EP1323498A1

EP1323498A1 - Process to manufacture a diamond cutting tool with oriented crystals and cutting tool manufactured with said process

Info

Publication number: EP1323498A1
Application number: EP02102685A
Authority: EP
Inventors: Paolo Bernieri
Original assignee: Stalber Srl
Current assignee: Stalber Srl
Priority date: 2001-12-06
Filing date: 2002-12-05
Publication date: 2003-07-02
Anticipated expiration: 2022-12-05
Also published as: ATE350198T1; EP1323498B1; ITMI20012580A1; DE60217281D1

Abstract

The invention concerns a diamond cutting tool, of the type comprising a layer of diamond crystals (3) anchored onto its surface (2), preferably by electrolytic deposit or by chemical means. According to the invention, said layer is formed by oriented diamond crystals (3); moreover, the surface (2) of anchorage of the diamond crystals (3) is preferably inclined in respect of the bottom surface (Y-Y) of the cutting performed by said tool. The invention also concerns a process to manufacture such a diamond cutting tool, comprising at least a working step - known per se - to form a fixing layer of electrolytic metal apt to retain a single layer of diamond crystals (3) onto the surface (2) of a metallic supporting body (1), and a previous working step - according to the invention - to orient said diamond crystals (3) in a uniform manner; for this purpose, a vibration is imparted on said metallic supporting body (1) for a short time, from a few seconds to some minutes, while it is dipped into the mass of diamond crystals.

Description

As known, to separate marble or stone blocks in general from the wall of a quarry, and to convert them into slabs, use is increasingly made of special tools, called "diamond tools", which can be made in the form of "diamond wires" for use in quarries, or in the form of "diamond blades" or "diamond disks" for use in sawmills and workshops.
The present invention specifically concerns the aforecited "diamond wires". They are tools in the form of a steel wire plait having a diameter of 4 to 5 mm, onto which are inserted and fixed at regular intervals the so-called abrasive "pearls", which consist of elements, generally shaped as a small cylinder having a diameter of 8 to 10 mm, provided with an axial hole through which extends said steel wire plait. These diamond wire tools are used on special machines, such as pulleys, which are meant to draw the wire plait, formed as a closed ring, along a preset path.
The diamond wire is especially used in quarries, to separate the stone blocks from the walls, but it can also be used in workshops to perform size cuttings; its use however extends also to works of civil or industrial engineering in general.
Two techniques are mainly adopted to produce these diamond tools: the "sintering" of mixtures of metal powders and diamond crystals, and the "deposit" of diamond crystals onto a metallic support, which is more commonly carried out with an electrolytic system, but which can also be carried out chemically or by fixing in a furnace with nebulized metal alloys.
In the specific case of diamond wire, both these techniques are adopted to form the so-called pearls. In the case of pearls formed by sintering of metal powders and diamond crystals, the maintenance of the cutting capacity, during the working life of the diamond wire, is determined by the wear of the metal which incorporates the diamond crystals and which thus allows to gradually place in sight the underlying diamond crystals as those which lie on the surface, after having performed their working cycle, break off and subsequently drop out under the cutting pressure. However, as known, "sintered" pearls are comparatively more fragile and their life is often shorter, especially if used in hard working conditions.
Whereas, the pearls formed by deposit with the electrolytic system, or the like - which, undoubtedly, do not have the brittleness proper to the sintered pearls - have however the drawback that, at least in general, their cutting capacity is not always uniform.
In 1977, the document DE-A-27 02 936 proposed to manufacture diamond cutting tools - both with the sintering technique and with the technique of electrolytic deposit - by giving to the abrasive grains (that is, not only diamond crystals, but also grains other than crystals, such as carbide grains, silicon grains and the like) a kind of "orientation". Although the description of this patent does not indicate the preferred orientation, it is quite evident that the object of this orientation is to create a highest possible compaction of the abrasive granules. This also appears evident from the fact that, in order to obtain said orientation, the actions of the compressive forces, the centrifugal forces, the magnetic fields or the vibration forces, are considered as possible alternative techniques. These techniques would allow to overcome the drawbacks tied, on one hand, to the difficulty in obtaining a tool profile complying with the project and, on the other hand, to the risk of abrasive grains breaking off from the abrasive body; there is no mention, instead, of the problem tied to a non-uniform behaviour of the abrasive body during its working life.
In 1983, the document EP-B-0.090.274 of the same Applicant proposed to manufacture the pearls of the diamond wire merely with the technique of electrolytic deposit, or like, using however a supporting body in the form of a frustoconical element, instead of a cylindrical element. In this way, the consumption of the diamond crystals occurs more progressively in time and the pearl is apt to maintain its initial cutting capacities for a longer period of time. Also in this case, however, the drawback of a non-uniform behaviour - and besides fully casual - of the abrasive body, during its working life, remains unsolved.
Following the experience acquired by the Applicant - starting from the assumption that, as known, the diamond crystals remain anchored onto the surface of the metallic supporting body by means of the nickel layer of micrometrical thickness deposited with the electrolytic system - it has been deemed that said non-uniform behaviour could be mainly determined by the fact that the diamond crystals may casually find themselves, in a higher percentage, in a position placing in sight their portion with less cutting capacity.
The object of the present invention - starting from EP-B-0.090.274, considered as the most pertinent prior art, according to the present technological trend practically in every production sector - is to produce diamond wires having improved performances, that is, with a better and more uniform cutting capacity, which keeps unaltered from the start till the end of their working life, by means of a relatively simple manufacturing process.
According to the invention, said result is obtained with a diamond cutting tool as defined in claim 1, and with a manufacturing process as defined in claim 10 of the accompanying claims.
Further characteristics and advantages of the cutting tool structure and of the manufacturing process according to the present invention will anyhow be more evident from the following detailed description of some preferred embodiments thereof, given by way of non-limiting example and illustrated on the accompanying drawings, in which:
Figs. 1A and 1B diagrammatically illustrate the configuration of a diamond electrolytic deposit, in the case of demagnetized diamond crystals and, respectively, in the case of diamond crystals incorporating metallic residues;
Fig. 1 is a diagrammatic axial section view of a pearl with a frustoconical profile according to the invention, highly enlarged in respect of the normal size;
Fig. 2 is a view similar to that of fig. 1, but showing a pearl with a frustoconical profile having a different vertex angle; and
Figs. 3 to 11 illustrate different synthetic diamond crystals, each shown in two views, one perpendicular to its major face and the other one perpendicular to its edge.
For a proper understanding of the invention, it is first of all appropriate to synthetically point out the method adopted to industrially produce the so-called "diamond electrolytic deposit" on the surface of the pearl designed for the production of a diamond wire. The body of the pearl, or generally the metallic body meant to be sheathed with diamond, is dipped into a Watt container, in a solution of nickel salts, and connected to the cathode. As current passes through, the nickel starts to deposit onto the surface of the supporting body (initial step of the process).
As soon as an initial nickel layer - for example having a thickness of a few micron - has been deposited, a quantity of small diamond crystals, sufficient to cover the whole supporting body, is introduced in the container and the nickel deposit is continued, increasing the nickel layer up to substantially incorporating therein a single layer of crystals.
In order to obtain a final high-quality product, it is indispensable for the diamond crystals to be treated so as to remove any trace of metal from their surface (operation commonly known as "demagnetization"), particularly residues of the metallic catalysts present during the forming of the synthetic crystals in cells at high temperature and pressure. In fact, the metallic residues eventually retained on the surface of the crystals, could prevent from obtaining compact galvanic structures, for the following reasons:

the metal (for instance nickel) deposited by galvanization on the body supporting the diamond crystals should start from the surface of said body and gradually extend up to incorporating each crystal; but this is possible only if each diamond crystal is non-conductive (see fig. 1A: nickel deposit on the supporting body, which incorporates the base of the demagnetized diamond crystals);
whereas, if the crystals become conductive due to the metallic residues mentioned heretofore, the metallic ions of the galvanic process would not be attracted and deposited merely on the supporting body, but they would be attracted by the single crystals - to a greater or lesser extent, according to the amount of inclusions of metallic residues - thereby preventing a proper bond with the supporting body, or producing a very fragile and irregular bond (see fig. 1B: nickel deposit which covers the tip of the diamond crystal, with evident protruding points owing to high electric fields in correspondence of the conductive points, due to metallic residues, and with the lack of any basic bond).

When the nickel layer has deposited to an extent sufficient to "seize", that is, temporarily restrain said layer of crystals (intermediate step of the process), all the other crystals in excess are removed and the electrolytic deposit of nickel on the same supporting body is further continued, so as to complete the anchorage (final step of the process) onto said body of said single layer of diamond crystals.
Normally, the nickel deposit should reach (in said final step of the process) a thickness corresponding to about two thirds of the size of the diamond crystals. In the case of the present invention, it is preferable to use crystals having a size with a diameter between 0.1 and 0.9 mm, whereby the thickness of the nickel deposit should reach from 0.07 to 0.6 mm. This guarantees a reliable restraint of the crystals and, at the same time, an "exposure" thereof sufficient to guarantee the subsequent cutting action.
When wishing to follow a technique of deposit carried out chemically, or by treatment in a furnace with metallic powders, a substantially similar process is adopted. Consequently, when reference is made hereinafter to the technique of electrolytic deposit, it is understood that said reference concerns also the two other technique mentioned heretofore.
It is anyhow important to note that the industrial diamond used in all these cases is almost exclusively a synthetic diamond. For the production of synthetic diamonds use is made of different types of metallic catalysts, which determine the characteristics of the crystals both by affecting the shape of the crystals obtained, and for what concerns the type of metallic inclusion which they release and which characterizes the compactness and toughness of the crystal, as well as its thermostability. Although these diamond crystals are, obviously, all of the octahedron cube group, their shapes may actually differ in the way illustrated, for example, in the sequence of figs. 3 to 11. According to these characteristics it is hence possible to divide such crystals into classes, which allow a more specific choice of the kind of diamond which should be adopted in relation to the type of use being made thereof.
Starting therefore from the known technique of electrolytic deposit of the diamond, the invention proposes to introduce - between the step in which the initial nickel layer is formed (initial step of the process) and the step in which said layer seizes the diamond layer adhering thereto (intermediate step of the process) - a step in which the diamond crystals are oriented; this orientation is obtained by imparting a vibration on the supporting body. Thanks to said vibration, when each diamond crystal bears onto the surface of said vibrating body, it tends to orient itself in a preferential way typical of a certain class of diamonds - essentially characterized by the shape of the crystal - which actually corresponds to the position in which the major face of the crystal bears onto the surface of the supporting body. Consequently, by using crystals which are all of the same shape, one obtains a layer of crystals which are all uniformly oriented.
This uniform orientation of all the crystals is actually obtained after a relatively short vibration time, that is, from a few seconds to some minutes and preferably, for example, 30 seconds. As the vibration stops, these crystals keep still in the oriented position taken up - throughout the seizure step (intermediate step of the process) - thanks to the pressure which the diamond crystals in excess impart on the crystals of the layer bearing onto the supporting body.
It is thus possible to start, without any risks of displacements, the step of electrolytic deposit of nickel to form the initial fixing layer of the crystals (intermediate step of the process), and then the subsequent step to form the layer which completes the anchorage (final step of the process), as described heretofore with reference to prior art.
It is known that diamond crystal, under the effect of the cutting pressure, tends to break according to the midplanes typical of the diamond, whereby it can be easily understood that, by giving to all the crystals the same orientation it is possible to obtain tools with very constant cutting characteristics. Moreover, as such a tool wears out, the diamond crystals forming the same all wear to the same extent.
This technique - which, as said, has the advantage of a great uniformity of the tool cutting characteristics - provides, moreover, an additional advantage when applied to a diamond wire of the type described in EP-B-0.090.274. In fact, according to the fundamental characteristic of EP-B-0.090.274, the diamond wire is formed with pearls which, instead of having the known cylindrical shape, have a slightly frustoconical configuration; this configuration allows - as described in EP-B-0.090.274 - to use up the diamond layer far more progressively and effectively, placing in sight new diamond crystals as those which have acted at first wear out.
By carrying out the electrolytic deposit according to known technique, the drawback pointed out further above - namely, that the diamond crystals could find themselves, in a higher percentage, in a position placing in sight their portion with less cutting capacity - could occur at different times, thereby producing differences in the behaviour of said tool.
By applying the invention to a diamond wire according to EP-B-0.090.274, it has instead been possible not only to overcome the above drawback, but also to give the possibility to produce the frustoconical pearls with a vertex angle adjusted according to the type of work which the tool must carry out. It is in fact quite evident that the process according to the present invention allows, by presetting the cone angle of the frustoconical pearl, to orient the crystals according to the same angle and, consequently, to plan the specific pressure on the crystal required during the cutting operation. In view of this, it will even be possible to act so that the diamond crystals are fixed onto the surface of the supporting body in a position oriented with their sharpest cutting edge in sight. It will hence be possible to produce tools which can be more easily planned according to the type of use being made thereof.
Figs. 1 and 2 clearly illustrate how this possibility to plan the characteristics of the tool can be achieved, on one hand, by choosing the type and shape of the diamond (see fig. 3) and, on the other hand, by choosing the inclination angle a of the surface 2 of the pearl 1 supporting the diamond crystals 3, in respect of the bottom surface Y-Y of the cutting performed by the tool, which is besides parallel to the axis X-X of the actual pearl 1. The wider the angle a, the smaller the amount of crystals being simultaneously in contact with said cutting surface; in fact, in the diagram of fig. 2, the cutting concerns in theory only one diamond crystal 3'; whereas, in fig. 1, two crystals 3" are involved.
It is anyhow understood that the invention is not limited to the particular configurations described heretofore, which merely form non-limiting examples of its scope, but that several variants can be introduced, all within reach of an expert of the art, without thereby departing from the protection field of the present invention.

Claims

Diamond wire cutting tool - of the type comprising a plurality of pearls inserted and anchored onto a steel wire plait, each pearl forming a metallic supporting body (1), onto the surface (2) of which diamond crystals (3) are fixed by means of a micrometric layer of metal, deposited by electrolyzation or an equivalent process - characterized in that a single layer of diamond crystals (3) is fixed onto the surface (2) of the supporting body (1), and in that said diamond crystals (3) are oriented in a uniform manner, with one of their major faces bearing onto said surface (2).
Diamond wire cutting tool as in claim 1), characterized in that the diamond crystals (3) are fixed onto the surface (2) of said supporting body (1) oriented with their sharpest cutting edge in sight.
Diamond wire cutting tool as in claim 1), characterized in that the diamond crystals (3) derive from an industrial synthetic diamond, with no metallic inclusions.
Diamond wire cutting tool as in claim 1) or 3), characterized in that the diamond crystals (3) are demagnetized.
Diamond wire cutting tool as in claim 1), characterized in that the diamond crystals (3) have a size with a diamater between 0.1 and 0.9 mm.
Diamond wire cutting tool as in claim 1), characterized in that the diamond crystals (3) are restrained by a layer of electrolytic metal applied on the supporting body (1), which reaches a thickness corresponding to at least two thirds of the diameter of said diamond crystals (3).
Diamond wire cutting tool as in any one of the previous claims, characterized in that the surface (2) of said supporting body (1) is set inclined by a given angle (a) in respect of the axis (X-X) of said body (1), that is, in respect of the bottom surface (Y-Y) of the cutting performed by said tool.
Diamond wire cutting tool as in claim 7), characterized in that the inclination angle (a) of said surface (2) of the supporting body (1) is chosen according to the desired cutting characteristics of the tool.
Diamond wire cutting tool as in claim 7) or 8), characterized in that said supporting body (1) has a frustoconical configuration, known per se.
Process to manufacture diamond wire cutting tools as in any one of the previous claims, of the type comprising at least an intermediate working step, in which a metal layer is formed to seize diamond crystals (3, 3', 3") and fix them onto the surface (2) of a metallic supporting body (1), while a mass of diamond crystals adheres thereto,
characterized in that, said intermediate working step to form the metal fixing layer is preceded by a step in which the diamond crystals (3) are oriented so that one of their major faces is caused to bear onto the surface (2) of said supporting body (1), forming a single layer of diamond crystals (3).
Process as in claim 10), characterized in that said step to orient the diamond crystals (3) is carried out by imparting a vibration on said supporting body (1) while said mass of diamond crystals (3) adheres thereto.
Process as in claim 10), characterized in that said step to orient the diamond crystals (3) is carried out by imparting a vibration on the container of said mass of diamond crystals (3) into which is dipped said supporting body (1).
Process as in claim 11) or 12), characterized in that said step to orient the diamond crystals (3) is carried out by imparting a vibration both on said supporting body (1) and on the container of said mass of diamond crystals (3) into which is dipped said supporting body (1).
Process as in claim 11) or 12), characterized in that the vibrating action is imparted for a short time, from a few seconds to some minutes.
Process as in claim 14), characterized in that the vibrating action is imparted for about 30 seconds.
Process as in claim 10), characterized in that use is made of industrial synthetic diamond crystals (3), with no metallic inclusions.
Process as in claim 10) or 16), characterized in that the diamond crystals (3) are previously demagnetized.
Process as in claim 10), characterized in that use is made of diamond crystals (3) having a size with a diameter between 0.1 and 0.9 mm.
Process as in claim 10) or 18) characterized in that, in order to retain the diamond crystals (3), a layer of electrolytic metal is formed on the supporting body (1), having a thickness corresponding to at least two thirds of the diameter of the diamond crystals (3) forming said single layer.
Process as in any one of claims 10) to 19), wherein said intermediate working step to form the metal fixing layer is carried out by electrolyzation, with said metallic supporting body (1) dipped into an electroliytic bath and fully surrounded by a mass of diamond crystals, characterized in that said step to orient the diamond crystals (3) is preceded by an initial step, known per se, to form a micrometric layer of electrolytic metal onto which bear said diamond crystals (3) with one of their major faces.
Process as in any one of claims 10) to 19), wherein said intermediate working step to form the metal fixing layer is carried out by electrolyzation, with said metallic supporting body (1) dipped into an electrolytic bath and fully surrounded by a mass of diamond crystals, characterized in that said step to form the metal fixing layer is followed by a step, known per se, to form a stiffening layer allowing to strengthen the anchorage of said single layer of diamond crystals (3).
Process as in any one of claims 10) to 19), wherein said intermediate working step to form the metal fixing layer is carried out chemically, with said metallic supporting body (1) dipped into a bath of nickel salts and fully surrounded by a mass of diamond crystals, characterized in that said step to orient the diamond crystals (3) is preceded by an initial step, known per se, to form a micrometric layer of metal onto which bear said diamond crystals (3) with one of their major faces.
Process as in any one of claims 10) to 19), wherein said intermediate working step to form the metal fixing layer is carried out chemically, with said metallic supporting body (1) dipped into a bath of nickel salts and fully surrounded by a mass of diamond crystals, characterized in that said step to form the metal fixing layer is followed by a final step, known per se, to form a stiffening layer allowing to strengthen the anchorage of said single layer of diamond crystals (3).