EP3356072A1

EP3356072A1 - Multi-wire frame and method for cutting blocks of stone material into slabs

Info

Publication number: EP3356072A1
Application number: EP16797984.8A
Authority: EP
Inventors: Dario Toncelli
Original assignee: Individual
Current assignee: Individual
Priority date: 2015-09-28
Filing date: 2016-09-28
Publication date: 2018-08-08
Also published as: WO2017056009A1; ITUB20153924A1

Abstract

A multi-wire frame (12) for cutting blocks of stone material into slabs comprises: at least two columns (14, 16), each of which has, mounted thereon, at least one slide (18, 20) designed to move along the respective column (14, 16); each slide being provided with at least one drum (24, 26), one of which is motor-driven and the others of the idle transmission type, designed to engage a plurality of diamond wires (28, 30) which extend between them. The frame also comprises two wire-guiding rollers (38, 40) provided at the ends of a cutting section of the diamond wires. The frame comprises means for detecting the force applied to the multi-wire frame during the cutting action. An associated method for cutting blocks of stone material into slabs is also described.

Description

"Multi-wire frame and method for cutting blocks of stone material into slabs".

DESCRIPTION

The present invention relates to a multi-wire frame and a method for cutting blocks of stone material into slabs.

The multi-wire frames according to the prior art comprise at least two multi-pulley rollers or two multi-groove drums, between which the diamond wires used for cutting travel.

In the case of a multi-pulley roller a plurality of pulleys are arranged grouped together, while in the case of a multi-groove drum a single element is provided with a plurality of grooves arranged adjacent to each other.

In the present description reference will be made generally to a multi-pulley roller and to a multi-groove drum, using the term "drum", since the specific constructional characteristics of these two elements are not of specific interest for the invention.

The number of diamond wires which are usually mounted on the grooves of the drums are relatively numerous and may even be as many as eighty, depending on the width of the block to be cut and the thickness of the slabs to be formed. The main technological developments in these machines relate to the adjustment of the tensioning of each diamond wire and therefore in the present state of the art different methods for tensioning diamond wires are known.

An example of a multi-wire frame is described for example in Italian patent No. TV2014A000029 filed on 24 February 2014 in the name of the present Applicant.

In this multi-wire frame configuration, there are two columns connected at the top by a cross-member. A slide with a drum mounted thereon slides along each column. The two drums have a small diameter and the diamond wires slides inside their grooves.

An arch-like structure is arranged between the two slides, provided with a plurality of tensioning rollers, one for each diamond wire, the movements thereof in the vertical direction being independent. During use, the tensioning roller is positioned inside the ring formed by the diamond wire. Therefore, when it moves in the vertical direction;

- upwards, it increases the tension of the wire;

- downwards, it decreases the tension of the wire.

A second example of a multi-wire frame configuration is that shown in Italian patent No. 1369929. In this multi-wire frame, the drums have a diameter greater than in the configuration described above, in particular greater than the height of the stone block which must be cut.

The frame comprises a cross-member which connects the top ends of the columns on which the slides travel. The column is provided with wire-tensioning jockey wheel for each diamond wire. The position in the vertical direction of each jockey wheel may be separately varied in order to adjust the tension of each cutting wire. During use, the jockey wheel is located on the outside of the ring defined by the diamond wire and in particular is situated above the wire so as to press on the wire in a vertical direction downwards. Therefore, when it moves in a vertical direction;

- upwards, it decreases the tension of the wire;

- downwards, it increases the tension of the wire.

There also exist other frame configurations, such as frames which have four drums which are smaller in size than in the configuration described above and arranged at the four corners of a rectangle. In these frames, tensioning of each wire is performed with a roller arranged along one of the two vertical sections of the wire situated between the two drums located on the same column, moving it in a direction perpendicular to the direction of the wire.

Multi-wire frames, irrespective of the arrangement and the number of drums, often also have two wire -guiding rollers or cylinders situated at the ends of the cutting section of the diamond wire, in the vicinity of the corresponding drums. The position of the wire- guiding rollers may be adjusted so as to be able to move as close as possible towards the block to be cut and reduce the span of the diamond wire between the wire -guiding rollers as far as possible. Wire -guiding rollers of this type are described for example in Italian patent application TV2014A000029 mentioned further above.

The present invention will be described with reference to the frames provided with two bottom drums and tensioning rollers at the top, even though the invention may also be applicable to other types of frame, as will be obvious to the person skilled in the art from the continuation of the present description.

During cutting, owing to the forces acting on each diamond wire, the cutting section of the diamond wires assumes an arch-like configuration with the convexity directed upwards.

In the present description the expression "cutting section" is used to indicate the section of diamond wire which at a given time instant is situated between two wire -guiding rollers and which with a portion thereof performs cutting of the block.

It is known that the cutting wires for performing cutting must exert a given pressure on the block to be cut. For this reason, along the cutting section, the diamond wire has a convex section with its concavity directed towards the block to be cut.

It is therefore possible to define a camber of the cutting section of the diamond wire, i.e. the maximum distance between the axis of the diamond wire in the operative cutting configuration and the axis of the diamond wire in the theoretical position, i.e. tensioned between the wire -guiding rollers.

In other words, the term camber is understood as meaning the maximum vertical displacement of the diamond wire with respect to the horizontal rest position.

The camber is necessary, in order to be able to generate vertical forces on the diamond granules of the tool and consequently a pressure on the stone material able to cause incision thereof. The pressure of the wires on the block to be cut is increased or decreased by adjusting the speed of movement of the slides along the columns, also called lowering speed of the diamond wires.

The camber, although necessary, must nevertheless be contained within certain limits since the greater the camber, the greater is the pressure exerted by the wires on the block, with the result of possible deviations during cutting or damaging of the tool.

For example, if the camber is too great, it could prevent rotation of the wire about its axis with consequent smoothing of the diamond beads.

In this situation the cutting efficiency tends also to be reduced also in the presence of high pressures. In this situation, the wire is said to "jib" on the material, to use the technical jargon.

On the other hand, if the camber is to small, the pressure of the wire is sufficient and consequently the incision capacity and therefore the cutting capacity are reduced.

Therefore, in order to obtain an optimum cut, it is necessary for the camber, and consequently the pressure of the diamond wire on the material, to be contained within a range of limit values, i.e. minimum value and maximum value.

The limits depend on many factors including, for example the length of the block, the relative distance of the two wire -guiding rollers, the hardness of the material to be cut, the tensioning of the wires, the cutting speed (sliding speed of the wires on the block) and the lowering speed of the diamond wires.

It should be noted that, given the block to be cut (made of a certain type of material and with given dimensions), considering that tensioning of the wires is fixed to the maximum permitted value and that the speed of travel of the wires is predefined depending on the type of diamond wires to be used, the only parameter which can be adjusted in order to optimize the process is the lowering speed of the diamond wires.

In the frames of the known type, the lowering speed is regulated manually by an operator who, once operation has been initiated, starting from a slow lowering speed, gradually increases its value so as to increase gradually the camber until the value considered to be optimum by the operator is reached.

Since, during cutting, the wires are inside the block, it is not possible for the operator to estimate exactly the amount of camber of the wires, so that the only parameter which is visible is the inclination which the wires assume between block and wire -guiding roller: the greater the inclination of the wires, the greater will be the camber.

The operator could also use other systems to determine the moment in which the lowering speed considered optimum is reached, for example detecting the power consumption of the motors needed for cutting. It is clear in fact that, with an increase in the camber, the power consumption of the motors also increases. However, this value also depends on other parameters, so that the system which is used is that of visually assessing the camber, which depends in particular on the experience of the operator.

The multi-wire frames described above, although they are widely appreciated and used, are not without drawbacks.

In fact, despite the operator's experience, determining the camber visually is not all easy or precise since, as already mentioned, the wires are arranged inside the block being cut and therefore are not visible.

The operator, no matter how experienced, may make an error of judgement, which may also be substantial in nature.

Moreover, the adjustment made is very subjective and, in particular, the adjustment made by an operator could differ, even substantially, from the adjustment made by another operator.

Finally, if there are changes in the hardness of the block to be cut, for example the block has zones which are harder or softer, adjustment will no longer be optimal and the cutting action will no longer be efficient. In fact, if the wires encounter a zone of the material which is harder, the camber would increase and, along with it, the cutting pressure, and consequently the efficiency of the cutting action would also decrease. In this case it would be desirable to decrease slightly the lowering speed.

In the opposite situation, if the wires encounter a zone of the material which is softer, the camber would decrease and, along with it, the cutting precision; in this case also, the cutting efficiency would decrease and it would be desirable to increase the lowering speed.

The object of the present invention is therefore to overcome at least partially the drawbacks of the prior art.

A first task of the present invention is therefore to provide a multi-wire frame in which the lowering speed may be set and adjusted automatically, without the need for continuous monitoring by the operator.

A second task of the present invention is to provide a multi-wire frame in which the lowering speed may be kept at the optimum value in accordance with the characteristics of the block to be cut, in particular when there is a variation in the dimensions of the block, the type of material and the hardness inside the block itself.

In the event of a variation in the characteristics of the block to be cut, but in particular the hardness, the system must be able to adapt the cutting conditions and in particular the lowering speed automatically so as to optimize the time required to perform cutting. Furthermore, a task of the present invention is to provide a multi-wire frame which may be used without requiring continuous supervision by an operator.

The object and tasks are achieved with a multi-wire frame according to Claim 1 and a method according to Claim 13.

The advantages and characteristic features of the present invention will emerge more clearly from the detailed description which follows of a number of non-limiting examples of embodiment provided with reference to the attached drawings in which:

Fig. 1 shows a schematic perspective view of a multi-wire frame according to the present invention;

Fig. 2 shows a schematic front view of the multi-wire frame according to Fig. 1 in the rest condition and therefore with the diamond wires arranged substantially in a horizontal direction;

Fig. 3 shows a schematic front view of the multi-wire frame according to Fig. 1 in the operating condition, where for illustrative purposes the camber of one of the diamond wires is shown on a larger scale;

Fig. 4 shows a schematic side view of a wire -guiding roller and its support structure according to the present invention;

Fig. 5 shows a schematic front view of the multi-wire frame part shown in Fig. 4; Fig. 6 shows a schematic, perspective, bottom view of the multi-wire frame part shown in Fig. 4;

Fig. 7 shows an enlarged view of a detail shown in Fig. 6;

Fig. 8 shows a schematic perspective view of the multi-wire frame part shown in Fig.

4;

Fig. 9 shows an enlarged view of a detail shown in Fig. 8;

Fig. 10 shows a schematic, partially exploded, perspective view of the multi-wire frame part shown in Fig. 4; and

Fig. 11 shows a schematic perspective view of the multi-wire frame part shown in Fig. 4 in a second operating configuration.

As mentioned at the start of the present description, reference will be made for the sake of convenience to a given type of machine, it being understood that the principles of the present invention may be adopted also in other types of multi-wire frame.

Figures 1-3 show a multi-wire frame according to the present invention indicated generally by the reference number 12.

The multi-wire frame 12 for cutting blocks of stone material comprises two columns 14, 16 on each of which a slide 18, 20, designed to move along the respective column 14, 16, is arranged.

A top cross-member 22 may be provided between the two columns 14, 16 so as to connect together the two top ends of the columns 14 and make the frame structure rigid.

The slides 18, 20 may be of the type known per se to the person skilled in the art and are equipped with at least one drum 24, 26, one of them being motor-driven and the others of the idle transmission type. Advantageously the speed of travel of the diamond wires may be kept in the range of between 27-32 m/min.

In the present description, the structure of the means which allow movement of the slides along the columns will not be described in detail, since they do not fall within the inventive principles described by the present invention.

The drums 24, 26 are designed to engage a plurality of cutting wires which extend between them, inside a plurality of grooves, in a manner known per se to the person skilled in the art and therefore will not be further described.

Figures 1-3 show for illustrative purposes two diamond wires 28, 30, it being understood that in machines of this type there may be a large number of diamond wires, for example eighty wires.

The diamond-wire frame shown in Figures 1-3 comprises a plurality of tensioning devices, indicated by the reference 32, one for each diamond wire. The tensioning device 32 may be an idle pulley, mounted on a movable support 34.

The tensioning devices may be mounted on a cross-member 36 arranged between the slides 18, 20.

A wire -guiding roller 38, 40 is arranged in the vicinity of each drum 24, 26. The wire- guiding rollers 38, 40 are provided with a series of grooves positioned so as to be able to seat the diamond wires and are designed to guide the diamond wires along the cutting section. In a similar manner to the drums 24, 26, the wire -guiding rollers may consist of a single cylinder provided with a plurality of grooves or a series of pulleys grouped together.

Advantageously, positioning of the diamond wires may be varied depending on the desired thickness of the slabs to be cut, normally one centimetre at a time starting from a minimum thickness of about 2 centimetres. Advantageously, the wire -guiding rollers have the same length as the drums 24, 26 so that their grooves are aligned in a vertical plane and therefore correspond.

Figure 3 shows in schematic form the multi-wire frame during cutting of a block of stone material indicated by the reference number 42. As already mentioned in the summary description of the figures, an example of a camber F to which the diamond wires are subject is indicated for illustrative purposes.

It is emphasized again that the illustration is only schematic and not to scale in relation to the real camber which the diamond wires have.

In accordance with a possible embodiment of the present invention, the multi-wire frame comprises movement means 44, 46 for adjusting the position of at least one of the wire -guiding rollers 38, 40. Preferably, both the wire -guiding rollers 38, 40 are provided with movement means 44, 46.

The movement means 44, 46 comprise a mechanism which allows the movement of at least one wire -guiding roller 38, 40 towards or away from the respective drum 24, 26.

With reference to Figures 4 and 5, a possible embodiment of the movement means 44 provided on the column 14 and therefore on the slide 18 will now be described, it being understood that the structure which will be described may be substantially similar to the structure of the movement means 46 provided on the opposite side of the multi-wire frame, namely provided on the column 16 and therefore on the slide 20.

The movement means 44 may comprise two support structures 48, 50. The support structures 48, 50 may be fixed to the corresponding slide 18, 20 or may be provided on the respective column 14, 16 slidably and be independent of the slide 18, 20.

The support structure 48, 50 may comprise a fixing plate 52, 54 which may be fixed to the slide 18, 20 by means of bolts (as shown in the attached figures) or alternatively by means of welding. However, other fixing systems per se easily imaginable by the person skilled in the art are possible.

The supports 48, 50 further each comprise a sliding seat 56 (not visible in Figure 4, but visible in Figures 5, 6, 8, 10) having an elongated form. An arm 58, 60 slides inside the two sliding seats 56.

A bush or bearing (not shown in the attached figures) may be provided between arm

58, 60 and sliding seat 56 in order to ensure the sliding efficiency.

A bracket 62, 64 is provided at one end of each arm 58, 60 in order to support the ends 66, 68 of the wire -guiding roller 40.

With reference to Figures 10 and 11, the movement of the arms 58, 60 may be performed by means of linear actuators 70, 72.

In accordance with a possible embodiment of the present invention, the actuators 70, 72 may comprise a threaded stem 74 which engages with a threaded seat 75 provided on the free end of the respective arm 58, 60. An electric motor 76, 78, designed to cause rotation of the threaded stem by means of a mechanical transmission 77, 79, is provided at the opposite end of the threaded stem.

The means for moving the wire -guiding rollers will not described in further detail since they are well-known to the person skilled in the art.

The arms are therefore movable between two positions:

- a first position in which they are completely extracted, where the wire -guiding roller is at the maximum distance from the respective drum (condition shown in Fig. 11); and

- a second position in which they are completely retracted, where the wire -guiding roller is at the minimum distance from the respective drum (condition shown in Fig. 10). The two arms may be arranged horizontally or may be inclined downwards.

In accordance with alternative embodiments a single actuator or a single electric motor may be provided for each wire -guiding roller.

The present invention is characterized in that it comprises means for detecting the force applied to the multi-wire frame during the cutting action.

In accordance with a possible embodiment of the present invention, said means are designed to detect the force applied to at least one of the wire -guiding rollers 38, 40 during the cutting action. Advantageously, said means are designed to detect the force applied to both the wire -guiding rollers 38, 40 during the cutting action.

Advantageously, the present invention is characterized in that it comprises means for detecting the vertical force applied to the multi-wire frame during the cutting action.

A possible embodiment of the means for detecting the force applied to at least one of the wire -guiding rollers during the cutting action will now be described in detail, with particular reference to Figures 4-10.

The enlarged view in Fig. 9 shows a block 80 with a circular seat 82 which may receive, inserted inside it, one of the ends 66, 68 of the spindle about which the wire -guiding roller 38, 40 rotates idly, for example via bearings.

The block 80 may be mounted with play between a top projection 84 and a bottom projection 86 provided on the brackets 62, 64.

A degree of play may be present between the block 80 and the top projection 84 and between the block 80 and the bottom projection 86. In accordance with a possible embodiment of the present invention the play may range between 1 and 3 mm.

The block 80 may be fixed to the bottom projection 86 by means of two load cells 88, 90 arranged in between. Advantageously, the bottom end of the two load cells 88, 90 is rigidly fixed to the bottom projection 86, while the top of the two load cells 88, 90 is fixed to two lugs 92, 94 projecting from the block 80.

In accordance with a possible embodiment of the present invention, the top and bottom projections 84, 86 comprise two circular seats 81, 83 for pins 85, 87 designed to cooperate with corresponding seats 89, 91 provided on the block 80, in order to limit oscillations of the block with respect to the vertical axis.

In accordance with a possible alternative embodiment, not shown in the attached figures, the block 80 may be fixed to the top projection 84 by means of two load cells 88, 90 arranged in between. Advantageously, the top side of the two load cells 88, 90 is rigidly fixed to the top projection 84, while the bottom of the two load cells 88, 90 is fixed to two lugs 92, 94 projecting from the block 80.

As is known, the load cell is an electronic component which is used to measure the force applied to a mechanical component, by means of measurement of an electric signal which varies because of the deformation which this force produces on the component. The wiring required is not shown in the attached figures and will not be described since it may be easily imagined by the person skilled in the art.

In accordance with a possible embodiment of the present invention, the load cells 88, 90 have a substantially circular shape with two staggered grooves substantially parallel to the axis of the wire -guiding roller 38, 40, so as to form a kind of "S".

Essentially, in the embodiment shown in the attached figures, the block rests on very rigid elastic elements formed by the load cells 88, 90.

As regards operation, when the frame starts cutting, a force having a dominant upwards component is applied onto the wire -guiding rollers and therefore onto the blocks. The cells are subject to a tractional force which is detected.

Advantageously, two load cells 88, 90 may be provided for each end 66, 68 of the wire -guiding roller. The multi-wire frame may therefore be provided with four load cells for each wire -guiding roller.

Obviously, with the load cells distributed in this way it is possible to detect not only the force acting in a vertical direction on the wire -guiding roller, but also its resultant which may be inclined relative to the vertical.

In accordance with a possible embodiment of the present invention, the multi-wire frame according to the present invention may comprise eight load cells, i.e. four for each wire -guiding roller, and therefore two for each end of the wire -guiding roller.

Also possible are simpler embodiments in which the force detection means may be present on only one wire -guiding roller. Moreover, embodiments are possible where only one load cell for each end of the wire -guiding roller is provided.

In the same way more complex embodiments may be provided where there are several load cells which may be provided on other parts of the multi-wire frame.

According to a possible embodiment of the present invention the detection means may be provided on the circular seat 82 of the block 80, 84.

The multi-wire frame further comprises a control unit (not shown in the attached figures). The control unit may be for example an electronic processor for managing and controlling operation of the multi-wire frame.

The control unit is connected by means of suitable wiring to the force detection means described further above. In particular, the control unit may be connected to the load cells for reception of the data and subsequent processing thereof.

In order to perform cutting of blocks of stone material into slabs it is therefore possible to measure the force applied by the diamond wires along the cutting section to at least one of said wire -guiding rollers and use this value to adjust the lowering speed.

In fact, the amount of the force measured depends not only on the aforementioned parameters (block length, relative distance of wire -guiding rollers, cross-section and number of diamond wires, initial tensioning), but also on the nature of the material and the cutting parameters (cutting speed of the wires and lowering speed) as well as other parameters such as amount of sprayed water, inclination of the axes of the wire -guiding rollers in the horizontal plane (since one end of the wire -guiding roller may be closer to the block than the other end) .

The control unit, based on the force measured, is designed to establish and set the optimum lowering speed by means of an algorithm and knowing the various working conditions.

Moreover, the control unit may be designed to calculate during machining, the optimum lowering speed at predetermined time intervals.

Obviously the data detected by the means described further above may be used in different ways depending on the predefined purpose.

For example it is possible to determine the lowering speed not only such that the cutting speed may be reduced, but also such that there is less wear of the rubber lining the grooves inside the diamond wires slide, or such that a longer working life of the wire may be obtained.

Advantageously the lowering speed may be adjusted at regular intervals during machining by means of the programmable control unit.

Based on the knowledge of the force measured by the load cells and the data known or detected such as the size of the block to be cut, relative distance of the wire -guiding rollers, material to be cut and other data, the lowering speed may be set so as to achieve the desired result which may consist in the reduction of the cutting time, less wear of the rubber protecting the grooves inside which the diamond wires slide, greater working life of the diamond wire, etc.

In connection with the embodiments described above the person skilled in the art, in order to satisfy specific requirements, may make modifications thereto and/ or replace parts described with equivalent parts, without thereby departing from the scope of the accompanying claims.

The multi-wire frame could have different configurations, for example as already mentioned, instead of providing two drums, four drums may be provided at the four corners of a rectangle, or two columns could be provided instead of four columns.

The same inventive principles could be applied equally well also to single-wire machines for shaping blocks of stone.

In the description explicit reference is made to the use of load cells, it being understood, as will be obvious to the person skilled in the art, that other devices, such as strain gauges, may also be provided. Moreover the detection means could be provided for example also on the tensioning

Claims

1. Multi-wire frame (12) for cutting blocks of stone material into slabs, comprising: at least two columns (14, 16) each of which has, mounted thereon, at least one slide (18, 20) designed to move along the respective column (14, 16);

the slides having, coupled thereto, at least one drum (24, 26), one of which is motor- driven and the others of the idle transmission type, adapted to engage a plurality of diamond wires (28, 30) which extend between them;

two wire -guiding rollers (38, 40) provided at the ends of a cutting section of the diamond wires;

characterized in that it comprises detection means for measuring the force applied by the diamond wires to the multi-wire frame during the cutting action.

2. Multi-wire frame according to Claim 1, characterized in that said detection means are designed to measure the force applied to at least one of the wire -guiding rollers (38, 40) during the cutting action.

3. Multi-wire frame according to Claims 1 or 2, characterized in that said detection means are designed to measure the force applied to both the wire -guiding rollers (38, 40) during the cutting action.

4. Multi-wire frame according to either one of Claims 2 or 3, characterized in that said detection means are designed to measure the force applied to the two ends (66, 68) of the spindle supporting each wire -guiding roller (38, 40) during the cutting action.

5. Multi-wire frame according to any one of the preceding claims, characterized in that said detection means are designed to measure the vertical component of the said force.

6. Multi-wire frame according to any one of the preceding claims, characterized in that it comprises movement means (44, 46) for adjusting the positioning of at least one of the wire -guiding rollers (38, 40).

7. Multi-wire frame according to the preceding claim, characterized in that it comprises movement means (44, 46) for adjusting the positioning of both the wire -guiding rollers (38, 40).

8. Multi-wire frame according to either one of Claims 6 or 7, characterized in that said movement means (44) comprise:

two support structures (48, 50) which are fixed to the corresponding slide (18, 20) by means of a fixing plate (52, 54),

a sliding seat (56) for an arm (58, 60); and

a linear actuator (70, 72).

9. Multi-wire frame according to Claim 2, characterized in that it comprises a block

(80) with a circular seat (82) inside which one of the two ends (66, 68) of the spindle supporting said wire -guiding roller (38, 40) may be inserted, said block (80) being mounted with play between a top projection (84) and a bottom projection (86) provided on a bracket (62, 64); said detection means comprising at least one load cell (88, 90) provided between said block and said bottom projection.

10. Multi-wire frame according to the preceding claim, characterized in that said block is fixed to the bottom projection by means of two load cells (88, 90) arranged in between and fixed to two lugs (92, 94) provided on the block.

11. Multi-wire frame according to Claims 9 or 10, characterized in that the load cells (88, 90) have a substantially circular shape with two grooves which are staggered and substantially parallel to the axis of the wire -guiding roller (38, 40) so as to form an "S".

12. Multi-wire frame according to any one of the preceding claims, characterized in that it comprises a programmable control unit for processing and managing the data supplied by the means for detecting the force applied to the multi-wire frame during the cutting action.

13. Method for cutting blocks of stone material into blocks by means of at least two diamond wires which are engaged against the top surface of the block to be cut by means of at least two drums (24, 26), at least one of which is motor-driven and between which at least two wires extend, each of said wires having a cutting section bounded at the ends by two wire -guiding rollers (38, 40),

characterized in that:

the force applied by the diamond wires along said cutting sections to at least one of said wire -guiding rollers (38, 40) is measured, said value of the force applied being used to adjust the lowering speed of said drums (24, 26).

14. Method according to the preceding claim, characterized in that the force value measured is used to calculate the lowering speed which allows a shorter time for sawing the block to be obtained.

15. Method according to Claim 13, characterized in that the force value measured is used to calculate the lowering speed which allows less wear of the rubber lining the grooves inside which the diamond wires slide to be obtained.

16. Method according to Claim 13, characterized in that the force value measured is used to calculate the lowering speed which allows a longer working life of the diamond wire to be obtained.

17. Method according to Claim 13, characterized in that the lowering speed is adjusted at regular intervals during machining by a programmable control unit.

18. Method according to any one of Claims 13-17, characterized in that the sliding speed of the diamond wires is kept in the range of between 27-32 m/min.