US2998201A - Grinding mills - Google Patents

Description

Aug. 29, 1961 T. A. RATKOWSKI GRINDING MILLS 2 Sheets-Sheet 1 Filed March 31, 1959 Inven to P Thomas :6. Ratkowski walfaca MdQxMW fl-liornegs Aug. 29, 1961 T. A. RATKOWSKI 2,998,201

GRINDING MILLS Filed March 31, 1959 2 Sheets-Sheet 2 Inventor Thomas AnRo tkqws kl H-HqraegS 2,998,201 GRINDING MILLS Thomas A. Ratkowski, Chicago Heights, Ill., assignor to American Brake Shoe Company, New York, N.Y., a corporation of Delaware Filed Mar. 31, 1959, Ser. No. 803,159 3 Claims. (Cl. 241- 183) This invention relates to grinding mills of the kind wherein balls are employed as the grinding media.

One well-known method for comminuting material such as ore is to confine the material to be comminuted within a rotating shell which is provided with grinding media of generally spherical form. The shell is then rotated causing the grinding media and the charge of material to be tumbled whereby the charge is gradually broken up to a finer state. The entailed apparatus is known in the art as a ball mill, and the balls can be composed of a wear-resistant alloy, and in some instances the balls are composed of hard, naturally-occurring materials.

It will be appreciated that the shell of the ball mill would normally undergo a terrific amount of wear if the charge to be comminuted and the grinding media were allowed to be in direct contact with the inner surface of the mill shell during operation of the mill. In view of this, it has long been a practice in the art to line the shell with removable liners of manganese steel or like wear-resistant alloy. Hence, it is the removable liner which takes the wear, and when the liners have been worn down beyond a useful condition, these are removed and replaced by like liners.

In a grinding mill, the most effective type of grinding or attrition of the charge to be comminuted occurs as a result of an actual impact of the grinding media on the individual bodies of the charge. In contrast to this, the most inelfective grinding or comminution occurs as a result of a mere sliding of the grinding media on the charge, although there is some effective comminution occurring as a result of a pair of grinding media rolling on a particle of the charge squeezed between a pair of such grinding media. In view of these phenomena, it has also been proposed heretofore to equip ball mill liners with ribs that will extend generally parallel to the axis of the mill, or in any event in such a direction as to have an actual lifting action on the grinding balls. Thus, by equipping the liners with lifter ribs, or like lifter elements, the grinding media will be carried upward by a positive acting force during rotation of the shell, and this lifting action will continue until a high point is reached Where gravity overcomes the effective centrifugal force tending to hold the grinding media against the liner. Thus, it will be seen that eventually the grinding media take flight of the liners, as the phenomenon is sometimes called, and drop with a violent force downward to the toe of the charge near the bottom of the shell causing a tremendous amount of impact in this area of the charge to be comminuted.

One of the primary objects of the present invention is to so construct a liner for a ball mill as to have ribs disposed at angles and so shaped as to afford a concave pocket at the area of the included angle between the ribs. This concave pocket will be shaped generally complemental to the shape of a grinding medium, and hence when a grinding medium takes flight of the liner in the manner explained above, this grinding medium in all probability will land in one of the concave pockets atforded in the foregoing manner at the bottom of the shell. In all probability there will be some of the charge to be comminuted in such a pocket, and hence the grinding medium will fall with a violent force into the pocket containing a part of the charge and will produce a violent 238,23 Patented Aug. 29, 1961 mortar and pestle action resulting in highly effective comminution. Another object of the present invention is to enable shell liners for ball mills to be afforded in thinner sections in comparison to what has heretofore been possible, and to accomplish this by so strengthening the liner by angled strengthening ribs as to make possible a liner of less thickness than has heretofore been attained in the art.

Other and further objects of the present invention will be apparent from the following description and claims and are illustrated in the accompanying drawings which, by way of illustration, show preferred embodiments of the present invention and the principles thereof and what is now considered to be the best mode contemplated for applying these principles. Other embodiments of the invention embodying the same or equivalent principles may be used and structural changes may 'be made as desired by those skilled in the art without departing from the present invention and the purview of the appended claims.

In the drawings:

FIG. 1 is a perspective view looking into one end of a ball mill constructed in accordance with the present invention;

FIG. 2 is a sectional view through the mill of FIG. 1;

FIG. 3 is an enlarged sectional view of a liner constructed in accordance with the present invention;

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

FIG. 5 is a perspective view of a liner constructed in accordance with the present invention;

FIGS. 6 and 7 are sectional views of a modified form of liner; and

FIG. 8 is a plan view illustrating still a further modified form of liner.

One form of ball mill liner installation contemplated by the present invention is illustrated in FIG. 1 in connection with a ball mill having a conventional cylindrical shell 10, and inasmuch as it is unimportant how the shell 10 is to be charged, supported or rotated, these details are not shown. In order that there will be no direct wear of the grinding balls or the charge on the inner surface of the shell 10, this inner surface is lined with individual liners 11 in the form of blocks or plates of predetermined dimension.

As mentioned above, it is common practice to utilize removable liners in a ball mill, and to form these liners with ribs that are aligned generally parallel to the longitudinal axis of the mill, the purpose of this being to apply a positive lifting force to the balls. In this connection, attention is directed to FIG. 2 wherein it is assumed that the shell 10 is rotating in the direction of the arrow, wherein the charge to be comminuted is generally indicated by the reference character C, and wherein the grinding media in the form of balls are identified at B. As will be explained in more detail hereinbelow, each of the liners 11 is formed with one or more longitudinal ribs LR, and it will be recognized from FIG. 2 that these ribs are so oriented and dimensioned as to enable the grinding balls B to repose in the grooves or valleys between the ribs LR. Hence, when the shell is rotating the grinding balls in the grooves between the longitudinal ribs will tend to be carried upward and around with the ribs LR on the liners until the force of gravity overcomes centrifugal force at the high point of the charge. This high point will of course vary depending upon operating conditions, and when the high point is reached the grinding balls will in effect fly from the high point of the charge to the low point or toe indicated generally at T in FIG. 2. It is this falling and resultant high impact on the charge at the toe of the charge which results in the most effective comminution of the charge, and consequently it Will be seen that it is the primary role of the longitudinal ribs as LR to move the 'balls upward and around with the shell to as high a point as practical.

Under and in accordance with the present invention, the liners 11 are so formed that the ribs LR are of sinusoidal arcuate form, and these ribs are crossed by transverse ribs TR which are also of sinusoidal arcuate shape and configuration.

The general construction contemplated by the present invention is best illustrated in FIG. 5 wherein details of a typical liner 11 are developed in perspective view. Thus, a liner as 11 will generally be cast of manganese steel or like tough, wear-resistant alloy and will be cast to have an arcuate back or rear face 11F which will have a radius of curvature conforming to the inside face of the shell 10. Inasmuch as the individual liners, for most practical installations, will be laid end-to-end the length of the shell and side-to-side about the inner circumference of the shell, each liner 11 has end faces 14 and 15 which are disposed in planes that are perpendicular to the rear face HP. On the other hand, each liner element or block will have side faces 16 and 17 which are sloped in a converging manner proceeding forward from the back l lF as best shown in FIG. 3, to enable a neat side- .by-side fit between successive elements 11 to be established about the circumference of the mill as illustrated in FIG. 1.

The front face or side of a liner element 11 opposite the back 11F is the face that will take the wear during operation of the mill, which is to say that the charge C and the grinding balls B will be in contact with the front face of the liner element opposite the back 11F. This Wear face of the liner element '11 is the one that is formed with the ribs LR which are to extend generally parallel to the axis of the mill. As mentioned above, the longitudinal ribs LR are of generally sinusoidal shape and hence have convex crests CX, FIG. 3. The spacing of the longitudinal ribs is such that the low part or valley of one rib merges immediately into the adjacent low part or valley of the next rib producing a somewhat shallow hemispherical concavely curved valley or pocket P, FIGS. 3 and 5. The dimensions are such that these pockets P have a radius of curvature just slightly larger than the grinding balls to enable the grinding balls to repose complementally therein, the grinding balls being indicated at dashed lines B in FIG. 3. Depending upon the predetermined size of a liner element 11 there will be one or more ribs LR formed thereon. In the embodiment of the invention illustrated in FIG. 5 there is a full-size or halfround rib LR located medially of the transverse width of the liner element 11 and the two sides of the liner element 11 terminate in two half ribs LR and LR of quarter-round section. It will be appreciated that when another liner element 11 is set against the side face 17 of the liner element 11 illustrated in FIG. 5, the half rib LR of this other liner element will complete a second full-size rib (but split) like the rib LR illustrated in FIG. 5. Similarly, when still a third liner 11 is set against the side face 16 of the liner element 11 illustrated in FIG. 5, its half rib LR" will cooperate with the half rib LR of FIG. 5 to afford a third full dimensioned longitudinal rib LR, and so on around the mill as will be apparent from FIG. 1.

The transverse ribs are shaped, spaced and sized as are the longitudinal ribs LR and join the longitudinal ribs at an angle. Inasmuch as the transverse ribs in adjacent rows are off-set for a purpose to be explained, the transverse ribs have been numbered in FIGS. 4 and 5. Thus, it will be observed that there are three equally spaced full-sized transverse ribs TRI, TRZ and TR3 located between the ribs LR and LR, and these are so spaced and sized, as shown in FIG. 4, as to have the low part of one rib merging into the low part of the next rib, and again the radius of curvature is such as to enable a grinding ball B, FIG. 4, to fit in the concavely rounded groove or valley between the low parts of adjacent transverse ribs in a fashion identical to that explained above in connection with FIG. 3.

Thus, each concave pocket P, FIGS. 3, 4 and S, is in reality cup-shaped or hemispherical and lies at the included angle where the longitudinal and transverse ribs meet. During operation of the mill, the pockets P of the liners near the toe of the charge will be carried upwardly clockwise therefrom as viewed in FIG. 2 and will contain some of the charge. The halls moving upward with the mill will tend to have some rotation in the pockets P moving up with the shell, and hence will rotate somewhat within the pockets and will necessarily produce some comminution. Moreover, the balls which take flight of the shell at the high point of the charge, in the manner explained above in connection with FIG. 2, will fall downward into the pockets P of the liners 11 near the toe of the charge, and will fall with a violent force on the charge in these pockets producing a highly effective mortar and pestle comminuting action.

As will be observed in FIG. 5, there are transverse ribs joined to the oppositely curved sides of the full-sized longitudinal rib LR, and it will be noted from FIG. 3 that the transverse ribs at their crests are bowed or curved concave to be parallel to the convex curve of the liner. Moreover, the concavely rounded sides of the transverse ribs not only merge into one another but also merge into the concave bottoms of the longitudinal ribs so that the concave pockets as P are closed on four sides and are continuous and unbroken.

Itwas mentioned that the transverse ribs are off-set, which is to say that the transverse ribs as TRS and TR6 (full-sized), FIG. 5, in the row of transverse ribs on the near side of the rib LR as viewed in FIG. 5 join the medial longitudinal rib LR at points immediately opposite the pockets P between the transverse ribs TRI, TR2 and TR3 on the opposite or far side of the rib LR as viewed in FIG. 5. Such off-setting of the transverse ribs in adjacent rows accounts for a highly effective strengthening of the longitudinal lifter ribs in the assembly, and hence enables the liner blocks or plates to be of less thickness than has heretofore been possible. Thus, liners as heretofore constructed. and formed solely with lifter ribs have been quite thick, and in fact on average are about twentyfive percent thicker than the liner in the present instance which is drawn to scale in FIGS. 3 and 4. Such excessive thickness of course results in higher costs and higher energy requirements for rotating the mill. Additionally, off-setting of the ribs produces corresponding off-setting of the pockets P.

Because of the off-setting of the transverse ribs in adjacent rows, the row of transverse ribs which includes the transverse ribs TRS and TR6, FIG. 5, will terminate at transverse ribs TR4 and TR7 of split or half size, but it will be realized that each of these half ribs will be com pleted by two adjacent liners at either end of the liner '11, FIG. 5, one such adjacent liner having a half rib to supplement the half rib TR4 when set thereagainst, and the other having the supplement of the other half rib TR7 when set thereagainst.

Insofar as the dimensions of the liner element are concerned, and the size of the pockets as well as the number and orientation of the ribs, these will vary depending upon operating conditions, the nature of the charge, and the grinding media. Thus, the specific construction of a liner in accordance with the present invention will vary depending upon the circumstances of use, and in FIGS. 6 and 7 a modified liner element 12 is illustrated wherein the transverse ribs, generally indicated at TR M, are of shortened height and of less section thickness in comparison to the transverse ribs described above in connection with the liner 1 1 illustrated in FIG. 5. The liner 12 is of the same longitudinal length and transverse width as the liner 11, and hence there are more transverse ribs per unit of length. How ever, the longitudinal ribs, LRZ, FIGS. 6 and 7, are of the same size as those incorporated in the liner element 11, and in view of this dimensioning of the longitudinal ribs the liner element 12 will also have a split longitudinal rib LRZ' and LR2" at the two sides as in the foregoing embodiment. Inasmuch as the transverse ribs in the liner element 12 have been increased in number, the pockets P in this instance will be somewhat elongated in the direction parallel to the transverse ribs, which is to say that this embodiment of the invention can be viewed as one wherein the grinding media to be used will on the average be somewhat smaller than the grinding media to be used with the liner element 11.

The transverse ribs in the liner elements 11 and 12 join the longitudinal ribs at right angles, but this is not a critical consideration. In fact it may be advantageous under some circumstances to impart a lead angle to the transverse ribs to induce movement of the charge toward one end of the mill during mill operation. Accordingly, the transverse ribs can be inclined relative to the longitudinal ribs as illustrated in FIG. 8.

Replaceable mill liners are conventionally bolted to the shell and this mode of securement is used in the present instance. Advantageously, however, the bolt receiving openings are located in the lifter ribs to free the pockets P as will be evident from FIGS. 5 and 8. The heads of the fastening bolts will thus rest on the crest of the lifter rib, but the bolt receiving openings can be recessed or countersunk to enable the heads of the bolts to be protected. In any event the shanks of the bolts will project through the mill shell, and retainer nuts will be threaded thereon in the usual fashion at the outside of the mill shell.

It will be seen from the foregoing that under the present invention there is afforded a shell liner for a ball mill having lifter ribs that are joined by ribs disposed generally transverse to the lifter ribs. The area of the liner at the included angle between the ribs is rounded concavely to conform generally to the radius of curvature of the grinding media, and this allows the grinding media to work with a mortar and pestle action in the resultant concave depressions at the included angles of the ribs. Additionally, the transverse ribs can be considered as tie beams which reinforce the longitudinal ribs. This greatly strengthens the liner and enables the liner for a given mill installation to be of less thickness dimension than has heretofore been possible.

Hence, while I have illustrated and described preferred embodiments of my invention, it is to be understood that these are capable of variation and modification, and I therefore do not wish to be limited to the precise details set forth, but desire to avail myself of such changes and alterations as fall within the purview of the following claims.

I claim:

1. A liner for a ball mill cast of a wear-resistant alloy and comprising a generally rectangular one-piece cast body having an arcuate back curved to fit complementally a portion of the inner circumference of the shell of such a mill, said body having the opposed two end faces thereof disposed in flat planes substantially perpendicular to said back to thereby enable a plurality of such liners to be assembled in a row axially of the shell of the mill substantially in flush end-to-end contact, said body having the opposed two side faces thereof disposed in flat planes sloped relative one to another in a converging manner proceeding in a forward direction from the back of the liner to enable a neat side-by-side fit between successive liners circumferentially in a row about the shell of the mill, said liner having a Wear face opposite the arcuate back thereof, said wear face being defined by substantially quarter-round ribs, located at the opposed sides of the liner and which extend parallel to said sides, said wear face being further defined by a substantially half-round sine-shaped rib parallel to the first-named ribs and centrally located therebetween, whereby the quarter-round ribs of three such liners set in side-by-side relation have the engaged quarter-round ribs thereof abutted to afford additional half-round ribs, and a plurality of transverse substantially half-round ribs disposed in different rows between the first-named ribs at an angle thereto and having the curved surfaces thereof cooperating with the curved surfaces of the firstnamed ribs to afford rounded pockets for receiving grinding balls.

2. A liner according to claim 1 wherein the transverse ribs in one row are off-set relative to those in the next adjacent row.

3. A liner for a ball mill cast of a wear-resistant alloy and comprising a generally rectangular one-piece cast body having an arcuate back curved to fit complementally a portion of the inner circumference of the shell of such a mill, said body having the opposed tWo end faces thereof disposed in flat planes substantially perpendicular to said back to thereby enable a plurality of such liners to be assembled in a row axially of the shell of the mill substantially in flush end-to-end contact, said body having the opposed two side faces thereof disposed in flat planes sloped relative one to another in a converging manner proceeding in a forward direction from the back of the liner to enable a neat side-by-side fit between successive liners circumferentially in a row about the shell of the mill, said liner having a wear face opposite the arcuate back thereof, said wear face being defined by spaced ribs parallel to the sides of the liner and spaced transverse ribs arranged in rows between the firstnamed ribs, said ribs having exposed curved surfaces which merge into one another to afford hemispherical shaped pockets at the wear face of the liner for receiving grinding balls, certain of the ribs terminating at selected of the side and end faces of the liner and being the complement of like terminal ribs on an identical liner.

References Cited in the file of this patent UNITED STATES PATENTS 730,900 Fuller June 16, 1903 1,176,040 Doherty Mar. 21, 1916 2,268,661 Kennedy Jan. 6, 1942 2,680,568 Weston June 8, 1954 FOREIGN PATENTS 1,096,407 France June 29, 1955 (Addition to 64,710)

104,482 Germany July 29, 1899 194,694 Austria Jan. 10, 1958 511,916 Italy Jan. 28, 1955 576,468 Great Britain Apr. 5, 1946 OTHER REFERENCES Grinding Ball Size Selection, by Fred C. Bond, Mining Engineering, May 1958, page 594, Table V.

Images