infusing with contour balsa

Hi Peter, wow, so much great info there. I was a bit nervous infusing the platform as i had no backup pump, i did have a standby generator in case of a power failure though, so i am shopping for a better settup. There is a lot of good info on the vacmobile site. I think that the two biggest problems we are having is air infiltration and i think we need to slow down the feed, perhaps with a 30% shade cloth instead of the greenflow we have been using, we had plenty of gel time using a slow catalyst. I need to spend a few days going through your post as there is a mine of great info there.

Steve.

 

Sorry for the delay in posting photos. I was hoping to get photos of the finished product but it is still not done.so Ithought I should put up what I have. The infusion went well but we think the table might be leaking. This has yet to be tested but the leak down tests would suggest that something's wrong and I am reasonably confident that the bags have beenn tight.

 

Steve; the infusion job looks good, only some traped air is evident in the coosa region.
Regarding the bridging you experianced, are you using a tool to push the laminate into the right angle corners? I use ~100mm wide sharp pointed flat edge that I cover with around 5 layers of masking tape to push the laminate into these corners. The tool can be a paint scraper, timber wedge or plastic offcut anything with a sharp edge. Have not holed a bag yet and dont have bridging issues.
I also dont see what there is to gain by starting the infusion at a lesser vaccum and then increasing to max.

Hi Peter; I agree that the ideal vacuum for infusion is a perfect vacuum from start to finish providing that you have no dissolved or mixed in gasses in the resin. But in situations when you have mixed in air in your resin reducing the vacuum after the infusion does make a better laminate in my opinion. I prefer to have less voids and accept a slight increase in resin content.

Cheers
Andrew

 

Steve, I'm new here and was just reading through this thread. I did an infusion of contour balsa on our last project. Sealed the already positioned/bent balsa off with a silica/microballoons and epoxy mix, roughed it up, then infused over that. This kept the resin out of the end grain.

I have a bunch of 1", unopened balsa left as well as mas infusion hardener, if you need any of that.

 

Hi Andrew, we didn't use any type of tool, we just tried to push the glass down into the corner with our fingers with the pump at low vacuum so we could still move things, it looked like we had it dicked but apparently not, next time we will try some sort of tool like you said, we had a 16mm radius in the corners. We didn't raise the vacuum once we started, we used full vacuum on the dry stack for about an hour I think and then lowered it to about 80% before introducing the resin and left it at that until we shut it down after exotherm. I don't think the bridging was in the glass but rather the peel ply as the resin is in the corner above the laminate, I could sand most of it out of there if it was a weight critical part. When we had the pump at low vacuum while we were pushing the glass into the corner it spat out a lot of oil which reduced a lot when we upped it but still a lot of mist. We have been using a Robinair 6cfm pump meant for the hvac industry but have no backup so I just bought a new old stock Busch R5 RC 0025 (about 18 cfm) pump on ebay, should have it Thursday, it is one of the pumps recommended by vacmobile and is a proper industrial pump capable of running for hours at rough vacuum which is what we have while chasing leaks. We will now be able to keep the existing pump plumbed into the resin trap ready to go as a backup and I do have a generator which we can have running at the ready.
ON2, The resin uptake in the core is a lot better than predicted by Baltek, we used 64 lbs of VE resin to wet 54Lbs of glass and about 60ft2 of 1" contour balsa. For future reference, baltek claim that the resin uptake is less with the 6lb balsa than the standard 10lb stuff.

Steve.

 

Steve; get an oil recovery system for the pumps if you are using them for anything less than full vacuum capacity.
I did understand that you reduced the vacuum to 80% prior to letting resin in and then held it constant. I assume that you still think that you can not use 100% vacuum with VE, has the resin manufacturer told you this? have you done your own check?
When pulling the bag down I draw the air out to a point just before you have vacuum and then isolate the pump from the chamber. This means the pump is then working at full capacity and not spitting oil while I go around and eliminate the bridging. When using a pointed edge tool only push into the corners dont run the tool along the corner as this increses the risk of puting a hole in the bag. Next stage I turn the vacuum on again to ~ 5% and isolate again and then go around again eliminating the bridging. When done then increase to full vacuum.

Peter; you have experiance with all resin systems, can you comment on vacuum levels with VE resin.

 

Andrew I have observed ve boiling in my catch pot when vac bagging stuff years ago. It may not be an issue as the dissolved air expands at the resin front when infusing and thus lowers the vacuum at the resin front.

 

Andrew, I have not done any specific tests re the reduced vacuum but have read in a number of places including on these forums to do so and I cant argue with the results, this part is better than the previous ones for sure. It seems that with the coosa I need to drill the holes closer, maybe 20mm oc instead of the 38mm I used but eliminate the saw kerfs on the tool side, the resin front raced ahead on the coosa and was coming up holes well ahead of the front on the bag side, but we still got some of those white dots in the middle of some blocks. I just received my new pump yesterday, its a proper industrial, run all day type of pump that will handle rough vacuum better, my existing pump will be plumbed into the resin trap as a ready to go backup. I would sure love one of the Vacmobile traps but $$$. Beautifully thought out trap though. Maybe one day. Ive finishing the platform now adding stringers, wet lammed on the bottom and cutouts for venting carbon monoxide from beneath. The cutouts are perfect, I love this infusion stuff.

Steve.

 

What kind of pump did you get Steve?I was eyeing up the Robinair like you have but since reading your posts I'm unsure.

Thanks,

 

Get the bigger, blue Robinair, not the red one!

The smaller red one breaks in no time. I have 2 broken red ones and 2 working blue ones to prove it. A total of 4 pumps bought.

 

Hi Andrew, I'm working with a contractor at the moment on fibreglass walkways and we are infusing with VE at <60millibar or 6000Pa absolute. Which is 94% vacuum producing very clear laminates. One atmosphere is 101000Pa. 101000-6000=95000Pa 95000/101000=94% this is measured with an absolute vac guage before infusing. At 1atm styrene boils at 154deg C so neglect that at 25degs it boils at 798Pa (99% vac). So unless you have an absolute vac guage and get an understanding of your process pressures you won't know. However its apparent that if you are infusing at 80-90% vac you can't boil the styrene, at 25deg C water boils at 5000Pa (95% vac) so you are above the water steaming pressure as well. But you have to consider the relative humidity in the area and the dew point to remove all possibilities. There are other solvents in PE and VE resins that can outgas at much higher pressures read the msds and see if there are other solvents components in there for that particular resin. I havn't had any outgassing from good quality PE,VE or epoxy resins at 1000Pa. But I degas most of my stuff because I only do small things. Doing big objects can't degas big volumes of resin but if the flow front is smooth and steady and the vacuum is scavenging correctly then jobs work fine. If you place a small cup of water in your resin trap and it boils at your process vacuum then you are removing water from your job unless to acheive say 90% vac you are bleeding air through the job of which you are bringing in new vapour from the air throguh the bleed. If this makes sense? Peter

We usually work lower then 60mbar but in this case the parts require a low cycle time to be viable so we are not vacuum soaking them just hitting the vac pump stable press and bag stable and turning on the taps. In the silicon and polyurethane industires that produce insulators and pot semiconductors 100Pa is a usual process spec. Gun boats in USA claim to infuse their 60 footers at 150Pa which I find difficult to swallow as its hard enough to get a small part to 300Pa in a lab vs a huge boat but hey I'm not an expert yet.

Since we are getting technical - The above vapour pressures are for the "free surface" in our case this is the flow front only. We then have the problem of the "champagne effect". If your a champagne drinker or soda drinker you will have seen that you can get streams of bubbles coming from a defect in your glass. This is called an initiation site. So gas molecules are much smaller then liquid molecules so gases can move around in between the liquid molecules. They are trapped by surface tension and molecular forces. They can only escape from a free surface if they have enough energy (this is provided by the local temperature)but if there is a little cave somewhere where the gasses can congregate and get some volume up then the free surface vapour pressure law does not apply and they can bust out of the liquid by themselves (they effectively create their own free surface at the defect). Our fibreglass and media and foam provide huge amounts of initiators (small defects or caves) that can provide this low energy path to gas freedom. And like the champane bubbles they can do this at a higher pressure then the free surface vapour pressure prediction says.

So at the flow front it must look like the waves breaking on the beach, turbulent and frothy including all the air that is available in a poor vacuum environment (this is why I choose to have as deep a vacuum as is possible) Then as the flow front moves away there is a pressure gradient so near the front we are at the process vacuum pressure say 90% vac then say 300mm away from the front we at near atmospheric pressure (remember we have the bag pushing down on this area so we must be near atmos) so any bubbles that were introduced at the beachfront should be compressed and dissappear. But then we have all those initiation sites that the gasses are rushing to find and this must be the fine porosity we see in all infusions when we look at them at say 10x magnification. They are at fibre intersections, groove intersections and surface roughness areas in cores. So the only way I see to produce very clear laminates is to degas degas degas and use as low a vac as you can get. Because of the gas law where pressure and volume are related only use bags that are decreasing or stable in volume (ie pressure), have no leaks on the wet side of the job and have lots of vacuum scavenging around the job. Plus I think perimeter feeding vs linear runners is the way to go as this is a better fill stategy and its a better vacuum stategy. There are a lot of areas such as double bags, semi permiable membranes (tyvek), double edge bags, autoclave vip, rigid moulds etc which I place in the advanced infusion area that will go public very soon that adresses all of these physical problems. Aerospace are adopting "out of autoclave " process (VIP) hand over fist at the moment so your all on the right path. Hope this helps. Peter

re vacuum traps - get a 20 litre plastic bucket that a 10l bucket fits into. Up-end 20l bucket on a melamine sheet. hand laminate over the top say 12mm thick. Break free and trim get a 25mm thick perspex lid, hurrey.. a beautiful trap thats easy to get a bucket into and out of!! easy to clean also.

 

Hi Tungsten, I read the through Vacmans notes on the Vacmobiles website and there is a very informative article on choosing a vacuum pump for composite work that made a lot of sense to me. I had originally bought the Robinair cooltech model 15600 (blue one) because my son and i had attended one of Derek Kelsalls 3 day workshops in 2012 and that was the pump they had used to build a 42ft cat and were starting on another so clearly it is up to the task. However i got a bit nervous not having a backup for the swim platform so i started looking for a better primary pump and will keep the Robinair as the backup. One of the pumps recommended on the vacmobile site came up on ebay last weekend so i bought it, its a Busch R5 RC 0025 model, a real industrial pump about 18cfm, about as big as i will ever need. Its a new, old stock, pump without a motor so i need a motor to get it up and running but i expect when the dust settles i will have less than $800 in it, well worth it imho for a pump that should last a lifetime. I also have had an Edwards pump for years the i used for vacuum bagging but i had problems with it last time i used it . I recommend reading the vacmans notes before choosing a pump.

Steve.

 

This is why i think its worth buying a real industrial pump and keep the smaller ones for a backup (and get a generator)

Steve.

 

The generator is so important, I'm not sure one should ever infuse without one.

I had a power failure during an absolutely huge infusion. Had the pump back on in moments, with generator power.

Also, an industrial pump woul work best. I agree.

 

Hi Peter, thanks for the styrene boiling point information. I think this supports my recommendation to infuse at maximum vacuum Steve's pump delivers.
I agree with all you say, but still not sure why you dont like my practice of reducing vacuum after impregnation for infusions when you have not degassed the resin.