WO2002009878A1 - Impeller for centrifugal crushers with vertical axis and method for making same - Google Patents

Abstract

The invention concerns an impeller for centrifugal crushers with vertical axis. Initially, that is when it is used for the first time, said impeller (1) does not comprise cavities or pockets, but it is provided on its working surface (5) with a reinforcing structure (4), made of a composite material obtained from an alloy based on iron and ceramic grains with high wear resistance and formed on site when the impeller is cast by infiltrating molten metal for forming the part body in a mass of ceramic grains and binder. The wear to which it is subjected in operating automatically causes pockets or cavities to be formed which, when they are filled with crushed material, act as a protection against impacts.

Description

 IMPACTOR FOR VERTICAL AXIS CENTRIFUGAL CRUSHERS AND PRODUCTION METHOD

OBJECT OF THE INVENTION The present invention relates to an impactor (also called an ejector or "impeller"), intended for so-called VSI (Vertical Shaft Impacter) crushers, that is to say centrifugal crushers with vertical axis and comprising a reinforcing structure.

Technological background underlying the invention [0002] Crushers of the aforementioned type are well known and widely used for crushing rock aggregates, inter alia in quarries and cement factories. Reference is made to it in document WO 99/47264 and in other documents cited in this publication.

In these documents, it is indicated that the centrifugal crushers include a cylindrical tank in which is disposed a rotary table which is supported by a vertical bearing and which comprises means for rotating the table around the central axis of the crusher . The crusher comprises a series of impactors or ejectors fixed to the rotary table, as well as a series of anvils arranged on the internal vertical wall of the cylindrical tank around the rotary table.

The impactor is most often in the form of a parallelepiped generally made of cast iron which is fixed to the rotary table of the crusher. The face of the impactor which is directed towards the axis of rotation of the table is called the nose of the impactor, while the opposite face of the anvils fixed on the cylindrical tank forms the exit face of the impactor. The front face of one impactor called the working face is that which meets the material to be crushed and which in the direction of rotation of the impactor precedes the rear face. This front working face of the impactor can be provided with one or more cavities which do not cross the entire structure of the impactor and which form pockets which fill with material during the rotation of the crusher and thus protect the impactor from impact and wear, under the effect of the material accumulated in the pockets.

[0008] During the crushing operation, the material to be crushed is poured into the center of the rotary table by known means. Under the effect of centrifugal force and under the impact with said working face, the material is projected towards the anvils on which it is crushed to fall, in crushed form, to the bottom of the crusher from where it is discharged . During the projection of the material, the impactors are subjected to very high stresses and are therefore subject to rapid wear.

The pocket impactors used make it possible in certain applications, by accumulating material in the pockets, to considerably increase the life of the impactors. Due to the fact that in this type of impactor, it is observed that the wear is preferably done at the level of the exit edge of the pockets, that is to say where the abrasion due to the particles projected by the force centrifugal is the highest. Document W099 / 47264 already mentioned, as well as various documents cited therein, provide protections or reinforcements to avoid or reduce these wear effects. The specific solution proposed in W099 / 47264, namely the manufacture of an impactor with one or more pockets having an essentially parallelepiped shape consists of creating over the entire periphery of the pocket or pockets or on a part thereof , a reinforcing structure of a composite material itself obtained from an iron-based alloy and very wear-resistant ceramic grains. This structure, which is formed in situ when the impactor is cast by the infiltration of the liquid metal used to form the body of the part in a mass of ceramic grains and binder, has been found to be particularly effective in ensuring a duration of increased impactor operation.

Despite the considerable technical progress and the significant technological advantages of this type of manufacturing, certain limitations or difficulties have appeared.

It will be noted first of all that in order to obtain effective reinforcement, ^' the support consisting of ceramic grains and binder must be perfectly infiltrated by the metal.

It is therefore necessary to provide a sufficient metal thickness on either side of the support to have good infiltration of the ceramic component of the reinforcing structure. This requires maintaining a good thickness of the walls of the part made of composite material and, consequently, limits the size of the pockets. This also leads to having to limit the thickness of the ceramic reinforcement to improve the infiltration; this limitation in thickness of the reinforcement makes it less effective and more brittle .

In addition, both in the case of impacters with a pocket and in the case of impactors with several pockets, during the first start-up, the pockets are empty and not protected by the material to be ground.

At this time, the thin walls are particularly exposed to the impacts of larger aggregates or foreign bodies (pieces of steel, shovel teeth, etc.). This can lead to the rupture of the most fragile reinforced walls, which seriously damages the part and often requires having to replace it very quickly after the first commissioning.

In the vertical axis crushers, it is also observed that the wear profile is generally not very controllable, because the operating conditions depend on various parameters which themselves change over time, such as: particle size with feed, aggregate abrasiveness, etc. ^: With the solution proposed in document W099 / 47264, a modification of the shape of the pockets requires a complete modification of the foundry models and of the core boxes, without the possibility of predicting the result that will be obtained. These operations are moreover very expensive and cause great loss of time.

Furthermore, if one wishes to modify the profile of the pockets, one is also limited in the form chosen linked to the difficulty of pre-mentioned infiltration. Finally, the wear of the impactors in the VSI crushers remains despite everything a major problem because the stresses of abrasion and shocks are excessively severe. Extending the life of impactors is a constant concern. Goals of the invention

The invention aims to solve the problems mentioned above and, in particular, to further improve the performance of the impactors by taking advantage of the intrinsic advantages of the technology for manufacturing the impactors described in document WO99 / 47264. Main characteristic elements of the invention The invention proposes an impactor intended for vertical axis centrifugal crushers which, unlike those of the aforementioned prior art, does not deliberately comprise initially, it is that is to say during the first commissioning, no cavities or pockets, but which is provided on its working face with a reinforcing structure consisting of a composite material obtained from an iron-based alloy and ceramic grains very resistant to wear and formed in situ when the impactor is poured by infiltration of the liquid metal used to form the body of the part in a mass of ceramic grains and binder. Said reinforcing structure is provided on the working face in an adequate geometrical arrangement in order to let the metal outcrop locally (that is to say in the zones without reinforcing structure) up to the working surface, so that wear in service automatically causes the formation of pockets or cavities which, when filled with crushed material, exert a shock protection function, while maintaining the reinforcing structure at the upper periphery of the pockets which are thus formed , that is, on the work surface.

The impactor obtained makes it possible to entirely solve the aforementioned problems.

Regarding the infiltration difficulties, the amount of metal available for infiltrating the support is, in the case of the invention, all of the metal constituting the part instead of being only the metal constituting a single wall. In addition, we can introduce a thicker reinforcement where it is deemed necessary because we are in better infiltration conditions because we have a larger mass of liquid metal.

The fact that the pockets are not formed from the start completely eliminates the risk resulting from the existence of thin walls during the first commissioning, due to the fact that sufficiently thick walls can be produced.

In the version proposed by the invention, only the profile of the reinforcement must be modified if one wishes to change the shape of the pockets, which ^• greatly reduces costs and also offers better possibilities of shape and design . In addition, it is possible to cast the part without recourse to one or more sand cores intended to form the pocket or pockets, which: considerably reduces the production costs.

Finally, the technique of the invention makes it possible to significantly improve the service life because as soon as the formation of the pockets is initiated, one already benefits from one self-protection due to the material retained in these pockets in formation. The progression of the formation of pockets is slowed down and when we arrive at the complete formation of these, we have gained in lifespan all the time necessary for this training. In summary, we can say that the invention incorporates the specific advantages described in the document

W099 / 47264 of a reinforcing structure, made of a composite material, obtained in situ by the infiltration of a liquid metal into a ceramic mass with the facilities and advantages of the production of a part, without the obligation to provide one or more pockets.

The method used is particularly simple to implement since it suffices to fix in the bottom of a mold, by conventional means such as gluing, mechanical fixing, nails, screws, anchor rods or others depending on the geometrical arrangement desired to subsequently allow the formation of one or more pockets by wear, a lining of wear-resistant technical ceramic material, preferably in the form of a mass of ceramic grains based on alumina and zirconia and d a binder, and then casting the metallic mass used to form the body of ^λ impactor. This metal, by infiltrating the ceramic mass, ensures its perfect connection with the cast part during the cooling of the part. Then it is enough to unmold the part and, after a possible finishing (deburring etc.), the impactor can be directly put into service.

Other features and advantages of the invention will appear on reading the description which follows, with reference to the accompanying drawings.

Brief description of the drawings

In the various accompanying drawings, there is shown: - Figure 1: a perspective view of a pocket impactor according to the prior art, with ceramic reinforcement infiltrated by metal;

Figure 2: a perspective view of an impactor with the same type of reinforcement and without pockets, according to the present invention;

Figure 3: a longitudinal sectional view of an impactor according to Figure 2 with the evolutionary outline of the profile of the pockets during their formation. Description of a preferred embodiment of the invention Identical reference marks are used in the different figures for identical or similar constituent elements.

A conventional pocket impactor 1 according to FIG. 1. Has one or more pockets, in this case the two pockets 2 and 2 'made of foundry, before the impactor 1 is put into service. This impactor advantageously includes reinforcements 4 in infiltrated ceramic. The nose 6 of the impactor and the outlet face 7 of the impactor, which are in principle also highly stressed, may include additional reinforcements, such as the reinforcement 8 shown in FIG. 1. In the case of the embodiment shown in Figure 2, the impactor 1 is designed before commissioning as a solid piece, without pockets on its working face 5, but provided with reinforcements 4 made of foundry. These reinforcements can be arranged, - as shown in the view of Figure 2, in a shape and an arrangement similar to those provided in the figure

1, if one wishes to form two pockets in service. Of course, depending on the aims pursued, other forms and arrangements are possible. Figure 3 illustrates the evolution in service

(progression I, II and III) of the profile of the pocket being formed, resulting from the presence of the reinforcements 4 before the part is put into service.

There is shown the intermediate reinforcement separating in Figure 1, the pockets 2 and 2 'and common to them, and the corresponding intermediate reinforcement in Figure 2 (and in Figure 3) as having the same thickness. In the case of the embodiment of FIG. 1, one is however limited in thickness because it is, in this case, particularly difficult to infiltrate the ceramic material completely in its mass by the metal, whereas this difficulty does not appear, in the case of FIG. 2, because of the "full" character of the part formed by casting .

The invention therefore provides a simple solution to various technical problems of producing impactors, in particular greater freedom of design thereof. The execution of the recommended technique is moreover inexpensive. The cost of the additional cast iron to be used is largely offset by the increased operating time, the ease of execution and the absence of the need to provide specific means for creating the pockets during the casting of the part. Additional reinforcements for the nose and the exit face of the impactor, such as that represented by the reference 8 in FIG. 1, can also be provided in the embodiment of the invention, in particular of the Figures 2 and 3. They are not shown there, only for the sake of clarity of the drawing.

Claims

1. Impactor intended for centrifugal crushers with vertical axis, characterized in that it does not initially, that is to say during the first commissioning, no cavities or pockets, but that it is provided on its working face (5) of a reinforcing structure (4) made of a composite material obtained from an alloy based on iron and ceramic grains very resistant to wear and formed in situ at the pouring of the impactor by infiltration of the liquid metal used to form the body of the part in a mass of ceramic grains and binder. 2. Impactor according to claim 1, characterized in that said reinforcing structure (4) is provided on the working face (5) according to an adequate geometrical arrangement in order to let the metal flush locally to the working surface (5 ), so that wear in service automatically causes the formation of pockets or cavities which, by filling with crushed material, exert a shock protection function while maintaining the reinforcement structure at the upper periphery of the pockets which form well, that is, on the work surface. 3. Impactor according to claim 2, characterized in that it comprises a reinforcing structure (4) whose shape and arrangement are such that it causes, during wear in service, the formation of at least one pocket. 4 .. impactor according to claim 3, characterized in that it comprises a reinforcing structure (4) whose shape and arrangement are such that it causes, during wear in service, the formation of at least two pockets. 5. Impactor according to any one of claims 1 to 4, characterized in that the ceramic grains are grains based on alumina and zirconia. 6. A method of producing an impactor according to any one of claims 1 to 5, characterized in that fixed in the bottom of a mold, according to the desired geometrical arrangement to later allow the formation of one or more wear pockets, a lining of wear-resistant ceramic material, infiltrable with molten metal and then pouring the metallic mass used to form the body of the impactor so that it is flush with the surface of working in areas not lined with ceramic material and, after the ceramic lining lined with the metallic mass has been secured by cooling, the part forming the impactor is removed from the mold. 7. Use of the impactors according to any one of claims 1 to 5, or obtained by the method of claim 6, in centrifugal crushers with vertical axis by progressively forming pockets by wear in service of its constituent material not protected by the reinforcing structure on the working face.