Composite wear component

Abstract

Composite wear component produced by casting and consisting of a metal matrix whose working face or faces includes inserts which have a very high wear resistance, characterized in that the inserts consist of a ceramic pad, this ceramic pad consisting of a homogeneous solid solution of 20 to 80% of Al₂O₃ and 80 to 20% of ZrO₂, the percentages being expressed by weights of the constituents, and the pad then being impregnated with a liquid metal during the casting.

Description

SUBJECT OF THE INVENTION

The present invention relates to a composite wear component produced by casting and consisting of a metal matrix whose wear face comprises inserts which have good wear resistance properties.

TECHNOLOGICAL BACKGROUND UNDERLYING THE INVENTION

The invention relates especially to wear components employed in plants for grinding, crushing and conveying various abrasive materials which are encountered in industries such as cement factories, mines, metallurgy, electricity generating stations or various quarries. These components are often subjected to high mechanical stresses in the bulk and to a high wear by abrasion at the working face. It is therefore desirable that these components should exhibit a high abrasion resistance and some ductility, to be able to withstand the mechanical stresses such as impacts and to be capable optionally of being mechanical.

Given that these two properties are difficult to reconcile with one another in the same material, composite components have already been proposed which have a core made of relatively ductile alloy in which isolated inserts which have a good wear resistance are embedded.

Document EP-A-0476496 proposes this technique for the production of grinding wheels whose working face has set-in inserts made of chrome pig iron.

Since it is known that ceramic materials have good abrasion resistance properties, it is also known to employ these materials for improving the abrasion resistance of wear components.

Document EP-A-0575685 proposes the use of ceramic materials in a moulding by lost-wax precision casting of small wear components.

This well-known process employs wax models which must be melted to obtain the mould cavity which must be filled with metal; this mould itself is made of ceramic and not of a conventional sand.

According to this document a ceramic pad (wafer core) is formed first, with a spongy structure which has a three-dimensional network of open pores all of which communicate with one another. This ceramic pad is formed by pouring grains of ceramic materials into an appropriate mould and, next, a liquid adhesive with a good fluidity, for example a liquid resin which, after curing, retains the grains to form the ceramic structure. The ceramic material may consist of aluminium oxide or of zirconium oxide. After having been pre-impregnated with wax, this pad is placed in a mould intended to produce the wax model of the component. The wax model is then case and, lastly, the ceramic mould is produced by dipping the wax model in a ceramic slurry. The ceramic mould containing the wax model is then heated so as to melt the wax model. The wax thus flows from the ceramic mould but the pads inserted beforehand in the wax model remain adhesively bonded to the walls of the ceramic mould.

For the casting of metal in the ceramic mould the latter is preheated to a temperature of the order of 1150° C., generally under vacuum.

This known technique is limited, however, to lost-wax precision moulding. Moreover, the compatibility between the metal matrix and the ceramic structure, especially in terms of temperature behaviour, presents hardly any problems in the case of the applications mentioned in this document, given that, when the metal is being cast, the mould and the ceramic structure are preheated to a high temperature. In addition, the technique is limited to the production of very precise special components, which are sold at a very high price because the lost-wax moulding process itself is very costly.

The document “Ullmann's Encyclopedia of Industrial Chemistry” (1985), W. Gerhartz, VCH Verslagsgesellschaft, 5^th Edition XP002023826, page 5 mentions compositions based on Al₂O₃—ZrO₂ for grinding devices intended for conditioning cast products (billets and slabs).

PROBLEMS UNDERLYING THE INVENTION

The technique described above cannot as such be adapted to the manufacture of wear components of larger dimensions for application such as those encountered in plants for grinding, crushing or conveying abrasive materials, where the components generally have sections of at least 25 mm and often larger than 40 mm.

In addition, in accordance with the technique of the present invention it is not possible to cast, or at least it is difficult to envisage casting, components with thin sections, for example of less than 25 mm, because neither the mould nor the ceramic insert is preheated to high temperature before the metal is cast.

Furthermore, the component usually undergoes a subsequent heat treatment. There must therefore be some compatibility from the viewpoint of temperature behaviour between the ceramic material and the metal, to avoid cracking due to the thermal shocks when liquid metal is being cast over the ceramic inserts, and those that can be produced during the subsequent heat treatment and caused by the different expansion coefficients of both these materials.

It is necessary, furthermore, that the mechanical properties of the ceramic material should be adapted to those of the metal in order to produce a component whose properties correspond to the requirements of the specific application for which it is intended.

The aim of the present invention is to provide a composite wear component with ceramic inserts satisfactorily corresponding to the requirements listed above.

A second problem arises from the fact that, above a thickness of 25 mm of the ceramic material, poor infiltration of the metal is observed. Another objective of the present invention is to solve this second problem by proposing specific geometries of the composite wear component.

MAIN CHARACTERISTIC ELEMENTS OF THE INVENTION

To meet the first objective the invention proposes a composite wear component produced by conventional or centrifugal casting. It consists of a metal matrix whose wear surface comprises inserts which have good abrasion resistance properties, these inserts being made of a ceramic material, itself composite, consisting of a solid solution or homogeneous phase of 20 to 80% of Al₂O₃ and 80 to 20% or ZrO₂, the percentages being expressed by weights of constituents.

The ceramic material may additionally contain other oxides whose proportion by weight does not exceed 3 to 4%.

According to a first preferred embodiment of the present invention the composition of the ceramic material is the following:

55-60% by weight of Al₂O₃, and

38-42% by weight of ZrO₂.

According to another preferred embodiment the composition of the ceramic material is the following:

70-77% by weight of Al₂O₃, and

23-27% by weight of ZrO₂.

with FIG. 1 being a sectional view1 which are superposed and leaving a 10 mm gap between them. These Ceramic pads 1 are placed in an appropriate mould, preferably made of sand, into which is next cast a liquid pig iron 2 including 3% or carbon, 26% of chromium and other conventional elements in a small proportion which is always encountered in alloys of this type. A wear component is thus produced with ceramic inserts 1 with a hardness of the order of 1600 Hv with an expansion coefficient close to 8×10⁻⁶, held in a pig iron matrix 2 with a hardness close to 750 Hv.

Example 2

Manufacture of a Crusher Rotor

The ceramic material is prepared as in Example 1 but this time choosing a composition which gives preference to the expansion coefficient at the expense of hardness, that is to say by taking 40% of ZrO₂ and 60% of Al₂O₃.

Given that the thickness is particularly considerable in this kind of component, a “honeycomb” form configuration is employed, as shown in FIG. 2, which is formed of ceramic inserts 1 and cast metal 2. In this case the structure is in the form of a “honeycomb” whose cells have walls the thickness of which is approximately 20 mm and the height of which is practically equal to the height of the composite component. This structure is produced with the aid of a manganese steel with a composition of 1% of carbon, 14% of manganese and 1.5% of molybdenum.

A composite component is thus produced with a hardness of approximately 1350 Hv with an expansion coefficient close to 9×10⁻⁶. The objective here is to decrease the risk of splits in the component because of the high impact level to which this type of component is subjected.

Example 3

Beater

FIG. 3 shows an example of a ceramic pad employed for an application in beaters, which allows the three wear phases of the beater to be strengthened. The ceramic pad 1 is a single component situated within the metal phase 2.

Claims

1. Composite wear component produced by classical or centrifugal casting and consisting of a metal matrix having a working face or faces including inserts which have wear resistance, wherein the inserts consist of a porous ceramic pad, the porous ceramic pad consisting of a homogeneous solid solution ceramic composite of 20 to 80% of Al₂O₃ and 80 to 20% of ZrO₂, the percentages being expressed by weights of the constituents, and the porous ceramic pad being integrated into the metal matrix by impregnation of a liquid metal in the porous ceramic pad during the casting.

2. Composite wear component according to claim 1, wherein the ceramic material includes from 55 to 60% by weight of Al₂O₃ and from 38 to 42% 40 to 45% by weight of ZrO₂.

3. Composite wear component according to claim 1, wherein the ceramic material includes from 70 to 77% by weight of Al₂O₃ and from 23 to 27 30% by weight of ZrO₂.

4. Composite wear component according to claim 1, wherein the content of ceramic materials in the insert is between 35 and 80% by weight volume.

5. Composite wear component according to claim 1, wherein the inserts consist of an aggregate of composite ceramic grains which have a particle size within the range F6 to F22 according to the FEPA standard.

6. Composite wear component according to claim 1 5, wherein the ceramic grains are manufactured by one of electrofusion, sintering and flame spraying.

7. Composite wear component according to claim 1 5, wherein the ceramic grains are joined integrally with the aid of an inorganic or organic liquid adhesive prior to the casting with the liquid metal with a view to the production of the ceramic pad .

8. Composite wear component according to claim 7, wherein the pad does not contain more than 4% of adhesive.

9. Composite wear component according to claim 1 produced by casting and composed of a metal matrix including at least one ceramic pad, and at least two ceramic pads are placed side by side superposed, leaving a gap of the order of 10 mm in order to permit the arrival of the liquid metal.

10. Composite wear component produced by classical or centrifugal casting according to claim 1 and made up of a metal matrix including a wear-resistant ceramic pad, wherein the ceramic pad is in the form of a honeycomb structure in which the various cells are of polygonal or circular shape within the ceramic phase.

11. Composite wear component according to claim 10, wherein a thickness of walls of the various cells constituting the ceramic phase varies from 5 to 25 mm.

12. Composite wear component produced by classical or centrifugal casting, said composite wear component comprising

a metal matrix having a working face or faces including inserts which have wear resistance, the inserts include a porous ceramic pad, the porous ceramic pad comprises a homogeneous solid solution of 20 to 80% of Al₂O₃ and 80 to 20% of ZrO₂, the percentages being expressed by weights of the constituents, and the porous ceramic pad being integrated into the metal matrix by impregnation of a liquid metal in the porous ceramic pad during the casting.

13. Composite wear component according to claim 12, wherein the ceramic material includes from 55 to 60% by weight of Al₂O₃ and from 38 to 42% by weight of ZrO₂.

14. Composite wear component according to claim 12, wherein the ceramic material includes from 70 to 77% by weight of Al₂O₃ and from 23 to 27% by weight of ZrO₂.

15. Composite wear component according to claim 12, wherein the content of ceramic materials in the insert is between 35 and 80% by weight.

16. Composite wear component according to claim 12, wherein the inserts include an aggregate of composite ceramic grains which have a particle size within the range F6 to F22 according to the FEPA standard.

17. Composite wear component according to claim 16, wherein the ceramic grains are manufactured by one of electrofusion, sintering and flame spraying.

18. Composite wear component according to claim 16, wherein the ceramic grains are joined integrally with the aid of an inorganic or organic liquid adhesive prior to the casting with the liquid metal.

19. Composite wear component according to claim 18, wherein the pad does not contain more than 4% of adhesive.

20. Composite wear component produced by classical or centrifugal casting according to claim 12 and made up of a metal matrix including a wear-resistant ceramic pad, wherein the ceramic pad is in the form of a honeycomb structure in which the various cells are of polygonal or circular shape within the ceramic phase.

21. Composite wear component according to claim 20, wherein a thickness of walls of the various cells constituting the ceramic phase varies from 5 to 25 mm.

22. Composite wear component accordint to claim 12 produced by casting and composed of a metal matrix including at least two ceramic pads superposed, leaving a gap of the order of 10 mm in order to permit the arrival of the liquid metal.