EP3080492A1

EP3080492A1 - Seal with elastic lips

Info

Publication number: EP3080492A1
Application number: EP14828211.4A
Authority: EP
Inventors: René Perratone
Original assignee: OSC Offshore Systems Concepts
Current assignee: OSC Offshore Systems Concepts
Priority date: 2013-12-13
Filing date: 2014-12-11
Publication date: 2016-10-19
Also published as: US20160312896A1; FR3014992A1; WO2015087014A1; FR3014992B1; SG11201604761WA

Abstract

The invention concerns a seal (1), comprising two flexible lips (2) engaging with a heel (5) and having a U-shaped section when in the idle configuration, the seal being characterised in that the heel (5) and the lips (2) consist mainly of a thermoplastic polymer or of one of the chemically neutral and mechanically strong derivatives thereof, and in that said lips (2) are arranged so as to be elastic. Preferably, polyetheretherketone is used.

Description

Elastic lip seal

The invention relates to the field of flexible lip seals. The latter are used for all types of uses and preferably but not exclusively, in application in rotary joints used for the transmission of fluid (s) between a fixed part and a rotating part.

A member provides a sealing function when it prevents the passage of a fluid from a first chamber to a second neighboring chamber. Such bodies are called "seals".

Different types of sealing can be defined depending on the flow of the fluid which one wishes to prevent the passage, but also the mechanical parts involved in this seal.

This is called simple sealing if it is to prevent the flow of a fluid from a first chamber in a second chamber. If the seal is provided in both directions, that is to say that the seal must prevent the flow of another fluid possibly contained in the second chamber to the first, the seal is said to be double . In the same way, the seal is said to be static if the two parts, between which leakage is likely to occur, are fixed relative to one another. Dynamic sealing is referred to if these two parts are in relative motion with respect to each other. In practice, two kinds of relative motion, combinable, are mainly observed: the linear translation, which can correspond, for example, to the sliding relative to a piston in a cylinder, and the rotation which may be, for example, a relative rotation about a common axis of a shaft in a hub or a housing. The seals can be made of different materials according to their applications: leather, plumbing and mechanical tow, fibrin valves, felt, rubber, elastomers, polymers, metals such as alloy steel, brasses, the nickel silver, etc. The material of the seals must be able to withstand the difference in pressure and the temperature of the fluid that is to be prevented from passing, as well as its chemical composition. The seals generally undergo natural aging, and it is thus necessary to change them after a certain time. Finally, a seal must be adapted to different operating conditions, including:

- the type of use, whether for static or dynamic sealing;

- the pressure imposed around the joint;

- the nature of the fluid to be sealed;

at the temperature of the fluid and the ambient medium;

at the speed of the fluid whose passage one wishes to prevent;

in the ambient environment, for example the presence of a corrosive or explosive atmosphere, or the chemical compatibility between the seal and the fluid to be sealed;

- the desired service life for the seal sealing;

- the tolerance of a leak ... etc.

As a preferred application, but in a nonlimiting manner, we will describe systems using dynamic sealing and more particularly sealing seals for rotating shafts.

For this type of application, many devices are used, such as:

- Return baffles or turbines, also called lateral seal: they provide sealing around an axis of rotation, between two perpendicular faces. These are frictionless joints that are not able to configure the required tightness when they are not moving;

- The cable glands: they consist of jams of fibrous materials, such as tow and tight on the shaft by an axial locking by means of nut. Today, many have been replaced by so-called "surface" seals or seals. They have a high friction torque and absorb a relatively high power;

- O-rings: ring-shaped, synthetic elastomers, variable profile, they are often used as static seals. Nevertheless, they can be used as joints for rotating shafts at low speed;

- rotary shaft lip seals: when they appear about fifty of years they consisted of a leather cuff whose lip was held tight on the rotating shaft by a toroidal spring. Due to the presence of leather, its longevity was limited because the leather does not withstand high temperatures especially. Leather is today replaced by synthetic elastomers, such as, for example, without limitation, nitrile (also known as "butadiene acrylonitrile"), a fluorocarbon elastomer such as polytetrafluoroethylene (also known as abbreviation "PTFE"), polyacrylates or silicones.

To ensure a dynamic seal, preferably rotating shafts with seals, U-profile seals combining different types of materials are used. An example of this type of seal is described in connection with FIG. 1. A U-shaped seal 1 consists of four main components: two lips 2a and 2b, advantageously polytetrafluoroethylene (PTFE). ) cooperating with a heel 5, a spring 4, preferably but not limited to flat stainless steel, and an anti-extrusion ring 3 of a suitable material, resistant to extrusion. Each of these components plays a very particular role in the operation of the joint. The two lips 2a and 2b maintain the contact of the seal 1 with the groove of said seal and the surface to be sealed and thus provide a seal. The lips 2a and 2b follow the profile and the shape of the groove of the seal and the surface to be sealed. The heel 5 allows the cooperation and maintenance of the lips 2a and 2b with the rest of the seal 1: said heel 5 and the lips 2a and 2b constitute a single entity. The material used for the manufacture of the lips 2a and 2b must require particular physical and chemical properties: it must be chemically inert, that is to say be able to guarantee any absence of chemical reaction between the material and the fluid to be sealed , have a low coefficient of friction to prevent any anticipated wear, reduce the torque and good thermal resistance.

Generally, PTFE is thus chosen as the manufacturing material for the lips 2a and 2b since:

it is practically inert with respect to all known products (it can be attacked only by very specific chemical components, such as molten alkali metals, chlorine trifluoride, or elemental fluorine );

it is one of the most stable thermoplastic materials physically and chemically. PTFE actually begins to decompose above 400 ° C;

- it has the lowest coefficient of friction of all solid materials. Indeed, its value is between 0.05 and 0.09.

Nevertheless, the PTFE has certain disadvantages: its very poor mechanical strength or its great flexibility do not allow it to exert a restoring force necessary to allow for example the contact of the sealing lips with the surfaces to be sealed. To overcome this drawback, a spring 4 is present in the seal: it is sealed between the two lips 2a and 2b and thus provides a radial force at the two lips 2a and 2b necessary to ensure sealing. Indeed, a seal is created by the presence of a closed space, not leaving the fluid included in this space or not leaving fluids outside this space enter. This space is almost always obtained using several pieces that, placed in contact with each other, form a closed space. It is the lips 2a and 2b in contact with the groove or the surface to be sealed that will allow the formation of said space. The spring 4 ensures a tightness of the lips against the walls of the groove or the surface to be sealed. Several types of springs are used: preferentially metallic for this kind of application, the flat springs will be chosen.

In addition, PTFE has a difficult and particular shaping: it can not be processed by fusion like most thermoplastic polymers, so it can not be molded using current conventional solutions. As a result, the seals are formed by a sintering method. Sintering is a part manufacturing process of heating a grain powder without conducting it until melting. Under the effect of heat, the PTFE grains weld together, forming the cohesion of the part. Faced with high pressures, significant elevations of temperature, an extrusion phenomenon can develop at the joint and lead to disintegration of the seal 1 and consequently a creep, that is to say an irreversible deformation of seal 1. The seal 1 can not then be ensure its sealing function. To overcome this problem, an anti-extrusion ring 3 is associated with the seal 1. Its function is to allow the seal 1 to resist the extrusion effects. Said anti-extrusion ring 3 is most often made of a thermoplastic polymer type material other than PTFE, in order to avoid and prevent the recurrence of wear and extrusion problems.

However, despite all the advantages provided by this type of joint 1 and all the solutions recommended to remedy the various disadvantages imposed by certain characteristics, difficulties are still not overcome or solved:

firstly, several problems arise from the use of the spring 4. As a first example, after a long period of use or unsuitable conditions of use, the spring 4 can deteriorate or even break. The same applies if the fluid to be sealed is not adapted to the spring material and provokes corrosion reactions on the spring 4. These two situations can lead to a significant loss of the sealing function of the seal 1 since, from caused by the deterioration of the spring 4, the latter does not provide the radial force to be applied to ensure the seal; other disadvantages relate to industrialization: in the context of certain applications, the seal 1 may have a large diameter, of the order of two meters.

The manufacture of the seal 1, consisting of the three components that are the lips 2a and 2b, the spring 4 and the anti-extrusion ring 3, imposes significant constraints: be careful to assemble all the components of the seal 1 properly, requiring attention at all times.

In addition, for certain applications such as the use of gaskets for rotating joints in an offshore station, the seal 1 may be in direct contact with oil. This oil may contain sand, which, in the case of a PTFE seal, may become embedded within the seal, causing seal crumbling, creep and rapid wear. As a result the PTFE seal 1 is no longer able to perform its sealing function. Other factors, such as pressure and temperature depending on the application, can affect the extrusion of the joint.

The invention makes it possible to meet the great majority of the disadvantages raised by the known solutions.

Among the many advantages provided by a seal according to the invention, we can mention that it allows:

to simplify the manufacturing processes of the seal, the latter being composed of a single material and a single piece; to reduce the problems of industrialization and the problems inherent in the presence of a spring;

- to extend the life of the seals, thanks in particular to the exploitation of a composite material with the properties exceptional physical and chemical properties, in particular minimizing wear and crumbling problems;

to improve the sealing of the seal, through the selection of a material with a very low coefficient of friction, a very good chemical inertness and good resistance to extrusion. To this end, there is provided a seal comprising a first flexible lip cooperating with a heel and having, when said first lip is in the rest configuration, a U-shaped section.

To optimize the tightness of the seal and its life and to simplify the manufacturing processes of said seal, the heel and the first lip of the seal according to the invention consist mainly of a thermoplastic polymer or a derivative thereof, chemically neutral and mechanically resistant, and said first lip is arranged to exert a sufficient restoring force to recover the rest configuration.

Preferably, the U-shaped section of the seal according to the invention may comprise a second flexible lip arranged to exert a sufficient restoring force to recover a rest configuration and the U-shaped section of said seal may have a symmetry of revolution by relative to the median plane (M) of the heel.

Advantageously, because of the exceptional physicochemical properties, the polymer thermoplastic used for the manufacture of the seal according to the invention may be polyetheretherketone (hereinafter referred to as PEEK).

Alternatively, the thermoplastic polymer used for producing the seal according to the invention may advantageously be polyamide-imide (hereinafter referred to as PAI).

In order to ensure its use as a seal for seals or pivoting devices, the seal may advantageously have an annular shape.

In order to make it possible to obtain a seal contact pressure greater than the pressure of the fluid to be sealed and consequently to ensure optimum sealing, the heel of said seal may further comprise one or more grooves arranged on the distal portion of said heel opposite the lips.

To ensure the tightness of rotating shafts using different assemblies such as assemblies "pistons" or "face", the lip or lips of said seal may be in radial position.

Alternatively, the lip or lips of said seal may be in axial position.

To ensure a simplified production of the seal and optimize the sealing process, the heel and the or lips of said seal may be one and the same entity.

According to a second object, the invention relates to a method of manufacturing a seal according to the invention. To make it possible to produce joints of different diameters, in particular enough diameters For example, such as two meters or more, the method of manufacturing a seal, including the one or more lips and heel in a single entity, may include a step of machining said seal.

Alternatively or additionally, to make seals small diameters and simplify the manufacturing means of said seals, the method of manufacturing a seal, comprising the or lips and the heel in one single entity may include a step of injection molding said seal.

According to a third object, the invention relates to a rotary joint, comprising a fixed part and a rotational part held concentric by a mechanical bearing, a toroidal chamber formed between said fixed and rotatable parts, arranged to form a restricted passage of fluid. To optimize the operation of the rotary joint and to ensure a maximum seal, in the context more particularly offshore stations, the toroidal chamber comprises at least one seal within it according to the invention.

According to a fourth object, the invention relates to a friction bearing. In order to guarantee both a minimal wear of the parts making up the rotating shaft and at the same time an optimum seal, the friction bearing advantageously comprises at least, at one of its ends, a seal according to the invention. .

Other features and advantages will appear more clearly on reading the description which follows and examining the figures that accompany it, among which:

- Figure 1, previously described, illustrates a detailed view of a seal according to the state of the prior art;

- Figures 2a and 2b describe a seal according to the invention;

FIGS. 3a and 3b show a graphic description of a U-shaped gasket axially and radially;

- Figure 4 schematically describes a rotary joint according to the invention;

- Figure 5 describes an alternative embodiment of a friction bearing according to the invention.

Figures 2a and 2b schematize a seal according to the invention.

The seal 1 according to the invention constitutes a single entity and comprises a U-shaped profile, comprising one or more, preferably two lips 2a and 2b and a heel 5. As a preferred application, the seal of sealing 1 comprises two flexible lips, according to the example described in connection with Figure 2a. The presence of one or more lips will depend on the desired seal. In the example described in connection with Figure 2b, the lip 2a faces a protrusion 5b of the heel instead of the lip 2b. In a variant, the seal 1 according to the invention could comprise only a lip 2b that faces a protrusion of the heel. Unlike the seal according to the state of the art described in connection with FIG. 1, the seal 1 conforms to the invention has no spring since the seal 1 is made entirely of a specific material: a thermoplastic polymer or a derivative thereof, chemically neutral and mechanically resistant. A thermoplastic polymer is a macromolecular material whose main characteristic is its possibility of reversible solid / liquid transformation by heat input. The intermediate state to said reversible transformation, when the polymer is being melted, allows the deformation of said thermoplastic polymer under the action of mechanical stresses, this deformation being frozen by cooling. Derivative means any filled thermoplastic polymer corresponding to the definition of the same nature or resin charged with said polymer. The thermoplastic polymer must have physicochemical properties ^¬ particular chemical: it must be chemically inert, that is to say being able to ensure absence of any chemical reaction between the material and the medium to be sealed to prevent deterioration or extrusion of the material and mechanically resistant. Mechanically resistant means not only the fact that the material must have a very low coefficient of friction to prevent premature wear of the seal during its operation in a joint for rotary joints, for example. The lips 2a and 2b are advantageously dimensioned, that is to say they have a dimensioning smaller than the heel, so that, when they are coupled with the appropriate material, said lips are elastic, that is to say that they are able to exert a sufficient restoring force to recover a resting configuration. Preferably, the material used for the manufacture of the seal 1 according to the invention may be polyetheretherketone (hereinafter referred to as PEEK). PEEK is a semi-crystalline thermoplastic polymer that has very good physico-chemical properties: a high melting temperature since it is around 343 ° C, a very good chemical resistance to solvents and various chemical compounds, good resistance mechanical with a ductile material and a Young's modulus around 3.6GPa. The Young's modulus, also called modulus of elasticity, is the constant that relates the tensile (or compressive) stress and the deformation for an isotropic elastic material. A material whose Young's modulus is very high is said to be rigid: thus, the PEEK is considered as a rather elastic material. The PEEK derivatives may be, by way of non-limiting examples, carbon-loaded PEEK or PEEK loaded with carbon and nanotubes.

Alternatively, the thermoplastic polymer may be advantageously polyamide-imide (hereinafter referred to as PAI), an amorphous thermoplastic polymer, which has exceptional thermal, physical and chemical properties. It has very high levels of resistance to chemicals, wear, irradiation and heavy loads. Its Young's modulus is around 4 to 5 GPa: like the PEEK, the PAI is considered a soft material.

The seal 1 according to the invention may advantageously comprise one or more grooves 6 in the heel. Said grooves 6 correspond to narrow recesses generally rounded to its part lower. They are advantageously machined in the heel to have a contact pressure of said seal 1 greater than the pressure of the fluid to be sealed in order to ensure optimum sealing of the seal 1, 1 'sealing can be done on the diameter or in front.

Advantageously, the U-shaped section of the seal 1 has a symmetry of revolution relative to the median plane (M) of the heel. This preferred form of U-shaped section, especially when using the seal 1 in a rotating shaft, allows the use of the seal in different configurations depending on the groove or the surface to be sealed.

Finally, two methods of manufacturing the seal 1 according to the invention can be implemented. These different processes depend on the application or the intended use for the seal 1, and therefore the diameter of the seal 1.

Firstly, preferably, but not limited to, the method of manufacturing the seal according to the invention may comprise a machining step. The principle of machining is to remove material so as to give the blank the desired shape and dimensions, using a machine tool. Among the various types of machining, mention may be made by way of non-limiting example: boring, broaching, milling, drilling, threading, tapping or even laser cutting.

Alternatively or additionally, the method of manufacturing the seal according to the invention may comprise an injection molding step. The molding allows the implementation of thermoformable materials, notably thermoplastics. The material plastic is in the form of powders or granules: in a first time it is heated and thermoregulated, and then injected under high pressure into a mold or a cavity having the shape of the desired part during a phase called "Dosing phase"; finally a constant pressure is applied for a given time to overcome the withdrawal of the material during cooling. The room is cooled for a few seconds and then ejected. Therefore, a new cycle can begin.

Figures 3a and 3b describe two configurations of a seal according to the invention.

In both examples proposed, the seal 1 has an annular shape, advantageously configured with respect to its use. Indeed, the preferred application is the use of the seal 1 to seal in the rotating joints. Indeed, the use in rotating shafts requires a dynamic seal, that is to say that the sealing surfaces are movable. Since the type of movement between the pieces is rotation, the movement in general is perpendicular to the pressure gradient.

In addition, two classes of sealing are distinguished: the radial sealing where the sealing surface is cylindrical, and the axial sealing where the sealing surface is perpendicular to the axis of rotation. These two classes of sealing require two different configurations described in connection with Figures 3a and 3b. According to FIG. 3a, the lips 2a and 2b of the seal 1 according to the invention are in axial position: by "axial position" is meant that the lips 2a and 2b are projecting parallel to the axis of revolution R of said seal. According to FIG. 3b, the lips 2a and 2b of the gasket 1 according to the invention are in the radial position: by "radial position", it is meant that the lips 2a and 2b project in a normal plane N to the axis of revolution R. The various configurations described in connection with FIGS. 3a and 3b are used in rotary joints, in particular in "piston" or "face" assemblies.

FIGS. 4a to 4d describe an alternative application of a seal 1 in rotating shafts or rotary joints according to the invention, as well as preferred arrangements for the use of the seal according to the invention .

A rotating joint, commonly known as a rotating joint, is a mechanical part used to transport different fluids, liquid or gaseous, from a fixed part to a mechanical member in motion, more specifically in rotation. The function of a rotary joint is to provide a leak-free connection for conveying a fluid between fixed supply points and receiving points in rotation or oscillation. Rotary joints are used in many applications, these applications depending on the diameter of the seals. They are particularly used in offshore stations in connection with oil containment systems, for example.

By way of a preferred but nonlimiting example described with reference to FIG. 4a, the rotary joint 10 according to the invention may consist of a fixed part 7 and a rotary part 8 kept concentric with the aid of a mechanical bearing 9, a toroidal chamber (not shown in the figure) formed between the fixed parts 7 and rotary 8. One or more seals 1 can cooperate with the fixed parts 7 and rotary 8.

Different configurations may be implemented according to the use of the rotary joint 10. Mention may be made, by way of non-limiting examples, of "piston" and "face" assemblies. Such arrangements are described in connection with Figures 4b to 4d. Preferably, a seal 1 according to the invention is used to seal between a rotating part 8 and a fixed part 7. Said seal 1 is placed in a groove 12 and can sealing between the rotating part 8 and the fixed part 7, either on a surface adjoining one of the lips 2a and 2b, or on an attenuation surface at the heel 5. FIG. 4b shows the use of the gasket sealing 1 according to the invention during its implementation in a "piston" assembly. Sealing is ensured by virtue of the lips 2a and 2b on the rotary part 8 and the fixed part 7. FIG. 4c describes the use of the seal 1 according to the invention when it is used in an assembly " face ". Sealing is ensured thanks to the lips 2a and 2b between the rotary part 8 and the fixed part 7. FIG. 4d illustrates the use of the seal 1 according to the invention when it is used in an assembly " piston ". Sealing is ensured thanks to the heel 5 on the rotating part 8 and the fixed part 7. Figure 5 illustrates another variant of use of the seal 1 incorporated in bearings and friction washers.

A friction bearing is a member used to support and guide, in rotation, a workpiece relative to another, and more specifically a transmission shaft. Depending on the desired use, several categories of bearings can be distinguished:

- Smooth bearings: parts, resting on bearings, are subject to sliding friction between the surfaces in contact;

- Rolling bearings: The contact between the different parts is carried out by means of balls or bearings contained in cages. This phenomenon of rolling friction allows a greater load on the bearings and a higher speed of rotation.

The friction bearing is inserted into a female part; a male piece is rotating inside. The operating clearance between the bearing and the male part is less than the clearance between the female part and the male part to avoid contact between the two parts. Preferably, the friction bearing is made of antifriction material, different from the moving parts that it supports and guides, said material having a coefficient of friction as low as possible and requiring or not a lubrication system. One or more, for example two, seals 1 according to the invention can be integrated or incorporated directly to the bearing 11 or the friction washer to ensure sealing and protection, especially against wear, rubbing surfaces. The materials envisaged for the joint, more particularly the PEEK and the PAI, are self-lubricating. Preferably, but not limited to, the same materials will be used for the bearing or the friction washer. The friction bearing and the one or more seals 1 according to the invention constitute one and the same entity.

The invention has been described in its operation in relation to rotating shafts to ensure the sealing of the latter. It can also be implemented for all types of dynamic sealing, especially those involving any relative movement including rotation.

It could also be expected that the seal has three, four or a greater number of lips. Similarly, it could also be envisaged that a plurality of seals or friction bearings is connected in series or in parallel to improve the effectiveness of the seal.

Other modifications may be envisaged without departing from the scope of the present invention defined by the appended claims.

Claims

1. Seal (1), comprising a first lip (2) cooperating with a flexible bead (5) and having, when said first lip is in the rest configuration, a U-shaped section, the seal being characterized in that the heel (5) and the first lip (2a) consist mainly of a thermoplastic polymer or one of its derivatives, chemically neutral and mechanically resistant, and in that said first lip (2a) is arranged to exert a force sufficient return to recover said rest configuration.

2. Seal (1) according to the preceding claim, comprising a second flexible lip

(2b) arranged to exert a sufficient restoring force to recover a rest configuration, and the U-shaped section of said seal having a symmetry of revolution relative to the median plane (M) of the heel.

3. Seal (1) according to claims 1 or 2, wherein the thermoplastic polymer is polyetheretherketone (PEEK).

4. Seal (1) according to the preceding claim, wherein the thermoplastic polymer is loaded with carbon. Seal (1) according to claims 1 or 2, wherein the thermoplastic polymer is polyamide-imide (PAI).

Seal (1) according to any one of the preceding claims, characterized in that the seal (1) has an annular shape. 7. Seal (1) according to any one of the preceding claims, wherein the heel (5) further comprises one or more grooves (6) arranged on the distal portion of said heel (5) opposite the lips (2a). 2b).

8. Seal (1) according to any one of the preceding claims, wherein the or lips (2a, 2b) are in the radial position. 9. Seal (1) according to any one of the preceding claims 1 to 7, wherein the or lips (2a, 2b) are in axial position.

Seal (1) according to any one of the preceding claims, wherein the heel (5) and the or lips (2a, 2b) constitute a single entity.

A method of manufacturing a seal according to claim 10, characterized in that it comprises a step of machining said seal (1).

12. A method of manufacturing a seal (1) according to claim 10, characterized in that it comprises a step of injection molding said seal (1).

13. Rotary joint (10), comprising a fixed part (7) and a rotatable part (8) held concentric thanks to a mechanical bearing (9), a toroidal chamber formed between said fixed (7) and rotary (8) parts, arranged to form a restricted fluid passage, the rotary joint (10) being characterized in that the toroidal chamber comprises at least one seal (1) as defined in any one of claims 1 to 10.

14. Bearing (11), the bearing being characterized in that it comprises one or more seals (1) according to any one of claims 1 to 10.