Post Curing Question

General Composites Discussions Composites Talk
#1

Hi Guys - I’ve been lurking and learning from you experts for a while now, so I thought I’d throw out a quick question. Should be an easy answer, but I can’t seem to get a reply from Pro-Set.

Anyway, after an infusion has reached “Stage B” cure (Maximum cure at room temperature), it must be brought to final cure via elevated temperature. No problem there - the question is the time between Stage B and the elevated temperature cure.

Is there a window, or not?

i.e. Do I have 24hrs after stage B is reached, or 24 days - maybe even 24 weeks…??

The reason I’m asking is that I plan on making several small parts and doing the final cure in larger batches. So some parts may be sitting around for a few weeks, while others might have just hit “Stage B”. I’ve looked through Pro-Set documentation, but I’m a guy… so, it’s probably right in front of me and I can’t see it!
:cheesy:
Anyway, thanks for your time and input!

Best Regards,
Dallas

#2

Generally once you mix a resin you only have X amount of time until it’s fully cured. This includes the B stage time.

The resin you’re using, does it need to be heated for full cure?

#3

I typically like to begin the elevated temperature cure within 2 days of the original layup time. I have no scientific data to support this though. I always do the elevated temperature cure in the mold if possible. Heat treating out of the mold will typically cause fabric print-through.

#4

It does not matter. You can wait days, weeks, probably even years.

This is fun when building a boat: You build the hull, then glue in bulkheads, stringers, etc. The deck goes on. Only after that, a postcure is performed (before final sanding). This has the advantage that all parts still have a reasonable amount of chemical bond. (all glued together at B-stage).

One thing though: postcuring is an art. You cannot just toss your parts in a hot oven, unless it is not demoulded yet, and vacuum is still on.
Free standing postcures require temperature control. No more than 5-10 degrees C of temperature rise per hour, untill you have reached ultimate Tg minus 10 degrees C. Keep the temperature there for at least 18 hours. Then ultimate Tg is reached. let the oven cool down before taking the parts out.

Large, cored constructions might need even slower ramp rates.

#5

Thanks Herman, you nailed it! Even down to the project itself (future boat building project. Looking really hard at the Farrier F-36 Trimaran). As for ramp schedule, I’ve got the numbers on that and will be building an oven with PID controller to manage the heat temp & time schedule.

Canyon - I’m looking at using Pro-Set 117LV/237 hardener for Resin Infusions. After the slow ramp up temperature, I have to maintain 140F for 8-16 hours depending on the required strength properties. After that is another slow cool down ramp time. So it can take almost two days to “bake” a part which is why I was looking to doing larger batches.

Thanks again for your time to reply!
Dallas

#6

When going through all the trouble, there is no excuse for not doing a 16 hour or even 24 hour bake cycle. Make sure you reach your desired Tg. As you can see from the datasheet, 8 hours is barely enough, 16 hours gives you a considerable better Tg at the same temperature.

Do you know www.fram.nl? I supplied most of the stuff there.

#7

This site and Henny (Fram.nl) has been my main source of EDUCATION on this subject. I really can’t thank you guys enough! I haven’t spent a penny yet, but I feel like I’ve already saved thousands in costly screw ups!

#8

I wonder why R&G recommends post-curing their resins within 48 hours?

#9

I sell resins from the same source as where R&G buys them, but no word on 48 hours…

OK admittedly, over time the resin on the surface may theoretically contaminate a bit, but that is not a structural problem. Actually I never even noticed any effect.

Oh, and one other thing. R&G is German, and Germans tend to over-specify things. This is not meant in a bad way, but it is just their way of living.