Strong skis vacuum bagged

[G a b e]

Can an applied vibration to a ski in a vacuum back cause the epoxy to "settle" and penetrate in between the fibers, and make a stronger ski as a result?

I find Vacuum bagging a very appealing process, and I think it has many advantages over the pneumatic press. However, the only thing that it lacks is the pressure that is possible with the pneumatic system.

After reading the article on epoxy on this site, I understand that it is pressure that pushes the epoxy in-between fibers, and makes a stronger ski.


If temperature is the other factor in building a strong ski, and can be just as easily applied to the vacuum process, I think that the vacuum bag process would be the best solution if the epoxy penetration issue can be solved.

So, can we get the epoxy to penetrate in-between the fibers at low pressure, and using some other technique?

As stated in the beginning, my first idea was to use vibration to settle out the epoxy.

What about using a lower viscosity epoxy?

What are your thoughts?


-Gabe

[teleman36]

Yes, pressure is key in total saturation of composite fibers. While i know less than nothing about vacuum bagging, I have garnered a layup tip from the Norwegian boys at Strands Ski Shop. Lief, Roy, and Paul have been very helpful in my ski build adventures. Their many years in the ski industry,touring factories and actually working in a Norwegian factory have gained them a wealth of knowledge about what works and what doesn't work in ski construction. They love to share any and all information they have to anyone who will listen. Back to saturation. Tip of the day; ROLLERS, as in the old washing machine ringers used to remove excess water in the fabric before hanging to dry. Big factories use the same process to force the epoxy into the weave of the composite. So, you get a stronger ski with less weight . I will be trying this method soon with some modified sheet metal rollers. Cleanup and mess issues still need to be figured out. Any input from others would be great. P.S. I use a pneumatic press.Will post more info as this technique evolves

[teleman36]

I guess it is alright to reply to your own reply. In the keep it simple vien, the ideas of using a pie crust roller came to me will thinking about food while in the shower this morning. I have been applying the resin to the fabric on a separate plastic covered bench with the standard plastic squeegee. This seems to work out fine, as any resin forced out through the bottom of the fabric gets incorporated into the next piece. Rollers are used to cover large areas in the boatbuilding scene, but are not rigid enough to really drive the resin into the fabric as a solid piece of wood, steel, [rollers], or a piece of round PE that I will put handles on and try. That's it for today.

[Idris]

Well fitting material is the key to a good vacuum ski. I've vacuum bagged at 5 psi (leaky bag and weak pump) and made a solid pair of skis. Ive also made plenty of trash pressing at 100psi. Sure you can get away with more if you have perfect molds and high pressure to force things into the shape you want but there is no substitute for good prep.

Ask Davide, I think he is responsible for more than 50 pairs of vacuum bagged home made skis (in his ski building classes) and has no history of skis falling apart.

Fisher vacuum pressed it's ski for decades! and never had durability issues.

I think vibration would cause problems....alignment to say the least......if you want epoxy penetration of the fiber, Use an epoxy with a resonable pot life (40 min or more) and a paint brush. You manually wet out the glass/carbon/bassalt etc. fibers, rather that slap on a layer as you make your cake and use the pressure to force it all together.

[RoboGeek]

low frequency would probably have no effect. The higher you go the more likely you are to cause cavitation and air bubbles - which would weaken the ski. I don't know the properties of epoxy at ultrasonic frequencies but I suspect it wouldn't be good.

Good layup and saturation of the fabrics prior to layup is the key. I've built fiberglass and carbon fiber things (entire car bodies) with no press or vacuum with no problems with saturation or weakness

[G a b e]

Good info. I will definitely try the roller method to "prepreg" (is that the correct term?) my fiber before I lay it up on the ski.

Idris, Thanks for rebuilding my faith in the vacuum method. I will make sure that it all fits together (I will def. pre-bend my tips/tails for the mold).

Maybe, with good fitting, prepreged material, and heat, I will have a tough ski.

On a side note. I am interested in building with basalt fiber. It is available on E-bay from http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... L:RTQ:US:1, but only in 13oz plain weave. I E-mailed the seller, and that is all that he has. He said that there are only a few US suppliers, and he hasn't seen any 22oz triax. I sent an E-mail to http://www.basfiber.com/index.shtml, A Russian supplier (Found their link on a post on this Forum). I am waiting for their reply.

-Gabe

[davide]

I think that heating is the best way to obtain a good resin penetration (it gets more fluid). Actually I made all my skis at low temperature, and I got no problems.
I read few days ago a paper by some researcher in Australia, who showed that carbon composite parts made at low pressure in water-heated moulds were stronger than similar ones made in a autoclave, at much higher pressure, buslowly heated by hot air.

Vacuum bagging at 40° or 60° is not difficult at all, you do not need any special equipment than doing at room temperature.