I always weigh out my resin when laminating. However, I’ve never worked out the actual ratio. Math isn’t my strong point. Here’s a typical carbon lay-up I did today;
Weight of carbon; 168g
Weight of resin (including hardener); 138g
Can somebody help me with the math?
I would use the weight of the reinforcement as for the resin, add a little more for fudge factor (left in cup or whatever) and the hardner on top of that as that is just to react to the resin…not bond (or what my former aide would say…“Dude, glued…”).
But what resin matrix are you using?
What %?
What process?
???
Total weight 306g (if that is your total weight) before and after measures helps for better acuracy
(168g100) / 306g Carbon is 55% of the total weight
(138g100) / 306g Resin is 45% of the total weight
168g/138g Carbon Ratio is 1.2 : 1
138g/168g Resin Ratio is .82 : 1
pretty sure thats how its done, lol, its been a while since I’ve done any math
Thank you for the rapid response. What I meant was, how do I express the resin to carbon fiber numbers (above)as a ratio?
The method I typically use is to pre-impregnate the fabric on the bench between two layers of plastic film, then cut out the pieces and place them in the mould. As well as keeping the weave in place (the top layer of plastic film is kept on until the fabric is in place - like real pre-preg),then vacuum bag,it lets me accurately keep a track on how much resin I’m using.
I know I’m less than 50/50, but would like the above example as a ratio.
if i took a guess. 1.2:.82 …
that would be a percentage ratio, so using your starting numbers you’ve got a 55/45 carbon to resin ratio
But thats not going to be your finished ratios, due to losses (drips, leftover in the cup, evaporated VOC’s etc etc)
Thanks. Good point. I’ll measure how much is left in the pot.
if you want to calculate your resin to fiber ratio you are getting for vacuum parts, the best way is to laminate a flat square that is bigger than a foot that simulates your laminate. then cut the piece down to a perfect foot square, weigh the panel, and then the dry material. subtract the total weight by the dry weight. you then have your resin weight, now divide the resin weight by the total weight, you will get a decimal number, for example, 5.7 oz plain/5.7 0z twill/5.7 oz plain carbon=52g ft squared. after lamination weighs 76.4 g which equals 24.4 g resin, 24.4 divided by 76.4 equals 0.32= 32% RC
Thanks, Hojo,I’ll try that. I’ve just made a one foot square test piece of a new carbon pre-preg. It’ll be intersting to measure the resin content of that also. It’s supposed to have been made out of the same dry fabric I’m using.
You can also do a burn out test. weigh the cloth, wet it out (or with CF PP you don’t need to), let it full cure, weigh it and then burn it up and weigh the cloth remains left over.
See the lower section “Everything un-related to composites”…
all so, if you want to figure what your prepreg actually is coming in at before it is cured. you can wash out the resin with acetone multiple times till it becomes just fiber, then let it air out completly. and weigh again. then you will get an accurate FAW and RC. you will find out how different batches can vary in both FAW and RC. just make sure you rinse all the resin out completely using multiple acetone baths or else you will loose accuracy