production builders and sandwich construction

[G-man]

Hi mattman,

Thanks for the info. I spent a little time looking over the sites you recommended and will spend more. Mostly what I'm looking for is a laminating epoxy (or other resin) that will adhere to ABS (the top surface of the sidewall strip) because the same resin will also have to be applied to the top layer of composite during lay-up. Maybe Loctite or Devcon has an actual laminating resin listed of their site and I just haven't found it yet.

Over the last few months, I've found bonding adhesives that will bond ABS quite well, but haven't found a laminating resin that does. One possible alternative/option that I came across during a patent search is to apply an approiate bond adhesive to the ABS surface during lay-up, allow it to set up a bit (but not completely cure), then finish the lay-up as usual with epoxy laminating resin. When the lay-up is heat cured, the bonding adhesive and the laminating resin chemically fuse together as a combination polymer, creating a strong bond.

As I indicated before, because a lot of ski manufactures are using ABS, it's probably quite a simple process to get it to bond well. Those in the know are probably reading this thread and chuckling at our efforts to figure it out.

G-man

[skicore]

I don't know what resin you guys are using but I use QCM and a heated press. I don't believe you can get UHMW and ABS to bond if you get the material from a general plastic supplier. The ABS and UHMW the big boys use are specifically made for adhesion. As far as I know this type of ABS is not availbile in the states. IMS/Guirt and Isosport in Austria are the main supppliers I believe. I use only UHMW from Durasurf and have never had a bonding issue after sanding and flame treating. I sand with an 80grit belt sander and flame treat with a MAPP gas torch. I run the flame over the UHMW until it starts to get a visible sheen. White UHMW will slightly brown on the surface in places. I've never done a surface tension test. I just sand and flame treat and have never had a problem, but I've only used UHMW from Durasurf which is specifically made for this.

Anyway thats my experience......

[Cadman]

K2, in particular, had a number of sandwich options. Some of them, upon close inspection, had no visible sign of a glass layer between the top sheet and the sidewall material... just a very tight bond line between the two plastics. However, a slight tri-axial composite pattern was visible in the top sheet, so, it seems that they must be using a pre-preg that is very precisely die cut just a tad smaller than the finished top surface dimensions. Another ski (a capped model) had some sort of rubber top sheet.

The reason you don't see the glass coming out on the K2 sidewall skis is because they use a knitted sock around the core. They have a machine that they run the core through that has a number of rolls of fiberglass thread that actually knits a sock around the core. I don't know about the present since they moved to China but they have always used wet layup on most of the skis that I saw.

[G-man]

Cadman,

Yes ,I recently saw a pic/video (can't remember which) of the glass sock. Thanks though for makin' sure I knew about it.

skicore,

Pretty much all of the on-line info that I've read over the past few months indicates that one shouldn't use Mapp gas to flame treat UHMW... that it doesn't create the proper oxidizing atmosphere for good surface treatment... yet you are having good success with it. What a big mystery this process is. I also use Durasurf UHMW, but, as you know, I can't seem to get it consistently right.

G-man

[skicore]

G-man-

Its crazy how we are not getting the same results. I cannot pry apart the layers with a heavy duty box knife. I even tryied a chisel and they still held. The only bonding difficultly I've had so far has sometimes been the topsheet to the glass underneth.

Anyway, like you said....a mystery...........

[powdercow]

A lot of things went wrong when i was pressing my first skis. Luckily this is one thing that went very right. My sidewalls are ABS the I procured from a local plastics distributor. I would tend to think that it isn't very high grade since a 4'x8' sheet cost only $150 even with haircell treatment on one side. I had tons of trouble getting a good bond between my core and the haircell side of the ABS which made it even more surprising when the bond between fiberglass and sidewall tops
(machined but totally untreated) is rock solid.

I can give no scientific explanation of what "went right" but only hope it will continue to do so in all my skis.