Material Prep

For discussions related to the type of materials to build skis/snowboards and where to get them.

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kelvin
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Material Prep

Post by kelvin »

There is some really good info on Hose-man's build log about materials, so I thought I'd start a new thread here.

What are you doing to prepare your material for bonding?

The edges come sandblasted and coated with some anti-rust agent. I wipe it with acetone before supergluing and once again before layup. I'm not sure if the anti-rust coating affects the bonding.

Bases are flame treated at the factory and I wipe it with acetone or denatured alcohol.

Sidewall and tip spacer abs; I've tried to flame treat with a mapp gas torch, but it doesn't seem to work all that well.

We've had some delamination problems and I think 90% of the failures are due to improper material preparation. I'm assuming in industry they are able to sandblast and clean with some harsh chemicals. While our skis have held up pretty well, I'm not confident that they can take a beating like commercial skis.

Any thoughts would be great.

-kelvin
Buuk
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Post by Buuk »

I am also busy trying to figure out what's the best way to bond UHMW sidewalls to wood (and gfiberglass).

The big problem is that plastics like ABS and UHMWPE, HDPE etc. are plactics with an low energy surface. There are some products out there that will help you to bond the plastic like Loctite Plastix Advanced Plastic Bonder with Surface Activator, 3M DP-8010 and 3M DP-8005. so Loctite comes with an activator, to activate the surface for bonding. This products might be good to bond the plastic to the wood, but how to do this during layup? I couldn't find a seperate surface activator and if there is one the question is if it will bond to the epoxy that is used.

As we know another method that's used a lot in industry is flame treatment.
Below I will suggest a method of how to do this that's a little bit different from the description in the 'How to' section of this GREAT site.
Sand the surface with some medium sandpaper (like 150), then clean/degrease the surface with some oil-free solvent like tolueen, spirit, thinner etc. Afterwards let the solvent evaporate till the material is dry. Then light up a torch that uses propane or mapp (no oxy-acetylene) and move this over the surface with some fast passes, so the material heats up quickly but not melts (little hairs on the sides can melt) and it slightly discolours. Using this flame treatment you produce hydroxyl and some assorted polar groups. Finally clean the surface again using some solvent.

Now you should have obtained a surface with a several times higher surface energy than the original. so it will bond a lot better.
To see the effect of the flame treatment you can test this the same way as you check the result of waxing your bases. Just drop a droplet of water on the surface and it will spread around instead of staying a nice droplet at the surface.

I hope this will add some usefull information to this topic, however for me there also keep on coming new questions.
Now I gonna get some sleep, before assembling my press tomorrow :) (it's 1:10 am overhere)
I'll try to post some pics of the flame treatment on some of my sample pieces UHMW and of my press this weekend.

Buuk
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hose-man
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Post by hose-man »

Buuk wrote:To see the effect of the flame treatment you can test this the same way as you check the result of waxing your bases. Just drop a droplet of water on the surface and it will spread around instead of staying a nice droplet at the surface.

Buuk
Now that is a usefull bit of information. I will have to test that out!
G-man
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Post by G-man »

Hi guys,

I'm getting up at 4:30 in the morning to go ski testing (finished another pair of skis tonight), so I won't get too involved in this thread right now, but I felt I needed to add a comment to the present topic. I just grabbed a random spare piece of UHMW and placed a drop of water on it. The water drop did not bead up, but instead spread out a little bit (it's very likely that I flame treated this piece at sometime in the past). Then I did an actual dyne level test on it, and it tested out at about 38 dyne. Even though the surface energy of this particular piece of UHMW was high enough to have a low hydrophobicity (did not tend to repel water), the surface energy was not high enough to provide for a good bond surface for epoxy resin. For a lasting bond with epoxy, you'd want at least 60 dyne. With a very good flame treatment, you can reach even a bit higher than 70 dyne, which is higher than any of the other surface treatment processes can obtain. Optimal flame treatment requires a precisely metered gas to oxygen ratio (use only propane, not mapp gas), proper distance from the flame, proper speed through the flame, and proper humidity. A very slight over treatment can result in a dramatically reduced surface energy level, resulting in poor bonding, so, more is not better. Guessing with a propane torch just isn't going to result in consistently good surface bonding, and most often will result in premature delamination. It takes lots and lots of testing to get a handle on the UHMW bonding process. I'm in the process of building a mini ski press just for the purpose of making samples that I can test to the point of failure... the right surface treatment, the right epoxy, the right composites, pressures, temperatures, etc.

Soon, I'll post a bunch of sites where one can find lots of information about surface treatments and sites where dyne level testing supplies are available. It will probably take a bit of time for me to figure out where I filed that stuff away.

I keep thinking that I'll slow down on the ski building and skiing... like next week... then that week comes and I say, "Well, maybe next week"... and yada, yada yada. Maybe next week.

Cheers,
G-man
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hose-man
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Post by hose-man »

G-man, you are rocking it! That's great that your too busy building skis & testing to spend too much time at the computer. I'm too busy working to spend much time building skis, or on the computer. I am soooo looking forward to the info you'll be sharing.

This site is incredible in that respect. One person's experience shared, can improve countless other peoples experience with building skis. If we can get to where delaminations are history that would be soo cool. No more rivets in ski tips!

-H
G-man
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Post by G-man »

Whoa... hold on there, Hose-man... no rivets??... just kidding. Seriously, though, I'm not sure that rivets in a ski tip are totally such a bad thing... even with optimal bonding of the UHMW. I just returned from a day of skiing at our local volcano (on the skis that I pressed yesterday). While getting my skis ready for the day in the parking lot (putting on skins, adjusting bindings, putting skis on my pack, etc.), I was watching other folks who were doing the same. I noticed that pretty much everybody was banging their skis around on the asphalt... tips, tails, sidewalls. Tips seemed to take a special beating. Given the materials and processes that we use to make a ski and then the abuse that we put the finished ski through, can we really be too surprised when the tips delaminate a bit? Then, there are the unplaned events like what happened to one guy on the mountain today when his tele ski came off only 2 turns into his descent, and the ski went down about 2,000 feet of rocky mountainside without him. Anyway, I like to use my skis pretty hard and I also like to pass them around for other skiers to try out. I'd like the skis to last quite awhile, but, I don't want to have to be all concerned about how badly they might be getting treated. So, at this point in time anyway, I'm pretty much leaning towards adding a bit of tip and tail reinforcement to the skis... and rivets work pretty good for that sort of thing.

I certainly understand, though, what you are saying about the new worlds that could open up with the optimal bonding of UHMW. I'm just thinking that, with all the performance that some of us ask of our skis (especially in light of the fact that UHMW was originally never intended to be a bondable material), a few well placed rivets could turn out to be a good thing. Have you seen the tip protectors on the Goode skis? They're not bad looking and they use a couple of screws instead of rivets, so, I would imagine that they are replacable if they get too messed up.

Okay, about to the ski testing today. I was on a tele rig and a friend of mine was on an AT rig attached to a pair of skis that I made for him last week. This was his second time out on the skis. He has spent much of his life on skis in Colorado, and he reported that these were the best turning skis he's ever been on. I skied some of the scariest high angle terrain that I've ever been on today, and after just a few turns, I was able to relax and enjoy just letting the skis run. As I've said before in other areas of this forum, I'm quite sure that the great performance of these skis is related to the smooth flex curve that a sandwich ski gives,.. that coupled with the proper core profile and the proper mounting location of the binding. When all of these things come together, it's mighty sweet. So, again, sandwich is the way to go, and sandwich construction is very reliant on the optimal bond quality of the UHMW components.

Oh, I might not have been very clear with my post last night regarding using a drop of water as an indicator of adequate surface energy for bonding UHMW with epoxy resin. A water drop that does not bead up when placed on the surface of a piece of treated UHMW is an indicator that the surface energy is greater than that of an untreated sample, but it does not take much surface treatment for that to take place. A much higher surface energy level (or dyne level) is required for optimal bonding of UHMW with epoxy resin, so a water droplet is not a very accurate or reliable test if a really strong bond is the goal. Buuk is completely correct, however, that it is one readily available method that will indicate that the surface energy is improved over a non-treated sample. It's just that water will not bead up over a wide range of dyne levels, like about 38 to 70, and we want to get as close to 70 as we can.

Okay, it's time for a disclaimer. All of this stuff that I'm submitting to this forum might make it sound like I know what I'm talking about. Well, that's probably quite up for debate. Mostly, I'm just a guy who wants to build the best skis I can, so I've spent MANY late nights over the past few months doing research (my wife will tell you that I've become obsessed... luckily she likes to ski... but she'll also tell you that she would really like for her house to get finished... sooner than later... okay, the snow will be gone soon, then I'll work on it). So, when I get the information websites posted, forum readers can read the info themselves, and, hopefully, I'll be off the hook and we'll all have more success bonding UHMW.

By the way, if you get the chance, check out a Rossignol ski from the last 2 or 3 years. Many of the ones that I've seen use cap construction at the tips and tails (for durabilty?) and sidewall construction at the mid-body of the ski (for smooth flex?). Pretty ingenious. And I've not heard of any delamination problems with these skis, so at least Rossi seems to have figured it out, so, it is possible... think we can buy off one of their R&D guys for some inside tech information?

G-man
Greg
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Post by Greg »

That's great to hear that the skis are doing so well. As for rivets, I use them if I think the bonding is at all unquestionable, or if you are making a pair of skis that are going to see a lot of slapping (like landing jumps or skiing moguls, yuck).

I love the way homemade skis ski, but one thing I find is that half of the "high quality ride" comes from the joy of skiing something that is truly hand crafted by yourself, and the pride that goes with building them. There was an inspirational speaker who's main quote is that "If you change the way you look at things, the things you look at change". Homemade skis are definitely that way. :D
G-man
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Post by G-man »

Okay, I took a couple of hours today to go through my computer files (what a mess) and pulled out some of the most helpful websites that I have found regarding the surface treatment and adhesive bonding of UHMW. I actually had dozens of different sites and pages filed away, but, much of the information was redundant or of limited use. So, I narrowed it down to just a few of the most useful sites/pages. The best online site that I have found is www.accudynetest.com. It has a wealth of information. I order my dyne testing supplies from the phone number listed on the site. The folks on the phone couldn't be any more pleasant and helpful... even though I insist that I am just a small fish. They also offer some very good books on the subject of plastic adhesion promotion at www.polysurfacesbookstore.com. The best site that I've found for flame treating equipment is www.combust.com.au. Cruise around the site for information about flame treating. The catalog page offers various burners and regulators. Unfortunately, this company is located in Australia, so I don't know about actually ordering parts from them. I've never ordered from Australia before, but I've seldom had much luck ordering outside of the U.S. on other occasions. I'm sure that these parts are relatively easy to come by in this country, I just have to figure out where to look. According to the info on the websites, the air/gas mixture is the most important parameter for good flame treatment, so a good set regulators seems to be the first goal, then an appropriate burner set-up. For testing the dyne level of the treated surface, I use the Accudyne test marker pens. They only test up to 60 dyne, but I'll worry about testing higher after I am consistantly successful at getting up to 60. As I said before, I'm shooting for 70 dyne or higher. If I find other useful information, I'll pass it on. Happy reading.

G-man
Mutombo
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Post by Mutombo »

Let me ask you something. All you are talking about is to improve bondability of the base with epoxy resin? I´ve read in this web that most manufacturers of ABS or P-Tex recommend that you flame treat the plastic before it is bonded. This can be done by simply using a torch and quickly passing the flame over the plastic.
Do you usually do over your base? I only wanted to brush the top of the base to get a rough side. Do you think is it neccesary to flame it?
The other question is that the HDPE I can buy here is not porous, these sheets are used to make water tubes and other products. Maybe in this case it´s neccesary to do it.
What do you think?
G-man
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Post by G-man »

Hey Mutombo,

Good questions. Sorry that I may not have been very clear when speaking of which UHMW parts I felt needed to be flame treated. Primarily I was talking about the UHMW sidewall components. After all of the machining and cutting that these parts go through during the ski building process, the remaining exposed surfaces have a surface tension of only about 31 dyne... no good at all for bonding. Generally, the base and top sheet material come pre-flame treated from the manufacturer and are good to go. But, after reading you post, I decided to do some testing on the base material anyway.

Now, keep in mind that when doing dyne level (surface tension) testing, that if the testing fluid wets the UHMW surface without beading up or breaking apart in less than 2 seconds, the testing fluid's dyne level is lower than the UHMW's dyne level. If, on the other hand, the testing fluid rapidly beads up, it's dyne level is higher than the UHMW's. When building a ski, we want the surface tension of the UHMW to be greater than the surface tension of the epoxy resin... that's what leads to a strong bond. I haven't yet been able to ascertain just what the surface tension of epoxy resin is, but even if I did find that out, it wouldn't fully answer what I need to know because the viscosity of a liquid effects it's surface tension, and as a heat cure resin heats up in the press, it's viscosity decreases as it gets thinner.

Okay... back to the morning's testing. First, I cut a 10cm x20cm piece of base material and performed a dyne level test on the factory treated side. I have dyne pens rated at 30, 46, 52 and 60 dyne. For this test, I went straight to the 60 dyne pen. The solution rapidly spread out from the application line, telling me that the dyme level of the treated side of the base material was at least 60 dyne. Then, I flipped the base material over to the non-treated side. I performed 46, 52, and 60 level tests. To my initial surprise, none of the test fluids beaded up, even after a minute or so. This told me that even the supposedly non-treated base surface had a dyne level of greater than 60. After a few moments of thought, I think I figured out why. Anyone who has attempted to flame treat the relatively thin base material before, has probably noticed that it deforms with heat quite severely. I'm betting that at the factory, in order to limit this deformity/warping problem, they flame treat both sides of the material at the same time. This is most likely also why the material sometimes exhibits some inherent internal stressing that manifests as warping when we cut out our base shapes.

Next I grabbed a piece of sidewall material. I order this material in a thickness of 1/2 inch (13mm) and it comes with one side abraided and flame treated. The other side is smooth and slick looking. I cut two pieces of materal about 10cm x 20cm each, and placed opposite sides up on the laboratory test surface (the kitchem table). I started with the 46 dyne fluid. When tested on the smooth side, it beaded up immediately, which told me that the smooth surface probably had not received any type of treatment and that it's dyne level was most likely at the 31 level, normal for this material. Then, I tested the treated side of the material with 46, 52 and 60 dyne test markers. All three of them immediately spread out into the adjacent material, which told me that the dyne level of the treated side was at least 60 dyne.

Now, the more interesting part of the testing. Next, I went back to the smooth, non-treated side of the 1/2" material. I used a piece of 60 grit sand paper and roughed up the surface, cleaned it with acetone, and tested it. To my surprise, none of the test fluids beaded up... or at least didn't appear to. Did this mean that by simply roughing up the surface with sandpaper, that I increased the dyne level from 31 to over 60? I don't really think this was the case. Rather, I think that roughing up the surface made it difficult to visualize the fluid break-up because there was not a smooth surface for the test fluid to re-assemble onto. Next, I flame treated 3 or 4 areas with a propane torch (varying speed of flame movement and distance of flame from the surface of the material) on the remaining smooth surface, and applied the dyne test fluid. Each of the 3 or 4 different areas tested out with differing dyne levels, from low 30's to up to 60 or greater. This told me that varients of flame exposure had much to do with how well the surface of the UHMW responded to the flame treatment process.

So Mutombo, in answer to your questions... You shouldn't need to flame treat the rough side of the base material... it should already be treated. A really old piece of base material may have lost some of it's surface tension over time and could use a 'bump' treatment, but, again, distortion could be an issue with the thin material. If you did need to bump treat. you could set up a flame treatment devise with a ribbon burner on both top and bottom and re-treat both sides of the material simultaineously... that might work. In my opinion, effective flame treating can not be done well by just quickly passing a flame over the plastic. My testing this morning exhibited vastly varying results with that method. Regarding HDPE... it's in the same polyethylene family as UHMW and the same surface treatment guidlines follow for both materials.

As for what I learned from the testing today, two major points stand out. Number one: don't test on abraided materials. They don't allow the test fluids to perform as intended and lead to false results. From now on, I'll do all of my flame treating and surface tension testing on smooth surfaces, then transfer what I've learned onto the abraided surfaces. Number two: Don't go solely on dyne level surface testing for determining projected epoxy bond strength. Instead, use the dyne testing to guide the in shop, hands-on sample testing... making lots of test samples and abusing them until I get one that I just can't get to come apart... then make sure that I can replicate it over and over again.

Man... I've got to get out of here and go skiing.

Cheers,
G-man
Buuk
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Post by Buuk »

Found an interesting article using our university database:

A Developed Method for Studying the Surface Energy Variation on High Density Polyethylene

Abstract:
In the gas flame treatment of low surface free energy (SE) substrates, such as high-density polyethylene (HDPE), problems might arise from under or over flaming, oxygen concentration differences in and around of the flame, etc. Consequently, in printing applications, the possible variation of induced SE existing on the surface, could cause distortion on printed letters. In this research, a new method based on the wetting and spreading phenomena was developed to display and study details of the SE variation on HDPE flame treated substrates. It was an easy and quick method. Results showed good agreements with previous works done on the flame treatment characteristics. The optimal flaming was achieved, while the substrate surface had been positioned about 10 to 12 mm below the tip of the flame's blue part. Also when the flaming speed had been controlled about 80 mm/s. Results from the adhesion strength test supported the optimum situations found previously by others. It was hoped that this new method could also be capable of estimating the critical SE of solid surfaces in future works.

The full article can be found at:
http://www.iranppi.org/journal/paper_pd ... 130606.pdf


I also have been thinking about some other simple solutions of increasing the bond strength.
For example cutting the edge and the UHMW under an angle. This will increase the bondable area and so increase the strength of the weld. Also it will reduce shear in the weld because the forces will be disintegrated.

Image

Regards, Buuk
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