Double sided smooth finish...Infusion?

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#1

I’m looking for some help at getting a cosmetically smooth finish on both sides of a sandwich panel and wonder if infusion is the way to go? Wet layup vacuum bagging is not getting the result I want in one shot.

I am looking to create a double sided flat panel (50" by 20") that is vacuumed on a plexiglass surface (no mold) using epoxy resin. The core is 3/4" 5lb Divinycell H80 because the panel must be able to handle repetitive slamming and impact abuse.

With wet layup vacuum bagging, I have only been able to get a cosmetically smooth surface on the bottom side, which cures against the plexiglass. The top surface is textured due to the peel ply. How do I get a smooth finish on top also?

My wet layup top bottom to top consists of:
plexiglass surface
3 layers glass
Divinycell H80 core
3 layers glass
Peel ply
Breather
Bag

With infusion, I am thinking of getting rid of the peel ply and breather and letting the top layer of glass lay directly under the vacuum bag. Then, use spiral wrap on both ends to draw the resin across the panel length wise. Will this work without flow media and peel ply?

I have done some research on infusion and feel I’ve got the basics of it down. However, I still have a few questions.

Is peel ply and flow media necessary with infusion? I am thinking of laying the bag directly onto the top layer of glass to get a smooth finish. I am going to use a low viscosity epoxy resin.

Can I infuse both the bottom and top sides at the same time without using a perforated core? Will the resin flow evenly on both sides?

With wet layup, I have sealed the core prior to vacuum bagging to prevent the divinycell from drinking up excess resin. Do I need to seal the Divinycell core with infusion? I don’t want to use a perforated core due the impact and slamming abuse the panel will take.

Any help would be appreciated before I begin my testing!

Thanks

#2

Basicly you could do without peelply, perf film and mesh. If your laminate is permeable enough…

I really would like to see your core perforated, to even the flow from top to bottom, or make the panel slightly larger, so if you waste one end, you can cut it off.

To get the neccessary permability you have several options, I would either use a permeable fabric (CFM) against the core, or use slightly grooved core. (both sides)

As for smoothness: With just a bag on top, you will get wrinkles or at least texture from the fabric. use a plexiglass plate on top as well.

Or if the fabric texture is not important, you can use normal infusion, without peelply, without perf film, but with a product from Fibertex in Denmark, I believe the SB150. This leaves a smooth finish. They also have it combined with mesh, which is even easier. (they also have peelply-surface-mesh)

#3

not sure why you would want to seal the core…get a core that isn’t an open cell sponge. Else you need the surface cells to lock the resin into, else you are bonding a smooth surface.
But anyway, yes you can use infusion and a caul plate. You must be VERY careful about racetracking. Have your core and fibers extend PAST the top plate. Infuse with long gel time resin, and add a good sized peelply delay line at your vent. Making channels in your core will help resin flow as well. Not sure what your application or core size is, but perforations shouldn’t change many properties. Try a 1-2mm hole every inch or so.

#4

About the sealing (completely forgot in my other post). No need for that. I can imagine you hotcoating (scraping on a layer of resin, then install wet) to fill the cells that got hit by the sander, but PVC foam is closed cell.

Which brings me to the point of outgassing. Heat and vacuum, perhaps with styrenated resins (polyester and vinylester) in combination with a fresh core CAN outgass, which can demolish a part. When a heat cure is to be done, it is good practice to “cook” the core before processing.

#5

Thanks for the help!

What I’m actually trying to create is a kiteboard, which is why I am using the H80 high density foam core. My ultimate goal is to be able to create smooth finish on both sides of the board in one shot under the vacuum and eliminate the step of hot coating and sanding on the top surface after bagging. A very thin peice of plexi on top just might work, Ill have to experiment. I use a mixture of carbon fiber, 6oz eglass and sglass depending on the layup with epoxy resin (room temp cure).

I don’t know if I can locally get a 3/4” perforated core material here in FL. Would a perforated core make the part structurally weaker or heavier? Does this just involve drilling holes through the foam? Seems this would be a lot of drilling.

I read in an earlier post about using chicken wire to create channels in the foam to get in to flow on both sides better, I may try this.

I’ll try skipping the sealing from now on. It is closed cell foam, but I was reading some years ago that Divinycell would drink up resin and produce a dry laminate with wet layup bagging, which is why I sealed it. Perhaps Divinycell has improved the foam’s cell structure recently.

Back to the testing garage!

#6

About H80: Over here they use H100, with high density inserts below the feet and around fittings.

Perforations will do practically nothing with the laminate strength or foam strength. Lot of drilling, yes… (you could use a punch, a piece of wood with nails in it.)

The guy stating that PVC foam is “drinking” resin might need to test a bit further. OK, PVC can take up to 500 grams of resin per side for filling the surface structure, but failing to do so will impair the bond. Do some destructive testing, and learn a lot. What you are aiming for is a bond that, when broken, has foam on both sides.

Foam improves year by year, but these problems actually never existed. They were made by people not having the skill to work with foam, cutting corners, or just plain “foam core bashing” like some guy with a whole website about why foam is “wrong”.

#7

Thanks Herman!

Anyone have experience with Mylar® (PET Polyester Film) for providing a glossy finish? Is it reusable? ACP composites has some that I’m going to try. I’m going to use it instead of a plexi top piece as it seems more flexible.

Also, does anyone know of an inexpensive resin infusion distribution medium that can cure with the laminate without adding significant weight or bulk? Is there even such a product? I would use it instead of the traditional removable distribution mesh on top of peel ply/perforated release film. My layup from top to bottom using a half bag method would be:

Vac bag
Mylar/Plexi top sheet
Laminate layers
Infusion medium that can cure with part (if it exists or is possible)
Foam core
Infusion medium that can cure with part (if it exists or is possible)
Laminate Layers
Plexi glass bottom surface

I’m also having a problem with cheap spiral wrap from Home Depot crushing while under vacuum, is the professional stuff from Air Tech or other manufacturers thicker/more durable?

#8

If you use Mylar make sure you release coat it so you can remove it after cure. It can give you a gloss finish. And yes it should be reusable. A caul plate would be better tho IMO.

I’ve seen people use the blue Enkafusion nylon matting flow media in laminates before. I don’t know if they had problems down the road, I didn’t here of any.

And for spiral wrap, I get mine from McMaster. 100’ rolls are really cheap and I’ve never had them collapse or any problems.
http://www.mcmaster.com/#spiral-bundling-wrap/=dhpjhe

#9

Enkafusion would be an option, but CFM mat or Soric would be a viable option as well. However, by definition a flow medium is a resin rich material, so you will add weight.

Wall thickness is most important with spiral wrap. I could not find what I needed over here, so I am having it made up to my specifications.

#10

Simply use a plexi glass caul plate/top mold and groove the core. We made a roller with a few “male” groove rings on it and just roll it accross the core and feed onto the end grain of the panel. As mentioned before be careful of racetracking, ensure no bag bridging around the edges and yes cfm works well too.

#11

Depending on the thickness of the film, it can, or can’t work. If it’s a thin film, like bagging, up to 5mil thick, then it will just conform to the farbic weave. Leave a shiney finish, but still not flat. Thick films might conform less.

#12

EXACTLY! I still remember when I first came across Mylar in composites and thought it would give me a gloss finish on top because of the smooth finish. ERRRR Wrong, just like you said Riff it conformed to the fabric. Tried the same thing with non porous peel ply once and got the same results.

#13

Thanks for all the suggestions everyone!

I’m still waiting for my low viscosity epoxy resin to arrive and am going to place an order for some thicker walled spiral wrap.

But I had the itch this weekend to do a little infusion experimenting with the supplies I currently have and here goes.

Test panel layup top to bottom:
1 mil cheap vac bag
3 layers 6oz eglass
Core 1ft by 2ft panel
3 layers 6 oz eglass
Plexi bottom

The epoxy resin I used was far from ideal for infusion. It was 1400 cps before hardener was added with a 50 min pot life. I mixed a little pigment in a well just for kicks. Pulled the vacuum on the dry layup to about 26hg, no leaks detected after 15 minutes so I was good to go as it was only a small test panel. I unclamped the resin line and this is where the fun started. Surprisingly, the resin flowed perfectly and infused about 4 inches into the laminate on top and bottom until the resin line slipped out of my bucket and pulled air. Once the air got introduced the resin line, the process was shot. I couldn’t get it pull anymore resin after that. Left the tube in the resin pot for 30 more minutes hoping it would start pulling again, but it didn’t. To make matters worse my garage was 97 degrees and humid (Florida) so the resin started to kick early and I had a hot mess with the resin left in the bucket! However, the 4 inches that infused had great results. I could definitely see the weave on the top side due to the thin bagging film, but the bottom side was perfect. There were some pinholes, but that was probably from the air being introduced when the resin line slipped. Its also worth mentioning that I didn’t groove or perforate the core on this piece.

Can wait to try again with the much appreciated suggestions from you all!

#14

Oh sweet Hezues…97??? Might want to wait until the winter to do any more composites :wink:

#15

epoxy 45 It would seem we’re headed down the same path for all the same reasons. So I’ll be very interested in your results. I have a couple of comments and questions. As to your quest for an inmold infusion material you might look at divinamat as I think it’s just what your looking for, except it might be used as a replacement for the core. With regard to your use of plexiglas for your mold can I assume you are not forming compound curves or have you heatformed your plexiglas? We are using ABS edging have you found that you can infuse around this or how are you treating your edges? We are using PBT films for our skins do you like the PET better? Bro Kites is using something called PMT but have not located it. Looking forward to exchanging ideas.

#16

lmunson,

I am not using a mold, just an adjustable rocker table using plexiglas. This allows me greater flexibility in experimenting with different shapes until I find a shape mold worthy. I usually do wet layup then vacuum, but now I’m experimenting with VIP. To get both sides smooth, you definitely need some sort of caul plate for the topside as mentioned above. The bag alone will show the fabric weave. I’m still testing some ideas with flow channels and perforations using VIP, ill keep you posted as to my results.

I’m from the surfing world and new to kiting, so I’m not using ABS or skins yet. I’m just wrapping the rails with fiberglass similar to surfboards. What is the purpose of skins…scratch/abrasion resistance, ability to easily add graphics/color?? Could you point me in the right direction of a PBT supplier?

Also, do you know of a skin that could handle a lot of abuse and be used on the bottom side to hold up for shallow water riding, sometimes less than a foot, almost dry sand? Are the skins just glued on with epoxy? Don’t quite know how you would attach the PBT using VIP, might need to be added after.

#17

Hi Epoxy45
So many options. We have many of the same questions.

  1. the advantage to the ABS edging is it’s easier on the kite lines and gives a nice finished edge. The disadvantage relative to VIP is that it’s a dam to the resin flow.
  2. I definitlly like the idea of using the core as the flow path, it’s so much simplier.
  3. The skins have several purposes. One it give the finish surface so solves the B side problem, it also provides scratch/abrasion resistance and it’s easy to add graphics - at a price.
    Sources for PBT skins - a) www.crownplastics.com b)www. codaboards.com c)www.isosport.com
    BRO Kites uses PMT because they’re in Corpis with a lot of shallow water. I have not found a vendor for PMT except a link to something in France. I have read about shops using Duraflex, but haven’t followed up on that yet. I think it’s from Crown also.
  4. Yes that’s the problem I’m working on now how to use skins and VIP? I pretty sure you can do it with something the size of a kiteboard just by using the core as the flow path and pull from a hole at the strap locations or maybe just from one side to the other. That still leaves the edge treatment issue. I look forward to hearing more of your test projects.

Have you tried using a plexglass caul kind of like a simple RTM? Again there’s the issue of the edge.

#18

If building kiteboards is anything like building skis (alpine), I am guessing you have a hell of a time getting the ABS to bond properly. Have you looked at using UHMW sidewalls from Crown? Granted UHMW is normally just as bad at bonding, but you can get sidewall material from Crown that is TFB (treated for bonding) on both sides…the same corona treatment finish that your “skins” (“topsheet” to skiers) should have. Plus, sintered UHMW takes more abuse than ABS in my experience.

#19

Interesting, We’ve not had a problem with bonding, with flame treating, It might be that the edges are not subject to as much stress in the water as against hard snow/ice. However, definitely look at UHMW.