US1822436A - Grinding mill - Google Patents

Description

Sept-8, 1931. I 1 s, s'n 1,822,435

GRINDING MILL Filed Feb. 15, 1950 CAD Patented Sept. 8, 1931- UNITED STATES.

PATENIT" OFFICE JOHAN S. FASTING, 0F VALBY, NEAR COPENHAGEN, DENMARK, ASSIGNOR TO F-L- SMIDTH & (30., OF NEW YORK, N. Y., A CORPORATION OF NEW JERSEY GRINDING MILL Application filed February 15, 1930, Serial No. 428,640, and in Great Britain September 24, 1929.

This invention relates to grinding mills of the type generally called tube mills, designed for the grinding of cement and the like, in which the material to be ground is placed, with grinding bodies, in a compartment of a rotating cylinder and is reduced to a more or less finely divided condition by impact of the grinding bodies in the rotation of the mill. Such mills are commonly provided with transverse partitions which form successive compartments, from one to another of which the material being ground passes as its particles reduce in size. "In such mills the grinding bodies themselves are commonly proportioned properly with respect to the fineness of the material in successive compartments, it having been found that the efficiency of such a mill is materially reduced if'the grinding bodies in the successive compartments are not suited to the progressive fineness of the material in successive compartments. In the operation of such mills the material undergoes a preliminary grinding in the first chamber or compartment, in which the grinding bodies are of such size that they will with certainty crush the largest pieces of material supplied to the preliminary chamber. From this first chamber the par ticles of material which have been reduced in size pass through openings in the transverse wall or partition into the next chamber where smaller grinding bodies continue the grinding operation and so on throughout the successive chambers of the mill. In this manner the grinding bodies may be in some degree suited 'to, the fineness of some of the material in the chamber, but it will be readily understood that in the processof grinding some of the particles of material are reduced in size much more than are other particles and are too small for the proper action of the grinding bodies with which the compartment is charged. Infact, the material as it is supplied to the first or preliminary chamber may contain grains or particles which are already smaller than those for which the grinding bodies in that chamber have been selected. A similar condition exists in the successive chambers, in

each of .which there is more or less material which is too. finely divided'for proper action of the grinding bodies and the presence of which clogs the action of the grinding bodies on the larger particles and so reduces the efliciency of the mill.

This difliculty in the operation of tube mills has been well recognized and efforts have been made to overcome the difficulty, as by increasing the screening action of the transverse partition or wall which forms the end of the chamber, as by fitting the partition on its rearward face with projections extending rearwardly into the chamber so as to come in contact with the material contained in the feeding end of the compartment. It has also been proposed to provide the partition or end wall with openings so large that large quantities of the material may "pass through and then be subjected to the action of screening devices whereby the finer :material may be passed on to the next cham ber while the coarser material is returned to the chamber for further grinding action.

Such efforts have been only partially sucoessful, being effective only on the material in the chamber near the end wall through whichit is to pass into the next chamber and failing to effect operation on the finer material near the feeding end of the chamber, whereit continues to clog the action of the grinding bodies and reduce the efficiency of the mill.

It has been the object of the present invention to overcome still further the difiiculty referred to and to'that end the construction of the mill has been so modified as to provide for the separation of the finer material from the coarser throughout the length of the compartment,so that the action of the grlnding bodies on the coarser lsno longer clogged, but the grinding bodies are relieved from action on the liner particles and their percussive effect is exerted more fully on the coarser material, with resultingincreased efliciency of the material. Since the separation of the finer material is more completely effected when it carries with it some particles or grains which are toolarge for introduction into the next grindingchamher, there is also provided, external to the grinding chamber, a screening device which serves to separate the material that is too coarse to be admitted to the next grinding chamber but should be returned for further grinding in the chamber from which it passed with the finer material. The construction of the screening device is such that inspection of the interior surface of the compartment and replacement of Worn parts are readily possible.

The invention will be more fully explained hereinafter with reference to the accompanying drawings in which:

Figure I is a View in longitudinal section of so much of a tube mill as is necessary to enable the application of the invention to be understood.

Figure II is a View in transverse section on the plane indicated by the broken line II-II of Figure I.

In the drawings there is shown only the preliminary grinding chamber of a tube mill, with its appurtenances, but it will be understood that the same or similar appurtenances might be applied to the mill in connection with each or any of the succeeding chambers or compartments. In. the construction shown the grinding chamber is provided with a series of non-concentric grinding plates 1 which are so arranged that the trailing edge of each plate overlaps inwardly the leading edge of the next plate, the plates being secured to each other and to the shell 1 of the mill by bolts 2. which pass through the plates and through the shell, as shown in Figure I, and receive nuts 2 on their outer ends so that they may be removed readily for inspection and replacement. An opening 3 for the passage inwardly of the material being ground is provided between the trailing edge of each plate and the leading edge of the next plate. The plates 1 extend from end to end of the chamber and may contact at their ends on transverse plates 4 and 5, the former being provided centrally with an aperture 6 through which the material to be ground may be introduced into the chamber from a chute 7. Each plate 1 is also provided, preferably near its leading edge, with apertures 8 through which the finer material may pass outwardly in the operation of the mill. It will be understood that the shell l of the mill is sectional, or formed with openings 1 between the leading edge of each section and the trailing edge of the preceding section, through which openings the material being ground may pass from the openings 3.

External to the shell 1 and overlapping the openings 1" are screens 9, preferably curved, as shown and secured at their edges to the sections of the shell 1 and within each screen 9 is placed a bafile or guide plate 11, preferabl curved as shown, its function being to receive the material from the holes 8 of the grinding plates and, in the rotation of the mill, to discharge the material upon the screen 9 near its leading edge, so that in the continued rotation of the mill the material will pass over practically the can tire screen surface, the finer particles passing through the screen and the coarser being returned. to the interior of the grinding chamber through the openings 3.

The finer particles which have passed through the screens 9 are received within a frusto-conical jacket 12 and in the rotation of the mill, pass toward the end of greater diameter, where the material is lifted by scoops 13 and, as each scoop reaches its highest point, is discharged upon a central cone 15, carried by the end plate 5" and is thereby directed through a central opening 16, in a transverse plate 14, into the next grinding chamber 17.

In a mill constructed as described the material introduced into the grinding chamber through the inlet opening, such as the opening 6, is subjected to the action of the grinding bodies 18. Such of the material as is already sufficiently fine to pass through the openings 8 or is reduced by the grinding bodies to such fineness escapes from the interior of the grinding chamber through the openings 8 throughout the length of the chamber and is screened by the screens 9. Such of the material. as is too coarse to pass through the screens 9 is returned into the grinding chamber while the material which is sufiiciently fine to pass through the screen is raised by the shovels 13 and is discharged by the shovels and cone 15 into the next grinding chamber 17. y

The assembling, inspection and replacement of parts of the grinding chamber may be effected readily as the nuts 2 of the bolts 2 are accessible from the outside and each screen 9 is independent of the other screens and may be replaced independently of the others.

It will be understood that various changes in details of construction and arrangement can be made to suit different conditions of use and that the invention, except as pointed out in the accompanying claim, is not limited to the particular construction shown and described herein.

I claim as my invention:

The combination in a tube mill of a shell formed with openings therethrough, grindmg plates forming a grinding chamber and secured within the shell and overlapping the openings within the shell, openings being provided for the passage of ground material from the interior of the grinding chamber outwardly through the grinding plates and for the return of the material inwardly into the grinding chamber, screens secured to the shell and overlapping the openings therethrough, said screens permitting the finer material to pass through the same and serving to return the coarser material to the grinding chamber, and guide plates, one Within each screen, to direct the material received through the openings of the grinding plates upon the leading portion of the screen.

This application signed this 25th day of January, A. D. 1930.

J OHAN S. FASTING.

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