US2731210A - Cylindrical rotating mill with stepped and studded liner for automatic classification of grinding balls and material - Google Patents

Description

Jan. 17, 1956 J. F. HENRICOT 2,731,210

CYLINDRICAL ROTA NG TH STEPPED AN TUDDED LL LINER OM C SSIFICATION FOR GRINDING BALLS AND MATERIAL Filed July 15 1953 \QKNW 4 s 5 INVENTOR.

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United States PatentO CYLINDRICAL ROTATING MILL WITH STEPPED AND STUDDED LINER FOR AUTOMATIC 'CLAS- lSIIFAIICATION F GRINDING BALLS AND MATE- Jacques Fernand Henricot, Court Saint-Etienne, Belgium Application July 13, 1953, Serial No. 367,649

Claims priority, application Great Britain August 6, 1952 1 Claim. (Cl. 241-183) This invention relates to a cylindrical ball grinding mill in which material to be processed enters at one end and is discharged at the other end, comprising an inner lining carrying studs arranged for exerting a gripping action on said material, and, for increasing, as compared with a similarly operating but not stud-lined mill, the angle of lift produced on the material and the grinding media i. e. the balls by rotation of the mill.

Such mills just as any other cylindrical mill with smooth, waved or ribbed interior lining, have no classifying effect on the mass of grinding media or balls contained in them.

It is well known that, in order to reduce the power consumption for the grinding operation, and also wear of the balls, it is advisable that bigger balls be maintained near the entrance of the mill with the other balls arranged in progressively decreasing sizes when advancing towards the outlet of the mill. To this end, it has been proposed to divide the mill into several compartments, separated by partitions perpendicular to the axis of the mill, and to pour into each compartment a mixture of balls which are of the greater average size the nearer said chamber is situated with respect to the feed end of the mill. Such partitions allow material to proceed from the feed to the discharge end as soon as it is suiliciently comminuted but prevent the balls from doing likewise and migrating through compartments.

This solution has the disadvantage of adding weight to the mill construction, and of requiring periodical emptying of the ball loads to have them sorted out in order to rebuild adequate individual chamber charges after these have been modied due to wear.

It has also been proposed, in order to obtain an automatic classification of grinding balls, to replace the cylindrical smooth mill lining by one composed of frustoconical rings having their large bases turned towards the feed end of the mill, the smaller bases facing towards the outlet end of the mill. These conical liners may be slightly waved transversely, so as to increase somewhat the lift produced on the material by rotation of the mill.

With a frusto-conically lined mill, a gradual decrease in size of the balls is automatically obtained from inlet to outlet ends of chamber, but unfortunately a notable quantity of material lumps of fair size are also sent in direction of the outlet end, where they will no longer find balls of sufficient dimension to break them. The choking-up of the outlet region of the compartment concerned will prevent the use of such a mill unless material be introduced in a considerable state of fineness, similar to sand. Therefore, a mill so equipped requires simultaneous use of another pre-grinding mill or apparatus wherein the material will be sufficiently comminuted to make a safe feed for the smoothdined frusto-conical mill.

The object of the present invention is to provide a grinding mill wherein the aforesaid movement of lumps of material may be suppressed or considerably reduced, whilst preserving the advantage of automatic classifica- I 2,731,210 Patented Jan. 17, 1956 ice tion of the balls which is known from the smooth-lined frusto-conical mill.

According to the invention, said studs have their heads at varying distances from the mill axis and are so grouped that in a longitudinal section through the mill, said heads appear, as is known for the surface of non-studded mills, along a line of successive taper step such that in each of these latter, the stud heads farthest from the mill axis are situated nearer to the feed end of the mill than the heads nearer to the mill axis.

The interior studs of the mill according to the invention not only serve to take a grip on the balls and material during rotation of the mill but also serve to exert a braking action on movements of lumps of material from the feed end towards the discharge end of the mill.

This retarding effect can be explained by considering that lumps of material coming to rest between the studs are shielded by them from the classifying action of the conical liner.

The aforedescribed use of studs, in combination with the taper arrangement, evidently gives rise to a novel and advantageous action, since it suppresses, or at least greatly reduces a difficulty which occurs with tapered liners although it does not exist with cylindrical liners whether they be smooth or studded.

The longitudinal grouping of the stud heads in a taper arrangement can be obtained either by studs of constant height fixed on frusto-conical sole plates'or by studs of variable height rising from cylindrical annular sole plates.

The distance between the studs can of course be gradually or intermittently reduced from the feed to the discharge end of mill, just as in the case of a cylindrical studded lining.

The drawings accompanying the present application schematically represent, by way of example only, two embodiments of a ball mill according to the invention.

Figure 1 is a schematic axial section through one embodiment of mill according to the invention.

Figure 2 is a developed view of part of the inner lining, a few studs only having been shown.

Figure 3 shows, to a larger scale, a longitudinal section through one plate of the inner lining which is shown in Figures 1 and 2 which is not possible because of the small scale of the latter figures.

Figure 4 represents an alternative form of lining plate for a mill according to the invention.

In these various figures, the same numbers refer to identical elements.

In Figure 1 is shown a ball mill of generally cylindrical shape having only one grinding chamber in which material to be processed is introduced at one end 2, and discharged at the opposite end 3. This mill comprises an outer shell 4 encircling frusto-conical rings 5 which are arranged end to end. In longitudinal section, the assembly of rings therefore appears as a succession of taper steps, in each of which any stud head is farther away from the mill axis than those encountered on the same taper step when-progressing in the direction of the mill discharge end 3.

The rings 5 are constituted by plates 8 (Figure 2) covered with studs 9 (Figs. 1 and 3). In Figure 3, the plate 8 is shown as hollow, which is not possible in figure 1 by reason of its small scale. For sake of clarity, only the sectioned parts of plates 8 and studs 9 have been shown. For the same reason, the grinding media i. e. the balls, and the material being processed have been omitted. The studs 9 have a constant length from the inner surface 11 of the corresponding plate. The heads 12 of the studs are so grouped that in a longitudinal section of the mill they appear as a line of successive taper steps just like the inner faces 11 of the plates 8.

Figure l'also shows that the studs 9 are so disposed in'a group of taper steps'situatedneartheoutlet 'ofth'e mill, their heads are farther. away from the axis of rotation than in a middle group, and .in a middle group are farther'away' th'an'in' a group'ofstu'ds near thefeed end.

As is clearly shown in Figure 1 the slope of cone generatrix with regardto the mill axis decreases stepwise when considering successive taper steps farther away from the inlet end z'andthe' dimensions and spacings of the studs decrease when progressing towards the outlet end 3.

In Figure 4, another embodiment for a plate 8' for a mill according to the inventioniis shown. This plate has a cylindrical sole plate, fitted on its inner face with studs 9" oflvariable heights, so that the heads 12 ot'thc studs are also disposed,lin; longitudinal section, on a taper alignment of which the extremity farthestfrom the mill axisis situated nearer to the feed end than the extremity nearer to the mill axis;

The invention is not to be limited exclusively to the two shapes illustrated, and many alternative forms, dispositions and' arrangement of the component elements are possible. without contradicting the following claim.

What I claim. is:

A cylindrical rotating mill for ball grinding comprising an inlet for the material to .be treated at one end, an outlet for the ground material at the opposite end, a lining within said cylindrical part, an annular group of projecting studs on the inner face of the lining arranged for exerting a gripping action on said material and on said "balls during rotation of the mill, said studs having their heads at varying distances from the mill axis" and being so grouped'thatin" a longitudinal section through the mill, said heads appear as successive taper steps such that in each of the latter, the stud heads farthest from the mill axis are seated nearer to the inlet end of the mill than the heads of the taper step considered. which arenearerto :the mill axis, the .slopeof cone generatrixx withregard to the mill axis decreasing=:step- Wise when considering-successive'taper; steps farther away from said inlet end and the dimensions and spacingsof said studs decreasing when progressing towards the outlet end of said mill.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Tube Mill Liners in the Cement Industry, by C. L. Carman, Rock Products, April 193 8, pp. 44-46, photostat in Div. 55L

Ser. No. 312,133; Henricot (A. P. (1.), published May 4, 1943.

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