heres another fin , it has a glass layer around the perimeter , the leading edge is 4 layers of uni directional woven roveings and the trailing edge is a single layer of 30z satin weave , the satin weave is the tightest weave available and can be sanded down to a razor edge
mabe we mite see this layup around in the future because the roveings are all in the one direction , there is no weave in the glass on the leading edge to cause serration 
Nice fin Keef, I like the idea of glass roving leading and trailing edge. I've been doing that since the 70s, but the glass to resin ratio was probably too low to be real good.
Select to expand quotedecrepit said...
Nice fin Keef, I like the idea of glass roving leading and trailing edge. I've been doing that since the 70s, but the glass to resin ratio was probably too low to be real good.
yes mike as you know carbon wears fast , the glass and the roveings are layed up in the center of the mould and there for becomes the leading and trailing edge , the resin im using is vinyl ester , its stiffer than epoxy but not as strong so epoxy mite be a better bet
I've found polyester is harder than vinylester but more brittle, so I think it's got better wear properties, but haven't done any real tests.
Have you made any fins with polyester?
yes basically poly ester is a cheep resin and ideal for big bulk jobs like boats ,pools, e,c,t , its too stiff and brittle for fins , vinyl ester is on the same spectrum as poly but a much better quality with a bit more flex, epoxy has more flex again but a much stronger resin , carbon will eliminate the flex factor of the epoxy and probably a better choice for fins
west system finish resin is self leveling and similar character as a poly resin , nukem are developing an epoxy surfboard resin , it's uv treated and self leveling and sets as hard as poly but it takes a long time to cure , once they have this resin curing quicker it will be hard to beet
Select to expand quoteDezza said...
Keef, how come its not red to match the board its pictured in?
because that's an RRD not a falcon
Same experience as Decrepit with Vinylester v's Polyester. VE has more resilience, not as brittle but I would not have said it is less stiff in lay ups. There are many different types of epoxy resins. Some are very stiff! But one probably needs a degree in chemistry to get the best of it. ?? 
Select to expand quotesailquik said...
Same experience as Decrepit with Vinylester v's Polyester. VE has more resilience, not as brittle but I would not have said it is less stiff in lay ups. There are many different types of epoxy resins. Some are very stiff! But one probably needs a degree in chemistry to get the best of it. ??
sailquick as you said there are resins and there purposes , the vinyl ester resin im using is a very low viscosity infusion resin so less fillers and as you mite say, a better quality resin for fins and less resin per carbon in the layup = more strength
bote-cote have epoxy resins from 90% flex to 20% flex, so depending on what your needs are , so there laminating resin is low flex
where there finish resin is high flex , and they claim there laminating resin is 300% stronger than there competitors, but what I have found is, it is low viscosity so you need more resin in the layup
until now I would never thought you could use epoxy for fins because of the flex factor, but as you said epoxies are getting stiffer and there UV promoted,
as I mentioned earlier Newkem are working on a surfboard epoxy resin that's UV stabilized (crystal clear) and as stiff as polyester so it could be interesting
Microwave radiation (and I suspect UV radiation as well) according to the article I read yesterday results in incomplete curing.
Marand et al compared thermal and microwave curing of epoxy resin and found that, in the latter, rapid crosslinking created a molecular network which was rigid enough to trap unreacted functional groups, thus actually causing a lower degree of cure.
E Marand, KR Baker and JD Graybeal
'Comparison of reaction mechanisms of epoxy resins undergoing thermal and microwave cure from in- situ measurements of microwave dielectric properties and infrared spectroscopy'
Macromolecules, 1992, 25(8), 2243-2252.
Also from another article, rather than worrying about resins types it may be better to just get as much of the gas/voids out as you can.
the three point bending tests show that the flexural strength exponentially decrease as much as 6.4% for the SPRINT and 6% for the prepreg for every 1% increase of the void content.
The four ply unidirectional carbon/epoxy composites were manufactured using the SPRINT and prepreg manufacturing methods. Manufacturing by these methods has successfully produced the composite materials with varied void contents and the voids are found to concentrate primarily in the area where the adjacent plies meet. The SPRINT materials contain voids in the range of 1.63- 2.89% while the prepreg laminates have an average void content of 3.6% for the debaulked laminates and 6.8% for the non-debaulked laminates.
SR Ghiorse
'Effect of void content on the mechanical properties of carbon/epoxy laminates'
SAMPE Quarterly, January 1993, 24(2), 54-59.
So I take it that in the latter case(non-debaulked prepreg laminates) the voids cause a 50% reduction in flexural strength.
So I hate to think just how much weaker my hand wetted out layups are! So far no broken fins (Bamboo/carbon)
I got a bit lost in the high tech stuff, gut I guess there talking about trapped air in the layup , I have been using infusion so the mold is layed up dry , all of the air is sucked out of the mold and set at the pressure you want to pull the resin through, once you have no pressure loss you open the resin intake and regulate the flow rate from the outlet, or you can adjust the vacuum at the pump
i use some recycled carbon dust in the resin and let it degas over night , I also like to do a fin first thing in the morning so there's no rush and I can open the mold before the end of the day ,
Select to expand quotedecrepit said...
Nice fin Keef, I like the idea of glass roving leading and trailing edge. I've been doing that since the 70s, but the glass to resin ratio was probably too low to be real good.
mike the process is resin infusion once you yet the hang of the rite amount of glass to stick in the mold resin is sucked through, basically when your laying up a mold by hand the resin is going off as your adding glass and you end up using more glass to resin ratio
