WO2003024648A1

WO2003024648A1 - Parts for crushing aggregates comprising a metal matrix with an internal ceramic insert and the production method thereof

Info

Publication number: WO2003024648A1
Application number: PCT/ES2001/000437
Authority: WO
Inventors: José Ignacio ERAUSKIN LOPETEGUI
Original assignee: Fundacion Inasmet
Priority date: 2001-09-17
Filing date: 2001-11-15
Publication date: 2003-03-27
Also published as: ES2190881A1; ES2190881B1

Abstract

The invention relates to parts for crushing aggregates comprising a metal matrix with an internal ceramic insert. The invention is characterised in that the metal matrix is made from white cast iron which is highly alloyed with nickel-chromium or chromium molybdenum close to the eutectic composition. Each insert is made from white corundum with a minimum Al203 purity percentage of 99 %. Said inserts form a body having a smaller thickness than that of the part, with n rows of perforations disposed on the front thereof and flanges projecting out from the side faces along the height of same. The invention is suitable for use in metal founding with ceramic reinforcements.

Description

"PARTS FOR GRINDING OF COMPOUND AIDES OF A METAL MATRIX WITH INTERNAL INSERT OF CERAMIC MATERIAL AND ITS MANUFACTURING PROCESS"

The object of the invention are pieces for grinding aggregates composed of a metal matrix with internal insert of ceramic material and its manufacturing process.

The metal matrix parts with internal insert / s of ceramic material are already known.

In EP-0 575 685 the use of ceramic materials in the precision molding of small wear parts is proposed and textually says "the castings according to this invention are executed by precision casting procedure, in which meltable or combustible models (wax) are used for mold production. " According to this document, a spongy cookie is first formed, presenting a three-dimensional network of open pores communicated between them, in a kind of ceramic sponge. On this structure the liquid metal that fills the pores and forms, after solidification, the metal matrix of the composite piece. The ceramic cookie can be obtained by molding in a suitable mold with the grains of ceramic material and a glue of a good fluidity, for example, a liquid resin, which after hardening, retains the ceramic grains to form the ceramic structure. The ceramic material may consist of aluminum oxide or zirconium oxide.

This technique of precision casting or lost wax molding is not applicable to the production of aggregate grinding pieces, since these (due to their dimensions) have a weight greater than 40 kg, some reaching 3,000 kg. and the lost wax molding is viable for pieces of between 5 gr. and 20 kg.

The reason for this weight limitation is that the representative models of the pieces are made with wax injected into a metal mold, which is subsequently coated with ceramic layers and evacuated by fusion. So, This procedure is unfeasible, technically and economically, for bulky and heavy parts such as those in the present case.

In addition, the previous ceramic layers must be preheated to about 1,000 ° C before pouring the liquid metal. Due to this, for other types of smelting, castings in this way are completely fragile, due to the microstructure (very thick, elongated and fragile carbides) that originates in a very slow solidification process, derived from a very small metal thermal gradient -mold.

On the other hand, according to the invention of EP-0 575 685, it is not possible to achieve metal-ceramic composites with the inserts thereof inside the metal, but only outside, with a contact surface (only of contact) between the two and with the only metal bond that can penetrate, only in one direction through the holes of the ceramic preform. For the grinding pieces of aggregates, this solution is completely inadequate, since the magnitude of the impacts of the aggregates (pieces of stone with high dynamic energy) together with the vibrations and the rotational movement to which they are subjected, makes jump in pieces the pottery in the first instant of operation of the machine.

WO009815373 concerns metal-ceramic composite parts with good wear resistance, in which the inserts consist of ceramic blocks formed by a homogeneous solid solution of 80-20% A1 ₂ O3 and 20-80% ZrO ₂ .

The applicant has developed some pieces in which the ceramic inserts are made of white corundum (99.6% Al ₂ O ₃ ) because the possibility of using a ceramic based exclusively on 100% A1 ₂ O ₃ presents the following advantages : - Lower cost of the material, derived from that of the starting raw materials (zirconium oxide is scarce and expensive), as well as the complexity of the process for obtaining the solid solution.

- Higher hardness of the ceramic, 40%, with respect to that of lower zirconia content and greater for the other contents and, consequently, greater wear resistance and longer service life. - Greater resistance to shear breakage and greater impact fracture toughness (both mechanisms, shear and impact, are those involved in the work of the pieces during the grinding of aggregates) of the ceramic grains. - Lower density of ceramics (alumina has 3.9 g / cm ³ compared to 5.7 g / cm ³ of zirconia). This makes the inserts based on corundum (practically pure alumina) lighter than those made of alumina-zirconia, so that the piece is lightened in the first case compared to the second.

- Lower risk of cracking of the piece during the casting process (in the cooling inside the mold as in the heat treatment), since the alumina possesses a lower coefficient of thermal expansion and a thermal conductivity greater than 80-20 solutions % At ₂ O ₃ -20-80% ZrO, the temperature between metal and ceramic is uniformized more quickly and easily, and in addition to the smaller changes in volume of the ceramic, the metal accommodates with less stress to it during its thermal cycle.

For the design of the metal matrix of the parts of the invention the following tests and experimental tests were carried out with different steels and ferrous alloys: a) .- Medium-alloy hypo-eutectoid steels, cast between 1,650-1,720 ° C (higher temperatures are practically technically and technologically unviable). Result: parts with pores, with filling defects and no metal penetration into ceramic inserts. b) .- Medium-alloyed hyper-eutectoid steels, cast between 1,600-1,720 ° C. Result: pieces with the same previous defects, although to a lesser extent. c). Hadfield steel (1.2% C; 12% Mn), cast between 1,500- 1,650 ° C. Result: cracked and porous pieces. d) .- White hypo-eutectic smelters, casts between 1,500- 1,650 ° C. Result: lack of metal-ceramic penetration. The applicant considers that the technical reasons for this different and unwanted behavior of the materials tested (virtually all ferrous alloys), are based on the following: Ceramic males are at room temperature (20-25 ° C) at When the liquid metal is poured and it, in contact with them, suffers a significant loss of temperature during the filling of the mold. This loss of temperature entails a reduction in the fluidity of the liquid metal, the higher the solidification temperature is higher (in the case of steels), so that the filling of the piece as well as the penetration and imbibition of metal-ceramics are inadequate . In addition, the higher the temperature of the liquid steel, the greater the absorption of gases and the parts are porous.

These findings led the applicant to test with eutectic white smelters since in the case of eutectic white smelting (highly alloyed to chromium, chromium-nickel or chromium-molybdenum), its solidification temperature is the lowest of all alloys railings that respond to the meta-stable Fe-CX diagram (300 ° C lower than that of steels), so that its pouring fluid can be easily increased in order to ensure both the filling of the piece and the imbibition of ceramic particles of the insert by the metal matrix. It was tested with eutectic white smelters or very close to the eutectic composition, highly alloyed to chromium, chromium molybdenum or chromium nickel, castings between 1,550-1,620 ° C. satisfactory result.

In addition, by containing these alloys around 30% carbides in their microstructure, they contribute to making the hardness of the metal matrix higher than that of steels. Otherwise, with a softer matrix, the wear of this and that of the ceramic are completely decompensated and the performance of the piece during grinding is significantly lower. On the other hand, parts manufactured with these materials can be used with or without heat treatment, depending on the specific conditions of their application.

Therefore, the parts of the invention are also characterized in that their metallic matrix is constituted by a white cast iron highly alloyed to chromium, chromium molybdenum or chromium nickel (Nihard) and whose chemical composition, in any of the three cases, It is close to the eutectic.

The composite piece is obtained by previously manufacturing "males" with grains of the aforementioned ceramic bonded with an organic cold setting resin, placing them, in an upright position, in cold hardened sand molds or in shell molds, and casting the liquid metal in the same. This surrounds, "wets" and mechanically traps, upon solidification, each grain of the ceramic core, resulting in a metal part reinforced internally by the ceramic grains, which retain their initial position (inside the work faces of the piece ) without spreading over the rest of the piece or towards the outside of it.

Being the resistance to wear of the piece, and therefore its duration in service, directly influenced by the hardness of the metallic and ceramic material, the wettability or cohesion metal-grains, the resistance to shear breakage of these grains, their toughness to the fracture, etc., the use of ceramics whose characteristics are the highest possible, inserted in a white cast metal matrix highly alloyed to chromium-nickel or chromium-molybdenum whose hardness is greater than that of the rest of the ferrous alloys, significantly increases this duration in service.

It is very important to note that the molds of the parts of the invention slip into the inserts placed vertically, since horizontally (as until now in other foundry processes) these are suspended by the two cantilevered ends and before the liquid metal catches them the resin burns and the male (when losing consistency) breaks, scattering the beans randomly. Once the piece solidifies, it is quickly demoulded in order to ensure that the microstructure of the base metal is formed by an austenitic matrix or is cooled in a conventional manner and subsequently subjected to heat treatment to achieve a martensitic microstructure. The geometry of the part and insert / s also intervenes in the invention.

With the parts of the invention, parts for grinding aggregates are achieved, with a service life exceeding 50% to those known so far and at a cheaper price. To better understand the object of the present invention, a preferred form of practical embodiment is shown in the drawings, susceptible to accessory changes that do not distort its foundation. In this particular case, the piece is parallelepipedic with an insert on each side and a longitudinal notch on its front and rear face. Each insert is constituted in a parallelepipedic body with n columns of frontal perforations and whose lateral faces project fins along its height.

Figure 1 is a front and side view of the part in its manufacturing process.

Figure 2 is a perspective view of the part as it exits the process of Figure 1.

Figure 3 is a cross-sectional view of the part of Figure 2.

Figure 4 is a perspective view of a male for the part of Figure 2. A practical, non-limiting example of the present invention is described below.

In order to obtain the male (1) of Figure 4, it is based on practically pure white corundum grains (99.6 of Al ₂ O ₃ ) (it is understood that percentages of 98 or 99% do not alter the object of the invention) and are mixed with an organic resin In a discontinuous malaxator, the male box is filled with the mixture, compacted by vibration and cold set.

The shape of the male (1) and of each insert (4) of the piece (2) is practically identical, since one gives rise to the other. A mold (not shown) filled with vibration-compacted gravel (18) is arranged in which the mold shells (15) are placed in an upright position and inside the males (1) are also upright along the longitudinal axis of the piece (2) to get.

In the shell-mold (15) holes (6) are made upper / lower to retain the covers (9) of the males 1), which in turn consist of lateral wings (10) of internal support in the mold shell (15) and that facilitate the exit of gases.

The holes (6) and the interstices in the male (1) act as a chimney for the gases that are released by the organic resin during casting. White cast iron (17) highly chrome-plated cast iron (17) is cast by the bucket (16) by means of a bucket with flow regulation device (not shown) so that the ceramic reinforcement resin does not burn until it is completely surrounded by the liquid metal, at which time it is replaced by it, thus maintaining the desired arrangement of the reinforcement material ^' within the piece.

When the foundry solidifies, it can be quickly demoulded in order to ensure that the base metal microstructure is formed by an austenitic matrix.

If it is cooled, for example, to the air, the subsequent operation of a heat treatment is added, obtaining martensitic structure.

The piece obtained (2) (Figure 2) is a parallelepiped that is rectangular in this case, its height being much greater than its frontal length and this much greater than its width.

A groove notch (5) with an approximate "V" shape, and offset between them, can be seen on each front and rear face. In a section (figure 3) the constituents of the piece (2) can be seen.

An insert (4) of white corundum, with almost pure alumina and with the same shape of the male (1) has been arranged on each side of the parallelepiped, close to its ends. The rest of the piece (2) is formed by the white cast die (3) highly alloyed to Cr. The piece (2) could have another shape.

The male-insert (1), (4) (figure 4) has a preferred parallelepiped shape of rectangular bases with covers (9) that rest upper-lower in the holes (6) of the shell-mold (15). It has frontally (8) or along its height, of n rows (11) of perforations, which in this case are two, and that will be filled with the white cast iron mentioned.

Laterally it has wings (10) with inclined faces, which allows each male its support on both sides in the shell-mold (15).

Claims

CLAIMS 1.- Parts for grinding aggregates composed of a metal matrix with internal insert of ceramic material, characterized in that: a) the metal matrix is of white cast iron highly alloyed to chromium-nickel or chromium-molybdenum and close to the eutectic composition b) each insert is white corundum with a purity percentage greater than 99% of Al ₂ O ₃ .

2.- Parts for grinding aggregates composed of a metal matrix with an internal insert of ceramic material, according to the preceding claim, characterized in that the microstructure of the metal matrix is austenitic.

3.- Parts for grinding aggregates composed of a metal matrix with internal insert of ceramic material, according to previous claims, characterized in that the microstructure of the metal matrix is martensitic.

4.- Parts for grinding aggregates composed of a metal matrix with internal insert of ceramic material, according to claim one, characterized in that each insert is constituted in a body of smaller thickness than that of the piece, with n columns of frontal perforations and of whose lateral faces project fins along its height.

5.- Manufacturing process for grinding parts, characterized in that: a) each male is obtained by mixing white corundum grains of more than 99% purity of Al ₂ O ₃ with an organic cold setting resin with the male having top covers / bottom and side fins; b) each male is placed in an upright position, in the sense of its length, in the corresponding shell or mold and there are holes for the machi-female of the upper-lower covers of the male; c) a white cast iron highly alloyed to chrome-nickel or chrome-molybdenum, properly superheated, is cast into the shell-mold by means of a spoon with a regulating device. flow rate so that the organic resin does not burn until the corundum grains are surrounded by the smelting liquid; d) the foundry solidifies and unmolds.

6. Process of manufacturing parts for grinding, according to claim five, characterized in that the piece is subjected to a heat treatment of tempering and a martensitic metal matrix is obtained.

7. Process of manufacturing parts for grinding, according to claim 5, characterized in that the piece is subjected to rapid demolding to obtain an austenitic matrix that gradually hardens during the work.