Alternative edge reinforcements --- kevlar pulp?

[doughboyshredder]

I have been trying to think of ways to reinforce the edges underfoot on my boards. Most edge damage on snowboards occur under the rear foot. I thought about using 333's idea of using kevlar string. The smallest diameter string available is still too thick (.2mm) to use without causing an indentation. There is however kevlar line that is made for fly tying (fishing) that could be used to tie a grid between the heelside and toeside edges. It's only 8lb test, but weaved back and forth it would be pretty strong I would think. This string would tie the tines together and be under the vds layer. I also am planning on running a strip of 5 oz kevlar tape along the edge for impact resistance and vibration dampening. I was thinking that this would also provide added edge retention, but if placed above the vds as it should be I don't think the kevlar will actually increase retention much at all if any. In comes kevlar pulp.

Kevlar® Pulp

Kevlar® pulp is the lightest of the fillers and highly abrasion resistant. Areas of high impact can easily be reinforced with this strong and durable material. Also, use it to make beveled fillets along edges of honeycomb cores to smooth the transition of fabric skins. Recommended for use with epoxy or vinyl ester resin.

http://www.fibreglast.com/showproducts- ... s-111.html

So, my idea is to somehow apply an epoxy mix with the kevlar pulp to the space between the edge tines.

I can't figure out how to do this in such a way that the mix stays seperate from the rest of the epoxy. I thought about applying the pulp mix very carefully and then curing that epoxy by laying a blanket over it and heating it, but I am worried that the heat could distort the ptex if it's not under pressure. Maybe build a flat vacuum setup apply the mix to the base and then apply the vacuum and lay the blanket on it and heat cure it. Or just use a room temp cure epoxy mix and apply it to the base on a vacuum table to keep the base flat. Or, maybe the vds will keep the pulp mix in during normal layup.

Another idea floating around in my head is a bit more outside the box. Using 1.4mm base material and somehow (electric arc?) heating the edge tines enough that the edge can be forced in to the ptex with the tines actually melting a pocket for themselves.

any bright 's?????

[Head Monkey]

I don’t believe you’ll see any indentation from .2mm (0.008”) Kevlar string. This will blend right in with your bottom glass layer and you won’t even know it’s there from the outside. The unidirectional Kevlar tape I use is 0.010” dry and I get no indentation from that. (This stuff: http://www.happymonkeysnowboards.com/HM ... GP4688.JPG) Give it a shot!

When you say “Kevlar tape” are you talking about the same unidirectional stuff I show above, or are you talking about a biax weave?

On the Kevlar Pulp: I’d just mix some into a bit of epoxy and dab it along the edge, then place VDS and layup as usual. Let the press force it into the edge windows, and don’t sweat it if some bleeds a little further beyond that. I don’t think it will hurt anything, or notice in any way. There’s extremely high value in the heat and pressure in your press… I wouldn’t try to cure epoxy in the edge windows separate from that.

My guess is you’ll get a much better bond with the edge T’s on top of the PTEX and in contact with the epoxy than you would attempting to melt them into the PTEX. I think the cured epoxy is stronger than straight PTEX, and the PTEX is probably too ductile to provide much edge retention.

I think your best idea here is the Kevlar Pulp mixed with the epoxy that fills the edge windows. Normally some part of the windows get filled with mostly just straight epoxy. That’s brittle, and a great place for cracks in the epoxy to start to spread to the rest of the matrix. By filling it with the pulp you’re filling the windows with something less brittle… seems like it’s got to be a good thing. I suspect any kind of pulp would do: Kevlar, carbon, glass. I’ve been told that the bottom layer of glass gets forced into the windows with the VDS to some extent, so they’re not pure voids of only epoxy, but I’ve never cut a board apart to check that specifically. How much the pulp could help probably depends on the degree to which you’re replacing pure epoxy voids with epoxy reinforced with the pulp. Might be worth cutting apart a test section to see what opportunity you’ve really got there, or layup with clear base material and see what you see.

I’ve often wondered if it would be worth my time to try to leave small bumps on the bottom of the PTEX sidewalls that would match with the windows. This would positively force the bottom glass layer into the windows when the board is pressed. It seems like a pain to actually do in practice, though, so I’ve never tried it.

I don’t know if any of this will really help with overall edge damage, though. The only way you’ll ever know for sure is to make some small test samples and do comparative destructive tests in the shop.

[doughboyshredder]

I think the string would cause a bump on the base if it was tied under the tine. Nonetheless, I am really liking the kevlar pulp idea. I might build a board or two with it and then plan on cutting them up after the season is over.

[Charles DeMar]

I'd suggest giving the string method a try. I'm new to building skis and boards but have done a lot of repair work and have had a lot of success with different versions of the string technique doing edge replacements on blown edges. Our technique at the shop I worked at was to use a strand of fiberglass pulled from a woven sheet and wrap it between the tines. This dramatically improved the survival rates of our longer edge replacements (up to 30cm), especially on the heel edges of boards and under the feet on skis. Before we started doing this we'd see a lot of the repairs come back and after we added the glass almost none of them. The dimpling wasn't really an issue in this setting. I'd say give it a try.
Have fun.

[smithrb]

Stitch and glue plywood boat construction uses thickened epoxy when filleting joints. Lots of info at bateau2 dot com. There are fairly high horsepower off-shore capable boats being built with this method. Seems similar to kevlar pulp.

[doughboyshredder]

When you say “Kevlar tape” are you talking about the same unidirectional stuff I show above, or are you talking about a biax weave?

missed this first go round.

5oz 0/90 1inch wide.

I also have some .25oz kevlar paper that is 12" wide, but can obviously be cut in to small strips. I am actually using the kevlar paper to sandwich the core on three 170 twins that I am building.

I like Kevlar. (tm) lol.

[doughboyshredder]

I'd suggest giving the string method a try. I'm new to building skis and boards but have done a lot of repair work and have had a lot of success with different versions of the string technique doing edge replacements on blown edges. Our technique at the shop I worked at was to use a strand of fiberglass pulled from a woven sheet and wrap it between the tines. This dramatically improved the survival rates of our longer edge replacements (up to 30cm), especially on the heel edges of boards and under the feet on skis. Before we started doing this we'd see a lot of the repairs come back and after we added the glass almost none of them. The dimpling wasn't really an issue in this setting. I'd say give it a try.
Have fun.

This just gave me a new idea. Thanks! I wonder about using a thin piece of kevlar or fiberglass tow and weaving it along the entire length of the edge in an over under pattern through the little extension to the tines. Obviously you would have to weave the glass in before supergluing, but damn that would be solid, and wouldn't give moisture a way in since the vds would be completely covering it. Hmmmmm.........

[Charles DeMar]

If you do try it, let us know how it works out. For the repair application we've done it a variety of ways, both the over under weave as well as wrapping each tine so basically around/over/around if that makes any sense.
Have fun.