MANUFACTURING PROCESS

The present invention relates to a shoe for hydrodynamic bearings .

The invention also relates to a process for manufacturing said shoe for bearing.

More specifically, the invention relates to a polymer- coated shoe, used in generators, turbines, pumps, transmission components.

Currently known polymer-coated bearings of this type are substantially based on a mechanical anchorage between the metal substrate and the coating polymer itself.

The solution proposed according to the present invention is in the field of hydrodynamic generator bearings, such as for example those described in patent WO 2004/001241 Al .

WO'241 describes a bearing for a rotor of a rotating machine, in particular a hydro-generator, which rotates around a vertically rotating axis. Said bearing is designed as a sliding bearing and comprises an axial bearing and a radial bearing. Normally, these bearings are coated with white metal (a tin alloy - white metal or "babbitt metal") .

However, in many cases polymer-coated bearings are used. In shoes of the known type, sintered bronze or a welded metal mesh or a series of tiny grooves machined in the bearing support part are mainly used.

Normally, in all known types of solutions for shoes, once said intermediate layer has been created, the polymer layer is pressed into it under conditions of high temperature and high pressure. This creates a mechanical connection between metal and polymeric materials.

This technology is characterized by a high degree of complexity, which also means high costs for the final product .

In fact, the process for obtaining known shoes involves various steps and the use of specialised equipment to manufacture the final product, which also limits the potential suppliers (in addition to the cost increase mentioned above) .

A further problem with the known and currently adopted technology is that there is inevitably a limit to the size that can be processed.

Furthermore, once the components are connected, they cannot be disconnected later without destroying the connection .

The polymer layer cannot therefore be replaced if the sliding surface is damaged due to wear or bearing seizure .

A recent solution that tries to answer the above- mentioned problem is the one described in EP 3 276 191 Al. In this patent application, an attempt is made to overcome the above-mentioned disadvantages by proposing a solution for a shoe in which the polymer and the metal part are decoupled, thus creating a shoe that can also be dismounted later if necessary (e.g. due to excessive wear) .

However, the solution according to EP ' 191 has some disadvantages, such as the need for machinings with very precise tolerances to ensure the coupling among the parts and the reduced possibility of controlling the total tolerances of the component (the shoes in the bearings have tolerances in the order of hundredths of a millimetre) .

Among the known patent documents, some are mentioned in particular, which relate to the specific solution proposed according to the present invention.

WO 2013/178266 Al describes a hydrodynamic bearing, which has a layered structure that is substantially uniform on the circumference of and comprises a base, a lead-free sliding layer having a thickness that is reduced in the edge areas compared to the central area, and a polymeric coating that is thicker in the edge areas than in the central area, so that the surface level of the coating is substantially flat as can be seen in the axial cross-section. This creates a kind of reservoir of coating material in the edge areas, which is particularly useful for the initial start-up phases of the rotating machines where wear occurs, where the bearing and the shaft adapt one another, increasing the resistance to edge seizure and achieving an improved alignment of the shaft to the bearing.

On the other hand, the patent US 6, 332, 716 describes a composite bearing in which a support metal is fixed to a resin layer, in which polytetrafluoroethylene (PTFE) is added to a base resin constituted essentially by polyether-ether-ket one , so that the proportion of polytetrafluoroethylene is between 0.1 and 50% by weight based on the resin layer. The polytetrafluoroethylene is then dispersed in the form of particles in the base resin .

The US patent 5,229, 198 in turn describes a material for low friction bearings which includes a matrix formed by a mesh screen wire which is fused with a metal support sheet. The polytetrafluoroethylene or other polymeric resin fills the interstices inside the screen, thereby being blocked rigidly together to impart high strength to the bearing material.

Patent application US 2005/0260431 Al describes a composite material for use in plain bearings and provides for a metal support and at least one reinforcing material having an open structure. Said support and reinforcing materials are connected through a metal connection.

Patent application EP 3 276 191 Al describes a shoe for the bearing of a hydrodynamic generator which comprises a polymeric part and a metal base, which combine to make up said shoe for bearing. Maintenance in the event of bearing failure is simplified and speeded up by the fact that the polymeric part is separated from the metal part. In particular, EP ' 191 proposes a resting shoe for bearing for hydrodynamic generators designed with a simplified approach compared to traditional polymer- coated shoes for bearing that allows to reduce production costs while increasing the main advantages thereof, such as high thermo-mechanical resistance and low wear in mixed lubrication. This is a bearing shoe of a hydrodynamic generator which has a polymeric part and a metal base, combined to form the bearing shoe. The shoe is characterized in that the polymeric part is a separate polymeric plate, the metal base is a support plate, and the polymeric plate is fixed to the support plate but is also removable.

According to EP ' 191, the polymeric plate is fixed in the resting plate by means of a seat in the resting plate that fits perfectly with the seat in the polymeric plate, the latter providing both the seat and an offset that protrudes from the plate on the perimeter forming a sealing strip with reduced thickness. The polymeric plate and the support plate have or may have the same edge contour. Again according to EP ' 191, the support plate and the polymeric plate may be coupled with at least one bolt. Furthermore, in the solution proposed in EP ' 191, locking means may be provided at the edge of the polymeric plate, which interact with the side wall of the pocket of the resting plate. In particular, said locking means may comprise a key and a slotted joint that extend along the edge of the polymeric plate, and a removable fixing plate may be provided on one side of the support bearing, to allow the polymeric plate to be inserted from one side by sliding it inwards and then, when closed, to be able to fix the polymeric plate in the pocket in its sliding position. The fixing plate can be fixed to the resting plate by means of fixing screws. In one example reported in EP ' 191, the polymeric part is at least partially constituted by polyetheretherketone (PEEK) .

It is well known that PEEK is a material with advantageous properties in terms of strength, which make it better than other polymers. The polymer could also be constituted least partly by polytetrafluoroethylene (PT- FE) .

Finally, according to EP ' 1919, the polymeric part may be constituted by a composition of different polymers and by a filler constituted by carbon fibers and/or graphite. EP ' 919 constitutes the major prior art document relevant to the invention described herein.

The solution proposed in accordance with the present invention, which proposes a bearing shoe consisting of a polymeric part and a metal base joined in an innovative manner that can significantly reduce costs by simplifying the production process, fits into this context .

In addition, the solution proposed according to the present invention makes it possible to achieve considerable improvements in the operation of the component, such as increasing the component's yielding at the most loaded points of the shoe or introducing sensors underneath the polymeric layer to monitor its behaviour .

These and other results are obtained with a shoe for hydrodynamic bearing comprising the features described in independent claim 1.

Further features of the shoe according to the invention are described in the dependent claims.

The present invention will now be described, by way of a non-limiting illustrative example, according to preferred embodiments thereof, with particular reference to the figures in the fixed drawings wherein:

Figure 1 is a perspective view of a shoe for bearing according to the invention;

Figure 2 is a close-up sectional view of the shoe in Figure 1;

Figure 3 shows a detail of the shoe of Figure 1;

Figure 4 shows a perspective view of a second embodiment of the metal base of the shoe for bearing according to the invention;

Figure 5 shows a perspective view of a second embodiment of the polymeric part of the shoe for bearings according to the invention;

Figure 6 shows a perspective view of the two elements shown in Figures 4 and 5;

Figure 7 shows a detail of the shoe in Figure 6;

Figure 8 shows the trends of the pressure loads of the bearing of the embodiment of Figures 5, 6 and 7;

Figure 9 is an exploded perspective view of a third embodiment of a shoe according to the invention;

Figure 10 shows a perspective view of the metal base of a fourth embodiment of the shoe according to the invention;

Figure 11 is a sectional view of the base of Figure 10;

Figure 12 shows a perspective view of the metal base of a fifth embodiment of the shoe according to the invention; and

Figure 13 is a sectional view of the base of Figure 12. Referring now to the figures in the drawings, and in particular initially to Figures 1 - 3, a resting shoe for bearing is shown, generically indicated by the numerical reference 10, in particular a hydrodynamic generator bearing, comprising a polymeric part 1 and a metal base 2.

In the embodiment of the shoe 10 according to the invention, it provides that the polymeric part 1 is constituted by a polymeric plate cast/moulded on the metal base 2, which constitutes a support plate.

The solution according to the invention proposes to cast (in the preferred embodiment described, 3D printing, but this technology must in no way be construed as limiting the scope of the invention) one or more layers of polyetheretherketone (hereinafter also indicated with the initials PEEK) reinforced with carbon fibers or graphite on the metal base 2. The use of PEEK is not to be understood as limiting the scope of protection of the invention; for example, the polymeric material may be constituted by other polymers, such as polyethylene terephthalate PTFE, or a mixture thereof. In fact, the polymeric element can also be made, for example, of PTFE or a mixture of PEEK and PTFE, with the addition of carbon fiber or graphite.

The metal base 2 is processed, with the creation of undercut 3, along at least one of the sides delimiting the perimeter of the metal base 2 (the geometry of the undercut 3 is shown in detail in Figure 3) .

With the construction of the undercuts 3, it is not possible to apply the techniques for example described in the Technical Document EP ' 191 as it would not be possible for a polymeric plate to slide freely in the undercuts 3.

In addition, it is not possible to use the hot-pressing technique inherent in some solutions of the known technique .

The undercuts 3 provided in this embodiment of the shoe

1 according to the invention for the coupling between polymeric part 1 and base 2, have depths in the order of millimetres and therefore it would not be possible to obtain a correct anchorage of the polymeric plate pressed on top by heat.

The undercuts 3, and the distribution thereof, are only one example of the coupling means that can be provided in the shoe 10 according to the invention, as will also be seen below.

The solution proposed according to the present invention allows for a polymeric part 1 anchored to the metal base

2 directly on the base itself. This process can be carried out by using machinery to deposit molten polymers on a metal surface, which allow the undercuts to be filled and then the polymeric part 1 to be anchored on the metal base 2.

The solution proposed according to the invention provides significant advantages over currently known solutions, and in particular:

- reduction in the production costs of polymer-coated guide and thrust bearings, due to less material wastage and a decidedly less demanding need for precise machining for the coupling between polymer and metal, as tight tolerances are not required to execute undercuts 3, which will be filled totally or partially (in any case sufficiently) to ensure the anchorage between polymer and metal support:

- possibility of decoupling the polymeric part 1 and the metal base 2 by making cuts along specially created seats in the metal support. In this way it is possible to reuse the metal base 2, the metal support to create a new shoe 10, should the latter become damaged or need replacing;

- possibility of providing further machining inside the metal base 2 which would further promote both the anchorage of the polymeric part 1 to the base 2 and the operation of the bearing 10 as a whole. In fact, by increasing the thickness of the polymeric material in the areas that are subject to higher pressures during operation, it is possible to exploit the yielding of the material itself, and in particular of PEEK, to favour a better distribution of pressure on each single shoe 10. This advantage is illustrated in Figures 4 to 8 of the drawings, in which a cavity 4 is provided on the metal base 2 with steps progressively decreasing towards the centre of the cavity 4. Figure 8 shows the effects obtained with this embodiment in the pressure relief;

- possibility of introducing sensors 5 inside the shoes 10 between the PEEK part 1 and the metal base 2, to monitor both the operating conditions and the state of health of the same. This type of embodiment is illustrated in Figure 9.

Coming now to the observation of Figures 10 and 11, a further embodiment of the shoe 10 according to the invention is shown, in which on the base element 2 a groove 6 is formed, in which, when the polymeric material of the element 1 is cast, a coupling is created between the elements 1 and 2.

In Figures 12 and 13, grooves 7 are made on the base element 2 in which, when the polymeric material of the element 1 is cast, a coupling is created between the elements 1 and 2.

The present invention has been described in the foregoing according to its preferred embodiments, but it is to be understood that they may be modified by experts in the art, without thereby departing from the scope of protection thereof, as defined in the appended claims.