Manufacturing process for electric lightbulb caps

Abstract

 Process for the manufacture of electric lightbulb caps, which comprises the following steps: forming a body of revolution (8) with a base (14), an internal surface (16), and an external surface (18) with a cylindrical segment (20), distanced from the base (14), and which is crowned by an annular protrusion (22), in which the forming step is constituted by an operation of the group formed by injection, extrusion, casting, sintering and machining; obtaining a permanent joined body (4) comprising the body of revolution (8) and a contact plate (6) having a flat annular base (10) and a tubular appendix (12); provision of a sheathing (2) with a lower aperture (24) delimited by a doubling (26) of the sheathing (2) directed towards the interior of the sheathing (2) and whose external surface (28) is cylindrical; and application of the sheathing (2) against the permanent joined body (4).

Description

[0001] This invention relates to a process for manufacturing caps for electric lightbulbs, said caps comprising: a sheathing to receive the glass bulb; a contact plate; and isolating material.

[0002] The caps to which the present invention refers have been known for a long time. The normal processes used for manufacture of such caps contemplate a phase known as "vitrification" during which a certain amount of glass melted at a temperature of approximately 1250°C is moulded onto a metallic sheathing in order to obtain two objectives: one objective concerns structure and is to give solidity to the bond between the two metallic parts (or electric poles or terminals) of the cap, which is to say the sheathing and the contact plate; the other objective concerns isolation, separating the two terminals of the cap.

[0003] However, these known procedures have some drawbacks since they do not attain high productivity, imply a relatively accrued level of energy consumption and in addition a high consumption of materials. Further, they have the drawback of needing to work the glass by means of moulding and at high temperatures, which leads to low productivity, a relatively long cooling operation and the possibility that the material of the moulded glass body is subjected to stresses giving rise to breaks or fissures.

[0004] The objective of the present invention is to provide a solution to these drawbacks. This is achieved by means of a process for manufacture of electric lightbulb caps characterised in that it comprises the following steps: [a] provision of a contact plate having a flat annular base and a tubular appendix which emerges from the internal edge of the flat annular base; [b] forming of a body of revolution which defines: [i] a base suitable for being applied to the flat annular base of the contact plate; [ii] an internal surface, cup shaped, whose lower part is suitable for entering into contact with the tubular appendix; and [iii] an external surface having a cylindrical segment, distanced from the base, and which is crowned with a slight annular protrusion, in which the forming step is constituted by at least one operation of the group formed by injection, extrusion, casting, sintering and machining and in which the body of revolution is made in an electric isolating material of the group formed by synthetic resins, ceramic materials, vitreous materials, natural electric isolating materials and combinations of the foregoing; [c] obtaining a permanent joined body comprising the body of revolution and the contact plate; [d] provision of a sheathing which has a lower aperture delimited by a doubling of the sheathing, this doubling being directed toward the interior of the sheathing and having a substantially cylindrical external surface; and [e] application, in axial direction, of the sheathing against the permanent joined body, in which this application leads to a retentive apposition between the doubling and the cylindrical segment.

[0005] Preferably the contact plate, formed by a flat annular base and a tubular appendix, is arranged in the mould used to form the body of revolution in an operation prior to forming of said body of revolution, constituting an insert of the resulting body of revolution, such that said steps [b] and [c] are carried out simultaneously. This improvement is particularly advantageous in the event that the forming step is an injection moulding or cast moulding step.

[0006] Other advantages and features of the invention will become apparent from the following non-limitative description of a preferable embodiment of the invention, with reference to the accompanying drawings, in which:

Fig. 1, is a section along an axial plane of the sheathing of a cap, facing the permanent joined body formed by the contact plate and the body of revolution; the latter assembly also being represented by means of a section along an axial plane;

Fig. 2, is a section of the cap along an axial plane;

Fig. 3, is a view of the cap in lateral elevation, cut away along an axial plane; and

Fig. 4, is a bottom plan view of the cap.

[0007] The cap substantially comprises a threaded sheathing 2 and a permanent joined body 4, formed by a contact plate 6 and a moulded mass of electric isolating material forming a body of revolution 8.

[0008] The contact plate 6 has a flat annular base 10 and a tubular appendix 12 which projects interiorly from the internal edge of the annular base 10; on this plate 6 is joined a body of revolution 8, having isolating characteristics. Preferably the body of revolution 8 is manufactured by moulding (advantageously by injection) and, advantageously, the contact plate 6 is included in the mould before introducing the material to be moulded. In this manner the permanent joined body 4 comprising the contact plate 6 and the body of revolution 8 is obtained directly, although both parts can be manufactured separately and joined subsequently by means of gluing, stapling, etc. The base 14 of the body of revolution 8 is applied to the flat annular base 10 of the plate 6. The internal surface 16 of the body of revolution 8 is cup shaped and its lower segment is in contact with the tubular appendix 12, whilst the external surface 18 of the body of revolution 8 has a cylindrical segment 20 which is delimited at the top by an annular protrusion 22.

[0009] With respect to the sheathing 2, it is open at the bottom by means of a lower aperture 24, from which stems a doubling 26 directed towards the interior and whose external surface 28 is substantially cylindrical; this doubling 26 has a certain amount of elasticity.

[0010] The sheathing 2 and the permanent joined body 4 are positioned facing each other, as shown in figure 1, and, in this position, assembly in axial direction of the sheathing 2 on the body 4 is effected. Initially in the assembly, the annular protrusion 22 forces the doubling 26 to inflect toward the interior of the sheathing 2 until the doubling, in its relative movement of descent, passes beyond the protrusion 22. At this point, the elasticity of the doubling 26 allows said doubling to recuperate its original position, giving rise to a retentive apposition between the doubling 26 of the sheathing 2 and the cylindrical segment 20 of the body 4.

[0011] The electric isolating material is selected from among those materials that are capable of resisting the temperature produced in the lightbulb cap during normal functioning thereof, and preferably is a material which, after moulding thereof to configure the body of revolution 8, is not subject to stresses that could cause internal fissuring or surface cracking that could negatively effect the level of electric isolation.
Advantageously a plurality of bodies of revolution 8 can be obtained simultaneously by means of conventional moulding in a multiple mould.

[0012] The electric isolating material suitable for the temperature that the lightbulb cap will have to endure can be, in one respect, synthetic resins of the group formed by engineering plastics, which can be, among others, polypropylene, polyamides, polycarbonates, etc. and, in a second respect, vitreous materials, ceramics, etc, whether considered singly or in their possible combinations or in possible combinations with other materials, as long as the resulting material has the pertinent electric isolating characteristics in all examples of use, such as could a "composite".

Claims

1. Process for the manufacture of electric lightbulb caps, characterised in comprising the following steps: [a] provision of a contact plate (6) which has a flat annular base (10) and a tubular appendix (12) which emerges from the internal edge of said flat annular base (10); [b] forming of a body of revolution (8) which defines: [i] a base (14) suitable for being applied to said flat annular base (10) of said contact plate (6); [ii] a cup-shaped internal surface (16), whose lower part is suitable for entering into contact with said tubular appendix (12); and [iii] an external surface (18) which has a cylindrical segment (20), distanced from said base (14), and which is crowned by a slight annular protrusion (22), in which said forming step is constituted by at least one operation of the group formed by injection, extrusion, casting, sintering and machining and in which said body of revolution (8) is made in an electric isolating material of the group formed by synthetic resins, ceramic materials, vitreous materials, natural electric isolating materials and combinations of the foregoing; [c] obtaining a permanent joined body (4) comprising said body of revolution (8) and said contact plate (6); [d] provision of a sheathing (2) which has a lower aperture (24) delimited by a doubling (26) of the sheathing (2), said doubling (26) being directed towards the interior of the sheathing (2) and whose external surface (28) is substantially cylindrical; and [e] application in axial direction of said sheathing (2) against said permanent joined body (4), said application leading to a retentive apposition between said doubling (26) and said cylindrical segment (20).

2. Process according to claim 1, characterised in that the contact plate (6), formed by a flat annular base (10) and a tubular appendix (12), is arranged in the mould used for forming the body of revolution (8) in an operation prior to the forming thereof, constituting an insert of the resulting body of revolution, such that said steps [b] an [c] are carried out simultaneously.

Drawing