release easier, but don't understand why they need to be released pre infusion. Why not either leave the resin to exothern to 35 or infuse it and heat it to 35.
I don't degas. Occasionally, some bubbles get caught in the surface and don't burst, but they are visual rather than structural. I don't see bubbles in solid laminates that have been properly infused. The thickest I have done is 20mm carbon, which was sliced and polished loking for voids, but didn't find any.

As far as Fallguys over specced laminate is concerned, we are comparing a good hand layup at maybe 10% (?) entrapped air and gas in solution with <1% entrapped air in an undegassed laminate and perhaps a little bit more than <1% in a degassed one. Is this worth the degassing effort and the associated risk of exotherming?

Andrew,
What is the reasoning behind 60% vacuum with a wet layup?

 

Fallguy, why would you go to the trouble of building a degassing chamber just to do a test infusion, after all you may decide its not for you.

Rob,
Do you need to degas? absolutely not.
Is the degassing worth the effort? to me Yes and I will do it only for smaller jobs as I have only one chamber say 15kg or less.
35'C is not a target for me, its a cut off point where I stop degassing even if it is not complete.

I found that there was very little dissolved gas in the neat resin and hardener so no benefit to degassing prior to mixing. Into a very high vacuum I placed small containers of resin, hardener, and a mix. I used fine crushed rock from my driveway to seed all three, the mix was a very small batch stirred only with no entrapped air. The neat samples generated hardly any bubbles, the mix some. My conclusion was that during the conversion process you can generate some out gassing under very high vacuum. I suspect the amount will be greater as the temperature increases. There would have been very little temperature rise in my small sample.

60% vacuum is only a recommendation not a target as I said I now use ~85% as that is the full capacity of one of my pumps. If I had a pump with a 60% full capacity I would be using it , I am not a fan of controlling vacuum with a bleed valve.
The 60% came about from two things.
One was from a batch of weft triax that I had, the +45/-45 fiber wet out easily the 90 was very difficult. Vacuum helped but oddly 100% was worse.
Second reason is that my observation with cutting up and pulling apart infused laminates at 100% vac (30-35% wt resin) made with common ambient cure boat building epoxy is that they will delaminate and fracture more easily than 40 -50% wt laminates made with same resin. Im not saying that they are not fit for purpose, but perhaps 40% wt resin is a better all round laminate if your goal is not to achieve the lightest possible structure.

My infusion practice now has also changed, after impregnating I change the pumps over to the low capacity pump, this increases the resin content and also gives the best visually looking laminates I have achieved consistently.
Cheers
Andrew

 

fallguy, I forgot to say if 100% vacuum is now giving you good results stick to that.

 

Fallguy, you would close your bleed valve and let the vac switch control the amount of vacuum.Also with a say 3-5 gallon storage tank to hold extra vacuum this gives you time to find the leaks not having to listen to the pump run.Yes you do get cycles of 2-3Hg but once the leaks are sealed your pump should't need to run.

 

Tungsten, what switch would you use? I am all for it because it would reduce fire risk.

As for the degas question, I know absolutely nothing about infusion. If you told me I needed chewing gum to make it work, I'd try it.

 

I posted a link in post #70,they have all you need.This also depends on what kind of pump you have.Some pumps don't like cycling on and off.Theres an article in the link that explains the different pumps.

 

Here is the link that shows the Physics behind it Avoiding voids by creating bubbles: degassing of resins before vacuum infusion http://www.lightweight-structures.com/index.php?option=com_content&view=article&id=34:avoiding-voids-by-creating-bubbles-degassing-of-resins-before-vacuum-infusion&catid=39

From a layman's term, dissolved gas is present in the resin and air is further introduced during mixing. High viscosity resin have trapped air that is difficult to remove but as it starts to catalyze, it heats up and releases some of the gas. Heating the resin will reduce viscosity and makes it easier to remove the trapped air. Normal degassing by introducing vacuum speeds up the process but is no guarantee of a void free laminate.

Two known method of degassing that guarantees void free laminate is by throwing in a Scotch Brite during degassing. It being porous and having a large surface area, helps break down the nucleod/trapped bubbles and facilitate the release. The other method, though counter intuitive is the Sparging method. Air is introduced at the bottom thru a fine mesh filter. This agitates the mixture and the smaller bubbles cling to the larger ones and floats to the top. I have not used this method but similar. We used ultrasonic vibrator and vacuum for small parts and a table vibrator for large parts.

So how much vacuum? 30" Hg (100%) vac is impractical to achieve as it means evacuating all air molecules. 28.5 Hg is the absolute vacuum. 28" Hg (93%) is the threshold used to prevent boiling off liquid styrene. "Typical vacuum", 27" Hg (90%) is known to have voids in the inter fiber areas. 24" Hg (80%) and 18" Hg (60%) are considered low vac levels.

Typical voids are from 5% to 7% range for open molding, to less than 2% for infusion with degassing. I would place the 3 to 2% as voids occurring in between fibers but not necessarily on the surface. This maybe acceptable to some as far as cosmetics is concerned but not to the composite designer.

Strength values drop about 25 to 40 percent at 5 percent voids, 2% void content has been shown to reduce interlaminar shear strength and flexural strength by 20%, flexural modulus by 10% (Ghiorse, 1993),longitudinal and transverse strength and moduli by 2% to 3.5% (Judd and Wright, 1978)and is cited by Judd and Wright (1978) as negatively affecting compressive strength.

One property which has been observed to increase with increasing void
content is impact strength. Judd and Wright (1978, p. 13) claim that “this was attributed to the weakened bonding contributing to a more extensive yielding plastic zone at a propagating crack tip.”

 

So how much vacuum? 30" Hg (100%) vac is impractical to achieve as it means evacuating all air molecules. 28.5 Hg is the absolute vacuum. 28" Hg (93%) is the threshold used to prevent boiling off liquid styrene. "Typical vacuum", 27" Hg (90%) is known to have voids in the inter fiber areas. 24" Hg (80%) and 18" Hg (60%) are considered low vac levels.

So, RX, a question.

Someone told me if I ran my vac too high, my epoxy would boil. Is there any truth to that? When I bury the needle on my vac setup; the thing reads 30" plus, but I don't necessarily believe it. Is this why the guy I talked to reduced his vac down to 26" you suppose (this boil concern)?

Is the boil concern the same for polyester, vinylester, epoxy? I'm assuming some of them have more styrene than others...etc.
My best parts so far have been under full vacuum.

 

I promised I'd post my numbers from the last panel that turned out much better.

Here they are.

Fabric weight 10.1#
Yards implied 7.35
Peelply wetout rate 35g/sq^m or 7 ounces
Bottom laminate wetout rate 120% or 177 ounces
Corecell wetout rate .7kg/m^2 at 100% or 134 ounces (this rate is completely wrong; it is for both sides of the panel and a wet mess!)
Top laminate wetout rate 100% = 143 ounces

PROCESS
Table wetout rate 17.5% of glass total = 32 ounces
Wetout above peelply rate 50% of glass total =76 ounces
Wetout above glass = 76 ounces
Wetout core 134 ounces and flip
Wetout core with 50% of top laminate rate
Wetout inside glass with 50% of top laminate rate (there is a lot of resin available in the perforations and wetting out the core and the glass at their given rates would result in wastage we have found)
Bagged at 70 minutes against 100g mass time of 120 minutes.
Full vacuum for 8 hours. (this is certainly excessive and I will reduce the vac time to 6 hours on the next smaller part off the table, but leave the part on the table for the same amount of time, minimum of 15 hours)

NOTES:

We did have a rather large amount of resin in the bleeder, however, we introduced 142% resin to glass to achieve the results. As I stated, my corecell wetout rate was for both sides of the core; not one, but we did not use any wetout rate on the top. The next time we are going to reduce the corecell wetout rate to 0.35kg/m^2 on the bottom, and perhaps introduce say 10% wetout to the top, as there was still too much resin on the bottom of the part with my error (spreadsheet). This would be roughly 5 pounds less resin to mix for a 10 pound glass. That resin all went into the bleeder... But the part is good. Perhaps with a little less resin; it might have been perfect. I had about 30 small bubbles in the part or roughly 4 defects per yard.

Thanks for any comments; even if you want to rip on my for the corecell wet mess bit. Good thing I reviewed it here, fixed my spreadsheet now!

 

Were you able to weight the panel to get a final fiber volume?

 

No. The panel is 32' 6" long and looks great. Weighing it would require lotsa fiddling with numbers as the panel has a rebate all around and high density inserts and some plastic staples, etc. we would have had to preweigh the 16' half panel sections first.

I do plan to weigh my bulkheads and can report back those numbers which will be same process, but 18 oz biax vs the 22 triax.

The resin percentages will be very similar. I'd say around 40.

 

Styrene is present in polyester resin and vinyl ester resin but not in epoxy resin. The liquid boils off at around 93% of full vacuum so keep at at less than 93% if you are using poly or VE.

Though it is possible to achieve full vacuum at 30" -Hg at sea level, not all vacuum pumps can achieve this. It takes a laboratory grade pump (whatever that means) for complete evacuation of air or full vacuum. Standard pistons and rotary vane pump can only achieve 28 to 28.5" -Hg, given the time. Either you have a laboratory grade vacuum pump or your gauge is not properly calibrated.

 

I have a lab grade pump, two actually. One is really old. I had it apart n cleaned the intake which had some graphite in it.

I think I ought to check the vac with another gauge just to be sure.

Welch 1402
5.6cfm


Maybe I ought to back it off after a bit?

Thanks for correcting the guy who told me my epoxy would boil under pressure. I couldn't find anything on it.

 

Hi sir I have noticed that you are very knowledgeable on many topics. My question is how would someone begin to learn about vacuum infusion. I have tried to read about it with minimal success. I am a visual learner. Is there anything that you recommend that mite help? Sorry this was off topic but I am new here and you seem extremely gifted on the topic.