Moving Out of Oven
Some companies are working outside of both the autoclave and the oven. Australian composites manufacturer Quickstep says its fluid-based Qure process provides faster curing and lower cost through the use of direct contact heating of materials instead of the convective heat transfer used in an autoclave.
In the Qure process, the heating chamber contains a heat transfer fluid (HTF) with a floating laminate sandwiched between a rigid or semi-rigid mold (also floating in the HTF) and a flexible membrane or bladder. The HTF can be rapidly heated and then cooled for curing.
“We can substantially increase the heat up rate of composite structures,” says Tim Olding, executive general manager, systems. “The system allows for fully controllable ramp rates and dwells under closed loop temperature and pressure control, all the way up to 190 degrees C (374 degrees F). Because the bladder is in direct contact with the composite, the heat transfer rate is higher and more uniform.” For some applications the heated bladder is placed on both sides of a thin shell tool, enabling highly uniform heating of the material through thickness. Faster heat transfer rates result in faster curing times, higher productivity and greater tool utilization, Olding says.
The company recently commissioned its first isothermal machine, which will provide the flexibility to preheat the fluid and do a hot flush of the tool to get fast ramp rates.
Manufacturers can use the Qure process with different material types and with either resin infusion or impregnation processes. There is no theoretical limit on part size, since the equipment can be scaled up as needed.
“Qure has been successfully used to cure laminate stacks up to 50 mm thick without any controlled exotherm. The largest Quickstep machine we have made to date is used to make parts for the satellite launch industry. This machine has a working tool area of 6,000 x 4,000 mm (19.6 feet x 13.1 feet),” says Olding.
Quickstep first used the Qure technology in the aerospace sector as an alternative method for curing prepreg materials. Now it’s also used for non-aerospace applications, including the production of carbon fiber housings for the medical imaging industry.