GB2028011A - Electric igniter element for use with pressurised gas cartridges - Google Patents

Abstract

An electric igniter element or a pressurised gas cartridge provided therewith having a housing 1 and a glass body 3 therein through which an uninsulated part or an otherwise insulated electric supply line (or lines) 4 pass(es) is reliably protected against electric flashovers particularly in a humid atmosphere by provision of an insulating body 6, for example of epoxide resin, which encloses the portion of the or each supply line 4 not carrying insulation disposed outside the glass body 3, which extends to enclose and be connected fast with a portion of the or each supply line 4 carrying electric insulation and which is connected fast with the glass body 3. <IMAGE>

Description

SPECIFICATION Electric igniter element for use with pressurised gas cartridges This invention relates to an igniter element for use with a pressurised gas cartridge.

Pressurised gas cartridges have hitherto been provided with an electric igniter element and an igniter composition which generates gas under pressure when ignited by the igniter element. Such cartridges can be provided with a glass lead-in or bushing for the electric supply lines of the igniter element which are usually two in number. In those cases where the housing of the pressurised gas cartridge is used as a second pole of the igniter element, only one supply line needs to be guided through the glass lead-in. This glass lead-in or bushing, having at least one supply line fused therein in the uninsulated state, enables a particularly tight closure of the housing of the pressurised gas cartridge or of an igniter element for use therein to be obtained. The closure is also watertight.With this constructional form electric supply line(s) is/are insulated at the portions thereof arranged outside the housing and the glass body, generally by provision of an electrically non-conducting hose or sleeve, formed for example, of polyvinylchloride and which can be shrunk on by heat. This electric insulation cannot be connected in a completely satisfactory manner to the glass body.

With these pressurised gas cartridges, or igniter elements to be used therein, a specific minimum insulation resistance is required. This is measured between the supply leads and the metallic outer housing and is usually larger than 10 MQ. Because of the generally very small spacing between the leads and the rim of the opening in the housing, it may happen that under unfavourable circumstances, the actual resistivity is, however, considerably lower than the generally high-ohmic rated resistivity. This lowering of the insulation resistivity is due, at least in part, to the fact that the insultion of the lead(s) does not bear in a completely tight manner against the glass bushing through which the lead(s) pass.This phenomenon is particlarly critical when the igniter element is subject to moisture ingress or to high air humidity. When the igniter element is subject to such unfavourable outside conditions, the actual insulation resistance measured between the housing and the two supply leads which are in electrical contact externally of the igniter element as a result of being twisted together, may drop, for example, to a few kiloohms, i.e. far below the rated resistivity.

According to the present invention, there is provided an electric igniter element for use with a pressurised gas cartridge, which igniter element comprises a housing, a glass body within the housing and at least one electric supply line which is guided through the glass body to ignition means of the igniter element, the supply line(s) carrying electric insulation on the portion thereof disposed outside the housing and the glass body, the portion of the or each supply line not carrying insulation being enclosed in an insulating body which extends to enclose and be connected fast with a portion of the or each supply line carrying electric insulation and which is connected fast with the glass body.

An electric igniter element according to the present invention possesses very high insulation resistance. The insulation resistance remains at a uniformly high level, so that, even under unfavourable circumstances, such as, more especially, a humid atmosphere, the standards set for it are met.

With an igniter element according to this invention, the insulating body is preferably produced from one of the synthetic resins which are used in the electrical art for electrical insulation purposes and which possess mechanical and electrical properties which enable the minimum required resistance to be obtained, for example, even when subject to high humidity and/or high ambient temperatures. Forthis reason, the synthetic resin is preferably applied while in a flowable or plastic state to the surfaces of the glass body and the supply lead insulation which are to be covered therewith. These surfaces will usually be cleaned beforehand, so that they are covered in the required manner, and preferably solidify by curing.The gap-free, tight connection, between the resin and both the supply wire insulation and the glass surface, prevents the resistancelowering deposition of moisture or creepage of moisture occurring at the critical points in the igniter element construction. The large thickness of the insulating body employed in the present invention, by comparison with the supply lead insulation, has also been found to be desirable It is preferred that the insulating body covers the entire opening in the housing at the end where the supply line(s) arrive(s) so that the insulating body is also connected free from any gap and tightly to the surface of the housing defining the opening.When, as will be usual, the housing is flanged over to form the opening therein, the thickness of the insulating body in its marginal region connected to the housing is preferably the same as the wall thickness of the housing and increasestowards the supply lead or leads, preferably to from 1.5 to 2.5 times its minimum thickness.

It has proved to be particularly desirable to form the insulating body of an epoxide resin composition.

This has a high insulation value and makes it possible to bridge the parts which are produced from the various different materials particularly safely. An epoxide resin composition can be connected fast to the sleeve-like or cup-like external housing made, for example, of a suitably surfacetreated aluminium alloy, copper alloy or steel with appropriate surface treatment, to the glass bushing and to the synthetic plastics insulation of the supply lead or leads. Thus, an epoxide resin composition possesses an elasticity such that it follows the various heat expansions of these different materials.

Any movement of the at least one supply line with respect to the housing which may take place, such as may occur during the handling or assembly of the igniter element or pressurised gas cartridge fitted therewith is also reliably absorbed by this composition. The ease with which such a composition may be worked and the mechanical or electrical prop erties of this composition in the cured state may be chosen in accordance with particular requirements by selection of the curing agents which are actually used and the addition of reactive thinning agents, plasticisers, fillers, etc. In particular, it has been found that the addition of a volatilisable plasticiserto the epoxide resin is to be desired.When such a plasticiser is volatilised after the curing, it provides an extraordinarily secure bonding of the insulating body to all the materials to which it is to be bonded.

The epoxide resin composition is composed of two components which are mixed with one another. This composition enters satisfactorily cavities which are very difficultly accessible, so that shrink-hole formation does not occur. Hence, such a resin composition uniformly wets the surfaces concerned and is reliably connected thereto.

With water-tight pressurised gas cartridges having a glass bushing through which pass the supply lines of the igniter element and provided with an insulating body employed according to the invention, produced, for example, from epoxide resin, the extent of insulation resistivity obtained in a humid environment at, for example, 50% relative air humidity and normal temperature, may be established using various environmental tests, for example temperature shock, impact and vibration tests.It has been found that when the spacing between the supply lines and the rim of the opening in the external metal housing or casing of the pressurised gas cartridge facing the said lines is about 1 mm and the insulating body is formed of epoxide resin, with a measuring voltage of 100 V, insulation resistances were measured which safely exceeded 100 MQ. The insulating body according to the invention thus protects pressurised gas cartridges and their igniter elements having glass bushings, in an effective manner against electric flash-overs, more especially in a humid atmosphere.

For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawing, wherein: Figure 1 shows in elevation, partly in section, a water-tight pressurised gas cartridge embodying this invention; and Figure 2 is a detail, in section, of Figure 1, to a larger scale.

Referring to Figure 1, the pressurised gas cartridge comprises a cylindrical external housing 1, formed for example of steel, and having at one end thereof an opening 2 within which is disposed a glass bushing 3 for two supply lines 4 of an electric igniter element which is not shown. The supply lines or conductors are provided with an insulation 5, for example, shrunk-on PVC tubes. The opening 2 is sealed off outwardly by means of an insulating body 6 according to this invention.

As can be more clearly seen from Figure 2, the insulating body 6, formed for example of epoxide resin, and employed for the improved electrical insulation of the pressurised gas cartridge is arranged on the outside 7 of the glass bushing 3 and encloses insulated end 8 of the conductors 4. The insulating body covers the entire opening 2 and is connected fast to the outside 7 of the glass bushing 3, to uninsulated sections 9 of the supply lines 4, to the insulation 5 thereof and to the cylindrical rim of the opening 2 in the housing 1, which rim is shown at 10. The lateral spacing between the rim 10 and the supply lines 4 in this case is, for example, barely 1 mm. The thickness of the insulating body 6 and the periphery thereof is equal to that of the housing wall and increases gradually towards the supply lines 4.

The glass bushing is set in an outer ring 11 formed for example of steel, by which it is connected to the housing 1, for example, by soldering of the ring 11 to the housing. The glass bushing 3 is supported in the axial direction on additional structural elements of the igniter element of the pressurised gas cartridge, which structural elements are not shown.

Claims (9)

1. An electric igniter element for use with a pressurised gas cartridge, which igniter element comprises a housing, a glass body within the housing and at least one electric supply line which is guided through the glass body to ignition means of the igniter element, the supply line(s) carrying electric insulation on the portion thereof disposed outside the housing and the glass body, the portion of the or each supply line not carrying insulation being enclosed in an insulating body which extends to enclose and be connected fast with a portion of the or each supply line carrying electric insulation and which is connected fast with the glass body.

2. An electric igniter element as claimed in claim 1, wherein the supply line(s) is/are set in a body of synthetic plastics insulating material cast therearound.

3. An electric igniter element as claimed in claim 1 or 2, wherein the insulating body covers fuliy an opening in the housing within which the glass body is disposed, the insulating body being connected fast, without the existence of any gap, to surface means of the housing defining the opening.

4. An electric igniter element as claimed in claim 3, wherein the housing is flanged-over to form said opening, and the thickness of the insulating body at its marginal region at which it is connected to the housing is the same as the wall thickness of the housing and increases as the supply line or lines is/are approached.

5. An electric igniter element as claimed in claim 4, wherein the maximum thickness of the insulating body adjacent the supply line(s) is from 1.5 to 2.5 times the minimum thickness.

6. An electric igniter element as claimed in any one of the preceding claims, wherein the insulating body is formed of an epoxide resin composition.

7. An electric igniter element as claimed in claim 6, wherein the insulating body contains a plasticiser which isvolatilised after curing of the resin composi tion.

8. An electric igniter element as claimed in any one of the preceding claims, which is in operative association with a pressurised gas cartridge.

9. An electric igniter element, substantially as hereinbefore described with reference to the accom panying drawing.