Heated weights have been found to be useful in adhesive bonding of clips, doublers, and other small parts to lightweight structures and structural components (e.g., face-sheet/honeycomb-core sandwich panels). The heated weights provide both the heat needed to accelerate curing of the adhesive and the force needed to clamp the bonded parts together until the cure is complete.
The heated-weight technique was developed in support of the Top Hat Balloon Project, wherein the technique is used to accelerate the cure of a paste adhesive for bonding inserts. The technique makes it possible to shorten the bonding process from two days to one. The technique can afford similar benefits in the fabrication of structural components for aircraft and spacecraft.
Local heating for accelerating the cure of an adhesive becomes necessary when the structure in question is too large to put in an oven or when heat-sensitive equipment has already been installed on the structure. Therefore, local heating has commonly been accomplished by use of heat lamps or electric heating blankets, and clamp-ing forces have been applied by weights, clamps, or vacuum bags. Heat lamps or electric blankets must be monitored closely to ensure that maximum allowable curing temperatures are not exceeded, and heat-sensitive equipment must be removed or protected. In contrast, the heated-weight technique does not require close monitoring or special preparations to protect heat-sensitive equipment, yet it inherently ensures that the maximum allowable curing temperature for a given bond is not exceeded and that heat is applied only in the vicinity of the bond.
In preparation for bonding by the heated-weight technique, a caul plate is machined from a highly thermally conductive material (e.g., aluminum or copper) to the profile of the small part to be bonded to a structure. In an oven, a suitable weight is preheated to a temperature equal to or less than the maximum allowable curing temperature for the adhesive used in the bond. The caul plate is placed on the part to be bonded, and the heated weight is placed on top of the caul plate (see figure). The caul plate distributes the weight and heat evenly over the part. If additional heating time is needed to complete the cure, then additional weights can be heated and used to replace the previous heated weight(s).
This work was done by James Parker and David Puckett of Goddard Space Flight Center. No further documentation is available. GSC-13866