A question asked about the necessary curing pressures for a composite resin in the autoclave. Looking through the corresponding datasheet (HexPly F155), I'm confused:
- Apply vacuum of 22 inches (74 kPa) Hg minimum.
- Apply 85 + 15 – 0 psig (586 + 103 – 0 kPa) pressure for laminates.
- Apply 45 + 15 – 0 psig (310 + 103 – 0 kPa) pressure for sandwich.
- Vent vacuum bag to atmosphere when pressure reaches 20 psi (138 kPa).
- During cool-down when the part temperature falls below 140°F (60°C), pressure can be released and the test panel removed from the autoclave and debagged.
The first step is clear, but not the next steps, for instance
85 + 15 – 0 psig (586 + 103 – 0 kPa) is causing me a headache and I can't make sense of it.
I'd guess that one is the external positive pressure and the other is negative vacuum pressure under the sheet, but I couldn't for instance have a 103 kPa vacuum.