Patent Application
20200018399
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The present invention relates to a mechanical seal, and particularly to a mechanical seal that is suitable for being disposed between a rotary shaft and an opening of a casing through which the shaft is mounted. The present invention finds a preferred, non-exclusive application in the seals of rotary pumps and in particular in pumps for the recirculation of refrigerant fluid in a motor of vehicle.
As it is known, a mechanical seal comprises:
In view of the fact that, when rotating, the second seal ring slides on the first seal ring, the two seal rings tend to rotate relative to their housings in the fixed portion and in the mobile portion. Therefore, the mechanical seal must provide for an anti-rotation system to prevent the rotation of the seal rings in their housings. However, it must be considered that, while the second seal ring can be blocked in its housing of the rotary portion, the first seal ring must be free to translate axially when pushed by the spring.
WO2018/020460, in the name of the same applicant, discloses a mechanical seal provided with an anti-rotation system of the seal rings that provides for an elliptical coupling between the seal ring and the housing of the seal ring. In such a case, the first seal ring is free to translate axially when pushed by the spring, and it is locked in rotation by means of the elliptical coupling.
The fixed portion comprises a receptacle wherein a cup is slidingly mounted, holding the first seal ring by means of a gasket. The spring is disposed in the receptacle between a bottom wall of the receptacle and the cup. The ends of the spring are neither constrained to the bottom wall of the receptacle nor to the cup. In fact, the first seal ring is blocked in rotation and therefore does not transmit any rotation to the cup. Obviously, if the first seal ring was not blocked in rotation, the first seal ring would rotate and transmit said rotation to the cup, impairing the operation of the seal.
For the second seal ring, i.e. the rotary seal ring, this type of elliptical coupling works well, because the second seal ring must not translate axially. Instead, for the first seal ring, this type of elliptical coupling is impaired by some drawbacks because the first seal ring must translate axially. Moreover, said mechanical seal is difficult to assemble because of the larger dimension of the elliptical portion relative to the cylindrical portion where the gasket slides.
Mechanical seals are known, which comprise a bellows disposed behind the fixed seal ring to provide a seal that prevents the passage of the fluid. If the bellows is made of metal material, the bellows is welded and sealed to the structure of the mechanical seal. However, it must be considered that the bellows has a totally different structure compared to a helical spring and consequently a completely different torsional behavior compared to a helical spring. Therefore, the mechanical seals with bellows are not compatible with mechanical seals with spring because the spring does not have a seal function. In fact, in the mechanical seals with spring, the seal function is obtained with an elastomeric gasket.
In some applications of mechanical seals with a helical spring, the helical spring is blocked with a pin. However, such a blocking of the spring has proved to be unreliable.
It must be considered that in the field of mechanical seals, the springs are generally blocked with mechanical locks, such as pins. In fact, there is a technical prejudice against the use of a welding to block a spring because the welding is not considered reliable and it is considered to impair the correct operation of the spring.
The purpose of the present invention is to eliminate the drawbacks of the prior art by providing a mechanical seal with anti-rotation system of the seal rings that is effective, reliable and capable of delivering an excellent performance with a reduced volume.
Another purpose is to disclose a mechanical seal that is simple and inexpensive to make.
Said purposes are achieved by a mechanical seal according to claim 1.
Advantageous embodiments of the invention appear from the dependent claims.
The mechanical seal of the invention is defined by claim 1.
The peculiar characteristics are represented by the fact that the first seal ring is free to rotate relative to the receptacle. Moreover, the first end of the spring is constrained to the cup by means of the first constraint means, and the second end of the spring is constrained to the receptacle by means of the second constraint means. In view of the above, the spring opposes a rotation of the cup relative to the receptacle.
The applicant surprisingly discovered that the constraint means of the spring can be welding. In fact, after making several experimental tests on the operation of the mechanical seal, the applicant discovered that the welding of the spring are perfectly reliable and do not impair the operation of the spring.
Additional features of the invention will appear manifest from the following detailed description, which refers to a merely illustrative, not limiting embodiment, as illustrated in the attached figures, wherein:
With reference to the Figures, a mechanical seal is disclosed, which is generally indicated with reference numeral 100.
With reference to
The mechanical seal (1) comprises a fixed portion (3) constrained to the casing (2), and a rotary portion (4) integrally and revolvingly mounted to the shaft (1). The fixed portion (3) comprises a first seal ring (30). The rotary portion (4) comprises a second seal ring (40). The two seal rings (30, 40) cooperate axially and provide a sliding front seal.
Advantageously, the seal rings (30, 40) are of ceramic material, such as silicon carbide or carbon material.
The fixed portion (3) comprises an annular receptacle (5) made of sheet metal by means of spinning. The receptacle (5) comprises:
The external wall (51) of the receptacle is fixed and sealed inside the opening (20) of the casing (2). The flange (52) of the receptacle is axially stopped against the casing (1) and determines the axial position of the mechanical seal (100) relative to the casing (2).
The first seal ring (30) is mounted in a cup (6) that is housed in the receptacle (5) with possibility of sliding in axial direction. A gasket (7) of elastomeric material is disposed between the first seal ring (30) and the cup (6).
With reference to
The bottom wall (60) of the cup has an internal edge (62) that is axially bent towards the bottom wall (50) of the receptacle and has an internal “J”-shaped rounded section.
The gasket (7) comprises:
The seal ring (30) is axially blocked inside the cup (6) by means of radial interference, i.e. by radially compressing the cylindrical wall (61) of the gasket (7). The annular wall (70) of the gasket is axially compressed between the bottom ball (60) of the cup (6) and the first seal ring (30).
The gasket (7) is of bellows type and comprises a lip seal portion (72) that cooperates with an internal cylindrical wall (53) of the receptacle.
The lip seal portion (72) comprises:
The second lip (74) elastically cooperates with the internal wall (53) of the receptacle and provides a static seal between the cup (6) and the internal wall (53) of the receptacle. The first and the third lip (73; 75) cooperate with the second lip (74) of the gasket to provide a seal and are prevalently designed to protect the seal area against the penetration of dirt particles. Moreover, together with the second lip (72), the first and the third lip (73; 75) define corresponding annular chambers that can be optionally filled with a fuel.
The mechanical seal (100) also comprises a spring (8) that is housed in the receptacle (5) and is axially comprised between the bottom wall (50) of the receptacle and the bottom wall (60) of the cup, in such a way to axially push the first seal ring (30) against the second seal ring (40).
In the example, the spring (8) is a helical wave spring obtained with a flat ribbon, such as for example the springs sold under the name of Crest-to-Crest® by Smalley. However, the spring (8) can be replaced by an annular wave spring or by a conventional spring with a cylinder helix.
With reference to
The sleeve (9) comprises:
The housing portion (91) of the sleeve comprises:
In view of the above, the tubular portion (90), the flange (93) and the external tongues (94) of the housing portion of the sleeve form a “U”-shaped housing where the second seal ring (40) is blocked.
Advantageously, the second seal ring (40) is blocked in the housing portion (91) of the sleeve by means of a cap (200) of elastomeric material disposed between the flange (93) of the sleeve and the second seal ring (40).
The cap (200) has a cylindrical body (201) with an annular flange (202) provided with openings that are obtained in the external edge of the annular flange. The openings (203) of the cap are suitable for receiving the external tongues (94) of the sleeve.
The second seal ring (40) has a plurality of recessed seats (41) that are obtained in an external edge. The recessed seats (41) are disposed between projections (42) shaped as an arched sector. The second seal ring (40) is compressedly coupled on the cylindrical body (201) of the cap, in such a way that the recessed seats (41) of the second seal ring are in register with the openings (203) of the cap. The external tongues (94) of the sleeve penetrate in the openings (203) of the cap and in the recessed seats (41) of the second seal ring, being disposed between the projections (42) of the second seal ring, in such a way to prevent the rotation of the second seal ring and of the cap relative to the sleeve.
Other anti-rotation systems, such as for example the elliptical coupling disclosed in WO2018/020460, can be provided between the second seal ring (40) and the sleeve (9).
The cap (200) can be omitted and the static seal between the second seal ring (40) and the sleeve (9) can be conveniently obtained by means of a FIP (formed in place) sealant disposed between the second seal ring (40) and the housing portion (91) of the sleeve.
With reference to
In view of the above, the spring (8) opposes a rotation of the cup (6) relative to the receptacle (5). Such a solution permits to leave the first seal ring (30) free to rotate relative to the receptacle (5). In fact, when the second seal ring (40) tends to transmit a rotation to the first seal ring (30), the first seal ring (30) tends to transmit a rotation to the cup (6); however, the cup (6) cannot rotated because the bottom wall (60) of the cup is constrained to the first end (80) of the spring, the spring (8) is subject to torsion and opposes the rotation of the cup (6).
Advantageously, the first constraint means (V1) can consist in welding (S), preferably spot welding, but also laser welding or condenser discharge welding.
Said first constraint means (V1) are easy to make because the first end (80) of the spring is constrained to the bottom wall (60) of the cup, outside the receptacle (5). Successively, the assembly formed of the first seal ring (30), the gasket (7), the cup (6) and the spring (8) is inserted in the receptacle (5).
The second constraint means (V2) can consist in welding (S) just like the first constraint means (V1).
With reference to
With reference to
This description continues by illustrating the operation of the mechanical seal (100).
During operation, the second seal ring (40) rotates integrally with the shaft (1). Therefore, a relative rotation with sliding is generated under the load of the spring (8) between the two seal rings (30, 40).
The rotational coupling of the second seal ring (40) is obtained by means of the cap (200) and the external tongues (94) of the sleeve that are engaged in openings (203) of the cap and in the recessed seats (42) of the second seal ring.
The rotational coupling of the first seal ring (30) is obtained by means of the spring (8) with the first end (80) constrained to the cup (6) and the second end (81) constrained to the receptacle (5).
The static seal between the gasket (7) and the receptacle (5) is obtained by means of the geometry of the lip seal portion (72) of the gasket, without the contribution of any rigid or elastic element to the compression of said portion against the internal wall (53) of the receptacle, except for the pressure of the fluid.
The function of the internal edge (62) of the cup is to contain the release of the lip seal portion (72) of the gasket in case of pressure on the inside, for example when a vacuum is generated before filling the cooling circuit.
Moreover, the function of the internal edge (62) of the cup is to prevent a possible adherence loss between the gasket (7) and the receptacle (5), with the consequent failure of the mechanical seal.
Such an adherence loss between gasket and receptacle can occur for many reasons, such as:
The lip seal portion (72) of the gasket is free to slide in axial direction and rotate relative to the receptacle (5); this avoids self-induced vibrations caused by stick-slip phenomena between the seal rings (30, 40) and consequently noise. Moreover, the number of parts is reduced, thus increasing the simplicity, the cheapness and the reliability of the seal.
The lip seal portion (72) has a suitable geometry to prevent the penetration of dirt in the static seal area with the receptacle (5) and can also act as tank for a lubricant.
Being free to slide in axial direction, the gasket (7) does not generate an elastic load on the seal rings (30, 40) to obtain the dynamic seal. The consequent absence of elastic deformation contributes to reduce the radial volume and to entrust the load between the seal rings only to the spring (8), thus obtaining a higher stability of the load throughout the entire life of the mechanical seal (100).
Evidently, several variants can be made to the mechanical seal (100) without leaving the protection scope of the claims.
In particular, the fixed portion (3) of the mechanical seal can be directly installed in the external ring of the bearing of the shaft, which is suitably extended.
Moreover, the first seal ring (30) can be directly disposed in the cup (6), without the interposition of the wall (71) of the gasket.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102018000007098 | Jul 2018 | IT | national |
