PIECE D'USURE COMPOSITE

Description

Object of the invention

[0001] The present invention relates to a composite wear part manufactured in a foundry by casting a ferrous alloy. More particularly, it relates to a wear part reinforced by a three-dimensional hollow ceramic structure integrated into the wear part and a geometric structure adapted to the wear stress. It also discloses a method for manufacturing said wear part. State of the art

[0002] Composite wear parts produced in casting are well known in the prior art. They are mainly cast iron parts reinforced in a targeted manner on the faces most exposed to wear by alumina-zirconia type ceramics or by carbides, nitrides or other intermetallic elements arranged according to specific three-dimensional geometries within the metal matrix.

[0003] The specific arrangement of the reinforcing structures allows for the creation of hierarchical composites with differentiated reinforcement depending on the arrangement or geometric shape of the particles or reinforcing structures. This is how ceramic discs can be produced in the form of hollow, honeycomb-like structures, or even aggregates of millimeter-sized granules arranged in "cakes" inside a sand mold on the most stressed side of the part, with interstices allowing infiltration by the molten metal during casting.

[0004] Two main families of composite parts produced in foundries are distinguished: those where the ceramic is positioned according to a particular three-dimensional geometry in a mold before the casting of the molten iron, those where the ceramic is formed before the casting and those where the ceramic is formed during the casting by a self-propagating thermal reaction from reagents present in the mold.

[0005] Thus, a composite wear part can, on the one hand, be reinforced with, for example, pre-formed titanium carbide that can be placed in the mold before casting and whose pores are simply infiltrated by the casting metal at around 1500°C, and, on the other hand, be reinforced with titanium carbide that will be formed in situ from titanium and carbon reagents previously mixed in powder form and forming TiC by self-propagating thermal reaction at around 2500°C, the reaction being initiated by the casting metal which will then be drawn by capillary action into the ceramic reinforcement structure to fill the interstices.

[0006] Document WO98 / 15373 discloses a composite wear part with a honeycomb-shaped alumina-zirconia ceramic reinforcement. EP0930948A1 discloses a cast composite wear part consisting of a metallic matrix whose working face(s) comprise inserts with good wear resistance, characterized in that the inserts are made from a ceramic wafer impregnated with a liquid metal during casting, this ceramic wafer being made of a homogeneous solid solution of 20 to 80% Al2O3 and 80 to 20% ZrO2, the percentages being expressed by weight of the constituents.

[0007] Document WO03 / 047791 discloses a composite wear part with carbide, nitride, oxide, or intermetallic ceramics. in situ according to a self-propagating thermal reaction initiated by the liquid molten metal which then infiltrates the ceramic structure once formed.

[0008] Documents WO2010 / 031660; WO2010 / 031661; WO2010 / 031663; WO2010 / 031662 disclose hierarchical composite wear parts reinforced with formed titanium carbide in situ or the reagents are introduced in granular form into the mold. Wear parts are illustrated by dredging teeth, cones and crushing hammers.

[0009] Document WO2018 / 069006 discloses a grinding roller where the wear areas are reinforced in a differentiated manner depending on the stress. Objectives of the invention

[0010] The present invention aims to provide a composite wear part with a ceramic reinforcement insert of improved geometry, the structure and positioning of which are adapted to the wear stress. It aims to recreate a resistant structure after initial wear of the ceramic reinforcement on the most stressed side of the wear part. Summary of the invention

[0011] The present invention discloses a composite wear part comprising a ferrous alloy matrix and at least one ceramic reinforcement in the form of an insert with an openwork structure, the openwork structure comprising blind holes, the blind side of the holes being positioned on the most stressed side of said wear part.

[0012] Preferred embodiments of the invention include at least one, or any suitable combination of, the following features: The ceramic insert comprises at least two zones (A, B), the more stressed zone (A) having a majority of blind holes and the less stressed zone (B) having a majority of through holes; the cross-sectional area of ​​the holes in the ceramic insert in zone (A) is smaller than the cross-sectional area in zone (B) of the wear part; the total cross-sectional area of ​​the openings in the insert on side (A) is smaller than the total cross-sectional area of ​​the openings on side (B); the blind side of the ceramic insert is partially or entirely formed by a ceramic of a different composition than that forming zone (B) with the through holes; the insert comprises at least two superimposed ceramic reinforcement structures (D, E) in zone (A); the blind holes are arranged obliquely in the insert; the blind holes have a frustoconical shape; the ceramic insert comprises alumina-zirconia; the ceramic insert comprises carbides formed in situby self-propagating exothermic reaction, preferably of titanium carbide; the ceramic insert comprises grains of a metallic ceramic composite (CERMET); the ceramic structure comprises zirconia alumina in proportions of alumina ranging from 10 to 90% by volume and zirconia ranging from 90 to 10% by volume, the zirconia being optionally stabilized with yttrium oxide.

[0013] The present invention also discloses a method for manufacturing a wear part according to the invention, comprising the following steps: provision of a mold for the production of a wear part by casting a ferrous alloy; placement of an insert according to the invention in the form of an aggregate of millimeter granules of ceramic material or of precursors of infiltrable ceramic material in the mold with the blind side of the most stressed side of the wear part; infiltration of the insert by the liquid ferrous alloy.

[0014] The method according to the invention is preferably carried out with: a ferrous alloy comprising steel or cast iron; aggregates of millimeter-sized ceramic granules where aggregates of infiltrable ceramic precursors are selected from the following compositions: ∘ Alumina-zirconia in proportions of 90 / 10 to 10 / 90, the zirconia being optionally stabilized with yttrium oxide; ∘ Carbon and titanium powder optionally comprising iron powder as a moderator of the reaction initiated by the casting of the ferrous alloy; ∘ Metal-ceramic composites (CERMET). Brief description of the figures

[0015] In the figures discussed below, "inserts" are defined as three-dimensional infiltratable structures formed of more or less porous aggregates or agglomerates of millimeter-sized particles with interstices.

[0016] For the sake of ease of representation, the figures only represent the three-dimensional outline of these inserts placed in the reinforced parts of the wear part. There figure 1 represents an element of a ceramic insert with blind holes according to the invention. The insert is shown here schematically in its simplest form. Such an insert is positioned with the blind side facing the surface most exposed to wear. Such an insert has numerous interstices, or pores (not shown), which are intended to be infiltrated by the ferrous alloy during casting. figure 2 represents a ceramic insert based on the same principle as that described in the figure 1 but with larger blind holes to illustrate the different possibilities for creating blind holes in such a ceramic insert. figure 3 represents a ceramic insert with blind holes based on the same principle as that described in the figure 1 But this time the insert comes in two different ceramic layers, D and E. figure 4 represents a ceramic insert with blind holes based on the same principle as that described in the figure 3 but this time with deeper blind holes penetrating into the second layer E. The figure 5 represents a ceramic insert with blind holes based on the same principle as that described in the figure 3 but this time made with enlarged holes. figure 6 represents a ceramic insert with blind holes based on the same principle as that described in the figure 1 but this time with blind holes associated in roughly half and half with larger through holes. figure 7 represents a ceramic insert with blind holes based on the same principle as that described in the figure 1But this time, blind holes are associated in a minority of cases with larger through holes. Here, blind holes, smaller in diameter than through holes, are in the majority. figure 8 represents a ceramic insert with two zones of different stress, A and B. Zone A, the most exposed to wear, mainly contains blind holes, while zone B, the least exposed to wear, mainly contains through holes. The through holes in zone B have a larger cross-section than the blind holes. figure 9 represents the same configuration as the figure 8 but this time with a different ceramic on side A and side B. Figure 10 represents the same configuration as the figure 8But this time, not only with a different ceramic on side A and side B, but also with two different ceramic layers, D and E, in zone A, with a more wear-resistant ceramic on the blind side of zone A. figure 11 represents a ceramic insert according to the invention with blind holes positioned obliquely. figure 12 represents a ceramic insert according to the invention with blind holes of truncated conical shape. figure 13 represents an illustrative example of a wear part according to the invention in the form of a grinding roller for a vertical rotary mill where zone A, the area most exposed to wear, comprises the ceramic insert with blind holes. Zone A is adjacent to zone B, which is less exposed to wear and has through holes. figure 14 This schematically represents the use of a grinding roller on a table of a vertical rotary mill. figure 15schematically represents a grinding cone with a ceramic insert with blind holes. List of reference symbols

[0017] 1: Ceramic insert 2: Blind holes 3: Most stressed face of the wear part 4: Through holes 5: Grinding roller 6: Schematic representation of a vertical rotary grinder with roller and grinding table A: Most stressed area of ​​the wear part B: Least stressed area of ​​the wear part D: Top layer of the ceramic insert E: Bottom layer of the ceramic insert oriented towards the side most exposed to wear Detailed description of the invention

[0018] Cast iron wear parts are widely used in the mining industry for crushing rocks and ores, as well as in dredging. Examples of rock crushing include composite impactors for impact crushers, moving cones for compression crushers, and roller tables for vertical compression crushers.

[0019] The stresses that wear parts in these machines face are both impact resistance and wear resistance. This is why the hardness of a ceramic material (carbides, nitrides, oxides of various types, etc.), which is highly resistant to wear but not to impact, is generally combined with a ferrous alloy such as cast iron or steel, providing a certain level of ductility that allows it to withstand impact but is less resistant to wear.

[0020] The combination of these two types of material is not simple because they have very different coefficients of expansion which can generate microcracks when the parts are cooled and cancel out this synergy effect in a composite wear part due to its potential defects.

[0021] An additional difficulty lies in the problem of complete infiltration of the ceramic insert by the liquid molten iron, which tends to cool upon contact, thus preventing satisfactory infiltration (except for ceramic formation reactions). in situ (by self-propagating exothermic reaction).

[0022] Manufacturers have tried numerous ceramic insert configurations. The most popular insert is a relatively easy-to-insulate "honeycomb" shape where areas with a high ceramic concentration alternate with areas with a low ceramic concentration.

[0023] Ceramic reinforcements are usually introduced in the form of a prefabricated ceramic insert or even as an insert in which the gaps have already been filled with molten iron and cooled before being reintroduced into a mold to cast the desired wear part.

[0024] There is a lot of know-how involved in making a ceramic insert because it must have a porous structure to be infiltrated by the liquid molten iron, the level of porosity being crucial, which has led to a whole series of technologies for the manufacture of agglomerates (aggregates) of powder in the form of sealed grains a few millimeters in diameter which are then assembled into a "cake" structure (padding in English) with more or less significant interstices, depending in particular on the thickness of the insert to be infiltrated and its positioning in the mold.

[0025] There are many possible compositions for creating an insert according to the invention. In a non-exhaustive list, we can mention: Alumina-zirconia 10 / 90 to 90 / 10, with or without stabilization, in the form of millimeter-sized granules assembled into aggregates within an impermeable structure; particles from ground CERMET based on carbides, nitrides, borides, or intermetallic elements, for example, subsequently agglomerated into an impermeable porous structure; ceramics formed by self-propagating exothermic synthesis (SHS), such as titanium carbide from carbon and titanium powders, possibly mixed with a powder to moderate the reaction, such as iron powder, which can be in the form of millimeter-sized grains agglomerated with interstices. The reaction between carbon and titanium is initiated by pouring the ferrous alloy; etc.

[0026] Maintaining the insert in the mold during pouring also requires a certain expertise acquired by manufacturers over the years.

[0027] The configuration and positioning of ceramic inserts within a composite wear part has been the subject of numerous studies, all of which have concluded that the wear rate results obtained during tests are relatively unpredictable because they depend on the specific application, i.e., the type of machine used and the type of rocks to be crushed, or the intermittency of uses.

[0028] The situation is further complicated by the fact that during wear, the geometry of the wear part changes, and areas initially under little stress become much more stressed as wear progresses. Therefore, a compromise in the insert design is often necessary to reconcile short-term and long-term wear, as these two concepts can vary considerably from one situation to another.

[0029] The inventors of the present invention have now created a ceramic insert structure that perfectly meets this compromise. This structure has an openwork design with blind holes, the blind side being positioned on the side most stressed by the wear part so as to offer high wear resistance at the beginning of use and, once the blind side (bottom of the holes) is worn, resistance to impact and wear by presenting through holes.

[0030] The holes made in the structure of the insert generally have a diameter between 1 and 10 cm, preferably between 1 and 8 cm and particularly preferably between 1 and 4 cm.

[0031] The depth of blind holes depends on the total thickness of the insert and the specific use; it generally represents between 20 and 85% of the total thickness, preferably between 30 and 80%, and particularly preferably between 40 and 70%.

[0032] The insert can be made in several superimposed layers (D and E) or with adjacent pieces (A and B). The blind side can therefore be made of a ceramic composition different from that containing the holes which is superimposed or adjacent to it (see figures).

[0033] Although a round cross-section is preferred for the holes, it is clear that the invention is not limited to this shape. The holes can therefore have any cross-sectional shape, for example, square, hexagonal, or any other shape.

[0034] A partially hollowed-out insert with blind holes can also be considered where the blind holes are alongside through holes, however the proportion of blind holes must be significant, i.e. greater than 20%, preferably greater than 40% and particularly preferably greater than 60%.

[0035] When the insert is formed of two adjacent zones, one mainly consisting of blind holes and the other mainly of through holes, the boundary holes in the most stressed zone of the wear part have a cross-section and / or an opening area smaller than that of the holes in the least stressed zone.

[0036] The general concept of the invention lies in the fact that the first wear occurs on a side reinforced by an insert mostly devoid of holes, here in this case the blind side of the insert, which once worn still offers strong resistance to wear with through holes of a reduced section compared to the sections of through holes found on the less stressed side of the wear part.

[0037] Although the invention is not limited by a precise composition of ceramics, alumina-zirconia or titanium carbide-based ceramics, placed as such in the mold (cermet grains) or formed in situ However, self-propagating thermal reactions are preferred. Alumina-zirconia proportions comprising 10 to 90% alumina and 90 to 10% zirconia by volume are preferred, the zirconia possibly being stabilized with yttrium oxide. Examples

[0038] The present invention has been exemplified by a roller of a vertical rotary mill and moving parts of a cone crusher which were made with, on the one hand, an insert having through holes according to the prior art and, on the other hand, with inserts having essentially blind holes according to the invention.

[0039] The rate of wear was compared under the following circumstances: Machine type Secondary cone crusher Type of wear part : Moving part Type of crushed material Rhyolite 50-150 mm

[0040] Number of operating hours with and without inserts opening onto the most stressed area: Cone crusher Lifetime Superiority coefficient (CS) Through-inserts 220 H 1 Blind hole inserts 308 H 1,4 Machine type Vertical shredder Type of wear part Pebble Type of crushed material Siliceous-Calcareous

[0041] Number of operating hours with and without inserts opening onto the most stressed area: Vertical shredder wear rate Superiority coefficient (CS) Through-inserts 32 mm / kh 1 Blind hole inserts 21 mm / kh 1,5

Claims

1. A composite wear part comprising a ferrous alloy matrix and at least one ceramic reinforcement in the form of an insert (1) with an openwork structure, the openwork structure comprising blind holes (2), the blind side of the holes being positioned on the most stressed side (3) of said wear part.

2. The composite wear part according to claim 1, wherein said ceramic insert comprises at least two areas (A, B), the more stressed area (A) comprising a majority of blind holes (2) and the less stressed area (B) comprising a majority of through holes (4) .

3. The composite wear part according to claims 1 or 2 in which the section of the holes of the ceramic insert (1) in the area (A) is smaller than the section in the area (B) of said wear part.

4. The composite wear part according to any one of the preceding claims wherein the total section of the openings in the insert (1) on side (A) is smaller than the total section of the openings on side (B).

5. The composite wear part according to any one of the preceding claims wherein the blind side of the ceramic insert (1) is partially or entirely formed by a ceramic which has a different composition than that forming the area (B) with the through holes (4).

6. The composite wear part according to any one of the preceding claims wherein there are at least two superimposed ceramic reinforcement structures (D, E) in the area (A).

7. The composite wear part according to any one of the preceding claims wherein the blind holes are obliquely arranged in the insert.

8. The composite wear part according to any one of the preceding claims wherein the blind holes have a frustoconical shape.

9. The composite wear part according to any one of the preceding claims wherein the ceramic insert (1) comprises alumina-zirconia.

10. The composite wear part according to any one of the preceding claims wherein the ceramic insert (1) comprises carbides formed in situ by a self-propagating exothermic reaction, preferably titanium carbide.

11. The composite wear part according to any one of the preceding claims wherein the ceramic insert (1) comprises grains of a ceramic-metal composite (CERMET).

12. The composite wear part according to any one of the preceding claims wherein the ceramic structure comprises alumina-zirconia in proportions of alumina ranging from 10 to 90 % by volume and zirconia ranging from 90 to 10 % by volume, zirconia being optionally stabilized with yttria.

13. A method for making a wear part according to any one of the preceding claims comprising the following steps: - providing a mold for making a wear part by casting a ferrous alloy, - placing an insert according to any one of claims 1 to 12 in the form of an aggregate of millimetric granules of ceramic material or infiltrable ceramic material precursors in the mold with the blind side on the most stressed side of the wear part, - infiltration of the insert by the molten ferrous alloy.

14. The method according to claim 13 wherein the ferrous alloy comprises steel or cast iron.

15. The method according to claims 13 or 14 wherein the millimetric ceramic granule aggregates or infiltrable ceramic precursor aggregates are selected from the following compositions: - Alumina-zirconia in proportions of 90 / 10 to 10 / 90, zirconia being optionally stabilized with yttria, - Carbon and titanium powder optionally comprising iron powder as a moderator of the reaction initiated by the casting of the ferrous alloy. - Ceramic-metal composites (CERMET).