Weird Room 2015

Document your personal work here. Show photos, movies, and share your secrets.

Moderators: Head Monkey, kelvin, bigKam, skidesmond, chrismp

IslandRider
Posts: 80
Joined: Wed Dec 19, 2012 11:00 am
Location: Kelowna BC

Post by IslandRider »

MontuckyMadman wrote:If you cook the ski for an hour, your good. Its the long press time and no heat that bleeds the resin.
Ok, that makes sense. I will up the priority on temperature control before the next pair and see if heat helps. Its up there anyways because I'm sick of running a space heater and waiting 8 hours for every pair.

Resin quality isn't the issue, I'm loving this new stuff so far aside from the getting it off the bases after the fact issue. If anyone's interested, its this stuff, with a 3663 compression hardener not shown on this tech sheet.

http://www.ptm-w.com/index.asp?pgid=176
Richuk
Posts: 1146
Joined: Sun Jan 31, 2010 9:53 am
Location: The Duchy of Grand Fenwick

Post by Richuk »

You've solved most of this yourself from what I have read, but I hope this helps.

The resin you are using is medium viscosity. My resin needs to be at 40oC before it would be at the same viscosity of your resin at 25oC.

I can't find the hardener 3663, but I have a good sense from what I have read and you've said.

Providing pressure is important to the strength of the bond - it tends to be really important for plastics. The lack of pressure around the tips is a real problem. Perhaps it can be fixed using racket straps or similar? If so, you will be able to press at a lower pressure. Falls mentions a few things, so I'm sure he's covered everything.

The resin you're using is an ambient cure resin, its slow to harden. This means the core will have plenty of time to absorb the epoxy it needs, a bonus - depending on your view. It improves the mechanical properties of the core, but adds weight, and its a bit random. If you're concerned about the core being a little too hungry and potentially starving the fabric, you can mix and apply a few coats to the core in advance of lay-up - an hour or so before. Put in a warm place, so by the time you come to use the parts they have started to gel/tack. Ditto for the veneer. Taking this approach will allow you to managing the thickness of the laminate really precisely, as the pressure applied will directly effect the thickness of the laminate only. If you really want, this method allows you can play around with the different resin ratio's for the top and bottom laminate - small variations to compensate for variation in a fabrics performance (tension & compression).

Don't expect the veneer to be saturated as such, results are species dependent, you're only really just coating the surface. So its a mistake to think the veneer has become harder or waterproof as a result of pressing.

Heat is what you need, direct to the cassette. Something like this would be the a good option - cheap, effective, no controller required.

http://www.discountfloorheatingltd.co.u ... _price.asp

Edit: You have a heat blanket, if it just the one at the moment, still consider this as an alternative. Given a bit of a push it can hold 60oC, it just doesn't have the power to get there on its own.

They won't raise the temperature massively, 30-40oC using 240v, but you will have a reliable cure cycle as a result. Initially add enough pressure to consolidate the parts, wait until the epoxy begins to gel and add max pressure required. Ideally, you want to be a little ahead of the gel time, so you can press out any last air bubbles and consolidate the parts effectively. I suspect you will max out at around 30-35psi - but that's just a guess. Run a test.

Talk to your supplier about how long it needs to be in the press at 40oC. They appear to recommend 12 hours at 50oC for the PH3665.

Edit: Rule of thumb, plus 10oC, half the time. So that's 6 hours at 60oC. You'll need to find that balance between temperature and viscosity. Ramp up too quickly with too much pressure and control over the thickness of the laminate will suffer.

I thought about suggesting a hot box (post cure). Personally wouldn't until you are happy with the performance of the epoxy/plastic bondline.

Hope this helps.
IslandRider
Posts: 80
Joined: Wed Dec 19, 2012 11:00 am
Location: Kelowna BC

Post by IslandRider »

Richuk, thanks for the feedback. Re viscosity, the 3663 hardener is 35cps compared to 150-200 or so for the other ones, so mixed resin even thinner still which may be contributing. Datasheets are all stated for room cure, but supplier assures they have customers getting good results with heated fast cures. I've found similar reports from guys doing heated cures in model rockets. Maybe the solution is enough temperature that it gels before it squeezes out. 3663 is designed for infusion (hence thinner and slow cure), but its what they recommended for compression molding. I think the logic with thinner for compression is that it will wet out evenly as pressure comes on, similar to wetting out under vacuum when infusing. Maybe viscosity stays more consistent as it warms up before it starts to gel too, not sure. Haven't had any issues with the core absorbing too much, and I mix what would give me a dry layup using West which is a definite bonus. Its not a lot, but it does add up. Next order I may try the 3660 just to see the difference. If I can get a pressure/temp curve dialed in it will be great stuff, once cured I like it way better than what I have been using. At the pressures we're talking you'll be able to squeeze too much out regardless of how thick the resin is, especially since most resins will go thin with temperature anyways. The rate of squeeze out may be different, but I should be able to control that. This resin is really nice to work with, wetting out laminates is much faster and more even, which probably has a lot to do with why they recommend as compression resin as well.

I think too much tip pressure is definitely contributing, the very tips and tails clamp down first at about the same time as the middle at about 20-30psi, but to get good consolidation in concave portion of tips and tails I need to take it up to 50 or so. I've messed around with shimming those areas between the cat track and bladder, but results in being able to see the cat track ridges on the top sheet even through a 16ga aluminum cassette. Extra base material around the tips will help with too much pressure for sure, but this pair is fairly square nosed so I'm not sure how much of an effect that is really having. The delaming I'm seeing is in the higher pressure areas, not the lower pressure concaves, so definitely letting it sit at pressure with a very slow room temp cure thin resin is bad news, as I've discovered and Montucky pointed out.

I'm not relying on veneers saturating, and did coat the topside between veneer and topsheet with this maple. The mohogany I used on the split basically came out of the mould finished with no dry spots on the topside of the veneer despite it going into the cassette dry which was just a bonus.

For heat I've got two 2kw blankets and two STC1000 temperature controllers sitting in a box collecting dust, I've just been too busy (lazy) to hook them up. Its going to involve getting 220 from one side of the garage to the other (about 10 feet), and that might as well be Mt Everest some days. I've only got one 220 outlet and the CNC is plugged into it, so rather than cobbling together some half assed shit that could burn my house down with a dryer extension cord I want to do it right, and that's turned it into a bigger project than it really needs to be.



As an aside to the whole delam issue, do you guys run a second sheet of metal between the cat track and the heat blanket on top of the cassette? I'm worried about tearing the blanked if the ribs pop unevenly as pressure comes on and I get a step between two pieces in the cat track. Downside to me is that another sheet of metal up there isn't going to help with forming to the tips and tails.
Richuk
Posts: 1146
Joined: Sun Jan 31, 2010 9:53 am
Location: The Duchy of Grand Fenwick

Post by Richuk »

Infusion resins are expecting circa 15 psi. It maybe what they recommended, but the hardener supplied makes this an infusion resin. So pressure is major factor to manage. The viscosity of the mixed resin does make a high fabric to resin ratio more achievable, and at a lower tooling cost - if that's what you want?

Do as you suggest and add enough heat to cause the resin to gel, but not so much heat that it creates issue with the thickness of the laminate, or creates issues with the quality of the laminate. Curing at an increase pace assumes a lot about the heat map being generated within the press.

Compression resins do become less viscous at higher temperatures, but they also begin to form polymer chains. So you manage the temperature to achieve some flow, knowing the cure cycle will retard the flow as the epoxy kicks.

Taking the core and veneer to B-stage in advance of use will help you get the best out of this product. Its a more efficient use of the heat being applied by the blankets, as you won't be heating all the resin applied to the various parts, just what you have freshly laid up. Using a slow even cure at low pressure, followed by a strong post cure cycle, will ensure you produce a superior laminate in the shortest amount of time. Its an infusion resin, it is what it is.

Oh, some of my comments are just for the sake of completeness.
IslandRider
Posts: 80
Joined: Wed Dec 19, 2012 11:00 am
Location: Kelowna BC

Post by IslandRider »

Yeah, we're on the same page. I will try slightly pre-curing the core and veneer if I can't manage with heat alone. There's some downsides to doing this though, both on process flow side, and in higher risk of both contamination and not getting the timing right and ending up with a bigger mess I think. Just more variables that would be nice to leave out.

Are you suggesting I'd be better off with a more traditional hardener and a thicker mixed resin to begin with?
Richuk
Posts: 1146
Joined: Sun Jan 31, 2010 9:53 am
Location: The Duchy of Grand Fenwick

Post by Richuk »

Run a test on a scrap piece of veneer. See how long it takes at ambient temperature before the resin will tack like tape and is practically dry to the touch. I suspect you can work 24 hours ahead of schedule with the core and veneer - something like that, if the parts have been left to cure at room temp. The cores will need a couple of coats - so start and finish with the core, in the knowledge that you are not under any time pressure )

Cover with silicone paper if you are worried about contamination. The first time you do this, you might want to be use them when they are still a little wet, don't store the parts on top of each other or together. Dividing the lay up like this reduces the variables and leaves you to concentrate on wetting out the laminate with the required amount of epoxy. Just take care when positioning the core and veneer, they can be a little resistant to re-positioning. That's just a heads up - its not an issue.

Ambient cure is a good way to go for the reasons we are discussing - you have a lot more control over the quality and thickness of the laminate. It sounds like the hardener you have been supplied with is your stumbling block. My ski specific compression resin is like treacle when used in a un-heated workshop, so perhaps its just a matter of switching out the hardener - maybe they will send you a small sample?
gav wa
Posts: 381
Joined: Tue Feb 18, 2014 8:58 pm
Location: Perth

Post by gav wa »

Hey mate, just reading an old journal and had an idea for your issue if you are still having problems. If you put a very light glass between the topsheet and veneer it will hold more resin and give an awesome bond. I've used plain weave cloth with a weight of 36grams per meter and it works well and ends up very clear when wet out.
IslandRider
Posts: 80
Joined: Wed Dec 19, 2012 11:00 am
Location: Kelowna BC

Post by IslandRider »

Hey nice update a year later. I like the idea, I'll give it a try on my next build. This is still something I'm struggling with. Now have heat and have made several pairs from slow ramp to 15 minute cure and results are hit and miss. Some skis seem indestructible, and some start peeling after a couple days.
Post Reply