Lightning-protection fastener

1. A lightning-protection fastener that fastens a skin of an aircraft and a structural member positioned inside the skin, the skin being constituted of conductive plastic material as a main element and having a conductive member laminated outside thereof, the lightning-protection fastener comprising:

a fastener main body having a head portion, the head portion having an engagement portion formed on an outer circumferential side surface of the head portion; and

an insulation layer which is directly melt adhered to and covers an axial end surface of the head portion, and which is also directly melt adhered to, mechanically engaged with and covers the engagement portion formed on the outer circumferential side surface such that the insulation layer is in direct contact with the axial end surface of the head portion and the engagement portion,

wherein the engagement portion and the axial end surface of the head portion covered with the insulation layer are insulated from the surrounding conductive member,

wherein a circumferential edge portion of the engagement portion has a convex portion along a circumferential direction, the convex portion protruding radially outward,

wherein the convex portion has a round shape along the circumferential direction when seen in a longitudinal section view,

wherein the fastener main body includes a shaft portion on an opposite side of the head portion with respect to the convex portion, and wherein the circumferential edge portion of the engagement portion has a concave portion along the circumferential direction, the concave portion being depressed radially inward and connecting the convex portion and the shaft portion, the concave portion being located below the convex portion.

2. The lightning-protection fastener according to claim 1 , wherein the insulation layer is formed by insert molding.

3. The lightning-protection fastener according to claim 1 , wherein the insulation layer is formed so as to surround the circumferential edge portion of the engagement portion.

4. The lightning-protection fastener according to claim 1 , wherein pre-processing for forming fine surface roughness is applied to at least a part of a surface of the engagement portion.

5. The lightning-protection fastener according to claim 1 , wherein the insulation layer is formed of material having—adhesion promoting—properties with a surface of the engagement portion.

6. The lightning-protection fastener according to claim 1 , which is used as a fastener that fastens the skin of the aircraft in which plastic material having an insulating property is laminated between the conductive plastic material and the conductive member, and the structural member positioned inside the skin.

7. The lightning-protection fastener according to claim 1 , wherein the insulation layer comprises a first layer that covers a surface of the engagement portion and a second layer that covers the first layer, and the first layer is formed of material having—adhesion promoting—properties with the surface of the engagement portion.

8. The lightning-protection fastener according to claim 7 , wherein the insulation layer is formed by insert molding being performed multiple times.

9. A lightning-protection fastener that fastens a skin of an aircraft and a structural member positioned inside the skin, the skin being constituted of plastic material as a main element and having a conductive member laminated outside thereof, the lightning-protection fastener comprising:

a fastener main body having a head portion, the head portion having an engagement portion tanned on an end surface of the head portion; and

an insulation layer which covers the end surface of the head portion such that the end surface of the head portion is insulated from the surrounding conductive member,

wherein a circumferential edge portion of the engagement portion formed on the end surface of the head portion has a convex portion along a circumferential direction, the convex portion protruding radially outward,

wherein the convex portion has a round shape along the circumferential direction when seen in a longitudinal section view,

wherein the fastener main body includes a shaft portion on an opposite side of the head portion with respect to the convex portion, and wherein the circumferential edge portion of the engagement portion has a concave portion along the circumferential direction, the concave portion being depressed radially inward and connecting the convex portion and the shaft portion, the concave portion being located below the convex portion.

10. An aircraft assembly comprising:

a skin constituted of conductive plastic material as a main element;

a structural member that supports the skin from inside; and

a fastener that fastens the skin and the structural member, wherein the fastener is the lightning-protection fastener according to claim 1 .

11. The aircraft assembly according to claim 10 , wherein a gap between the lightning-protection fastener and the skin is filled with sealing material.

12. The aircraft assembly according to claim 10 , wherein the insulation layer is formed so as to create a gap between an inner circumferential surface of a hole bored through the skin and an outer circumferential surface of the insulation layer that opposes the inner circumferential surface of the hole such that the insulation layer is not in contact with the skin.

13. The aircraft assembly according to claim 10 , wherein a top surface of the insulation layer and a surface of the skin are processed to be flush with each other.

14. An aircraft assembly comprising:

a skin constituted of conductive plastic material as a main element; a structural member that supports the skin from inside; and

the lightning-protection fastener according to claim 9 that fastens the skin and the structural member.

15. The aircraft assembly according to claim 10 , further comprising a conductive member laminated outside of the conductive plastic material, wherein plastic material having an insulating property is laminated between the conductive plastic material and the conductive member.

16. An aircraft assembly comprising:

a skin which includes conductive plastic material as a main element;

a structural member that supports the skin from inside; and

a lightning-protection fastener that fastens the skin and the structural member, wherein the lightning-protection fastener includes

a fastener main body having a head portion, the head portion having an engagement portion formed on an outer circumferential side surface of the head portion, and

an insulation layer which is attached to and covers an axial end surface of the head portion, and which is attached to and covers the engagement portion formed on the outer circumferential side surface,

wherein a circumferential edge portion of the engagement portion formed on the outer circumferential side surface of the head portion has a convex portion along a circumferential direction, the convex portion protruding radially outward and having a round shape along the circumferential direction when seen in a longitudinal section view,

wherein a gap between the insulation layer and the skin is filled with sealing material so as to be in —direct—contact with the insulation layer and the skin, the sealing material being in an inverted triangular shape having a larger width and a larger area toward a surface of the skin when seen in a longitudinal section view such that formation of a space between the sealing material and the insulation layer or a space between the sealing material and the skin is prevented,

wherein the fastener main body includes a shaft portion on an opposite side of the head portion with respect to the convex portion, and wherein the circumferential edge portion of the engagement portion has a concave portion along the circumferential direction, the concave portion being depressed radially inward and connecting the convex portion and the shaft portion, the concave portion being located below the convex portion.

17. An aircraft assembly comprising:

a skin which includes conductive plastic material as a main element;

a structural member that supports the skin from inside; and

a lightning-protection fastener that fastens the skin and the structural member, wherein the lightning-protection fastener includes

a fastener main body having a head portion, the head portion having an engagement portion formed on an outer circumferential side surface of the head portion, and

an insulation layer which covers an axial end surface of the head portion and which covers the engagement portion formed on the outer circumferential side surface,

wherein the engagement portion and the axial end surface of the head portion covered with the insulation layer are insulated from the skin,

wherein the insulation layer is formed so as to create a gap between an inner circumferential surface of a hole bored through the skin and an outer circumferential surface of the insulation layer that opposes the inner circumferential surface of the hole such that the insulation layer is not in contact with the skin,

wherein a circumferential edge portion of the engagement portion has a convex portion along a circumferential direction, the convex portion protruding radially outward, wherein the convex portion has a round shape along the circumferential direction when seen in a longitudinal section view,

wherein the fastener main body includes a shaft portion on an opposite side of the head portion with respect to the convex portion, and wherein the circumferential edge portion of the engagement portion has a concave portion along the circumferential direction, the concave portion being depressed radially inward and connecting the convex portion and the shaft portion, the concave portion being located below the convex portion.

18. An aircraft assembly comprising:

a skin which includes conductive plastic material as a main element;

a structural member that supports the skin from inside; and

a lightning-protection fastener that fastens the skin and the structural member,

wherein the lightning-protection fastener includes a fastener main body having a head portion, the head portion having an engagement portion formed on an outer circumferential side surface of the head portion, and

an insulation layer which is directly melt adhered to and covers an axial end surface of the head portion and which is also directly melt adhered to, mechanically engaged with and covers the engagement portion formed on the outer circumferential side surface such that the insulation layer is in direct contact with the axial end surface of the head portion and the engagement portion,

wherein the engagement portion and the axial end surface of the head portion covered with the insulation layer are insulated from the skin,

wherein a circumferential edge portion of the engagement portion has a convex portion along a circumferential direction, the convex portion protruding radially outward,

wherein the convex portion has a round shape along the circumferential direction when seen in a longitudinal section view,

wherein the fastener main body includes a shaft portion on an opposite side of the head portion with respect to the convex portion, and wherein the circumferential edge portion of the engagement portion has a concave portion along the circumferential direction, the concave portion being depressed radially inward and connecting the convex portion and the shaft portion, the concave portion being located below the convex portion.

19. The aircraft assembly according to claim 1 , wherein the insulation layer is formed by insert molding.

20. The aircraft assembly according to claim 18 , wherein the insulation layer is formed so as to create a gap between an inner circumferential surface of a hole bored through the skin and an outer circumferential surface of the insulation layer that opposes the inner circumferential surface of the hole such that the insulation layer is not in contact with the skin.

21. A method of manufacturing a lightning-protection fastener that fastens a skin of an aircraft and a structural member positioned inside the skin, the skin being constituted of conductive plastic material as a main element and having a conductive member laminated outside thereof, the lightning-protection fastener having a head portion and a fastener main body including a shaft portion, said method comprising:

forming an engagement portion on an outer circumferential side surface of the head portion such that a circumferential edge portion of the engagement portion has a convex portion along a circumferential direction, the convex portion protruding radially outward, the convex portion having a round shape along the circumferential direction when seen in a longitudinal section view, and such that the circumferential edge portion of the engagement portion has a concave portion along the circumferential direction, the concave portion being depressed radially inward and connecting the convex portion and the shaft portion, the concave portion being located below the convex portion; and

melt adhering an insulation layer directly to an axial end surface of the head portion so as to cover the axial end surface of the head portion, and melt adhering the insulation layer directly to the engagement portion formed on the outer circumferential side surface so as to cover and be mechanically engaged with the engagement portion, wherein the insulation layer is in direct contact with the axial end surface of the head portion and the engagement portion, and

wherein the engagement portion and the axial end surface of the head portion covered with the insulation layer are insulated from the surrounding conductive member.