WO2013046239A1

WO2013046239A1 - Multi-lobed annular seal for pneumatic and hydraulic applications and sealing unit equipped with such seal

Info

Publication number: WO2013046239A1
Application number: PCT/IT2011/000339
Authority: WO
Inventors: Marcello Conte; Guido Belforte; Luigi Mazza
Original assignee: POLITECNICO Dl TORINO; Fundacion Tekniker
Priority date: 2011-09-30
Filing date: 2011-09-30
Publication date: 2013-04-04
Also published as: EP2761212A1

Abstract

An annular seal (1) is described, made of polymeric material for pneumatic and hydraulic applications adapted to be operatively placed into an annular seat (12,35), and having a cross-section shaped as a first rounded part with slanted flanks and equipped, in a second part opposite to the first part, with at least three rounded sealing projections, or lobes (3,5,7).

Description

MULTI-LOBED ANNULAR SEAL FOR PNEUMATIC AND HYDRAULIC APPLICATIONS AND SEALING UNIT EQUIPPED WITH SUCH SEAL

The present invention relates to a multi-lobed annular seal for pneumatic and hydraulic applications, and to sealing units equipped with such seal. The proposed seal is suited to operate in the pneumatic and hydraulic fields, in applications both for actuators (linear and rotary) and for valves.

The state of the art related to such type of seals is represented by the following documents: 1. Dl: John H. Rentschler, Robert . Carlson, Jr.

Edina Min, Sealing device, US-B1-3550990, 1970: such document deals with an annular seal presenting a rectangular section characterized by convex lobes in each one of the edges. It is stated that such seal perfectly seals particularly at high pressures. For its correct operation, it needs a slight pre-compression upon assembling. D2 : Leonard J. Sieghartener, Floating seals, US-B1-4173350, 1979: such document deals with an O-ring type seal type mounted in floating configuration for surfaces in relative rotary motion, and claims not only the seal itself, but also the housing configuration.

D3 : Richard M. Boyd, Multi-lobed rectangular sealing ring, US-B1-4693343, 1987: such document deals with a dynamic seal of a mainly rectangular shape and characterized by many lobes on the sealing surfaces. The number of- lobes on the two surfaces is not compulsorily the same: the number of lobes is greater on the surface that performs the seal.

D4 : Jerry G. Jelinek, La Habra California, Bi- lobed sealing element and retainer, US-B1- 5011162, 1991: such document describes an assembly composed of a static seal between two bodies having smooth surfaces, where fluid passes, and an assembling ring. The latter replaces an O-ring and related limitations regarding positioning and surface finishing of the housing.

D5: Zhigang Fang, Chris Cawthorne, Nephi M. Mouriok, Sujian Huang, Rock bit seal with multiple dynamic seal surface elements, US-B1- 6536542, 2003: such document deals with an annular seal with a static surface and a multiple-lobed dynamic surface. At least one of the two surfaces is composed of a more wear- resistant material.

6. D6: George J. Kotz, Tri-lobed O-ring seal, United States Patent US-A1-2008/0191474 , 2008: such document deals with an assembly composed of a three-lobed static seal (O-ring type) and its lip-type housing. Two lobes are arranged at 180°, while the third lobe is at 90° with respect to the other two. The seal cross-section is symmetrical with respect to an imaginary axis. The document also deals with the dimensional proportions of lobes and seal.

Other documents relevant for the field of application of the present invention are:

1. Richard Asplund, David Varnon, Richard Spratling, Chad Hamilton, Multi-lobed seal member, US-A1-2009/0218772 Al, 2009;

2. Richard E. Tisch, Robert George E. Carlson, Sealing ring, US-Al-2954264, 1960;

3. G. Belforte, A. Manuello, L. Mazza, "Optimization of the Cross-Section of an Elastomeric Seal for Pneumatic Cylinders", Journal of Tribology, 128, pp. 406-413, (2006) .

With reference to the above prior documents, the multi-lobed seal of the present invention has the following differences and improvements:

1. with respect to Dl, the seal of the present invention is particularly suitable for pressures that are commonly used in pneumatics (low pressures) and is of the floating type (absence of pre-compression upon assembling) ;

2. with respect to D2, the seal of the present invention is a dynamic seal also for . reciprocating linear movement;

3. with respect to D3, the seal of the present invention operates with a rotation of its section, allowing to "discharge" the interstitial pressure between the lobes; moreover, sealing is performed both radially and sideway;

4. with respect to D4, the seal of the present invention is a dynamic seal, and its compact and rounded shape avoids the extrusion problem in the gap space between the parts in relative motion;

5. with respect to D5, the seal of the present invention is only a dynamic and floating seal; sealing occurs through the contact with the side surface of the housing and the contact with the counter- surface. Moreover, the compact and rounded shape allows a certain resistance to extrusion;

6. with respect to D6, the seal of the present invention is a dynamic seal, whose compact shape avoids the extrusion problem in the gap between the parts in relative motion. Moreover, the lack of contact at the inner or external diameter (floating seal) , if mounted on a piston faced to a bore or in a housing faced on a rod respectively, makes it independent on manufacturing tolerances.

Moreover, the state of the art presents the International Patent Application Publication N. WO 2006/120528 in the name of Politecnico di Torino, one of the Applicants of the present invention: such document discloses a seal with a cross- section substantially shaped as an egg, that guarantees an optimum fluid sealing between a fixed part and a mobile part. However, the seal of document WO 2006/120528 has, when time passes and when reciprocating motions between mobile part and fixed part increase, wear problems in the external (internal) part of the seal at the contact surface, and therefore reduced operating seal life.

Object of the present invention is therefore solving the deficiencies of the above-mentioned seals, by providing a multi-lobed annular seal which allows to obtain the following innovative features, and the following advantages offered by the proposed geometry:

' presence of cavities on the external (internal) sliding surface which work as pockets inside which lubricants and greases can be stored; grease held inside the pockets will provide a constant lubricant film at the interface along the working life; in fact, in most of commercial seals the lubricant is not entirely benefitted because swept away after a few cycles ; ^• reduction of the amount of lubricant with respect to traditional seals, which means an increase of energy savings and an increase of environmental eco-compatibility ; * presence of rounded areas on the contact surface with the sliding counterpart; such rounded areas avoid damaging the seal during its contact with counterpart edges;

^• chance of using a wide typology of pneumatic components (actuators, slide valves, etc.);

^• absence of thin and weakening areas, in order to confer more toughness to the seal section;

^• easy assembling;

^• use in rectangular seats which can be easily manufactured, but also in seats with slanted or asymmetrical flanks;

^• symmetry of the cross-section of the seal thereby advantaging its manufacturing process. Another object of the present invention is considering a sealing unit that uses the above- cited seal.

The above mentioned and other targets and advantages of the invention, as will appear from the following description, are obtained with a multi-lobed annular seal as claimed in Claim 1. Preferred representations and non-trivial variations of the present invention are the subject matter of the dependent claims.

It is intended that all enclosed claims are an integral part of the present specification.

The present invention will be better described by some preferred representations thereof, provided as a non-limiting example, with reference to the enclosed drawings, in which:

Figure 1 is a cross-sectional view of an embodiment of the seal of the present invention in a rest position immediately after its installation;

Figure 2 is a cross-sectional view similar to Figure 1 with the seal in a possible operating position after its installation;

- Figure 3 is a cross-sectional view similar to Figure 1 with the seal in its operating position after its installation;

Figure 4 is a partially sectioned side view of the seal of Figure 1; and Figure 5 is a schematic sectional view that shows two possible mounting positions of the inventive seal on a piston and its related liner .

It will be immediately obvious that numerous variations and modifications (for example related to shape, sizes, arrangements and parts with equivalent functionality) can be made to what is described, without departing from the scope of the invention as appears from the enclosed claims.

With reference to the Figures, the seal 1 of the present invention is an annular sealing body for pneumatic and hydraulic components (actuators, valves) . The proposed seal 1, herein below also called "multi-lobed seal", has a new geometry of its cross-section in order to reduce the friction force and increase the component life. For such purpose, the proposed geometry guarantees an optimum compromise between sealing efficiency and minimum friction.

Figure 1 shows the geometry of the section of the multi-lobed seal 1. The main geometrical feature is the presence, in this case, of three rounded projections (lobes) 3, 5, 7 on the sliding side that, under operating conditions, will get in sliding contact (as a minimum two at a time) with a fixed counterpart (for example, as shown, a fixed liner 14 within which a piston 16 slides, on which the seal 1 is assembled) .

Between the lobes 3, 5, 7, there are two cavities 9, 11. The sliding surface of the seal 1 is therefore of the ondulated type, with alternate cavities 9, 11 and lobes 3, 5, 7.

The presence of cavities 9, 11 on the sliding surface allows forming pockets, inside which lubricant (generally present at the contact interface between the seal 1 and the counterpart 14) can be stored. Grease held inside the pockets will establish a sort of standby tank useful for keeping the . lubricant film along the working time.

The ondulated shape of the sliding seal surface will prevent the lubricant film from breaking, and it will enable holding^' the grease allowing to improve the operation with a greasing for life of the seal itself. The capability of holding grease, due to the formation of standby pockets, will allow reducing the amount of lubricant, with respect to the amount used in commonly used seals, with a further advantage regarding energy savings. The presence of lobes allows reducing the sealing area, locally increasing the contact pressure enabling the sealing at low fluid pressures.

It is obvious that the number of lobes 3, 5, 7 and of related cavities 9 and 11 can also be greater than three, like in the shown embodiment, without any modification of the functionality of the inventive seal deriving from such different arrangement .

The assembling first seat 12 or second seat 35 of the seal 1 can be a common rectangular seat, but can also be a seat with slanted flanks or an asymmetrical seat; the seal 1 does not require the use of particular seats but can be used with slanted flanks or undercuts.

A further innovative feature, coupled with the above cited at least three lobes 3, 5, 7, is the "compact and rounded" geometry of the seal 1, made through a slanted arrangement (with respect to the longitudinal axis of the seal 1) of the two side flanks 18, 20 of the seal 1, whose sides are mutually fitted through a lobe-shaped end 22 placed on the opposite side with respect to the side where the above lobes 3, 5, 7 are. The flanks 18, 20 are made in a rectilinear profile and mutually diverge with respect to the joining lobe-shaped end 22.

Preferably, the flanks 18, 20 are slanted with respect to their related wall 24, 26 of the first annular seat 12 or of the second annular seat 35 by an angle γ included between 15° and 20°, or anyway such as to keep the rotation centre of the seal section to 1/3 of the height h of the seal 1. Moreover, the ratio between the curvature radius rl of the arc of circumference CI of which the lobe- shaped end 22 is composed and the height h of the seal 1 is included between 0.20 and 0.28. Still preferably, the ratio between width w and height h of the seal 1 is included between 0.65 and 0.75.

The preferred dimensions of each one of said lobes 3, 5, 7 are greater than the distance between element 14 and element 30 and/or 32.

Through the above embodiment, as can be clearly seen in Figura 3, the inventive seal 1, once having been pushed against the first annular seat 12 or the second annular seat 35 by the movement force (for example of the piston 16 shown in Figure 4), performs, in this case with its flank 20 faced to the annular seats 12, 35, a perfect sealing against high-pressure fluids (for example air, gas, oil, etc.), to whose force it is subjected. Figure 3 also shows the deformation to which the lobes 3, 5, 7 are subjected following the same force to which the seal 1 is subjected; such deformation, as can be seen, jointly with the contact between flank 20 and annular seat 12 or 35, allows performing a perfect sealing guaranteed by the inventive seal 1.

The proposed compact, rounded and lobe-type geometry is suitable for common moulding technologies for elastomers (injection, compression) .

In general, therefore, the inventive seal 1 is adapted to be applied in a fluid sealing unit as disclosed below.

Figures 1 and 2 also show operating situations in which the seal 1 is: in particular, Figure 1 shows how the seal 1 is arranged once mounted into the first annular seat 12 of a piston 14, as an example embodiment of the mobile member 14: assembling occurs through a common fitting onto the already-arranged piston 14, or an insertion into the first annular seat 12 with its following closure through covering with the end part of the piston 14 itself. In its rest position after mounting, as can be seen in Figure 1, the seal 1 is inserted with a certain clearance into the first annular seat 12: such clearance is given in Figure 1 by the distance between the lobe-shaped end 22 and the corresponding counterfaced wall 28 of the first annular seat 12. It can also be seen how the lobes 3, 5, 7 project outside the encumbrance of the piston 14.

When the piston 14 is inserted into its own fixed liner 14 (as example embodiment of the above fixed member 14), without any pre-load or pre- compression of the seal 1, it will simply be pushed inwards into the first annular seat 12 (with an assembling' called "floating" by the Applicant of the present invention) , so that the lobe-shaped end 22 comes in contact with the wall 28 of the first annular seat 12 and the three lobes 3, 5, 7 keep the operating contact with the corresponding wall 30 of the liner 14.

When the piston 16 moves inside the liner 14, as can be seen in Figure 2, the seal of the lobes 3, 5, 7 against the liner 14 is kept unchanged, due to the particular configuration of the inventive seal 1, in addition to the sealing guaranteed by the contact with one respective of the flanks 18, 20 (according to the movement direction of the piston 14 and the application direction of the force to which the gasket 1 is subjected) with the related wall 24, 26 of the first annular seat 12.

As test of the inventive seal 1, a starting prototype was prepared, through injection moulding, for making the dynamic seal of the piston of linear pneumatic actuators (bore: 50 mm); the used material has been HNBR 80, hydrogenated nitril- butadiene rubber - hardness 80 ΙΚΗϋ. Some samples of such prototype have been assembled onto the piston of commercial pneumatic actuators, in order to perform continuous tests of a length according to ISO Standard 19973-3 (Pneumatic Fluid Power - Assessment of component reliability by testing - Part 3: Cylinders with piston rod, 2007) . The test procedure has defined supply pressure and filtering conditions of compressed air, stem speed and amount of load applied to stem; the tests have been complete two-way strokes of the stem, recording the travelled distance, till seals have not been able any more to prevent leakages. The tests have been performed using dry air and a type of assembling with initial greasing; a reduced amount of grease has been used with respect to the amount used upon assembling commercial seals, in order to apply more severe test conditions.

The preliminary tests have shown satisfactory results in terms of sealing duration and capability of the seals. The positive outcome of obtained preliminary results has allowed keeping valid the proposed design methodology and section.

Figure 5 is a schematic sectional view that shows two possible mounting positions of the inventive seal on a piston 16 and its related liner 14. It is clear that the two mounting positions can be made separately (namely the seal 1 can be mounted either on the piston 16 or on the liner 14), or they can even be made together, with two seals 1, one on the piston 16 and one on the liner 16. Three different arrangements of sealing units can then be obtained:

(1) a sealing unit comprising a fixed body 14 and a mobile body 16 that are mutually coaxial, the mobile body 16 being equipped with a first annular seat 12 on a first cylindrical surface 32 thereof radially facing a second cylindrical surface 30 of the fixed body 14, and an annular seal 1, as described above, housed into the first seat 12 of the mobile body 16 and cooperating with the second surface 30 of the fixed body 14; the at least three lobes 3, 5, 7 of the seal 1 are arranged in contact with the second surface 30, the lobe-shaped end 22 of the seal 1 is arranged in contact with the most internal wall 28 (with respect to the axis of the piston .16) of the first annular seat 12, and the flanks 18, 20 of the seal 1 are arranged, respectively and alternatively, in contact with the walls 24, 26 of the first seat 12 when the mobile member 16 reciprocates.

(2) a sealing unit 1 comprising a fixed body 14 and a mobile body 16 that are mutually coaxial, the fixed body 14 being equipped with a second annular seat 35 on a third cylindrical surface 36 thereof radially facing a fourth cylindrical surface 38 of the mobile body 16, and an annular seal 1, as described above, housed into the second seat 35 of the fixed body 14 and cooperating with the fourth surface 38 of the mobile body 16; the at least three lobes 3, 5, 7 of the seal 1 are arranged in contact with the fourth surface 38, the lobe-shaped end 22 of the seal 1 is arranged in contact with the most internal wall 40 (with respect to the axis of the piston 16) of the second annular seat 35, and the flanks 18, 20 of the seal 1 are arranged, respectively and alternatively, in contact with the walls 42, 44 of the second seat 35 when the mobile member 16 reciprocates.

(3) a sealing unit comprising a fixed body 14 and a mobile body 16 that are mutually coaxial, the mobile body 16 being equipped with a first annular seat 12 on a first cylindrical surface 32 thereof radially facing a second cylindrical surface 30 of the fixed body 14, and an annular seal 1, as described above, housed into the first seat 12 of the mobile body 16 and cooperating with the second surface 30 of the fixed body 14, the fixed body 14 being also equipped with a second annular seat 35 on a third cylindrical surface 36 thereof radially facing a fourth cylindrical surface 38 of the mobile body 16, and an annular seal 1, as described above, housed into the second seat 35 of the fixed body 14 and cooperating with the fourth surface 38 of the mobile body 16; the at least three lobes 3, 5, 7 of the seal 1 are arranged in contact with the second surface 30, the lobe-shaped end 22 of the seal 1 is arranged in contact with the most internal wall 28 (with respect to the axis of the piston 16) of the first annular seat 12, the flanks 18, 20 of the seal 1 are arranged, respectively and alternatively, in contact with the walls 24, 26 of the first seat 12 when the mobile member 16 reciprocates, the at least three lobes 3, 5, 7 of the seal 1 are arranged in contact with the fourth surface 38, the lobe-shaped end 22 of the seal 1 is arranged in contact with the most internal wall 40 of the second annular seat 35, and the flanks 18, 20 of the seal 1 are arranged, respectively and alternatively, in contact with the walls 42, 44 of the second seat 35 when the mobile member 16 reciprocates .

Claims

Annular seal (1) made of polymeric material for pneumatic and hydraulic applications adapted to be operatively placed into an annular seat (12, 35) , characterised in that it has a cross- section shaped as a first rounded part with slanted flanks and equipped, in a second part as sliding surface, opposite to the first part, with at least three rounded sealing projections, or lobes (3, 5, 7).

Annular seal (1) according to claim 1, wherein the annular seat (12, 35) is a first annular seat (12) made in a mobile body (16), or a second annular seat (35) made in a fixed body (14), characterised in that it includes:

a lobe-shaped end (22) adapted to come in contact with the most internal wall (28) of said annular seat (12, 35) ;

two side flanks (18, 20) that depart from said lobe-shaped end (22) in a slanted position by an angle γ with respect to the related walls (24, 26) of said annular seat (12, 35); and

at least three lobes (3, 5, 7) mutually spaced by at least two cavities (9, 11), said lobes (3, 5, 7) and said cavities (9, 11) being placed on an opposite side of said seal (1) with respect to said lobe- shaped end (22), the two extreme lobes (3, 7) being operatively connected to said two side flanks (18, 20), said lobes (3, 5, 7) being adapted to get in contact with a surface (30) of said fixed body (14) with respect to said mobile body (16), or to get in contact with a surface (38) of said mobile body (16) with respect to said fixed body (14), in order to seal against fluid that is present between said fixed body (14) and said mobile body (16).

Annular. seal (1) according to claim 2, characterised in that said cavities (9, 11) are adapted to form pockets, inside which lubricant is stored, present at a contact interface between seal (1) and fixed body (14), the grease held inside the pockets being a standby tank useful for keeping a lubrifying film along the whole life-time of the seal (1).

Annular seal (1) according to claim 2, characterised in that the flanks (18, 20) are slanted with respect to the related wall (24, 26) of the annular seat (12, 35) by an angle γ typically included between 15° and 20° and anyway such as to keep the rotation centre of the section of the seal (1) at 1/3 of the height h of the seal (1) .

Annular seal (1) according to claim 2, characterised in that the ratio between curvature radius rl of the arc of circumference CI of which the lobe-shaped end (22) is composed, and height h of the seal (1) is in between 0.20 and 0.28.

Annular seal (1) according to claim 2, characterised in that the ratio between width w and height h of the seal (1) is in between 0.65 and 0.75.

Annular seal (1) according to claim 2, characterised in that said mobile body (16) is a piston and said fixed body (14) is a liner of said piston ( 16) .

Annular seal (1) according to any one of the previous claims, characterised in that said fluid is air, oil or gas.

Sealing unit against fluids comprising a fixed body (14) and a mobile body (16) that are mutually coaxial, said mobile body (16) being equipped with a first annular seat (12) on a first cylindrical surface (32) thereof radially facing a second cylindrical surface (30) of said fixed body (14), and an annular seal (1) housed into said first seat (12) of said mobile body (16) and cooperating with said second surface (30) of said fixed body (14), characterised in that said seal (1) is made according to any one of the previous claims, in that said at least three lobes (3, 5, 7) of said seal (1) are arranged in contact with said second surface (30), and in that said lobe- shaped end (22) of said seal (1) is arranged in contact with the most internal wall (28) of said first annular seat (12), and in that the flanks (18, 20) of said seal (1) are arranged, respectively and alternatively, in contact with the walls (24, 26) of said first seat (12) when said mobile member (16) reciprocates.

Sealing unit against fluids comprising a fixed body (14) and a mobile body (16) that are mutually coaxial, said fixed body (14) being equipped with a second annular seat (35) on a third cylindrical surface (36) thereof radially facing a fourth cylindrical surface (38) of said mobile body (16), and an annular seal (1) housed into said second seat (35) of said fixed body (14) and cooperating with said fourth surface (38) of said mobile body (16), characterised in that said seal (1) is made according to any one of claims 1 to 8, in that said at least three lobes (3, 5, 7) of said seal (1) are arranged in contact with said fourth surface (38), and in that said lobe- shaped end (22) of said seal (1) is arranged in contact with the most internal wall (40) of said second annular seat (35), and in that the flanks (18, 20) of said seal (1) are arranged, respectively and alternatively, in contact with the walls (42, 44) of said second seat (35) when said mobile member (16) reciprocates.

Sealing unit against fluids comprising a fixed body (14) and a mobile body (16) that are mutually coaxial, said mobile body (16) being equipped with a first annular seat (12) on a first cylindrical surface (32) thereof radially facing a second cylindrical surface (30) of said fixed body (14), and an annular seal (1) housed into said first seat (12) of said mobile body (16) and cooperating with said second surface (30) of said fixed body (14), said fixed body (14) being also equipped with a second annular seat (35) on a third cylindrical surface (36) thereof radially facing a fourth cylindrical surface (38) of said mobile body

(16), and an annular seal (1) housed into said second seat (35) of said fixed body (14) and cooperating with said fourth surface (38) of said mobile body (16) , characterised in that said seal (1) is made according to any one of claims 1 to 8, in that said at least three lobes (3, 5, 7) of said seal (1) are arranged in contact with said second surface (30), and in that said lobe-shaped end (22) of said seal

(1) is- arranged in contact with the most internal wall (28) of said first annular seat

(12), in that the flanks (18, 20) of said seal

(1) are arranged, respectively and alternatively, in contact with the walls (24, 26) of said first seat (12) when said mobile member (16) reciprocates, in that said at least three lobes (3, 5, 7) of said seal (1) are arranged in contact with said fourth surface

(38), and in that said lobe-shaped end (22) of said seal (1) is arranged in contact with the most internal wall (40) of said second annular seat (35), and in that the flanks (18, 20) of said seal (1) are arranged, respectively and alternatively, in contact with the walls (42, 44) of said second seat (35) when said mobile member (16) reciprocates.

Sealing unit according to claim 9, 10 or 11, characterised in that said mobile body (16) is a piston and said fixed body (14) is a liner of said piston (16) .

Sealing unit according to any one of claims 9 to 12, characterised in that said fluid is air, oil or gas.

Sealing unit according to any one of claims 9 to 13, characterised in that the sizes of each one of said lobes (3, 5, 7) are greater than the gap between the second surface (30) and the first surface (32) or the fourth surface (38) and the third surface (36).