Seal arrangement

A seal arrangement for sealing a gap between a machine element comprising a shaft and a housing includes: at least one sealing element formed, at least partially, from polymeric material. The at least one sealing element is of annular design and is made of PTFE. The at least one sealing element has at least one first annular element and at least one second annular element. The at least one first element is electrically conductive and the at least one second element is electrically insulating. The at least one first element is arranged axially adjacently to the at least one second element. The at least one sealing element is provided with electrically conductive contact elements. The housing has an installation space forming an annular groove for the at least one sealing element. The installation space is provided with a lining forming an insulation.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is a U.S. National Phase application under 35 U.S.C. § 371 of International Application No. PCT/EP2018/071917, filed on Aug. 13, 2018, and claims benefit to German Patent Application No. DE 10 2018 000 935.2, filed on Feb. 6, 2018; German Patent Application No. DE 10 2017 010 981.8, filed on Nov. 28, 2017; and German Patent Application No. DE 10 2017 010 979.6, filed on Nov. 28, 2017. The International Application was published in German on Jun. 6, 2019 as WO 2019/105606 under PCT Article 21(2).

FIELD

The invention relates to a seal arrangement for sealing a gap between a machine element and a housing, comprising at least one sealing element which is at least partially formed from polymeric material, wherein the sealing element is of annular design.

BACKGROUND

Seals, in particular dynamically stressed seals, wear over the intended service life, wherein various wear phenomena have an effect. The contact tension of the sealing element decreases due to material fatigue, and the contact force also decreases. The dimensions of the sealing element change due to wear and setting behavior. Such processes result initially in leakage and then in failure of the sealing system.

For leakage monitoring of seals, integrating a device for leakage monitoring into the seal is known. DE 10 2007 007 405 B4 discloses an electrical device for detecting the state of wear of a dynamic sealing element. The sealing element comprises an electrically conductive section and an electrically non-conductive section which is in contact with the machine element to be sealed. The machine element is also electrically conductive. As a result of wear of the sealing element, the electrically non-conductive sealing material wears so that the electrically conductive sealing material comes into contact with the machine element. In the process, a circuit closes and it can be ascertained that the sealing element is worn out.

In this embodiment, it is disadvantageous that no gradual changes in state can be detected. It can only be ascertained that the wear limit has been reached and that the sealing element has to be replaced in the short term.

SUMMARY

In an embodiment, the present invention provides a seal arrangement for sealing a gap between a machine element comprising a shaft and a housing, comprising: at least one sealing element comprising, at least partially, polymeric material, wherein the at least one sealing element is of annular design and comprises PTFE, wherein the at least one sealing element has at least one first annular element and at least one second annular element, wherein the at least one first element is electrically conductive and the at least one second element is electrically insulating, wherein the at least one first element is arranged axially adjacently to the at least one second element, wherein the at least one sealing element is provided with electrically conductive contact elements, wherein the housing has an installation space comprising an annular groove for the at least one sealing element, and wherein the installation space is provided with a lining forming an insulation.

DETAILED DESCRIPTION

In an embodiment, the present invention provides a seal arrangement which allows permanent state monitoring of the sealing function and which can be produced at low cost and is easy to install at the same time.

In an embodiment, the seal arrangement for sealing a gap between a machine element and a housing comprises at least one sealing element which is formed at least partially from polymeric material, wherein the sealing element is of annular design, wherein the sealing element has at least one first annular element and at least one second annular element, wherein the first element is electrically conductive and the second element is electrically insulating, wherein the first element is arranged axially with respect to the second element.

The elements may be produced in one manufacturing process and subsequently connected to each other to form the sealing element. This is advantageous in particular when the sealing element consists of a material which is not capable of injection molding. One such material is PTFE, for example. In this respect, the seal arrangement according to the invention is particularly advantageous when the sealing element is formed from PTFE.

A particular aspect about PTFE is that, in the case of a combination of a conductive and a non-conductive PTFE material, very good adhesion of the two materials to one another is achieved in the sintering process. A solid firmly bonded connection is obtained. Subsequently connecting the materials, on the other hand, is very difficult.

A sealing lip which bears against the machine element can be formed from the second element. The sealing lip results in a linear contact between sealing element and machine element and, as a consequence thereof, an improved sealing effect.

The material of the first element may be provided with electrically conductive particles. Especially ferrous or carbonaceous particles come into consideration as electrically conductive particles. It is in particular conceivable for the sealing element to be formed from an elastomeric material which is provided with electrically conductive particles.

For this purpose, a contact element may be attached to the sealing element on the outside. A contact surface is also understood here as a contact element.

The sealing element may have at least two elements, wherein a first element is arranged between the two second elements. A sealing lip may be formed from each of the two second sealing elements. This results in uniform pressing of the sealing element on the machine element. This reduces in particular the risk of tilting of the sealing element. Furthermore, the sealing lips may be arranged in such a way that they seal in opposite directions. In particular in the case of a translationally moved machine element, bidirectional sealing is thereby possible.

The housing may have an installation space for the sealing element, wherein the installation space is provided with a lining forming an insulation. In particular, when the machine element is configured as a shaft, the housing opening is generally circular. In this case, the installation space is formed in the shape of an annular groove in which the sealing element is arranged.

A further sealing element may be provided, which brings about the radial prestressing of the sealing element on the machine element. Thereby, the further machine element may be designed as an O-ring. The further sealing element is arranged on the outer circumferential side of the sealing element and causes the radial pressing of the sealing element on the machine element. In this embodiment, the sealing element is activated by the further sealing element.

The further sealing element may be formed from an elastomeric material and used as a contact element.

The figures show a seal arrangement1for sealing a gap between a machine element2and a housing3. A sealing element4arranged between the machine element2and the housing3seals the gap. The sealing element4is arranged in an installation space9introduced into the housing3. The installation space9is in the shape of a circumferential groove.

In the present embodiments, the machine element2is a rotationally and/or translationally movable machine element2, for example a shaft.

The sealing element4consists of a polymeric plastic, here PTFE.

The sealing element4is of annular design, wherein the sealing element4has at least one first annular element5and at least one second annular element6, wherein the first element5is electrically conductive and the second element6is electrically insulating, wherein the first element5is arranged axially adjacently to the second element6. The first element5is bonded to the second element6in a firmly bonded manner.

A sealing lip7which bears in a sealing manner against the machine element2is formed from the second element6. The material of the first element5is provided with electrically conductive particles.

FIG. 1shows a first embodiment of the seal arrangement1. The sealing element4is associated on the outer circumferential side with a further sealing element12, which brings about radial pressing of the sealing element4on the machine element2. The further sealing element12is designed as an O-ring and consists of an electrically insulating elastomeric material. The material of the further sealing element12may alternatively be provided with electrically conductive particles.

FIG. 2shows a seal arrangement1according toFIG. 1. In the present embodiment, the inner wall of the installation space is provided with an insulation10, which brings about an electrical insulation of the sealing element4with respect to the housing3. The insulation10is in the form of a lining11and consists of polymeric material.

Alternatively, the elements of the sealing element4and/or of the further sealing element12may also be designed to be electrically insulating. An enclosure may, for example, be provided for this purpose.

FIG. 3shows a seal arrangement according toFIG. 1. In addition, the measuring path8of the capacitive measurement is shown here. The wear measurement is carried out by determining the capacitance between the two components machine element2and element5, wherein changes in state of the seal arrangement1due to wear and the like are associated with a change in the capacitance. A continuous change in state can also be detected so that monitoring of the seal arrangement1is possible. The monitoring is carried out by means of an evaluation unit which may be connected to contact elements.

FIG. 4shows a seal arrangement1according toFIG. 1, wherein the sealing element4has two second elements6, wherein a first element5is arranged between the two second elements6.

FIG. 5shows a seal arrangement1according toFIG. 4, in which the measuring path for capacitive measurement is indicated.

FIG. 6shows a seal arrangement1, with which the sealing element4is designed as a groove ring, wherein a spring element13which brings about radial pressing of the sealing element4on the machine element2is associated with the groove of the groove ring. The sealing element4is made of PTFE and comprises an electrically conductive first element5and an electrically insulating second element6. The sealing element4must be insulated with respect to the housing3.

FIG. 7shows a seal arrangement1according toFIG. 6, wherein the measuring path8for capacitive measurement is also indicated, which detects the capacitance between the machine element2and the first element5by means of an evaluation unit.

FIG. 8shows a seal arrangement1according toFIG. 6, wherein a contact element18is provided, which is embedded in a disk-shaped insulation10. The contact element18bears against the second element6of the sealing element4and may be integrated in a measuring path8.