Postcuring

I have heard guys talk about postcuring in molds. I am curious to how long you let your part "air cure" before you move into your baking booth. What I have heard is that heat your booth to 150 F and then turn it off when you put your part in and let it cure all night. Any help would be apperciated.

Ian

 

You need the spec sheet from the resin company. There are no set times for all resins, they each are different.

Bill H.

 

Correcto, all resins have a 'postcure' period. Polyester resins about a week to 10 days, mostly they go into a 2nd mould to cure after the moulding process, epoxy resins follow another procedure, dependent on the used system and process.
A thorough knowledge of the lamination-procedure is required for successful handling of the project. If still in doubt, contact your supplier. In case of epoxy-resins are used as a matrix-material, heatcuring after the lamination process often improves the strength of the laminated product.
Bind-off times vary strongly and are depending on used formulae of the particular resin(s).

 

Here is where I got the idea. It was from another post on this forum which I found doing a Goggle search.I have done some some molding with a iso tooling resin and silicone rudder molds. My parts always came out fine but would noticably shrink and they were not very large parts. I was using chopped mat and hand layup with brushes and rollers. I am wanting build some larger pieces and start using vinyl ester resin to help minimize shrinkage. Any help or guidance would be appreciated. I am basically self taught on this and understand the importance of mixing ratios etc. But there is alot I do not know. I am also curious about using a E or S glass to make better stronger parts, but I am concerned about tight radiuses and details. Thanks Alot.





Hi Lew .

And thanks Mike for the excellent link .

Im in New Zealand and regularly read the CFA magazine . It had never occured to me to look at the website . The magazines are an excellent source of information and I expect to learn even more via that site .

We make automotive parts as well as sanitary ware and kayaks .
We control shrinkage and distortion in the auto parts by postcuring each part in the mould . Our spray/bake painting oven runs at 60 C [ about 150 F ]
Each night the moulds are wheeled into the oven which is then turned off . The next morning the residual heat is still about 30 C [90F ] .
It helps a lot to eliminate unwanted distortion and shrinkage . As a bonus we have a preheated mould to gelcoat on in cold mornings .
All our tooling is made with vynil ester tooling gelcoats to help handle the heat . Recently a salesman tried to sell me a "new improved" polyester tooling gelcoat which may well be a wonderful product but it didnt have the heat distortion temp of the VE
Our conditions here ,and certainly our environmental laws are substantially different to the USA . Your local resins may be formulated to meet emmission requirements rather than say ease of use . Probably contacting the technical help of your resin manufacturer is the best option . Im sure they will know what products are used in your environment etc .
I really doubt you need iso resins for your componentry and good mould making technique should keep shrinkage and distortion minimal

 

Tja

Quit using iso resin in your tooling and in your parts. I can't think of any resin that shrinks more then iso. My exsperiance has been that vinyl ester resins have the lowest rate of shrink. Hpoe this helps, Tom.

 

Iso resins are better than ortho resins, correct. Without going to vinyl ester, your best polyester would be an iso, at least thats what I have gathered. I am willing to go to vinyl ester, but I'm sure if you know what you are doing their is probably guys who can do good with polyester resins.Again any comments are appreciated.

Ian

 

If shrinkage bothers you, stay away from the polyester type resins. Ortho, Iso and Vinyl do shrink considerable, Vinyl is in this issue the best option, depending on formulation; it shrinks generally between 5 and 7,5 % - again it depends on mfr's formulation. The shrinkage of epoxy-matrixes is much less, much, much less.
According the glasstypes you want to use, is S-glass the best option before you enter the field of hybrid woven's. In this field there have been a rapid development of aramid's, carbon's graphite's and even boron's. It all depends on your budget, your experience with high tech materials and the environment you are building in (of extreme importance).
Generally speaking I would advise you that you discuss this matter further with people from the US rather than us in Europe. We have diffrent standards as well as methods. ( Our environmental rulings are our biggest nightmare )
If you are a novice in the production-process of GRP building, stay with the application of Vinyhlester resin, and leave the epoxy's alone.

 

tja

Well I would have to say that iso is still the worst choice even over an ortho. If cost is an issue then epoxy sure won't be the way to go. A good choice might be a low styrine ortho dcpd blend which will give you good cosmetics and relatively low shrink if you leave the parts in the molds for as long as is practicle for what your making. The bottom line is low shrink and inexspensive don't go togeather. Just my opinon, Tom.

 

404 Tooling Polyester Resin-Isophthalic
404 is an isophthalic polyester resin that is used where strength and durability is a must. Experiences lower shrinkage and a higher heat distortion temperature than orthophthalic type polyester resins. Used extensively in boat hulls and in fiberglass mold construction

Tom, I appreciate your time and input. That above is a quote from the U.S. Composites catalog. I found another thread on this site that mentioned ortho dcpd resin, but said it has very poor elongation - 0.5%. I need a more durable part than that because it's going on a car. Thanks, Ian