Method of repairing damage of aircraft engine components made of weldable thermoplastic materials

Abstract

Disclosed is a method of repairing damage of an aircraft engine component made of or comprising weldable thermoplastic material, which method comprises welding of the weld filler material into an initially prepared damaged area. Also disclosed are the use of plastic welding technique for repairing damaged aircraft engine components made of weldable thermoplastic materials.

Claims

1. A method of repairing a damaged area of an aircraft engine component made of or comprising weldable thermoplastic material or thermoplastic-elastomer composite, wherein the method comprises: cleaning the damaged area of the component; preparing the damaged area for welding by notching of a crack or other type of damage to a predetermined shape of a notch; providing weld filler material; heating a contact area of weld filler material and the notch and at the same time applying pressure to the weld filler material to introduce softened weld filler material into the notch and fuse the weld filler material with material of walls of the notch; allowing a resultant weld to cool down, the weld filler material being obtained from one or more original aircraft engine components of weldable thermoplastic material by crushing of one or more initially prepared components to a granulate of predetermined granule size, melting a resultant granulate and extruding the weld filler material to form regularly shaped rods for use in the repair method.

2. The method of claim 1, wherein welding comprises using a hot air nozzle as a heat source.

3. The method of claim 1, wherein an initial preparation of the components to be crushed comprises removal of all metallic elements, and cleaning the components.

4. The method of claim 1, wherein the weld is subjected to additional heat and/or ultrasound post-treatment to improve material properties.

5. The method of claim 1, wherein the weldable thermoplastic material comprises poly(dodecano-12-lactam).

6. A method of making a weldable thermoplastic material for repairing a damaged area of an aircraft engine component made of or comprising weldable thermoplastic material, wherein the method comprises making weld filler material from one or more original aircraft engine components of weldable thermoplastic material by crushing of one or more initially prepared components to a granulate of predetermined granule size, melting a resultant granulate and extruding the weld filler material to form regularly shaped rods for use in repairing the damaged area of an aircraft engine component.

7. The method of claim 6, wherein the weldable thermoplastic material comprises poly(dodecano-12-lactam).

8. The method of claim 1, wherein the aircraft engine component is a shielding panel surrounding a jet engine fan.

9. The method of claim 1, wherein the predetermined shape of the notch corresponds to a shape of a rod of filler material.

10. The method of claim 1, wherein the predetermined granule size is from 1 mm to 10 mm.

11. The method of claim 1, wherein the rods have a circular cross-section with a diameter ranging from about 1 mm to about 5 mm.

12. The method of claim 9, wherein the rods have a circular cross-section with a diameter ranging from about 1 mm to about 5 mm.

13. The method of claim 6, wherein the predetermined granule size is from 1 mm to 10 mm.

14. The method of claim 6, wherein the rods have a circular cross-section with a diameter ranging from about 1 mm to about 5 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the invention are described with reference to the following drawings, which are provided for the purpose of illustration only, the full scope of the invention being set forth in the claims that follow.

(2) FIG. 1 is an exploded perspective view of a jet engine fan and shielding panels of thermoplastic material;

(3) FIG. 2 is a perspective view of a single jet engine fan shielding panel provided with metallic bushings for mounting thereof onto the fan;

(4) FIG. 3 shows different types of most typical damages/cracks occurring in thermoplastic shielding panels close to a metallic bushing;

(5) FIG. 4 illustrates the welding step of the method according to the invention;

(6) FIG. 5 shows the images of a damaged section of a thermoplastic shield bearing a metallic bushing after sequential steps of the method according to the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(7) The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description in combination with the drawings making apparent to those of skill in the art how the several forms of the present invention may be embodied in practice.

(8) Shielding panels of a weldable thermoplastic mounted onto a jet engine fan body as shown in FIG. 1 are exemplary plastic components that can be repaired by employing the method of the invention. In order to be mounted onto the fan body, the panels are provided with metallic bushings, usually made of aluminum alloys. These bushings, shown in FIG. 2, provide through openings for receiving connecting elements such as bolts or screws and at the same time protect the thermoplastic material of the panel adjacent to the opening from damage, thereby securing the panels in predetermined location. Irrespectively of these advantages, the area of panels adjacent to each such bushing is specifically exposed to stresses during operation and thus majority of typical damages such as shown in FIG. 3 occur in the direct vicinity of the bushings.

EXAMPLE 1

Repair of a Shielding Panel of Jet Engine Fan

(9) The repaired aircraft engine thermoplastic component was a shielding panel of a jet engine fan. Each such engine fan bears 5-15 such panels mounted around its circumference (see FIG. 1). The tested panel was made of PA12composite and involved 6 bushings of aluminum alloy (see FIG. 2). After disconnection from the engine fan the panel was cleaned using isopropyl alcohol. Alternatively, other cleaning methods known for use with dirty panels can be applied such as using e.g. Ardrox6077 (a blend of a solvent and detergent in an aqueous base). Once cleaned the panel was visually inspected for determination of the actual scope of damages to be repaired. FIG. 5, left top drawing, shows the damaged section of thermoplastic shield panel with a crack extending along the bushing after cleaning step.

(10) Subsequently, the damaged panel area was prepared for welding by notching of the crack using a hand held tool. The notching was performed until the predetermined notch shape was obtained, the shape generally corresponding to the size of the welding rod to be used in subsequent step. FIG. 5, right top drawing, shows the damaged section prepared for welding (by notching the crack to a predetermined shape).

(11) After notching the crack, the welding step is performed using a previously prepared welding rod 1 made of the same thermoplastic material as the repaired panel. The welding process is shown in FIG. 4. The welding rod 1 was brought into close proximity of one end of the notch and hot air was blown from a nozzle 2 of a hot air torch 3. At the same time pressure 4 was applied to the rod 1 to force the melted rod material into the notch. The temperature of hot air leaving the nozzle 2 was within the range of 150-300 C., so as to soften the thermoplastic material of the welding rod 1 and edges 5 of the notch above the melting point to allow the fusion 6 of the rod material and the panel material within the notch area. The process of gradual melting and pressing the welting rod 1 into the notch proceeds in the filling direction 7. The hot air leaving the nozzle 2 heats up the rod 1 so that the melted material of the latter forms a bow wave 8 directly filling the notch. Air stream bounced from the bow wave 8 follows along the notch in the air motion direction 9 (essentially the same as the filling direction) so that the notch walls and bottom are preliminarily heated even before the rod material reaches the respective notch section. FIG. 5, left bottom drawing, shows the damaged section after the welding step.

(12) Once the welding step was completed the weld was allowed to cool down to solidify completely. After cooling down the original geometry of the panel was restored by first mechanical removal of excessive weld material by means of a hand held tool, and then the weld area was polished by means of a hand held tool. The repaired panel section after removal of the excessive weld material is shown in FIG. 5, right bottom drawing. (The repaired section after the final step of polishing is not shown in FIG. 5.)

EXAMPLE 2

Preparation of Welding Rod

(13) Original shielding panels of a jet engine fan were cleaned using isopropyl alcohol and comminuted in a shredder tool with rotating knives until a granulate of particle size ranging from about 1 mm to about 10 mm was obtained. Resulting granulate was heated, melted and fed into a screw extruder by whole heat section to a specially shaped nozzle giving the regular welding rods a predetermined circular cross-section having a diameter ranging from about 1 mm to about 5 mm. The welding rod leaving the extruder nozzle is cooled in a water tank and after drying is stored for future use in the repair method according to the present invention.

EXAMPLE 3

Testing of Mechanical Strength of Repaired Component(s)

(14) A 3-point bending test was performed to compare the mechanical properties of repaired and non-repaired thermoplastic material. Accordingly, samples of base material without repair, conventionally repaired (glued) samples and samples repaired by the described welding technique were prepared and assessed. Setting the base material results as 100% the conventionally repaired samples reach a bending strength of 25-50% and a strain of only 30%. The samples repaired with the welding method according to the present invention achieve a bending strength of 80-90% and a strain level of 100% compared to the base material.