GB1585460A

GB1585460A - Method of manufacturing a lamp

Info

Publication number: GB1585460A
Application number: GB48696/76A
Authority: GB
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1976-11-23
Filing date: 1976-11-23
Publication date: 1981-03-04
Also published as: DE2752316A1; FR2371636A1; IT1090349B; FR2371636B1

Description

(54) A METHOD OF MANUFACTURING A LAMP (71) We, LUCAS INDUSTRIES LIMITED, of Great King Street, Birmingham B19 2XF, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a method of manufacturing a lamp of the kind including a hollow reflector body having a reflective layer on an internal surface thereof and a lens secured by means of an adhesive to said internal surface of the body. Lamps of this kind find particular use in road vehicle driving lamps, such as headlamps and fog lamps.

A problem exists in the manufacture of lamps of the kind specified in that if the lens is adhesively secured to the reflector body through the intermediary of said reflective layer, it is found that the reflective layer tends to separate from the body in service. Although the problem can be avoided by masking the area of the body to be joined to the lens during application of the reflective layer, masking is undesirable for use in large scale production techniques. Accordingly, an object of the present invention is to provide an improved solution to the above-mentioned problem of manufacturing lamps of the kind specified.

Accordingly, the invention resides in a method of manufacturing a lamp of the kind specified, comprising the steps of:- (a) starting with a lamp reflector body having a reflective layer on an internal surface of the body, (b) locating the working tip of a plasma torch adjacent said reflective layer and passing an inert gas through the annular space between the central and outer elec trodes of the torch to traverse a region of said layer at or adjacent the periphery of said internal surface, whereby said region of the reflective layer is removed from the reflector body, and (c) without transferring said arc to the reflector body, imparting relative move ment to the body and the torch to cause the torch to traverse a region of said layer at or adjacent the periphery of said internal surface, whereby said region of the reflective layer is removed from the reflector body, and (d) securing with an adhesive a lens to the area of said internal surface from which the reflective layer has been removed.

It is to be appreciated that in steps (b) and (c) of the method described in the preceding paragraph the plasma torch is operating in which is normally termed its non-transfer mode since the electric arc is maintained between the central and outer electrodes of the torch. This mode of operation differs from the alternative, transfer mode in which the arc is transferred between the central electrode and the workpipe, with the inert gas also being passed between the outer electrode and and annular ceramic housing surrounding the outer electrode.

Preferably, the power supplied to the torch to generate the arc and the rate of traverse of the torch relative to the body are arranged so that the energy supplied to remove the reflective layer is between 3 and 30 Joules/mm of the coating traversed.

Preferably, the working tip of the torch is maintained at a distance in the range 2.5mm to 12.5mm from said coating, the energy required to remove the reflective layer being greater at the larger distance in said range.

Preferably, said reflective layer is aluminium and is provided with a transparent coating of a protective synthetic resin material, the portion of said coating overlying said region of the reflective layer also being removed during step (c).

Preferably, said reflective layer is provided on a base lacquer which adheres to the body and said reflective layer, and the portion of the base lacquer underlying said region of the layer remains after step (c) so that the adhesive join between the lens and the reflector body being made by way of the base lacquer.

Alternatively, said portion of the base lacquer is removed during step (c).

Conveniently, the reflector body is formed of metal.

Alternatively, the reflector body is formed of a synthetic resin material and preferably a cured, low profile, polyester moulding composition containing glass fibres.

The accompanying drawing is a diagrammatic illustration of a method according to one example of the invention.

Referring to the drawing, in the example shown it is required to secure a lens (not shown) to the dished reflector 10 of a road vehicle driving lamp. The reflector 10 includes a body 11 which is formed of a metal or of a synthetic resin material, preferably a cured, low profile polyester moulding composition reinforced with glass fibres, and which is provided on its internal and external surfaces with an adherent coating of a base lacquer 12. Adhering to the base lacquer 12 and extending over the concave, internal surface of the body 11 is an aluminium, reflective layer 13 which is protected by an oxidation resistant, transparent, synthetic resin coating 14. In one practical embodiment, the aluminium reflective layer had a thickness of 500A, while the protective synthetic resin coating 14 was defined by a 150A thick layer of polydimethylsiloxane.

In order to allow a lens to be secured to the reflector 10, a portion of the protective coating 14 extending around the periphery of the body 11, and the underlying region of the layer 13, are initially removed by treatment with the plasma torch shown in part at 15. The torch 15 is conveniently 6f the type supplied for welding by the British Oxygen Company Limited and includes, at its working tip, a centrally generally cylindrical tungsten cathode 16 which has a pointed end and is surrounded by an annular, copper anode 17. At its free end, the anode 17 tapers inwardly to define the periphery of the aperture 18 which communicates with the annular space 19 defined between the cathode 16 and anode 17.In said one practical embodiment, the tungsten cathode 16 had a diameter over the majority of its length of 4.5mm and defined an included angle of 300 at its pointed end, the latter lying flush with the inner axial end of the aperture 18. Moreover, the aperture 18 had a diameter of 1.15mm and an axial length of 3mm, while the radial thickness of the annular space 19 was 2mm.

To effect removal of the required portions of the layer 13 and coating 14, an arc is struck between the cathode 16 and anode 17, while argon, or any other convenient inert gas, is passed through the annular space 19 at a flow rate, in said one practical embodiment, of 0.75 litres/minute. In this way a plasma of the inert gas is produced at the region of the aperture 18, at which stage the tool 15 is removed to a position in which the free end of the anode 17 is at a distance of between 7.5 and 9.5 mm above the coating 14 adjacent the periphery of the reflector, the torch 15 is traversed around the circumference of the reflector, whereby an annular region of each of the coating 14 and layer 13 is removed, while the base lacquer 12 remains intact.In said one practical embodiment the arc voltage and current were 18 volts and 30 amps respectively and the torch 15 was traversed over the reflector at a speed up to 75mm/sec such that the energy supplied to remove the layer 13 and coating 14 was 7.1 Joules/ cm of the reflector traversed. In this way, an annular region of 2.5mm radial thickness was removed from each of the layer 13 and coating 14.

After removal of said regions of the layer 13 and coating 14 it is found that a strong adhesive join can be produced between the required lens and the exposed region of the base lacquer 12 without any problems of lamination. A suitable adhesive in this respect is an epoxy resin. By way of contrast, securing the lens to the reflector body 11 by way of the layer 13 and coating 14, as well as the base laquer 12, is found to result in lamination in service.

As an alternative to the example described above, treatment with the plasma torch can also be arranged to remove the portion of the base lacquer 12 underlying said regions of the layer 13 and coating 14.

WHAT WE CLAIM IS:- 1. A method of manufacturing a lamp of the kind specified, comprising the steps of: (a) starting with a lamp reflector body having a reflective layer on an internal surface of the body, (b) locating the working tip of a plasma torch adjacent said reflective layer and passing an inert gas through the annular space between the central and outer elec trodes of the torch to traverse a region of said layer at or adjacent the periphery of said internal surface, whereby said region of the reflective layer is removed from the reflector body, and (c) without transferring said arc to the reflector body, imparting relative move ment to the body and the torch to cause the torch to traverse a region of said layer at or adjacent the periphery of said internal surface, whereby said region of the reflective layer is removed from the reflector body, and (d) securing with an adhesive a lens to the area of said internal surface from

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. and the reflector body being made by way of the base lacquer. Alternatively, said portion of the base lacquer is removed during step (c). Conveniently, the reflector body is formed of metal. Alternatively, the reflector body is formed of a synthetic resin material and preferably a cured, low profile, polyester moulding composition containing glass fibres. The accompanying drawing is a diagrammatic illustration of a method according to one example of the invention. Referring to the drawing, in the example shown it is required to secure a lens (not shown) to the dished reflector 10 of a road vehicle driving lamp. The reflector 10 includes a body 11 which is formed of a metal or of a synthetic resin material, preferably a cured, low profile polyester moulding composition reinforced with glass fibres, and which is provided on its internal and external surfaces with an adherent coating of a base lacquer 12. Adhering to the base lacquer 12 and extending over the concave, internal surface of the body 11 is an aluminium, reflective layer 13 which is protected by an oxidation resistant, transparent, synthetic resin coating 14. In one practical embodiment, the aluminium reflective layer had a thickness of 500A, while the protective synthetic resin coating 14 was defined by a 150A thick layer of polydimethylsiloxane. In order to allow a lens to be secured to the reflector 10, a portion of the protective coating 14 extending around the periphery of the body 11, and the underlying region of the layer 13, are initially removed by treatment with the plasma torch shown in part at 15. The torch 15 is conveniently 6f the type supplied for welding by the British Oxygen Company Limited and includes, at its working tip, a centrally generally cylindrical tungsten cathode 16 which has a pointed end and is surrounded by an annular, copper anode 17. At its free end, the anode 17 tapers inwardly to define the periphery of the aperture 18 which communicates with the annular space 19 defined between the cathode 16 and anode 17.In said one practical embodiment, the tungsten cathode 16 had a diameter over the majority of its length of 4.5mm and defined an included angle of 300 at its pointed end, the latter lying flush with the inner axial end of the aperture 18. Moreover, the aperture 18 had a diameter of 1.15mm and an axial length of 3mm, while the radial thickness of the annular space 19 was 2mm. To effect removal of the required portions of the layer 13 and coating 14, an arc is struck between the cathode 16 and anode 17, while argon, or any other convenient inert gas, is passed through the annular space 19 at a flow rate, in said one practical embodiment, of 0.75 litres/minute. In this way a plasma of the inert gas is produced at the region of the aperture 18, at which stage the tool 15 is removed to a position in which the free end of the anode 17 is at a distance of between 7.5 and 9.5 mm above the coating 14 adjacent the periphery of the reflector, the torch 15 is traversed around the circumference of the reflector, whereby an annular region of each of the coating 14 and layer 13 is removed, while the base lacquer 12 remains intact.In said one practical embodiment the arc voltage and current were 18 volts and 30 amps respectively and the torch 15 was traversed over the reflector at a speed up to 75mm/sec such that the energy supplied to remove the layer 13 and coating 14 was 7.1 Joules/ cm of the reflector traversed. In this way, an annular region of 2.5mm radial thickness was removed from each of the layer 13 and coating 14. After removal of said regions of the layer 13 and coating 14 it is found that a strong adhesive join can be produced between the required lens and the exposed region of the base lacquer 12 without any problems of lamination. A suitable adhesive in this respect is an epoxy resin. By way of contrast, securing the lens to the reflector body 11 by way of the layer 13 and coating 14, as well as the base laquer 12, is found to result in lamination in service. As an alternative to the example described above, treatment with the plasma torch can also be arranged to remove the portion of the base lacquer 12 underlying said regions of the layer 13 and coating 14. WHAT WE CLAIM IS:-

1. A method of manufacturing a lamp of the kind specified, comprising the steps of: (a) starting with a lamp reflector body having a reflective layer on an internal surface of the body, (b) locating the working tip of a plasma torch adjacent said reflective layer and passing an inert gas through the annular space between the central and outer elec trodes of the torch to traverse a region of said layer at or adjacent the periphery of said internal surface, whereby said region of the reflective layer is removed from the reflector body, and (c) without transferring said arc to the reflector body, imparting relative move ment to the body and the torch to cause the torch to traverse a region of said layer at or adjacent the periphery of said internal surface, whereby said region of the reflective layer is removed from the reflector body, and (d) securing with an adhesive a lens to the area of said internal surface from

which the reflective layer has been removed.

2. A method as claimed in claim 1 wherein the power supplied to the torch to generate the arc and the rate of traverse of the torch relative to the body are arranged so that the energy supplied to remove the reflective layer is between 3 and 30 Joules/mm of the coating traversed.

3. A method as claimed in claim 1 or claim 2 wherein the working tip of the torch is maintained at a distance in the range 2.5mm to 12.5mm from said coating, the energy required to remove the reflective layer being greater at the larger distances in said range.

4. A method as claimed in any one of claims 1 to 3 wherein said reflective layer is aluminium and is provided with a transparent coating of a protective synthetic resin material, the portion of said coating overlying said region of the reflective layer also being removed during step (c).

5. A method as claimed in any one of claims 1 to 4 wherein said reflective layer is provided on a base lacquer which adheres to the body and said reflective layer, and the portion of the base lacquer underlying said region of the layer remains after step (c) so that the adhesive join between the lens and the reflector body being made by way of the base lacquer.

6. A method as claimed in any one of claim 1 to 4 wherein said reflective layer is provided on a base lacquer which adheres to the body and said reflective layer, and the portion of the base lacquer underlying said region of the layer is removed during step (c) so that the adhesive join between the lens and the body is made directly to said body.

7. A method as claimed in any one of claims 1 to 6 wherein the reflector body is formed of metal.

8. A method as claimed in any one of claims 1 to 6 wherein the reflector body is formed of synthetic resin material and preferably a cured, low profile, polyester moulding composition containing glass fibres.

9. A method of manufacturing a lamp of the kind specified substantially as hereinbefore described with reference to and as shown in the accompanying drawing.

10. A lamp of the kind specified manufactured by a method as claimed in any one of the preceding claims.