DE102014205300A1 - Mechanical seal assembly with graphene-containing lubricant - Google Patents

Abstract

The invention relates to a mechanical seal assembly comprising a rotating seal ring (2) and a stationary seal ring (3) defining between them a sealing gap (4), wherein in the sealing gap (4) a liquid medium (9) is arranged and wherein the liquid medium a graphene-containing material (10).

Description

The present invention relates to a mechanical seal arrangement in which a lubricating medium comprising graphene-containing material is arranged in the sealing gap. Furthermore, the invention relates to a method for operating a mechanical seal assembly and the use of a graphene-containing material as the lubricant of a mechanical seal assembly.

In fluid-lubricated mechanical seal assemblies, a liquid lubricant is disposed in the sealing gap between the rotating and stationary seal rings. The lubricating film in the sealing gap ensures the functionality of the mechanical seal assembly. In principle, the lubricating film can be built up from the medium to be sealed or a foreign medium (blocking medium). As a barrier medium oils or deionized water are often used. The main aim of the lubricating film between the sliding surfaces of the slip rings is to reduce the friction as possible. There is a constant effort in the industry to keep the friction in the sealing gap as low as possible.

It is an object of the present invention to provide a mechanical seal assembly and method for operating a mechanical seal assembly which, with a simple structure and simple, inexpensive manufacturability, provides the smallest possible coefficient of friction in a sealing gap between sliding surfaces of slip rings.

This object is achieved by a mechanical seal assembly having the features of claim 1 and a method having the features of claim 9 and a use having the features of claim 11. The dependent claims each show preferred developments of the invention.

The mechanical seal assembly according to the invention with the features of claim 1 has the advantage that a coefficient of friction in the sealing gap between sliding surfaces of slip rings can be further reduced. This is inventively achieved in that in the sealing gap, a liquid medium is arranged, which comprises a graphene-containing material. In other words, a graphous suspension is arranged in the sealing gap, whereby a friction coefficient can be significantly reduced in comparison with a same liquid medium without graphene-containing material. It has now surprisingly been found, according to the invention, that the use of graphene-containing material with a liquid medium provides an excellent lubricant for a mechanical seal assembly. This is all the more surprising, since usually solids in the lubricant increase the coefficient of friction. In addition, the use of a graphene-containing lubricant improves the dry-running property of the mechanical seal assembly when, for example, lubricant supply is interrupted. Another surprising advantage in the operation of the mechanical seal assembly with a liquid medium with graphene-containing material results in the field of mixed friction. The mixed friction lies between the pure solid friction, in which the sliding surfaces touch, and the pure liquid friction, in which the sliding surfaces no longer touch. In mixed friction, the sliding surfaces touch at points, with a lubricant between the sliding surfaces is present. The mixed friction is therefore of great importance in the case of mechanical seal assemblies, since leakage through the sealing gap is minimized. With pure liquid friction, the gap between the slip rings becomes so large that increased leakage is present. Excessive solids friction results in high wear on the sliding surfaces. Therefore, in mechanical seals many applications arise in which the mechanical seal assembly is preferably operated in the field of mixed friction. Furthermore, according to the invention, the use of the graphene-containing material in the lubricant between the sliding surfaces also does not result in any negative effect on fluid friction.

The graphene-containing material is preferably graphene in the form of pure graphene and / or graphene oxide and / or technically reduced graphene oxide (TRGO) and / or functional graphene (graphene with attached further molecules or other attached atoms).

A particularly good reduction of the friction in the sealing gap is achieved when the graphene-containing material has a planar arrangement and not z. B. rolled into a single-layer nanotube. During operation, the planar structure of the graphene-containing material can be arranged excellently parallel to the sliding surfaces, so that friction in the sealing gap is further reduced.

Particularly preferred is a proportion of the graphene-containing material in the liquid medium in a range of 0.05 to 0.6 wt .-%, and in particular 0.1 wt .-%. If the proportion of graphene-containing material drops below 0.05% by weight, the advantage according to the invention of reducing the friction in the sealing gap is no longer present. If the proportion of the graphene-containing material is more than 0.6% by weight, the coefficient of friction deteriorates again. If the proportion of the graphene-containing material in the lubricating medium is too great, a highly viscous lubricating medium is obtained which increases the friction in the sealing gap.

The liquid medium in the sealing gap, which comprises the graphene-containing material, is preferably water. Here, very low friction coefficients in the range of 0.02 are achieved. Particularly preferably, the liquid medium in the sealing gap ultrapure water. Ultrapure water is a specially purified water that contains no foreign substances. Ultrapure water has an electrical conductivity of less than or equal to 1.1 μS / cm at 20 ° C. Ultrapure water is also used in power plants, for example. Alternatively, the liquid medium is oil.

According to another preferred embodiment of the present invention, at least one of the slip rings, preferably both slip rings, comprises a diamond coating. In conjunction with diamond-coated sliding surfaces, particularly low friction coefficients are achieved. Further, by the use of the diamond-coated sliding surfaces, a dry running property of the mechanical seal assembly is further improved.

More preferably, at least one of the sliding rings comprises, as a sliding ring material, tungsten carbide or silicon carbide, which optionally may preferably have a diamond coating.

According to a further preferred embodiment of the invention, the mechanical seal assembly further comprises a supply system, in particular a barrier pressure system, for supplying a barrier medium to the sealing gap. The barrier medium is the liquid medium with graphene-containing material. Thus, by using a graphene-containing barrier medium, a mechanical seal assembly having excellent tribological properties can be provided.

Furthermore, the present invention relates to a method for operating a mechanical seal assembly, wherein in the sealing gap between the slip rings, a liquid lubricant with graphene-containing material is present. The liquid lubricant containing graphene-containing material preferably circulates in a closed circuit, for example a barrier pressure system.

Furthermore, the present invention relates to the use of graphene-containing material as a lubricant in a sealing gap of a mechanical seal assembly. The graphene-containing material is preferably used in a suspension, in particular with demineralized water. More preferably, the graphene-containing material is used in conjunction with a barrier medium of the mechanical seal assembly. The graphene-containing lubricant can also be used in already existing mechanical seal arrangements.

Hereinafter, a preferred embodiment of the invention will be described in detail with reference to the accompanying drawings. In the drawing is:

1 a schematic sectional view of a mechanical seal assembly according to an embodiment of the invention,

2 a schematic diagram illustrating a comparison between a graphene-containing lubricating medium and a lubricating medium according to the prior art and

3 a schematic, perspective view of the graphene-containing material used in the sealing gap.

The following is with reference to the 1 to 3 a mechanical seal assembly 1 according to a preferred embodiment of the invention described in detail.

How out 1 it can be seen comprises the mechanical seal assembly 1 a rotating seal ring 2 and a stationary slip ring 3 , which between them a sealing gap 4 define. The rotating seal ring 2 is about a driver element 6 with a shaft bushing 5 connected, with the shaft bushing 5 together with a wave 7 rotates.

The stationary seal ring 3 is on a housing 11 arranged. Furthermore, as secondary seals 12 . 13 O-rings provided.

To the sealing gap 4 with a barrier medium 9 to supply is a barrier pressure plant 14 intended. The barrier pressure system 14 includes a pump 17 and a reservoir 18 and provides a barrier medium circuit. The barrier medium is via a supply line 15 to the sealing gap 4 supplied and a return line via a discharge line 16 , The arrows in 1 indicate the circulation of the barrier medium 9 in a closed circuit.

The barrier medium 9 is a liquid medium, for example deionized water, which is a graphene-containing material 10 includes. The term graphene-containing material includes graphene in the form of pure graphene, graphene oxide, technically reduced graphene oxide and / or functional graphene, in which further molecules or atoms are attached. The barrier medium 9 is thus a graphene-containing suspension. A weight proportion of the graphene-containing material is in a range of 0.05 to 0.2 wt .-%.

The slip rings can each have a diamond coating, which in known Way can be applied to the sliding surfaces of the seal rings.

This in 3 shown graphene-containing material is a technically reduced graphene oxide, which is produced via a two-stage process. For this purpose, starting from a graphite material, the graphite is oxidized, whereby graphite oxide is obtained. The graphite oxide is then thermally reduced to give the thermally reduced graphene oxide (TRGO). In this way, in particular, molecules containing oxygen and oxygen can be chemically bound to the graphene-containing material.

2 shows a diagram of a comparison of the graphene-containing barrier medium according to the invention with a graphene-free barrier medium. More precisely, the diagram of 2 two series of experiments, over the time t in minutes, a coefficient of friction R is shown. The comparative experiments were carried out on the one hand with demineralized water whose coefficient of friction in 2 represented by the curve B. As a comparison, a barrier medium consisting of deionized water with a proportion of graphene oxide of 0.1 wt .-% was used, whose curve in 2 marked with the letter A. Both slip rings were provided with a diamond coating.

The comparative experiments were carried out at different speeds n in 1 / min and at different axial forces F in Newton (N). The experiments were first carried out at a relatively low speed of about 40 1 / min over a period of about 90 minutes and then the speed n was increased to about 800 1 / min for about another 60 minutes. Furthermore, an axial force F was changed during the experiments. At the beginning of the experiments, an axial force F in the range of 100 N was maintained for about 15 minutes. Subsequently, the axial force F was constantly increased up to a value of 700 N. Subsequently, the axial force F was again reduced to the value of about 100 N constant.

In 2 is the curve of the friction coefficient of the graphene-containing lubricant (demineralized water with graphene oxide) denoted by A and shown as a solid line. In comparison, the graph of the grapheless lubricant (excluding demineralized water) is designated B and shown as a dashed line. As immediately out 2 As can be seen, the curve A of the graphene-containing lubricant has a coefficient of sliding friction R in the range of 0.02 at low speeds n in the range of approximately 40 rpm. In contrast, the sliding friction coefficient R of the demineralized water containing no graphene is in a range of slightly over 0.04. In this case, the sliding friction coefficient changes only insignificantly even when an additional axial force F is exerted. When the speed n is increased significantly, as in 2 from a time t of about 90 minutes, the sliding friction coefficient R of the graphene-containing lubricant A increases abruptly to a value of slightly above 0.05. The non-graphene-containing deionized water (curve B) has a coefficient of sliding friction R of about 0.06 at the high speed n of about 800 rpm.

During the time t between 0 and 90 minutes, the mechanical seal assembly is operated in the area of so-called mixed friction. Although there is lubricant between the sliding surfaces, however, the sliding surfaces still touch each other at certain points. This operating condition is particularly preferred since low wear occurs with low leakage and smallest slip ring coefficient. From the time t> 90 min, the mechanical seal assembly is in the pure liquid friction. This forms a complete lubricating film between the sliding surfaces, where, as out 2 it can be seen that there is no negative effect of the graphene-containing lubricant in pure liquid friction.

As the experiments shown thus illustrate, reduces the graphene-containing lubricant 9 the coefficient of friction R to a value of about 0.02. This is achieved in particular in the field of preferred mixed friction. Such a value has not yet been achieved in liquid-lubricated mechanical seals. In this case, an additional axial force F has only marginal negative effects on the excellent friction coefficient. Even at higher speeds n, a lower coefficient of friction is achieved after a transient phase immediately after increasing the rotational speed than in comparison with a graphene-free lubricant. At around 0.05, this is still in an excellent range for fluid-lubricated mechanical seals. Thus, by using the graphene-containing material in the lubricant, surprisingly, a coefficient of friction, especially at low speeds, can be suppressed to a value of 0.02, which was previously not possible with liquid-lubricated mechanical seals in this form. According to the invention can thus be significantly improved by using a graphene-containing lubricant in particular a life of the mechanical seals.

LIST OF REFERENCE NUMBERS

1

The mechanical seal assembly

2

Rotating seal ring

3

Stationary slip ring

4

sealing gap

5

shaft sleeve

6

dogging

7

wave

8th

Medium to be sealed

9

barrier medium

10

Graphene in a planar structure

11

casing

12, 13

O-rings

14

Blocking pressure system

15

supply line

16

discharge line

17

pump

18

reservoir

Claims (12)

Mechanical seal assembly comprising - a rotating seal ring ( 2 ) and a stationary sliding ring ( 3 ), which between them a sealing gap ( 4 ), - wherein in the sealing gap ( 4 ) a liquid medium ( 9 ) and wherein the liquid medium is a graphene-containing material ( 10 ). Mechanical seal assembly according to claim 1, characterized in that the graphene-containing material comprises graphene in the form of pure graphene and / or graphene oxide and / or technically reduced graphene and / or functional graphene. Mechanical seal arrangement according to one of the preceding claims, characterized in that the graphene-containing material has a planar arrangement. Mechanical seal arrangement according to one of the preceding claims, characterized in that a proportion of the graphene-containing material in the liquid medium is in a range of 0.05 to 0.6 wt .-%. Mechanical seal arrangement according to one of the preceding claims, characterized in that the liquid medium is water or oil. Mechanical seal arrangement according to one of the preceding claims, characterized in that at least one of the sliding rings ( 2 . 3 ), preferably both slip rings, have a diamond coating. Mechanical seal arrangement according to one of the preceding claims, characterized in that at least one of the sliding rings comprises tungsten carbide or silicon carbide as a sliding ring material. Mechanical seal assembly according to any one of the preceding claims, further comprising a supply system ( 14 ) for supplying a barrier medium to the sealing gap ( 4 ), wherein the barrier medium is the liquid medium containing graphene-containing material. Method for operating a mechanical seal assembly ( 1 ) with a rotating sliding ring ( 2 ) and a stationary sliding ring ( 3 ), which between them a sealing gap ( 4 ), wherein in the sealing gap ( 4 ) a liquid lubricant is present with a graphene-containing material. A method according to claim 9, characterized in that the liquid lubricant circulates graphite-containing material in a closed circuit. Use of graphene-containing material as lubricant in a sealing gap ( 4 ) a mechanical seal assembly ( 1 ). Use according to claim 11, wherein the graphene-containing material forms a suspension with a liquid medium, in particular a barrier medium of the mechanical seal arrangement.

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