GB2279592A

GB2279592A - Selective colour powder coating of extruded aluminium window frames using enclosure mask

Info

Publication number: GB2279592A
Application number: GB9313835A
Authority: GB
Inventors: Trevor Vella Tomlin
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-07-05
Filing date: 1993-07-05
Publication date: 1995-01-11
Anticipated expiration: 2013-07-05
Also published as: GB9313835D0; GB2279592B

Abstract

To apply different colour finishing coatings to respective sections of an aluminium window frame extrusion, a first metal enclosure (10) is applied to surround one portion of the extrusion and the remaining exposed portion (1) is coated by electrostatic powder spraying and heating, and after removal of the first enclosure a second metal enclosure (20, Fig. 2) is applied to surround the previously coated section of the extrusion and the remaining exposed section is then similarly coated. The enclosure (10) includes flanges (11, 12) defining a slot through which the bottom wall of the thermal break channel (3) passes. The enclosures may be unitary or formed in two parts. <IMAGE>

Description

MANUFACTURE OF COATED METAL PARTS This invention relates to the manufacture of coated metal parts and in particular a method of enabling two-stage coating of metallic components. The invention is of particular relevance to the application of coatings to aluminium extrusions for assembly of window frames, door frames, framework for partitioning and the like.

It is well known for window frames, etc. to be assembled from aluminium extrusions. Conventional paints do not adhere well to aluminium and it has become common practice to apply coloured finishing coatings to aluminium extrusions as a final stage in their manufacture. During the finishing process a powder coating is applied using electrostatic spraying techniques, and this coating is heated to an elevated temperature to effect cure and on cooling leave a hard smooth coating layer on the metal extrusion. This known method is very satisfactory provided a single colour coating is required on the metal extrusion. In some instances it is desirable for different portions or sections of the same extrusion to be coated with finishing surface layers of different colours. In the case of window frames for instance it may be desirable to have one decorative finish on the outside of the frame and another decorative finish on the inside of the frame. Previous attempts to produce coatings of different hues on the same metal extrusion have failed to produce acceptable results. These attempts have been based on the use of thermally resistant masking tape which is used to cover one part of the extrusion while the remaining exposed surfaces are coated according to the known technique described above. The masking tape is then removed, and fresh tape is applied to the already coated surfaces while the freshly exposed surfaces are coated by a second powder spraying and heating stage. The initial results appear satisfactory, but the adhesive of the masking tape has been found to attack the underlying coating during the second heating step with the result that in time the coating first applied will crack and flake away from the metal.

Attempts to solve this problem have so far proved unsuccessful and the only other way to obtain the result desired it to coat two separate metal parts and then join them together, which is very inconvenient.

In accordance with the present invention, there is provided a method of applying a finish coat to a metal part, comprising the steps surrounding a first section of the metal part with a first enclosure defining a substantially sealed chamber around said section, applying a coating to the remaining exposed section of the metal part by powder coating and heating, removing the first enclosure and surrounding the coated section with a second enclosure defining a substantially sealed chamber around the coated section, and applying a coating to the exposed section by powder coating and heating.

The second enclosure may be the same as the first enclosure if the shape of the metal part permits, but most frequently two different enclosures will be employed. Furthermore, by providing suitably shaped and dimensioned enclosures it becomes possible for coatings to be applied in turn to several sections so that they may be finished in different colours. The enclosures can be re-used many times allowing a substantial cost saving compared with the prior art technique in which substantial amounts of expensive thermal tape are consumed.

Metallic enclosure can gave the effect of forming a Faraday cage around the metal section enclosed within it thereby deterring entry of powder particles into the chamber during electrostatic powder coating of the metal section outside the chamber.

Metal extrusions intended for window frames and the like commonly include sections designed to provide a thermal break in the assembled frame. More specifically, a channel portion is provided which is filled with a thermally insulating plastics resin and after the resin has been cured the bottom wall of the channel is cut through. When performing the method of the invention the enclosures are preferably arranged to engage the extrusion at the thermal break section so that the respective coatings terminate at the edges of the subsequently separated metal portions.

A full understanding of the invention will be gained from the following description given with reference to the accompanying drawing in which: Figure 1 is a schematic sectional view showing an aluminium window frame extrusion during a first coating stage; and Figure 2 is a similar view showing the extrusion during a second coating stage.

The precise configuration of the window frame extrusion illustrated in the drawings is unimportant and forms no part of the present invention. It is sufficient to note that it includes a first longitudinal portion 1 which will define one, say the inner side of the frame, a second longitudinal portion 2 which will define the other, outer side of the frame, and a thermal break portion 3 connecting these portions. It is assumed that the inner edge surface 4 is to be finished with a surface coating of different colour to that applied to the outer edge surface 5. For this purpose, according to the invention a metal enclosure 10 is provided to define around the outer extrusion section a substantially closed chamber. The enclosure includes confronting flanges 11,12 defining a continuous slot through which the bottom wall of the thermal break channel 3 passes with a close fit. Projecting inwardly from the inner surface of the enclosure are spacing webs 14 arranged to contact the enclosed extrusion section to maintain the enclosure in correct position surrounding this section, and also to form a series of sub-chambers between the slot formed by the flanges 11,12 and the main surface 5 of the enclosed section to prevent any powder particles reaching this surface. It will be noted that the inner edges of the flanges 11,12 and webs 14 are concave to provide a better sealing effect. Any powder particles attempting to flow into and through the chamber will tend to become trapped at these edges due to creation of vortices within the small spaces formed by the concave surfaces, and the sub-chambers between the webs further hinder passage of particles to the surface 5. The enclosure extends at least the full length of the extrusion and is closed by end walls at both its ends. If required, high temperature seals could be provided at the edges of the flanges 11,12.

The enclosure can itself be made as an aluminium extrusion, in which case thermal tape may be applied for closing the ends.

With the enclosure 10 fitted to the extrusion, and if required clamped in place, the exposed section of the extrusion is coated by the well known technique of electrostatic spray powder coating followed by baking in an oven. In this way a thick finishing coat is applied to the main surface 4 and a somewhat thinner coat is applied to the remaining surface. The extrusion section enclosed within the chamber defined by enclosure 10, and especially the main surface 5, is protected and remains uncoated. After cooling, the enclosure 10 is removed and another enclosure 20 of different shape but of essentially the same basic form as enclosure 10 is applied to surround the previously coated extrusion section. The flanges 11,12 of this enclosure contact the extrusion along the same line as did those of the first enclosure. The section of the extrusion now left exposed is then coated in the same manner as described above to provide a thick finishing coat to the main surface 5 and a thinner coating to the other surfaces.

The enclosure 20 is removed after the assembly has cooled following baking leaving the extrusion with two different coatings on the inner and outer portions. The thermal break can then be provided by filling the channel section 3 with thermally insulating synthetic resin, and when it has set machining through the bottom wall of this channel along the same line as that at which the flanges 11,12 of the enclosures engaged this wall. In this way a clean division between the differently coated parts is obtained.

The enclosures 10,20 may be of unitary construction and applied to and removed from the extrusion by longitudinal sliding movement. Alternatively, each enclosure may be formed in two parts which can be closed together around the extrusion. The two parts could be secured together solely by clamping or they could be hinged or have a snap engagement.

The enclosures can be re-used time and time again. If they become coated with paint it will not have any adverse effect on their performance and if the paint should become too thick it can be removed e.g. by burning it away.

In addition to the method of coating in stages using enclosures to protect selected portions of the metal part being coated, the invention includes in its scope the enclosures for use in performing the method and the coated extrusions obtained by the method.

Claims

CLAIMS:

1. A method of applying a finishing coat to a metal part, comprising the steps of surrounding a first section of the metal part with first a enclosure defining a substantially closed chamber around said section, applying a coating to the remaining exposed section of the metal part by powder coating and heating, removing the first enclosure and surrounding the coated section with a second enclosure defining a substantially closed chamber around the coated section, and applying a coating to the exposed section by powder coating and heating.

2. A method according to claim 1, wherein the powder coating is applied by electrostatic spraying.

3. A method according to claim 1 or 2, wherein the enclosures are made of metal.

4. A method according to claim 3, wherein the enclosures comprise extrusions.

5. A method according to any one of claims 1 to 4, wherein at least one of the enclosures comprises two openable and closable parts.

6. A method according to any one of claims 1 to 5, wherein each enclosure comprises a slot defined by opposed flanges and through which the metal part projects.

7. A method according to claim 6, wherein the flanges are provided with sealing means.

8. A method according to any one of claims 1 to 7, wherein at least one enclosure includes internal webs for engaging the enclosed section of the metal part to retain the enclosure in correct position and to divide the space within the chamber into a plurality of sub-chambers.

9. A method according to any one of claims 6 to 8, wherein the flanges and/or webs have concave surfaces at the free edges thereof.

10. A method according to any one of claims 1 to 9, wherein the metal part is an extruded frame member including a thermal break portion, and said first and second enclosures are arranged to surround sections of the frame member to either of a line extending along said thermal break portion.

11. A method of applying a finishing coat to a metal part substantially as herein described.

12. A metal part having a finishing coat applied thereto by the method of any one of the preceding claims.

13. A set of enclosures for use in applying a finishing coat to a metal part by the method of claim 1, each enclosures being detachably mountable to surround a section of the metal part and shaped to define a substantially sealed chamber around said section, the sections being applicable to the metal part in turn to leave respective sections thereof exposed for coating in turn by powder coating and heating.

14. A set of enclosures according to claim 13, wherein each enclosure comprises a metal extrusion.

15. A set of enclosures according to claim 13, wherein each enclosure includes two openable and closable parts.

16. A set of enclosures according to claims 13, 14 or 15, wherein each enclosure comprises a slot defined by opposed flanges for the metal part to protrude through.

17. A set of enclosures according to claim 16, wherein the flanges comprise sealing means.

18. A set of enclosures according to any one of claims 13 to 17, wherein each enclosure includes internal webs for engaging the enclosed section of the metal part for maintaining the enclosure in correct position and dividing the space within the chamber into a plurality of sub-chambers.

19. A set of enclosures according to claims 16, 17 or 18, wherein the flanges and/or webs have concave surfaces at the free edges thereof.

20. A set of enclosures for use in applying a finishing coat to a metal part, substantially as herein described with reference to the accompanying drawings.