EP0548239B1 - Excavating tool tooth - Google Patents

Abstract

The tooth according to the invention is composed, in the usual manner, of a mounting area (10) and a working area (11). The steel working area (11) comprises longitudinal bars made of a hard material (14-18). Said bars are inserted in the steel and snugly contact the tooth's cutting face. The presence of the rods made of a hard material substantially increases the tooth's service life. The bars are produced by infiltration.

Description

The present invention relates to excavation tools such as excavator wheels for mining or dredging cutters.

The excavator wheels comprise a drive wheel, pivoting about an axis and driven by means of rotation drive. The periphery of the shovel wheel carries a series of buckets equipped with teeth arranged in substantially radial orientations. Dredging strawberries do not have buckets, and their teeth are distributed around the periphery of a rotating ogival structure. Each tooth comprises a one-piece tooth body structure of metal or mechanically resistant alloy such as steel, having a fixing zone for attachment to the bucket or to the ogival structure, and a working zone for digging the ground. The working area is generally flat in the shape of a shovel, bounded by a leading face oriented in the direction of progression of the wheel periphery or of ogival structure in the preferential direction of rotation, a trailing face or face opposite to the attack face. The leading face and the trailing face are generally flat or slightly curved and are connected by a beveled front facet defining a transverse cutting edge. When the tooth is mounted on the bucket or the ogival structure, the transverse cutting edge is substantially parallel to the axis of rotation of the assembly, and the general plane formed by the tooth shovel or work area is generally inclined in the direction of tooth progression in the preferred direction of rotation.

During operation, the bucket or cutter scrapes, through part of its peripheral zone, into the ground, the teeth biting into the ground through the transverse cutting edge and repelling the material from the leading face. This results in significant wear of the transverse cutting edge and the leading face.

A usual solution to increase the service life and efficiency of the teeth is to recharge the outer surface of the attack face and the bevelled front facet to coat them with a layer of molten carbide, by melting a weld bead.

Although this process appreciably increases the life of the tooth, it can be seen that wear, relatively slow at the start of use when the hard material still covers the front facet, becomes much faster when the hard material covering the facet front was itself deteriorated by wear. The tooth can only be used until its working area has been reduced in length in too large proportions, defining the maximum admissible wear area of the tooth.

In particular, from the moment the front facet has lost its protective layer of hard material, wear becomes much faster, despite the existence of a layer of hard material on the leading face of the tooth.

Another disadvantage of the known structures is that they require the production of a protective hardfacing surface layer, a layer produced by fusion with a torch or an electric arc. For example, a deposit can be made consisting of a mixture of fused carbide grains embedded in a fusible matrix. Such reloading of a surface is long and tedious, and produces relatively irregular surfaces, consisting of the juxtaposition of several weld beads side by side. The intermediate zones between two successive beads are most often hollow zones whose metallurgical structure is slightly different from the central structure of the weld beads. This results in a lack of homogeneity of the material forming the protective layer of hard material, which leads to the appearance of preferential wear zones promoting faster wear of the material. In addition, such a process is expensive, and requires skilled labor.

Dredging teeth with a composite structure are also known, comprising a metal tooth body containing inserts made of hard abrasion-resistant material. Thus, in document US-A-3 805 423, a prefabricated insert is added in suitable housings of the metal tooth body, in which it is fixed by welding or brazing. The insert, in the embodiment of Figures 3 and 4, comprises two intermediate bars each occupying the half height of the tooth.

Document US-A-4,052,802 also teaches to provide a prefabricated insert added to the tooth body. The insert is sandwiched between metal surface plates, between which it is assembled by brazing. Thus, the insert does not occupy the entire height of the tooth. There is no suggestion in this document to replace the metal plates with hard grain material.

In document FR-A-2 373 500, an excavation tool is produced by providing cover plates of sintered carbide on a steel body. The steel body is cast around the cover plates. There is no suggestion in this document to replace the inner steel body with a hard grain material. It would result, moreover, a great brittleness of the tooth.

The structures and production methods described in documents US-A-4,052,802 and FR-A-2,373,500 are not compatible with one another. In fact, the production of a tooth with an internal insert with grains of hard material according to document US-A-4,052,802 is carried out by assembling several sub-assemblies by brazing, while document FR-A-2,373 500 provides for such assembly by overmolding. Those skilled in the art are therefore not encouraged to combine the teaching of these two documents.

In document US Pat. No. 3,286,379, fingers of hard material are produced by pouring hard material into longitudinal grooves of the metal tooth body. JP-A-62 99 527 describes a tooth for an excavation tool in which prefabricated inserts are formed from sintered carbide, and are joined to the tooth body by brazing.

It appears that these known structures with longitudinal inserts do not provide the expected results of efficiency and longevity. There is indeed still a fairly rapid wear of the tooth, in particular by erosion of the bars of hard material. The bars of hard material, which do not occupy the entire height of the tooth, do not provide a sufficient increase in longevity of the tooth, and their manufacturing process does not allow sufficient cohesion of the parts of such a heterogeneous structure.

The object of the present invention is in particular to avoid the drawbacks of the known structures of teeth of excavation tools and of their production methods, and firstly proposes a new composite structure of tooth comprising several longitudinal bars of hard material occupying the entire height of the tooth. The new tooth structure is compatible with the presence of protective surface layers of molten hard material, but can also be used in the absence of such a protective surface layer.

But one of the problems is that, by the usual methods of soldering or welding, it is difficult or difficult to insert and securely securing bars occupying the entire height of the tooth, without disturbing the mechanical properties of the abrasion-resistant material constituting the bars. The invention solves this difficulty by a new method of infiltration on the tooth blank itself.

The invention therefore proposes to produce such a tooth structure by means of a so-called infiltration process. The infiltration process can be implemented in a relatively simple manner, without requiring great dexterity of the user, unlike techniques of recharging with a weld bead, and leads to a reduction in the cost of production. The method avoids the need for a delicate step of welding or brazing an insert.

When using such an infiltration process, the tooth structure thus obtained is characterized in that the bars of hard material are bonded to the metal of the tooth body by a brazing alloy forming the matrix itself binding the grains hard material between them. This characteristic appears particularly important for obtaining a good cohesion effect between the bars of hard material and the metal forming the tooth body.

During the implementation of such an infiltration process, the molding structures are particularly reduced and simple to produce, since the metal parts of the tooth structure themselves function as a mold.

The invention makes it possible to considerably improve the longevity and efficiency properties of an excavation tool tooth, in surprising proportions compared to known techniques, for comparable amounts of hard material. During wear, the tooth remains sharp.

Finally, the risk of breakage or crumbling of the coating and of the bars of hard material is appreciably reduced, a risk which is often encountered in known teeth.

The invention therefore makes it possible to obtain better cohesion of the excavation tooth, better hardness of the bars of hard material, and greater ease of production.

To achieve these and other objects, the tooth for excavation tool according to the invention has a general structure similar to known teeth; however the working area of the tooth according to the invention comprises bars made of a base mixture of hard material grains bonded in a matrix, said bars being embedded in the metal of the tooth body and forming longitudinal bars substantially perpendicular to the transverse cutting edge. The longitudinal bars of hard material form a row of bars inserted into the interstices of a metal comb formed by the rest of the body structure. In the cross-sectional parts comprising the longitudinal bars with grains of hard material, grain material of hard material advantageously occupies the entire height of the tooth between the leading face and the trailing face.

According to one possibility, the longitudinal bars of hard material are separated from the front facet by a metal zone, or metal crosspiece. This structure facilitates the production of the tooth by infiltration, since the metal crosspiece then forms a mold part to contain the molten material intended to form the bars.

According to a particular embodiment, the longitudinal bars of hard material are connected to each other by bridges of hard material of height smaller than the bars and with which they form a plate of hard material constituting the central face face. attack. In this case, the front ends of the bars of hard material can advantageously be connected to each other by a crosspiece of hard material of height substantially equal to the height of the bars.

• la figure 1 est une vue en coupe transversale schématique d'une fraise de dragage ;
• la figure 2 est une vue de dessus d'une dent, montrant la face d'attaque ;
• la figure 3 est une vue de côté de la dent de la figure 2 ;
• la figure 4 est une vue de dessous de la dent de la figure 2, montrant la face de fuite ;
• les figures 5 à 7 montrent respectivement la face d'attaque, la vue de profil et la face de fuite d'une dent selon un autre mode de réalisation de l'invention ;
• la figure 8 est une coupe longitudinale en vue de côté selon le plan A-A de la figure 9 ;
• la figure 9 est une vue de dessus de la dent de la figure 5, en coupe longitudinale selon le plan B-B de la figure 8 ;
• la figure 10 est une coupe transversale selon le plan C-C de la figure 9 ;
• les figures 11, 12 et 13 sont des vues similaires des figures 8, 9 et 10 respectivement dans un second mode de réalisation de l'invention ;
• les figures 14, 15 et 16 sont des vues similaires des figures 8, 9 et 10 dans un troisième mode de réalisation de l'invention ;
• les figures 17, 18 et 19 sont des vues similaires des figures 8, 9 et 10 respectivement pour un troisième mode de réalisation de l'invention ;
• les figures 21 et 22 sont des vues similaires des figures 9, 10 respectivement pour un quatrième mode de réalisation selon l'invention, la figure 20 étant une coupe longitudinale selon le plan D-D de la figure 21 ; et
• les figures 23 à 27 illustrent les étapes d'un procédé de réalisation de dents selon l'invention par infiltration.

Other objects, characteristics and advantages of the present invention will emerge from the following description of particular embodiments, given in relation to the attached figures, among which:

• Figure 1 is a schematic cross-sectional view of a dredging cutter;
• Figure 2 is a top view of a tooth, showing the leading face;
• Figure 3 is a side view of the tooth of Figure 2;
• Figure 4 is a bottom view of the tooth of Figure 2 showing the trailing face;
• Figures 5 to 7 respectively show the leading face, the side view and the trailing face of a tooth according to another embodiment of the invention;
• Figure 8 is a longitudinal section in side view along the plane AA of Figure 9;
• Figure 9 is a top view of the tooth of Figure 5, in longitudinal section along the plane BB of Figure 8;
• Figure 10 is a cross section along the plane CC of Figure 9;
• Figures 11, 12 and 13 are similar views of Figures 8, 9 and 10 respectively in a second embodiment of the invention;
• Figures 14, 15 and 16 are similar views of Figures 8, 9 and 10 in a third embodiment of the invention;
• Figures 17, 18 and 19 are similar views of Figures 8, 9 and 10 respectively for a third embodiment of the invention;
• Figures 21 and 22 are similar views of Figures 9, 10 respectively for a fourth embodiment according to the invention, Figure 20 being a longitudinal section along the plane DD of the Figure 21; and
• Figures 23 to 27 illustrate the steps of a method of producing teeth according to the invention by infiltration.

In the embodiment schematically illustrated in FIG. 1, an excavation tool such as a dredger for dredging or a shovel wheel for mining generally comprises a rotary support structure 1, rotatably mounted on a drive axis 2 and solicited by means for driving in rotation along a preferential axis of rotation represented by the arrow 3. The periphery 4 of the rotary supporting structure carries teeth such as tooth 5, in generally radial orientations slightly inclined in the direction of direction 3 preferential rotation, as shown in the figure. The teeth are all normally identical. The tooth 5 comprises a leading face 6 oriented towards the preferred direction of rotation 3, an opposite trailing face 7, and a front facet 8 defining a transverse cutting edge 9. The transverse cutting edge 9 is substantially parallel to the axis of rotation 2 of the wheel.

The tooth 5 is shown in more detail in Figures 2 to 4. Figures 2 to 4 show only the outer surface of the tooth, which can be a traditional tooth or a tooth according to the present invention.

As shown in FIGS. 2 to 4, an excavation tool tooth according to the invention comprises a tooth body structure of metal or mechanically resistant alloy such as steel, having a fixing zone 10 for the attachment to the drive wheel structure, and a work area 11 for digging the ground. The attachment zone 10 may be of the traditional type, and has no particular effect as regards the present invention. The invention relates to work area 11.

The working area 11 is generally flat in the form of a shovel bounded by the leading face 6, the trailing face 7, the front facet 8 and two lateral edges 12 and 13. The leading face 6 and the trailing face 7 are generally flat and slightly curved, possibly parallel to each other. The front facet 8 is inclined at a bevel. The tooth thus has a transverse cutting edge 9.

Traditional teeth generally have layers of hard material coating such as grain-based layers. molten tungsten carbide embedded in a metal matrix. The leading face 6, the front facet 8 and the side edges 12 and 13 are covered with a protective layer of hard material.

The structure according to the invention is particularly characterized by the presence and the shape of hard material zones embedded in the metal structure of the working zone 11. Such hard material zones are apparent for example in the embodiment of FIGS. 5 to 7: in FIG. 5, five rectangular zones 14, 15, 16, 17 and 18 appear respectively on the leading face 6. The hard material, consisting of a mixture based on grains of hard material linked in a matrix, comes flush with the attack face 6 along the five rectangular zones, of longitudinal axis, regularly spaced from one another. The rectangular areas come close to the transverse cutting edge 9, without however touching the edge. Likewise, similar rectangular zones 19, 20, 21, 22 and 23 appear on the trailing face 7 shown in FIG. 7. In reality, the respective zones such as zone 17 in FIG. 5 and zone 22 in the FIG. 7 are the visible faces of a bar 24 (FIG. 8) made of hard material inserted in a slot passing through the metal forming the basic structure of the working area 11.

Figures 8 to 10 show the tooth of Figures 5 to 7, according to different transverse and longitudinal sections. Thus, Figure 8 is a longitudinal section, along a plane perpendicular to the leading face 6 and cutting the bar of hard material 24 of Figure 9 corresponding to the surfaces 17 of Figure 5 and 22 of Figure 7. The material of the bar 24 is laterally limited by two intermediate metal beams 25 and 26, by the base 27 of the metal structure of the working area, and by a metal end cross member 28. The material of the bar 24 is flush with the face of attack 6 to form the rectangular area 17, and is flush with the trailing face 7 to form the rectangular area 22.

In this embodiment, the metal part of the working area 11 has a series of longitudinal slots separated by side members, for example six side members 25, 26, 29, 30, 31 and 32 defining five slots for receiving five bars 24, 33 , 34, 35 and 36. The longitudinal slots are filled with hard abrasion-resistant material such as tungsten carbide or the like. The metal beams are all connected on the one hand to the base of the metal structure 27 and on the other hand to the front metal cross member 28.

In this embodiment, the outer faces of the tooth are not covered with a wear-resistant protective layer based on hard material. The presence of internal zones of hard material such as the bar 24 is sufficient to considerably delay the wear of the tooth.

The structure shown in Figures 11 to 13 is similar to that of Figures 8 to 10: the internal structure is identical; the only difference is the presence of a protective outer layer 100 of hard material, such as grains of molten tungsten carbide bonded by a metal matrix, the outer face of said protective layer forming the leading face 6, the front facet 8 and the side edges 12 and 13. The external appearance of such a tooth is identical to that shown in FIGS. 2 to 4.

The embodiment shown in FIGS. 14 to 16 is similar to that of FIGS. 11 to 13, and differs therefrom by the fact that the metal crosspiece 28 is eliminated. In this case, the metal beams such as the beams 25 and 26 have free anterior ends which do not meet, and the space 24 is an open slot. The metal beams thus form a sort of comb, the interstices of which are occupied by a row of bars made of hard material. The hard material filling the interstices such that the space 24 propagates to the protective layer 100, the outer face of which forms the front cutting facet 8. As a variant, the same internal tooth structure may be used, devoid of a protective layer. 100 outdoor.

In the embodiment of FIGS. 17 to 19, the structure is similar to that of the embodiment of FIGS. 14 to 16. It differs therefrom by the fact that, in the anterior zone of the side edges 12 and 13, the thickness of the protective layer 100 of hard material is increased. These zones in fact constitute zones of preferential wear, subject to wear stresses greater than those undergone by the other working parts of the tooth. It has been found that a slight increase in the thickness of the protective layer in these two lateral parts leads to a significant increase in the longevity of the tooth.

The embodiment of FIGS. 20 to 22 differs from the previous embodiments in that bridges of hard material are provided to connect the successive internal bars of hard material of the tooth. As in the embodiment of FIGS. 8 to 10, the metal structure of the tooth comprises a metal base 27 to which the intermediate beams 25, 26, 29 and 30 are connected as well as two lateral beams 31 and 32. The front ends of the side rails 31 and 32 are connected by the metal cross member 28. The metal intermediate beams 25, 26, 29 and 30 have free anterior ends set back from the metal cross member 28. The hard material thus forms the longitudinal bars 24, 33, 34, 35 and 36, and the front ends of the bars are connected to each other by a cross member 37 of hard material. The crosspiece 37 of hard material can advantageously occupy the entire height of the active tooth part, that is to say the entire distance separating the leading face 6 and the trailing face 7, as shown in FIG. 20. In this case, during use, the metal cross member 28 wears out fairly quickly, and reveals the cross member 37 made of hard material which prevents wear. Likewise, the metal side rails 31 and 32 wear out fairly quickly, and then reveal the lateral bars of hard material 33 and 36, which prevent wear.

In this same embodiment, the longitudinal bars of hard material are connected to each other by bridges of hard material of height smaller than the bars and with which they form a plate of hard material constituting the central part of the face d 'attack 6. Thus, as shown in Figure 22 in cross section, the longitudinal bars of hard material 24 and 33 are connected by the bridge 38. Figure 20 is a section along the longitudinal plane DD of Figure 21, and represents the longitudinal section of this same bridge 38. The bridges 39, 40 and 41 connect two by two the other longitudinal bars of hard material. In other words, the intermediate metal beams have a lower height than the total height of the active tooth part, so that the hard material covers the intermediate longitudinal bars on the leading face 6 of the tooth.

In all the embodiments which have been described, the bars of hard material can have a thickness of 4 to 15 approximately millimeters, and be separated by metal zones or metal beams whose thickness is approximately 4 to 15 millimeters. The thickness is defined as the dimension in a direction parallel to the transverse cutting edge 9. The length of the bars of hard material is substantially equal to the length of the maximum admissible wear area of the tooth. The hard material constituting the longitudinal bars may advantageously contain grains of molten tungsten carbide, preferably spheroidal grains free of angular zones. Improved anti-wear characteristics are obtained by using a mixture of grains of different calibers, some of the grains of molten tungsten carbide having a diameter equal to or greater than 2 millimeters.

• a) selon la figure 23, réaliser une ébauche 42 en métal ou alliage, comprenant la zone de fixation 10 et la partie métallique de zone de travail 11, ladite partie métallique de zone de travail comportant une série de fentes longitudinales 43 débouchant sur la face d'attaque 6 et sur la face de fuite 7 et séparées par des longerons 25, 26, 29, 30, 31, 32 ;
• b) selon la figure 24, disposer ladite ébauche 42 sur un support 44 avec sa face d'attaque 6 au dessus et en orientation sensiblement horizontale ;
• c) selon la figure 25, remplir lesdites fentes longitudinales 43 avec des particules de matière dure anti-abrasion 45 telle que le carbure de tungstène fondu ou similaire, en vibrant l'ensemble, de sorte que les particules viennent au maximum en appui contre les parois des fentes et sont jointives les unes aux autres ;
• d) selon la figure 25, préparer une quantité suffisante d'un alliage approprié 46 sous forme adaptée pour assurer une répartition ultérieure de l'alliage au cours d'une phase de fusion ultérieure, l'alliage étant un alliage de brasage susceptible de mouiller les particules de matière dure 45 et la matière formant l'ébauche 42 et de fondre à une température inférieure à la température de fusion de l'ébauche 42 et du support 44 ;
• e) selon la figure 26, chauffer l'ensemble à une température supérieure à la température de fusion de l'alliage 46 et inférieure à la température de fusion de l'ébauche 42 et du support 44, pour assurer l'infiltration de l'alliage en fusion entre les particules de matière dure 45 ;
• f) selon la figure 27, laisser refroidir et séparer la pièce obtenue de son support.

According to the invention, the preferred method shown in FIGS. 23 to 27, for producing the internal zones of hard material such as the longitudinal bars, comprises the following steps:

• a) according to FIG. 23, make a blank 42 of metal or alloy, comprising the fixing zone 10 and the metal part of the work zone 11, said metal part of the work zone comprising a series of longitudinal slots 43 opening onto the face 6 and on the trailing face 7 and separated by side members 25, 26, 29, 30, 31, 32;
• b) according to FIG. 24, placing said blank 42 on a support 44 with its leading face 6 above and in substantially horizontal orientation;
• c) according to FIG. 25, filling said longitudinal slots 43 with particles of hard abrasion-resistant material 45 such as molten tungsten carbide or the like, vibrating the assembly, so that the particles come to bear as much as possible against the walls of the slots and are joined to each other;
• d) according to FIG. 25, preparing a sufficient quantity of an appropriate alloy 46 in a form suitable for ensuring a subsequent distribution of the alloy during a subsequent melting phase, the alloy being a brazing alloy capable of wetting the particles of hard material 45 and the material forming the blank 42 and melt at a temperature below the melting temperature of the blank 42 and the support 44;
• e) according to FIG. 26, heat the assembly to a temperature higher than the melting temperature of the alloy 46 and lower than the melting temperature of the blank 42 and the support 44, to ensure the infiltration of the molten alloy between the hard material particles 45;
• f) according to FIG. 27, allow to cool and separate the part obtained from its support.

In the embodiment described in relation to FIGS. 23 to 27, the blank 42 is such that the intermediate metal beams 25, 26, 29 and 30 are set back from the leading face 6 defined by the end beams 31 and 32. In this way, during the filling and infiltration step of FIG. 25, the hard material 45 fills the slots 43 and covers the intermediate beams 25, 26, 29 and 30 to form a plate of infiltrated hard material 47, shown in FIG. 27, forming the central zone of the attack face 6.

Alternatively, the front ends of the end rails 31 and 32 are connected to each other by a metal cross member such as the cross member 28 shown in Figure 20, while the intermediate side members 25, 26, 29 and 30 have a free end separated from the cross member 28 by an interval. In this way, during the filling and infiltration step illustrated in FIG. 25, the hard material 45 fills said gap separating the free ends of the intermediate beams and the metal cross member 28, to form a cross of hard material 37 such as shown in Figures 20 and 21.

The method is compatible with a subsequent step during which a surface coating 100 of hard material can be produced on the leading face 6 and the front facet 8, as shown in FIGS. 11 to 16. The surface coating 100 of material hard can for example be made by welding with a torch or an electric arc of a weld bead, according to conventional methods of reloading by welding.

• meulage ou grenaillage de la surface,
• métallisation d'un voile d'alliage de type nickel/chrome/bore/silicium autofusible, à l'aide d'un chalumeau.

To improve the cohesion between the metal structure of the tooth body and the parts made of hard material, recourse may be had, before infiltration-welding, to a prior step of preparing the surface of the blank to be in contact with the hard material. Preparation can include the following phases:

• surface grinding or shot blasting,
• metallization of an alloy veil of nickel / chromium / boron / autofusible silicon type, using a torch.

The present invention is not limited to the embodiments which have been explicitly described, but it includes the various variants and generalizations thereof contained in the field of claims below. It is possible in particular, without departing from the scope of the invention, to provide a number of bars of hard material other than five, sections of bars different from the rectangular section, non-planar shapes of leading face and trailing face of tooth.

Claims (15)

1. Tooth for excavating tool such as a dredger or revolving cutter head excavator for use in mines consisting of a tooth body structure made of a mechanically resistant metal or alloy having a fixing area (10) to join it to a drive structure (1) and a working area (11) to dig the soil, the working area (11) generally being flat, shaped like a shovel and limited by a leading face (6) and a trailing face (7) which are generally flat or slightly curved and connected by a front tapered facet (8) that defines a transverse cutting edge (9), the working area (11) consisting of a row of bars (24, 33, 34, 35, 36) consisting of a mixture based on particles of hard material bonded in a matrix, the said bars being longitudinal and essentially perpendicular to transverse cutting edge (9) and forming a row of bars inserted in the interstices of a metal comb with several spars (25, 26, 29, 30, 31, 32) made up by the rest of the body structure characterised in that, in those parts of the cross section that include longitudinal bars made of particles of hard material (24, 33, 34, 35, 36), the material with particles of hard material takes up the entire height of the tooth between the leading face (6) and the trailing face (7).
2. Tooth according to claim 1 characterised in that the longitudinal bars made of hard material (24, 33, 34, 35, 36) are separated from the front facet (8) by a metal crosspiece (28).
3. Tooth according to claim 2 characterised in that the longitudinal bars made of hard material (24, 33, 34, 35, 36) are linked to each other by bridges of hard material (38, 39, 40, 41) of which the height is less than that of the bars and with which they form a plate of hard material (47) which constitutes the central part of leading face (6).
4. Tooth according to claim 3 characterised in that the front ends of the bars of hard material (24, 33, 34, 35, 36) are joined to each other by a crosspiece made of hard material (37) of which the height essentially equals the height of the bars.
5. Tooth according to any of claims 1 to 4 characterised in that the bars made of hard material (24, 33, 34, 35, 36) are roughly 4 to 15 mm thick and are separated by metal areas (25, 26, 29, 30) which are roughly 4 to 15 mm thick.
6. Tooth according to any of claims 1 to 5 characterised in that the bars made of hard material (24, 33, 34, 35, 36) are essentially as long as the length of the maximum permissible area of wear of the tooth.
7. Tooth according to any of claims 1 to 6 characterised in that the leading face (6), front facet (8) and the lateral edges (12, 13) are covered in a layer (100) of material based on particles of hard material bonded in a matrix.
8. Tooth according to any of claims 1 to 7 characterised in that the longitudinal bars made of hard material (24, 33, 34, 35, 36) contain particles of molten tungsten carbide.
9. Tooth according to claim 8 characterised in that some of the particles of molten tungsten carbide have a diameter equal to or greater than 2 mm.
10. Tooth according to any of claims 1 to 9 characterised in that the bars made of hard material (24, 33, 34, 35, 36) are bonded to the metal of the tooth body by a brazing alloy forming the said matrix that links the particles of hard material.
11. Process to produce a tooth according to claims I to 10 for an excavating tool such as a dredger or revolving cutter head excavator for use in a mine of the type consisting of a tooth body structure made of metal or alloy which is mechanically resistant having a fixing area (10) to join it to a drive structure (1) and a working area (11) to dig the soil, the working area generally being flat and shovel shaped and limited by a leading face (6) and a trailing face (7) which are generally flat or slightly curved and connected by a tapered front facet (8) defining a transverse cutting edge (9), the working area consisting of bars (24, 33, 34, 35, 36) consisting of a mixture based on particles of hard material bonded in a matrix, the said bars being embedded in the metal of the tooth body and forming longitudinal bars that are essentially perpendicular to transverse cutting edge (9), this process being characterised in that it comprises the following steps:

    a) Produce a blank (42) made of metal or alloy consisting of the fixing area (10) and the working area metal part (11), the said working area metal part consisting of a series of longitudinal slots (43) opening out into leading face (6) and trailing face (7) and separated by spars (25, 26, 29, 30, 31, 32);

    b) Place the said blank (42) on a mounting (44) with its leading face (6) upwards and in an essentially horizontal direction;

    c) Fill the said longitudinal slots (43) with particles of a hard anti-abrasion material (45) such as molten tungsten carbide or the like, vibrate this assembly so that the particles are in as close as possible contact with the walls of the slots and are contiguous with each other;

    d) Prepare a sufficient quantity of an appropriate alloy (46) in a form suitable to ensure subsequent distribution of the alloy during a subsequent melting phase, the alloy being a brazing alloy capable of wetting the particles of hard material (45) and the material which forms the blank (42) and of melting at a temperature less than the melting point of the blank (42) and the mounting (44);

    e) Heat this assembly to a temperature higher than the melting point of the alloy (46) and lower than the melting point of the blank (42) and the mounting (44) in order to ensure infiltration of the molten alloy between the particles of hard material (45);

    f) Allow to cool and separate the piece thus obtained from its mounting.
12. Process according to claim 11 characterised in that it includes an initial operation to prepare the surface of the blank which is in contact with the hard material, this preparation stage consisting of the following phases:

    - Grinding or shot blasting of the surface,

    - Plating of a thin film of alloy of the self-fusing nickel-chrome-boron-silicon type by means of a welding torch.
13. Process according to any of claims 11 or 12 characterised in that:

    - The blank (42) is such that the intermediate metal spars (25, 26, 29, 30) are offset from leading face (6) defined by the outer spars (31, 32),

    - During the filling and infiltration stage, the hard material (45) fills the slots (43) and covers the intermediate spars to make a plate of infiltrated hard material (47) forming the central area of leading face (6).
14. Process according to claim 13 characterised in that:

    - The front ends of the outer spars (31, 32) are linked to each other by a metal crosspiece (28) whereas the intermediate spars (25, 26, 29, 30) have a free end that is separated from the metal crosspiece (28) by a gap,

    - During the filling and infiltration phase, the hard material (45) fills the said gap separating the free ends of the intermediate spars and the metal crosspiece (28) to form a crosspiece of hard material (37).
15. Process according to any of claims 11 or 12 characterised in that it includes a subsequent stage to produce a surface coating (100) of hard material that covers, in particular, leading face (6) and front facet (8) by fusing a welding bead.

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