How do you do the postcure of a resin infused piece?
Do you demold the part and then postcure it? Or postcure befor demolding?
I usually postcure before demolding, I have had problems with distorsion and surface finish with post cure after demolding…the surface has become corrugated and rough like the fiber.
I post cure usually before removing bag, peel ply ecc, or I heat the mold directly after infusion, so the resin hardens first, then i demold
For the best surface finish you want to do the heat treatment while the part is still in the mold.
Of course the mould should be able to withstand the heat from postcuring. If not, you need to postcure freestanding. In that case a gentle ramp-up temperature is needed.
Johannes, how is your oven controller coming along?
slowly, like a freestanding postcure (.2 degrees celcius a minute, or 10 degrees c/hour)
Take a resin with less shrink. There are few to buy wich do not have much shrink. Using a gelcoat/ in mould coat minimizes the problem.
Also heat curing can minimize the problem. I have not realized a different between freestanding and in mould post curind if you use a slow heat ramp.
Hi, any chance you might be able to share your setup equipment used for post curing, i would realy like to post cure but i have no idea of what parts to buy for a home DIY curing oven, any help will be highly appreciated.
Also make sure the part is at room temp before removing from the mold
How high of a temperature do you need to post-cure to?
I have not realized a different between freestanding and in mould post curind if you use a slow heat ramp.
I have noticed a significant difference…at least with the structural epoxy resins that I use. Almost all the parts that my shop produces come out painted. I’ve done heaps of testing to try and eliminate the problem of fabric print-through. When you look at the shrinkage curve of most resins you see that most of the shrinkage happens during the latter part of the cure. Very little shrinkage happens during the first 70% of the cure. After this point the shrinkage climbs dramatically with each phase of the cure progression. The cross-linking of the resin progresses as the heat enables a higher degree of molecular mobility. If the part is left in the mold the molecular lattic builds itself around the molecules that are “stuck” to the molding surface. Given enough time and heat no more molecular links are possible and the surface becomes stable (unless the Tg is exceeded). If the part is not in the mold the surface molecules are free to rearrange themselves and the fabric pattern becomes visible.
you should post cure to a temp 40 or so degrees above you think the part will see in use. if you plan on the part being outside and paint it a dark color 200. if it’s for indoor use 150 or so.
It would be really depend on the type of resin that was used. Post-curing a resin with a max Tg of 200F to 240F could do harm to the resin.
how big should it be? my home made oven is 1,20 x 0,50 x 0,50 m, is made with sheet metal, with inside a fan and a 1KW electric resistance. Outside a thermoregulator for the temperature control and temperature ramp.
I use it until about 80° C, but it’s able to 120°C.
It’s not very isolated, so I can do better
I don’t do a postcure like this, my thermoregulator doesn’t accept ramp like this, too slow. I increase 1 or 1,5 °C a minute…for exaple until 50°C, then I wait a few minutes, then I increase of 5°C, when it reaches the temperature I wait a few minutes, then increase other 5°C. Very home made, but for the moment si the best I can do.
I do thin laminate, so maybe the rate of themperature increase is secondary
if a resin has a max temp of use of 80°C , can be post cured for example at 85/90 °C? If I do it, I shorten the time of postcure, or I waste the resin?
Yes, you can postcure at high-than-ultimate-tg temperatures. Just expect some deformation. When the part is still in the mould (and preferably the vacuum on) this is not a problem.
1 thing however: never never ever raise the temperature near or even over the Tg of the mould material.
yes ok, I usually cure with the vacuum on, after I cool down and then I vacuum off and demold.
ok thanx for the second info…my molds are made with poliester resin, with a tg of 98°C if I remember well, so 80°C of postcure are ok.
…sorry for my terrific english
Your English is molto bene.
Tg 98 and 80 postcure should be possible. Are your moulds postcured yet? If not, be careful the first time with raising temperature. Do it slowly.
I was always taught that don’t want to over-shoot the Tg during any part of cure. You always want the heat level behind it as the Tg rises with the cure progression. I was taught that can end up with molecular suspension (less cross-linking) if the Tg is over-shoot. Is this correct or only applicable to the Space Shuttle?
I guess it is space shuttle level. I have a couple of test reports, which are based on a cured sample 2H at 120C, where the ultimate Tg is 82 degrees.
I will ask this nasty question halfway September, when I meet a couple of specialists from Huntsman.
Yesterday I have measured, start the oven at 25°C, after 10 minutes I have 37°C on the probe of the oven and 45 in the centre of the oven (the oven’s probe is at the side…I have to move it), after 18 minutes 48 and 58°C.
This with the slower ramp I can do.
Hello guys, ready for 1 week at Lignano’s sea
You are heating way too fast for a freestanding postcure.