Heating apparatus for composite structure repair

DETAILED DESCRIPTION A heating apparatus in accordance with the present invention comprises, as a single unit, a sealed bladder containing a thermally conductive fluid and an electrical heating element in thermal contact with the thermally conductive fluid.
The multiple heat transfer interfaces of prior arrangements are avoided by the construction of the apparatus, in which the heating element is in substantially direct thermal contact with the thermally conductive fluid.
As electrical power is applied to the heating element, the thermally conductive fluid is efficiently heated due to the relatively direct thermal contact with the heating element and the temperature applied to a repair site by the apparatus can be accurately ramped to the desired cure temperature.
In one configuration, the heating element is immersed in the thermally conductive fluid and heat from both sides of the heating element is absorbed by the fluid, thereby increasing the heating efficiency.
In addition to heating efficiency, substantially equal temperatures are maintained across the repair site by conductive and convective heat transfer through the thermally conductive fluid, even on repair sites having non-uniform heat transfer characteristics.
The source of electrical power for the heating element is generally external to the bladder and power is conveyed to the heating element by wires which pass through sealing arrangements at the surface of the bladder.
Arrangements are also provided for pressing the heating apparatus against the repair site to improve bonding.
The heat applied to the repair site and patch is monitored by a temperature sensing device at the repair site to regulate the power applied to the heater.
The sealing arrangements for the bladder may be comprised of silicone based adhesives and/or heat curing processes such as vulcanization.
Separately or in conjunction with other sealing arrangements, bladder seals can include a pair of semi-rigid frames having substantially the same perimeter as the bladder