Pre-curing the whole lay up

classic Classic list List threaded Threaded
15 messages Options
Reply | Threaded
Open this post in threaded view
|

Pre-curing the whole lay up

mattma
Administrator
Downunders efforts with protective topsheets has got me thinking about something related that I think might be worth a try. Namely, how to get the pristine finishes on the top and bottom of the board without the excess weight that comes along with using either commercial topsheet of pre-cured topsheets.

As I was walking the dog today down at the dam, watching him put his head about 10cm under the water to retrieve a sunken log ( it never fails to make me smile or laugh out loud) I had an ah moment, which on reflection may be the process that I heard about on Kiteforum.

Pre-cure the full lay-up of FG for both sides, not just the last layer of FG as I did before, so that the final step of putting all the glass and core together only involves putting  enough epoxy onto the core to bond the pre-cured stack to the core.

So for example with the last board I did I used 450gm stitched eglass + graphics+ 180gm eglass. The idea would be to have a separate step of pre-curing 2 separate stacks of 450gm+graphics+180gm and vacuum bag them to squeeze out the excess resin, using peel ply to leave the surface rough so its better for bonding. This could be done on the rocker surface just laied flat and result in  2 pre-cured skins with that shiny finish that naturally comes out on the underside of boards. But with a few extra pluses ( theoretic pluses at the moment).

1.) Vacuuming them squeezes out excess resin (reduced weight problem) so that only a bonding layer of resin in the final layup needs to be squeezed out. As you'd be wetting out either the core of the cured surface of the fg there is very little work involved in ensuring that the minimum amount of resin is there to start with.
2.) The skins would get under the vac pump within about 15 mins instead of the 1 hour that I had last time with the managing the core and wetting out the top layer.  This means the resin is still very mobile and excess can be squeezed out easily.
3) It might be that its easier to get air bubbles out via the vacuuming process. As the bubbles no longer have to content with the core getting in the way of their exit, its possible that more air bubbles can be squeezed out.
4) the final layup will also be very quick as it would involve just 3 steps. Wet out the bottom skin, core down, wet out the top skin. Bang, under the vacuum. Maybe 20 minutes tops and you could be squeezing out excess resin asap.
5) would be possible to stockpile the skins.
6) Both skins are vacuumed against a shiny surface so you have a lush finish top and bottom.

The main unknown is how much 3D shaping the precured skin would conform nicely to. Shallower angles on the step down from one deck level to the next, not step downs just smooth curves, no smooth curves just a constant thickness core with flex controlled by the layup (ala Brokites).

Oooo. This is definitely worth a try, I think.



Reply | Threaded
Open this post in threaded view
|

Re: Pre-curing the whole lay up

downunder
Definitely worth of effort.

Adding inserts in is a bit of work. They must be perfect size to match the core. The holes too. I’ve found this as a quite time consuming task since I do not drill the core all the way with the same diameter fastener bit.
Weight might be about 400 grams more with both topsheets. I guess, much thinner than 0.3mm topsheet should be less. But how much tinner can we get?

With this layup one must be careful with handling and storing skins, ie I didn’t use alcohol or similar to prep the topsheet and it is possible that we touched it and hence bonding problem. Or dust etc.

My next board will be as my current one, smooth top just enough CF for rocker/concave on top. Let it be flexible, will never break .
But finish might sell...Ok, I can have a great finish with varnish but it's not scratches proof option. However, it won’t delaminate eather.
Reply | Threaded
Open this post in threaded view
|

Re: Pre-curing the whole lay up

mattma
Administrator
Hey Dean

yes,  some good points.

I am hoping that the weight might be less than the 200gm per side that seems to go with the impermeable skins ( I had the same weight gain when i used just pre-cure FG skins) because each skin would be squeezed under a vacuum during precuring with one side peel-plied so excess resin can escape. If doing a normal layup with topsheet sheet the only way for resin to escape is to travel across the board which means less gets out.

Re inserts, having them under sized allows resin to flow up from bottom to top. This is what I did on my last board. The problem that came up was that I was laying it up on the curved surface of the rocker table and so they fell through the core. I'm thinking that the remedy for this is to do the layup with the rocker table surface flat, put it under a light vacuum and then bend it into the rocker table jigs.

Also, it would probably be easier to make the core complete before doing the final layup. Get the core with inserts and rails all ready to go then sandwich it between the skins (the skins being pre-cured pile of topsheet+graphics+FG). Once this pile is pre-cured the topsheet bonding side is no longer exposed so handling after that should be an issue.

I think I'll give this a go without investing in topsheets - just FG. I'll try and see if the benefits really to materialise.

Cheers
Reply | Threaded
Open this post in threaded view
|

Re: Pre-curing the whole lay up

Nickb
Hi Matt

Did you try this method would be interested to hear any feedback you might have

I will be doing my vac bagging this weekend so if this method is good I could try it
My core is already made up with inserts and rails done.

Evan if I just made the base up before hand then laid the top sheets with the core
As I have shaped the core and this could put stresses into a per made top sheet.

What's your thoughts.

Nickb
Reply | Threaded
Open this post in threaded view
|

Re: Pre-curing the whole lay up

Chris
In reply to this post by mattma
Hi, I'm new to the forum, I had to make a load of coupons last year so got to play around with different layups and processing methods. If you are looking at moulding up both halves seperate then joining them after you might as well infuse rather than just vac bag. You should be able to get the fibre/matrix volume to at least 50% fibres by weight, I got it up to 60% with the odd pinhole

Just lay out all the dry fabric, use a peel ply as the infusion mesh as this will slow it down significanly enough to ensure full saturation then just vac it down making sure there are no bridges over features just as you would with vac bag. Hold for a while with the vac disconected to ensure it holds then turn on the vac and open up the resin tube.

I've also played with double bagging, which produced very good results but obviously you are using twice the consumables so can be quite costly.

You just need to get hole of some resin that has a viscosity at room temp of less than 500 mPa.s I've used Hunstman LY1564 with good results
Reply | Threaded
Open this post in threaded view
|

Re: Pre-curing the whole lay up

mattma
Administrator
Hey Chris,

Welcome to the forum and thanks for the very helpful post!

Sounds like you've really been rolling you're sleeves up and going for it. Thanks for the ideas on infusing. I had thought about trying it from time to time but it just seemed like a more involved and more failure prone process so I balked. However, what you're describing it just to use the same set up as a wet layup which makes it much more appealing. Did you still use the tube over the length of the skin deliver the resin or did you just have a single point of entry for the resin?

Thanks for the feedback the 500 MPa.s is worked. This has been a hard figure to nail down.

I think word correction might have taken out a critical word in you post below. What was it that you made loads of last year?

Cheers
Matt





Reply | Threaded
Open this post in threaded view
|

Re: Pre-curing the whole lay up

Chris
Hi Matt,

Infusion is a much cleaner method of working with minimal exposure to the resin, you can layup the cloth dry and in the time you need to get it all nice and right, especially when you have ribs or features so you can minimise corner bridging. You only get the resin out and mixed once you have everything under vacuum and ready. You don't need many extra bits, you can clamp the pipe with a couple of kinks and a pair of mole grips or tape, you just need an infusion media, but this replaces the breather fabric.

I was doing an MSc project last year and was testing the effect of the layup on the bearing capacity and failure mode of a bolt/dowel connection. The results were quite interesting... (I ended up making 25 different layups and taking/testing 6 samples from each layup)
Sprocket
Sprocket-4
Sprocket-3
Sprocket-2

If you can get the viscosity down to sub 300 it works even better, especially for thicker laminates. Do a couple of test pieces with the layup you want to use first so you can get the hang of it. I've down up to 7mm thk of pure carbon.

This is a test piece with 4 layers of 200gsm plain
Sprocket-6
The lines show how far the resin had moved in 5 or 10s (can't remember now) so you can see the lines get closer the futher from the resin entry point so you can work out the spacings of the entry points.
Sprocket-7
The finished face, there are a couple of dry patches, this was because I used 4 layers of plain, if I'd used a twill or UD and/or mixed them then the pinholes would be less. A polyester infusion resin was used but with quite a high catalyst ratio so it gelled pretty darn quick (again another reason for the pinholes). If you use a resin with a long gel & working time then you will get a better finish.
Sprocket-2-2

The next is an RC boat hull (infused), the slightly opaque areas are where the clear gelcoat was too thick of had run and the lighter air pockets are as before the resin gelling too quick and the weave used.
Sprocket-3-2
Sprocket-8

For the boat, I infused from bow to stern but it would have worked better with a perimeter ring or a couple of exit points to the vac and the entry point somewhere down in the hull
Reply | Threaded
Open this post in threaded view
|

Re: Pre-curing the whole lay up

downunder
Nice Chris. Really clean.

I do have some questions tho.

How would one do this layup with a topsheet? I am using the UHMWPE.

If not using a topsheet, what you would use as a protective layer?

Cheers and can't wait to see your work !
Reply | Threaded
Open this post in threaded view
|

Re: Pre-curing the whole lay up

Chris
Matt was talking about precuring the top and bottom so you have 2 shells and the core, this is more of a method for making the top and bottom shell as light as possible aka 50-60% fibre to resin and still getting a decent finish.

I'm thinking about a one shot process with a flowable core, you can get high density closed cell foam with pin holes in it at regular intervals, there's also a 3d EPS core now which you can make conform to the mould. That way I can make a top part of the mould and place this as the final layer before vacuum and infusion, should get pretty good A faces straight out with minimal finishing.

Flowable cores:
http://easycomposites.co.uk/products/core-materials/lantor-soric-SF-3mm.aspx
http://easycomposites.co.uk/products/core-materials/EasyCell75G-Infusion-Grooved-Closed-Cell-PVC-Foam-Core.aspx

3d core
http://www.ecfibreglasssupplies.co.uk/p-2604-3d-core-5mm.aspx

Another topic though, I'm trying to find a way to produce the rails using a mould but I'm having trouble finding the correct resin/material to use. I like to cure my stuff at 80deg for 8 hours so you get a Tg of around 110degC, hot enough for a pure carbon finish for most days here in the UK without softening. (Huntsman LY5052 and Aradur 5052 resin/hardener btw)

back on topic, if you precured the top sheet you could dry stack from the bottom and infuse the lot in one go. The release agent you use definately has an effect on the surface finish, I use TR104 hi temp wax, but I've also used a chemical semi permanent coating which was superb but costs about £100 per litre + tax (circa 180 AU$) so can't justify it!

You also need to knock off the stippled surface left over from removing the peel ply, the resin bonds at a microscopic level (especially if you are infusing) so if you dont remove this bit you are just weakening the bond and adding weight.
Reply | Threaded
Open this post in threaded view
|

Re: Pre-curing the whole lay up

downunder
Fair enough.

The problem is and will always be the scratch proof finish for a home builder. And as I see it the vacuum infusion does not solve this. UHMWPE does (expensive and soooo difficult to buy).

I like the infusion tho. Not sure if is feasible with a high cost of consumables for DIY. Only a pneumatic press can lower this cost. The whole ski and snowboard industry is based on a cassette and p. press and the consumables cost is minimal.

Yes, I'm using a closed cell. It's a bastard since drinks epoxy a lot if is not sealed. And expansive - Au$140 for a sheet 2.4x1.2x0.5

I'm reading you about the pre cured rails. The industry is using the PU. And that is a separate can of worms. Would like to see your input on this topic as well:)
Reply | Threaded
Open this post in threaded view
|

Re: Pre-curing the whole lay up

Chris
The consumable cost is very comparable to basic vac bagging, you still need the vac bag and you replace the breather with an infusion mesh or if you are just doing a couple of layers you can get away with just the peel ply after a few test runs.

I just love it because you don't have to mess around rollering, consolidating etc and getting the workshop or yourself messy with uncured resin.

wrt the scratch free finish, I'm going to be trying this stuff
http://www.marineware.com/index.php?option=com_content&view=category&id=88:durepox-clear&Itemid=88&layout=default

It's flexible but is rock hard, the rep reckoned it gets so hard after about a week that you can't even sand it plus its UV stable
Reply | Threaded
Open this post in threaded view
|

Re: Pre-curing the whole lay up

mattma
Administrator
Hi Chris,

Great stuff!!! thanks for sharing your experience and great that you've got the kiting bug as well. What a combo. Its great to see the fresh ideas and materials. Its got my mind ticking over having a crack at resin infusion. The idea or not bathing in acetone afterwards and spending less time strapped into the mask is very appealing.

I've gone to reply to your posts twice and both time browser has crashed and thread has moved along.

Anyhow, how cool that you get to do this stuff as part of your research. That is gold.

Its a bit hard to see from the pic's how long the pieces are that your infusing. Would you use the same set up and orientation of the infusion spiral for say a 140cm or would you run the spiral down the center line??

One thing that really caught my attention is the core material with the infusion 'mesh' carved into it.  I'm steering away from foam cores and fibreglass as I've had a couple of foam core boards break. The bond to the foam is typically very good but when I look closely the break I can see the a fair bit of foam has come away and remains stuck to the epoxy. I think the culprit is the amount of flex and shear pressure under the footpads that the cores are subject to that makes wood a safer choice.  However, the idea of cutting or scoring the infusion 'channels' into the wood seems like a great idea. In fact, the carved channels could even be quite decorative.

do you think it would be possible to infuse the top and bottom at the same time? what would be the layout of the various ports to do it?

Really looking forward to see your handy work.

Cheers
Matt



Reply | Threaded
Open this post in threaded view
|

Re: Pre-curing the whole lay up

Chris
The infused flat piece is 1m long x 250mm wide (1m2 of 200gsm carbon plain woven cut into 4 strips), as you can see it slows down considerably towards the end so about 700 would give a decent infusion using those specific infusion materials and resin.

You will only know how far you can infuse sucessfully by doing this with the layup, resin and infusion mesh you intend to use as it's very dependant on the materials.

When you infuse and you are thinking of where to put the inlet just remember that the resin doesn't know where the outlet is, all it sees is the vacuum pulling it into all the voids so if you had the same as my test sheet but 2000 long and the inlet in the middle the drawn lines would look pretty much identical on both sides even if the outlet was only on one side.

I still reckon foam is the way forwards as you can use localised reinforcement under the binding positions/heal/toe to act as a load spreader i.e. a very small beam or slab subject to a UDL or Variable UDL to ensure the load transmitted to the core is less than it's crushing strength... akin to when you design foundations on soft of variable ground you make the foundation stiff in localised areas to spread the load or bridge the soft spot.

You could even have a wood core under the binder to prevent core crush and revert to foam elsewhere in the board to help keep the weight down and the inertia low as you won't have all that heavy wood outside of your binding positions. Thats the beauty about composites, you only put the strength or flexibility where you need it.

If you were hell bent on a wood core and one shot infusion you could i suppose as you mentioned score flow lines into the top and bottom face of the core but you would also have to drill a shed load of small holes (probably 1-2mm i would think) at fairly close centres say a grid of 30x30mm to ensure the resin flowed through the entire laminate on both sides, akin to the foam board in the previous links.

Reply | Threaded
Open this post in threaded view
|

Re: Pre-curing the whole lay up

downunder
Chris wrote
If you were hell bent on a wood core and one shot infusion you could i suppose as you mentioned score flow lines into the top and bottom face of the core but you would also have to drill a shed load of small holes (probably 1-2mm i would think) at fairly close centres say a grid of 30x30mm to ensure the resin flowed through the entire laminate on both sides, akin to the foam board in the previous links.
Yep:

http://boardbuilders-forum.1077691.n5.nabble.com/German-manufacturer-Carved-Core-td890.html

Perforated with flow lines.

Beautiful boards.  If you like wood tho. Expensive.

1000 Euros.

If you have a chance check new Burton snowboards. They are made of tiny strips of wood vertically positioned in some places, 100-150mm long.

I recon this is for controlling flex and the overall feeling of the board.
Reply | Threaded
Open this post in threaded view
|

Re: Pre-curing the whole lay up

sijandy
Very interesting thread... so whats the advantage of resin infusion over hand layup? Better resin to glass ratio? Cleaner/quicker process? Any others?

Did anyone end up trying the pre-cured layers method Matt talks about at the start of the thread?