GB2536098B

GB2536098B - Object processing

Info

Publication number: GB2536098B
Application number: GB1521655.9A
Authority: GB
Inventors: Oliver Ashworth Sam; Bowden Craig
Original assignee: BAE Systems PLC
Current assignee: BAE Systems PLC
Priority date: 2014-12-17
Filing date: 2015-12-09
Publication date: 2019-08-28
Anticipated expiration: 2035-12-09
Also published as: GB201521655D0; EP3234231A1; WO2016097695A1; EP3234231B8; US20170342587A1; AU2015365719B2; EP3234231B1; AU2015365719A1; GB2536098A

Description

OBJECT PROCESSING

FIELD OF THE INVENTION

The present invention relates to the processing of objects.

BACKGROUND

Many aluminium aircraft parts, for example aircraft panels, frames, ribs etc., are painted.

Typically, some regions of the surface of an aircraft part are chromate conversion coated, while the remaining regions of the parts of the surface of an aircraft part are anodised. Typically, only the chromic acid anodised regions of the aircraft part are painted, while the chromate conversion coated regions of the aircraft part are left unpainted.

Figure 1 is a process flow chart showing certain steps of an example conventional process for painting an aircraft part.

At step s2, the unpainted aircraft part is masked by selectively applying masking tape to certain regions of the aircraft part. In this example, only those regions of the aircraft part that are to be later chromate conversion coated are masked. In other words, only those regions of the aircraft part that are to be anodised and later painted are left unmasked. Such masking may be performed using 3M 425 Aluminium Foil Tape.

Typically, such masking processes, including cutting making tape to desired shaped and applying the cut masking tape to the aircraft part, may take about 3 hours.

At step s4, the masked unpainted aircraft part is anodised. Thus, an anodic layer (or oxide layer) is formed on the unmasked surface of the aircraft part.

Typically, this step of anodising the aircraft part may take about 1 hour.

At step s6, the anodised aircraft part is de-masked and cleaned. In particular, the masking tape applied to the aircraft part at step s2 is removed. Also, any adhesive residue left on the aircraft part by the masking tape is wiped from the aircraft part. Solvents or other cleaning chemicals may be used to remove the adhesive residue.

Typically, this step of de-masking and cleaning the aircraft part may take about 1 hour.

At step s8, the cleaned aircraft part is prepared for chromate conversion coating. In some examples, such preparation of the aircraft part includes selectively masking (for example, using masking tape and/or paper) the aircraft part. In particular, the anodised regions of the aircraft part may be masked.

At step s10, the prepared aircraft part is chromate conversion coated. In some examples, the aircraft parts is chromate conversion coated by hand. In other words, a human being manually applies a chromate conversion layer to the un-anodised regions of the surface of the aircraft part. Thus, each region of the surface of the aircraft part is either chromate conversion coated or anodised.

Typically, the steps of preparing the aircraft part for chromate conversion coating, and chromate conversion coating the aircraft part may take about 2 hours.

At step s12, the chromate conversion coated aircraft part is cleaned. Such cleaning may include the use of clean, cold water.

Typically, this step of cleaning the chromate conversion coated aircraft part may take about 1 hour.

At step s14, the cleaned aircraft part is masked by selectively applying masking tape to certain regions of the aircraft part. In this example, only chromate conversion coated regions of the aircraft part are masked. Also, only anodised regions of the aircraft part are unmasked.

At step s16, the masked aircraft part is painted. In this example, paint is only applied to unmasked (i.e. anodised) regions of the aircraft part. Masked, chromate conversion coated regions of the aircraft part are left unpainted.

Typically, this step of painting the aircraft part may take about 3 hours.

In some examples, the masking tape applied to the aircraft part at step s14 is removed after the paint has dried.

Thus, an example conventional process for painting an aircraft part is provided.

SUMMARY OF THE INVENTION

The present inventors have realised that, using a conventional method such as that described in more detail above with reference to Figure 1, paint tends not to adhere correctly to the aircraft part in certain regions. The present inventors have realised that, at least during de-masking and cleaning process (such as that performed at step s6 of Figure 1), residue from the masking tape may remain on the aircraft part. The present inventors have also realised that such masking tape residue may be spread to previously unmasked regions of the aircraft part during cleaning e.g. after or during a de-masking process. The present inventors have realised that masking tape residue tends to detrimentally effect the adhesion of paint to the aircraft part. The present inventors have realised that it would be beneficial to provide a method for painting an aircraft part that reduces the number of times an aircraft part is masked and demasked.

The present inventors have further realised that aircraft parts undergoing a conventional painting process, such as that described in more detail earlier above with reference to Figure 1, tend to exhibit blemishes and/or superficial damage. The present inventors have realised that inspection tape used during paint adhesion tests may remove paint from that painted aircraft part. The present inventors have further realised that, in conventional painting processes, tools (such as scalpels) often have to be used to remove masking tape from the aircraft part. Use of such tools may cause damage, such as scratches, to the aircraft part which may introduce stress concentration points to a part. The present inventors have realised that it would be beneficial to provide a method for painting an aircraft part that reduces the number of times masking (e.g. masking tape) is removed from the aircraft part.

In a first aspect, the present invention provides a method of painting an object, wherein the object is at least part of an aircraft and wherein the at least part of the aircraft is a panel, frame, rib, trailing edge spar, or left hand horizontal tail, the method comprising: performing a chromate conversion coating process to dispose a chromate conversion coating onto the entirety of a surface of the object; partially masking the chromate conversion coating disposed on the object; performing an etching process to remove, from the object, an unmasked portion of the chromate conversion coating while retaining the masked portion of the chromate conversion coating on the object; and performing an anodising process to dispose an anodic layer onto a region of the surface of the object from which the unmasked portion of the chromate conversion coating was removed; wherein the method further comprises applying a layer of paint onto the anodic layer and not onto the portion of the chromate conversion coating retained on the object.

The present disclosure also describes a method of processing an object, the method comprising: performing a first conversion coating process to dispose a first conversion coating onto at least part of a surface of the object; partially masking the first conversion coating disposed on the object; performing an etching process to remove, from the object, an unmasked portion of the first conversion coating while retaining the masked portion of the first conversion coating on the object; and performing a second conversion coating process to dispose a second conversion coating onto a region of the surface of the object from which the unmasked portion of the first conversion coating was removed.

The first conversion coating is a chromate conversion coating process. The first conversion coating is a chromate conversion layer.

The first conversion coating is different to the second conversion coating. The first conversion coating may be relatively electrically conductive. The second conversion coating may be relative electrically resistive, i.e. the first conversion coating may have a higher conductivity than the second conversion coating.

The method further comprises applying a layer of paint onto the second conversion coating.

The layer of paint may be applied onto the second conversion coating and not onto the portion of the first conversion coating retained on the object.

The method further comprises, after the second conversion coating process, de-masking the object.

The first conversion coating process comprises disposing the first conversion coating onto the entirety of the surface of the object, i.e. over the whole surface of the object.

The second conversion coating process is an anodising process. The second conversion coating is an anodic layer.

The object is at least part of an aircraft. The object may be made of a metal or alloy such as aluminium or aluminium alloy.

The first conversion coating may define an electrically conductive path through at least part of the coated object. For example, when the object is at least part of an aircraft, the first conversion coating may define an electrically conductive path through at least part of the part of an aircraft for the transmission of lightning strike energy.

The first conversion coating process may comprise: exposing at least part of the object to a cleaning substance; rinsing the object to remove the cleaning substance from the object; exposing at least part of the object to a first conversion coating substance, thereby disposing the first conversion coating onto the at least part of a surface of the object; and rinsing the object to remove residual first conversion coating substance from the object.

The etching process may comprise: exposing at least part of the object to a cleaning substance; rinsing the object to remove the cleaning substance from the object; exposing at least part of the object to an etching substance, thereby removing, from the object, an unmasked portion of the first conversion coating; and rinsing the object to remove residual etching substance from the object.

The second conversion coating process may comprise: exposing at least part of the object to a cleaning substance; rinsing the object to remove the cleaning substance from the object; exposing at least part of the object to a second conversion coating substance, thereby disposing the second conversion coating onto the at least part of a surface of the object; and rinsing the object to remove residual second conversion coating substance from the object.

Partially masking the first conversion coating disposed on the object may comprise applying vinyl tape (for example, a 3M 484 vinyl tape) onto part of the first conversion coating.

In a further aspect, the present invention provides apparatus for painting an object, wherein the object is at least part of an aircraft and wherein the at least part of the aircraft is a panel, frame, rib, trailing edge spar, or left hand horizontal tail, the apparatus comprising: means for performing a chromate conversion coating process to dispose a chromate conversion coating onto the entirety of a surface of the object; masking means for partially masking the chromate conversion coating disposed on the object; means for performing an etching process to remove, from the object, an unmasked portion of the chromate conversion coating while retaining the masked portion of the chromate conversion coating on the object; means for performing an anodising process to dispose an anodic layer onto a region of the surface of the object from which the unmasked portion of the chromate conversion coating was removed; and means for disposing a layer of paint onto the anodic layer.

In a further aspect, the present invention provides a painted object that has been painted using a method according to any of the above aspects, wherein the object is at least part of an aircraft and is a panel, frame, rib, trailing edge spar, or left hand horizontal tail and wherein the coated object comprises: a chromate conversion coating disposed onto a first region of a surface of an uncoated object, the first region being the entirety of a surface of an uncoated object; an anodic layer disposed onto a second region of a surface of an uncoated object, the second region being different to the first region, the second region being a region from which the chromate conversion coating has been removed; and a layer of paint disposed onto the anodic layer and not disposed on the chromate conversion coating.

The present disclosure also describes apparatus for processing an object, the apparatus comprising: means for performing a first conversion coating process to dispose a first conversion coating onto at least part of a surface of the object; masking means for partially masking the first conversion coating disposed on the object; means for performing an etching process to remove, from the object, an unmasked portion of the first conversion coating while retaining the masked portion of the first conversion coating on the object; and means for performing a second conversion coating process to dispose a second conversion coating onto a region of the surface of the object from which the unmasked portion of the first conversion coating was removed.

The present disclosure also describes an object that has been processed using a method according to any of the above objects. Such objects tend to be discernible from objects that have undergone conventional treatments such as that described in more detail above with reference to Figure 1. The object is at least part of an aircraft.

The present disclosure also describes an aircraft comprising an object according to the preceding aspect.

The present disclosure also describes a method of producing an aircraft including a method of processing an object according to any of the preceding aspects, the object being at least part of the aircraft.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a process flow chart showing certain steps of an example conventional process for painting an aircraft part;

Figure 2 is a schematic illustration (not to scale) of a painted aircraft part;

Figure 3 is a process flow chart showing certain steps of an embodiment of a process for painting an aircraft part;

Figure 4 is a process flow chart showing certain steps of a process of chromate conversion coating the aircraft part;

Figure 5 is a process flow chart showing certain steps of a process of selectively stripping the aircraft part; and

Figure 6 is a process flow chart showing certain steps of anodising the aircraft part.

DETAILED DESCRIPTION

Figure 2 is a schematic illustration (not to scale) of a painted aircraft part 2. The painted aircraft part 2 is a trailing edge spar, left hand horizontal tail, or an aircraft frame.

An embodiment of a method of producing the painted aircraft part 2 is described in more detail later below with reference to Figure 3.

In this embodiment, the painted aircraft part 2 comprises an initial aircraft part 4 to which coatings have been applied. A surface of the initial aircraft part 4 comprises two regions, namely a first region 6 and second region 8.

The initial aircraft part 4 is made of a metal or alloy such as aluminium or aluminium alloy.

In this embodiment, the painted aircraft part 2 comprises a chromate conversion coating or layer 10. The chromate conversion layer 10 is disposed on the first region 6 of the surface of the initial aircraft part 4. The chromate conversion layer 10 is a chromate conversion film formed from potassium dichromate.

In this embodiment, the painted aircraft part 2 further comprises an anodic coating or layer 12. The anodic layer 12 is disposed on the second region 8 of the surface of the initial aircraft part 4.

In this embodiment, the painted aircraft part 2 further comprises a paint layer 14. The paint layer 14 is disposed on the anodic layer 12 such that the anodic layer 12 is sandwiched between the paint layer 14 and the second region 8 of the surface of the initial aircraft part 4.

What will now be described is an embodiment of a process of producing the painted aircraft part 2.

It should be noted that certain of the process steps depicted in the flowcharts of Figures 3 to 6 and described below may be omitted or such process steps may be performed in differing order to that presented below and shown in Figures 3 to 6. Furthermore, although all the process steps have, for convenience and ease of understanding, been depicted as discrete temporally-sequential steps, nevertheless some of the process steps may in fact be performed simultaneously or at least overlapping to some extent temporally.

Figure 3 is a process flow chart showing certain steps of an embodiment of a process for painting an aircraft part.

At step s20, the uncoated aircraft part (i.e. the initial aircraft part 4 without the coatings 10, 12, 14 applied) is chromate conversion coated. In this embodiment, the entirety of the surface of the initial aircraft part 4, including the first and second regions 6, 8, is chromate conversion coated. A process of chromate conversion coating the entirety of the surface of the initial aircraft part 4 is described in more detail later below with reference to Figure 4.

At step s22, the chromate conversion coated initial aircraft part 4 is masked by selectively applying masking tape to certain regions of its surface.

In this embodiment, only those regions of the surface of the initial aircraft part 4 that are to be later anodised are left unmasked. Also, only those regions of the surface of the initial aircraft part 4 that are to be chromate conversion coated are masked. Thus, in this embodiment, the first region 6 of the surface of the initial aircraft part 4 is masked, while the second region 8 of the surface of the initial aircraft part 4 is left unmasked.

In this embodiment, the masking tape used to mask the chromate conversion coated initial aircraft part 4 is 3M 484 electroplating and anodizing vinyl tape, often referred to as “yellow tape”.

At step s24, the chromate conversion coating is stripped from the unmasked regions of the surface of the chromate conversion coated initial aircraft part 4. A process of stripping the chromate conversion coating from the unmasked regions of the surface of the initial aircraft part 4 is described in more detail later below with reference to Figure 5.

Thus, in this embodiment, the chromate conversion coating is stripped from the second region 8 of the surface of the initial aircraft part 4. Also, the chromate conversion layer 10 remains disposed on the masked first region 6 of the surface of the initial aircraft part 4.

At step s26, the selectively stripped initial aircraft part 4 (with the chromate conversion layer 10 and masking tape applied to the first region 6 of its surface) is anodised. A process of anodising the selectively stripped initial aircraft part 4 is described in more detail later below with reference to Figure 6.

Anodising the selectively stripped initial aircraft part 4 forms the anodic layer 12 only on the unmasked regions of the surface of the initial aircraft part 4. Thus, the anodic layer 12 is formed on the second region 8 of the surface of the initial aircraft part 4 and not on the first region 6 of the surface of the initial aircraft part 4.

Preferably, the below described process of applying paint to the aircraft part is performed within 16 hours of anodising the initial aircraft part 4.

At step s28, the paint layer 14 is applied to the anodised initial aircraft part 4, thereby forming the painted aircraft part 2. In this embodiment, the paint layer 14 is only applied to the unmasked regions of the surface of the initial aircraft part 4. Thus, the paint layer 14 is disposed on the anodic layer 12 on the second region 8 of the surface of the initial aircraft part 4. The paint layer 14 is not applied to the first region 6 of the surface of the initial aircraft part 4.

The paint layer 14 may include multiple paint layers, e.g. a primer layer and a top coat.

Thus, an embodiment of a process for painting an aircraft part is provided.

Returning now to the description of step s20 of Figure 3, Figure 4 is a process flow chart showing certain steps of an embodiment of a process of chromate conversion coating the entirety of the surface of the initial aircraft part 4.

At step s30, the initial aircraft part 4 is prepared.

In this embodiment, preparation of the initial aircraft part 4 includes, but is not limited, checking the initial aircraft part 4 for signs of damage (e.g. abrasions, nicks, scratches, etc.) or excessive contamination, and ensuring all heat treatments, machining, welding, brazing, forming, and flaw detection processes that have been performed on the initial aircraft part 4 have been performed satisfactorily. The preparation process may be performed by a human being, or may be an automated process.

In some embodiments, if damage, contamination, or the like are detected on the initial aircraft part 4, no further steps of the painting process are performed, and the damaged initial aircraft part 4 may be referred for further inspection or repair.

At step s32, the initial aircraft part 4 is wholly submerged in alkaline cleaner.

In this embodiment, the alkaline cleaner is Turco 4215 NCLT having a concentration of between 40g/l and 60g/l. The temperature of the alkaline cleaner is between 45°C and 55°C. The initial aircraft part 4 is submerged in the alkaline cleaner for between 2mins and 10mins.

Thus, the initial aircraft part 4 is cleaned.

At step s34, the cleaned initial aircraft part 4 is drained. In this embodiment, the initial aircraft part 4 is not left to completely dry.

Draining of the alkaline cleaner from the cleaned initial part 4 tends to reduce or eliminate contamination of subsequent processing liquids by the alkaline cleaner.

At step s36, the drained initial aircraft part 4 is rinsed. In this embodiment, rinsing of the drained initial aircraft part comprises spraying the initial aircraft part 4 using clean, cold, running water for between 5mins and 60mins.

Rinsing of the initial aircraft part 4 tends to ensure complete removal of any residual alkaline cleaner.

At step s38, the rinsed initial aircraft part 4 is inspected.

In particular, in this embodiment, the rinsed initial aircraft part 4 is inspected for a water break free surface. If a water break free surface of the initial aircraft part 4 is visible, the method proceeds to step s40. However, if a water break is observed on the initial aircraft part 4, the process returns to step s32.

This inspection of the initial aircraft part 4 may be performed by a human being or automatically.

At step s40, the initial aircraft part 4 is wholly submerged in an etching solution.

In this embodiment, the etching solution is an agitated acid solution. In this embodiment, the acid solution is a so-called “deoxidiser” solution which may be a “de-smut” solution. The deoxidiser solution is Deoxidiser 7/17 (as Cr6+) having a concentration of between 4.5g/l and 10.5g/l. The initial aircraft part 4 is submerged in the deoxidiser solution for between 5mins and 10mins.

At step s42, the initial aircraft part 4 is rinsed. This rinsing process may be performed in the same or a similar way to that performed at step s36 for between 5mins and 60mins.

Rinsing of the initial aircraft part 4 tends to ensure complete removal of any residual deoxidiser solution.

At step s44, the rinsed initial aircraft part 4 is wholly submerged in chromate conversion coating solution.

In this embodiment, the chromate conversion coating solution is Alocrom 1200. The initial aircraft part 4 is submerged in the chromate conversion coating solution for between 2mins and 3mins.

Thus, the chromate conversion layer 10 is applied across the whole surface of the initial aircraft part 4.

At step s46, the chromate conversion coated initial aircraft part 4 is rinsed. This rinsing process may be performed in the same or a similar way to that performed at step s36 for between 2mins and 5mins without spray.

Rinsing of the initial aircraft part 4 tends to ensure complete removal of any residual chromate conversion coating solution.

At step s48, the rinsed initial aircraft part 4 is completely dried.

In this embodiment, the rinsed initial aircraft part 4 is air dried at a temperature of less than or equal to 60°C for at least 10mins.

At step s50, the dried initial aircraft part 4 is inspected.

In this embodiment, the dried initial aircraft part 4 is inspected for the presence of damage, detached deposit, and non-adherent or powdery coating. Detection of non-adherent or powdery chromate conversion coating may be performed by rubbing the surface of the coated initial aircraft part 4, for example, using a test paper such as Whatman, Style No. 40 filter paper.

In some embodiments, if non-adherent or powdery coating is detected, the initial aircraft part may be re-processed, for example, using one or more of the above described process steps.

This inspection of the dried initial aircraft part 4 may be performed by a human being or automatically.

After the inspection process of step s50, the process proceeds to masking step s22 described in more detail earlier above with reference to Figure 3.

In some embodiments, the below described process of applying paint to the aircraft part is performed within 16 hours of the chromate conversion coating the initial aircraft part 4

Thus, a process of chromate conversion coating the entirety of the surface of the initial aircraft part 4 is provided.

Returning now to the description of step s24 of Figure 3, Figure 5 is a process flow chart showing certain steps of an embodiment of a process of stripping the chromate conversion coating from the unmasked regions of the surface of the initial aircraft part 4.

At step s52, the selectively masked chromate conversion coated initial aircraft 4 part is prepared.

In this embodiment, preparation of the aircraft part 4 includes, but is not limited, checking the initial aircraft part 4 for signs of damage. In some embodiments, if damage or the like is detected on the initial aircraft part 4, no further steps of the painting process are performed, and the damaged initial aircraft part 4 may be referred for further inspection or repair.

Prior to masking, the conversion coated area may be solvent wiped to ensure any debris collected between processes is removed and the masking adheres to the conversion coated surface.

Edges of masked areas may be sealed and masking tape boundaries may be overlapped with further masking tape. This tends to reduce or eliminate ingress of treatment liquids into masked areas of the aircraft part.

The preparation process may be performed by a human being, or may be an automated process.

At step s54, the masked initial aircraft part 4 is wholly submerged in alkaline cleaner. This cleaning process may be performed in the same or a similar way to that performed at step s32 for 5-10 minutes.

At step s56, the masked initial aircraft part 4 is drained. In this embodiment, the masked initial aircraft part 4 is not left to completely dry.

At step s58, the drained initial aircraft part 4 is rinsed. This rinsing process may be performed in the same or a similar way to that performed at step s36 for between 4-6 minutes.

At step s60, the rinsed initial aircraft part 4 is inspected. This inspection process may be performed in the same or a similar way to that performed at step s38.

At step s62, the rinsed initial aircraft part 4 is wholly submerged in etching solution or stripping solution.

In this embodiment, the etching solution is, for example, Aluminetch #2. The initial aircraft part 4 is submerged in the etching solution for between 1min and 2mins.

Thus, the chromate conversion layer 10 is etched, i.e. removed, from the unmasked regions of the surface of initial aircraft part 4, for example, from the second region 8. The timings tend to be such that minimal aluminium is removed and only conversion coating film is removed.

At step s64, the etched initial aircraft part 4 is rinsed. This rinsing process may be performed in the same or a similar way to that performed at step s36 for between 2m ins and 5m ins.

Rinsing of the initial aircraft part 4 tends to ensure complete removal of any residual etching solution and stops any further etching.

At step s66, the rinsed initial aircraft part 4 is wholly submerged in deoxidiser solution e.g. to perform a “de-smut” operation. This deoxidising process may be performed in the same or a similar way to that performed at step s40 for a maximum of 30 seconds.

At step s68, the de-oxidised initial aircraft part 4 is rinsed. This rinsing process may be performed in the same or a similar way to that performed at step s36 for between 4mins and 6mins.

Thus, a process of selectively stripping the chromate conversion coating from the unmasked regions of the surface of the initial aircraft part 4 is provided.

After the rinsing process of step s68, the process proceeds to anodising step s26.

Returning now to the description of step s26 of Figure 3, Figure 6 is a process flow chart showing certain steps of an embodiment of a process of anodising the selectively stripped initial aircraft part 4.

At step s70, the selectively stripped initial aircraft 4 part is prepared. Preparation may be performed in the same or a similar way to that performed at step s30 or s52 above.

At step s72, the selectively stripped initial aircraft part 4 is wholly submerged in alkaline cleaner. This cleaning process may be performed in the same or a similar way to that performed at step s32.

At step s74, the selectively stripped initial aircraft part 4 is drained. In this embodiment, the masked initial aircraft part 4 is not left to completely dry.

At step s76, the drained initial aircraft part 4 is rinsed. This rinsing process may be performed in the same or a similar way to that performed at step s36 for between 5m ins and 60mins.

At step s78, the rinsed initial aircraft part 4 is inspected. This inspection process may be performed in the same or a similar way to that performed at step s38.

At step s80, the initial aircraft part 4 is wholly submerged in deoxidiser solution. This deoxidation process may be performed in the same or a similar way to that performed at step s40.

At step s82, the initial aircraft part 4 is rinsed. This rinsing process may be performed in the same or a similar way to that performed at step s42.

At step s84, the rinsed initial aircraft part 4 is inspected.

In this embodiment, the rinsed aircraft part is inspected for, for example, signs of contamination, defects, and damage. This inspection process may be performed by a human being, or may be an automated process.

In some embodiments, if damage, contamination, or the like are detected, no further steps of the painting process are performed, and the damaged initial aircraft part 4 may be referred for further inspection or repair.

At step s86, the rinsed, selectively stripped aircraft part 4 is connected to an anode.

At step s88, the selectively stripped initial aircraft part 4 is wholly submerged in anodising electrolyte.

In this embodiment, the anodising electrolyte comprises: free chromic acid having a concentration of between 30g/l to 50g/l; a sulphate (e.g. Na2SO4) having a maximum concentration of 0.5g/l; a chloride (e.g. as NaCI) having a maximum concentration of 0.2g/l; and water. The maximum total chromium content of the anodising electrolyte is 100g/l. The operating temperature of the anodising electrolyte is between 35°C and 40°C.

At step s90, while the initial aircraft part 4 is wholly submerged in the anodising electrolyte, a voltage is applied to the selectively stripped initial aircraft part 4 via the anode connected thereto.

In this embodiment, the voltage applied to the anode is increased from OV to 22V (+/- 2V) at a rate not exceeding 7V/min. The maximum voltage of 22V (+/- 2V) is then maintained for between 30min and 60min. The voltage is then reduced to less than or equal to 5V.

This reducing of the voltage to less than or equal to 5V, allows for the initial aircraft part 4 to be retained in the anodising electrolyte for an addition time period, for example, for an additional 5mins maximum, if desired.

At step s92, the anodised initial aircraft part 4 is drained. In this embodiment, the anodised initial aircraft part 4 is not left to completely dry.

At step s94, the anodised initial aircraft part 4 is rinsed at least once. This rinsing process may be performed in the same or a similar way to that performed at step s36 for at least 5mins.

Rinsing (e.g. multiple rinsing) of the initial aircraft part 4 tends to ensure complete removal of any residual anodising electrolyte.

At step s96, the rinsed initial aircraft part 4 is inspected. This inspection process may be performed in the same or a similar way to that performed at step s50.

At step s98, the anodised initial aircraft part 4 is wholly submerged in a sealing solution.

In this embodiment, the sealing solution is a dichromate seal. The sealing solution comprises: potassium dichromate having a concentration of between 0.1 g/l to 0.15g/l; a silicate having a maximum concentration of 7.5ppm; a sulphate having a maximum concentration of 90ppm; a chloride having a maximum concentration of 50ppm; and water. The anodised initial aircraft part 4 is submerged in the sealing solution for 10mins (+/-2mins). The operating temperature of the sealing solution is 91 °C (+/- 3°C).

At step s100, the rinsed initial aircraft part 4 is completely dried. This drying process may be performed in the same or a similar way to that performed at step s48.

At step s102, the dried aircraft part 4 is inspected. This inspection process may be performed in the same or a similar way to that performed at step s50.

After the inspection process of step s102, the process proceeds to painting step s28. Further inspection processes may be performed after anodising has been performed, and prior to the painting of the unmasked regions of the initial aircraft part 4.

Thus, a process of anodising the selectively stripped initial aircraft part 4 is provided.

The above described process for painting an aircraft part advantageously tends to be much quicker than conventional process. For example, whereas conventional painting processes typically take around 11 hours to complete, the above described painting process may be performed in around 2.5hours. Thus, the above described method tends to provide significant time and cost savings.

The above described process tends to provide improved better paint adhesion to the aircraft part. The masking tape used in the above described process tends not to be removed until the painting process has been completed. Thus, there tends to be no masking tape residue left beneath the paint layer from de-masking cleaning operations. This advantageously tends to improve paint adhesion. The number of times an aircraft part is masked and demasked during painting is advantageously reduced.

The number of times masking is removed from the aircraft part during painting tends to be advantageously reduced. This tends to reduce the use of tools (such as scalpels) to remove masking tape from the aircraft part. This tends to reduce the likelihood of damage (e.g. scratches etc.) to the surface of the aircraft part.

The masking tape used in the above described process (which may be applied in a pre-cut form or may be cut at time of application to the aircraft part) is a vinyl type. This tends to allow for the use of plastic tools to remove the tape from the aircraft part following application. The aluminium based foil used in conventional processes tends to be difficult to remove and tended to bake onto the surface of the aircraft part, for example, during the anodise process which exotherms as a result of the electrolytic process, or during a paint curing process.

In the above described method, only a single masking of the aircraft part is performed.

Advantageously, the above described method tends to have a reduced use of solvents compared to conventional methods. Also, a need to manually (i.e. by hand) chromate conversion coat the aircraft part tends to be eliminated.

Thus, detrimental health effects to humans caused by solvents etc. tend to be reduced.

The above described method may be wholly or partially automated. For example, the aircraft part may be mounted to a frame or jig and processed as described above by moving the frame or jig between treatment stations. Automated application of, for example, the chromate conversion coating tends to produce higher quality and more repeatable finish.

Advantageously, due at least in part to the improved finish, it tends to be possible to discern aircraft parts processed using the above described process from those processed using a conventional process. For example, it tends to be possible to discern aircraft parts conversion coated using the above described process from those conversion coated using a conventional process. Also, it tends to be possible to discern aircraft parts painted using the above described process from those painted using a conventional process.

The above described process may be implemented as a production line process.

Advantageously, the above described process may be implemented to process multiple aircraft parts simultaneously.

In the above embodiments, the chromate conversion coating is relatively electrically conductive whereas the anodic (or oxide) is relatively electrically resistive. Thus, the chromate conversion coating defines an electrically conductive path through at least part of painted aircraft part. Such an electrically conductive path may be, for example, for transmitting a lightning strike safely through the aircraft.

The above described alkaline cleaning or deoxidising operations may be, for example, air powered (oil free), or liquid agitation processes.

In the above embodiments, the various treatment liquids, treatment times, voltage cycles, and treatment temperatures etc. are as described in more detail earlier above. However, in other embodiments, one or more different appropriate treatment liquids, and/or other types of treatment (such as treatment using a gas or vapour), may be used instead of or in addition to one or more of the above mentioned treatment liquids. In some embodiments, a different treatment time may be used instead of one or more of the above mentioned treatment times. In some embodiments, a different treatment temperature may be used instead of one or more of the above mentioned treatment temperatures. In some embodiments, a different voltage cycle may be used instead of one or more of the above mentioned voltage cycles.

In the above embodiments, a chromate conversion layer is applied to the aircraft part using a chromate conversion coating process. However, in other embodiments, a different type of conversion coating is applied to the aircraft in addition to the chromate conversion coating layer. For example, in some embodiments a phosphate conversion coating process, or an anodising process is used in addition to the chromate conversion coating process.

In the above embodiments, an anodic layer is applied to the aircraft part using an anodising process, which may be regarded as a type of conversion coating process. However, in other embodiments, a different type of conversion coating is applied to the aircraft part in addition to the anodic layer. For example, in some embodiments a tartaric anodic process, or a different anodising process is used in addition to the chromic acid anodising process.

In the above embodiments, the masking tape used to mask the chromate conversion coated initial aircraft part is 3M 484 electroplating and anodizing vinyl tape. However, in other embodiments a different type of making tape is used to perform the masking process. For example a different vinyl tape may be used, e.g. P21 “Green Tape” which, for example, may be used in masking processes performed up to about 220°C.

In some embodiments, the type of masking tape used in the masking process may be selected depending upon properties of the masking tape and the object being masked. For example, a thicker and/or less flexible masking tape may selected for application onto and the masking of relatively flat surfaces of an object, and may, for example, be applied as a pre-cut template. In contrast, a thinner and/or more flexible masking tape may be selected for application onto and the masking of relatively highly curved surfaces of an object, such as double curved surfaces. Such selection of an appropriate making tape advantageously tends to facilitate the making process, and moreover tends to provide for an improved mask.

The terminology “conversion coating” may be used herein to refer to processes including, but not limited to: coatings for metals where the part surface is converted into the coating with a chemical or electro-chemical process, chromate conversion coatings, phosphate conversion coatings, bluing, black oxide coatings on steel, plating and anodizing. Conversion coating may be applied to any appropriate material including but not limited to titanium, magnesium, niobium, aluminium or tantalum parts. Anodizing may be regarded as a conversion coating process generated by a combination of both chemical conversion and electric current at an object’s surface.

Claims

1. A method of painting an object (4), wherein the object is at least part of an aircraft and wherein the at least part of the aircraft is a panel, frame, rib, trailing edge spar, or left hand horizontal tail, the method comprising: performing a chromate conversion coating process to dispose a chromate conversion coating (10) onto the entirety of a surface of the object (4); partially masking the chromate conversion coating (10) disposed on the object (4); performing an etching process to remove, from the object (4), an unmasked portion of the chromate conversion coating (10) while retaining the masked portion of the chromate conversion coating (10) on the object (4); and performing an anodising process to dispose an anodic layer (12) onto a region of the surface of the object (4) from which the unmasked portion of the chromate conversion coating (10) was removed; wherein the method further comprises applying a layer of paint (14) onto the anodic layer (12) and not onto the portion of the chromate conversion (10) coating retained on the object (4).

2. A method according to claim 1, the method further comprising, after the anodising process, de-masking the object (4).

3. A method according to any of claims 1 to 2, wherein the chromate conversion coating (10) defines an electrically conductive path through the coated object (2).

4. A method according to any of claims 1 to 3, wherein the chromate conversion coating process comprises: exposing at least part of the object (4) to a cleaning substance; rinsing the object (4) to remove the cleaning substance from the object (4); exposing at least part of the object (4) to a chromate conversion coating substance, thereby disposing the chromate conversion coating (10) onto the entirety of the surface of the object (4); and rinsing the object (4) to remove residual chromate conversion coating substance from the object (4).

5. A method according to any of claims 1 to 4, wherein the etching process comprises: exposing at least part of the object (4) to a cleaning substance; rinsing the object (4) to remove the cleaning substance from the object (4); exposing at least part of the object (4) to an etching substance, thereby removing, from the object (4), an unmasked portion of the chromate conversion coating (10); and rinsing the object (4) to remove residual etching substance from the object (4).

6. A method according to any of claims 1 to 5, wherein the anodising process comprises: exposing at least part of the object (4) to a cleaning substance; rinsing the object (4) to remove the cleaning substance from the object (4); exposing at least part of the object (4) to an anodic substance, thereby disposing the anodic layer (12) onto the at least part of a surface of the object (4); and rinsing the object (4) to remove residual anodic substance from the object (4).

7. A method according to any of claims 1 to 6, wherein partially masking the chromate conversion coating (10) disposed on the object comprises applying a vinyl tape onto part of the chromate conversion coating (10).

8. Apparatus for painting an object (4), wherein the object is at least part of an aircraft and wherein the at least part of the aircraft is a panel, frame, rib, trailing edge spar, or left hand horizontal tail, the apparatus comprising: means for performing a chromate conversion coating process to dispose a chromate conversion coating (10) onto the entirety of a surface of the object (4); masking means for partially masking the chromate conversion coating (10) disposed on the object (4); means for performing an etching process to remove, from the object (4), an unmasked portion of the chromate conversion coating (10) while retaining the masked portion of the chromate conversion coating (10) on the object (4); means for performing an anodising process to dispose an anodic layer (12) onto a region of the surface of the object (4) from which the unmasked portion of the chromate conversion coating (10) was removed; and means for disposing a layer of paint (14) onto the anodic layer (12).

9. A painted object (2) that has been painted using a method according to any of claims 1 to 7, wherein the object is at least part of an aircraft and is a panel, frame, rib, trailing edge spar, or left hand horizontal tail and wherein the coated object (2) comprises: a chromate conversion coating (10) disposed onto a first region of a surface of an uncoated object (4), the first region being the entirety of a surface of an uncoated object (4); an anodic layer (12) disposed onto a second region of a surface of an uncoated object (4), the second region being different to the first region, the second region being a region from which the chromate conversion coating (10) has been removed; and a layer of paint (14) disposed onto the anodic layer and not disposed on the chromate conversion coating (10).