Hey ahhh, why these parts getting so soft in the sun?

 

How can I fix this? I do resin infusion, is it time to get a parts oven and switch to a higher temp tooling gel?



If Brute Force Isn''''t working your not using enough...

You can post cure the parts using an infrared heat lamp the same type of lamps used for curing paint any thing from a single 30cm single bulb lamp to a large multi bulb array 

Hi Don,

All of the comments about post-curing are right, what's happening when you parts are getting 'soft' in the sun is not that the resin is at its Tg (glass transition) temperature but just that it was not fully cured when you demoulded it and then still not fully cured when it went out into the sun. For as long as the resin stays at the room temperature (or even quite a bit higher) than it first cured at, it will feel hard but when it's been exposed to the much higher temperatures of direct sunlight then it's effectly 're-curing' at the higher temperature. You'll find that these parts that seem to have gone soft in the sun then won't do it again because they have now effectively been 'post-cured' in the sun and so now have a higher HDT (heat distortion temperature).

Direct sunlight can take a black carbon fibre part to 80'C (176'F) quite easily which is enough of an increase to make the resin soften and then re-cure.

Post-curing is best done in the mould (which means moulds that can take elevated temperature without distorting themselves) but can also be done out of the mould. If you post cure out of the mould then you should go for a much steadier heat-ramp, maybe several hours at 40'C, several hours at 50'C, several hours at 60'C. If you're in the mould (particularly if you're still under vac) then you can be a lot more robust with the post cure, maybe even just dropping the mould straight into a 60'C or 70'C oven.

Most standard mould making materials (even those not designed for elevated temperature use) can take 60'C and you should find that this is all the post-cure you need to anneal the resin and prevent any HDT problems caused by high operating temperatures.

Heat lamps, as Bruce suggests can be used by you should excercise caution because you can accidentally get some very hot spots which would be beyond the temperatures you can safely expose the resin to. If you use heat lamps or other very localised heating be sure to diffuse the heat through breather cloth or some other insulating material which will dissipate the heat more or even flip the mould over (if it's still under vac) and shine the heat onto the reverse side of the mould, rather than directly onto the part.

--Matt

Matt Statham
Easy Composites / Carbon Mods - Technical Sales

What about post curing parts that are skinned?  I'm assuming it's still required.  Is it possible to just sun cure them? 

Is it ok to use the kitchen oven or do I need to worry about toxic chemicals?