This invention is directed to the field of structural panels. More particularly, this invention is directed to the construction of a light-weight structural panel which can be formed in continuous long lengths making it less expensive to manufacture. This light-weight structural panel is usable as an aircraft cargo pallet, capable of meeting the specific requirements of the US Air Force set forth in MIL-DTL 27443F, hereby incorporated by reference. Subparagraph 4.5.9 c) requires                “Using a 1 inch square steel mandrel, apply a 900-pound load to the top surface of one test panel. At the option of the supplier, the corners of the mandrel may be slightly rounded. The test panel may be from either test pallet number 1 or 2. The test specimen shall withstand the 900-pound load. Permanent deformation of the test panel in the load area shall not exceed 0.005 inch in depth. Deflection while under load shall not exceed 0.015 inch.”        
Pallet number 1 enumerated in the spec has dimensions of 88″×104″×2.25″, while pallet number 2 is 88″×54″×2.25″. Prior to the development of the present invention, no light-weight structural panel has been able to comply with this requirement. Existing compliant panels are made of heavier materials that are susceptible to moisture absorption, making them heavier yet. As the pallet weight increases, the fuel cost associated with transporting the pallet also increases. The present pallet saves 50 lbs over existing pallets and, as mentioned, the closed-cell structure is water-resistant.
The structural panel of the present invention has sandwich construction: a properly sized core of 2″ thickness made of a closed-cell thermoset foam having lower and upper skin layers made of woven fiberglass wetted out by a polyurethane resin. A series of reinforcing pins in rows and columns extending throughout the dimensions of the panel, are spaced apart by 1″ both laterally and axially. The pins are made of pultruded glass wetted out by a thermoset polymer resin, for example, a urethane resin. A key feature of the panel is that the lengths of the reinforcing pins exceed the 2″ thickness of the core and compress both the lower and upper skin layers by 30-50% of the nominal thickness of each skin layer. Accordingly, the pins form pockets in the skin layers which accumulate excess resin effectively reinforcing these contact points. Desired sizes of the panel are cut into appropriately sized pallets. Excess material is removed from the periphery of the pallet and rails are adhesively secured in place.
Various other features, advantages, and characteristics of the present invention will become apparent after a reading of the following detailed description.
USPTO Backgrounds
USPTO Backgrounds