Title

Method of surface protection of fasteners by application of sealant and paint

Field of the invention

The present invention is encompassed within the field of aerospace, and all the fields which manage the union of different elements, and fastening means subjected to rigorous quality processes. The invention is related to the protection of fasteners in metal-fibre unions for aircraft structures.

Background

Nowadays, in aircraft structures there is a great number of unions between different pieces, which are part of critical elements and systems, so that they must be joined by fastening means subjected to rigorous quality processes. This is the case for many metal-fibre unions in different elements for the fuselage of different aircrafts.

One of the key processes of the manufacture of these unions is the protection of the fasteners that perform the unions with sealant and paint, after they have been installed.

The current process of protection of fasteners in metal-fibre unions for aircrafts requires a first application of sealant, and then a further application of paint, which implies a series of sequenced steps:

The first step is an application of a sealant to all the fasteners of the union by means of overcoat nozzles, which have previously been cleaned and filled with the sealant, and then installed over the fasteners. After the sealant has been applied over the fasteners, the overcoat nozzles are removed immediately from the fasteners

Secondly, sealant curing, which implies a lot of time, depending on the conditions and the sealant composition. This is downtime process, since no further steps can be performed until the sealant is completely cured.

A visual inspection is needed in order to check that the sealant has been properly applied.

Further, once the sealant is properly cured, an overcoating paint is applied over the sealant on the fasteners, manually by means of a brush.

Again, paint curing, which implies downtime again depending on the conditions and composition of the paint.

A further visual inspection is required to check that the paint is correctly applied.

Figures 2-4b show different stages of this current process.

This method involves a lot of time due to the curing downtimes and it provides fasteners with certain defects on the protection, since the overcoating paint is applied on sealant with certain irregularities.

It is therefore desirable a method of protection of fasteners applying sealant and paint which increases the final quality of the protection of the fastener and reduces the downtime of the process, avoiding the drawbacks of the conventional method.

Description of the invention

The present invention provides a method of surface protection of fasteners by application of sealant and paint in one shot.

The fasteners are of the kind of used to join different elements in aerospace field, such as metal-fibre unions for aircrafts.

The method has the following sequenced steps:

Positioning a plurality of overcoat nozzles on a rack. There will be necessary the same number of overcoat nozzles as the number of fasteners to be treated. Painting the interior of the overcoat nozzles on the rack. The paint has to be applied on the interior surface of all the overcoat nozzles placed on the rack, and it will be applied preferably by means of spray gun, although any other conventional painting procedure may be used.

Curing the paint of the overcoat nozzles during the required time, depending on the conditions and paint composition. - Once the paint is properly cured, filling each painted overcoat nozzle with sealant directly over the cured paint, which will be made preferably by a manual sealant filler.

Positioning each overcoat nozzle over a fastener, being each fastener covered by an overcoat nozzle with sealant already painted on the outside of said sealant.

Curing the sealant during the required time. In this step the sealant will be adhered to the paint.

Once the sealant is properly cured, removing the overcoat nozzles from fasteners, remaining thus each fastener covered by sealant painted on the outside by means of an overcoating one shot.

With regard to a preferred embodiment of the invention, after removing the overcoat nozzles from the fasteners, the method comprises a further step of painting the excess of sealant around the fasteners and the top of the fasteners, which will provide a perfect surface finish to the fasteners and the surrounding area. This further step preferably will be made by brush, although it may be performed by any other conventional painting means. Preferably, before painting the interior of the overcoat nozzles on the rack, the method comprises a further step of cleaning the interior of the overcoat nozzles in order to remove any remains from previous operations.

Further, according to a particular embodiment, before positioning of each overcoat nozzle over a fastener, the surface of each fastener will be cleaned to facilitate the adhesion of the sealant with the paint of the overcoat nozzles.

According to a particular embodiment of the invention, the method may comprise a visual inspection stage after curing the paint of the overcoat nozzles. The method may comprise a further visual inspection stage after removing the overcoat nozzles from fasteners. Finally, the method may include a final adhesion checking of the overall protection.

Therefore, this method performs an overcoating and painting process for fasteners in one shot, always fulfilling with standard requirements. The sequence of the method object of the invention, in a way is inverted regarding the prior art method, since in the present invention the overcoat nozzles are painted before to be filled with the sealant.

Further, this method of applying the sealant in the inside of the overcoat nozzle already painted provides a sealant covering the fastener more homogeneous than the method of prior art in which the sealant was applied directly over the fastener. The reason is that in the prior art method the sealant is applied directly over the fastener, and there is no layer surrounding it and containing it. Instead, in the method object of the present invention the sealant is applied first over the paint of the overcoat nozzle, and when it is applied over the fastener, the layer of paint of the overcoat nozzle is surrounding it and containing it, that is, the sealant is trapped by the layer of paint during the curing, and so this final sealant is more homogeneous.

This new method increases the final quality of the overcoated fastener and reduce considerably the lead times, due to a reduction of downtimes, which means a significant saving cost. Further, this new method is enough robust and offers guaranties of adherence, coverage and protection for fasteners, together with an aesthetic appearance greatly improved.

The features, functions and advantages that have been discussed can be achieved independently in various embodiments or may be combined in yet other embodiments. Further details of which can be seen with reference to the following description and drawings. Brief description of the drawings

Next, in order to facilitate the comprehension of this disclosure, in an illustrative rather than limitative manner a series of embodiments with reference to a series of figures shall be made below.

Figure 1 a is a schematic view of a type of fastener for the union of two different elements. Figure 1 b is a schematic view of a type of fastener for the union of three different elements.

Figure 2 is a representation of the filling of an overcoat nozzle with sealant according to the prior art method.

Figures 3a and 3b show a sequential application of sealant to fasteners according to the prior art method.

Figures 4a and 4b show a sequential application of overcoating painting over the sealant according to the prior art method.

Figure 5 represents a plurality of overcoat nozzles placed on a rack according to the method of the present invention. Figure 6 shows the painted plurality of overcoat nozzles on the rack according to the method of the present invention.

Figures 7a and 7b are sequential representations of the filling of a previously painted overcoat nozzle with sealant according to the method of the present invention.

Figure 8 shows the positioning of an overcoat nozzle over a fastener according to the method of the present invention.

Figure 9 shows the removal of the overcoat nozzle from the fastener, thus remaining the fastener covered by sealant painted on the outside. Figure 10 is a representation of a further step of painting the excess of sealant around the fastener and the top of the fastener, according to a preferred embodiment of the invention.

Figure 1 1a is an image of a macrographic evaluation of a fastener treated according to the prior art method. Figure 1 1 b is an image of a macrographic evaluation of a fastener treated according to the present invention.

These figures refer to the following set of elements:

1. overcoat nozzles

2. rack

3. paint

4. sealant

5. fasteners

6. manual sealant filler

Detailed description The present disclosure refers to a method for surface protection of fasteners by application of sealant and paint.

The fasteners 5 are of the kind of used to join different elements in aerospace field, such as metal-fibre unions for aircrafts. Figures 1a and 1 b show different unions made by fasteners 5.

The method has the following sequenced steps:

First, positioning a plurality of overcoat nozzles 1 on a rack 2. The number of overcoat nozzles 1 will be the same as the fasteners 5 to be treated. Figure 5 shows this plurality of overcoat nozzles 1 placed on a rack 2.

Second, painting the interior of the overcoat nozzles 1 directly on the rack 2. The paint 3 is applied on the interior surface of the overcoat nozzles 1 , preferably by means of spray gun, although any other conventional painting procedure could be used. Figure 6 shows the overcoat nozzles 1 already painted by a spray gun.

According to a preferred embodiment of the invention, this painting step is performed at a temperature of 23°C (±2°C) and humidity of 50% (+10%).

Third, curing the paint 3 of the overcoat nozzles 1 during the required time, depending on the conditions and paint composition.

According to a particular embodiment, this curing step is performed at a temperature of 60°C during 2 hours. According to an alternative embodiment, the curing step is performed at a temperature of 80°C during 35 minutes.

Four, once the paint 3 is properly cured, filling each painted overcoat nozzle 1 with sealant 4 directly over the cured paint 3, which will be made preferably by a conventional manual sealant filler 6. Figure 7a shows a manual sealant filler 6 filling the interior of a painted overcoat nozzle 1 with sealant 4, and the figure 7b shows the painted overcoat nozzle 1 completely filled with sealant 4. Preferably this step is performed at a temperature of 23°C (±2°C) and humidity of 50% (±5%)

Five, positioning each overcoat nozzle 1 over a fastener 5, in such way that each fastener 5 is covered by an overcoat nozzle 1 with sealant 4 already covered with paint 3. Figure 8 shows this stage of the method.

Six, curing the sealant 4 during the required time. In this step the sealant 4 will be adhered to the paint 3. According to a preferred embodiment, this step will be performed at a temperature between 15°C and 30°C and humidity between 35% and 75% during 14 days.

And finally, once the sealant 4 is properly cured, removing the overcoat nozzles 1 from fasteners 5, remaining thus each fastener 5 covered by sealant 4 painted on the outside, since during the previous stage the sealant 4 was adhered to the paint 3 of the interior of the overcoat nozzle 1 . Figure 9 shows the removal of an overcoat nozzle 1 from a fastener 5. At the end of this stage the overcoat nozzle 1 is ready to be immediately reused when required. This method applying the sealant 4 in the inside of the overcoat nozzle 1 already painted provides a sealant 4 covering the fastener 5 more homogeneous than the method of prior art in which the sealant was applied directly over the fastener 5, as shown in comparative figures 1 1 a and 1 1 b. Figure 1 1 a is an image of a macrographic evaluation of a fastener treated according to the prior art method, in which certain air bubbles can be observed in the sealant 4. Figure 1 1 b is an image of a macrographic evaluation of a fastener treated according to the present invention, in which the sealant is more homogeneous and there are no air bubbles in the sealant 4. According to a macrographic evaluation, it is visible a paint optimization reducing thickness and some weight, and certain increase of thickness of sealant, assuring inner quality security of the protection of the fasteners 5.

In accordance with a preferred embodiment of the invention, after removing the overcoat nozzles 1 from the fasteners 5, the method comprises a further step of painting the excess of sealant 4 around the fasteners 5 and the top of the fasteners 5. This stage will provide a perfect surface finish to the fasteners 5 and surrounding area. This further step preferably will be made by brush, as shown in figure 10, although it may be performed by any other conventional painting means.

Preferably, before painting the interior of the overcoat nozzles 1 on the rack 2, a cleaning of the interior of the overcoat nozzles 1 is performed in order to remove any remains of paint 3 or sealant 4 from previous operations.

Additionally, according to a particular embodiment, before positioning of each overcoat nozzle 1 over a fastener 5, the surface of the fastener is cleaned to facilitate the adhesion of the sealant 4 coated with the paint 3 of the overcoat nozzles 1 .

According to particular embodiments of the invention, the method may comprise a visual inspection stage after curing the paint 3 of the overcoat nozzles 1 , and the method may comprise a further visual inspection stage after removing the overcoat nozzles 1 from fasteners 5. Finally, the method may include a final adhesion checking of the overall protection (sealant 4 covered with paint 3).

The features, functions and advantages that have been discussed can be achieved independently in various embodiments or may be combined in yet other embodiments. Further details of which can be seen with reference to the following description and drawings.