Fastener using lubricated interference fit
The invention relates to a metallic fastener ( 10; 40 ) for the interference fit assembly of at least two structural elements ( 20, 22 ) comprising a through hole, the fastener comprising an enlarged head ( 12; 42 ), a shaft ( 14; 44 ) having an external diameter before installation that is greater than an internal diameter of the hole, said shaft comprising a conductive surface ( 26; 56 ). Before installation, at least the conductive surface ( 26; 56 ) is coated with a lubricating layer ( 30 ), which comprises a mixture of at least one polyolefin and one polytetrafluoroethylene, for example, having sufficient adherence to prevent its abrasion by manual manipulation of the fastener and being weak enough to be at least partly stripped from the conductive surface during the interference fit assembly of the fastener. The invention further relates to a method for obtaining such a fastener and to a method for installing such a fastener in a structure. The invention is applicable to the assembly of aircraft structures.
1. Metallic fastener for an interference fit assembly of at least two structural elements comprising a through hole, the fastener comprising an enlarged head, a shaft having an external diameter (D 1 ) before installation that is greater than an internal diameter (D 3 ) of the hole, said shaft comprising a conductive surface,
in which fastener at least the conductive surface is coated with a lubricating layer, the composition of which lubricating layer comprises a mixture of at least one polyolefin and one polytetrafluoroethylene, said composition being determined so as to have sufficient adherence to prevent its abrasion by manual manipulation of the fastener and to be weak enough to be at least partly stripped from the conductive surface during the interference fit assembly of the fastener, characterized in that the lubricating layer comprises at least 80% by weight of polyolefin and polytetrafluoroethylene.
2. Fastener according to claim 1 , wherein the polyolefin is a polyethylene or a polypropylene.
3. Fastener according to claim 1 , wherein said layer further comprises a desiccant and/or a biocide.
4. Fastener according to claim 1 , wherein the conductive surface comprises a sulfuric anodization layer that is less than 1 μm thick.
5. Fastener according to claim 1 , wherein the conductive surface is a metal having undergone a passivation operation.
6. Fastener according to claim 1 , wherein the conductive surface is an aluminum layer deposited in a vacuum.
7. Fastener according to claim 1 , wherein the conductive surface comprises the entire external surface of the shaft.
8. Fastener according to claim 1 , wherein the conductive surface comprises only one portion of the external surface of the shaft.
9. Fastener according to claim 8 , wherein the conductive surface comprises an annular portion of the shaft of the fastener.
10. Fastener according to claim 8 , wherein the conductive surface comprises an axial portion of the shaft of the fastener.
11. Fastener according to claim 1 , wherein the lubricating layer further coats a threaded portion of the fastener.
12. Fastener according to claim 1 , further comprising a traction tail and a shear groove designed to break under a certain tensile stress.
13. Use of at least one metallic fastener according to claim 1 , through a hole passing through at least two structural elements of an aircraft, in order to dissipate electric currents in at least one structural element when the head of at least said fastener is struck by lightning.