EP1570905A1 - Grinding roller for a roller mill - Google Patents

Abstract

The roller has inserts with zones (14) having strong resistance and zones (13) having weak resistance to wear and tear. The zones (14) incorporated with a ceramic reinforcement (18) have a jointed part, and the zones (13) have a non-jointed part. The spacing in the non-jointed part is filled with a cast ductile metal (19) permitting sufficient mechanical connection of the inserts.

Description

Object of the invention

The present invention aims to provide improvements to grinding rollers for grinders in general and in particular for so-called axis mills vertical.

Technological background on which the invention is based

The so-called vertical axis mills are used for example to grind coal or clinker. They are essentially consisting of a rotating track supporting pebbles which are driven by the rotary movement of the track along the vertical axis. The material to be grinded is introduced into a central feeding channel and falls on the track, where it is crushed and crushed between the track and the pebble. The crushed material is then removed to the periphery of the track.

Various types of pebble shapes are possible, such as frustoconical rollers or rollers.

Specific forms of vertical axis crushers are shown in Figures 1 and 2. The subject is in EP 0 476 496 B1.

This patent describes among other things a configuration particular grinding rollers whose characteristic is that the wear surface is essentially constituted by peripheral inserts made of very hard material at high wear resistance (such as high-grade fonts) chromium), mechanically sealed in a matrix of material ductile.

In this version, the inserts are obtained at with a protruding rib on at least one flank longitudinal and are then placed against each other others in a mold leaving, between them, a space defined by the thickness of their ribs. We get the roller as a bi-metallic piece by a Casting technique by casting a more ductile material which ensures a mechanical connection of the inserts in the mass remaining roller formed by the ductile material.

The peripheral inserts being thus spaced the one against the other by ribs, the material ductile, during the manufacture of the roller by molding, can infiltrate between the inserts up to the wear surface the device itself, thus guaranteeing a good fixation of the inserts in the room. This provision leads to a succession of hard inserts basically separated by spacing in more ductile material (except spacing ribs).

So that the ductile metal can infiltrate between the inserts continuously, it is appropriate that the space created between the inserts when they are positioned in the mold, either gradually growing from the periphery to the center so that the molten metal does not freeze on contact with cold inserts preventing thus a complete filling of this space by the metal ductile. However, as a result of the wear of the piece service, this configuration evolves by creating in the periphery a ductile space more and more wide, result of the inclination of the sides of this space. This causes however the detrimental effect of decreasing the surface device hard inserts and, therefore, of promote the wear of the room.

Moreover, in the case of grinding rollers, observe a localized preferential wear, usually on the outer sides of the roller. This wear conditions the duration of use of the rollers but also the quality of the crushed product as well as the grinding efficiency since the surface of the roller on the track is reduced and this especially since this track itself undergoes wear, in operation.

In the case where the inserts contain, according to a recent development of the technique, an internal reinforcement of ceramic materials to reduce wear, the presence of a unprotected space between the inserts does that in service, a groove is hollowed between the inserts thus giving off ceramic reinforcement and causing a chipping of the edges of this one. This phenomenon greatly reduces the effectiveness of the ceramic reinforcement because it becomes a producer of very abrasive materials, in addition to the fact that its potential wear resistance decreases with its size.

In the aforementioned patent also described (in relationship with FIGS. 5 to 9), a mode of execution of a fret allowing a compensation of the wear profile following the generator.

To do this, the inserts do not extend into their longitudinal direction along the entire length of the generator so as to leave on the edge outside the pebbles, a peripheral nose forming part of ductile iron support, constituting the rest of the roller.

So provokes, voluntarily in this roller region, faster wear to compensate for the makes that this region is used normally less quickly. This procedure, however, has the disadvantage that nose wear made of ductile iron exposes the end of the insert to a chipping similar to that described previously for the longitudinal edges of the insert, causing the same harmful consequences.

Purpose of the invention

The purpose of the present invention is to provide a new form of inserts so as to avoid disadvantages of the solutions of the state of the art.

Characteristic elements of the invention

The present invention discloses a roller of grinding comprising several peripheral inserts in material with high wear resistance and high hardness, mechanically sealed in a cast material matrix ductile, said roller having first zones subjected to high stress to wear as well as second areas subject to low wear stress characterized in that in said first zone said roller presents on its peripheral face inserts comprising a contiguous part and in said second zone, a part non-contiguous, the spacing in said non-joined part being filled with said ductile material of the cast matrix allowing a sufficient mechanical attachment of the inserts.

In a preferred embodiment of the invention, the contiguous faces coming into contact with their neighbors in successive inserts have a line of contact corresponding to the radii of the circle formed by the roller.

In accordance with the present invention, the report the length of the faces contiguous to the length of the zones where the faces are not contiguous is equal to or greater than 0.2.

In general, the invention specifies that the ratio between the length of the areas where the faces are joined to the length of the zones where the faces are joined is between 0.2 and 20.

In a particular embodiment preferred embodiment of the invention, the wear resistance of the inserts, especially in joined parts, is accentuated by a ceramic reinforcement selected from the group of oxides, carbides, nitrides or borides.

Still according to the invention, said insert comprises at least one undercut allowing its sealing in said cast matrix of ductile material.

Brief description of the figures

Figure 1 schematically shows a crusher says to vertical axis.

Figure 2 shows the grinding mechanism taking place between the track and the wheel 1 with zones to higher wear 2 and 4 and lower wear 3. It shows also the wear that can occur on the track.

Figure 3 schematically represents perspective a roller according to the state of the art for which shows a number of spaced inserts extending longitudinally over the total length of the generator of the roller.

FIG. 4 represents the insert according to the state of the technique revealing the spacing ribs 20 which have not been shown in Figure 3.

Figure 5 shows an example of profiles of wear observed on two types of rollers a and b following the state of the art.

Figure 6 illustrates the formation of grooves 16 in the inserts according to the state of the art;

Figure 7 illustrates the flaking of the edge of ceramic reinforcements 17 and 18 inserts resulting from the forming grooves illustrated in Figure 6.

Figure 8 is a view of a set of inserts juxtaposed according to the invention.

FIG. 9 is a sectional view of an insert in zone 14, according to FIG.

Figure 10 is a plan view of the partially contiguous arrangement of three inserts according to the invention.

FIG. 11 is a sectional view of an insert according to Figure 10.

Figures 10 and 11 respectively correspond to in Figures 8 and 9 for the case where the inserts contain a ceramic reinforcement (illustrated by dotted lines).

Identical reference marks are used in the different figures for constituent elements identical or substantially similar, both for the description of the state of the art only for the form according to the invention.

In Figures 3 and 4 which illustrate shapes according to the state of the art, it has been indicated by the general reference 1 a roller provided with inserts 5 which, by following the presence of ribs 20 during the formation of the roll by molding, are longitudinally in position spaced, the ribs 20 serving as spacers.

As indicated above, with a view to during the molding of the roller the passage of the ductile metal 19 intended to form globally the remaining part of the roller 1 between the inserts up to the wear surface neatly said, a progressive spacing is provided between the inserts at an angle α from the periphery to the axis of the roller (see Figure 3).

In operation it is observed that following wear differential, the space between the roller and the table in the longitudinal direction is no longer constant, which reduces strongly the efficiency of grinding especially as the table can itself be worn. This is represented in the figure 2. Moreover, the wear of the rollers is all the more important that the peripheral surface of the insert is reduced by the fact of grooves of increasing width which are created in service between the hard inserts.

Depending on the shape of the roller, namely frustoconical or toroidal and of the type of crusher, one observes the wear profile 4 as shown in Figure 5, varying for example between one or two areas of high wear 2 and 4 and a zone with less wear 3.

To increase the wear resistance of inserts 5, in particular in their outer part 14, it can be provided reinforcement by infiltration of a porous ceramic core: oxides, carbides, nitrides, borides or others as described for example in the patent EP 0 930 948 B1 or by creating a structure ceramic in situ.

In the case of using a composite ceramic reinforcement, the appearance of grooves Increasing resulting from wear 16 in use would be a very important drawback because these grooves give off the ceramic contained in the insert (fig. 6) which, under the effect of shocks and pressure, snips to the edges (Fig. 7). This increases considerably wear and lose a lot of the interest of this ceramic reinforcement.

Figure 6 shows the formation of grooves 16 following the old design, with inserts 5 without ceramic reinforcement.

Figure 7 shows what happens in service when a ceramic reinforcement 18 has been incorporated into the inserts 5. It is found that after the formation of grooves 16 in the ductile metal, the ridges 17 of the mass of infiltrated ceramic 18 break, releasing material very abrasive and accelerates the formation of the wear profile irregular.

Taking into account these experimental data, the inserts are designed according to the invention so as to create a differential wear resistance between the parts to heavy wear 2 and 4 and parts with less wear 3.

According to the invention, this effect is obtained by the use of inserts 5 (see FIG. 8 and following) which are joined in the high-wear part 2 mentioned above and which retain spacings 12 in the part with less wear stress 3 that are filled by a ductile cast metal 19. A zone 14 is thus obtained. high strength and a zone 13 with less resistance to wear. The faces 6 and 7 coming into contact with their neighbors in successive inserts (see Figures 8 and 10) are drawn on the center of the roller, that is to say that cut, their contact line corresponds to the spokes of the circle formed by the pebble. This ensures perfect contact between the inserts 5 at their juxtaposition, while the recessed faces 10 and 11 define a spacing between the inserts thus creating a less resistant area to wear 13 on the inner part of the roller, while the most stressed surface 14 will be continuous, without risk initiation of grooving and, consequently, wear resistance.

The relative position of the area or areas with strong wear compared to the position of one of the low areas wear will depend on the type of grinder and type of roller and, more particularly its geometric form.

The ratio of the width of the zone (s) heavily loaded with wear to the width of the areas with low wear stress is generally equal to or greater than unity. Relationships between respective widths of these same areas from 1 to 1.5 allow both to have a grinding surface adequate and suitable interlocking of the inserts in the matrix.

The fact that the inner part 3 of the insert retains the possibility of groove formation is in itself beneficial in that it thus makes it possible to better training of the roller by reducing the effect of slipping or skidding on the material to be ground.

Fixing the inserts in the matrix is ensured mechanically and this essentially by the form of the lower part 15 of the insert, which is illustrated by the figure 9.

This form is chosen to allow a strong against draft of the dovetail type, hole or other means of attachment.

Figures 10 and 11 show the continuity according to the invention of ceramic reinforcements 18 in the part 14 of the wear surface of the inserts constituted of the two parts 13 and 14, which eliminates the edges fragile and, consequently, the loss of material intended to resist wear.

Legend

1

grinding roller with inserts

2 and 4

area with high wear

3

low wear zone

5

peripheral inserts

6 and 7

contiguous faces in the zone with strong resistance to wear

10 and 11

indented or non-joined faces in the zone of less resistance to wear.

12

spacings in the least resistance part to wear

13

area subject to the lowest wear stress

14

outer part of the inserts subject to the most high wear stress

15

undercut of the lower part of the insert

16

wear groove in use

17

brittle edges of the ceramic reinforcement

18

ceramic reinforcement of the insert

19

ductile material

20

spacing ribs

Claims (6)

Grinding roller (1) comprising a plurality of peripheral inserts (5) of high wear and high hardness material, mechanically sealed in a cast matrix of ductile material (19), said roller (1) having first zones subjected to with high wear stress (14) as well as second zones subject to low wear stress (13), characterized in that in said first zone (14) said roller (1) has on its peripheral face inserts ( 5) having a contiguous portion (6, 7) and in said second zone (13) a non-contiguous portion, the spacing in said non-contiguous portion (12) being filled by said ductile material of the cast matrix (19) allowing a sufficient mechanical attachment of the inserts. Roller according to claim 1, characterized in that the contiguous faces (6) and (7) coming into contact with their neighbors in successive inserts have a line of contact corresponding to the radii of the circle formed by the roller (1). Roller according to claim 1 or 2, characterized in that the ratio of the length of the contiguous faces to the length of the areas where the faces are not contiguous is equal to or greater than 0.2. Roller according to claim 3, characterized in that the ratio between the length of the areas where the faces are contiguous to the length of the areas where the faces are non-contiguous is between 0.2 and 20. Roller according to any one of claims 1 to 4, characterized in that the wear resistance of the inserts (5), in particular in the contiguous parts, is accentuated by a ceramic reinforcement selected from the group of oxides, carbides, nitrides or borides. Roller according to any one of the preceding claims, characterized in that said insert (5) comprises at least one undercut (15) allowing its sealing in said cast matrix of ductile material (19).

Images