infusing with contour balsa

Discussion in 'Fiberglass and Composite Boat Building' started by Steve W, Jan 9, 2014.

  1. groper
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    groper Senior Member

    Yep, stupid mistake - i always work with weights... The setup and numbers look fine with me... not sure where your going with this, but carry on...
     
  2. AndrewK
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    AndrewK Senior Member

    Peter; make a start at 300Pa I have a very good pump.
    You asked earlier for weights and thicknesses of laminates with the vacuum backed of to 85% after infusion. I havent checked these as my priority is not resin fraction when I do this. I allow for 35% wt in my calculations and it must be close to this as I have not been caught short or had resin in the vacuum lines.
    The only accurate figure that I have is not for a tipical laminate, it was a test sample with a 4:1 ratio of UD:DB. Resin content was 29%wt, but dont hold me to the 85% vacuum as I did not measure this accurately as I was not concerned with that. Its what my diphragm pump delivers.
    For infusions undre full vacuum that my pump delivers I calculate for 31%wt so that I have a margin of safety. My initial trials showed 29.5 - 30.5%wt for thin laminates of DB, Biax and triax, so agree with the 30%wt typical.
    Best I have seen is 22.4%wt for 12,000g UD alone.

    Intresting that you say CS matt has same resin wt% fraction as stitched. I assumed not as I have found that DB with stitched CS backing (no binder) aids flow. At times I use it for this and also as the first layer for secondary bonding infusions assuming it will make a better bond. I think I may have seen some literature supporting this.
     
  3. petereng
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    petereng Senior Member

    Hi Andrew,
    If you infuse at 300Pa then I'm sure you will get 30% Rw every time. But if you back off to 15,150Pa (85% vacuum) then I'd expect 35% to 38%. So when you use the diaphram pump you just pump down and use it at max vac through the whole process? I've had woven roving and csm tested at 30%. By using an internal "bag" and vacuum scavenging I have built at 20% but its not a scaleable process for bigger parts. Happy to use 1000Pa as the maths are easier.

    Re: bonding infused laminates. Some of my clients have had trouble bonding to infused laminates. Theres not much resin to bond to. Plexus is good as it has different surface functionallity to PE or VE systems. We had to develop a priming process to get up to spec bondline tests. Cheers Peter s
     
  4. groper
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    groper Senior Member

    No Pete, Andrew infuses at 300 pa then drops the vacuum back to 850mbar once the resin line is clamped.

    Both of us don't do a lot with PE or VE. .. Mostly just epoxy...
     
  5. Jim Caldwell
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    Jim Caldwell Senior Member

    Groper, Looks like your out of the Cyclone impact area?
     
  6. petereng
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    petereng Senior Member

    Hi Groper -Yes hope Ita was OK? To answer the Q about where I'm going... I'm going to describe the infusion process using hydraulic pipline theory. I've been researching VIP and doing VIP for over 20 years and everyone has an opinion about whats going on but theres no overall theory to expain various effects. I think an hydrualic approach is useful here (I've never seen nit described as an hydraulic system yet it is). So the next question is where do we put our resin bucket? If the resin level is below the job this is called a sypon (because if we didn't have the vac pressure at the other end the resin would fall back into the bucket), if its above the job its called pressure feed. Most set up the resin so its below the job. ie the vacuum pressure has to lift the resin a small amount to get to the job. This places the resin in a negative (suction) pressure profile which is a disadvantage in terms of bubble production. Our vacuum is below 1000Pa , 1atm is equivalent to 10m of head so using vacuum is the same as setting up two reservoirs with the levels at 10m difference and our job in the middle. This allows us to establish the energy line, the hydraulic gradient and the dynamic gradient. Then we add friction and the whole system is described. We can then use entry and exit loss theory to predict local pressure spikes. So now we would have a tool to understand and improve the process. Currently we use Darcys law for porous flow to predict the flow front speed and distance and this is very accurate, on the gas side we use the ideal gas law and this is OK as well, but we don't tie the lot together, hopefully hydraulics will. So Andrew do you have a "T with valve" at the vac pump and bleed air through the pump to control your line pressure? Need to describe our theory "system" accurately. Cheers Peter S
     
  7. oceannavigator2

    oceannavigator2 Previous Member



    Putting peel ply in the infusion stack helps a lot with this. If you use the right stuff, you can bond directly to the infused part without sanding.
     
  8. petereng
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    petereng Senior Member

    Hi ON2,
    Not really. We do considerable testing on these things as the bits we design/build hold people up in the air and need to meet crane codes. On one test rig the pass load is 7 tonnes and we have had things fail at <100kg!! If you just use peel ply you will get whats called "weak bonds" see attached white paper. The current state of the art secondary bonding technique is to grit blast surface then use a plasma torch or arc to clean and "excite" the surface. The plasma adds extra functionality to the surface and you get excellent bonds even on low surface energy plastics. Thats how they print on PP and PVC they clean the surface with plasma. I'm looking at designing/ building my own plasma arc cleaner at the moment. Theres lots of video showing this type of process on the net if you search for plasma cleaning/arc cleaning etc. The other thing we have found is that the secondary bonding using putties leads to weak bonds as well . Due to the high viscosity of these adhesives they do not wet the surface entirely. We found this through our high voltage testing programme. The 60kV finds its way through the bondline unless its perfect. So we had to develop a priming system to ensure insulation values were met and this also increased our bond strength. Cheers Peter s

    http://www.youtube.com/watch?v=DN5rCKOS52k PLASMA VIDEO
     

    Attached Files:

    Last edited: Apr 13, 2014
  9. AndrewK
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    AndrewK Senior Member

    Peter; 1000Pa satrting point is fine, when infusing on the table my bucket is 300mm below. Guessing the maximim I have had is ~1000mm below.
    No I dont have a T, I precalculate my resin requirement for the job and by the time I have only a small amount of resin left I clamp the lines, the resin front is usualy ~20-40mm shy of completion. Next I phisicaly exchange the oil vane pump for the diphragm pump, the job bleeds down through the pump to the diaphragm pum capacity. I then unclamp a reisin line and slowly allow all of the resin in the bucket to enter the job. I think contoling the bag pressure via bleeding air through the pump is more difficult and can lead to unsteady pressure. It can be done using a needle flow control valve.

    Perhaps we should start another thread dicussing resin wt% fractions and what is considered too low for the typical boat building epoxy and VE resin. Including secondary bond infusion practicess, should it be done??
    My gutt feeling is that 30%wt may be too low? 35 -40% makes a tougher and allround better laminate??
    Only contribution I can make is based on observations of breaking and delaminating off cuts. Can you share findings from test samples from your clients?

    Cheers
    Andrew
     
  10. petereng
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    petereng Senior Member

    Hi Andrew- I typically spec 30-35% Rw for infused laminates. This is a good range to have. Your pump crossover sounds complicated, a needle valve would do the same thing as long as your pump can cope with the blow through. Nearly have my first pressure profile figured out for discussion, I have swapped it for a 300x1200mm laminate I did some years ago becuase I have all the flow data. I can't discuss secondary bonding much more because most of it is propriety info at the moment. Lets just say prep as speced by the manufacturer but use as runny a putty as possible! and check your dew point temps and run a hot air gun over the surface to remove water vapour! & buy one of my plasma cleaners when I get it on the market!! Peter

    lap shear strength of adhesives - most composite adhesives specifiy a lap shear strength of 15-30Mpa there are a couple at 40MPa. When you test with very good preparation you can match the manufacturers numbers. When you get the guys on the floor to do it you get about 2MPa for all the adhesives. This is epoxy, acrylic (plexus) and urethanes and combos. So be very cautious and use as big an area as possible and use big safety factors at least 10x based on area. One area of surprise is that in a workshop you get lots of fallout and contamination so be very vigalent with keeping dust out. Dust attracts moisture so use a hair dryer or heat gun on parts before bonding and get it up past the dew point temp but not too hot to affect the gel time. Finally don't sqeeze the bondline too tight try to get a 1mm + bondline or the suppliers spec thickness. A zero thickness bondline is zero strength! so control this as best as possible with toothpicks, washers, dry cloth, whatever you have to get a consistant thickness. Cheers Peter S
     
  11. groper
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    groper Senior Member

    Used to put a High density plastic into the decored foam parts of some stuff i used to make years ago... the process was to scuff the hell out of the plastic using a very coarse grit, then after the resin was catalyzed and directly before applying the resin to it, id go over the plastic with a gas blow torch to help ionize the surface. The process worked well, i never had any adhesion issues doing it like that...
     
  12. Steve W
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    Steve W Senior Member

    Hi guys, ive got to say this has turned into the best thread ever for me, so much good info. On the secondary bonding subject, most people "get away with" their bondlines because the majority of attachments in a boat are fairly lightly loaded and the faying surfaces fairly large. Ive been bonding with epoxy since the early 70s so when I got into manufacturing snowboards in the early 90s i thought i knew something. Rude awakening, i soon discovered how easy we have it in boatbuilding. Try glueing together an item that is only 10mm thick comprising of a whole lot of different materials, some of them very difficult to bond such as the sintered uhmwpe base and hardened steel edges. You've all seen what these things have to endure. Interestingly the strongest bondline was the one between the screen printed uhmwpe base and the epoxy/triax glass bottom laminate. The keys to success was the sanded and corona treated pe, the epoxy screen printing, and the use if a rubber foil in the bondline above the steel edge to give a more flexible interface between very dissimilar materials and a very nasty toughened press molding epoxy resin system.

    Steve.
     
  13. petereng
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    petereng Senior Member

    Hi Steve - The hot bonding epoxys are the best thing on the planet literally. Unfortunately we can't heat up boats or large structures. Interesting that you have a corona connection! The hot epoxy has very low viscosity which means it wets very well. thats the simplest explaination plus the heat provides extra energy. Surfaces you mention have a surface energy of less then 50dyne/m and laminating epoxies have about 45dyne energies. Hot epoxies must be well below the 45 mark. I'm about to start using dyne pens to check surface energies before bonding. Currently the workshop uses the water break test prior to all critical bonding, which is all bonds.

    In the VIP theory area I'm having trouble getting my inflow and outflows to agree due to the elastic nature of the vac bag. But last night I sorted that and now I'll re write the problem to fix this. This also predicts why the resin inlet side gets thicker and it has presented the solution to how to balance the inflow and outflow of the stack, hence get the lam the same thickness all the way across. When I get the maths right I'll publish it here. Cheers Peter s
     
  14. AndrewK
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    AndrewK Senior Member

    Peter; are you saying that you should not infuse over an existing laminate?
    I had some concerns but not enough as I was satisfied to just incorporate the DB with CS backing at the interface. Looks like I will have to check my assuption that the CS has a higher resin wt%.
     

  15. Steve W
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    Steve W Senior Member

    Peter, most materials are bondable with proper prep and in the case of the ski/snowboard base material ( sintered uhmwpe) that involved running the printing/glueing side through a wide belt sander and then corona treating it, this was done by the material manufacturer and had to be printed within a certain time frame. When we received the material it had the graphics were screen printed with 2 part epoxy screen printing inks and then the laminate bond was actually to the ink so the ink bond to the PE was exceptional. The surface treatment is about altering the surface tension, the best example of this that i know is the difference between the way water beads on a shiny new car vs an old sun baked car that hasn't been waxed in years where the water doesn't bead at all but rather spreads out and wets the surface, this surface is bondable. We used to flame treat smaller abs plastic parts by moving the blue part of a propane torch flame over the sanded surface.

    Steve.
     
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