Cap with sealant flow path

1. A cap for forming a sealed cavity around an end of a fastener protruding from a surface of a structure, the cap comprising:

a cap body with an annular base terminating at a base rim which surrounds an opening into a central cavity for receiving the end of the fastener and lies in a base rim plane around at least a majority of a circumference of the annular base;

an annular skirt providing an annular pocket for receiving a sealant material between the skirt and the annular base, and

a biasing configuration configured to positively bias the base rim against the surface of the structure,

wherein the biasing configuration comprises at least one protrusion extending inwardly from the base into the central cavity, and

wherein the at least one protrusion comprises a cam surface arranged to locate against the fastener, the cam surface being inclined to slope towards the base rim plane away from the base to a free end of the at least one protrusion.

2. The cap of claim 1 , wherein the cap body comprises a cap axis, the biasing configuration being displaceable radially away from the cap axis and being biased radially towards the cap axis upon displacement.

3. The cap of claim 2 , wherein the annular base acts on the biasing configuration to bias the biasing configuration radially inwardly.

4. The cap of claim 1 , wherein the at least one protrusion comprises at least two, and optionally at least three, opposing protrusions distributed around the base.

5. The cap of claim 4 , wherein the at least two opposing protrusions are distributed around an internal face of the annular base, wherein the annular base has a lobed shape in cross-section such that a radially outwardly bulging lobe extends between each neighbouring pair of protrusions.

6. The cap of claim 1 , wherein the at least one protrusion comprises a guide element forming the cam surface.

7. The cap of claim 6 , wherein the at least one protrusion comprises a rib projecting inwardly from the annular base, and the guide element projects from the rib.

8. The cap of claim 1 , wherein the cam surface is inclined at between 15-60 degrees to the base rim plane.

9. The cap of claim 1 , wherein the at least one protrusion is in a fixed relationship with the annular base.

10. The cap of claim 1 , wherein the at least one protrusion is proximate to or at the base rim.

11. The cap of claim 1 , wherein the at least one protrusion comprises an open face configured to abut the fastener as the cap is received over the end of the fastener to urge the at least one protrusion to distend radially outwardly.

12. The cap of claim 1 , comprising an inlet hole in the skirt, wherein the inlet hole is in fluid communication with the pocket to permit a flow of sealing material through the skirt via the inlet hole into the pocket; and an outlet in the skirt, wherein the outlet is in fluid communication with the pocket and arranged to enable air to escape the annular pocket through the skirt via the outlet as the sealing material flows from the inlet hole into the pocket.

13. The cap of claim 1 , wherein the base rim lies in the base rim plane around the full circumference of the skirt.

14. A spark prevention cap for forming a sealed cavity around an end of a fastener, the cap comprising:

a cap body with an annular base terminating at a base rim which surrounds an opening into a central cavity for receiving the end of the fastener and lies in a base rim plane around at least a majority of a circumference of the annular base;

at least two guide elements distributed around an internal face of the annular base, each guide element extending inwardly into the central cavity from the annular base;

wherein the annular base has a lobed shape in cross-section such that a radially outwardly bulging lobe extends between each neighbouring pair of guide elements, and

wherein each guide element comprises a cam surface, the cam surface being inclined to slope towards the base rim plane away from the annual base to a free end of each guide element.

15. The cap of claim 14 , wherein each guide element is a retention tab.

16. The cap of claim 15 , comprising an annular skirt providing an annular pocket for receiving a sealant material between the skirt and the annular base.

17. A joint comprising:

a structure;

an end of a fastener protruding from the structure; and

a cap for forming a sealed cavity around an end of a fastener protruding from a surface of a structure, the cap comprising:

a cap body with an annular base terminating at a base rim which surrounds an opening into a central cavity for receiving the end of the fastener and lies in a base rim plane around at least a majority of a circumference of the annular base;

an annular skirt providing an annular pocket for receiving a sealant material between the skirt and the annular base, and

a biasing configuration configured to positively bias the base rim against the surface of the structure;

wherein the biasing configuration comprises at least one protrusion extending inwardly from the base into the central cavity, and

wherein the at least one protrusion comprises a cam surface arranged to locate against the fastener, the cam surface being inclined to slope towards the base rim plane away from the base to a free end of the at least one protrusion;

the cap forming a sealed cavity around the end of the fastener, the cap comprising a cured sealing material in the annular pocket which secures the cap to the structure.

18. A method of assembling the joint of claim 17 , the method comprising: fitting the cap over the end of the fastener; and injecting sealing material into the annular pocket, wherein the cam surface provides a biasing force to aid positive engagement of the base rim with the surface prior to the sealing material being injected.