Ring for grinding mill

Abstract

A segmented grinding ring for centrifugal vertical roller mills is provided. The segmented grinding ring includes multiple cast segments which may be vaulted together using pin rods and shims to form a continuous ring. The segmented grinding ring enables the manufacture of the segments in a cast composite material.

Claims

1. A centrifugal vertical roller mill, the vertical roller mill comprising: a grinding ring assembly comprising: a plurality of segments arranged to form an annular grinding cylinder, wherein each segment of said plurality of segments comprises a working face, wherein the working face of each segment of said plurality of segments is positioned radially inwardly on the annular grinding cylinder, each segment of the plurality of segments further comprising a recess for the introduction of a positioning pin located between each couple of segments, each segment of said plurality of segments further comprising hangers; and a plurality of pin rods, wherein a pin rod is positioned in the recess between each couple of segments, wherein the plurality of segments forms a continuous grinding ring, a supporting ring comprising holes cooperating with the hangers to support each segment of said plurality of segments; and a plurality of centrifugally operating grinding rollers.

2. The grinding ring assembly according to claim 1, wherein each segment of said plurality of segments comprise a composite structure on the working face, said composite structure comprising ceramic particles, and wherein said ceramic particles are embedded in a cast metal.

3. The grinding ring assembly according to claim 2, wherein a thickness of the composite structure comprising the ceramic particles is at least 10 mm.

4. The grinding ring assembly according to claim 2, wherein a thickness of the composite structure comprising the ceramic particles is between 20 and 30 mm.

5. The grinding ring assembly according to claim 2, wherein the composite structure comprising the ceramic particles is a honey comb structure.

6. The grinding ring assembly according to claim 2, wherein the ceramic particles are selected from the group consisting of metallic oxides, metallic carbides, borides and nitrides.

7. The grinding ring assembly according to claim 2, wherein the ceramic particles are selected from the group consisting of Al.sub.2O.sub.3, ZrO.sub.2, Al.sub.2O.sub.3ZrO.sub.2, WC, TiC, SiC, B.sub.4C, BN and Si.sub.3N.sub.4.

8. The grinding ring assembly according to claim 2, wherein the ceramic particles are spheroid ceramic grains of a size between 0.5 to 6 mm, said spheroid ceramic grains comprising an alumina-zirconia composite comprising 20 to 80 wt % ZrO.sub.2 and 80 to 20 wt % Al.sub.2O.sub.3.

9. The grinding ring assembly according to claim 2, wherein the ceramic particles are spheroid ceramic grains of a size between 1 and 5 mm, said spheroid ceramic grains comprising an alumina-zirconia composite comprising 35 to 45 wt % ZrO.sub.2 and 65 to 55 wt % Al.sub.2O.sub.3.

10. The grinding ring assembly according to claim 1, wherein said ring presents 3 to 12 segments.

11. The grinding ring assembly according to claim 1, wherein the hangers are operable to cooperate with mounting holes in a cylindrical supporting ring.

12. The grinding ring assembly according to claim 1, wherein said cylindrical grinding ring comprises shims between the segments.

13. The grinding ring assembly according to claim 1, wherein the hangers of each segment of said plurality of segments cooperate with specific holes in the supporting ring.

14. The grinding ring assembly according to claim 1, wherein each segment of said plurality of segments maintained in the continuous grinding ring by a vaulting effect by introduction of a positioning pin located between each couple of segments.

15. The grinding ring assembly of claim 1, wherein the recess between each couple of segments does not contact the working face of each segment of said plurality of segments.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 represents a roller grinding mill of the state of the art disclosed in U.S. Pat. No. 4,022,387, showing in which configuration a monolithic grinding ring (38) with its surface (39a) is arranged on a support (10) and cooperates with the centrifugal grinding rollers (10) for grinding operations.

(2) FIG. 2 represents a three-dimensional view of the segmented grinding ring, in this example with 6 segments, according to the invention.

(3) FIG. 3 represents a top view of the segmented grinding ring according to the invention.

(4) FIG. 4 represents a section view of the segmented grinding ring according to the invention with reinforcing ceramic particles (in grey).

(5) FIG. 5 represents a detailed section view of the reinforced part of the grinding ring with reinforcing ceramic particles embedded in the metal matrix.

(6) FIG. 6 represents the principle of the casting of a segment of the ring according to the invention with a reinforced part comprising an insert with ceramic particles or with a powder precursor of ceramic particles.

DETAILED DESCRIPTION OF THE INVENTION

(7) The present invention is related to segmented grinding rings for vertical centrifugal mills. In this type of mills, also called pendulum roller mills, two or more rollers using centrifugal force grind various materials by rolling on a circular ring. This machine is frequently used to feed the coal burners of power plant stations.

(8) The segmented grinding ring 100 of the present invention comprises multiple cast segments 102 which are vaulted together by vaulting effect using pin rods 104 and shims 106 to form a continuous ring 108. The number of segments varies generally between 3 and 12 and preferably between 4 and 10. The diameter of the assembled grinding ring 100 according to the invention is dependent on the type of the grinding mill and varies roughly between 1 and 4 meters, preferably between 1.5 and 3 meters. A segmented grinding ring enables the manufacturability of the segments 102 in a much harder cast material and in particular in composite material, which thus lengthens the lifetime and improves the performance of the grinding ring.

(9) The casting of smaller pieces allows the embedding or the preparation in situ of hard ceramic particles such as, without being limitative, metallic oxides (Al.sub.2O.sub.3, ZrO.sub.2, Al.sub.2O.sub.3ZrO.sub.2 composites) or metallic carbides (WC, TiC, SiC), borides (B.sub.4C) or nitrides (Si.sub.3N.sub.4). To hold ceramic particles or a powder precursor of this particles (in the case of a SHS synthesis) in place, an insert of said particles is prepared and placed in the mould before the cast metal is poured on it. The cast metal impregnates the porous ceramic structure and builds a very wear resistant composite structure on the working side of the grinding ring segment.

(10) This type of composite structure would be difficult to achieve on a monolithic grinding ring, because the casting as such is often too large and it is always difficult to hold a ceramic insert along a vertical surface when pouring the metal. Furthermore, on such a big monolithic block, the risk of tears/breakage during the metal solidification is too high with the risk of final rejection of the casting.

(11) Additionally, the segmented ring according to the invention allows a substantial reduction of the downtime when replacing the ring, since it is not necessary anymore to remove the entire upper mill housing when installing or replacing the one-piece fabricated ring according to the prior art. An individual replacement of each segment becomes possible via the existing mill door (manhole).

(12) The segmented ring according to the present invention offers in particular the advantages of supplying a grinding ring comprising reinforced working faces with high-performance wear-resistant composite material as compared to classical monolithic rings with weld overlay. This improves the lifetime of the ring by two or three, maintains the grinding profile much longer and thus improves the performance of the mill and reduces the operating and maintenance costs.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

(13) Non-reinforced individual segments for the grinding ring of the present invention can be cast according to classical methods well known by those skilled in the art.

(14) For the preparation of a reinforced individual segment for the grinding ring according to the invention, the working face 122 of the segment 102 is reinforced in depth with ceramic particles. The thickness of the reinforced layer 120 is generally higher than 10 mm, preferably higher than 20 mm and generally situated between 10 and 50 mm, preferably between 20 and 30 mm. Usually inserts of porous ceramic pads 124 of about 25 mm thickness are placed in the cast mould 126 on the working face 120 of a segment 102 followed by the pouring of iron-based cast metal 128 in the mould 126. The principle of this operation is represented in FIG. 6. The ceramic pad 124 is obtained by the agglomeration of ceramic granules 130 of a size between 0.5 and 6 mm, preferably between 1 and 5 mm. Such an agglomeration can occur in a press or with additional mineral glue. The ceramic pad can present any geometrical configuration, but it is always adapted to the depth of the working face 122 to be reinforced.

(15) During the cast operation, the ceramic insert is impregnated by the liquid cast metal and the ceramic particles are completely embedded in this way in the metal matrix. This impregnation leads to a substantially pore-free composite structure on the working face of the segment. Such a detailed structure is represented in FIG. 5.

Example

(16) A grinding ring with 6 segments and with a diameter of about 1.6 meters is assembled via pin rods and shims. Each segment comprises hangers 110 cooperating with specific holes in the supporting ring 114 of the grinding mill (see FIG. 2).

(17) Each segment comprises in this case a reinforced composite wear layer of about 20 mm. The wear layer is reinforced by granules (0.5 to 5 mm) of a ceramic composite of alumina-zirconia (57 wt % Al2O3-43 wt % ZrO2) from which a compacted insert is placed in the mould before the segment is cast at about 1500 C.

(18) The result of this pouring operation is represented in FIG. 4. A reinforced wear layer 120 of about 20 mm thickness is achieved on each individual segment 102.

(19) After the casting of each of the six segments, a grinding ring 100 according to the invention is assembled. Each segment comprises a recess 116 for a positioning pin 104 to be placed between each couple of segments 102. This type of assembling allows maintaining the segments by vaulting effect.