PRIORITY CLAIM

This application claims priority from Italian Patent Application No. 102017000009799 filed on January 30, 2017, the disclosure of which is incorporated by reference.

TECHNICAL FIELD

The present invention relates to a production method of a diamond wire for cutting stone-like material.

BACKGROUND ART

As is known, most of the diamond wires for cutting stone-like material currently on the market are essentially made up of a multi-strand metal cable arranged in a closed loop; of a series of substantially cylindrical tubular-shaped diamond beads, that are fitted onto the metal cable at a given and constant distance one from the other; and of an outer tubular sheath made of thermoplastic material, that completely encases /covers the metal cable interposing itself between the metal cable and the single diamond beads, so as to prevent direct contact between the diamond beads and the metal cable and, at the same time, block the individual diamond beads in rigid manner on the metal cable.

The production of the diamond wire provides, in sequence, the steps of: threading the diamond beads onto the metal cable; joining the two ends of the metal cable so as to form a closed loop; distributing the diamond beads in regular manner on the metal cable; and finally realizing the outer sheath directly over the metal cable via injection-moulding, so as to block the individual diamond beads on the metal cable. The joining of the two ends of the multi-strand metal cable is usually made by properly intertwining the individual strands that contribute in forming the multi-strand metal cable. The most used technique is that of splicing.

Regardless of the joining technique used, at the end of the operation the two ends of each strand will be on the outer surface of the metal cable, one facing and closely adjacent to the other.

Obviously, the discontinuity points of the individual strands, i.e. the areas of the metal cable where the two ends of each strand reciprocally butt, are conveniently spaced along the metal cable so as not to locally weaken the metal cable.

In addition, before distributing and blocking the diamond beads onto the metal cable, the areas of the metal cable where the two ends of each strand reciprocally butt are covered by tubular sleeves suited to prevent the two ends of the strand from, during use, detach/rise from the surface of the metal cable, thus compromising the structural integrity of the diamond wire.

Considering that the diamond wires currently on the market normally use metal cables with at least 7 strands, the positioning of the protective sleeves on the metal cable significantly affects the time and cost of assembling the diamond wire. In patent application WO2012/142633A1 the areas of the metal cable where the ends of the strands reciprocally butt are wrapped by sheaths made of heat-shrinkable material . Despite being quite fast to put in place, unfortunately the sheaths made of heat-shrinkable material have a very limited containment capacity so that, in the long run, the multi- strand metal cable tends to unravel, thus compromising the structural integrity of the diamond wire.

DISCLOSURE OF INVENTION

Aim of the present invention is to provide a diamond wire for cutting stone-like material, which is free from the drawbacks highlighted above and also provides, for the same size, a greater mechanical resistance to traction and bending.

In compliance with the above aims, according to the present invention there is provided a production method of a diamond wire for cutting stone-like material as defined in claim 1 and preferably, though not necessarily, in any one of the claims depending thereon.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to the appended drawings, which illustrate an example of non- limiting embodiment, wherein:

- Figure 1 is a partially sectioned, side view of a diamond wire for cutting stone-like material made according to the teachings of the present invention;

- Figure 2 is an enlarged-scale view of a portion of the length of the diamond wire shown in Figure 1, with parts in section and parts removed for clarity;

- Figures from 3 to 11 schematically depict as many steps of the production method of the diamond wire shown in Figure 1; whereas

- Figure 12 is a partially sectioned, side view of a different embodiment of the diamond wire shown in Figure 1.

BEST MODE FOR CARRYING OUT THE INVENTION With reference to Figures 1 and 2, number 1 denotes as a whole a diamond wire for cutting stone-like material, which can be advantageously used for cutting marble and granite. The diamond wire 1 comprises: a central supporting cable 2 preferably made of metal material, which has a multi-strand structure and is arranged in a closed loop; a series of substantially cylindrical, tubular-shaped abrasive beads 3 that are fitted onto the supporting cable 2 spaced one after the other, and are externally made of an abrasive material capable of carving/cutting the stone-like material; and an outer tubular sheath 4 made of plastic material, preferably of a thermoplastic type, which is made by injection-moulding directly over the supporting cable 2, and completely encases/ covers the supporting cable 2 additionally interposing itself between the supporting cable 2 and the individual abrasive beads 3, so as to block the abrasive beads 3 in rigid manner on the supporting cable 2. The outer tubular sheath 4, therefore, protects the supporting cable 2 substantially for the whole length, and has an external diameter preferably smaller than or equal to the external diameter of the abrasive beads 3. The abrasive beads 3 thus delimit /define, in pairs along the supporting cable 2, a series of uncovered longitudinal segments, each of which is covered by the outer tubular sheath 4. The supporting cable 2, in addition, comprises a series of strands 5 that are preferably made of a metal material and are helically wound one on the other, and is arranged in a closed loop by appropriately intertwining the strands 5. The supporting cable 2, therefore, has a series of discontinuity points P where the two ends of each strand 5 of the supporting cable 2 are separately located/butt.

The abrasive beads 3, instead, have an internal diameter slightly greater than the external diameter of the supporting cable 2, and are locally coaxial and rigidly fixed to the supporting cable 2 by the outer sheath 4 that fills the space/ gap between the two components. In the example shown, in particular, the supporting cable 2 is preferably made of steel, and is preferably formed by 7 or more strands 5 suitably wound and interweaved one with the other . Preferably, the two ends of supporting cable 2 are also joined together by interweaving the strands 5 with the splicing technique .

In addition, the supporting cable 2 has an external diameter preferably less than 8 mm (millimetres), and preferably, though not necessarily, ranging between 1 and 5 mm (millimetres) . Preferably, the difference between the internal diameter of the abrasive beads 3 and the external diameter of the supporting cable 2 furthermore ranges between 0,1 and 0,5 mm (millimetres) .

Preferably the outer tubular sheath 4 is, in turn, made of thermoplastic polyurethane (TPU) or other similar polymeric material .

With reference to Figure 1, in addition, the abrasive beads 3 are preferably distributed on the supporting cable 2 with a substantially constant spacing/pitch and preferably even greater than or equal to 2,5 cm (centimetres) . In other words, the distance d between two adjacent/ consecutive abrasive beads 3 is preferably always greater than or equal to 2,5 cm (centimetres) .

Preferably, each abrasive bead 3 moreover comprises: a preferably substantially cylindrical tubular-shaped, supporting tubular sleeve 6 which is preferably made of metal material and is fitted directly onto the tubular sheath 4, locally coaxial to the longitudinal axis of the supporting cable 2; and a substantially cylindrical tubular-shaped, bushing 7 which is made of abrasive material and is fitted/ fixed in immovable manner directly onto the sleeve 6. Preferably, the bushing 7 additionally has an axial length smaller than the axial length of the supporting sleeve 6, and is preferably arranged substantially in the middle of the sleeve 6. In the example shown, in particular, the axial length of sleeve 6 is preferably less than 1,2 cm (centimetres) . Furthermore, the difference between the internal diameter of supporting sleeve 6 and the external diameter of supporting cable 2 is preferably ranged between 0,1 and 0,2 mm (millimetres) .

The supporting sleeve 6, moreover, is preferably made of steel or bronze, and is preferably also provided with an internal thread suitable for fitting/sinking into the tubular sheath 4 to increase the grip of the abrasive bead 3 on the tubular sheath 4.

The bushing 7, in turn, is preferably made of an abrasive material comprising diamond grains. In more detail, the bushing 7 is preferably made of a sintered composite material incorporating grains of sintered diamond, and is fixed in immovable manner on the supporting sleeve 6 preferably by brazing.

In other words, the abrasive beads 3 are externally coated in sintered diamond. With reference to Figures 1 and 2, furthermore the diamond wire 1 comprises a series of plastic-material tubular containment collars 10, preferably of a thermoplastic type, that are at least partially embedded/incorporated into the tubular sheath 4, and are made by injection moulding directly over the supporting cable 2, so as to locally bind the portions/sections of the supporting cable 2 which are located in the neighbourhood of/at the various discontinuity points P, so as to trap/block the ends of the strands 5. In other words, each tubular containment collar 10 has a given axial length λ preferably less than 2 cm (centimetres), and extends astride a respective discontinuity point P of the supporting cable 2. Preferably each tubular containment collar 10 is moreover dimensioned so as to remain spaced/distanced from the two abrasive beads 3 that are located at both sides of the discontinuity point P. More in detail, each tubular containment collar 10 has a given axial length λ, and is injection moulded directly over the supporting cable 2 so as to enclose and cover/encase a corresponding segment /section of the supporting cable 2 which is located/extends astride a discontinuity point P of the same cable .

Preferably, the discontinuity point P is moreover arranged substantially at the centre of the tubular containment collar 10.

Furthermore, the axial length λ of the tubular containment collars 10 is preferably greater than 50% of the value of the external diameter of the supporting cable 2, and is preferably also less than the distance or pitch p between two adjacent/ consecutive abrasive beads 3.

Preferably, the axial length λ of the tubular containment collars 10 is also less than 5 times the value of the external diameter of the supporting cable 2.

In other words, the axial length λ of the tubular containment collars 10 preferably ranges between 0,5 and 5 times the value of the external diameter of the supporting cable 2.

Preferably, the tubular containment collars 10 are moreover made of a plastic material having an elasticity modulus greater than that of the plastic material forming the tubular sheath 4, and optionally also having a hardness less than that of the plastic material forming the tubular sheath 4.

Preferably, the tubular containment collars 10 are furthermore made of a plastic material having a density greater than that of the plastic material forming the tubular sheath 4.

More in detail, the tubular containment collars 10 are preferably made of polyamide (PA) or other similar polymeric material . In other words, the tubular containment collars 10 are preferably made by injection-moulding in a plastic material different from that forming the outer tubular sheath 4.

More in detail, with particular reference to Figure 2, in the example shown each tubular containment collar 10 preferably has a thickness less than the local thickness of the tubular sheath 4, and an axial length λ preferably ranging between 1,2 and 2 times the value of the external diameter of the supporting cable 2, and also preferably less than 1 cm (centimetre) .

Preferably, each tubular containment collar 10 is moreover made of nylon.

Alternatively, the tubular containment collars 10 could also be made of polyamide PA66 or polyamide PA12 or a mixture of polyamide PA66 and polyamide PA12. In addition, the tubular containment collars 10 could also be made of polyether ether ketone (PEEK) .

Operation of diamond wire 1 is easily inferable from what is written above, and does not require further explanations.

With reference to Figures from 3 to 11, the production method of diamond wire 1 firstly comprises, in sequence, the steps of:

- threading a given number of abrasive beads 3 onto the supporting cable 2;

- joining the two ends 2a of the supporting cable 2 by appropriately intertwining the strands 5 forming the supporting cable 2, so as to form a closed loop; - distributing, optionally, the diamond beads 3 on the supporting cable 2 upstream and downstream of the discontinuity points P where the two ends of the various strands 5 of the supporting cable 2 are arranged/butt; and then

- injection-moulding the tubular containment collars 10 directly over the segments of the supporting cable 2 which are in the neighbourhood of the discontinuity points of the cable P where the two ends of the various strands 5 of the cable 2 are arranged/reciprocally butt, so as to locally bind the supporting cable 2.

Preferably, prior to the injection-moulding of the tubular containment collars 10, the production method of the diamond wire 1 also further comprises the step of tensioning the portion of the supporting cable 2 where each tubular containment collar 10 must be injection moulded.

Preferably, though not necessarily, the joining of the two ends of the supporting cable 2 additionally occurs with the splicing technique. Alternatively, it is also possible to use the closed loop technique.

After injection-moulding the tubular containment collars 10 over the supporting cable 2, the production method of diamond wire 1 moreover comprises the steps of:

- distributing the abrasive beads 3 on the supporting cable 2 at a given distance d and preferably substantially constant from one another; and then

- injection-moulding the outer tubular sheath 4 directly over the supporting cable 2, so as to substantially completely cover the supporting cable 2, thus firmly blocking the individual abrasive beads 3 onto the supporting cable 2 and at least partially incorporating the tubular containment collars 10 into the tubular sheath 4.

Obviously, the step of distributing the abrasive beads 3 on the supporting cable 2 according to the given spacing can be omitted if the abrasive beads 3 have already been distributed on the supporting cable 2 at the given and preferably also substantially constant distance d one from the other, before injection-moulding the tubular containment collars 10 over the supporting cable 2.

Preferably, before distributing the abrasive beads 3 on the supporting cable 2, the production method of the diamond wire 1 furthermore comprises the step of tensioning the portion of the supporting cable 2 where the outer tubular sheath 4 is to be injection moulded.

More in detail, with reference to Figures 6 and 7, the injection-moulding of the tubular containment collars 10 preferably comprises, in sequence, the steps of:

- tensioning, preferably in succession, the portion or portions of the supporting cable 2 that are located in the neighbourhood of the discontinuity points P of the cable, so as to make them substantially straight;

- inserting, preferably in succession, the portion or portions of the supporting cable 2 that are located in the neighbour ^¬ hood/astride of the discontinuity points P of the cable, inside a first mould for injection-moulding 100 which is provided with a pass-through straight cavity that copies in negative the shape of the portion of the supporting cable 2 and of the tubular containment collars 10 to be made on the same portion of the supporting cable 2;

- injecting a first plastic material inside the pass-through cavity of the mould 100, so that the polymeric material can completely fill the empty space inside the pass-through cavity, forming the tubular containment collars 10 on the portion of the supporting cable 2; and then

- extracting the portion of the supporting cable 2 with the tubular containment collar or collars 10 from the mould 100.

Preferably, the plastic material injected into the mould 100 is also a thermoplastic polymer. More in detail, the plastic material injected into the mould 100 is preferably a nylon or other similar polymeric material.

Alternatively, the plastic material injected into the mould 100 could also be a polyamide (PA) or a polyether ether ketone (PEEK) .

With reference to Figures 8, 9, 10 and 11, in addition, after having removed the portion of the supporting cable 2 with the tubular containment collar or collars 10 from the mould 100, the production method of diamond wire 1 preferably comprises, in sequence, the steps of:

- tensioning a section of the supporting cable 2 of given length and such as to support a plurality of diamond beads 3 (for example a segment of 50 cm in length) , so as to make it substantially straight;

- distributing the abrasive beads 3 on said section of the supporting cable 2 according to the given spacing/pitch;

- inserting the section of the supporting cable 2 together with the diamond beads 3, inside a second mould for injection- moulding 200 which is provided with a pass-through straight cavity that copies in negative the shape of a corresponding segment of the diamond wire 1 to be made;

- injecting a second plastic material inside the pass-through cavity of the mould 200, so that the polymeric material can completely fill the empty space inside the pass-through cavity, including the gaps between the supporting cable 2 and the individual abrasive beads 3, thus forming the outer tubular sheath 4 of the diamond wire 1; and finally

- extracting the resulting segment of diamond wire 1 from the mould 200.

Preferably, the plastic material injected into the mould 200 is furthermore a thermoplastic polymer.

More in detail, the plastic material injected into the mould 200 is preferably a thermoplastic polyurethane (TPU) or other similar polymeric material. Preferably, the plastic material injected into the mould 200 is therefore different from the plastic material injected into the mould 100.

The production method of the diamond wire 1 described above offers numerous advantages.

Experimental tests have shown that the injection-moulding of the tubular containment collars 10 directly over the supporting cable 2, allows the polymeric material forming the tubular containment collar 10 to penetrate between the strands 5 before solidifying. This localized supply of plastic material prevents the two ends of the strand 5 from rising during use of the diamond wire 1, practically bringing to zero the risks of premature unravelling of the metal cable 2.

Furthermore, the addition of plastic material in the neighbourhood of the discontinuity points P significantly increases the tensile strength and fatigue strength of the diamond wire 1. Thanks to the presence of the tubular containment collars 10, in fact, the diamond wire 1 has a tensile strength and a fatigue strength of at least 75% greater than those of a diamond wire of the same size and in which the discontinuity points on the multi-strand metal cable are covered by protective sleeves or sheaths made separately and subsequently fitted onto the metal cable, astride the discontinuity points. Finally, it is clear that modifications and alternatives can be made to the production method described above without thereby departing from the scope of the present invention.

For example, in a less sophisticated embodiment, the tubular containment collars 10 may be made of a thermoplastic polyurethane (TPU) preferably with a elasticity modulus greater than that of the thermoplastic polyurethane (TPU) forming the tubular sheath 4. With reference to Figure 12, in a different embodiment the outer tubular sheath 4 in addition has, in the area of at least one and preferably each tubular containment collar 10, a preferably cylindrical-shaped, respective enlarged segment 100 which at least partially surrounds/incorporates/contains the corresponding tubular containment collar 10, and which is also spaced/distanced from the two abrasive beads 3 flanking the same tubular containment collar 10. Preferably, the axial length λο of the enlarged segment 100 is also greater than the axial length λ of the tubular containment collar 10 at least of 10%.

Preferably, the maximum diameter of each enlarged segment 100 is also less than or equal to the external diameter of the adjacent abrasive beads 3. In addition, the maximum diameter of each enlarged segment 100 is preferably also at least 20% greater than the minimum diameter of the outer tubular sheath 4. More in detail, the enlarged segment or segments 100 of the outer tubular sheath 4 are made by injection-moulding directly over the supporting cable 2, together with the rest of the tubular sheath 4, and are preferably dimensioned so as to incorporate/contain substantially the whole corresponding tubular containment collars 10.

The enlarged segment or segments 100 of the tubular sheath 4 therefore extend over the areas where the discontinuity points P of the supporting cable 2 are located.

In the example shown, in particular, the enlarged segment or segments 100 of the outer tubular sheath 4 preferably have a maximum diameter substantially equal to the external diameter of the adjacent abrasive beads 3. Preferably, the axial length λο of the enlarged segment or segments 100 is also comprised between 1,2 and 2 times the value of the nominal diameter of the supporting cable 2, and even preferably less than 1 cm (centimetre) . With reference to Figure 12, preferably the tubular sheath 4 also has an enlarged segment 100 along each exposed longitudinal section of the supporting cable 2, regardless of the simultaneous presence of a tubular containment collar 10, so as that all the abrasive beads 3 are flanked, on both sides, by two enlarged segments 100. Preferably, the various enlarged segments 100 are also substantially equidistant from the two immediately adjacent abrasive beads 3. Obviously in this case the straight pass-through cavity of th mould 200 is shaped so as to also form the enlarged segment 100 of the tubular sheath 4.