US2801804A - Ball mill linings and grinding body charges - Google Patents

Description

Aug. 6, ,1957 o; P. FRANKERT BALL MILL LININGS AND GRINDING BODY CHARGES Filed May 10, 1955 2 Sheets-Sheet l 2 FIG/l if PRIOR ART' FIG.-

j 4 ATTORNEY;

6, 1957 o. P. FRANKERT I 2,801,804

BALL MILL LININGS AND GRINDING BODY CHARGES Filed May 10, 1955 2 Sheets-Sheet 2 FIG;

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ATTORNEYS United States Patent BALL MILL LININGSi AND GRINDING BODY CHARGES Otto Peder Frankert, Copenhagen, Denmark, nssignor to F. L. Smid'th & C03, New York, N. Y., a corporation of New Jersey 1 Application May 10, 1955, Serial No. 507,218

4 Claims. (Cl. 241-183) This invention relates to grinding mills ofthe tube and ball types and is concerned more particularly with a mill of the kind stated, which is provided with a novel lining constructed to effect a desired distributionof the grinding bodies and so formed as to have a long life.

Tube and ball mills have heretofore been provided with linings made up of plates having spaced projections, which act to distribute the grinding bodies within the grinding chamber andmay be ribs of a width smaller than the width of the spaces between adjacent ribs. The ribs have the form of sections of a helix and the platesare so mounted that the helices formed by the ribs are of a hand the same as the direction of rotation of the mill shell, when the latter is viewed from the inlet end. The projections are spaced sufficiently to permit the larger grinding bodies to enter the depressions between them and, in the operation of the mill, the projections lift the grinding bodies and then release them with such action chiefly affecting the grinding bodies of the larger sizes. As the projections are helical and thus lie at an angle to the generatrices of the cylindrical shell, the proje'ctions acts to advance the lifted grinding bodies lengthwise of the mill axis and, with the helices of the hand described, the movement of the larger grinding bodies is toward the inlet end of the mill, through which the material to be ground is fed. Such distribution of the grinding bodies within the mill is desirable and the grinding action in a mill equipped with a liner as described is superior to that in mills, in which the liner performs no distributing function. However, such projections narrower than the spaces between them wear down rapidly during the operation of the mill with the result that the distributing effect is lost or the liner must be replaced to maintain the effect.

Mills as heretofore constructed have commonly been subdivided into a series of grinding chambers or compartments separated from one another by grids, which retain the grinding bodies within the several compartments while permitting the sufficiently ground material to pass from one compartment to the next. The grinding bodies within the respective compartments are about uniform in size, so that bodies of different size may be introduced into the several compartments, and kept in those compartments by the grids. However, the grids tend to become clogged by the material being ground or by the grinding bodies and such clogging reduces the efficiency of the mill and may necessitate its being stopped, so that the grids can be cleaned.

The present invention is directed to the provision of a tube or ball mill having a shell lining, which causes proper distribution of the grinding bodies, but is so constructed as to have a long life. The use of the new lining makes possible the sorting or distribution according to size of a charge of grinding bodies varying widely in size, as, for example, a charge, in which the bodies forming at least by weight of the charge are all of a diameter. at least 75% greater than the average diameter at the bodies forming another fraction of the charge 2,801,804 Patented Aug. 6, 1957 The lining of the invention is formed with spaced,

projections on its inner surface, which have an average width at least twice and preferably more than twice the average width of the spaces between them. The projections have the shape of sections of helices of a hand opposite to the direction of rotation of the mill viewed from the inlet end, and are so close together and of such radial depth that grinding bodies making up at least 10% by weight of the charge are too large to penetrate to the bottom of the spaces between the projections. As a result of forming the lining as described, the smallest grinding bodies enter the spaces between the projections and slide through the spaces during rotation of the mill, so that they are conveyed axially of the mill toward the outlet end. At the same time, the projections are of such width that the lining undergoes almost uniform wear over its entire surface.

For a better understanding of the invention, reference may be made to the accompanying drawing, in which Fig. l is a diagrammatic developed view of a section of a mill lining of the prior art;

Fig. 2 is a sectional view on the line 2-4 of Fig. I;

Fig. 3 is a diagrammatic developed view of a section of a mill lining of the invention;

Fig. 4 is a sectional view on the line 4-4 of Fig. 3;

Fig. 5' is a view similar to Fig. 3 showing. a modified construction;

Fig. 6 is' a sectional view on the line 66 of Fig. 5;

Fig- 7 is a view similar to Fig. 3 showing a second modified construction;

Fig. 8 is a sectional view on the line h-8 of Fig. 7;

Fig. 9 is a view in side elevation of a grinding mill with parts broken away to show the installation of the liner of the invention;

Fig. 10 is a view of the inlet end of the mill of Fig. 9 with a portionof the head broken away; and

Figs. 11, 12, and 13' are diagrammatic developed views showing three different mill linings embodying the invention.

The prior mill lining, of which a portion is shown in Figs. 1 and 2, is made up of a plurality of plates 11, which are of arcu'ate form and are mounted on the inner face of the shell 12. The plates are formed on their exposed inner faces with spaced helical ribs 13, which are of less width than the depressions 14 between them. Ordinarily, the plates are so mounted that the ribs on one plate are aligned with those on the adjacent plates, so that the lining is provided with continuous helical ribs extending from one end of the shell to the other and separated by continuous depressions. The helices formed by the ribs are of a hand the same as the direc; tion of rotation of the shell when viewed from the inlet end, as indicated by the arrow.

In the operation of the mill equipped with the prior lining, the larger grinding bodies enter the depressions 14 and are lifted. by the projections and also advanced axially of the mill. As a result of this action, the charge of grinding bodies in the mill is distributed according to the size of the individual bodies and the larger grinding bodies accumulate at the inlet end of the mill and the distributing effect is soon lost or can be maintained D y by replatiemg nt pf the The lining of the invention in the form illustrated in Fig. 3 is made up of arcuate plates 15' formed with depressions 16 separated by projections or lands 17. The projections are wide in relation to the depressions and are preferably more than twice as wide as the depressions. The depressions may be of V-section, as shown, and the depth of the projections measured from their top to the bottom of a depression is such that a large grinding body B cannot penetrate to the bottom of a depression, while a small grinding body B may do so. The projections are sections of helices of a pitch between 30 and 60 with a pitch of 45 preferred and the plates are so mounted in the shell that the projections form continuous helical channels from one end of the shell to the other, although the helices may be interrupted. The helices are of a hand opposite to the direction of rotation of the shell viewed from the inlet end. Since the large grinding bodies cannot penetrate to the bottom of the depressions, the latter have little lifting efiect on such bodies, but the small grinding bodies entering the depressions are moved lengthwise of the mill toward the outlet end thereof .as the mill rotates. The movement of the smaller grinding bodies toward the mill outlet results in the larger bodies accumulating near the the inlet, as is desirable. The distributing action of the new lining is thus the same as that of the prior lining of Fig. 1, but the new lining has a much greater life than the prior one, since the wear on the new lining is taken by the relatively wide projections. The wear on the new lining is more uniform than that on the prior lining and the new lining will perform its distributing function throughout substantially the entire life of the lining.

The modified form of the lining shown in Figs. and 6 is especially suitable for use in grinding chambers containing a charge of small cylindrical grinding bodies and is made up of relatively narrow depressions 20 separated by relatively wide bars 21 of helical shape. Each depression is a row of long narrow holes 22 extending through the plates to the inner face of the mill shell and separated by bridge pieces 2.3 connecting adjacent bars and lying against the mill shell with the tops of the bridge pieces below the tops of the bars. When such a lining is installed, the holes 22 may be filled with the material, such as cement mortar, which is less resistant to wear than the bars 21. The width of the depressions 20 is such as to allow only the smallest grinding bodies to enter them and thereby subject the sides of the bars and the filling material in the holes to wear.

The lining shown in Figs. 5 and 6 may be provided, if desired, by replacing the plates by bars corresponding in shape and size to the bars 21 and mounted within the shell'in spaced relation. If desired, plates of the height of bridge pieces 23 may be mounted in the spaces between the bars.

The modified form of the new liner shown in Figs. 7 and 8 is made up of plates formed with frusto-conical projections 24 lying in helical rows 25. Adjacent rows are spaced apart and the spaces form depressions 26, which are of varying width. The average width of the depressions 26 is less than the average diameter of the projections, so that the depressions perform the same functions as the depressions 16 in the construction shown in Fig. 3.

The liner of the invention may be used in tube or ball mills, one of which is diametrically shown in Figs. 9 and as comprising a cylindrical shell 27 with heads 28 at its opposite ends. One head is provided with an inlet 29 for introduction of the material to be ground and the other with an outlet 3% for discharge of ground material. The direction of rotation of the mill, when viewed from the inlet end, is clockwise and the grooves 16 in the liner plates thus tend to advance the small grinding bodies toward the outlet end of the mill. As

a result, the larger grinding bodies accumulate near the inlet, which is the desired distribution of the grinding bodies.

The use of the new lining in compartment mills is illustrated diagrammatically in Figs. 11, 12, and 13. The mill shown in Fig. 11 is a typical tube mill having a shell 31 with an inlet 32 at one end and an outlet 33 at the other. The interior of the mill is divided into two chambers or compartments by a grid 34, which may have openings about 4 mm. in diameter, and another grid 35 is disposed near the outlet 33. The first compartment 36 is provided with a lining 37 made up of plates as shown in Figs. 3 and 4, while the second compartment 38 is provided with a lining 39 made up of plates as shown in Figs. 5 and 6. Near the grid 35, the lining 39 is formed with a zone 39a, in which the plates are so mounted that the depressions indicated by the lines 40 are helical and of a hand opposite to that of the helical depressions elsewhere in compartments 36, 38 and the same as the direction of rotation of the mill viewed from the inlet end. The depressions in the zone 39a act to move the smallest grinding bodies away from the grid 35 so as to avoid clogging of the openings in the grid by the worn bodies.

The mill shown in Fig. 11 is intended for grinding materials, which are soft and easily ground. The grinding bodies in compartment 36 may, accordingly, be balls varying from 30 mm. to 100 mm. in diameter, while the bodies in compartment 38 may be cylindrical pebbles of a size varying between 8 mm. and 22 mm.

The mill shown in Fig. 12 is generally similar to that shown in Fig. 11 and includes a shell 41 with an inlet 42 at one end and an outlet 43 at the other. The interior of the mill is divided into two compartments by a grid 44 and another grid 45 is disposed near the outlet 43. The first compartment 46 is shorter and the second compartment 47 is longer than the corresponding compartments in the millof Fig. 11. The mill of Fig. 12 is intended for grinding relatively hard materials and the charge of grinding bodies in compartment 66 may consist of steel balls of diameters varying from mm. to mm., while the charge in compartment 47 may consist of balls of diameters varying from 30 mm. to 40 mm. and cylindrical pebbles of a size varying between 8 mm. and 2.2 mm. The grid 44 passes only pieces of material less than about 4- mm. in diameter and the greater length of compartment 47 insures that the materials will remain in that compartment a sufficient length of time for grinding to the desired fineness. The zone 47a corresponds to zone 39:: and, in it, the liner plates are so disposed that the helical depressions are of a hand the same as the direction of rotation of the mill viewed from the inlet end.

The mill shown in Fig. 13 is of the single compartment type and comprises a shell 48 with an inlet 49, an outlet 50, and a grid 51 near the outlet. The lining 52 is formed of plates as shown in Figs. 3 and 4 except for a zone 52a near the outlet, in which the plates are of the type shown in Figs. 5 and 6 and are so mounted that the depressions indicated by the lines 5'3 are of a hand the same as the direction of rotation of the mill viewed from the inlet end. The mill is intended for grinding coal and may have a charge of grinding bodies consisting of steel balls of diameters varying between 30 mm. and 50 mm. and cylindrical pebbles of sizes varying between 8 mm. and

22 mm. By causing the mill to be air-swept to withdraw the finished ground material, it is possible to eliminate grid 51 and thereby increase the mill efficiency.

I claim:

1. A grinding mill, which comprises a cylindrical shell containing a charge of grinding bodies of varying sizes and having an inlet at one end and an outlet at the other, and a lining within the shell having projections on its inner surface separated by depressions and of an average width greater than the average width of the depressions, the projections beingbars having the shape of sections.

of helices of a hand opposite to the direction of rotation of the shell viewed from the inlet end and the depressions containing bridge pieces connecting the bars and lying in spaced relation.

2. The mill of claim 1, in which the width of the projections is at least twice the width of the depressions.

3. The mill of claim 1, in which the depressions are filled at least in part by a material softer than that of the lining.

4. The mill of claim 1, in which the lining is made of plates, the depressions are formed by holes extending through the plates, and the bridge pieces lie wholly within the holes and against the inner surface of the shell.

References Cited in the tile of this patent UNITED STATES PATENTS 689,347 Hundeshagen Dec. 17, 1901 6 Barry May 12, 1908 Hardinge Feb. 8,1921 Bonnot et al. June 22, 1926 Hardinge May 26, 1931 Fitzgerald Nov. 14, 1944 Henricot Ian. 16, 1945 FOREIGN PATENTS Great Britain of 1902 Germany Mar. 3, 1902 France Mar. 15, 1926 OTHER REFERENCES Ser. No. 312,133, Henricot (A. P. 0.), published May

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