Vacuum drop following the temperature step

General Composites Discussions Composites Talk
#1

Dear colleagues.

We are facing some issues regarding abnormal vacuum drops which follow the thermal curing profile (autoclave).

We have analysed the possibility that micro-cracks open with the temperature increasing the leaking rate and dropping the vacuum but that is very unlikely once that is happening on several tool we put in this autoclave loading.

We checked that maybe the air channel between vacuum source and an gauge has been blocked (breeder collapsed) and the gauges are reading the constant volume thermal expansion of the air in connection with the gauge. Again that is very unlikely for all the gauges we have in one large part (more than 5).

We are really getting crazy because the drop doesn’t make any sense.

Any idea?

Thanks in advance guys

#2

What is your starting vacuum level and what does it rise to?

#3

Where in China are you? I’m in Shanghai

What your tool made out of? Carbon/epoxy?

Whats the drop rate, and at what temp?

#4

Vac always drops once you put 90psi on it
How big is the part ? What’s the drop ? Why do you need 5 gauge readings ?
Do a simple back to back test,envelope bag a flat sheet with a vac and gauge the same distance apart as your problem job
Cook the sheet and see what readings you get through the cycle
If vac drops you know its the breather,if it doesn’t you will know your clave is fine and so is your breather and the problems with the mould

#5

Can be moisture or/and degassing of the resin. A pressure drop of about 20mbar when heating above 60C is not unusual.
If more it can be the tacky tape or the bagging film.

#6

Doubtful in a clave thou
Leak through the tape or bag would just get worse as pressure enters an trips an alarm