GB2273677A

GB2273677A - Method of sealing a tubular member

Info

Publication number: GB2273677A
Application number: GB9324115A
Authority: GB
Inventors: Gunter Ludwig
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1992-11-26
Filing date: 1993-11-23
Publication date: 1994-06-29
Anticipated expiration: 2013-11-23
Also published as: GB2273677B; FR2698498B1; DE4239820C1; GB9324115D0; FR2698498A1

Description

2273677 METHOD OF SEALING A TUBULAR MEMBER The invention relates to a

method of sealing a tubular member, and particularly although not exclusively a tubular bushing or sheath for guiding and 5 protecting electrical cables.

In many technical fields it is necessary to seal a tubular bushing or sheath which contains electrical cables, leads or other installations. One example is the testing of electronic control devices in the motor vehicle industry. The operational capabilities of the control devices are tested over a wide temperature range. The control devices are, for this purpose, introduced into thermal cabinets in which they are exposed, for example, to temperatures of -40C to +850C. For operational testing they are connected to equivalent circuit arrangements which lie outside the thermal cabinet and with which the peripheral equipment of the control device in a motor vehicle is simulated.

The electrical connection between the control device and the equivalent circuit arrangements is made by way of a connector which, by means of several electrical leads, is connected to the electronic circuit arrangement components of the equivalent circuit arrangement and to which a cable leading to the control device is connected. The leads run in a tubular bushing which extends out of the thermal cabinet. The interior of the thermal cabinet must be closed off in a heat- and gas-tight manner to maintain an artificial environment. As the connector itself is not heat and gas tight, the bushing must be sealed.

It is known to seal bushings through the end wall of a control device with elastic moulded portions (US-PS 3 904 812). Such a seal, however, is expensive, since special moulded sealing bodies have to be produced for each application. Moreover, the sealing effect, especially in the case of comparatively great fluctuations in temperature, is not guaranteed.

In the case of another known method (FR 25 01 926 A) a tube-like sheath for cables is sealed by injecting therein under pressure an expanding plastics foam which can be polymerized. Two layers of elastic sealing lips which are glued together and which in the centre have a circular opening for the leadthrough of the cable are provided as a block for the plastics foam. They must be sufficiently elastic that they can adapt to the outside diameter of the cable which is to be guided through, yet they must form a block for the sealing foam. Consequently, the production of the two-layer, elastic lips and their securement to the tube-like sheath is very expensive.

According to the present invention there is provided a method of sealing a tubular member comprising:

immersing an end of the member in an inert liquid; subsequently introducing a settable liquid sealing mass, which has a density lower than that of the inert liquid, into the interior of the member; and causing or allowing the sealing mass to set while the member remains immersed in the inert liquid.

The setting of the sealing mass introduced into the bushing can be accelerated by heating it.

For a better understanding of the present invention and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:

Figure 1, is a diagrammatic representation, of an apparatus for sealing a bush; Figure 2 shows two seals produced in the apparatus of Figure 1.

A tubular bushing 1 contains electrical leads 2 which connect electronic equivalent circuits 3, which are used to test a control device, by means of a connector 4. In the case of the present exemplary embodiment, the bushing 1 is used to guide the cables 2 through the wall or door of a thermal cabinet which is not represented. The bushing 1 can be realized as a glass tube, can consist of any other suitable materials and can have a great variety of cross-sectional forms.

The bushing 1 contains a stopper-like seal 6 which closes it off in a liquid-, gas- and heat-tight manner and the production of which is described in the following.

The bushing 1 is introduced with its longitudinal axis substantially vertical into an open container or trough 7, the end of the bushing 1 which Is to be sealed is dipped into a confining liquid 8 which fills the container 7 up to a level 9.

The confining liquid 8 preferably comprises an inert liquid of high specific weight. For example, a heat-transmitting medium which is distributed by the firm of Montedison under the name of Galden LS/215 S for vapour-phase soldering, is suitable for use as the confining liquid 8. In any case, it is recommended that a liquid be selected, the specific weight or density of which is approximately twice as high as that of the mass used for sealing purposes.

Finally, a settable liquid sealing mass is poured into the bushing 1 from above - for example with the aid of a pipette 10. The sealing mass now floats on the confining liquid 8 which forms a barrier inside the work piece and surrounds the leads 2 - if such are present.

A silicon rubber 622 A and B which is distributed by the firm of Wacker Chemie (a two-component system having a mixture ratio of 100:10) is an example of a suitable sealing mass.

In order to obtain a desired position of the seal 6,1 the depth of immersion of the bushing 1 and the quantity of sealing mass poured in must be selected as a function of the density of the confining liquid and the sealing mass. The dimensions and positions of two examples of sealing stoppers 6 can be seen from Figure 2. In this connection, h is the height of the surface of the liquid above the base of the container 7. The other dimensions follow from the drawing. Suitable values for the various dimensions are as follows:

a, = 10 mm bl = 21.7 mm h = 23.3 mm a2 = 6.3 mm.

b2 = 28 mm.

If applicable the volume of the installations/components contained in the bushing 1, for example of the leads 2, are to be taken into consideration. The work piece, that is, the bushing 1, is held in the position illustrated after the sealing mass has been poured in until the sealing mass has set.

The setting of the sealing mass can be accelerated by heating. After setting, the seal 6 forms a stopper which adheres to the walls of the bushing 1, encloses the leads 2 in a fixed manner and results in a perfect seal in respect of solid, liquid and gaseous media and, in addition, acts in a heat-insulating manner.

After setting or hardening, further materials, for example, special sealing masses or insulating masses, can be applied to the seal 6 without requiring the use of container 7 and the confining liquid 8.

Claims

1. A method of sealing a tubular member comprising:

2. A method as claimed in claim 1, in which the member contains a component which becomes embedded in the sealing mass when it sets.

3. A method as claimed in claim 2, in which the component is an electrical lead.

4. A method as claimed in any one of the preceding claims, in which the longitudinal axis of the member is held substantially vertical, while the member is immersed in the inert liquid.

5. A method as claimed in any one of the preceding claims, in which the sealing mass is heated.

6. A method as claimed in claim 5, in which the sealing mass is heated after it has been poured into the tubular member.

7. A method of sealing a tubular member as claimed in claim 1 and substantially as described herein.

8. A thermal cabinet provided with a tubular member sealed by a method as claimed in any one of the preceding claims.