RTM High-pressure RTM (Image supplied courtesy of Cannon Afros) Production cycle comparison RTM – moving from low- to high-pressure systems Epoxy RTM systems used in automotive are bi-component systems and most commonly consist of a formulated resin and a formulated hardener. At the beginning of the process, the chemical components are warmed to the required temperature in storage tanks and kept separately in continuous re-circulation through the circuit of the dosing machine up to the inner part of the mixing head. This ensures that their viscosity remains constant through the complete process. Araldite® epoxy systems for fast RTM The low viscosities of Huntsman’s resin systems play an essential role in the entire process, from dosing and mixing right through to impregnation and fibre wet-out in the mould. The standard RTM process is also known as low-pressure RTM because the system components (resin and hardener) are usually mixed through a static, helicoidal mixer at a relatively low pressure, usually lower than 15 bars. The mixture then feeds the mould containing the reinforcement, also at low pressure. In comparison, for high-pressure RTM, the mixing process is managed by pulverising the reactive components with appropriate injectors or ‘jets’ in a cylindrical mixing chamber (whose diameter can be as small as 4-5mm) at high pressure, most commonly above 50 bars. When not in use, the mixing chamber is sealed by a precisely-machined piston which prevents the components from getting mixed at the wrong time. The computerised control determines the precise amount of liquid materials required by each different mould and calculates a precise injec- (1): Time at mould T to reach 300 mPas (2): Tg obtained with 1% internal release agent Product designation Mix viscosity at mould T Injection/curing T Maximum injection time (1) Typical cure time Resulting Tg (2) DMA onset point Conditions Unit Araldite LY 1564 Hardener XB 3458 ® mPa.s < 50 < 50 75 - 100 °C sec min °C 78 - 88 Resin XB 3585 Hardener XB 3458 Resin XU 3508 Hardener XB 3458 Resin XB 3585 Aradur® 5003-1 Araldite® LY 1564 Aradur ® 5003-1 New development 100 ca 30 5 93 - 103 93 - 103 110 - 120 < 50 110 ca 60 10 94 - 104 < 50 110 ca 60 3 95 - 105 38 jec composites magazine / No74 July 2012