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Post curing question re trailing edges

 
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tonyrenshaw268(at)gmail.c
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PostPosted: Thu May 21, 2020 1:52 am    Post subject: Post curing question re trailing edges Reply with quote

Quote:
Gidday,
I am considering post curing my tailplanes, ailerons and flaps and am wondering if people believe I should support the trailing edges, I’m very happy with how straight they are at the moment, and I don’t want to wreck them. I have T shaped aluminium straight edges I could use with double sided tape to stabilise them, or do people believe with 50 degrees for 15 hours it should be materially stable already and should just boil off the hardener? Any advice or suggestions about supporting these components would be appreciated, even whether I can simply prop them up so air can get completely around them, without any hotspots. I’m concerned even whether having them rest on specific hard points could be an issue at 50 degrees.... personally I think not, but I don’t want to find out the hard way.

Regards
Tony Renshaw

Quote:



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JonathanMilbank



Joined: 14 Apr 2012
Posts: 292
Location: Aberdeen area

PostPosted: Thu May 21, 2020 4:19 am    Post subject: Re: Post curing question re trailing edges Reply with quote

Hi again Tony,

When I did my post curing about 25 years ago, I didn't support the trailing edges as far as I can remember. But then I had the leading edges pointing down, so the trailing edges were up and unlikely to sag. Also I didn't post cure at 50 C, but rather at 45 C to leave a safety margin in case the heat control was inaccurate. The end result seemed / is satisfactory.

Provided that the trailing edges have been trimmed to approximately the final dimensions and therefore don't have any excess material to contribute to potential sagging, then I don't believe that there will be any problem with post curing in the horizontal attitude.

To the best of my limited understanding the hardener doesn't "boil off", but simply continues to react with the resin while further facilitating the hardening process. I'm ready to be corrected in this matter. Ampreg 20 is the product which I was using.

As long as you post cure in the 45 to 50 C range, there should be little or no fear of deformations.


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budyerly@msn.com



Joined: 05 Oct 2019
Posts: 29
Location: Florida USA

PostPosted: Thu May 21, 2020 3:22 pm    Post subject: Re: Post curing question re trailing edges Reply with quote

Being in Florida in a hot barn I never have done a heater post cure on the stock XS E glass aircraft, during the summer, but on the carbon fiber spar work in the winter, I did as the Gurit literature states to do a post cure to achieve proper cure of its slower hardeners.

Never lay a freshly cured aileron flat between supports, it will sag. Always allow a component to cure above 75F-80F for 8-12 hours minimum. Even Gurit medium hardener cures fully at these temperatures. To get a bit more stiffness one should post cure Ampreg 20 series epoxy used in thin components laid up with thin glass over foam. Aeropoxy 2032/PH3660 fully cures at room temp in 8-12 hours and for those very thin components exposed to desert sun, a heat cure to 120 F is recommended. Paint the component any color you want as long as it is white and you won't have issues with the glass parts deforming. Dark colored painted surfaces should be heat cured in a well supported mold or surface to preserve their final shape before heat curing in an oven (normally heated to about 140-150F) as the surface temperature will be quite hot for a dark blue painted surface, but a white painted surface will be cool to the touch even in direct sunlight, therefore high temp heat cure is not necessary for white finished Aeropoxy parts.

In Florida my metal building in the hot sun post cures even Ampreg 20 series within one day at roughly 100-110F for 8 hours. Over a few weeks at these temps it really hardens the cure. For those in a hurry Gurit says 50C or 120F for 16 hours is sufficient for slow cure hardener (which really stays sticky for a long time and does not deep cure without heat ((NASTY). Dark painted surfaces should be cured at a slightly higher temp for about 8 hours. The Gurit rep I contacted was comfortable with a room temp layup and cure of their medium hardener if the temps throughout the layup time and cure was accomplished over a few days at this warm room temp. But even if post cured at 50C, the thin glass structures like an aileron will not be stiff enough to be stored only supported on its ends in a horizontal position if stored in high heat. He suggested that thin parts be stored long axis horizontal with the parts either vertical (TE down or up) if supported only on its ends or just stack it vertical leaning against the wall perfectly vertical.

PTW Aeropoxy preferred all components be supported fully if stored at high temperatures (like dessert sun in a hot metal building) even if heat cured to 120 F.

Gurit has declared their Ampreg 20 series epoxy laminating systems obsolete. Their new 3X series fully cures at a warm room temp 20C like Aeropoxy 2030. Post curing the laminate will greatly increase mechanical/thermal properties. The system will achieve similar properties with a cure of 5 hours at 70 - 80°C or 16 hours at 50°C. The latter temperature is easily achievable with low cost heating and insulation techniques.
The post cure need not be carried out immediately after laminating. It is possible to assemble several composite components and post-cure the
entire assembly together. It is recommended, however, that elevated temperature curing should be completed before any further painting /
finishing operations. Furthermore, care should be taken to adequately support the laminate if it is to be post cured after demoulding, and the
laminate must be allowed to cool before the support is removed.

Bottom line: Properly support your components while curing, post curing, and in storage.

Best Regards,
Bud Yerly


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wdaniell.longport(at)gmai
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PostPosted: Thu May 21, 2020 6:09 pm    Post subject: Post curing question re trailing edges Reply with quote

I made supports/cradles from eps

William Daniell
LONGPORT
+57 310 295 0744
On Thu, May 21, 2020, 05:55 Tony Renshaw <tonyrenshaw268(at)gmail.com (tonyrenshaw268(at)gmail.com)> wrote:

Quote:
--> Europa-List message posted by: Tony Renshaw <tonyrenshaw268(at)gmail.com (tonyrenshaw268(at)gmail.com)>

> Gidday,
I am considering post curing my tailplanes, ailerons and flaps and am wondering if people believe I should support the trailing edges, I’m very happy with how straight they are at the moment, and I don’t want to wreck them. I have T shaped aluminium straight edges I could use with double sided tape to stabilise them, or do people believe with 50 degrees for 15 hours it should be materially stable already and should just boil off the hardener? Any advice or suggestions about supporting these components would be appreciated, even whether I can simply prop them up so air can get completely around them, without any hotspots. I’m concerned even whether having them rest on specific hard points could be an issue at 50 degrees.... personally I think not, but I don’t want to find out the hard way.
Regards
Tony Renshaw

>

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