i guess you can’t laminate boards here in ewa beach where it gets to the low 90’s in the summer and mid 70’s in the middle of winter.
kind of like making a board in the garage at nanakuli or maile
try walking to the beach in barefeet across the asphalt or sand in the summer like at o-beach and you’ll burn the bottoms of your feet.
even at night during summer you’d have to wait till 9pm to get to some of these recommended temps to glass without a temp controlled facility.
not a backyarders dream. Lucky Bud is up north and UncleD out on the bay.where its cooler but they just do PU.
its weird but bammbamm showed me a technique to use with a heat gun to liquify ResinX to allow the bubbles to rise and smooth out the hot coat and final coat. ResinX was definitely harder to sand. Ended up buying a bunch of champagne sanding paper like BammBamm to do the job. ResinX also kicks the more pressure you put it under and using a water mister which was great. Too bad I got sick from it.
You’re referring to using heat to pop the bubbles trapped in a specific surface hot or gloss coat… Which is fine.
Not the same as the bubbles being off gassed from the foam core and the trapped bubbles induced from mixing the resin and then forcing it through exterior glass fibers down to the core.
You want the cooling of the blank after lamination to implode those laminate pinhole bubbles, not explode them outward through the glass layer with the addition of excess applied heat…
Vacuuming bagging allows you to to use heat to increase cure times with no regard to out gassing. I have a negative pressure in my bag no matter what the heat is. I do agree that hand lay up on foam is better for falling temps. I hve no experience doing that though. Thats why I like vac bagging skins on boards. I never have that issue during the hand glassing portion of the process.
Could you explain how a resin can both elongate more and at the same time be harder?
i try to understand, but no comparison i found can explain it…
The molecules are all the same, so that really changes, more cross linking with the heat = check = needs more energy to break it = car doors etc… shattering less bc more elongation [like spider web with many threads maybe?]
but the sanding part?? i dont understand it, the barcol measure increases, what does that mean? and why does it sand easier?
Hey Wouter,
Yes it is a little counter intuitive. I will try to explain for the materials that I usually test and this won’t be applicable to all materials. It is something like measuring two sides of the same coin, but using a different method for each side. In the end, it is mainly about the final crosslink density. I will also say that for well formulated room temp cure systems, these properties should be close to maximum after appropriate cure time at room temp (75-80F), but that means continuous exposure to those temps for whatever time the manufacturer recommends. Also, a partially cured system may have properties very different than its fully cured state. Some partial cures give very brittle material while other partial cures give very rubbery material.
% elongation is measured by applying a tensile stress and measuring the amount of elongation that occurs from the before the stress until the failure point. For epoxies, this is a plastic deformation that generally increases with an increase in the crosslink density. In other words, if you have more crosslinking, you can stretch the epoxy further before it breaks entirely. For a composite (foam+glass+epoxy) it is a little bit different, but you can still think about a ding that occurs when a hard object hits your board. The skin will “stretch” around that object. If you have higher ultimate elongation, the skin can stretch further (to a point) before a rupture and less likely to get a “shatter ding”. That is not saying you won’t be left with a compression ding.
Hardness (Barcol or Shore) is measured as the depth of impression left after a impact of known force per area. For most epoxies, as you increase the crosslink density, you get less indentation which we report as an increase in “hardness”. I think improvement in sanding is actually two fold because the higher hardness is also occurring with a higher HDT. A higher HDT means the material doesn’t go rubbery or gummy under the heat generated by the friction of the sandpaper and higher hardness means the material resists indentation from the impact of the “sand” particles, but rather cuts cleanly. You might say yeah but there is also an increase in % elongation. Which is true, but there is always a yield point that induces fracture and sanding force definitely exceeds that yield point or it would not remove any material at all. Most of the problems people have with sanding is the clogging of the sandpaper when the material does not cut cleanly and not because the surface is too hard. Many people can attest to the improvement in sanding with increased cure (heated or not). I could go into the reasons that so-called sanding additives help in some cases, but that gets into the different chemistry of formulations and I don’t want to go there on an open forum.
Again this is a fairly simplistic explanation and the engineers in the audience will surely find something to take me to task over, but I hope this helps some,
The post is very old but in case someone is interested… I use an epoxy resin whose curing time is 10-15 hours at 60ºC. 4 hours after applying the Hot Coat, the temperature can be increased from 10ºC/hour to 60ºC (75ºC) and the results are very good.