US3533570A - Grinding plate lining for tube- and ball-mills - Google Patents

Description

Oct. 13, 1970 P. BERNUTAT 3,533,570

GRINDING PLATE LINING FOR TUBE- AND BALL-MILLS Filed Aug. 6, 1958 I IIIIIIIVII" INVENTOR.

BY A MW? United States Patent 3,533,570 GRINDING PLATE LINING FOR TUBE- AND BALL-MILLS Paul Bernutat, 99 Graf-Recke-Strasse, 4 Dusseldorf, Germany Filed Aug. 6, 1968, Ser. No. 750,580 Int. Cl. B02c 17/22 U.S. Cl. 241-299 3 Claims ABSTRACT OF THE DISCLOSURE A grinding plate lining for tubeor ball-mills, which comprises a mill jacket and elastic intermediate layers disposed between the mill jacket and the grinding plates. Each of the grinding plates is spaced apart by a slit from the adjacent grinding plates, and glue means are provided for securing the grinding plates to the intermediate layers and the latter to the mill jacket over their entire engaging faces.

The present invention relates to a grinding plate lining for tubeor ball-mills, in general, and with intermediate elastic layers disposed between a mill jacket and the grinding plates, in particular, whereby each grinding plate is separated from the adjacent grinding plates by a split.

Drums of tubeand ball-mills receive in known manner wear resistant linings, so-called grinding plates. These grinding plates are subjected, in addition to high wear, also to the wear by jolt and hit, which have their cause in the fact that the grinding balls knock directly on the grinding plate. This last-mentioned stress makes many working materials unsuitable which, due to the high hardness, have a very large resistance against frictional or abrasive wear for the insert in ball mills. Working material again, which are resistant, in view of a sufiicient toughness, to a jolt and hit wear, have been found in many instances as not sufficiently resistant against erosive wear.

Thus, the problem exists, to find a working material which has, due to its hardness, a high resistance against frictional and erosive wear, simultaneously, however, has so much toughness, in order to resist the hit wear by the grinding balls. Since, however, knowingly the hardness of all steel alloys increases to the same degree as its toughness is reduced, the problem can be solved only with a plurality of non-desirable compromises.

For particularly two reasons, lately the solution of the problem of the present invention has become particularly urgent. In the first place, tube mills are designed today with diameters of up to 4.2 m. The hitting wear of the grinding plates has correspondingly increased, due to the higher kinetic energy of the grinding balls during the hitting stroke. On the other hand, lately, grinding balls with very particular high hardness (HB 600 kg./qmrn.) have been used.

Particularly, the last-mentioned circumstance rendered completely unsuitable many grinding plate materials, which showed, with the grinding balls of carbon wrought steel, used preferably up to now, in addition to its great resistance against erosive wear, also a sufficient resistance against jolt and hit.

Upon use of these so-called hard grinding balls which, based on their extraordinary hardness, have about 510 3,533,570 Patented Get. 13, 1970 times less wear, than the grinding balls used up to now, and for this reason are particularly economical, in a few cases several tons of grinding plates have been broken within a short time.

The movement path of the grinding bodies in ball mills, which can be assumed as being known, shows that the prevailing wear of the grinding plates is of frictional and erosive type and its duration of use depends basically upon the fact, whether they show a high resistance against this type of wear. This frictional wear is created when the grinding balls must be accelerated again to the angular speed of the mill drum after their stroke. Since in case of great mills, the peripheral speed inside of the drum amounts to more than 3.0 m./s. and the quantity of balls to be accelerated amounts to more than t./s., the time period available for the acceleration of the grinding balls is, however, very low, the acceleration force reacting on the grinding plate is correspondingly large.

The number of the grinding balls striking the grinding plates directly is surprisingly low. It amounts to only about 3%. All other balls strike again on balls, whereby the stroke on the grinding plate is dampened to a great extent or even completely caught. The few direct ball strokes cause then hardly a wear of the grinding plate, rather they destroy the grinding plate by the high pressureand bending-tensions produced in the grinding plate during the stroke.

In spite of the fact that erosive wear prevails, which fact points to the use of very hard and brittle working materials for the grinding plate, on the other hand, such working materials which are in addition mostly particularly reasonable as to their price, cannot be used consequently due to their large sensitivity against each type of jolt wear.

It has been now attempted to avoid the large pressureand bending-tensions in the grinding plates created by the stroke of the balls such, that elastic intermediate layers are provided between the mill jacket and the grinding plates. In a number of known embodiments, the grinding plates, of which adjacent ones can be separated by a slit, jointly with the elastic intermediate layers are secured on the mill jacket by means of screwor wedge-connections. In order to avoid a loosening of the screwand wedgeconnection, respectively, the securing of the grinding plates by means of screws or wedges had to take place with a high pretension force. By this arrangement, already during the screwing or wedging of the grinding plates, a break of the brittle-hard plates could be experienced. This great pretensioning force caused, however, first of all a correspondingly high compression of the elastic intermediate layers disposed between the grinding plates and the mill jacket, the elasticity of the intermediate layers being reduced to such an extent that no assurance for the prevention of plate breakage during the operation was available any more. Also by variations of the thickness or quality of the elastic intermediate layers, an increase of the elasticity of the desired measure could not be obtained, since in each case the necessary and very predetermined pretension force brought the prevailing elasticity of the intermediate layer always to the extinguishing point, save a rest which is hardly still effective.

In accordance with another embodiment, the grinding plates equipped with an elastic layer are secured to the mill jacket by relative clamping, for instance, by pressing towards each other without a screw. The pushing force created during the stroke of a ball on the grinding plates secured in this manner must be assumed to a great extent by the friction forces holding the plates, because the plates supported substantially against each other, cannot transfer the pushing force practically on its base. For this reason,

during engagement or stroke of the balls it comes to high bending tensions in the plates and as their consequence easily to a plate breakage. Furthermore, it is nearly of no importance, whether the dampening layer is elastic or non-elastic in this known securing type.

All securing types, known until now, for grinding plates have inherently the drawback that the plates cannot be secured without a high pretension. The consequence therefor is, that the pressureand bending-tensions resulting from the pretensioning force add up to the corresponding tensions from the pushing force created by the striking of a ball. On the other hand, the pretension prevents the desired complete effectiveness of the elastic intermediate layer, either by the fact that the latter, for instance during screwing or wedging reduces its elasticity, by compression of the intermediate layer to a non-effective rest or, as for instance during relative clamping, it renders practically impossible to a great extent the transfer of the fullpushing force and its reception by the elastic intermediate layer.

It is one object of the present invention to provide a grinding plate line for tubeor ball-mills, wherein the grinding plates are secured to a mill jacket, through which the drawbacks of known structures are avoided.

It is another object of the present invention to provide a grinding plate lining for tubeor ball-mills, which includes an elastic intermediate layer between the mill jacket and the grinding plates whereby adjacent grinding plates are separated from each other by a slit. It is furthermore provided to bring about a securing between the grinding plates and the intermediate layers as well as between the intermediate layers and the mill jacket merely by gluing along the entire engaging surfaces.

By the arrangement made in accordance with the present invention, the above stated drawbacks of the known securing means are completely removed. The grinding plate remain-s absolutely free from pretensioning forces and the pushing force is assumed completely by the elastic intermediate layer. By a proper selection of elasticity and thickness of the intermediate layer, it is possible to bring the pressureand bending-tensions in the grinding plate to a value which is not dangerous for the used grinding plate material.

A further advantage of the grinding plate lining in accordance with the present invention resides in the reduction of the grinding noise getting outwardly from the mill. This noise reduction has its purpose in the fact, that the body noise created by ball abutment in the grinding plate takes place always only over the elastic intermediate layer and is thereby transferred appreciably dampened to the grinding drum.

A further advantage of the proposed securing resides in the fact, that a grinding plate performs even then its function it it is broken, for instance, due to a work material defect. A falling out of broken parts is not possible.

In order to be able to improve the spring characteristic line of the elastic intermediate layer independently from its thickness and the elasticity of its material, such that it approaches a straight line, in accordance with a further feature of the present invention, the elastic intermediate layer is perforated. The holes on perforations can be chosen in any selected number, form and size, such that a very flatly extending spring characteristic line is obtained.

By this arrangement, it is brought about that also in case of the striking of grinding balls with a high kinetic energy, the force between the grinding plate and the mill jacket does not lead to the break of the grinding plate.

In order to improve the sound dampening, which is, as a matter of course, lower in case of a perforated intermediate layer than in case of a non-perforated one, finally, in accordance with the present invention, the holes or perforations are filled up with an easily compressible sound absorbing material.

With these and other objects in view which will become apparent in the following detailed description, which discloses the present invention by example only, the present invention will be clearly understood in connection with the accompanying drawing, in which:

FIG. 1 is a fragmentary cross-section of a mill-jacket lined with grinding plates;

FIG. 2 is a top plan view of a grinding plate;

FIG. 3 is a top plan view of a grinding plate which is glued to a perforated intermediate layer;

FIG. 4 is a section of the grinding plate, of the intermediate layer and of a mill jacket along the lines 44 of FIG. 1; and

FIG. 5 is a diagram depicting the spring characteristic lines of a nonperforated and a perforated grinding plate.

Referring now to the drawings, and particularly to FIGS. 1 and 2, which discloses a first embodiment of the present invention, the grinding plate 1 is glued over its entire rear face to an elastic intermediate layer 2, which, in turn, is glued to the inner face of a mill jacket 3. Adjacent grinding plates 1 are, as can be determined from FIG. 1, separated from each other by means of a slit 5, so that no relative interference of the grinding plates 1 with their capacity of movement results.

Referring now again to the drawings, and in particular to FIGS. 3-5, which disclose a second embodiment of the present invention, again a grinding plate 1' is glued to an elastic intermediate layer 2 and the latter, in turn, is glued to the inner face of a mill jacket 3. Each pair of adjacent intermediate layers 2 are again separated from each other by a slit 5'. As clearly shown in FIGS. 3 and 4, the intermediate layer 2' is perforated. In this matter, the spring characteristic line of the intermediate layer 2' is not only influenced by the spring, the thickness and the elasticity of the material, but still to a greater extent by the number, size and form of the perforations 4.

The perforated intermediate layer 2' can be deformed not only at its edges, but also on the edges of the perforations 4, so that by the selection of form and number of these perforations 4' such extensive deforming possibility is created that a very flat extending spring characteristic line results for the intermediate layer 2'.

Referring now to FIG. 5, the spring characteristic line of a nonperforated intermediate layer is indicated as a curved line a and the spring characteristic line of the perforated intermediate layer 2 is indicated by a curved line b, whereby P is the force betwen the grinding plate and the mill jacket and f is the spring path.

For the increase of the sound dampening, the perforations 4 can be filled up with an easily compressible, sound absorbing material 6, as it is shown in the left half of FIG. 4. By this arrangement, it is assured that the sound created in the grinding plate is transmitted to the mill jacket 3 at no place without dampening.

I claim:

1. A grinding plate lining for tubeor ball-mills, comprising a mill jacket,

grinding plates disposed in said mill jacket, and

elastic intermediate layers disposed between said mill jacket and said grinding plates,

each of said grinding plates being spaced apart by a slit from the adjacent grinding plates, and

glue means for securing said grinding plates to said intermediate layers and the latter to said mill jacket over their entire engaging face.

2. The grinding plate lining, as set forth in claim 1, wherein said intermediate layer has perforations.

6 3. The grinding plate lining, as set forth in claim 2, 1,748,039 2/1930 Kennedy 241 -183 which includes an easily compressible, sound absorbing 2,909,335 10/ 1959 Janelid 241-483 t lfill' 'd ma mg Sal perforatwns ROBERT c. RIORDON, Primary Examiner References Cited 5 D, G, KELLY, Asistant Examiner UNITED STATES PATENTS US. Cl. XR.

1,538,620 5/1925 Canda 241-183 241300

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