CN1240374A - Insert for composite wear part, method for producing a wear part with the insert and wear part thus realized - Google Patents

Abstract

The insert (10) of the invention is substantially in the shape of a ring segment or closed ring having an outer region (12) and an inner region (14) which is less thick than the outer region (12) and has a series of holes (16) passing through it from side to side in the direction of its thickness. The inserts are stacked one on top of the other before casting the cladding and are temporarily held in place by means of rods passing through the holes (16). The holes (16) ensure a secure fixation between the insert (10) and the cladding after casting of the cladding.

Description

Insert for composite wear part, method for producing a wear part with the insert and wear part thus realized

The present invention relates to inserts for composite wear parts, and methods of making wear parts using such inserts. The invention also relates to the wear parts thus realized, in particular, but not exclusively, for crushing rollers or drums used in so-called vertical crushers and roller compactors.

Many wearing parts, such as those in crushers and crushers, are subject to high mechanical loads as a whole and their working surfaces are subject to great wear. Thus, it is of course desirable that these parts have high wear resistance and a certain toughness to be able to withstand mechanical loads such as impacts. In addition, if these parts may have to be machined, a certain degree of toughness is also indispensable. However, it is well known that these properties conflict with each other. Of course, a compromise can be made between these two contradictory properties, but this will necessarily compromise wear resistance or toughness.

In order to avoid this compromise, it is known to manufacture bimetallic parts whose parts subject to wear consist of highly wear-resistant chromium cast iron, supported by a more flexible alloy core. This reduces wear on the components and at the same time reduces the risk of core fracture.

Therefore, patent document EP0476496 proposes insert technology for realizing such components. According to this document, the hard alloy insert is coated with a cladding of a ductile alloy cast on the insert previously placed in a mould. In the crushing roller proposed in this document, the inserts are placed next to each other on the roller surface in the direction of the roller generatrix.

Although the technology seems like an ideal solution to the above problems from a design point of view, it has several difficulties in its implementation. One of these is the securing of inserts, especially of small dimensions, against displacement during the metal cladding casting process. It is precisely this difficulty that is addressed by patent document EP0620065, which proposes a method for the production of wearing parts, according to which the insert is fixed on a destructible temporary base serving as the defining surface of the mould.

The solution of the round insert described in document EP0620065 has its fatal flaw, that is, its hard surface is too narrow, and its disadvantage is also that the insert is not rod-shaped as described in document EP0476496, which can damage the mechanical properties of the assembly stiffness.

One of the problems to be solved with using hard inserts, regardless of their design, is cracks during casting due to thermal shock.

The risk of cracks in the insert during casting actually increases with the hardness of the insert, especially if the insert is very hard cast iron or ceramic; this risk also increases with the size of the insert, because, the insert The larger the part, the higher the temperature required for cladding casting.

To solve all of these problems mentioned above, it is common practice to preheat the insert to about 400 to 500°C. But this kind of preheating is not easy to implement, because either a bulky heating device needs to be installed next to the sand mold, or the insert structure needs to be placed in a heating furnace, which is not easy to implement because the insert is only temporarily fixed Once, unstable, easily shaken.

The purpose of the present invention is to overcome these difficulties, proposing new inserts that allow the manufacture of new composite wear parts with a high insertion rate, inserts surrounded by their metal cladding, with new machining methods The fixation is strengthened, and it has good thermal shock resistance during casting.

To achieve these objects, the invention proposes an insert for a composite wearing part realized in a highly wear-resistant material, characterized in that it is substantially in the shape of a ring segment or closed ring, which has an outer zone and an inner zone , the thickness of the inner zone is smaller than that of the outer zone, and the inner zone has a series of holes, and the holes penetrate from one side to the other side along the thickness direction of the inner zone.

According to the invention, the design of the insert additionally allows optimization of the grinding efficiency, as will be described in more detail below.

At least one side wall of the outer zone has several protrusions, according to a preferred embodiment, said protrusions are formed by ribs extending in radial direction, between which grooves are formed.

These protrusions or ribs may be located on both side walls of the outer zone.

The ribs may also terminate in front of the outer edges of the side walls.

The present invention also proposes a method for manufacturing wearing parts using such inserts, which is characterized in that first a certain number of inserts are stacked one by one, so that the holes in the inner zone and the protruding parts in the outer zone overlap respectively. Two rods pass through two sets of holes aligned in a straight line to temporarily stabilize and fix the stack of inserts thus achieved, said stack is preheated, said stack is placed in a mold, and casting can A more ductile material resistant to mechanical loads to fill the space not occupied by the insert, in particular the recess between the hole and the projection, so as to form a mechanical connection between the insert and the casting material.

Preheating is preferably carried out by placing the entire stack in an oven preheated to about 300 to 700°C.

To further reduce the risk of thermal shock, the inserts can be pre-coated with a thin layer of refractory paint.

The holes in the inserts can be used to easily pass rods through them, so that the stack of inserts is well stabilized prior to casting. The stack is easy to handle because two rods ensure the alignment of the inserts. Thus, the insert stack can be preheated without any risk by placing it in a furnace, which greatly reduces the risk of cracks due to thermal shock during casting. The ease of this manufacturing method will of course have a favorable effect on the production cost of the part.

The invention also proposes a cylindrical composite wearing part having a relatively flexible core of mechanically resistant material, machinable, and a series of peripheral inserts supported by the core by means of mechanical connections , characterized in that the insert is an annular insert as defined above, and the material of the tough core is filled in the cavity formed by the groove between the hole in the inner area of the insert and the protruding part of the outer area of the insert.

Since the malleable metal cladding fills all the pores in the inner area of the insert, said insert is firmly fixed on its support, ie the core.

Furthermore, the fastening effect is also improved due to the alignment and orientation of the insert parts of the composite part. In the roller proposed in the patent document EP0476496, the insert is actually positioned in the direction of the generatrix. This means that when rollers are used, the insert is alternately subjected to shear stresses perpendicular to the orientation of the insert, transverse to the orientation of the insert and the release of these forces. This continual shear stress and release can lead to fatigue cracking at the base of the insert, especially at the high pressures that characterize rolling machines.

On the contrary, the insert of the composite according to the invention avoids this drawback by virtue of its annular design and its orientation with respect to the direction of the forces exerted on the insert during grinding.

In addition, the fact that the insert is a ring-shaped insert that completely surrounds its support can only serve to strengthen the fixation of the insert so that separation is impossible as long as the insert does not crumble. The composite part according to the invention therefore has a greater mechanical reliability than hitherto known wear parts.

Using annular inserts with optimal preheat conditions allows for high insertion rates, ie a much greater percentage of wear-resistant surface.

Furthermore, the absence of a mechanical connection prevents cracks from forming on the outer surface of the component at the insert/support interface and preventing cracks from propagating towards the core of the component.

In order to compensate for the preferential wear of the crushing roller in its middle zone, thereby preventing the formation of a concave rolling surface during use, it is possible to equip the axial ends with wear-resistant inserts with a wear resistance slightly lower than that of the middle zone inserts.

The design of the parts proposed by the invention can form a hoop of the crushing drum and for this purpose have a central cylindrical hole for receiving the support hub.

It is also possible not to form the drum hoop, but instead to cast several ring segments, which are fixed on the hub by, for example, staples or bolts to form the drum.

Other particularities and characteristics of the invention will be described hereinafter with reference to the examples and drawings. In the attached picture:

- Figure 1 is a schematic perspective view of a ring segment of an insert according to the invention;

- Figure 2 is a radial cross-sectional view of a hoop with an insert according to the invention;

- Figure 3 is a front view of the hoop along arrow II in Figure 2 .

Figure 1 shows a section of a ring segment of an annular insert 10 according to the invention, the particularity of which can be closed so as to completely surround the wear part in which it will be used. Insert 10 may be cast from a highly wear-resistant alloy, such as chromium cast iron, which may include special carbides. It can also be realized with carbide, boride, nitride, oxide type or any other type of ceramic material.

As shown in FIG. 1 , insert 10 has an outer region 12 and an inner region 14 which is thinner than outer region 12 . The inner zone 14 has a plurality of holes 16 which can be realized during the casting process and pass through the thickness of the inner zone from one side to the other.

In the embodiment described, the outer zone 12 has radial ribs 18 on each side wall and on the entire profile of the insert, between which grooves 20 are formed. Ribbing on only one of the side walls is also possible, although an insert having ribs on opposite side walls is preferred. The ribs can also be replaced by other protruding elements, such as dotted islands, the point being that, as will be seen below, grooves and cavities are formed between the inserts so that they can be encased with cast metal.

In the case of cast inserts, the latter are subjected to an annealing heat treatment after trimming to increase their thermal shock resistance. The thermal shock resistance can also be increased by using a thin layer of refractory coating.

A number of identical inserts 10 are stacked next to each other so that the holes 16 are aligned with each other and the ribs 18 contact each other to form radial cavities 22 (see Figure 3). The inner zone 14 of thin thickness then forms an annular gap 24 between each pair of inserts 10 (see FIG. 2 ).

The two outer inserts forming the bottom of the stack preferably have no ribs on their outer walls.

The rods are then inserted into at least two of the channels formed by the two sets of linearly aligned holes 16 to stabilize the stack thus achieved and to keep the sets of inserts 10 aligned.

The entire stacked structure is then placed in a furnace, preheated to a temperature of approximately 300 to 700°C. When all inserts have reached the desired temperature, the stacked structure is removed from the furnace, placed into a cylindrical mold, and cast into the desired part.

The more flexible alloy cladding that forms the insert 10 and the future component support core 26 is then cast in the mold. This alloy, preferably of ductile iron, fills the annular gap 24, the holes 16 and the cavities 22 between the inserts 10, and after solidification of the alloy ensures a firm fixation of the insert 10 in the support core 26 thus formed. The casting temperature is chosen to avoid any metallurgical connection between the insert and the casting alloy.

The casting mold has a central cylindrical limit so that the support 26 has a central cylindrical hole 28 and the finished part forms the crushing drum or the hoop of the crushing drum.

After recooling and hardening, the components are subjected to casting routines such as edge trimming, pre-machining, and then quenched before final machining of the bore.

The important role of the holes 16 of the insert 10 can be noted. In fact, they can act as a stable temporary fix before casting, especially during preheating, and can be used to move groups of 10 inserts without fear of them falling apart. The holes also securely hold the insert in the core 26 after casting.

The cavity 22 formed between the inserts 10 also plays a dual role. First, they allow the casting alloy to flow all the way to the outer surface of the insert, so this is helpful for strengthening the fixation. Furthermore, these cavities obtain a strong negative profile, as shown schematically at 30 in FIG. 2 , formed by the faster wear of the more flexible cast iron filling the cavities 22 . These recesses 30 between the inserts actually have a favorable effect on the grinding efficiency.

Furthermore, the shape of the cavities 22 can easily be adapted to the specific requirements of the crushing process or the material to be crushed. In some cases it may be useful or necessary for the recess 30 to form an annular groove around the entire part and not just limited to the cavity, especially in order to allow compressed air to escape. This can be easily implemented by having the ribs 18 not extend to the outer edge of the insert.

The invention has been described with reference to a preferred embodiment using annular inserts, it is also possible to use open arcuate inserts in a manner similar to that described above to realize the crushing drum or a segment of the crushing drum.

Claims (12)

1. An insert for composite wear parts, made of highly wear-resistant metal or ceramic material, characterized in that it is generally in the shape of a ring segment or closed ring, which has an outer zone (12) and a An inner zone (14), said inner zone having a thickness less than that of the outer zone (12), the inner zone (14) having a series of holes (16). 2. Insert according to claim 1, characterized in that at least one side wall of the outer zone (12) has protrusions. 3. Insert according to claim 2, characterized in that said protrusions are formed by radially extending ribs (18) between which grooves (20) are formed. 4. Insert according to claim 3, characterized in that said ribs (18) are located on both side walls of the outer zone (12). 5. Insert according to claim 3 or 4, characterized in that the rib (18) ends in front of the outer edge of the side wall. 6. The method for manufacturing a composite wearing part by means of an insert according to one of claims 1 to 5, characterized in that a certain number of inserts are stacked one on top of the other so that the holes on the inner zone (14) ( 16) and the protruding parts (18) of the outer zone (12) overlap each other, by passing the two rods through the two sets of holes (16) arranged in a line, the insert superimposed structure is temporarily stabilized and fixed, and the The superposed structure is preheated, the superposed structure is placed in a mold, and a tough material resistant to mechanical loads is cast to fill the spaces not occupied by the inserts, especially the holes (16 ) and the groove (20) between the protruding part, thereby forming a mechanical connection between the insert (10) and the casting material. 7. The method according to claim 6, wherein during preheating, the whole stacked structure is heated in a furnace preheated to about 300 to 700°C. 8. The method according to claim 6, characterized in that a thin layer of refractory paint is applied to the insert (10) in advance. 9. Cylindrical composite wear part with a machinable relatively flexible core of mechanically load-resistant material and a series of peripheral inserts supported by the core by mechanical connections, characterized in that the inserts (10) An annular insert according to one of claims 1 to 5, the material of the ductile core (26) being filled in the holes (16) in the inner zone (14) of the insert and in the outer zone (12) of the insert In the cavity (22) formed by the groove (20) between the protrusions (18). 10. Wear part according to claim 9, characterized in that the wear resistance of the peripheral insert on one side of the cylindrical support is slightly lower than the wear resistance of the insert in the central zone. 11. The wear part of claim 9, wherein the outer side walls of the two peripheral inserts are free of protrusions. 12. Wear part according to one of claims 9 to 11, characterized in that it is used to form a hoop of a crushing drum, the core (26) of which has a cylindrical hole (28) for receiving a support hub .

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