EP4450164A1 - One-piece composite milling roller - Google Patents

Abstract

The present invention relates to a single-piece grinding roller (1) for vertical axis grinders produced by casting a metal matrix in a foundry, said roller comprising at its periphery an openwork reinforcement structure (2) consisting of a plurality of ceramic inserts assembled in a jointed manner, the jointed assembly of the ceramic reinforcements being produced along wavy lines.

Description

Subject of the invention

The present invention relates to a composite wear part made in a foundry by casting a ferrous alloy. It relates more particularly to a single-piece grinding roller reinforced by an openwork ceramic structure integrated into the roller with a specific assembly of the reinforcement elements possibly adapted to the wear stress by practicing differentiated openwork. It also discloses a method of manufacturing said roller.

State of the art

Composite wear parts made in foundries are well known to those in the art. They are mainly cast iron parts reinforced locally and in a targeted manner by alumina-zirconia ceramics or carbides, nitrides, borides or other intermetallic elements, on the faces most exposed to wear. These ceramics have studied geometries and are adequately located within the metal matrix.

The particular arrangement of the reinforcement structures makes it possible to create hierarchical composites with differentiated reinforcement depending on the arrangement or geometric shape of the ceramic reinforcements, which are generally composed of aggregates of grains that can be infiltrated by the casting metal. This is how aggregates of granules measuring on average 3 to 8 mm can be produced with gaps of around 1 to 3 mm allowing infiltration by the liquid cast iron during casting. It is thus possible to form "cakes" or "wafers" in the form of openwork structures such as honeycombs, for example. These "inserts" are generally arranged in a studied manner inside a sand mold on the most stressed face of the wear part. These "inserts" are called "padding" in English. When these cakes are infiltrated individually, before being arranged once cooled in the casting mold, they are called bars.

The present invention aims to improve the wear resistance of grinding rollers for mills in general and in particular for so-called vertical axis mills. Vertical axis mills are used for example for grinding coal, raw material or cement clinker. They consist of a rotating track supporting rollers which are driven by the rotary movement of the track along the axis vertical (see figure 1 ). The material to be ground is fed through a central feed path and falls onto the track, where it is crushed and ground by the rollers. This principle is illustrated in detail in figure 2 . The crushed material is then centrifuged out to the periphery of the track and collected in a wind tunnel with a cyclone to recycle the material that has not yet been sufficiently crushed. Various types of roller shapes are possible, with truncated rollers and toric rollers being the most common.

The documents WO98/15373 discloses a composite wear part made in a foundry with a honeycomb-shaped ceramic reinforcement and an alumina-zirconia-based ceramic.

The document WO2005/084809 discloses a grinding roller comprising several peripheral bars made of a material with high wear resistance mechanically sealed in a die cast in ductile material, said roller comprising areas subject to high wear stress as well as areas subject to low wear stress, the roller having on its peripheral face bars comprising a contiguous part in the area subjected to the most stress and a non-contiguous part in the area subjected to the least wear stress, the gap in the non-contiguous part being filled by the ductile material of the casting die allowing mechanical sealing of the bars.

The document WO2018/069006 discloses a grinding roller for vertical axis crushers produced in a foundry by casting a metal matrix, the roller comprising at its periphery a plurality of reinforcing inserts, certain portions of the peripheral surface of the same insert being located at different distances from the periphery of the roller depending on the wear stresses.

The document WO 2021/1160381 discloses a grinding roller where the areas subject to wear are reinforced in a differentiated manner with ceramic inserts comprising blind holes and through holes, the blind side of the blind holes being oriented towards the side most subjected to wear.

Aims of the invention

The present invention aims to provide a single-piece composite grinding roller with a ceramic reinforcement composed of a plurality of inserts of an improved geometry, both the structure and the positioning of which are adapted to the wear stress. It aims in particular to eliminate the straight lines between the adjoining ceramic inserts which constitute propagation initiations and preferred paths for wear.

Summary of the invention

The present invention discloses a single-piece grinding roller for vertical axis grinders produced by casting a metal matrix in a foundry, said roller comprising at its periphery an openwork reinforcement structure consisting of a plurality of ceramic inserts assembled in a jointed manner, the jointed assembly of the ceramic reinforcements being produced along wavy lines.

• La structure de renfort 2 comporte au moins une première zone 21, la moins ajourée et la plus exposée à l'usure et au moins une seconde zone 22, la plus ajourée et la moins exposée à l'usure ;
• les premières et secondes zones 21 et 22 de la pluralité d'inserts en céramique sont formés par plusieurs anneaux superposés, lesdits inserts étant assemblés en quinconce de manière jointive selon des lignes ondulées ;
• l'ajourage de la première zone 21, la plus exposée à l'usure, est formé par des trous passants de forme tronconiques 3 avec un diamètre allant en se réduisant vers la périphérie du galet ou par une association de trous passants de forme quelconque 4 avec des trous borgnes dont le côté borgne est situé du côté de la périphérie du galet ;
• l'ajourage de la seconde zone 22, la moins exposée à l'usure, est formé par des trous passants de forme quelconque 4, de préférence de forme cylindrique et positionné de manière perpendiculaire ou inclinée par rapport à la surface à la périphérie du galet ;
• la pluralité d'inserts est assemblée pour former un galet tronconique ou un galet torique ;
• l'amplitude (a) des lignes ondulées représente entre 2 et 20 %, de préférence entre 5 et 15 % par rapport à la longueur « L » de l'insert en céramique ;
• l'amplitude (A) des lignes ondulées représente entre 2 et 20 %, de préférence entre 3 et 15 %, par rapport à la largeur « ℓ _» de l'insert en céramique ;
• la composition de la céramique de la structure de renfort est choisie parmi des oxides, des carbures, des nitrures et des borures ;
• les inserts en céramique comportent un agrégat de grains composites de céramique-métal dans lesquels des particules micrométriques de céramique sont cimentés dans un liant métallique, les grains composites ayant un taille moyenne D₅₀ de 2 à 8 mm, de préférence de 3 à 6 mm déterminée par tamisage avec une maille carrée ou par un Camsizer de Retsch selon la norme 13322-2 :2006;
• les grains composites de céramique-métal comportent du carbure de titane d'une taille moyenne D₅₀ comprise entre 3 et 20 µm, de préférence entre 5 et 15 µm cimenté dans un liant métallique, la taille de particules étant mesurable par diffraction laser en utilisant la théorie MIE selon les directives données dans la norme ISO 13320:2020 en utilisant par exemple un Mastersizer 2000 de Malvern et en fixant un indice de réfraction à 3 et un indice d'absorption à 1. L'obscuration doit se trouver dans une plage entre 10 et 15 % et le résidu pondéral moins de 1 %;
• la composition de la céramique de la structure de renfort de la première zone 21 est différente de la composition de la céramique de la seconde zone 22.

Preferred embodiments of the invention include at least one, or any suitable combination of the following features:

• The reinforcement structure 2 comprises at least a first zone 21, the least openwork and the most exposed to wear, and at least a second zone 22, the most openwork and the least exposed to wear;
• the first and second zones 21 and 22 of the plurality of ceramic inserts are formed by several superimposed rings, said inserts being assembled in a staggered manner in a contiguous manner along wavy lines;
• the opening of the first zone 21, the most exposed to wear, is formed by through holes of truncated cone shape 3 with a diameter decreasing towards the periphery of the roller or by an association of through holes of any shape 4 with blind holes whose blind side is located on the side of the periphery of the roller;
• the opening of the second zone 22, the least exposed to wear, is formed by through holes of any shape 4, preferably cylindrical in shape and positioned perpendicularly or inclined relative to the surface at the periphery of the roller;
• the plurality of inserts are assembled to form a truncated cone roller or a toric roller;
• the amplitude (a) of the wavy lines represents between 2 and 20%, preferably between 5 and 15% relative to the length “L” of the ceramic insert;
• the amplitude (A) of the wavy lines represents between 2 and 20%, preferably between 3 and 15%, relative to the width “ ℓ _” of the ceramic insert;
• the composition of the ceramic of the reinforcement structure is chosen from oxides, carbides, nitrides and borides;
• the ceramic inserts comprise an aggregate of ceramic-metal composite grains in which micrometric ceramic particles are cemented in a metallic binder, the composite grains having an average size D ₅₀ of 2 to 8 mm, preferably 3 to 6 mm determined by sieving with a square mesh or by a Retsch Camsizer according to standard 13322-2:2006;
• the ceramic-metal composite grains comprise titanium carbide of an average particle size D ₅₀ of between 3 and 20 µm, preferably between 5 and 15 µm cemented in a metallic binder, the particle size being measurable by laser diffraction using MIE theory according to the guidelines given in ISO 13320:2020 using for example a Malvern Mastersizer 2000 and setting a refractive index of 3 and an absorption index of 1. The obscuration must be in the range of 10 to 15% and the weight residue less than 1%;
• the composition of the ceramic of the reinforcement structure of the first zone 21 is different from the composition of the ceramic of the second zone 22.

• mise à disposition d'un moule pour la réalisation d'un galet de broyage monobloc par coulée d'un alliage ferreux ;
• positionnement d'une structure de renfort composée d'une pluralité d'inserts en céramique et assemblés de manière jointive selon des lignes ondulées, les inserts se présentant sous forme d'agrégats de granulés millimétriques ajourés, l'agrégat étant perméable et donc infiltrable;
• infiltration de l'insert par l'alliage ferreux liquide.
• refroidissement et démoulage du galet de broyage.

The present invention also discloses a method for producing a grinding roller according to the invention comprising the following steps:

• provision of a mold for the production of a single-piece grinding roller by casting a ferrous alloy;
• positioning of a reinforcement structure composed of a plurality of ceramic inserts and assembled in a jointed manner along wavy lines, the inserts being in the form of aggregates of openwork millimetric granules, the aggregate being permeable and therefore infiltrable;
• infiltration of the insert by the liquid ferrous alloy.
• cooling and demolding of the grinding roller.

• l'alliage ferreux comporte de l'acier ou de la fonte ;
• la structure de renfort comporte au moins une première zone 21, la moins ajourée et la plus exposée à l'usure et au moins une seconde zone 22, la plus ajourée et la moins exposée à l'usure ;
• les agrégats infiltrables de granulés millimétriques de céramique utilisés pour les inserts des galets de broyage sont sélectionnés parmi les compositions suivantes:
  • ∘ alumine-zircone dans des proportions 90/10 à 10/90, la zircone étant éventuellement stabilisée à l'oxyde d'yttrium;
  • ∘ carbone et titane en poudre comportant optionnellement de la poudre de fer en tant que modérateur et précurseurs d'une réaction de synthèse thermique autopropagée (SHS) initiée par la coulée de l'alliage ferreux;
  • ∘ composites céramique-métal de carbure de titane cimenté dans un liant métallique.

The method according to the invention preferably comprises at least one, or any suitable combination of the following characteristics:

• ferrous alloy includes steel or cast iron;
• the reinforcement structure comprises at least a first zone 21, the least openwork and the most exposed to wear and at least a second zone 22, the most openwork and the least exposed to wear;
• The infiltrable aggregates of millimetric ceramic granules used for the inserts of the grinding rollers are selected from the following compositions:
  • ∘ alumina-zirconia in proportions 90/10 to 10/90, the zirconia being optionally stabilized with yttrium oxide;
  • ∘ carbon and titanium powder optionally comprising iron powder as a moderator and precursors of a self-propagating thermal synthesis (SHS) reaction initiated by the casting of the ferrous alloy;
  • ∘ ceramic-metal composites of titanium carbide cemented in a metallic binder.

Brief description of the figures

In the figures commented below, the inserts are represented schematically. In reality, these ceramic inserts are infiltrable three-dimensional structures formed by permeable aggregates such as agglomerates of millimetric grains (with an average size of 2 to 8 mm, preferably 3 to 6 mm) aggregated by a glue with millimetric interstices and infiltrable by the casting metal.

• La figure 1 représente un exemple de broyeur à axe vertical équipé de galets de broyage tronconiques s'appuyant et tournant sur une table rotative alimentée en minerai à broyer.
• La figure 2 représente le principe du broyage par un galet de broyage tronconique.
• La figure 3 représente un galet de broyage réalisé avec des barreaux renforcés par des céramiques selon l'état de la technique WO2005/084809 . Ici une pluralité d'inserts en céramique en forme de nid d'abeille sont infiltrés individuellement pour former des barreaux avant d'être disposés, une fois refroidis, dans un moule en veillant à maintenir une distance entre chaque élément de renfort individuel (assemblage non-jointif) pour permettre la pénétration du métal de coulée entre les éléments individuels et assurer un scellage de l'ensemble dans le galet coulé.
• La figure 4a représente un barreau constitué d'une matrice métallique intégrant un insert en céramique sous forme de nid d'abeille. La figure 4b montre un détail de l'assemblage des barreaux avant la coulée du galet de broyage.
• La figure 5 représente une image d'un galet de broyage tronconique fortement usé sur sa partie inférieure. Il s'agit d'un galet de broyage selon l'état de la technique et réalisé selon les techniques représentées dans les figures 3, 4a et 4b. On y voit une structure en céramique sous forme de nid d'abeille ressortir à travers une matrice métallique fortement érodée. Les espaces laissés entre les barreaux individuels (sillons droits) sont également fortement érodés.
• La figure 6 représente une image d'un galet de broyage torique qui présente un niveau d'usure important. Il a été réalisé selon l'état de la technique WO2005/084809 en disposant des barreaux infiltrés et refroidis dans un moulée et en respectant une distance entre les barreaux pour assurer le scellage des barreaux dans le galet.
• La figure 7a représente un galet de broyage monobloc de forme torique selon l'invention. La figure 7b ne représente que l'assemblage des inserts ajourés correspondants où les inserts sont assemblés sur un anneau unique de manière jointive et selon une ligne ondulée.
• La figure 8a représente un galet de broyage monobloc de forme torique selon l'invention. La figure 8b ne représente que l'assemblage des inserts ajourés correspondants où les inserts sont assemblés sur deux anneaux superposés en quinconce et de manière jointive selon une ligne ondulée.
• La figure 9a représente un galet de broyage monobloc de forme tronconique selon l'invention. La figure 9b ne représente que l'assemblage des inserts ajourés correspondants où les inserts sont assemblés sur un anneau unique de manière jointive selon une ligne ondulée.
• La figure 10 représente un galet de broyage tronconique monobloc selon l'invention semblable à celui de la figure 9a dans lequel une pluralité d'inserts ajourés en céramique sont disposés de manière jointive selon une ligne ondulée. On y montre cependant deux types d'ouvertures (alvéoles) avec une proportion d'ajourage différentiée et adaptée à la sollicitation à l'usure pour une utilisation spécifique. Les inserts ajourés montrent deux zones 21 et 22. La zone 21, la plus exposée à l'usure, comporte un ajourage limité avec des trous coniques disposés dans la partie la plus sollicitée à l'usure et une conicité dont le diamètre évolue de l'intérieur du galet vers la surface extérieure du galet en diminuant. La zone 22 la moins sollicitée à l'usure a une proportion d'ajourage plus importante et comporte des trous cylindriques perpendiculaires à la surface de broyage. Les trous peuvent également former un angle avec la normale à la surface périphérique.
• La figure 11a représente un galet de broyage torique monobloc selon l'invention dans lequel une pluralité d'inserts ajourés en céramique sont disposés de manière jointive selon une ligne ondulée. On y voit également deux types d'ouvertures avec une proportion d'ajourage différente et adaptée en fonction d'une sollicitation à l'usure spécifique. Les inserts ajourés montrent aussi dans ce cas deux zones 21 et 22. La figure 11b montre uniquement la pluralité d'inserts assemblés avant la coulée du galet de broyage. On constate ici que les assemblages des inserts sont non seulement jointifs mais que les éléments ont des formes complémentaires permettant de s'assembler parfaitement avec leurs voisins. Un assemblage selon une forme ondulée a été choisi pour éviter les lignes droites qui constituent une amorce et une voie privilégiés pour l'usure. Une fois qu'une telle usure est amorcée, elle continue à se propager trop facilement selon une ligne droite et les lignes plus ou moins fortement ondulées permettent de ralentir ou même d'entraver ce phénomène. L'expérimentation a d'ailleurs montré qu'une simple ligne d'assemblage jointive courbe de faible amplitude et sans ondulations, bien qu'étant plus encline à propager des voies d'usure que la ligne jointive droite, ne donnait qu'un résultat intermédiaire entre la ligne droite et la ligne jointive ondulée.
• Les figures 12 et 13 représentent d'autres possibilités d'assemblage d'inserts selon la présente invention. Les inserts peuvent êtres dédicacés aux zones 21 et 22 et former plusieurs anneaux superposés avec des dimensions éventuellement différentes. Lorsque les inserts sont dédicacés aux zones 21 et 22 à forte et faible sollicitation à l'usure respectivement, la disposition en quinconce est préférée pour éviter autant que possible la propagation de l'usure selon une ligne continue. Cette figure montre également en détail des différences d'ajourage importantes entre les zones 21 et 22 avec des trous tronconiques 3 et des trous cylindriques 4 en exemple (détail non représenté).
• Les figure 14a et 14b représentent respectivement un galet de broyage torique de grande taille une fois coulé et un assemblage de ses inserts correspondants. On y distingue à nouveau deux zones distinctes 21 et 22 adaptées à des sollicitations différentes. La disposition des inserts est réalisée selon deux anneaux superposés et en quinconce. Le galet de broyage peut être légèrement incliné (penché) sur la table de rotation ce qui nécessite une telle configuration.
• Les figure 15a et 15b représentent respectivement un assemblage d'inserts pour un galet de broyage torique et le galet de broyage une fois coulé. Il s'agit ici d'un galet de très grande taille (18 tonnes et 3 m de diamètre). On y distingue à nouveau deux zones distinctes 21 et 22 adaptées à des sollicitations différentes. La disposition des inserts est réalisée selon trois anneaux superposés et en quinconce. Les zones à forte sollicitation sont disposées de part et d'autre d'une zone à plus faible sollicitation. Cette disposition symétrique permet l'utilisation des galets de broyage qui sont un peu inclinés sur la table de rotation alternativement des deux côtés. Une fois qu'un côté est usé, on peut retourner le galet.
• La figure 16 représente un insert de renfort avec sa longueur « L » et sa largeur « ℓ » ainsi que l'amplitude des ondulations « A » sur sa largeur « ℓ » et la façon de les mesurer.
• La figure 17 représente un assemblage en quinconce de différents inserts où l'on voit que l'amplitude de l'ondulation n'est pas forcément la même sur une même ligne d'assemblage. L'amplitude se mesure en valeur absolue entre un minimum et un maximum de l'ondulation, « A » ou « A' » par rapport à la largeur « e » ou encore « a » par rapport à la longueur « L » ou « L' » des inserts assemblés. Les amplitudes « A » et « a » sont évaluées respectivement en pourcentage par rapport à la largeur « ℓ _» et à la longueur « L ».
• La figure 18 représente une méthode de mesure du profil d'usure d'un galet de broyage torique en utilisant des tiges de comparaison avec une surface d'un galet de broyage neuf.
• La figure 19 représente un profil d'usure d'un galet de broyage tronconique avec une flèche en ligne plus épaisse montrant la position de l'usure maximum qui est déterminante pour le remplacement du galet.

For ease of representation, the figures only represent the outline of these inserts placed in the reinforced parts of the grinding roller.

• There figure 1 represents an example of a vertical shaft crusher equipped with truncated cone-shaped grinding rollers resting and rotating on a rotary table fed with ore to be ground.
• There figure 2 represents the principle of grinding by a truncated cone-shaped grinding roller.
• There figure 3 represents a grinding roller made with bars reinforced with ceramics according to the state of the art WO2005/084809 . Here a plurality of honeycomb-shaped ceramic inserts are individually infiltrated to form bars before being arranged, once cooled, in a mold, taking care to maintain a distance between each individual reinforcing element (non-jointed assembly) to allow the penetration of the casting metal between the individual elements and ensure sealing of the assembly in the cast pebble.
• There Figure 4a represents a bar made of a metal matrix integrating a ceramic insert in the form of a honeycomb. The Figure 4b shows a detail of the assembly of the bars before casting the grinding roller.
• There figure 5 represents an image of a truncated grinding roller that is heavily worn on its lower part. This is a grinding roller according to the state of the art and produced according to the techniques shown in the Figures 3, 4a and 4b . A ceramic honeycomb structure is seen emerging through a heavily eroded metal matrix. The spaces between the individual bars (straight grooves) are also heavily eroded.
• There figure 6 represents an image of a toric grinding roller which presents a significant level of wear. It was produced according to the state of the art WO2005/084809 by placing infiltrated and cooled bars in a mold and respecting a distance between the bars to ensure the sealing of the bars in the pebble.
• There Figure 7a represents a single-piece grinding roller of toroidal shape according to the invention. The Figure 7b only represents the assembly of the corresponding openwork inserts where the inserts are assembled on a single ring in a contiguous manner and along a wavy line.
• There Figure 8a represents a single-piece grinding roller of toroidal shape according to the invention. The figure 8b only represents the assembly of the corresponding openwork inserts where the inserts are assembled on two rings superimposed in a staggered manner and in a contiguous manner along a wavy line.
• There Figure 9a represents a single-piece grinding roller of truncated cone shape according to the invention. The figure 9b only represents the assembly of the corresponding openwork inserts where the inserts are assembled on a single ring in a contiguous manner along a wavy line.
• There figure 10 represents a single-piece truncated cone-shaped grinding roller according to the invention similar to that of the Figure 9a in which a plurality of ceramic openwork inserts are arranged in a contiguous manner along a wavy line. However, two types of openings (cells) are shown with a differentiated proportion of openwork adapted to the wear stress for a specific use. The openwork inserts show two zones 21 and 22. Zone 21, the most exposed to wear, has limited openwork with conical holes arranged in the part most subject to wear and a conicity whose diameter evolves from the inside of the roller towards the outside surface of the roller while decreasing. Zone 22, the least subject to wear, has a greater proportion of openwork and has cylindrical holes perpendicular to the grinding surface. The holes can also form an angle with the normal to the peripheral surface.
• There Figure 11a shows a single-piece toric grinding roller according to the invention in which a plurality of ceramic perforated inserts are arranged in a contiguous manner along a wavy line. It also shows two types of openings with a different proportion of perforated inserts adapted according to a specific wear stress. The perforated inserts also show in this case two zones 21 and 22. figure 11b shows only the plurality of inserts assembled before casting the grinding roller. It can be seen here that the insert assemblies are not only contiguous but that the elements have complementary shapes allowing them to assemble perfectly with their neighbors. An assembly in a wavy shape was chosen to avoid straight lines which constitute a preferred start and path for wear. Once such wear has started, it continues to propagate too easily in a straight line and the lines more or less strongly wavy lines can slow down or even hinder this phenomenon. Experimentation has also shown that a simple curved joint assembly line of low amplitude and without undulations, although more likely to propagate wear paths than a straight joint line, only gave an intermediate result between the straight line and the wavy joint line.
• THE figures 12 And 13 represent other possibilities for assembling inserts according to the present invention. The inserts can be dedicated to the zones 21 and 22 and form several superimposed rings with possibly different dimensions. When the inserts are dedicated to the zones 21 and 22 with high and low wear stress respectively, the staggered arrangement is preferred to avoid as much as possible the propagation of wear along a continuous line. This figure also shows in detail significant differences in opening between the zones 21 and 22 with truncated cone holes 3 and cylindrical holes 4 as an example (detail not shown).
• THE Figure 14a and 14b respectively represent a large toroidal grinding roller once cast and an assembly of its corresponding inserts. There are again two distinct zones 21 and 22 adapted to different stresses. The arrangement of the inserts is carried out according to two superimposed and staggered rings. The grinding roller can be slightly inclined (leaning) on the rotation table which requires such a configuration.
• THE Figure 15a and 15b respectively represent an assembly of inserts for a toroidal grinding roller and the grinding roller once cast. This is a very large roller (18 tonnes and 3 m in diameter). Here we can again distinguish two separate zones 21 and 22 adapted to different stresses. The arrangement of the inserts is carried out in three superimposed rings and in a staggered pattern. The high stress zones are arranged on either side of a lower stress zone. This symmetrical arrangement allows the use of grinding rollers which are slightly inclined on the rotation table alternately on both sides. Once one side is worn, the roller can be turned over.
• There figure 16 represents a reinforcement insert with its length “L” and its width “ ℓ ” as well as the amplitude of the undulations “A” on its width “ ℓ ” and how to measure them.
• There figure 17 represents a staggered assembly of different inserts where we see that the amplitude of the undulation is not necessarily the same on the same assembly line. The amplitude is measured in absolute value between a minimum and a maximum of the undulation, "A" or "A'" relative to the width " e " or “a” relative to the length “L” or “L'” of the assembled inserts. The amplitudes “A” and “a” are evaluated respectively as a percentage relative to the width “ ℓ _” and the length “L”.
• There figure 18 represents a method of measuring the wear profile of a toric grinding roller using comparison pins with a surface of a new grinding roller.
• There figure 19 shows a wear profile of a truncated grinding roller with a thicker line arrow showing the position of maximum wear which is decisive for roller replacement.

List of reference symbols

• 1: Single-piece grinding roller
• 2: ceramic inserts
• 21: first area of ceramic inserts placed on the side most exposed to wear
• 22: second zone of ceramic inserts, the least exposed to wear
• 3: example of truncated cone-shaped openings in the ceramic inserts positioned on the most stressed face of the grinding roller
• 4: example of cylindrical openings in the ceramic inserts positioned on the least stressed face of the grinding roller

Detailed description of the invention

Cast wear parts are widely used in the mining and cement industries for crushing rocks and ores. These include vertical compression mill tables and their grinding rollers in general and truncated and toric grinding rollers in particular, which illustrate the present invention.

To increase the wear resistance of grinding rollers, ferrous alloys such as cast iron or steel are combined with the hardness of a ceramic material (such as carbides, nitrides, oxides of various types, etc.), which are highly resistant to wear.

However, the combination of these two types of material is not easy because they have very different expansion coefficients which can generate micro-cracks when the parts cool and, through their potential defects, cancel out this synergy effect in a composite wear part.

An additional difficulty lies in the problem of complete infiltration of the ceramic insert by the liquid cast iron which tends to cool on contact with it, which prevents satisfactory infiltration.

Many ceramic insert configurations have been tried by manufacturers. The most popular ceramic insert is a relatively easy to infiltrate "honeycomb" shape such as those cited in the prior art WO98/15373 .

Ceramic reinforcements are generally introduced in the form of bars, i.e. in the form of an insert in which the interstices have already been infiltrated by liquid cast iron and cooled before being reintroduced into a mold to cast the wear part in a single block that is desired. This technology is illustrated in Figures 3 to 5 of this document and is the subject of the publication WO2005/084809 .

There is a lot of know-how in the production of a ceramic insert because it must have a permeable structure to be infiltrated by the liquid cast iron, the level of permeability being decisive, which has led to a series of technologies for the production of agglomerates (aggregates) of powder in the form of aggregated grains of a few millimeters which are then assembled into a "cake/wafer" structure in a mold and compacted by vibration. Once removed from the mold, these inserts always have irregular interstices of the order of 1 to 5 mm.

• l'alumine-zircone 10/90 à 90/10 avec ou sans stabilisation à l'oxyde d'yttrium sous forme de granulés millimétriques assemblés en agrégats au moyen d'une colle inorganique dans une structure perméable au métal fondu et donc infiltrable par une coulée classique;
• des particules issues de composites céramiques métal broyés ou frittés à partir de mélanges de poudres à base de carbures, nitrures, borures ou d'éléments intermétalliques cimentés dans un liant métallique avant d'être agglomérés en structure perméable et donc infiltrable par un alliage ferreux fondu;
• les céramiques formées par synthèse exothermique auto-propagée (SHS) comme par exemple le carbure de titane à partir de poudres de carbone et de titane, éventuellement mélangés à une poudre pour modérer la réaction comme par exemple de la poudre de fer pouvant se présenter sous forme de grains millimétriques agglomérés avec des interstices millimétriques. La réaction entre le carbone et le titane étant initiée par la coulée de l'alliage ferreux ;

There are many possibilities of compositions for the production of a ceramic insert usable in a reinforced grinding roller according to the invention. In a non-exhaustive list we can for example cite:

• alumina-zirconia 10/90 to 90/10 with or without yttrium oxide stabilization in the form of millimeter granules assembled into aggregates by means of an inorganic glue in a structure permeable to the molten metal and therefore infiltrable by a conventional casting;
• particles from ceramic-metal composites ground or sintered from mixtures of powders based on carbides, nitrides, borides or intermetallic elements cemented in a metallic binder before being agglomerated into a permeable structure and therefore infiltrable by a molten ferrous alloy;
• ceramics formed by self-propagating exothermic synthesis (SHS) such as titanium carbide from carbon and titanium powders, optionally mixed with a powder to moderate the reaction such as iron powder which may be in the form of agglomerated millimeter grains with millimeter interstices. The reaction between the carbon and titanium is initiated by the casting of the ferrous alloy;

Maintaining the insert in the mold during casting also requires a certain amount of know-how acquired by manufacturers over the years.

The configuration and positioning of ceramic inserts within a single-piece composite grinding roller has been the subject of much research, all of which has resulted in the observation that wear rate results obtained during testing are relatively unpredictable as they depend on the specific application, i.e. the type of machine used and the type of rocks to be ground.

The situation is made even more complex by the fact that during the wear phenomenon, the geometry of the grinding roller changes and the areas that were initially under little stress can become much more so as the wear progresses. It is therefore often necessary to make a compromise on the structure of the insert to reconcile short- and long-term wear, these two notions being able to vary considerably from one case to another.

The inventors of the grinding roller according to the invention have now produced a reinforcement structure comprising a plurality of ceramic inserts meeting this compromise. This reinforcement structure is adapted to the final shape of the roller and is for example of a generally truncated cone or toroidal shape and comprises on its periphery an assembly of ceramic inserts which can take different forms such as for example a side-by-side assembly, therefore adjoining, of inserts having approximately the same dimension as the grinding roller or even a superposition of two or more "rings" of ceramic inserts according to wavy lines. The assembly on one or more rings depends largely on the final size of the roller since there is always a feasibility limit of an insert for reasons of handling by an operator (mass, volume, friability). This is how a one-ton roller may only require one ring with a limited number of inserts to assemble while a roller of >15 tons will require at least 2 or 3 rings with many superimposed inserts. (See figure 15b For example).

Depending on the demands for specific uses, differentiated opening can be considered depending on the position of the insert in the roller. For example, a different proportion of opening can be considered depending on whether it is the side subjected to the greatest stress, zone 21, or the side subjected to the least stress, zone 22, by wear. An example of an assembly of a ring of inserts of this type, for a toric grinding roller is shown in Figure 11a and an example of two superimposed rings is shown in Figures 14a . Three rings of superimposed inserts are shown 15b. To avoid the propagation of wear along a predetermined line, the assembly of the superimposed inserts is preferably done in a staggered pattern.

The ceramic openwork structures have openings of generally any shape. The openings made in the insert structure have a diameter generally between 1 and 10 cm, preferably between 1 and 8 cm and particularly preferably between 2 and 4 cm. When the opening is differentiated within the same grinding roller, the peripheral zone most exposed to wear 21, the holes preferably have a truncated cone shape 3 or are associated with blind holes. The most exposed zone can also comprise a judicious association of blind holes and through holes. When blind holes are used, the blind side is placed on the side most stressed by wear. When truncated cone openings 3 are used, the opening will taper towards the outer surface most exposed to wear. In the least exposed and most openwork zone 22 the holes have any shape but the cylindrical shape will be preferred. (see figure 12 ).

The inventors have also observed that straight or even slightly curved lines constitute important initiators for the wear of a grinding roller. The wear propagates much more quickly in a straight line because it no longer encounters any obstacle once initiated.

To dampen this phenomenon, the inventors have eliminated the spaces between the inserts, the technological evolution of which in their manufacture now allows for better infiltration. The assemblies of the inserts according to the invention are therefore adjoining and are made along a wavy line to prevent the initiation and propagation of wear in a straight line. All forms of undulations are of course possible, but for logistical reasons, preference is given to parts that all have the same shape with a concavo-convex side allowing a perfectly adjoining complementary assembly.

The amplitude of the ripple and how to measure it is shown in figures 16 And 17 . In these figures the amplitude of the ripples is exaggerated for the purposes of the demonstration.

Examples

Tests were carried out on different rollers according to the invention on a vertical rotary mill of two different types adapted to the rollers to be tested. To neutralize the variable due to the influence of the composition of the ceramic on wear, the same ceramic was used for all the tests. These are millimetric grains of a ceramic metal composite of the titanium carbide type cemented in a metal binder of the manganese steel type. These grains with an average size of approximately 5 mm were compacted to form perforated inserts with a thickness of approximately 50 mm used for all tests.

For the purposes of the test, the configurations of inserts distributed over several rings were produced, whereas on a one-ton roller, for example, several rings would not necessarily have been necessary. The inventors nevertheless wanted to test the behavior of the rollers according to the invention when the inserts were configured in several superimposed rings with a staggered positioning.

Each of the 2 truncated rollers was tested in parallel with a reference roller for 500 hours and the wear was extrapolated to 1000 hours. For each of the 3 toric roller tests, two rollers were arranged alternately with two reference rollers and rotated for 1000 hours. The tests were carried out continuously.
The test conditions are summarized in the table below. Crushed material Lignite type coal Silico-calcareous ore Crusher type Polysius RM25/12(Type1) Loesche LM15.2 (Type 2) Type of pebbles Toric Truncated Number of rollers on the crusher 4 2 Mass of the roller (T) 1.4 1 External size 130x33 cm 120/104 x33cm Flow rate (T/h) 27-30 25 Duration of the trial 1000 hours 500 hours Positioning the rollers 2 reference rollers and 2 rollers according to the invention alternately on the same crusher 1 reference roller and a roller according to the invention on the same crusher The determination of the wear of the roller can be carried out from profile measurements, along generatrices, by means of a template resting on surfaces not subject to wear. The distance between the surface of the roller and the template is recorded at several points along the template on a representative number of points on the contour of the roller. (see figure 18 ). These measurements are then compared to the distances recorded. on a new roller. An average wear profile is determined, providing information on the geometry of the wear that can be used by the manufacturer.

The wear measurement used to compare roller performance is, however, the maximum wear depth on the roller, which determines its replacement. It is this maximum wear that will be used in the table below for performance measurements. Grinding rollers made with bars according to WO2005/084809 and represented in the Figures 3, 4 and 5 are used as comparative reference toroidal and truncated cone rollers. These reference rollers are each associated with rollers according to the invention on the same crusher during the test. In the latter, the wear is measured above the bars and not between the bars on the heavily worn ductile matrix.

Tests on type 1 crusher with toroidal rollers Example 1

Example 2

Example 3

Tests on type 2 crusher with truncated cone rollers Example 4

Example 5

Results

Examples Number of rings Alveoli (mm) A / ℓ % a/L % Wear mm/1000h Coeff. Improvement Reference 1 23 - - 11 1.00 1 1 23 14 9.9 1.11 2 1 23 and 13 12 8.8 1.25 3 2 * 23 and 13 13 12 9.2 1.19 Reference 23 37 1.00 4 1 23 and 13 4 29.1 1.27 5 2 * 23 and 13 9 5 33.6 1.10 (*) the inserts are assembled in a staggered pattern

Interpretation of results

Compared to the reference truncated and toric grinding rollers made with bars according to WO2005/084809 , all grinding rollers according to the invention exhibit an improvement in wear performance. It is between 10 and 27%, which is significant.

The rollers with differentiated opening depending on the wear stress with zones 21 and 22 (Examples 2 and 4 with 13 and 23 mm cells) have the best performance when the reinforcement insert consists of a single assembly ring with a minimum of joint lines.

Rollers with several rings superimposed in a staggered manner and differentiated openings have lower performance due to the increase in the number of inserts and therefore of joining lines which will be necessary for large grinding rollers.

The undifferentiated opening, without specific zones 21 and 22 also allows an improvement in performance of 11% on the toric grinding roller.

Claims (16)

Single-piece grinding roller (1) for vertical axis grinders produced by casting a metal matrix in a foundry, said roller comprising at its periphery an openwork reinforcement structure (2) consisting of a plurality of ceramic inserts assembled in a tight manner, the tight assembly of the ceramic reinforcements being produced along wavy lines. Single-piece grinding roller (1) according to claim 1, said reinforcing structure (2) comprising at least a first zone (21), the least openwork and the most exposed to wear and at least a second zone (22), the most openwork and the least exposed to wear. Roller (1) according to any one of claims 1 or 2 in which the first and second zones (21, 22) of the plurality of ceramic inserts are formed by several superimposed rings, said inserts being assembled in a staggered manner in a contiguous manner along wavy lines. Roller (1) according to any one of the preceding claims, in which the opening of the first zone (21), the most exposed to wear, is formed by through holes of truncated cone shape (3) with a diameter decreasing towards the periphery of the roller or by an association of through holes of any shape (4) with blind holes whose blind side is located on the side of the periphery of the roller. Roller (1) according to any one of the preceding claims, in which the opening of the second zone (22), the least exposed to wear, is formed by through holes of any shape (4), preferably of cylindrical shape, positioned perpendicularly or inclined relative to the peripheral surface of the roller. A roller (1) according to any preceding claim wherein the plurality of inserts are assembled to form a frustoconical roller or a toroidal roller. Pebble (1) according to any one of the preceding claims in which the amplitude (a) of the wavy lines represents between 2 and 20%, preferably between 5 and 15% relative to the length “L” of the ceramic insert. Pebble (1) according to any one of the preceding claims in which the amplitude (A) of the wavy lines represents between 2 and 20%, preferably between 3 and 15%, relative to the width “ ℓ _” of the ceramic insert. Roller (1) according to any one of the preceding claims in which the composition of the ceramic of the reinforcement structure is chosen from oxides, carbides, nitrides and borides. Pebble (1) according to any one of the preceding claims in which the ceramic inserts comprise an aggregate of ceramic-metal composite grains in which micrometric particles of ceramic are cemented in a metallic binder, the composite grains having an average size D ₅₀ of 2 to 8 mm, preferably of 3 to 6 mm determined by sieving. Pebble (1) according to claim 11 in which said grains comprise titanium carbide with an average size D ₅₀ of between 3 and 20 µm, preferably between 5 and 15 µm cemented in a metal binder. Roller (1) according to any one of the preceding claims in which the composition of the ceramic of the reinforcement structure of the first zone (21) is different from the composition of the ceramic of the second zone (22). Method for producing a grinding roller (1) according to claims 1 to 12 comprising the following steps: - provision of a mold for the production of a single-piece grinding roller by casting a ferrous alloy; - positioning of a reinforcement structure composed of a plurality of ceramic inserts and assembled in a jointed manner along wavy lines, the inserts being in the form of openwork aggregates of millimetric granules, the openwork aggregates being permeable and therefore infiltrable by a casting ferrous alloy. - infiltration of the insert by the liquid ferrous alloy. - cooling and demolding of the grinding roller A method according to claim 13 wherein the ferrous alloy comprises steel or cast iron. Method according to any one of claims 13 or 14 in which the reinforcing structure comprises at least a first zone (21) less openwork and more exposed to wear and at least a second zone (22), the most openwork and less exposed to wear. A method according to any one of claims 13 to 15 wherein the infiltrable aggregates of millimetric ceramic granules used for the inserts of the grinding rollers are selected from the following compositions: - alumina-zirconia in proportions 90/10 to 10/90, the zirconia being optionally stabilized with yttrium oxide; - carbon and titanium powder optionally comprising iron powder as a moderator and precursors of a self-propagating thermal synthesis (SHS) reaction initiated by the casting of the ferrous alloy; - ceramic-metal composites of titanium carbide cemented in a metallic binder.

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