TT2
Posts: 648
Joined: 3/19/2002
From: Osborn, MO, USA
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The microballoon / glass mixture has cured to a point where I thought I'd start evaluating it. The resulting density figured (very loosely) to be around 21 lb / cu ft...much less than the dough and less than one-fourth that of the sand matrix. The sample was MUCH harder than expected...full thumbnail force would just barely dent it. The stiffness was quite acceptable and would be further enhanced by sandwiching this mixture between layers of glass cloth as the majority have recommended. The resistance to breakage was far better than expected...the test piece was 2 5/8" diameter and averaged about 0.20" thick. The piece could be snapped in half by hand but only when considerable force was applied...nearly all I could give it and I’m no girly-man. Understand to that the sample had probably not reached a 'full' cure yet.
The strength of this 'dough' is probably overkill as is but could certainly be increased by additional amounts of chopped glass.
The surface that was against the coffee-can lid ‘mold’ was glossy with very few voids, and certainly no voids larger than one or two thousandths of an inch. Cross-sections of the sample showed hardly any void content. I didn’t go to extremes when I was packing the mixture onto the mold and would probably take more time on a production piece.
I have rethought the Q-Cells and believe that glass (not phenolic) microballoons should be used since they are the hardest of the hollow spheres.
I would think that the dimensional stability would be the same as the sand matrix molds even over time. The advantage here is that much lighter framework, parting boards, etc. could be used, and the mold wouldn't have any tendency to sag under it's own weight over time…which may be a serious consideration with larger sand molds. I'm sure a 'drop test' of the microballoon / chopped glass mold would far outperform the sand mold...
Bottom line is that I’m lovin’ the microballoon / chopped glass / epoxy and will be using it on my upcoming canopy, cowling, and wheel pant molds for the 30% 50cc Edge 540 that I’m developing. I’m fully convinced that it will produce extremely strong, yet lightweight, molds…far superior to using Coremat as a thickening layer. When you really think about it, substituting the microballoons for the sand makes perfect sense...they're made from silica just like grains of sand, but they're smaller in diameter (which seems to be desirable) and HOLLOW! Though I haven't experimented with the sand I would guess that placement of the microballoon / chopped glass onto the mold would be a bit easier...not quite as nice as the apparently supreme handling qualities of the RT2C dough though...
My question to all of you is this: Has anyone heard of using microballoons during moldmaking before? I’ve been playing around with composites for over a decade and haven’t heard anything good or bad about the subject. What seems the most curious is that chopped glass and microballoons are as common in any composite shop as epoxy! I’m just wondering if someone has tried this method and it proved to result in poor quality molds over time. Just being paranoid I guess…everyone thinks I’m paranoid…
UPDATE: I mixed up another batch in an attempt to arrive at somewhat accurate mixture ratios for those of you who want to try it. By volume: 1 part resin, 1/3 parts chopped glass, 2.5 parts microballoons. This results in an easy handling mixture. I added a layer of 6 oz glass to the mold (coffee can lid) face and spread out the mixture, then backed it up with another layer of glass. I found that after the dough is placed in a fairly consistent thickness on the mold, applying the top layer of glass makes it very easy to smooth the underlying dough out without any of it sticking to the gloves. Also, the top layer of glass becomes wet-out without any additional resin (though an additional application of resin may be desirable to smooth out the outside of the mold).
-Tom
< Message edited by TT2 -- 12/16/2004 6:06:35 AM >
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RE: Sand / epoxy molds - 
