Solar Post Curing

[AndrewK]

I have a 5.4 x 3m x 25mm core-cell glass panel (catamaran bridgedeck) and I am wondering if sloar curring is a good practice? Reason being that I can only expose one surface to the sun at a time and expect to see ~30'C difference between the two faces.

Any suggestions?

Thanks
Andrew

[tauruck]

Hey Andrew, I've done what you are asking about many times. I just used some black plastic ground sheet or cut open garbage bags and covered the mould/part. Taped it down with duct tape and it was fine. Australia and South Africa have similar weather so I don't think it should be a problem. Works especially well in winter with parts too big for an oven.

[Jimbo1490]

Spray can flat black lacquer works great for this, too. You can wipe it off with thinner afterward. We have measured 170F at the surface with this method.

Jimbo

[AndrewK]

Thanks Tauruck & Jimbo.
I have done this on smaller parts in the past and know I can get things very hot.
My concern is with the temperature difference approx 30'C (90'F) between the faces.
Will it do more harm than good?

[Ad Hoc]

normally most curing agents do not react below 90c, although you can get some polymerisation as low at -16c, which affects the tack, drapability and flow characteristics.

If you're getting some 77c (170f) in the sun, then you're not far off...so for non structural its probably ok. But for major structural, you may be risking it!

Might pay to ask the supplier to be sure...it's their product they should know better than anyone.

[AndrewK]

Hello Ad Hoc
Epoxy and hardener I am using is marketed as ambient cure, if cured at 25'C as in our climate they say not to bother post curing. This formulation does not benefit as greatly as other formulations from post cure. Also my core is core-cell A, recommended processing temp for this is up to 60'C.
Manufacturer does not like solar curing, they say even 5'C difference between faces is undesirable.

[Ad Hoc]

AndrewK
Yes, the key is the consistent ambient temp (which an oven provides), hence difference between the two faces and also the length of time at the temp. If there is a temp gradient through thickness it could affect the final strength of the laminate. Also there wouldn't be any control on the temp to the extent that localised areas could become permanently heat-damaged.

If the manufacturer doesn't like solar curing...it's a no brainer

[AndrewK]

I ended up making the deck in two pieces 5.3 x 1.5m each. After 24hr ambient cure I enclosed the sides of the laminating table with foil backed bubble wrap and placed an electric fan heater inside to heat this space and the underside of the table.
The top I covered with electric blankets then wool blankets and finally foil backed bubble wrap over the entire thing again.
With the electric blankets on setting 1 from 3 (only approx 20W each) the top laminate slowly reached 50'C, the air heated underside 45'C. Cured at this temp for 24hrs, will not be solar curing.
Laminates are infused 1000gm2, so only thin.

[Ad Hoc]

What's your electricity bill like..??? ;)

[apex1]

Andrew
you could have achieved that by just installing a ventilator for an even airflow between surface and shadowed area, was´nt that possible?
Postcuring up to 70°C is never a bad idea, cos it can "repair" some (minor) unevenness in a homemade resin compound.
Regards
Richard

[AndrewK]

Electricity would have cost $10.

Richard, I'm not sure what you had in mind.
The only way I can think of using solar heat to heat both surfaces evenly at the same time is to have the component in a hot house where the enclosed air is heated. Then you could circulate it with a fan.
Is there another way?

[apex1]

AndrewK
I do´nt know why, but I presumed you use a tarp (plastic film) covering the component, to increase the heat. Then, the vent. would work.
Regards
Richard