Relating to foam filled honeycomb structures

Abstract

Spherical heat foamable pellets (2) are used for reinforcing honeycomb structures (4). The pellets are preferably of average diameter from 0.5 mm to 0.9 mm and preferably at least 80% of the pellets have a diameter in this range. The pellets can form a free flowing stream which can be poured into the cells (5) of the honeycomb where they can be foamed by heating to form a reinforcing foam which can also bond the honeycomb structure to facing sheets. It is preferred that the pellets are based on a thermosetting resin and contain a curing agent that can cure the foamed resin to produce an integral rigid reinforcing foam within the cells of the honeycomb.

Claims

1. Substantially spherical pellets for strengthening a sandwich panel comprising a honeycomb core wherein the pellets: i) comprise a polymer and a thermally activated blowing agent; ii) have an average diameter in the range of 0.5 mm to 0.9 mm; iii) include a thermally activated curing agent; wherein the substantially spherical pellets are dry, free flowing, and readily pourable and the substantially spherical pellets upon foaming in the honeycomb structure, results in a foam with substantially uniform mechanical properties throughout the foam.

2. The pellets according to claim 1 in which the polymer is an epoxy resin.

3. The pellets according to claim 1 in which at least 80% of the pellets have a diameter in the range of 0.5 mm to 0.9 mm.

4. A honeycomb structure in which at least one or more cells are filled by a foam obtained by providing the substantially spherical pellets of claim 1 that have been heated to cause the pellets to foam.

5. The honeycomb structure according to claim 4 in which the polymer is a thermosetting resin.

6. The honeycomb structure according to claim 5 wherein the thermosetting resin is an epoxy resin.

7. The honeycomb structure according to claim 4 in which at least 80% of the pellets have a diameter in the range 0.5 mm to 0.9 mm.

8. The honeycomb structure according to claim 4 provided with a facing sheet on at least one surface.

9. The honeycomb structure according to claim 8 wherein the facing sheets on the at least one surface comprise a prepreg of fibres in a curable matrix.

10. The honeycomb structure according to claim 9 in which the curable matrix is cured at the temperature used to foam the pellets.

11. The honeycomb structure according to claim 9 in which the curable matrix is an epoxy resin.

12. Substantially spherical pellets of average diameter in the range of 0.5 mm to 0.9 mm wherein the pellets comprise a thermosetting epoxy resin, a thermally activated blowing agent and a thermally activated curing agent for the thermosetting epoxy resin; and wherein the substantially spherical pellets are readily dispensed as a dry free flowing state and are substantially free of agglomeration in the dry free flowing state.

13. Substantially spherical pellets according to claim 12 wherein at least 80% of the pellets have a diameter in the range of 0.5 mm to 0.9 mm.

Description

(1) The invention is illustrated by the attached Figures in which

(2) FIG. 1 shows the pellets of the invention.

(3) FIG. 2 shows how the pellets of the invention may be dispensed by pouring into the cells of a honeycomb structure.

(4) FIG. 3 is a flow chart of a honeycomb manufacturing process.

(5) FIG. 4 shows a honeycomb with a section of the cells filled with pellets.

(6) FIG. 5 shows a honeycomb containing a foam derived by heating and curing the pellets within the cells of the honeycomb.

(7) FIG. 1 shows the spherical pellets based on a thermosetting epoxy resin (1) of average diameter about 0.6 mm compared with conventional oval granules (2) of size about 4 mm.

(8) FIG. 2 shows the pellets (1) being fed into a hopper (3) and dispensed into the cells of a honeycomb structure (4).

(9) FIG. 4 shows the honeycomb (4) with some cells (5) filled with the unfoamed pellets (1).

(10) FIG. 5 shows the honeycomb of FIG. 4 after the pellets have been foamed (6).