GB2521444A

GB2521444A - Sealing arrangement

Info

Publication number: GB2521444A
Application number: GB1322675.8A
Authority: GB
Inventors: Jos Holsnijders
Original assignee: SKF AB
Current assignee: SKF AB
Priority date: 2013-12-20
Filing date: 2013-12-20
Publication date: 2015-06-24
Also published as: GB201322675D0; WO2015091722A1

Abstract

Sealing arrangement 1 for sealing first space A against second space B of machine arrangement 2 comprises first carrier element 3 which is fixed to first machine part 4 of the machine arrangement and second carrier element 5 which is fixed to second machine part 6, which may be a rotating shaft, of the machine arrangement, wherein the second machine part can rotate relatively to the first machine part. To obtain good sealing performance the invention is characterized in that at least one magnet 7 is arranged at the first carrier element, wherein magneto-rheological fluid 8,9 is arranged at at least a part of the surface of the magnet and/or the surface of a part 10 of the sealing arrangement in which a magnetic field is induced by the magnet, wherein at least part of the second carrier element is arranged in the proximity of the magneto-rheological fluid, wherein a gap 11,12,13, which may be hollow cylindrical shaped, is established between the second carrier element and a surface of the magneto-rheological fluid and wherein ferro fluid 14 is arranged in the gap.

Description

Sealing Arrangement

Technical Field

The invention relates to a sealing arrangement for sealing a first space against a second space of a machine arrangement, comprising a first carrier element which is fixed at or in a first machine part of the machine arrangement and a in second carrier element which is fixed at or in a second machine part of the machine arrangement, wherein the second machine part can rotate relatively to the first machine part.

Background

In general, sealing arrangements are known which work with one or more sliding sealing lips to seal a first space against a second space. Also, sealing arrangements are known which have no sliding sealing lips but establish a sealing effect with small gaps, i.e. those sealing arrangements are free of slid-ing contact.

In the latter case the sealing effect depends significantly on the magnitude of the gap which remains between the respective sealing parts. The manufactur- ing of the required parts is sometimes costly because a high degree of preci- sion must he obtained to establish a sufficiently small gap. During the manu-C, facture and the assembly of such a sealing arrangement the tolerances and the mounting method are critical parts as the gap is the most sensitive variable for the sealing capability, e.g. to resist a pressure difference between the two spaces which are sealed against another.

Thus, it is an o bj cc t of the present invention to further develop a sealing arrangement of the kind mentioned above so that the manufacturing of the re-quired parts is easier and the assembly is not so complex, while in spite of this a high sealing capability is maintained. The realization of the sealing ar-rangement should be possible in an economic manner.

Summary of the invention

A s o hit i o n according to the invention is characterized in that at least one magnet is arranged at the first carrier element, wherein a magneto-rheological fluid is arranged at at least a part of the surface of the magnet and!or at at least a part of the surface of a part of the sealing arrangement in which a magnetic field is induced by the magnet, wherein at least a part of the second carrier el-ement is arranged in the proximity of the magneto-rheological fluid, wherein a gap is established between the second carrier element and a surface of the magneto-rheological fluid and wherein a ferro fluid is arranged in the gap.

The first machine part is preferably a housing of the machine arrangement; the second machine part is preferably a rotating shaft. The first carrier dc-ment is preferably arranged stationary and the second carrier element rotates relatively to the first carrier element during regular operation of the sealing arrangement.

The magnet is preferably a permanent magnet.

Normally, the carrier elements are at least partly made of iron. Also, the part in which a magnetic field is induced by the magnet can consist at least partial-ly of iron.

The first carrier element can comprise a radially extending section at which the magnet is fixed.

The part in which a magnetic field is induced by the magnet can be arranged at an axial end of the magnet. The second carrier element can have a radially extending section. wherein an axially extending section is arranged at the end of the radially extending section remote from the second machine part. The magneto-rheological fluid can then he arranged in a cup-shaped manner at the part in which a magnetic field is induced by the magnet. Furthermore, a gap can be established between the axially extending section of the second ma-chine part and an axially extending section of the first carrier element. Also, a ferro fluid can he arranged in the gap between the axially extending section of the second machine part and the axially extending section of the first carrier element.

The gaps have preferably a hollow cylindrical shape.

The sealing arrangement is preferably a part of a bearing arrangement.

Thus, the establishment of a proper sealing capability is done using magneto-rheological fluids (MRF) and ferro fluids (FF). The proposed seal design is based on the use of the two mentioned fluids in such a way that the ferro fluid is located in the gap, so that the size of the remaining gap is mininilzed. This results in an accurate and extremely think sealing compartment.

The strength of the ferro fluid is based on the strength of the magnetic fields and the gap it is operating in.

The magneto-rheological fluid acts as a semi-solid flux guiding component which is compatible with the ferro fluid. The ferro fluid is used as a seal ele- ment and as a lubricant between the magneto-rheological fluid and the adja-io cent carrier element (finger). The gap itself is filled with the ferro fluid and can be extremely small.

Thus, the combination of a magneto-rheological fluid and a ferro fluid allows to establish a very small gap between the rotating parts in an easy way. The magneto-rheological fluid will he attracted to the permanent magnet This creates a layer on the magnet, which will remain in a quasi solid state due to its properties. The magneto-rheological fluid will settle itself and can be smoothened in its shape by the rotating carrier element (finger). The gap be-tween the magneto-rheological fluid and the carrier element (finger) will he filled with the ferro fluid which should be compatible with the magneto-rheological fluid.

When the adjacent carrier element (finger) rotates, a mixed layer or transition layer will be created between the ferro fluid and the magneto-rheological flu-id. The transition layer is a stable layer when the magneto-rheological fluid and ferro fluid are compatible with each other. Otherwise, it can happen that churning occurs.

Thereby, the gap can be controlled in width (thickness) more accurately and can be smaller due to the fact that the carrier element (finger) is able to "polish" the magneto-rheological fluid, keeping the gap extremely small without destroying the two components (magneto-rheological fluid and carrier element) when they would touch.

So, the magnet holds the magneto-rheological fluid in position; the adjacent carrier element (finger) defines the smoothness of the gap between the carrier element and magneto-rheological fluid during rotation. The ferro fluid which io is also attracted by the magnet performs the sealing itself. Due to the fact that the gap (containing the ferro fluid) can be extremely small, the magnetic field will he high, and giving a better sealing effect. The ferro fluid can act as a lubricant between the magneto-rheological fluid and the carrier element (finger).

Beneficially, the gap can be established with a very small width in an easy way, resulting in a higher magnetic field and resulting in a better sealing per-formance.

With regard to the employed magneto-rheological fluid and ferro fluid the fol-lowing information should be given: Magneto-rheological fluids are dispersions of micron-sized magnetic particles in a liquid carrier, which can reversibly and instantaneously change from a liquid state to a semi-solid or plastic state in the absence or presence of a magnetic field. Moreover, in their on-state (i. e. semi-solid state) these fluids show a viscoplastic behavior, which is characterized by a magnetic field-dependent yield stress.

These main characteristics render magneto-rheological tluids useful for sever- al controlled electro-mechanical applications. The properties of a magneto-rheological fluid are mainly determined by the composition and nature of its magnetic particles, its dispersion additives, and its carrier fluid.

Ferro fluids are colloidal dispersions of magnetic nano-particles which carry a permanent magnetic nionient. They have a diameter of around 10 nm, show-ing single magnetic domains. Several types of particles can he dispersed, such as magnetite and cobalt ferrite.

A significant aspect in magnetic tluids is the particle stabilization in a certain solvent, otherwise the particles will aggregate and separate due to Van-der- Waals interactions. The additional presence of magnetic dipole-dipole interac-tion also plays a significant role in colloidal stability of ferro fluids, especially is when they are subjected to external magnetic fields Two distinct types of stabilization are known: steric stabilization and electro-static stabilization. They can both be present in some cases. Steric stability is obtained by coating the particles with surfactants, which may lead to highly stable colloids (used typically for non-polar solvents). Electrostatic stabiliza-tion occurs if the particles become electrically charged (this is seen typically in polar solvents).

When an external magnetic field is applied, the particles tend to align their di- polar moments parallel to the field. This process is called super-para-magnetism. Also, due to increased dipole-dipole interactions, the formation agglomerates is quite likely to occur. Small chain formation is normal, but large structures may destabilize the ferro tluid or lead to undesired effects in the applications. In well stabilized ferro fluids, the latter phenomenon is less likely to occur.

In general, increasing the particle concentration leads to a strong response of the ferro fluid.

Ferro fluids can he easily positioned or used in many mechanical devices by means of a magnetic field. A variety of phenomena have been observed for these systems in magnetic fields which are appropriate for different applica-tions. These effects must be taken into account when utilizing magnetic fluids in different applications.

Brief description of the drawing

The drawing shows an embodiment of the invention. The only figure shows a radial cross sectional view through a machine arrangement with two machine parts with a sealing arrangement which is arranged effectively between them.

Detailed description of the invention

In the figure a machine arrangement 2 is shown having a first machine part 4 which is a housing and having a second machine part 6 which is a rotating shalt. To seal a first space A against a second space B a sealing arrangement 1 is provided.

The sealing arrangement 1 has two carrier elements, i.e. a first carrier element 3 which is connected with the housing 4 and a second carrier element 5 which is connected with the shaft 6.

The first carrier element 3 has section which runs in axial direction a and which is in press fit connection with the housing 4. Furthermore, the first car-rier element 3 has a radial section 3' which runs in radial direction r. At this radial section 3' a permanent magnet 7 is fixed, e.g. by means of an adhesive.

The magnet 7 is generally of ring-shape with the radial cross section as de-picted.

The second carrier element 5 has also a section which runs in axia' direction a; this section is connected with the shaft 6 by press fit. Then, the second car-Her element 5 has a radial section 5' which runs in radial direction r. At the end of the radial section 5' a further section is arranged, i. e. an axial section 5" which runs in axial direction a. Thus the second carrier element 5 forms a cup-shaped structure in the radial cross section.

A ferromagnetic part 10, made of a ferromagnetic metal, is arranged at the ax-ial end of the magnet 7 and extends into this cup-shaped structure. The part 10 is generally of ring-shape and is made of iron (Fe430) in the depicted exam-ple.

Furthermore, a magneto-rheological fluid 8 is arranged around the surface of the part 10 which forms a respective cup-shaped structure in the cross sec-tional view and which fits basically into the structure which is formed by the second carrier element 5 with its sections 5' and 5". So, ring-shaped gaps 11 and 12 are given between the second carrier element 5 and the niagneto-rheological fluid 8.

The same applies for a magneto-rheological fluid 9 which is arranged at the radial inner end of the radial section 3' of the first carrier element 3. Also here, a gap 13 is formed between the magneto-rheological fluid 9 and the ra-dial outer surface of the second carrier element 5.

Finally, a gap 15 is formed between the axial section 5" of the second carrier element 5 and the first carrier element 3.

io In all gaps 11, 12, 13 and 15 a ferro fluid 14 is filled as depicted. Due to the magnetic force which is induced in the adjacent parts by the magnet 7, the fer-ro fluid 14 is kept in the depicted position.

By this design it is guaranteed that a very small remaining gap only is given is hetween two adjacent parts of the sealing arrangement which are rotating rela-tively to another during regular operation of the machine arrangement 2.

Reference Numerals: 1 Sealing arrangement 2 Machine arrangement 3 First carrier element 3' Radial section of the first carrier element 4 First machine part Second carrier element 5' Radial section of the second carrier element 5" Axial section of the second carrier element 6 Second machine part 7 Magnet 8 Magneto-rheological fluid 9 Magneto-rheological fluid

Part for inducing a magnetic field

11 Gap 12 Gap 13 Gap 14 Ferro fluid Gap A First space B Second space r Radial direction a Axial direction

Claims

Patent Claims:SSealing arrangement (1) for sealing a first space (A) against a second space (B) of a machine arrangement (2), comprising a first carrier ele-ment (3) which is fixed at or in a first machine part (4) of the machine arrangement (2) and a second carrier element (5) which is fixed at or in a second machine part (6) of the machine arrangement (2), wherein the second machine part (6) can rotate relatively to the first machine part (3), characterized in that at least one magnet (7) is arranged at the first carrier element (3), wherein a magneto-rheological fluid (8, 9) is arranged at at least a part of the surface of the magnet (7) and/or at at least a part of the surface of a part (10) of the sealing arrangement (1) in which a magnetic field is in-duced by the magnet (7), wherein at least a part of the second carrier element (5) is arranged in the proximity of the magneto-rheological fluid (8, 9), wherein a gap (11, 12, 13)is established between the second carrier element (5) and a surface of the magneto-rheological fluid (8, 9) and wherein aferro fluid (14) is arranged in the gap (11, 12, 13).
2. Sealing arrangement according to claim 1, characterized in that the first machine part (4) is a housing of the machine arrangement (2).
3. Sealing arrangement according to claim 1 or 2, characterized in that the second machine part (6) is a rotating shaft.
4. Sealing arrangement according to one of claims 1 to 3, characterized in that the first carrier element (3) is arranged stationary and the second carrier element (5) rotates relatively to the first carrier element (3) during regular operation of the sealing arrangement.
5. Sealing arrangement according to one of claims 1 to 4, characterized in that the magnet (7) is a permanent magnet.
6. Sealing arrangement according to one of claims 1 to 5. characterized in that the carrier elements (3. 5) are at least partly made from a ferromag-netic metal.
7. Sealing arrangement according to one of claims 1 to 6, characterized in that the part (10) in which a magnetic field is induced by the magnet (7) is at least partly made from a ferromagnetic metal.
8. Sealing arrangement according to one of claims 1 to 7, characterized in that the first carrier element (3) comprises a radially (r) extending section (3') at which the magnet (7) is fixed.
9. Sealing arrangement according to one of claims 1 to 8, characterized in that the part (10) in which a magnetic field is induced by the magnet (7) is arranged at an axial end of the magnet (7).
10. Sealing arrangement according to one of claims 1 to 9, characterized in that the second carrier element (5) has a radially (r) extending section (5'). wherein an axially (a) extending section (5") is arranged at the end of the radially (r) extending section (5') remote from the second machine part (6)
ii. Sealing arrangement according to claim 9 or lO, characterized in that the magneto-rheological fluid (8) is arranged in a cup-shaped manner at the part (10) in which a magnetic field is induced by the magnet (7).
12. Sealing arrangement according to claim 10 or 11, characterized in that a gap (15) is established between the axially (a) extending section (5") of the second carrier element (5) and an axially (a) extending section (3') of the first carrier element (3).
13. Sealing arrangement according to claim 12, characterized in that a ferro fluid (14) is arranged in the gap (15) between the axially (a) extending section (5") of the carrier element (5) and the axially (a) extending sec-tion (3') of the first carrier element (3).
14. Sealing arrangement according to one of claims 1 to 13, characterized in that the gaps (ii, 12, 13, 15) have a hollow cylindrical shape.
15. Bearing arrangement comprising a sealing arrangement according to one of claims ito 14.