The present invention regards an annular element or abrasive bead for a wire for cutting stone materials, as well as a cutting wire including one such annular element, as well as a method for the obtainment of the bead and the wire.

Blocks and slabs of stone materials, such as marble, granite and the like, in and outside quarries, can be cut using various, different tools. Among such tools, the most commonly used are the so-called "bead wires", employed in the "wire machines" with two or more transmission pulleys (at least one of which is motorized) for the bead wire or wires. Each wire engages the block or slab to be cut at a roughly rectilinear section between one pulley and the next.

The wires are usually constituted by central stranded wire made of steel or another ductile metal, on which a plurality of annular elements or beads spaced from each other are fit or mounted, such elements or beads formed by sintered material incorporating abrasive granules or abrasives, typically diamonds embedded in a matrix.

For the production of beads or annular elements, various methods have been proposed, such as the molding of a mixture of a powder metal material and a granular abrasive material in order to obtain the so-called "cold preform", in which a through hole is provided for the insertion of a support pin, usually metal, and the whole is then sintered. After the sintering step, a longitudinal through hole is obtained, preferably a threaded hole in the support pin, thus obtaining a finished annular element or bead constituted by two coaxial layers or rings: an external diamond layer and an internal metal layer.

A plurality of finished beads are inserted on a metal stranded wire; the injection molding follows, at least at each bead, of a suitable thermosetting plastic material, which acts as an element for anchoring and fixing the beads in position on the wire.

As will be understood, the internal metal ring:

- only carries out the function of anchoring the respective bead to the stranded wire, but has no any active role or work in the cutting step;

- in addition, it involves an operation of perforation of the support pin and possibly threading, with additional production costs; and

- requires caution in the obtainment of the sintering step, since the ring could be excessively deformed and cause the fracture of the external abrasive annular matrix.

Another problem that can be encountered with a cutting wire like that described above is that the beads are firmly fixed to the steel wire and hence cannot be moved or rotated with respect to the stranded wire, hence a cutting wire thus structured is not suitable for being adapted to the various cutting conditions, such as in particular the configuration of the block, the progression of the veins in the block, and the like.

The European patent EP-1 724 064 in the name of the same applicant of the present patent application teaches a cutting wire equipped with beads fixed on a stranded wire by means of molding of a suitable plastic material on such beads. Each bead delimits an axial opening with a transverse notch or groove or a thread portion, such that once the plastic material injected between the bead and the stranded wire has molded and hardened, the beads result firmly anchored thereto. Also according to such solution, therefore, the beads are rigidly constrained to the wire.

The obtainment of one such bead with processed opening is moreover rather complex, requiring a rather precise and costly processing.

The document JP-H11_48034 teaches the processing of beads for cutting wires by means of sintering of a super-abrasive material made of granules compressed on a helical spring. The beads thus formed are insertable on a wire, to which they are rigidly constrained.

The document WO 2008/063002 teaches a cutting wire comprising: one or more beads containing metal or diamond powders, arranged at regular intervals around the external surface of a wire; at least one elastic spring arranged on the external surface of the wire and coupled with one or more of such beads; and a support portion for the beads obtained between one bead and the other in a manner so as to cover the wire with synthetic resin such that the spring and the beads are rigidly constrained thereto.

The document IT-2 226 973 teaches a cutting wire comprising a metal wire, at least one spring on which one or more beads are arranged and welded. The spring, with the beads welded thereto, is arranged on a metal wire and is rigidly constrained thereto by means of injection of plastic material which completely covers the metal wire, thus obtaining a single body.

Thus, the main object of the present invention is to provide a new annular element or bead for a wire for cutting stone materials which is capable of being adapted to the cutting conditions, in particular to the different configurations and hardness of the block or slab material to be cut. Another object of the present invention is to provide an annular element for a cutting wire, which can even be obtained using worn beads.

Another object of the present invention is to provide an annular element for a wire for cutting stone materials which is simple and inexpensive to achieve.

Another object of the present invention is to provide a cutting wire equipped with an annular element or bead.

Another object of the present invention is to provide a cutting wire equipped with one such bead.

According to a first aspect of the present invention a process is provided for obtaining an annular element for a wire for cutting stone material, comprising the following sequential steps:

fitting at least one elastically yieldable element on a bar;

placing a portion of such bar with said elastically yieldable element in a mold; and

molding, around at least such elastically yieldable element, an embedding matrix whereby in such mold, an annular element is delimited having:

• an external work surface and an internal surface delimiting a through opening;

• the elastically yieldable element being placed at such internal surface and comprising a helical spring placed with position substantially coaxial with such through opening, whereby the turns of such helical spring delimit respective spirals with centers substantially aligned with a longitudinal axis of such through opening; • such elastically yieldable element being at least partly embedded in such embedding matrix;

waiting a certain time period for the hardening of such matrix; extracting, from the mold, such bar with such at least one annular element thus obtained;

removing such bar from such at least one annular element, thus obtaining a finished annular element.

Preferably, the at least one elastically yieldable element comprises a helical spring placed with position substantially coaxial with the axial opening.

Still more preferably, the turns of the helical spring delimit respective spirals with centers substantially aligned with the longitudinal axis of the through opening.

Advantageously, the at least one elastically yieldable element is slightly projecting into the through opening.

Still more advantageously, the annular element comprises at least one external ring substantially coaxial and winding around the at least one elastically yieldable element and at least partially embedded in the matrix, the external work surface being delimited by the external side wall of the at least one external ring.

According to another aspect of the present invention, a wire for cutting stone materials is provided, comprising a wire on which multiple annular elements according to the present invention are inserted and maintained in spaced position.

Advantageously, the annular elements are rotatably mounted on the wire by means of or due to the presence of the elastically yieldable element. According to a further aspect of the present invention, a process is provided for obtaining a wire for cutting stone materials, comprising the following sequential steps:

arranging a plurality of annular elements obtained according to the first aspect of the present invention;

arranging at least one wire;

mounting the plurality of annular elements spaced from each other on the wire, each annular element of the plurality being rotatably mounted around the wire; and

disposing at least one spacer means between two immediately adjacent annular elements of such plurality rotatably mounted around the wire.

Further aspects and advantages of the present invention will be clearer from the following detailed description of several preferred embodiments thereof, given as a mere non-limiting example with reference to the enclosed drawings, in which:

- Figure 1 is a longitudinal section view of a bead according to the present invention;

- Figures 2, 3 and 4 are similar views to Figure 1 of respective bead embodiments according to the present invention;

- Figures 5 to 7 illustrate respective steps of the process for obtaining the bead of Fig. 1 ;

- Figures 8 and 9 illustrate steps for anchoring a bead according to the present invention to a stranded wire; - Figures 10 to 13 are section views that illustrate respective steps of a process for obtaining a bead according to the present invention fixed on a stranded wire; and

- Figures 14 and 15 are views with parts in section of two embodiments of a cutting wire according to the present invention.

In the accompanying drawings, equivalent or similar parts or components have been marked with the same reference numerals.

Firstly, with reference to Figure 1 , an annular element or abrasion bead 1 a is illustrated for a wire according to the present invention for cutting stone materials, comprising an external work surface 2 and an internal surface 3 delimiting a through opening 4.

The bead 1a also comprises one or more (one in the drawings) elastically yieldable elements, typically a helical spring 5, e.g. made of harmonic steel, at least partly embedded in a matrix 6. The spring 5 is placed in a position substantially coaxial with the axial opening 4 and is at or close to the internal surface. Preferably, the spring 5 is slightly projecting into the internal surface 3. More particularly, the turns of the spring 5 delimit respective spirals with centers substantially aligned with the longitudinal axis x-x of the through opening 4.

Advantageously, the annular element 1 a also comprises an external work ring 7 substantially coaxial and winding around the spring 5. The external ring is at least partly embedded in the matrix 6, whereas the external work surface 2 is delimited by the external side wall of the external ring 7. According to such variant, the external work surface 2 remains free, i.e. projects from the matrix 6.

Advantageously, the matrix 6 is obtained from a material selected from the group constituted by polyacrylate resins, linear polyamides, mixed polyamides and polyamine products, polyamides (PA), polymethacrylamide, polyamide-imide, polyarylamide, polyphthalamide, polyetherimide, thermoplastic polyurethane polymers, amorphous polyamides, polybutylene-1 , polymethylpentene, styrene polymers, fluorinated polymers, polymethacrylic plastic materials, PMMA (polymethylmethacrylate) molding masses, polycarbonate, polyalkylenterephthalates (PTP), polyarylates, oxides - sulphides (PPS) - linear polyaryl sulphides, modified polyphenylenoxide (PPO), polyarylethers (ketones, polysulphones, PEEK), thermoplastic polyesters (LCP).

The elastically yieldable element 5 can for example be made of metal shavings, metal springs, springs made of plastic material, etc.

The work ring 7 is instead obtained from a mixture of sintered metals such as iron, bronze, copper, phosphor copper, cobalt, stainless steel, e.g. steel 316L, phosphor iron, alloys of the aforesaid metals with the addition of nickel, tungsten, wolfram, molybdenum and other metals with anti-oxidant function.

According to a variant illustrated in Figure 2, a bead or annular element 1 b according to the present invention does not have the external ring 7, but is mainly constituted by the spring 5 at least partly embedded in the matrix 6. One such annular element, while it has a lower abrasive or cutting capacity than that of the element of Figure 1 , is less expensive than the latter and even easier to obtain.

With reference now to Figure 3, a bead 1 a is illustrated according to the present invention equipped with a work ring 7 with cracks or surface defects 7a, which are at least partly filled and hence repaired by means of insertion of the matrix 6 therein. In a bead according to the present invention, it is therefore possible to also use components (work rings) that are defective or not perfectly intact, but which, following the application and hardening of the material constituting the matrix, ensure efficient cutting and a satisfactory useful lifetime.

Figure 4 shows two beads 1a similar to those described above, but having an elastically yieldable element 5 in common; the spring 5 is much longer than a bead 1a and has two terminal sections 5a, 5b each making up part of a respective bead 1a, as well as a portion 5c for connecting the terminal sections 5a, 5b. As will be understood, a spring element 5 can also be provided that is much longer than that illustrated in Figure 4 and intended to connect multiple beads according to the present invention.

An annular element in accordance with the present invention can be obtained by inserting a bar or core 8 in a spring 5 (Fig. 1) and possibly fitting a work ring 7 on the bar 8 (Fig. 2), so as to move such ringso as to receive or to be at least partly around the spring 5. At this point, at least the core or bar 8 with spring element 5 and, possibly, external ring 7, is arranged in the impression of a mold 9 (Fig. 3) and a material, e.g. a plastic material is molded around the spring 5 and work ring 7. Once the plastic material has hardened, a finished bead is obtained according to the present invention. Of course, multiple beads can be simultaneously molded, which are obtained on a same bar or core 8.

The core or bar 8 with the bead(s) is extracted from the mold 9 and the bead(s) thus finished is/are removed from the bar 8 ready to be inserted on a stranded wire 10 (see Figs. 8 and 9), to which the finished bead(s) can be fixed by means of any suitable method, as is further illustrated hereinbelow.

With reference now to Figs. 10 to 13, another process is illustrated for obtaining a bead element and a cutting wire 1 1 in accordance with the present invention, according to which the bar or core 8 is not provided, but the spring 5 and possibly the work ring 7 are fit directly on a stranded wire 10, and the portion of the wire with such components inserted thereon is placed in a mold 9 for the molding of the not-yet-hardened embedding matrix 6 around it. Once the hardening of the matrix has been attained, the respective section of finished wire 11 can be extracted from the mold 9. The aforesaid steps are then repeated for connecting or bringing a certain number of beads over the entire extension of the wire 10.

A cutting wire 11 according to the present invention thus comprises a plurality of bead elements inserted or fit on a wire 10, preferably a stranded wire, the bead elements being maintained in spaced position on the wire, e.g. by means of molding of a suitable plastic material therebetween (Fig. 14), for example selected from the group constituted by thermoplastic polyurethanes, vulcanized rubbers and thermoplastic rubbers, e.g. forprene. The plastic material can also be molded around each spring element 5 and also partly around the respective work ring 7. Alternatively, the beads are maintained in spaced position on the wire 10 by means of a spacer element arranged between two adjacent bead elements, e.g. a secondary spring 12, i.e. a spring different from the spring 5.

As will be understood, due to the provision of elastically yieldable elements 5 in the beads, the impact sustained by the beads themselves during the processing of cutting the stone material is damped, and therefore the beads can be adapted to the cutting conditions to a certain extent.

With particular reference to the case in which the beads are not fixed to the stranded wire, but rotatably mounted thereon, i.e. around the longitudinal axis of the wire, this occurring for example when the beads are maintained spaced by spacers, the presence of the springs 5 ensures the possibility of the respective annular elements or beads to carry out angular movements or rotation on the wire 10 during the cutting operations. Due to this expedient, the annular elements or beads work (cut) the stone material along the entire circumferential extension thereof, i.e. they engage the stone material at all portions or sectors thereof, so as to prevent the bead from ovaling or deforming. If instead the annular element or bead is fixed or in any case not able to rotate with respect to the wire 10, then the same sector of the bead would always engage and cut the stone material and, after a certain period of use, this can give rise to a localized consumption with consequent ovaling of the annular element or bead.

The above-described invention is susceptible to numerous modifications and variants within the protective scope defined by the claims.