Indoor News and Views

Carbon Prop Outline Follow-Up

June 13, 2013

Brett Sanborn

Since publishing the carbon prop outline article, a few people have been contacting me to point out problems and concerns.

Apparently, since the article was written and published, http://www.r-g.de no longer offers Toray M60J carbon fiber. Unfortunately, there is no supplier here in the US for the fiber. Kevin Lamers pointed out that spools are available on another German composites website http://www.litronics2000.de/, though shipping to the US may be a problem.

The ProSet 145-224 epoxy system I suggested does not seem to be available from the CST composites store. I originally used a different Pro-Set epoxy that as of January 1, 2013 is no longer available (old formula 145-226). MGS epoxy has good properties, but also may be cost prohibitive. EZ-Lam 60, available from acp-composites seems to have good properties and can be cured at similar temperatures as the 145-224 of ~140º F.

Finally, there has been concern over the size of the M60J fibers being similar to asbestos fibers which can cause lung problems. In general, the body can clear away larger particulates, but smaller particulates might not be cleared as easy. While the diameter of the M60J fibers (5 µm) is much larger compared to asbestos (~0.5 µm or less), some studies have shown that fibers in this diameter range could cause similar affects as asbestos by becoming permanently lodged in the lungs. While the overall aspect ratio of the fibers also plays a role, it is rare to find asbestos fibers thicker than 1 µm in the lungs [1]. It has also been shown that fibers longer than 8 µm and of diameter smaller than 1.5 µm are the most potent cause of malignant cancers in the human respiratory system [2]. The smaller the fiber diameter, the greater number of fibers per mass unit of asbestos dust (or any small particle dusts), which increases the chance of their inhalation and penetration into deeper parts of the lungs [2]. Furthermore, studies suggest that fibers of diameter greater than 3 µm cannot penetrate air sacs in the lungs (are not respirable) [2]. Hence, it seems that M60J fibers are probably slightly larger than what can be dangerous. We also do not know what affect of coating the fibers first in epoxy followed by sanding will do to the size of the particles. This may indeed increase the size and thus reduce the likelihood that the fibers become permanently stuck in the lungs.

All this is to say that when dealing with the M60J fiber it is probably not a bad idea to wear a P100 particulate filter respirator, which will stop small particulates. A further step would be to construct a small particulate hood as shown in the figure below. The hood below is a Lexan box with holes on either end to which a small HEPA air filter is attached. When sanding, the filter is turned on while sanding takes place inside the box.

For an in-depth review of Sources of Asbestos and Other Mineral Fibers Present in Ambient Air, see [2].

Filter setup – Polycarbonate box with hole cut in back for HEPA filter and working hole in front to provide negative pressure and airflow into the box 

[1] D. Liddell, K. Miller. Mineral Fibers and Health. 1991. CRC Press.

[2] L. Wachowski, L. Domka. Sources of Asbestos and Other Mineral Fibers Present in Ambient Air. Polish Journal of Environmental Studies Vol. 9, No. 6 (2000), 443-454

Tyson Glue Bottle Mods

Steve Fujikawa

steve_fujikawa (at) verizon.net

Applying clear silicone around the top of the bottle slows evaporation.

Dennis Tyson’s glue bottles are great, but if you’re like me you’ve had a couple of problems with them.  First, the acetone evaporates from the bottle before you’ve used it all, necessitating an annoying clean out job.  Second, the supplied polyethylene nozzle develops leaks from the acetone.  I’ve found a solution to both of these.

First, apply clear silicone sealer around the cap, aluminum tube, nozzle, and especially the wire and it’s hole as shown in the photo.  This slows evaporation to virtually zero.  Apply the silicone with everything fully assembled and let harden thoroughly.  The wire can be carefully pulled free while leaving a tight seal around it and the hole.  Since doing this I’ve never had the glue harden in the bottle or the nozzle, even after several weeks.  You can even pull the cap off to add more glue without replacing the silicone.

The nozzle can be replaced with the Sig CA applicator tip shown below.  You will need to cut both ends to get a tight fit around the wire and the aluminum tube.  Do this a little at a time so you don’t waste more than one tip like I did!  The Sig nozzle seems impervious to acetone and never develops a leak.

Replace the polyethylene nozzle with Sig CA applicator tip.

Another more minor issue that I’ve noticed is that the wire corrodes from either the glue or the acetone.  After a while the oxide can contaminate the glue.  I’m not a chemist so I’m not sure why this happens, maybe the glue is hygroscopic?  But I suspect the problem could be solved by using stainless wire.  I need to order some soon to make pushrods for a DLG so I’ll try it out.