AU4724793A - Seal made of a cross-linked elastomer - Google Patents

Description

Seal made of a cross-linked elastomer

The invention relates to a sealing system of the type set out in the principal section of claim 1.

Providing casings, containers etc., more particularly cable sleeves, the internal space of which must be protected as durably as possible against environmental influences, especially dampness, with seals is familiar, at least where casing closing elements, such as doors and lids are present or where elements enter the casings, such as incoming and outgoing cables in the case of cable sleeves. In the older solutions it was known to apply an insulating mass in excessive quantities to the cable input area, which generally as a result of two separate casing halves was designed separately, in order to ensure that during pressing together of the sleeve halves the insulating mass surrounds the incoming cable and completely seals it. One problem of such compressing agents, for example those based on butyl rubber, is often that such components are subjected to strong temperature change loadings, whereby as a result of different thermal expansion coefficients and different heat transfer values between the sealing surfaces and the sealing mass during such temperature change loadings, leakages occur. In order to avoid such problems, so-called shrink-on sleeves were developed, whose cable input connections shrink when heat is applied and adhere tightly to the incoming cable casing, whereby hot-melt adhesive coatings ensure the necessary adhesion. Although this technology has considerable advantages, one of its disadvantages is that a flame always has to be used for shrinking, which often leads to local problems on site.

The aim of the invention is to create a solution, which avoiding the disadvantages of the known solutions produces a sealing system which is simple to use and can take up the alternating loadings without problem.

With a sealing system of the type described above, this task is solved by the invention in that the seal is formed of a first element having an adhesive external surface and a springy or elastic second element. By way of the sealing element which has an elastic or springy effect, it is possible to intercept or by¬ pass various expansion paths in temperature variations, while through the other, adhesive, element adhesion to the component surface is ensured which is allocated to the seal or the corresponding seal surface. The elasticity on the one hand and adhesiveness on the other also result in the seal being pressed into uneven areas, thus increasing the sealing effect even further.

Due to the dual nature of the system it is also possible to easily adapt to the appropriate application, both in terms of dimensioning and also special material properties and geometric features.

In the design it is envisaged that the springy and/or elastic element is completely surrounded by the first element with the adhesive surface.

The complete surrounding of the elastic and/or springy elements means that the restoring forces can act in all directions.

The invention also envisages that the springy element is formed by a mechanical spring, a pneumatic chamber or an elastomer.

The invention also provides for a seal made of a cross-linked elastomer, more particularly an HTV silicon rubber.

In the case of such seals various applications are known. An elastomer and/or synthetic rubber often has very favourable properties, whereby a silicon rubber vulcanized at high temperature, e.g. type MVQ, is frequently used here. In order to achieve complete cross-linking of such a material, a peroxide quota of 1.0 to 1.5% by weight must generally be added. Depending on the peroxide quota and silicic acid content of the raw material, various hardnesses of elastomers are obtained. If these materials are used as seals, the seal produces, exclusively reversible mechanical deformation of such elastomers, i.e. the sealing effect is guaranteed by the restoring forces. Usually such deformability is measured in accordance with German standard DIN 53517, i.e. a pressure deformation residue is given as a yardstick after constant deformation.

In addition to the cross-linked sealing materials there are other sealing materials such as non-cross-linked systems with very high viscosity and adhesiveness based on butyl rubber for instance. In the case of these materials the sealing effect is achieved not as a result of deformation, but due to the surface adhesion to neighbouring surfaces, such sealing material exhibiting a restoring capability. In this way such sealing systems have the disadvantage that they cannot be used on components subject to great temperature variations and thus greater deformation paths.

In further embodiments the invention provides for a seal , which is characterised by such incomplete cross-linking, that the surface has an adhesiveness, with such a seal having a peroxide quota lying under 1.0% by weight.

In such an incompletely cross-linked elastomer seal a sufficient restoring capability remains guaranteed on the one hand, and on the other attachment of the material to the surface through the residual adhesiveness is possible.

Expediently the peroxide quota lies under 0.5% by weight, whereby in the case of a silicon rubber of type MVQ with various mixing ratios in peroxide cross-linking it has been shown that even with a peroxide quota of 0.2% there are adequate mechanical propertiess in various cases. In particular, the required restoring force was achieved as well as an adhesiveness which allows for adequate surface adhesion to the neighbouring surfaces bordering on the seal. At this point it should be noted that not only chemical cross- linking is possible, but also physical cross-linking, e.g. through high-energy radiation.

In another embodiment the invention also provides for the seal being formed of at least two differently cross-linked layers. In this way at least one of the layers, irrespective of the type of cross-linking, be it chemical or physical, can be completely cross-linked.

Various layer structures can be realized here or half-shells and/or pot forms produced, whereby the half-shells or pot casings are formed of a completely cross-linked material with partially cross-linked sealing material inside, or vice-versa, the partially cross-linked sealing material is arranged on the outside and the fully cross-linked material inside.

Further embodiments according to the invention consist in them being formed of at least two layers containing cross-linked material but not yet cross-linked, which in the non-cross-linked state are connected to each other and subsequently subjected to cross-linking, or in the seal being formed of at least two connected layers with a varying peroxide content, whereby the overall composite is subjected to cross-linking, and in the seal being formed of an under-cross-linked first section and an as yet non-cross-linked second section which are connected to each other and subjected to joint cross-linking.

The invention is described below in more detail with the aid of the diagrams. These show the following:

Fig. 1 a simplified spatial representation of a sealing system as described in the invention.

Fig. 2 a cross-section through a sealing area with a sealing system shown in simplified form, Fig. 3 a three-layer seal in the relaxed state,

Fig. 4 the seal shown in Fig. 3 in the compressed state.

Fig. 5 and 6 another sealing system with different types of loading,

Fig. 7 a sealing system with a sealing body lying within it, in cross section.

Fig. 8 a semi-cylindrical sealing system, and in

Fig. 9 a cylindrical sealing system in longitudinal section.

The sealing system which is designated generally with 1 in the figures, comprises at least a first element 2 with an adhesive external surface 2a which is partially indicated in Figure 1 by dots, and a spring and/or elastic second element 3 which is shown symbolically in Figure 1 as a spring indicated by a broken line. The invention is not limited to the form of this sealing system which is shown. A closed, rotating ring can be just as possible here as angular cross section shapes and suchlike.

In Figure 2 a sealing system 1 ' is shown in section, consisting of a first enveloping element 2 ' which has the adhesive external surface, and an internal, e.g. pneumatic elastic second element 3'. The wall parts, e.g. a cable sleeve, are only indicated and designated with 9.

A sealing system 1" is shown in Figures 3 and 4, whereby the inner elastic element 3" here is formed, e.g. by an elastomer, which is inserted between two sealing faces 2^,/ and 4 respectively, which are characterised e.g. by an incomplete cross- linking such that their surface still has an adhesive property. Under compressive loading an image as shown in Figure 4 then results. A similar sealing system is shown in Figure 5, however provision can be made here for tensile loading according to the arrow 5, whereby the fully cross-linked elastic element 3'" is disposed between the partly cross-linked surfaces 2'" and 4' and adheres to these.

In figures 7 to 9 various embodiments of a seal are shown, for example in internal seal 7 can be taken up by a cross sectioned enveloping body, as shown in Figure 3, or as in Figure 4, where a half-shell enveloping body 6a itself can be formed of a completely cross-linked synthetic material or of other materials.

Finally, Figure 9 shows a longitudinally sectioned sealing body with the material properties according to the invention. This sealing body is marked there with 3b, with an inner enveloped cable 8, for example cable bundles 8, if the seal is provided in the edge area of a cable sleeve, which is not shown here in more detail.

The seal embodiments shown in the figures only apply as examples, without restriction of the invention thereto.

In general, we prefer that the sealing material have a compression set of 20% or less (more preferably 15% or less), a Shore A hardness of 25% or less (more preferably 20%) or less, a brittleness temperature of - 40°C or less, a petroleum resistance of better than 15% after 24 hours at room temperature, and have fungi and bacteria resistance (preferably rated 1) and be resistant to termites and other damage. These properties will in general apply to both components, but in particular to the second element especially when the first component is thin and serves only to form a bond or to fill small leak paths. Improved performance can be achieved by protecting exposed or otherwise vulnerable surfaces of the system with a resistant material such as a fluorosilicone rubber, a chloroprene rubber and /or a nitrile rubber. Such materials may be affixed to one or both elements of the system by any suitable fixing means, for example bonding, cross-Uii-king and/or vulcanizing. Also, or instead, such vulnerable surfaces may be protected by encasing the system in some rigid plastics shell or other part. One or more such parts may be provided to encase the system.

Claims (11)

Claims

1. Sealing system for components to be sealed with regard to each other, such as casings, containers and particularly cable sleeves as protection of the internal space of the components against environmental influences, characterised in that the seal (1) is formed of a first element having an adhesive outer surface (2a) and a springy and/or elastic second element (3) .

2. Sealing system according to claim 1, characterised in that the springy and/or elastic element (3) is completely surrounded by the first element (2) having the adhesive surface (2a) .

3. Sealing system according to claim 1 or 2 , characterised in that the springy element is formed by a mechanical spring (3) , a pneumatic chamber (3') or an elastomer (3").

4. Sealing system made of a cross-linked elastomer, in particular an HTV silicon rubber, characteised by such incomplete cross-linking that the surface has an adhesiveness.

5. Sealing system according to any one of the above claims, characterised in that the peroxide quota is under 1.0% by weight.

6. Sealing system according to any one of the above claims, characterised in that in order to achieve an adequate restoring capability on the one hand and adhesiveness on the other, the peroxide quota is under 0.5% by weight.

7. Sealing system according to any one of the above claims, characterised in that it is formed of at least two differently cross-linked layers ( 2 ' ' , 2 ' ' ) .

8. Sealing system according to any one of the above claims, characterised in that at least one of the layers (3") is completely cross-linked, irrespective of the type of cross- linking, be it physical or chemical.

9. Sealing system according to the above claims, characterised in that it is formed of at least two as yet non-cross- linked layers ( 2 ' ' , 3") containing cross-linking agents, which in the non-cross-linked state are connected with each other and then subjected to cross-linking.

10. Sealing system according to any one of the above claims, characterised in that the seal is formed of at least two connected layers with a (2^, ) differing peroxide quota, whereby the overall composite is subjected to cross- linking.

11. Sealing system according to any one of the above claims, characterised in that the seal (2'' ' ) is formed of an under-cross-linked first section and an as yet non-cross- linked second section, which are connected to each other and then subjected to joint cross-linking.