REPAIRING PLASTIC SADDLEBAGS
Jeff Dunkle <firstname.lastname@example.org>
Date: Fri, 14 Jan 2000 04:53:10 -0500
Robert S. Atkinson wrote, in part, to a thread I started:
> The application is correct. The baking soda is 'filler'(?) & the load
> is light for airplane models.
> Is there belief that the baking soda shortens the cure time? This
> is the part I'm interested in!
I asked Paul Burns from the Classic Wings Club list if I could repost a piece he wrote there. He said.....
Sure thing... (I hope the Beemer folks are as pleasant as the CWC people.) The only caveat that I have is that this was written based on my knowledge of the GL1000 -- I can't say for sure what materials BMW has used where.
(here's a copy of what he wrote to that list - based on some professional background)
If anyone is interested, there is a reason that the superglues work well with the side cover repairs: The covers are molded out of ABS (Acrylonitrile-Butadiene-Styrene polymer or plastic). Most of the superglues on the market are methacrylates of one kind or another, and are particularly good at bonding to the acrylonitrile. Someone mentioned earlier about using baking soda in conjunction with Crazy Glue. The baking soda is a base (as in acid-base) material that causes the methacrylate to "kick" or cure quickly. As a rule, it isn't a recommended practice for the material as, if it cures too quickly, the bond that develops isn't as strong as when you let it cure more slowly. Also, be careful of using methacrylate glues around polycarbonate (like helmets, visors, etc.) as many of them can cause crazing and cracking of the polycarbonate (not too good for appearance and absolutely a time bomb for strength of the polycarbonate).
The folks who are advocating welding using a soldering iron -- that is probably about as good a structural bond as you're going to get. If those of you who are so inclined can get your hands on some ABS sheet (check with spa, plastic fabrication, or sign shops in your area -- they will sometimes let you get between the workbench and the trash can, if you know what I mean), and have the patience for it, you can make a welding tool suitable for the job out of a piece of 1/4" or thicker bar stock -- stainless is best, but cold roll steel will work. The method you are going to perform is called hot plate welding. You need to put a decent polish on it (400 grit or finer emery paper). Get a piece that is as wide as the tab and long enough that you can clamp one end in a vise and still have at least five or six inches sticking out like a blade itself. Next, heat the bar until it is hot with a torch or heat gun. If you have a way of measuring its temperature, you want to heat it to around 350 to 400 F. (If you don't have a way of measuring it, put a drop of water on top of the bar; heat until it boils off. Keep heating until water dropped on the bar "dances" or skids around or off like a ball. For the culinarily inclined, kinda like the temperature you want a skillet at when you are going to fix pancakes.) Remove your heat source and push the pieces to be bonded from opposite sides of the bar until their surfaces soften -- probably less than 15 seconds. If it takes much longer than 15 seconds, the bar was probably too cold. Be careful not to heat the cover portion so much that it causes the outside to move or deform. When the parts are good and soft, pull them away from the bar and press them together, making sure the parts are properly aligned with each other. Now, hold that pose. After a while, the plastic will harden and, voila -- the welded assembly.
Whew. This may have been more than any of you really wanted to know! Hopefully those interested enough to make it this far might like to know where all that came from -- in my misspent youth I attended University and obtained a degree in Plastics Engineering, of all things. I knew it might come in handy someday! ;-P (<--- tongue firmly in cheek!)
Lake Elsinore, CA
Senior Member, Society of Plastics Engineers
Big Blue, '78 GL1000, Dressed
All contents Copyright © Internet BMW Riders and the original author(s).
This material is for personal use only.
Republication and redissemination is expressly prohibited without the prior written consent of The IBMWR.
Maintainer: BungeeBob Durrstein
Last Update: Sunday, February 20, 2000