Patent Description:
This sliding discoidal element has a low coefficient of friction, and an elastic compressibility obtained through the mechanical qualities of the material and through the geometry of the discoidal element.

Civil structures, such as highway bridges, viaducts for medium and high-speed trains, aqueducts, buildings, and other similar structures, must resist high stresses caused by wind, traffic, thermal changes, earthquakes, and different kinds of impacts; these stresses must be transferred to the ground, in turn ensuring freedom of rotation and movement in accordance with the requirements of structure calculation.

The connection between the upper portion of these structures (board) and the ground is carried out through pillars (columns) and abutments, and these elements in turn connect to the foundation and finally to the ground.

Both parts, Board/Pillars - abutments, have an interface that connects them together by means of said structural bearing that acts as a mechanical hinge, wherein its design and materials are specific to each manufacturer, the sliding material on which the useful life of the bearing depends and which, consequently, will affect the structure being of great importance.

The sliding materials for use in structural bearings used to build bridges, and in general in any type of structure, follow the criteria of European Standard EN <NUM>/Part <NUM> "Sliding elements" with regard to their properties and specifications.

The sliding system is made up of a pair of flat, curved or spherical surfaces suitable for sliding and/or rotation, one with respect to the other. To minimise friction between the sliding surfaces, one of the surfaces is made of metal (such as austenitic steel, anodised aluminium alloy, or chrome-plated steel, or other equivalent finishes), and the other surface is a non-ferrous material.

In recent years, mixtures of polymer-type materials such as Polyamides (PA6, PA66) with Polyethylenes (PE, UHMWPE) have been developed, where the obtained product is a product of two materials without chemical bonds between the macromolecules; therefore the properties are not homogeneous or stable, since PA have the characteristic of water absorption and, consequently, these mixtures result in a response from their different mechanical characteristics depending on the level of moisture, i.e., the greater or lesser degree of water saturation of the mixture.

Solutions to this problem have been proposed, such as keeping the polymers saturated with water, something that is viable in a laboratory but cannot be guaranteed in civil works structures located in all sorts of places, under different atmospheric conditions and for periods of several decades.

On the other hand, the geometry of the sliding elements used is made up of a laminar discoidal arrangement where the sliding face usually has dimples, which serve to house some type of grease that provides less friction, while the fixed face is smooth.

Document no. <CIT> is known, which discloses a structural bearing provided with a sliding element having a circular perimeter and that can be made of various materials, such as, for example, polyamide, polyphenylene sulphide or UHMWPE (ultra-high molecularweight polyethylene), which common features are part of the preamble of claim <NUM>.

Document no. <CIT> is also known, which discloses a structural bearing system for bridges comprising a lower basin, an upper plate, and a sliding spherical cap that has a plurality of dimples over its entire surface which all have the same geometry. Moreover, it is worth mentioning that the dimples present on both faces have the function of lubricating the movable components of the mechanism, using the grease that is confined in said dimples, since they have been pre-filled with grease to facilitate sliding on both faces. Therefore, the elastic compressibility of the cap to improve the deformability thereof to adapt to different situations can be enhanced.

Other discoidal elements of the prior art are described, for example, in documents <CIT>, <CIT>, <CIT> and <CIT>, which are mentioned as a reference since they describe structural bearings provided with a sliding element.

However, none of the documents known in the prior art define a sliding discoidal element that is made from the material defined in the present invention, such that it provides greater mechanical stability when subjected to adverse weather conditions throughout its application, thus extending its useful life.

An object of the present invention is to therefore provide a sliding discoidal element for a structural bearing assembly in civil engineering as described in claim <NUM>.

By the alloy with two resins, in which the first resin will be called (A) and the second resin will be called (B), and by means of an adhesion promoter and an α-olefin copolymer-based additive, a new material is produced, with very beneficial properties for the most demanding requirements of new civil structures, such as a low coefficient of friction (less than <NUM>%).

The presence of an α-olefin copolymer-based additive provides a greater degree of stability of the mechanical characteristics under different atmospheric situations of temperature, moisture, ageing, etc..

Thus, by means of this new sliding material, it is possible to maintain the mechanical characteristics throughout the useful life of the structure (<NUM> or <NUM> years or more) while maintaining the stability of its mechanical properties throughout the life of the mechanism, regardless of the different levels of moisture and the atmospheric conditions.

This sliding material provides a great advantage for use as a sliding element for mechanical hinges located in infrastructures, such as bridges or viaducts, since it allows the size of structural bearings to be reduced and to better adapt to civil structures with increasing loads and slimmer formats.

This material not only complies with the suitability tests of the coefficient of friction values established in accordance with standard EN <NUM>-<NUM>:<NUM>, but also with regard to surface pressure, sliding path and/or sliding speed.

Values greater than the normalised value corresponding to the value established and tested in accordance with standard EN <NUM>-<NUM>:<NUM> are achieved, with regards the surface pressure greater than <NUM> MPa, the sliding path greater than <NUM>, and the sliding speed greater than <NUM>/s, in which this alloy is used as a sliding material, more particularly those that comply with standard EN <NUM>-<NUM>:<NUM>.

The rest of the dependent claims disclose secondary inventive aspects of the object of the invention.

According to another aspect of the invention, the sliding discoidal element comprises a body made up of two faces opposite each other, one face intended to be removably coupled to a support that forms part of the bearing assembly and one face intended to face a movable portion of an infrastructure, wherein the face facing the movable portion has a first plurality of dimples defined by concavities, while the opposite face also has a second plurality of dimples defined by secondary concavities.

By means of this arrangement of dimples on the non-sliding face, it is possible for the material subjected to loading and unloading cycles (during its useful life) to deform in the direction of the force, behaving as if it were resting on a large number of small springs, increasing elastic compressibility (modulus of elasticity less than <NUM> MPa). In other words, an additional elastic behaviour to that of the material itself is facilitated, greatly reducing tangential stresses and thus improving the stability of its properties throughout its life.

The sliding discoidal element is also characterised in that the alloy of the sliding material absorbs a surface pressure greater than the maximum normative value according to EN <NUM>-<NUM>: <NUM>, even at a temperature above <NUM>.

Moreover, the sliding discoidal element is characterised in that the alloy of the sliding material meets the requirements according to EN <NUM>-<NUM>: <NUM> at a temperature of -<NUM>.

Furthermore, the sliding discoidal element of the invention is characterised in that the limit value of the Pressure Speed of the alloy of the sliding material is greater than <NUM> MPa/m*Minute, V=<NUM>/min, with a load residence time of <NUM>.

On the other hand, this sliding discoidal element (<NUM>, <NUM>') is characterised in that at a temperature of <NUM> it absorbs a surface pressure of less than <NUM> MPa.

It is also important to mention that the sliding discoidal element (<NUM>, <NUM>') is characterised in that the modulus of elasticity is greater than <NUM> MPa and less than <NUM> MPa under temperature conditions in a range comprised between <NUM>-<NUM>.

Furthermore, the sliding discoidal element (<NUM>, <NUM>') of the invention is characterised in that it has an elongation limit at room temperature greater than <NUM>% and less than <NUM>%.

In light of the aforementioned figures, and in accordance with the adopted numbering, one may observe therein a preferred exemplary embodiment of the invention, which comprises the parts and elements indicated and described in detail below.

<FIG> shows a bowl-type structural mechanism (also commonly known as the acronym POT), configured for highway bridges, viaducts for medium and high-speed trains, aqueducts, buildings, and other similar structures, which comprises a lower pot (<NUM>) intended to be linked to a pillar or the like, an upper plate intended for a board or beam to be linked, between which a piston (<NUM>) or bowl, an elastic pad (<NUM>) and a sealing gasket (<NUM>) are provided, there being a sliding discoidal element (<NUM>) on the piston (<NUM>).

<FIG> shows a second embodiment of a structural mechanism, of the spherical type, configured for highway bridges, viaducts for medium and high-speed trains, aqueducts, buildings, and other similar structures, which comprises a lower basin (<NUM>') intended to be linked to a pillar or the like, an upper plate (<NUM>') intended for a board or beam to be linked, between which a spherical cap (<NUM>') is provided, characterised in that two discoidal elements (<NUM>, <NUM>') are provided, a first discoidal element (<NUM>) being in contact with the upper portion of the spherical cap (<NUM>') and the upper plate (<NUM>'), and a second discoidal element (<NUM>') being located below and in contact with the spherical cap (<NUM>').

In this way, the first discoidal element (<NUM>) has the function of facilitating the sliding of the plate (<NUM>'), while the second discoidal element (<NUM>') has the function of facilitating the rotation of the cap (<NUM>') on the lower basin (<NUM>').

Going into greater detail about the manufacture of the sliding discoidal element (<NUM>, <NUM>'), it is made of a sliding material from an alloy consisting of a first resin composed of polyamide, polyacetal (POM), polybutylene terephthalate (PBT), polycarbonate (PC) and polyphenylene sulphide (PPS) resins; a second high-molecular-weight polyethylene (UHMWPE) resin; a non-ferrous oxide adhesion promoter and, in particular, Maleic anhydride (C<NUM>H<NUM>O<NUM>), that is intended to establish a chemical bond between the first and second resins; and an α-olefin copolymer-based additive.

It is worth noting that the α-olefin copolymer-based additive is in a proportion of less than <NUM>% by weight.

Table <NUM> below shows the compression values of the sliding materials of the state of the art and the values with the sliding material object of the present invention, at a temperature of <NUM> and <NUM>.

The compression values were obtained through tests in accordance with standard EAD <NUM>; EAD <NUM>; EAD <NUM> for <NUM> hours at different temperatures and carried out in a materials laboratory:.

In particular reference to <FIG>, it can be seen how the aforementioned sliding discoidal element (<NUM>) is made up of a body in which it has a face (<NUM>) intended to be removably coupled to a support that forms part of the bearing assembly and an opposite face (<NUM>) intended to face a movable portion of an infrastructure, in which the opposite face (<NUM>) that faces the movable portion has a first plurality of dimples (<NUM>) defined by concavities, while the opposite face also has a second plurality of dimples (<NUM>) defined by secondary concavities.

It is important to note that the dimples (<NUM>) of the first plurality have a greater depth than the dimples (<NUM>) formed in the second plurality.

The result of this arrangement is that the elastic deformation of the discoidal element increases, which, when subjected to loading and unloading cycles (during its useful life), deforms in the direction of the force, behaving as if it were resting on a large number of small springs, in other words, an additional elastic behaviour to that of the material itself is provided. Moreover, a more homogeneous distribution of the compressions on the material is obtained, since it has better adaptability, thus improving the stability of its properties throughout its useful life.

Table <NUM> below shows the results of a series of tests on the modulus of elasticity, elastic limit, percentage elongation, breaking stress and percentage elongation at break, carried out under different environmental conditions, initial state, ageing at <NUM>, rest for <NUM> days after ageing at <NUM>:.

<FIG> shows the deformations of two discoidal elements in a comparative way, subjected to the same state of loads (<NUM> MPa), the element under the reference (A) being provided with dimples on its two opposite faces and the element under the reference (B) being provided with dimples on one of its faces, so that the disc (A) has a deformation of <NUM> and the disc (B) has a deformation of <NUM>.

For this reason, the dimples of the second plurality make it so that the discoidal element (A) offers a more elastic behaviour when subjected to compression, since it behaves as if the disc were resting on a set of small springs, thus obtaining a distribution of more uniform pressures on the discoidal element (A), and a better adaptability to possible deformations of the ferrous material that slides on the discoidal element (A).

Claim 1:
A sliding discoidal element (<NUM>, <NUM>') for a structural bearing assembly in civil engineering, characterised in that it is made of a sliding material from an alloy consisting of:
- a first resin composed from polyamide, polyacetal (POM), polybutylene terephthalate (PBT), polycarbonate (PC) and polyphenylene sulphide (PPS) resins;
- a second high-molecular-weight polyethylene (UHMWPE) resin;
- a non-ferrous oxide adhesion promoter that is intended to establish a chemical bond between the first and second resins; and
- an α-olefin copolymer-based additive.