Radome Autoclave Cure Cycle (HELP SUPPORT) 1

[Cisnerjo]

Hello Everyone,

I work for a manufacturing company that fabricate Radomes, we have an issue with an Autoclave cure cycle that lasted for at least 200 minutes at 140°F while perfoming the ramp down. Which in the autoclave is set to 125°F. But due a malfunction on the Autoclave the temperature remained at 140°F until the segment was change manually to end uo the run. This part is made in to two processes that include two cure cycles that are very similar to one another except that for the first one the Soak time is set at 250°F for 60 minutes while on the second part of the process its cured at 250°F for 90 minutes. Our M&P Engineer Scrapped because the part lasted those 200 minutes at 140°F. We already contacted the prepeg manufacturer and they determined the 140°F has inconsequential effect on the part since the dry Tg values for the type of prepeg E-761 are around 230°F. The lab results from the Test Coupon for Drum Peel (its the only test its performed) are 44 and 45 IN.-LBS/3IN WIDTH our Spec calls for 23 .-LBS/3IN WIDTH Minimum but he still not feel confident with buying it.

Is there anyone with more experience with support knowledge than our M&P that could help us fight this back? or should we let it be scrapped?

Forgot to mentioned during the second stage of the process Issue found on the First one was not shown again during cure cycle so everything was good with no issues at all.The prepeg we use to make this part is E-761 Epoxy Prepreg.

 

[Compositepro]

The 140F is inconsequential. The cure cycle was already over before cooling to 140F. A radome will see 140F+ on a sunny day on the tarmac. A rule that is generally used for aerospace applications is that the service temperature of a part should be limited to 50F less than the Tg.

 

[Cisnerjo]

Thanks a lot for your support and reply Compositepro !! Is there any technical or scientific way to prove this to our M&P so he can feel confident?

 

[Compositepro]

Dealing with idiots is not a technical problem. The manufacturer's statement and simple logic should be sufficient. The logic is that the part will see temperatures greater than 140F for significant periods in service. Therefore 140F for a couple hours is inconsequential. The ending temperature of a cure cycle is usually selected so that the part is safe to handle.