EP3525934A1

EP3525934A1 - Grinding roller

Info

Publication number: EP3525934A1
Application number: EP17768810.8A
Authority: EP
Inventors: Xavier Prignon
Original assignee: Magotteaux International SA
Current assignee: Magotteaux International SA
Priority date: 2016-10-12
Filing date: 2017-09-20
Publication date: 2019-08-21
Anticipated expiration: 2037-09-20
Also published as: CN109843442B; MX2019004261A; EP3308861A1; DK3525934T3; EP3525934B1; RU2730026C1; PL3525934T3; CN109843442A; WO2018069006A1; AU2017342978A1; CL2019000786A1; JP6931387B2; PT3525934T; ZA201901867B; US11123742B2; US20200055055A1; CA3036461A1; ES2965916T3; KR20190065283A; AU2017342978B2

Abstract

The present invention relates to a grinding roller for vertical grinding mills used to grind materials such as rocks, coal and cement clinker.

Description

GRINDING GALET

Object of the invention

The present invention relates to a grinding roller for vertical axis mills used for grinding materials such as rocks, coal, cement clinker or other related material such as slag. These rollers are particularly wear-resistant thanks to specially shaped reinforcing inserts placed near the working surfaces of the roller, allowing uniform and constant wear over the entire work surface and thus longer service life. State of the art

[0002] Grinding rollers for vertical axis mills are well known to those skilled in the art. They are generally made of relatively ductile cast iron in which inserts made of extremely wear-resistant materials, usually chromium cast iron, sometimes including ceramic grains, are included to reinforce the most stressed surfaces during grinding.

[0003] EP 1570905A1 discloses a grinding roller comprising a plurality of peripheral inserts made of material with high wear resistance and high hardness, mechanically sealed in a cast matrix of ductile material with first zones subject to a high stress of wear. as well as second zones subject to low wear stress. In the first zone, the roller presents on its peripheral face inserts comprising a contiguous part, and in the second zone, a non-contiguous part.

[0004] WO 9605005 discloses a bimetallic casting part mounted on the hub of a vertical axis milling roller. It comprises a core made of a ductile iron provided with mechanical connection elements in the form of studs which are made integral by casting a casing, made of a non-ductile wear material with a high chromium content. [0005] WO 2015 / 162047A1 discloses a grinding roller with high mass inserts embedded in a metal matrix composed of ductile iron and steel, the roller comprising inserts with a V / S massivity module of between 3 and 5 cm. Goals of the invention

The present invention provides a roller reinforced by inserts whose profile has a particular design that causes constant wear of the entire working surface of the roller avoiding local occasional wear. These rollers allow to maintain the performance of the mill to a satisfactory level while minimizing the risks of breakage and reducing manufacturing costs.

Characteristic elements of the invention

The present invention discloses a grinding roller for a vertical axis mill produced by casting a metal matrix casting, said roller having in its periphery a plurality of reinforcing inserts, including portions of the peripheral surface of the same insert is located at a distance d1 or d2 from the working surface depending on the stresses to wear, said roller comprising:

at least one zone of high wear stress Z1, with at least a portion of the insert positioned at a distance d1 near the working surface of said roller;

a zone of low wear stress Z2, with a portion of the insert positioned at a distance d2 set back from said working surface of said roller with d1 <d2.

According to preferred embodiments of the present invention, the roller comprises at least one or a suitable combination of the following characteristics:

the roller comprises at least one intermediate zone Z3 connecting the zones Z1 and Z2;

d1 is less than 10 mm, preferably less than 5 mm and d2 is greater than or equal to 10 mm, preferably greater than 20 mm;

- d1 = 0; the roller comprises two zones of high stress Z1 located on either side of a zone of low stress Z2 for a roller for symmetrical use;

the inserts have on the face facing the work surface ceramic reinforcements

the inserts contain up to 60% by volume of ceramic grains;

the ceramic grains comprise alumina, zirconia, alumina-zirconia and / or metal carbides;

the roller is of frustoconical shape. Brief description of the figures

[0009] Figure 1 shows an example of a vertical axis mill.

Figure 2 shows a roller with inserts at the periphery and ceramic reinforcements included in these inserts work surface side according to the state of the art. Figure 3 shows schematically the grinding mechanism in a vertical axis mill with its turntable and a layer of material to grind.

Figure 4 shows different examples of embodiments of the invention according to different forms of rollers.

Figure 5 shows a section of an asymmetrical roller with its different biasing zones, the distances d1 and d2 representing unreinforced thicknesses between the work surface and the insert. For reasons of graphic representation, the distance d1 has been exaggerated with respect to reality.

Figure 6 shows a section of a symmetrical roller with its different biasing zones, the distances d1 and d2 representing unreinforced thicknesses between the work surface and the insert. Here too, for reasons of graphic representation, the distance d1 has been exaggerated with respect to reality.

Figure 7 shows a grinding roller having an insert without a transition zone between a zone of high wear stress Z1 and a zone of low wear stress Z2. Figure 8 shows a symmetrical grinding wheel of the same type as that shown in Figure 6 but which is reinforced only one side and is therefore supposed to be used only one side.

List of reference symbols

1. pebble

2. Insert

3. Working surface of the roller

Z1: Area of maximum stress to wear at the beginning of the use of the roller.

Z2: Minimum stress area at the beginning of the use of the roller.

Z3: Transition zone between zone Z1 and zone Z2.

d1: distance between the original working surface (new peripheral surface of the roller, not yet used) and the reinforcement insert in zone Z1.

d2: distance between the original working surface (new peripheral surface of the roller, not yet used) and the reinforcement insert in zone Z2.

Detailed description of the invention

Vertical axis mills are known to those skilled in the art. There are different types and they generally have a table rotating about a vertical axis on which the material to be grinded is fed. The mill is equipped with a plurality of very heavy wheels of generally cylindrical or frustoconical shape, called "rollers", which are positioned above the table. As the table rotates, the material to be ground is driven outwardly by the centrifugal force and passes between the rollers and the table.

The self-weight and a vertical force applied to the rollers cause compaction and grinding of the bed of material passing below the rollers. This material itself serves as a frictional connection between the table and the rollers, so that the rotation of the table causes the rotation of the rollers or vice versa. Grinding in the material bed is by compression and shearing of the material.

The compressive stresses and the relative speeds between the rollers and the table vary over the width (the thickness) of the roller. The level of compressive stress depends on the height of the bed of material and the spacing between the rollers and the table over the width of the roller. The wear of the rollers and shields of the table is an inevitable consequence of the grinding process. Manufacturers of vertical axis mills therefore optimize the shapes of the rollers and tables according to the materials to be milled, which makes it possible to obtain an optimum grinding efficiency when the grinding equipment is new.

Given the differences in stresses to which the material and therefore the grinding equipment are subjected, the level of wear is not constant over the width of the roller. Over time, more marked wear zones are formed along the generatrix of the rollers, which cause a drop in grinding efficiency and ultimately require the rollers to be replaced.

This problem is all the more marked as the bed of optimal material and therefore the distance between the roller and the table is low for crushing conditions and material data, especially for the materials that we want to grind high-fineness such as cement or granulated slag. In such circumstances, a 10% yield drop can already be seen after a local wear of only 20 mm on the roller, and a 40% drop after a wear of about 35 mm.

This drop in performance is explained by the very operation of a vertical mill. This comprises a mechanical safety stop preventing the work surface of the grinding roller from coming into contact with the table. In general this stop is set to provide a safety clearance of about 10 mm between the table and the work surface of the grinding roller. For efficient grinding, in particular cement and slag, attempts are made to minimize the thickness of the material bed beyond 10 mm. If the wear of the roller is not uniform, that is to say parallel to the mill table having the bed of material to be grinded, but locally, it is impossible to lower the roller towards the mill table and thus reduce the layer to grind without touching the mechanical stop. The grinding performance therefore greatly decreases at local wear areas without being able to influence the thickness of the bed of material to be ground.

To minimize this problem, various solutions are currently used by those skilled in the art: · Use of steel rollers rechargeable by welding. This solution makes it possible to reload the rollers in places of greater wear and to restore at least partially the original profile of the roller. The disadvantages of this solution are costs and production losses related to interventions and downtime to reload the pebbles. In addition, the number of possible refills is limited since the risk of breakage is increased at each intervention. High chromium steel rollers including ceramic grains are also used to increase the service life. Rollers with a high chromium content, however, are fragile and can break during operation. In addition, the problem of localized wear and the associated yield losses remain unresolved.

EP 1570905A1 discloses a grinding roller comprising a plurality of peripheral inserts made of a material with high wear resistance and high hardness, mechanically sealed in a cast matrix of ductile material with first zones subject to high wear stress, and second areas subjected to low wear stress. In the first zone, the roller presents on its peripheral face inserts comprising a contiguous part and in the second zone, a non-contiguous part. This proposal does not give the expected results, especially for cement crushers.

The intensity of wear on a roller of a vertical axis mill mainly depends on the abrasiveness of the material, the pressure applied locally and the relative speed between the surface of the roller and the material to be ground. As the mill rotates, the material builds up on the outside of the turntable, resulting in a much greater wear stress on the outer portion of the work surface of the milling roller (see Figure 3). . This is the reason why this part must be particularly reinforced by inserts. The invention discloses grinding rollers whose metal matrix is a relatively ductile material such as a GS cast iron or a mild steel. These rollers are provided with a plurality of high-wear inserts distributed over the entire periphery near the work surface of the roller (see Figure 2).

The originality of the grinding roller according to the present invention lies in the design of the inserts which are profiled such that a portion thereof is in the immediate vicinity, or even flush with the work surface (at the new condition of the roller) at the places of strong stress, and another part set back from the working surface (in new condition of the roller) in the areas of least stress. This original distribution of reinforcement makes it possible to ensure more constant wear over the entire width of the working surface of the grinding roller.

In the present application, we mean in new condition, the condition of the roller with its original profile and therefore not yet used. It is obvious that we can define distances between the inserts and the working surface of the roller in new condition because these distances can no longer be measured on a roller already heavily used.

The distance between the portion of the insert near the working surface and the actual working surface in the area of high stress (Z1) is defined by d1. The distance between the portion of the insert set back from the working surface and the working surface itself in the zone of low stress (Z2) is defined by d2, the distance d1 in the zone of strong stress (Z1) being always less than d2 in the zone of low stress (Z2). In the prior art the distance between the outer surface of the insert near the work surface and the working surface itself in new condition is constant and d1 = d2. When the portion of the outer surface of the insert is flush with the work surface of the grinding roller, d1 = 0 or is close to zero. The concept "flush with the work surface" must however be relativized knowing that the size of grinding rollers whose diameter is sometimes close to three meters for a mass of 15 tons. The distance d1 is generally less than 10 mm, preferably 8 mm or even 5 mm or less depending on the practical conditions of the casting.

The portion of the outer surface of the insert which is set back from the working surface of the grinding roller is at a distance d2 generally greater than 10 mm, preferably greater than 15 mm and particularly preferably greater than 10 mm. 20 mm. The inserts will often have a transition zone (Z3) joining the nearby portions and those set back from the work surface. These portions correspond to a zone (Z3) where the outer surface of the insert progressively moves away from the working surface of the roller in new condition. The ductile material filling the volume between the outer surface of the inserts and the original surface of the roller thus has a variable thickness on the thickness of the roller. The presence of a transition zone Z3 is not always necessary and in some cases, the area of high wear stress Z1 can pass without transition to a zone of low wear stress Z2 ( see Figure 7).

In its simplest version, the roller will therefore have two areas on its working width, the zone 1 (Z1) being subjected to a strong stress where the outer surface of the insert will be closest or flush with the work surface (original profile) of the roller, the zone 2 (Z2) being subjected to a low stress where the outer surface of the insert will be furthest away and set back from the working surface (original profile ) of the roller (peripheral surface). However, the rollers will often have a transition zone 3 (Z 3) corresponding to an average stress intensity where the distances d 1 and d 2 meet. Within zones Z1 and Z2, the distances d1 and d2 are not necessarily totally constant but may vary slightly with the difficulties encountered in placing the inserts in the molds during the preparation of the casting. Compared to the solutions of the state of the art, the invention aims to accelerate wear in the zones 2 and possibly 3, which has the consequence that the wear gradient between the zone 1 and the rest of the thickness of the pebble is lower. The rollers can thus keep a profile closer to the original profile and therefore have a longer life. Depending on the thickness of the bed and the type of material, the observed increase in life is between 0 and 80%, preferably between 30 and 70%. The most significant improvements have been observed on frusto-conical models.

The grinding rollers which have an axial symmetry with a generator of revolution giving rise to a roller type "cylinder" or "tire" (see Figure 4) are used on both outer peripheral faces and can be returned (by for example, rollers for RM type mill). In this case, it is possible, according to the invention, to have two zones Z1 and 2 zones Z2 as well as two transient zones Z3 as shown in FIG. 6 (tire-shaped roller).

For the other rollers (non-symmetrical profile) the most reinforced zones (Z1, d1) must be placed on the outer side of the rotary table of the vertical axis mill, where the material to grind accumulates at the periphery and / or the pressure on the material to be ground is the highest (see figure 4) According to the invention, the inserts may contain ceramic grains (oxides, carbides, nitrides or metal borides, intermetallic compounds) in order to improve the resistance to wear. Preferably these grains will be arranged in the part of the insert which is closest to the peripheral (original) surface of the roller in zone Z1. The arrangement of the ceramic grains is preferably in the form of infiltrable slab by melting of the casting. The slabs are preformed to a desired section and placed in the mold before casting.

The advantages of reinforced rollers according to the present invention compared to the state of the art are: - need for less chromium cast iron (HiCr) insofar as the profile of the insert is now configured according to a "useful" profile to gradually oppose the wear where previously it was unnecessarily reinforcing the roller over the entire thickness. Manufacturing costs are thus lower and the roller is more resistant to breakage; as explained above, the uniform wear of the roller over its entire width also brings the roller closer to the table as soon as there is the beginning of wear in the inserts, which increases the grinding efficiency.

Claims

1. Grinding roller (1) for mills with a vertical axis produced by casting a metal matrix in the casting, said roller (1) having at its periphery a plurality of reinforcing inserts (2), some portions of the peripheral surface of which the same insert is located at a distance d1 or d2 from the working surface (3) as a function of the wear stresses, said roller comprising: at least one zone of high wear stress Z1, with at least one portion of the insert (2) positioned at a distance d1 near the work surface (3) of said roller; a zone of low wear stress Z2, with a portion of the insert positioned at a distance d2 set back from said working surface (3) of said roller with d1 <d2.

2. Roller (1) according to claim 1 characterized in that it comprises at least one intermediate zone Z3 connecting the zones Z1 and Z2.

3. Roller (1) according to any one of claims 1 or 2 characterized in that d1 is less than 10mm, preferably less than 5 mm and d2 greater than or equal to 10mm, preferably greater than 20mm.

4. Roller (1) according to any one of the preceding claims, characterized in that d1 = 0.

5. Roller (1) according to any one of the preceding claims, characterized in that it comprises two zones of high stress Z1 located on either side of a zone of low stress Z2 for a roller for symmetrical use.

6. Roller (1) according to any one of the preceding claims, characterized in that the inserts (2) comprise on the face facing the working surface (3) ceramic reinforcements.

7. Roller (1) according to any one of the preceding claims, characterized in that the inserts (2) contain up to 60% by volume of ceramic grains.

8. Roller (1) according to any one of the preceding claims, characterized in that the ceramic grains comprise alumina, zirconia, alumina-zirconia and / or metal carbides.

9. Roller (1) according to any one of the preceding claims characterized in that said roller is of frustoconical shape.