PLASTIC CAPS FILLED WITH SEALING COMPOUND AS COMBINED PROTECTION AGAINST FUEL AND HYDRAULIC FLUID AND AGAINST LIGHTNING STRIKES

Abstract

Provided herein are sealing compound-filled plastic caps for sealing of connecting elements in aircraft construction against liquids, wherein these plastic caps function as combined protection against fuel and hydraulic oil, especially that based on tributyl phosphate, and against lightning strikes, and can be produced and applied in an economically viable manner. The plastic cap for sealing of connecting elements in aircraft construction consists predominantly of at least one high-performance polymer having a breakdown resistance of at least 10 kV/mm to DIN IEC 60243, and has been filled with a sealing compound having a high energy absorption capacity and including at least one filler selected from the group consisting of gas- and/or air-filled hollow packings, where the plastic cap and the sealing compound are cohesively bonded to one another. Additionally provided is a method of filling and application of such plastic caps, and a corresponding aircraft.

Claims

1. A plastic cap for sealing of connecting elements in aircraft construction, which consists predominantly of at least one high-performance polymer, has a breakdown resistance of at least 10 kV/mm to DIN IEC 60243 and has been filled with a sealing compound having a high energy absorption capacity and including at least one filler selected from the group consisting of gas- and/or air-filled hollow packings, where the plastic cap and the sealing compound are cohesively bonded to one another.

2. The plastic cap according to claim 1, wherein the at least one high-performance polymer is a polyetherimide and/or a polyphenylene sulfide.

3. The plastic cap according to claim 2, wherein the at least one high-performance polymer is a polyetherimide.

4. The plastic cap according to claim 1, wherein the at least one high-performance polymer has been impact-modified.

5. The plastic cap according to claim 1, wherein the at least one high-performance polymer has a water absorption of not more than 1.5%.

6. The plastic cap according to claim 1, wherein the sealing compound is one based on polysulfide and/or polythioether.

7. The plastic cap according to claim 6, wherein the sealing compound is a polysulfide and/or a polythioether in combination with manganese dioxide, an isocyanate compound, an isocyanate prepolymer and/or an epoxy compound as hardener.

8. The plastic cap according to claim 1, wherein the sealing compound has a density between 0.7 and 1.5 g/cm.sup.3.

9. The plastic cap according to claim 1, wherein the hollow packings in the at least one filler are microballoons.

10. The plastic cap according to claim 1, wherein the sealing compound has a content of the at least one filler in the range from 1% to 13% by weight.

11. The plastic cap according to claim 1, wherein the sealing compound comprises a filler combination consisting of at least one filler selected from the group consisting of gas- and/or air-filled hollow packings and of at least one further filler selected from the group consisting of mineral and polymeric, non-gas- and/or -air-filled fillers.

12. The plastic cap according to claim 1, wherein the plastic cap and the sealing compound are cohesively bonded to one another by a chemical attachment.

13. A method of filling and mounting a plastic cap according to claim 1, wherein the plastic cap is filled with a sealing compound according to claim 1 by means of a metering robot or manually, then applied to a connecting element in an aircraft by means of an automated method step or manually, and the sealing compound is cured.

14. The method according to claim 13, wherein the plastic cap is filled with the sealing compound by means of a metering robot and then applied to a connecting element in an aircraft by means of an automated method step.

15. An aircraft having at least one connecting element to which a plastic cap according to claim 1 has been applied.

Description

EXAMPLES

[0039] Lightning-proof plastic caps of the invention have been tested for their stability to hydraulic oil and fuel.

Test Setup

[0040] Titanium screws were mounted with the aid of titanium nuts on correspondingly drilled carbon fiber sheets.

[0041] Plastic caps that consisted of a polyetherimide (PEI) and had been filled with a sealing compound that was a polysulfide containing with up to 4% by weight of gas-filled microballoons were fitted onto said screws and nuts. The sealing compound was then cured at 23 C. for 14 days, in the course of which the plastic cap and the sealing compound were cohesively bonded to one another.

[0042] Subsequently, some of the plastic caps filled with cured sealing compound were stored in hydraulic oil (HyJet IV A.sup.+) at 70 C. for 168 hours, and some others were stored in kerosene (Jet A1) at 100 C. for 336 hours.

[0043] The plastic caps that had been stored in hydraulic oil, those that had been stored in kerosene and those that had not been stored were then each fixed in a metal block having a corresponding cutout. The metal blocks were then pulled away from the carbon fiber sheets at right angles by means of a machine. At the same time, the force required to pull the plastic caps away from the screws and nuts was ascertained (pull-off force).

[0044] In addition, after the plastic caps had been pulled off, the cohesion failure on the plastic caps and the visual appearance of the sealing compound were ascertained by inspection. Cohesion failure is defined here such that the rivet connection and the plastic cap are completely covered with sealing compound.

[0045] The results obtained are summarized in tab. 1 below.

TABLE-US-00001 TABLE 1 Visual appearance Storage of the of the plastic Cohesion failure on sealing caps in . . . Pull-off force in N the plastic caps in % compound 354 100 OK, normal fracture Hydraulic oil 312 100 OK, normal fracture Kerosene 332 100 OK, normal fracture

[0046] As can be inferred from tab. 1, there was no significant change in results when the plastic caps were stored in hydraulic oil or in kerosene.