The present invention relates to a jig and a method of and apparatus for applying a surface treatment to a member on the jig. The invention is primarily but not exclusively concerned with a jig used in the anodising and painting of an elongate member such as a wing stringer for an aircraft.
Anodisation is a process by which a hard non-corroding oxide film is deposited on a material such as aluminium or light alloy to protect against corrosion. It is achieved by making the material the anode in an electrolytic cell containing chromic (VI) or sulphuric acid and during anodisation an oxide film is deposited on the surface of the material.
In the aerospace industry, it is common for aluminium and light alloy members to be anodised prior to use in an aircraft so that the members will not be susceptible to oxidisation when the aircraft is in service.
In one known anodising method, wing stringers of an aircraft are mounted on an anodising jig. The anodising jig comprises a hanger having two downwardly depending beams connected to it. Each of the downwardly depending beams carries an identical metal tree mounting which consists of a vertical hanger and a plurality of horizontal supports extending therefrom. The horizontal supports are grouped into oppositely directed pairs which are spaced apart along the length of the hanger. All the supports of one tree mounting lie in the same plane. The supports of the other tree mounting are similarly arranged and lie in a plane parallel with that of the one tree mounting. Each support of one tree mounting has a corresponding support on the other tree mounting at the same level. A free end of each support has an upward projection, and upper surfaces of the supports are covered with an insulating material. This type of mounting is termed a “Christmas tree” mounting.
In use, a wing stringer is placed on the anodising jig so that part of the wing stringer is supported on one support of the first tree mounting and another part of the wing stringer is supported on a corresponding support of the second tree mounting. The insulating covering prevents direct contact between the wing stringers and the supports. Additional wing stringers are placed on adjacent empty supports in a similar manner. The upward projections on the supports prevent the wing stringers from sliding off the supports. If desired, the stringers can be further secured by tying for example with nylon string. Each of the wing stringers has a tooling tang at one of its ends, and the wing stringers are arranged on the jig so that all of the tooling tangs are arranged generally adjacent each other on the same side of one tree mounting.
A rigid electrical contact of serpentine form has spaced apart clamps connected thereto along its length in positions corresponding to the tooling tangs of all the wing stringers on the jig. In use, the tooling tang of each wing stringer is positioned in its corresponding clamp with flat surfaces of each tooling tang in contact with a flat surface of the rigid electrical contact and a flat surface of the associated clamp. The clamps of the electrical contact are tightened and the electrical contact is made ready for connection to a power supply.
The anodising jig is lowered into a tank of chromic acid solution and an electrical current provided by the power supply is passed through the electrical contact to the wing stringers. The wing stringers act as the anode and the tank chromic acid solution deposits an anodic film on the surface of the stringers. After an anodic film of sufficient thickness has been deposited on the wing stringers the anodising jig is removed from the tank. The electrical contact is then unclamped from the tooling tangs of the wing stringers and the wing stringers are removed from the jig.
A problem with the known anodising method is the time taken to individually clamp and unclamp the electrical contact to each wing stringer.
An aim of the invention is to provide an improved jig suitable for use in the surface treatment of an elongate member, such as a wing stringer.
According to a first aspect of the invention there is provided a jig for holding an elongate member to be surface treated, the jig comprising a beam and a plurality of hangers spaced apart along the beam, the hanger having respective V-shaped supports thereon which have an upstanding abutment on either side of the V and which are arranged to receive spaced apart sections of the elongate member and which provide a resilient grip for holding the member in position.
In that way, an elongate member to be surface treated can be manually positioned on the supports and held in position on the jig by the resilient grip without other forms of clamp.
In one embodiment, each support may comprise a resilient clip which grips the elongate member.
In another embodiment, the support may comprise a holder for the elongate member and a resilient member for retaining the elongate member against the holder.
In one embodiment of the present invention the support, primarily when in the form of resilient clips, actually provides an electrical contact by means of which electric current can pass, in use, between the holders and the elongate member. Therefore, the electric current is passed through the same means as that used to support the elongate member. The resilient clip is preferably of such a design as to support the component whilst permitting adequate conduction of electric current and, at the same time, presenting the minimum area capable of masking the elongate member during post anodising operations, such as painting.
Three or more hangers may be mounted on the beam at spaced apart positions so that the supports will, in use provide support for the elongate member at several places along its length.
Where the supports are in the form of resilient clips, each clip preferably comprises two spaced apart arms. At least one of said arms may be moveable resiliently with respect to the other to provide a clipping action. In a preferred embodiment the two arms of each resilient clip define a mouth. The mouth of each clip provides an entry into the clip to enable said part of the elongate member to be surface treated to be inserted easily into the clip. Preferably, the mouth faces upwardly whereby the said part of the elongate member can be inserted, from above, with the assistance of gravity, into each resilient clip.
In the preferred embodiment of resilient clip, upper ends of the arms of each resilient clip are preferably inclined away from each other so that the mouth is of increasing width from a relatively narrower part of the clip in which the elongate member is to be gripped when fully inserted in the clip. In that way, the elongate member such as a wing stringer can be rested in the mouth of each resilient clip prior to full insertion in the clip. Therefore, the position of the elongate member can be adjusted longitudinally relative to the jig by sliding it while resting in the mouths of the clips. Once in the correct position, each clip can be manipulated to allow the elongate member to be fully inserted and gripped in the clips.
In a preferred embodiment, one arm only of each resilient clip is movable resiliently relative to the other, the other being relatively immovable. In that arrangement and where the elongate member is to be inserted into each resilient clip by a single operative, the operative can use one hand to move the said one arm to open the clip while using the other hand to insert or guide the elongate member into the resilient clip.
The resilience of the clip can be effected by spring means acting on one of the arms. In such a case, the said one arm may be connected to a support for the clip through the spring means. In a preferred embodiment, the spring means is provided by forming part of the said one arm as a coil spring.
At least one of the arms may define a notch in which the elongate member is to be located for gripping by the clip. In a preferred embodiment, both arms of each clip have respective notches preferably at opposing positions.
Both arms of each resilient clip preferably have arcuate surfaces for gripping contact with the elongate member. With such an arrangement there will be virtually point or line contact only between the arms and the elongate member thereby increasing the percentage of the surface of the elongate member which is treatable when compared to the wing stringers and the supports of the prior art jig described in the introduction where there is a relatively larger surface to surface contact.
Where the jig is intended to hold elongate members such as heavy stringers or even wing spars, the jig preferably further comprises a plurality of supplemental supports. Each of the supplemental supports is preferably in the form of a pillar in the region of each resilient clip. The pillar is preferably arranged between the arms of the resilient clip and helps to support the elongate member when the latter is gripped by the clip. In that way, the supplemental supports can bear some of the weight of a heavy member and thus reduce stress on the resilient clips themselves.
Where each of the supports is in the form of a holder and resilient member, the holder may provide a narrow section which provides virtually point or line contact between the support and the elongate member, with the aforementioned advantages.
Edges of the V-shape may be narrowed to provide the said point or line contact.
The resilient member of the support may comprise a resilient arm which is arranged to contact the elongate member and urge it against a surface such as a surface of the holder.
If desired, the abutment may also have a narrow section to provide virtually point or line contact between itself and the elongate member.
Where each of the supports is in the form of a holder and resilient member, an electrical contact may be provided for attachment to each elongate member to enable electrical current to pass through the elongate member.
The vertical positions of the supports on their respective hangers is preferably adjustable. To provide such adjustment, the supports may be slidable vertically on the associated hanger and lockable in a desired adjusted position.
In the preferred embodiment of the invention, the jig is used to support elongate members to be anodised. Where electric current is to be conducted to the support, for example where the resilient clips are used, the beam, the hangers and the supports may all be of conductive material to allow electric current introduced to the beam of the jig and pass through the supports to the elongate member. Preferably the beam is made of aluminium and provides good electrical current conduction whilst keeping weight down to a minimum.
Preferably the beam, which helps give the jig structural rigidity, remains out of solution and does not become anodised.
Another problem which arises with the known anodising method is that the jig has to be de-anodised. The serpentine contact is made of aluminium and in order for the electrical contact to be made with a new batch of stringers, the insulating anodic film has to be removed before a new contact can be made. The current method of doing that involves a chemical stripping process, which also erodes the jig itself. Preferably, in the present invention, those parts of the jig that are submerged in chromic acid in use are made of Titanium which does not anodise in the same way that aluminium does and therefore does not require the same destructive method of anodic film removal prior to reuse.
At points or lines of contact between the support and the elongate member to be anodised there will be no anodic film deposited. Such points of contact will need to be treated separately for example in a process known as Alocroming using Alodine so as to complete the anodic film on the elongate member. Preferably, the jig is adapted so that between two and four supports are provided for each elongate member. In such a case, an elongate member to be anodised receives sufficient support while maintaining only a low number of contact points between the supports and the member.
The anodising jig previously used and described on page 1 hereof is fixed in situ in the anodising area. Therefore, where the elongate members need further processing, e.g. painting, in a different area, it is necessary to remove the elongate members from the jig and transport them to the other areas. In accordance with the present invention, the beam may have hook-like members spaced apart along the beam which are engageable with a lifting bar of a crane. The lifting bar can be lowered so as to engage in the hook-like members and then raised so as to lift the jig for transport between desired treatment stations for the elongate member on the jig.
Each hook-like member may be shaped somewhat like an upwardly pointing arrow head in vertical cross section having a shank attached at its lower end to the beam and a barb at its upper end defining an undercut for locating on the bar of the crane. Preferably, the barb defines two undercuts one on each side of the shank. In that way, the jig can be picked up using an undercut on one side and then put down on a suitable support which locates in the undercut on the other side. Therefore, the elongate members do not need to be put down in a rack for example thereby minimising the risk of contamination.
Normally, it is desirable to paint wing stringers after they have been anodised sufficiently. The prior art jig described on page 1 hereof is not suitable for use when painting the wing stringers as the large surface to surface contact between the supports and the wing stringers prevents paint from being applied to a significant part of the surface of the wing stringers. Instead, the wing stringers are removed from that jig and individually painted, which is inconvenient. Thereafter the jig needs to be de-anodised before it can be used again.
Another aim of the invention is to provide a more efficient way of applying a surface treatment and paint to an elongate member.
In that respect, the jig may form part of apparatus comprising a surface treatment station for treating the elongate member by an electrolytic process, a painting station, a first crane for transporting the jig to the surface treatment station and a second crane for transporting the jig with the surface treated elongate member thereon to the painting station.
According to a second aspect of the invention there is provided apparatus for applying a surface treatment and paint to an elongate member comprising a jig having a support for carrying an elongate member to be surface treated and painted, a surface treatment station for treating the elongate member by an electrolytic process, a painting station, a first crane for transporting the jig to the surface treatment station and a second crane for transporting the jig with the surface treated elongate member thereon to the painting station.
If a support is used which provides virtually point or line contact with the elongate member, the paint will be applied substantially to the entire elongate member leaving only the areas of point or line contact to be painted manually after removal of the elongate members from the jig. The invention is, therefore, particularly advantageous as it enables the same jig to be used for both line anodising and painting processes without having to handle the elongate members between the anodising and painting stages. Paint removal from the jig can be achieved simultaneously with removal of a thin anodised coating from the jig, if it is made of titanium.
A location device may be provided for locating the beam in a desired horizontal position relative to the tank. The location device may have features of the location device described below in relation to the surface treatment of a panel.
Preferably, the apparatus is in the form of an installation which is computer controlled.
The jig may comprise a jig in accordance with the first aspect of the invention or any of the subsidiary clauses relating thereto.
According to a third aspect of the invention there is provided a method of applying a surface treatment and paint to an elongate member, the method comprising the steps of providing a jig for carrying an elongate member to be surface treated and painted, mounting the elongate member to be surface treated on the jig, immersing the jig and elongate member in an electrolyte at a surface treatment station, introducing an electrical current to the jig so as to surface treat the elongate member, removing the jig from the electrolyte, transferring the jig with the treated elongate member thereon to a painting station, applying paint to the elongate member on the jig, removing the jig from the painting station and removing the painted elongate member from the jig.
In accordance with the third aspect of the invention, the elongate member is painted without removing it from the jig between the surface treatment and painting stations leading to a more efficient way of reaching the painting stage.
The method may involve using a first crane to transport the jig to the surface treatment station and a second crane to transport the jig to the painting station. Each crane may have a lifting bar which is engageable with hook-like members. In such a case, the method may comprise using the lifting bar of the first crane to locate beneath hook-like members of the jig and to lift and transport the jig to the surface treatment station and then using the lifting bar of the second crane to locate beneath the hook-like members after the lifting bar of the first crane has been detached therefrom to enable the second crane to lift the jig after the elongate member thereon has been surface treated and to transport the jig to the painting station.
The method may comprise using a jig in accordance with the first aspect of the invention or any of the subsidiary clauses relating thereto.
It is known to anodise and paint panels prior to use in an aircraft. A jig of known kind comprises a horizontal beam and aluminium straps depending therefrom. A panel is bolted to the straps. A crane lifts the jig into a tank of Chromic acid solution and the panel is anodised using the method described above.
Another aim of the invention is to provide improved apparatus for use in the surface treatment of a panel.
According to a fourth aspect of the invention, there is provided apparatus for use in the surface treatment of a panel, the apparatus comprising a beam having an upwardly projecting lifting member for location beneath a hook-like member which, in use, is attached to the panel, a treatment tank into which the panel is to be lowered and a location device for locating the beam in a desired horizontal position relative to the hook-like member.
The location device preferably comprises a horizontally moveable member which is moveable so as to clamp the hook-like member against a part of the beam. In a preferred embodiment, two of said horizontally moveable members are provided which are arranged to move towards each other to clamp the hook-like member against the part of the beam.
Preferably, electric current passes, in use, through the beam and from the beam preferably through the hook-like member to the panel. The aforesaid clamping of the hook-like member against the said part of the beam helps to maintain good electrical contact between the beam and the hook-like member.