CA1038356A - Mill, particularly tube mill or ball mill - Google Patents
Mill, particularly tube mill or ball millInfo
- Publication number
- CA1038356A CA1038356A CA205,049A CA205049A CA1038356A CA 1038356 A CA1038356 A CA 1038356A CA 205049 A CA205049 A CA 205049A CA 1038356 A CA1038356 A CA 1038356A
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- CA
- Canada
- Prior art keywords
- mill
- plates
- annular
- courses
- inside surfaces
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B02—CRUSHING, PULVERISING, OR DISINTEGRATING; PREPARATORY TREATMENT OF GRAIN FOR MILLING
- B02C—CRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN
- B02C17/00—Disintegrating by tumbling mills, i.e. mills having a container charged with the material to be disintegrated with or without special disintegrating members such as pebbles or balls
- B02C17/18—Details
- B02C17/22—Lining for containers
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- Engineering & Computer Science (AREA)
- Food Science & Technology (AREA)
- Crushing And Grinding (AREA)
Abstract
Abstract A mill, particularly a tube mill or ball mill, has apolygonal, pre-ferably square cross-section with rounded corners and straight or less strong-ly curved sides, and the grinding action is performed by the falling and roll-ing motion of the filling consisting of the grinding elements and the mate-rial to be ground. The size of the grinding elements is only a small fraction of the side length of the basic cross-section of the mill and the interior of the mill is lined with liner plates arranged in a series of annular courses arranged one behind the other in the longitudinal direction of the mill. In-dividual annular courses formed by these plates are angularly displaced or offset relative to each other, preferably by equal angles, the annular cour-ses of the mill comprising plates (f1...f4 or f?...f? respectively) which have inside surfaces that are inclined toward the interior of the mill ant in the direction of travel of the material being ground alternating with courses having plates with inside-surfaces parallel to the axis of the mill. The plates are so arranged that those with inside surfaces extending in the long-itudinal direction and parallel to the mill axis alternate with plates having inside surfaces inclined to the axis of the mill.
Description
~0383s6 This invention relates to a mill, particularly a tube mill or ball mill, which has a polygonal, preferably square cross-section with rounded corners and straight or less strongly curved sides, and in which the grinding action is performed by the falling and rolling motion of the filling consist-ing of the grinding elements and the material to be ground, the size of the grinding elements, e.g., short cylindrical shapes (cylpebses) or balls, is only a small fraction of the side length of the basic cross-section of the mill.
For this reason the invention will be explained hereinafter mainly with reference to such a mill, although the explanation is applicable with corresponding modification also to the other mills of the kind described which have a polygonal basic cross-section.
In a known mill having a square basic cross-section, the grinding action can be strongly influenced by the selection of a proper radius for the rounded portions. A decrease of the radius of the rounded portion relative to the diagonal of the cross-section of the mill will result in a stronger impact, and an increase of the radius of the rounded portions will result in a lighter impact and in a stronger frictional action. Since the successive individual annular courses are angularly displaced or offset, a passage is formed in the mill which, owing to the square basic cross-section of the millJ is similar in shape to a four-thread screw. Owing to this design, an additional impulse in the direction toward the axis of the mill is imparted to the grinding elements. Besides, the helical design also influences the flow of the material being ground in the longitudinal direction of the mill because the flow of the material being ground can be braked or accelerated by a suitable selection of the lead or hand of the screw resulting from the offset of the annular courses. The lead of this helical passage and the hand thereof can be determined by the selection of the angle between successive annular courses.
A
'1038356 The movement of the material being ground through the mill also depends strongly on the specific gravity of the material being ground.
Easily flowing materials to be ground in a dense bed of grinding elements tend to remain on the surface and virtually to float rather than to enter the bed of grinding elements. On the other hand, thorough mixing of the grinding elements and the material to be ground is required particularly for a very fine grinding. If the individual annular courses are relatively offset by up to 45 to each other in the direction of rotation, material to be ground which has a higher specific gravity will move from the inlet of the mill to its outlet. If the annular courses are offset opposite to the direction of rotation, the movement will be retarded and the material will be retained because the screw promotes a movement in the opposite direction.
Practical operations and experiments have shown that the helical passage formed in the mill by the offset annular courses also has a certain sorting action on the grinding elements, so that most of the larger grinding elements collect at the inlet and most of the smaller grinding elements col-lect at the outlet. This effect is not complete, however, because it is obtained only with grinding elements, such as balls or short cylindrical shapes (cylpebses), up to 40 mm. at most. For non-fine grinding it is necessary, however, to use also grinding elements which are larger in diameter than 40 mm., e.g., grinding elements which are 60 to 70 mm. in diameter; this is the si7e of the grinding elements in the second chamber of a multichamber mill.
In an economical grinding operation, large grinding elements must be used to grind the coarse material, and the size of the grinding element e.g., balls, must progressively decrease as the material becomes finer. So far, this has been accomplished by the mill being divided in its longitudinal direction into chambers, so that the different grinding elements, e.g., balls of greatly different si~es, cannot mix with each other, whereas .''1~
.~.
~ ~Q38356 the material being ground can pass through slots in the chamber walls to the next chamber nearer to the outlet.
An additional impulse is re4uired to improve the sorting action on the grinding elements in the above-mentioned known mill and particularly to provide a sorting action also for larger grinding elements, so that they remain in the desired region of the mill. This holds true for all mills of the present kind which have a polygonal basic cross-section with rounded corners and straight or less strongly curved sides. It is an object of the present invention to provide such additional impulse.
The invention provides a mill having at each position along its length an internal cross-section which is substantially polygonal and is de-fined by rounded corners between sides which are straight or less curved than the corners, and in which the grinding action is performed by the falling and rolling motion of a filling consisting of grinding elements and the material to be ground, the dimensions of the grinding elements being only a small fraction of the length of any of said sides of the mill, wherein the interior of the mill is defined by liner plates forming a series of annular courses arranged adjacent each other in the longitudinal direction of the mill, each of said annular courses consisting of a plurality of liner plates and at least some of said annular courses being angularly displaced or offset relative to adjacent annular courses, and wherein plates of at least some annular courses have inside surfaces that are inclined to the longitudinal axis of the mill and are convergent in the direction of travel of the material being ground, and remaining plates, if any, have inside surfaces which are parallel to the longitudinal axis of the mill. Such plates having inside surfaces which are inclined toward the axis of the mill and in the direction of travel of the material being ground will be referred to hereinafter as in-clined plates. The inside surfaces of the inclined plates may be inclined throughout the total width of the respective annular course, or they may be inclined only in part of the width of the annular course whereas they e-xpand parallel or almost parallel to the longitudinal axis of the mill in the other part of the width of the annular course. In a specific embodiment, at least every third annular course, and preferably every other annular course comprises inclined plates. It will be particularly desirable if the mill has a square basic cross-section with rounded corners and straight sides and at least every third annulsr course and preferably every other annular course is composed of inclined plates having inside surfaces which are inclined to-ward the interior of the mill and in the direction of travel of the material being ground, and the plates are preferably so arranged that plates which have inside surfaces extending in the longitudinal direction of the mill paral-lel to the axis of the mill alternate with plates which have inside surfaces which are inclined to the axis of the mill, the annular courses composed of plates having inside surfaces that are parallel to the axis of the mill are mutually offset and the annular courses composed of the inclined plates are also mutually offset.
The angle of inclination (angle ~) of the inside surfaces of the inclined plates may be S to 30, preferably 5 to 15. The inclined surface of the inclined plates need not be flat but may be concaVely curved. Besides, i* is not necessary to use inherently inclined plates but the inclination may be provided in that plates having inside surfaces extending parallel to the axis of the mill are provided with protruding strips which extend at a de-sired angle other than 90 to the axis of the mill.
In a development of the invention, an annular course comprising plates having inside surfaces which are parallel to the axis of the mill and an adjacent annular course which comprises inclined plates may be combined in a unit, and each of said units may be offset from the adjacent unit.
The angle (~) by which the annular courses or units are angularly spaced or offse~ relative to each other may preferably be between 15 and 50.
'; 10383S6 In general, in a mill of the present kind the balls or other grind-ing elements will be sorted more quickly if a larger number of annular courses are composed of inclined plates. The fastest ball-sorting action will be ob-tained if all annular courses comprise inclined plates, and in this case the grinding elements above 60 mm. will be more accurately sorted into several fractions. The use of plates whose inside surfaces have the same inclination in all annular courses affords the additional advantage that only one type of plate is required to line the mill. It is known, however, that grinding el-ements in different sizes are mostly desired in the coarse grinding region of the mill. The optimum lining can be selected for any material to be ground.
Best results will be obtained in all cases with those mills accord-ing to the invention which have a square basic cross-section with rounded corners and straight sides and in which the radius of the rounded corners is preferably approximately one thirt of the side length of the basic square.
To minimize the loss of grinding space in mills which are larger in diameter, a polygonal basic cross-section rather than a square one may be used in spe-cific cases although best results will be obtained only if the geometric re-quirements relating to the ratio of the side length to the curvature of the corners are complied with and inclined plates are used or co-used in accord-ance with the invention.
Annular courses of plates having inclined inside surfaces areknown per se but only in mills having a circular cross-section. In the known embodiments either each annular course has an inclined inside surface or the inclined surfaces are steep and high and are formed by separate internal fix-tures rather than by inclined liner plates. That system is subject to heavy wear. ~nly the design according to the invention, and particularly the com-bination of annular courses which consist of plates having inside surfaces that are parallel to the axis of the mill to provide for a square cross-sec-tion of flow, and annular courses of plates whose inside surfaces have a re-latively slight inclination in such a manner that every other or every third ' 1038356 annulsr course is composed of inclined plates, whereas annular courses of the same kind, or units consisting of an annular course of plates having parallel inside surfaces and an annular course of inclined plates, are mutually offsetJ
will result in a satisfactory grinding as well as a sorting and also a small wear of the liner. It may be mentioned here that the known mills having a circular cross-sectiOn provide for a sorting of grinding elements above 60 mm.
or above 40 mm. but it is very difficult in such mills to sort small grinding elements below 40 mm. and particularly below 20 mm. Experiments have shown that only the design of the mill lining according to the invention enables an ent1rely satisfactory sorting of all grinding elements without a division of the mill into chambers.
A mill according to the invention having a square basic cross-sec-tion with rounded corners and straight sides will now be described more fully with reference to two embodiments shown by example in the drawing.
Figure 1 is a transverse sectional view showing such a mill.
Figure 2 is a longitudinal sectional view taken on line A-B and show-ing a portion of the mill ccnsisting of straight and inclined plates, and Figure 3 is also a longitudinal sectional view taken on line A-B and show~ a portion of a mill consisting only of inclined plates.
The mill has a cylindrical shell M, in which annular courses of liner plates are installedO These courses are arranged one behind the other in the axial or longitudinal direction of the mill. Those annular courses which are accommodated in the portion shown in Figure 2 are designated el, fl...e4,f4 in Figure 2. Reference characters e designate annular courses of plates which have inside surfaces that are parallel to the axis of the mill.
The plates of the annular courses designated with the reference character f have inside surfaces which are inclined at an angle of inclination ~ toward the interior of the mill and in the direction of flow, indicated by the arrow, of the material being ground. The angle of inclination of the inside surfaces of these inclined plates will depend on the requirements, namely, the nature ' 1038356 of the material being ground, etc., and to a certain degree also the width of each plate. It has been found that it is generally desirable to select an angle ~ in the region of 5 to 15, although good results may be obtained in special cases with different angles ~ up and above 30. Alternatively, dif-ferent inclinations may be s01ected in successive annular courses f or some of them or groups of them compared to the inclination in preceding or succeed-ing annular courses f or groups thereof. The width of each plate and of each annular course may be, e.g., 250 mm. or one-half that distance. In a special embodiment, one annular course e and one annular course f may be combined in a unit in that plates are used which extend continuously over the correspond-ing width and are bent so that their inside surfaces are inclined in part of their dimension extending in the longitudinal direction of the mill. To clar-ify the combination of two annular courses e, f in a group or unit, these pairs of annular courses are designated El...E4 in Figure 2. These combined annular courses or units are offset or angularly spaced relative to the suc-ceeding and preceding annular courses by an angle a (see Figure 1) whereas there is no offset within such combined annular courses or units.
To clarify the offset in Figure 2, the parting lines between each annular course e and the adjacent annular course f are represented by a thin-ner line than the parting lines between successive units El-E2, E2-E3, etc.
For the sake of clearness, the parting lines are represented in exaggerated width; they have actually only a width of 2 to 3 mm. The thicker lines are intended to indicate that the annular courses on opposite sides of the respec-tive parting line are offset or angularly spaced. This offset will depend on the conditions, such as the material to be ground, the desired velocity of travel thereof through the mill, etc. Good results have been obtained with an offset (angle a) of 15 to 45, although this statement is not intended to impose a limitation on the selection of the offset.
The succession of annular courses of plates having inside surfaces which are not inclined but parallel to the axis of the mill, and of plates having inside surfaces which are inclined toward the interior of the mill may be modified in that only every third annular course consists of inclined plates.
The length of annular courses e of plates having inside surfaces which are parallel to the axis of the mill, and annular courses f of inclined plates can be varied as required so that units of, e.g., longer annular courses e and shorter annular courses f of inclined plates are installed in the shell M of the mill.
The mill according to Figure 3 is composed only of inclined plates fl...f4; in other respects that embodiment is similar to that one of Figure 2.
Figure 1 illustrates the offset of annular courses or units. To a-void an overcrowding of the drawing at the expense of clarity, only the inside contours of the first two units El and E2 in Figure 2 (plates fl and f2 in Figure 3) are shown; these are the inner edge contours of the inclined plates of the annular courses fl and f2.
Different angles of offset could be selected between successive annular courses e or f (or f') or units E over the length of the mill. The _ variation of the local lead angle of the resulting helix defined at the begin-ning of the specification will be selected in view of the nature of the desir-ed grinding operation and the desired distribution or sorting of the different sizes of grinding elements over the length of the mill.
To maintain the required sorting of the grinding elements also for a long period of operation, it is not necessary in a mill designed according to the invention to provide a plurality of chambers separated by partition walls. Such partition walls can usually be entirely omitted, so that the mill consists only of a single chamber. Even if grinding elements of extreme sizes are used, only a single partition for the entire mill will be required, so that the mill then comprises two chambers.
The result as regards the sorting of the grinding elements in a mill according to the invention having a square basic cross-section and rounded cor-ners and straight sides will now be explained with reference to a practical ;` 1038~S6 test made with such a mill.
A tube mill having a length of 9 m and 2.4 m, in diameter was fed with balls in sizes of 20 to 60 mm. in the following proportions in percent by weight:
Size of balls, mm. 20 2S 30 40 50 60 % by weight 20.2 20.2 16.8 16.8S 14.30 11.6S
The mill was rotated in the clockwise sense. Each annular course hat a witth of 250 mm. Each pair Gf annular courses were combined in a unit.
The first annular course of each unit was offset in the direction of rotation by an angle of 15 from the first annular course of the adjacent unit. Every other annular course had an inclination of 15.
The balls were fed as an unsorted mixture. The degree of fullness was 26%. The mill was then operated for 24 hours at a speed of 0.7 times its critical speet, so that a stationary equilibrium hat then been obtained as re-gards the distributian of the balls. The distribution in the mill length por-tions 0 to 1.5 m., 1.5 to 3.0 m., 3.0 to 4.5 m., 4.5 to 6.0 m., 6.0 to 7.5 m., ant 7.5 to 9.0 m., in the direction of flow of the material was then examined with the following results:
Length portion 0 to 1.5 m.
Ball diameter, mm. 20 25 30 40 50 60 Proportion, % by weight -- -- 0.5 10.9 30.4 58.2 Length portion 1.5 to 3.0 m.
Ball diameter, mm. 20 25 30 40 S0 60 Proportion, % by weight -- 0.1 6.2 40.2 45.2 8.3 `'1~
Length portion 3.0 to 4.5 m.
Ball diameter, mm. 20 25 30 40 50 60 Proportion, % by weight -- 2.1 41.0 47.0 9.9 --Length portion 4.5 to 6.0 m.
Ball diameter, mm. 20 25 30 40 50 60 Proportion, % by weight 0.5 38.2 56.5 4.6 0.2 --Length portion 6.0 to 7.5 m.
Ball diameter, mm. 20 25 30 40 50 60 Proportion, by weight 29.5 67.2 3.3 -- -- --Length portion 7.5 to 9.0 m.
Ball diameter, mm. 20 25 30 40 50 60 Proportion, % by weight 89.9 10.1 Por a check, the direction of rotation was reversed in some tests, so that the mill rotated in the counterclockwise sense. To cause the mate-rial being ground to flow in the same direction, the offset of the annular courses (in this case too every other course was offse~ 15 in the counter-clockwise direction of rotation) was changed. The ball mixture and the other conditions were entirely the same. The following distribution of balls was stated after an operation for 24 hours.
Lenth portion O to 1.5 m. _ Ball diameter, mm. 20 25 30 40 50 60 Proportion, ~ by weight -- -- 0.13 5.77 30.8 63.3 --lo_ .''iO3B356 Length portion 1.5 to 3.0 m.
Ball diameter, mm. 20 25 30 40 50 60 Proportion, % by weight -- -- 1.7 41.8 54.8 1.7 Length portion 3.0 to 4.5 m.
. ~
Ball diameter, mm. 20 25 30 40 50 60 Proportion, % by weight -- 1.6 31.4 45.8 21,2 --Length portion 4.5 to 6.0 m.
Ball diameter, mm. 20 25 30 40 50 60 Proportion, by weight 1.3 38.8 56.1 3.8 -- --Length portion 6.0 to 7.5 m.
Ball diameter, mm. 20 25 30 40 50 60 Propostion, by weight 29.1 67.10 3.90 -- -- --Length portion 7.5 to 9.0 m.
Ball diameter, mm. 20 25 30 40 50 60 Proportion, % by weight 91.3 8.70 -- -- -- --The same results as with balls are obtained with short cylindrical shapes ~cylpebses) or other grinding elements and with any desired degree of fullness. The liner designed according to the invention eliminates the need for a subdivision into several chambers entirely or to a substantial degree.
For this reason the invention will be explained hereinafter mainly with reference to such a mill, although the explanation is applicable with corresponding modification also to the other mills of the kind described which have a polygonal basic cross-section.
In a known mill having a square basic cross-section, the grinding action can be strongly influenced by the selection of a proper radius for the rounded portions. A decrease of the radius of the rounded portion relative to the diagonal of the cross-section of the mill will result in a stronger impact, and an increase of the radius of the rounded portions will result in a lighter impact and in a stronger frictional action. Since the successive individual annular courses are angularly displaced or offset, a passage is formed in the mill which, owing to the square basic cross-section of the millJ is similar in shape to a four-thread screw. Owing to this design, an additional impulse in the direction toward the axis of the mill is imparted to the grinding elements. Besides, the helical design also influences the flow of the material being ground in the longitudinal direction of the mill because the flow of the material being ground can be braked or accelerated by a suitable selection of the lead or hand of the screw resulting from the offset of the annular courses. The lead of this helical passage and the hand thereof can be determined by the selection of the angle between successive annular courses.
A
'1038356 The movement of the material being ground through the mill also depends strongly on the specific gravity of the material being ground.
Easily flowing materials to be ground in a dense bed of grinding elements tend to remain on the surface and virtually to float rather than to enter the bed of grinding elements. On the other hand, thorough mixing of the grinding elements and the material to be ground is required particularly for a very fine grinding. If the individual annular courses are relatively offset by up to 45 to each other in the direction of rotation, material to be ground which has a higher specific gravity will move from the inlet of the mill to its outlet. If the annular courses are offset opposite to the direction of rotation, the movement will be retarded and the material will be retained because the screw promotes a movement in the opposite direction.
Practical operations and experiments have shown that the helical passage formed in the mill by the offset annular courses also has a certain sorting action on the grinding elements, so that most of the larger grinding elements collect at the inlet and most of the smaller grinding elements col-lect at the outlet. This effect is not complete, however, because it is obtained only with grinding elements, such as balls or short cylindrical shapes (cylpebses), up to 40 mm. at most. For non-fine grinding it is necessary, however, to use also grinding elements which are larger in diameter than 40 mm., e.g., grinding elements which are 60 to 70 mm. in diameter; this is the si7e of the grinding elements in the second chamber of a multichamber mill.
In an economical grinding operation, large grinding elements must be used to grind the coarse material, and the size of the grinding element e.g., balls, must progressively decrease as the material becomes finer. So far, this has been accomplished by the mill being divided in its longitudinal direction into chambers, so that the different grinding elements, e.g., balls of greatly different si~es, cannot mix with each other, whereas .''1~
.~.
~ ~Q38356 the material being ground can pass through slots in the chamber walls to the next chamber nearer to the outlet.
An additional impulse is re4uired to improve the sorting action on the grinding elements in the above-mentioned known mill and particularly to provide a sorting action also for larger grinding elements, so that they remain in the desired region of the mill. This holds true for all mills of the present kind which have a polygonal basic cross-section with rounded corners and straight or less strongly curved sides. It is an object of the present invention to provide such additional impulse.
The invention provides a mill having at each position along its length an internal cross-section which is substantially polygonal and is de-fined by rounded corners between sides which are straight or less curved than the corners, and in which the grinding action is performed by the falling and rolling motion of a filling consisting of grinding elements and the material to be ground, the dimensions of the grinding elements being only a small fraction of the length of any of said sides of the mill, wherein the interior of the mill is defined by liner plates forming a series of annular courses arranged adjacent each other in the longitudinal direction of the mill, each of said annular courses consisting of a plurality of liner plates and at least some of said annular courses being angularly displaced or offset relative to adjacent annular courses, and wherein plates of at least some annular courses have inside surfaces that are inclined to the longitudinal axis of the mill and are convergent in the direction of travel of the material being ground, and remaining plates, if any, have inside surfaces which are parallel to the longitudinal axis of the mill. Such plates having inside surfaces which are inclined toward the axis of the mill and in the direction of travel of the material being ground will be referred to hereinafter as in-clined plates. The inside surfaces of the inclined plates may be inclined throughout the total width of the respective annular course, or they may be inclined only in part of the width of the annular course whereas they e-xpand parallel or almost parallel to the longitudinal axis of the mill in the other part of the width of the annular course. In a specific embodiment, at least every third annular course, and preferably every other annular course comprises inclined plates. It will be particularly desirable if the mill has a square basic cross-section with rounded corners and straight sides and at least every third annulsr course and preferably every other annular course is composed of inclined plates having inside surfaces which are inclined to-ward the interior of the mill and in the direction of travel of the material being ground, and the plates are preferably so arranged that plates which have inside surfaces extending in the longitudinal direction of the mill paral-lel to the axis of the mill alternate with plates which have inside surfaces which are inclined to the axis of the mill, the annular courses composed of plates having inside surfaces that are parallel to the axis of the mill are mutually offset and the annular courses composed of the inclined plates are also mutually offset.
The angle of inclination (angle ~) of the inside surfaces of the inclined plates may be S to 30, preferably 5 to 15. The inclined surface of the inclined plates need not be flat but may be concaVely curved. Besides, i* is not necessary to use inherently inclined plates but the inclination may be provided in that plates having inside surfaces extending parallel to the axis of the mill are provided with protruding strips which extend at a de-sired angle other than 90 to the axis of the mill.
In a development of the invention, an annular course comprising plates having inside surfaces which are parallel to the axis of the mill and an adjacent annular course which comprises inclined plates may be combined in a unit, and each of said units may be offset from the adjacent unit.
The angle (~) by which the annular courses or units are angularly spaced or offse~ relative to each other may preferably be between 15 and 50.
'; 10383S6 In general, in a mill of the present kind the balls or other grind-ing elements will be sorted more quickly if a larger number of annular courses are composed of inclined plates. The fastest ball-sorting action will be ob-tained if all annular courses comprise inclined plates, and in this case the grinding elements above 60 mm. will be more accurately sorted into several fractions. The use of plates whose inside surfaces have the same inclination in all annular courses affords the additional advantage that only one type of plate is required to line the mill. It is known, however, that grinding el-ements in different sizes are mostly desired in the coarse grinding region of the mill. The optimum lining can be selected for any material to be ground.
Best results will be obtained in all cases with those mills accord-ing to the invention which have a square basic cross-section with rounded corners and straight sides and in which the radius of the rounded corners is preferably approximately one thirt of the side length of the basic square.
To minimize the loss of grinding space in mills which are larger in diameter, a polygonal basic cross-section rather than a square one may be used in spe-cific cases although best results will be obtained only if the geometric re-quirements relating to the ratio of the side length to the curvature of the corners are complied with and inclined plates are used or co-used in accord-ance with the invention.
Annular courses of plates having inclined inside surfaces areknown per se but only in mills having a circular cross-section. In the known embodiments either each annular course has an inclined inside surface or the inclined surfaces are steep and high and are formed by separate internal fix-tures rather than by inclined liner plates. That system is subject to heavy wear. ~nly the design according to the invention, and particularly the com-bination of annular courses which consist of plates having inside surfaces that are parallel to the axis of the mill to provide for a square cross-sec-tion of flow, and annular courses of plates whose inside surfaces have a re-latively slight inclination in such a manner that every other or every third ' 1038356 annulsr course is composed of inclined plates, whereas annular courses of the same kind, or units consisting of an annular course of plates having parallel inside surfaces and an annular course of inclined plates, are mutually offsetJ
will result in a satisfactory grinding as well as a sorting and also a small wear of the liner. It may be mentioned here that the known mills having a circular cross-sectiOn provide for a sorting of grinding elements above 60 mm.
or above 40 mm. but it is very difficult in such mills to sort small grinding elements below 40 mm. and particularly below 20 mm. Experiments have shown that only the design of the mill lining according to the invention enables an ent1rely satisfactory sorting of all grinding elements without a division of the mill into chambers.
A mill according to the invention having a square basic cross-sec-tion with rounded corners and straight sides will now be described more fully with reference to two embodiments shown by example in the drawing.
Figure 1 is a transverse sectional view showing such a mill.
Figure 2 is a longitudinal sectional view taken on line A-B and show-ing a portion of the mill ccnsisting of straight and inclined plates, and Figure 3 is also a longitudinal sectional view taken on line A-B and show~ a portion of a mill consisting only of inclined plates.
The mill has a cylindrical shell M, in which annular courses of liner plates are installedO These courses are arranged one behind the other in the axial or longitudinal direction of the mill. Those annular courses which are accommodated in the portion shown in Figure 2 are designated el, fl...e4,f4 in Figure 2. Reference characters e designate annular courses of plates which have inside surfaces that are parallel to the axis of the mill.
The plates of the annular courses designated with the reference character f have inside surfaces which are inclined at an angle of inclination ~ toward the interior of the mill and in the direction of flow, indicated by the arrow, of the material being ground. The angle of inclination of the inside surfaces of these inclined plates will depend on the requirements, namely, the nature ' 1038356 of the material being ground, etc., and to a certain degree also the width of each plate. It has been found that it is generally desirable to select an angle ~ in the region of 5 to 15, although good results may be obtained in special cases with different angles ~ up and above 30. Alternatively, dif-ferent inclinations may be s01ected in successive annular courses f or some of them or groups of them compared to the inclination in preceding or succeed-ing annular courses f or groups thereof. The width of each plate and of each annular course may be, e.g., 250 mm. or one-half that distance. In a special embodiment, one annular course e and one annular course f may be combined in a unit in that plates are used which extend continuously over the correspond-ing width and are bent so that their inside surfaces are inclined in part of their dimension extending in the longitudinal direction of the mill. To clar-ify the combination of two annular courses e, f in a group or unit, these pairs of annular courses are designated El...E4 in Figure 2. These combined annular courses or units are offset or angularly spaced relative to the suc-ceeding and preceding annular courses by an angle a (see Figure 1) whereas there is no offset within such combined annular courses or units.
To clarify the offset in Figure 2, the parting lines between each annular course e and the adjacent annular course f are represented by a thin-ner line than the parting lines between successive units El-E2, E2-E3, etc.
For the sake of clearness, the parting lines are represented in exaggerated width; they have actually only a width of 2 to 3 mm. The thicker lines are intended to indicate that the annular courses on opposite sides of the respec-tive parting line are offset or angularly spaced. This offset will depend on the conditions, such as the material to be ground, the desired velocity of travel thereof through the mill, etc. Good results have been obtained with an offset (angle a) of 15 to 45, although this statement is not intended to impose a limitation on the selection of the offset.
The succession of annular courses of plates having inside surfaces which are not inclined but parallel to the axis of the mill, and of plates having inside surfaces which are inclined toward the interior of the mill may be modified in that only every third annular course consists of inclined plates.
The length of annular courses e of plates having inside surfaces which are parallel to the axis of the mill, and annular courses f of inclined plates can be varied as required so that units of, e.g., longer annular courses e and shorter annular courses f of inclined plates are installed in the shell M of the mill.
The mill according to Figure 3 is composed only of inclined plates fl...f4; in other respects that embodiment is similar to that one of Figure 2.
Figure 1 illustrates the offset of annular courses or units. To a-void an overcrowding of the drawing at the expense of clarity, only the inside contours of the first two units El and E2 in Figure 2 (plates fl and f2 in Figure 3) are shown; these are the inner edge contours of the inclined plates of the annular courses fl and f2.
Different angles of offset could be selected between successive annular courses e or f (or f') or units E over the length of the mill. The _ variation of the local lead angle of the resulting helix defined at the begin-ning of the specification will be selected in view of the nature of the desir-ed grinding operation and the desired distribution or sorting of the different sizes of grinding elements over the length of the mill.
To maintain the required sorting of the grinding elements also for a long period of operation, it is not necessary in a mill designed according to the invention to provide a plurality of chambers separated by partition walls. Such partition walls can usually be entirely omitted, so that the mill consists only of a single chamber. Even if grinding elements of extreme sizes are used, only a single partition for the entire mill will be required, so that the mill then comprises two chambers.
The result as regards the sorting of the grinding elements in a mill according to the invention having a square basic cross-section and rounded cor-ners and straight sides will now be explained with reference to a practical ;` 1038~S6 test made with such a mill.
A tube mill having a length of 9 m and 2.4 m, in diameter was fed with balls in sizes of 20 to 60 mm. in the following proportions in percent by weight:
Size of balls, mm. 20 2S 30 40 50 60 % by weight 20.2 20.2 16.8 16.8S 14.30 11.6S
The mill was rotated in the clockwise sense. Each annular course hat a witth of 250 mm. Each pair Gf annular courses were combined in a unit.
The first annular course of each unit was offset in the direction of rotation by an angle of 15 from the first annular course of the adjacent unit. Every other annular course had an inclination of 15.
The balls were fed as an unsorted mixture. The degree of fullness was 26%. The mill was then operated for 24 hours at a speed of 0.7 times its critical speet, so that a stationary equilibrium hat then been obtained as re-gards the distributian of the balls. The distribution in the mill length por-tions 0 to 1.5 m., 1.5 to 3.0 m., 3.0 to 4.5 m., 4.5 to 6.0 m., 6.0 to 7.5 m., ant 7.5 to 9.0 m., in the direction of flow of the material was then examined with the following results:
Length portion 0 to 1.5 m.
Ball diameter, mm. 20 25 30 40 50 60 Proportion, % by weight -- -- 0.5 10.9 30.4 58.2 Length portion 1.5 to 3.0 m.
Ball diameter, mm. 20 25 30 40 S0 60 Proportion, % by weight -- 0.1 6.2 40.2 45.2 8.3 `'1~
Length portion 3.0 to 4.5 m.
Ball diameter, mm. 20 25 30 40 50 60 Proportion, % by weight -- 2.1 41.0 47.0 9.9 --Length portion 4.5 to 6.0 m.
Ball diameter, mm. 20 25 30 40 50 60 Proportion, % by weight 0.5 38.2 56.5 4.6 0.2 --Length portion 6.0 to 7.5 m.
Ball diameter, mm. 20 25 30 40 50 60 Proportion, by weight 29.5 67.2 3.3 -- -- --Length portion 7.5 to 9.0 m.
Ball diameter, mm. 20 25 30 40 50 60 Proportion, % by weight 89.9 10.1 Por a check, the direction of rotation was reversed in some tests, so that the mill rotated in the counterclockwise sense. To cause the mate-rial being ground to flow in the same direction, the offset of the annular courses (in this case too every other course was offse~ 15 in the counter-clockwise direction of rotation) was changed. The ball mixture and the other conditions were entirely the same. The following distribution of balls was stated after an operation for 24 hours.
Lenth portion O to 1.5 m. _ Ball diameter, mm. 20 25 30 40 50 60 Proportion, ~ by weight -- -- 0.13 5.77 30.8 63.3 --lo_ .''iO3B356 Length portion 1.5 to 3.0 m.
Ball diameter, mm. 20 25 30 40 50 60 Proportion, % by weight -- -- 1.7 41.8 54.8 1.7 Length portion 3.0 to 4.5 m.
. ~
Ball diameter, mm. 20 25 30 40 50 60 Proportion, % by weight -- 1.6 31.4 45.8 21,2 --Length portion 4.5 to 6.0 m.
Ball diameter, mm. 20 25 30 40 50 60 Proportion, by weight 1.3 38.8 56.1 3.8 -- --Length portion 6.0 to 7.5 m.
Ball diameter, mm. 20 25 30 40 50 60 Propostion, by weight 29.1 67.10 3.90 -- -- --Length portion 7.5 to 9.0 m.
Ball diameter, mm. 20 25 30 40 50 60 Proportion, % by weight 91.3 8.70 -- -- -- --The same results as with balls are obtained with short cylindrical shapes ~cylpebses) or other grinding elements and with any desired degree of fullness. The liner designed according to the invention eliminates the need for a subdivision into several chambers entirely or to a substantial degree.
Claims (13)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A mill having at each position along its length an internal cross-section which is substantially polygonal and is defined by rounded corners between sides which are straight or less curved than the corners, and in which the grinding action is performed by the falling and rolling motion of a filling consisting of grinding elements and the material to be ground, the dimensions of the grinding elements being only a small fraction of the length of any of said sides of the mill, wherein the interior of the mill is defined by liner plates forming a series of annular courses arranged adjacent each other in the longitudinal direction of the mill, each of said annular courses cosisting of a plurality of liner plates and at least some of said annular courses being angularly displaced or offset relative to adjacent annular courses, and wherein plates of at least some annular courses have inside surfaces that are inclined to the longitudinal axis of the mill and are convergent in the direction of travel of the material being ground, and re-maining plates, if any, have inside surfaces which are parallel to the longitudinal axis of the mill.
2. A mill according to claim 1, wherein the internal cross-section is substantially square.
3. A mill according to claim 1, wherein successive annular courses of liner plates are angularly displaced or offset relative to each other by equal angles.
4. A mill according to any of claims 1 to 3, wherein the inside surfaces of the inclined plates of the annular courses (f1...f4 or f?...f? respectively) are inclined throughout the width of the respective annular course.
5. A mill according to any of claims 1 to 3, wherein the inside surfaces of the inclined plates of the annular courses (f1...f4 or f?...f? respectively) are inclined only in part of the annular courses, whereas the inside surfaces of the inclined plates extend parallel or almost parallel to the longitudinal axis of the mill in the other part of the width of the annular courses.
6. A mill according to any of claims 1 to 3, wherein at least every third annular course of liner plates comprises inclined plates.
7. A mill according to any of claims 1 to 3, wherein every other annular course of liner plates comprises inclined plates.
8. A mill according to claim 1, which has an internal square cross-section with rounded corners and straight sides, wherein every other annular course of liner plates comprises inclined plates and the liner plates are so arranged that, in the longitudinal direction of the mill, plates having in-side surfaces which are parallel to the longitudinal axis of the mill alter-nate with plates having inside surfaces which are inclined to the longitudinal axis of the mill, the annular courses (e1...e4) composed of plates having inside surfaces which are parallel to the longitudinal axis of the mill are mutually offset, and the annular courses (f1...f4) composed of the inclined plates are also mutually offset.
9. A mill according to any of claims 1, 3 or 8, wherein the inclination (angle .beta.) of the inside surfaces of the inclined plates of the annular courses (f1...f4 and f?...f?) is from 5 to 30°.
10. A mill according to claim 1, wherein an annular course (e1...) com-prising liner plates having inside surfaces parallel to the axis of the mill and an adjacent annular course (f1...) comprising inclined liner plates are combined in a unit (E1...), there being a series of such units each angularly offset from adjacent units.
11. A mill according to claim 10, wherein the annular courses of liner plates of adjacent units are angularly spaced from each other by an angle of from 15 to 50°. 13
12. A mill according to any of claims 1, 8 or 11, wherein the inside surfaces of the inclined liner plates of annular courses (f or f' respective-ly) have a concave curvature.
13. A mill according to claim 1, 8 or 10, wherein liner plates extending parallel to the axis of the mill are provided on their surface with one or more protruding strips which extend at an angle other than 90° relative to the axis of the mill.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AT635473A AT332199B (en) | 1973-07-19 | 1973-07-19 | MILL, IN PARTICULAR TUBE OR BALL MILL |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1038356A true CA1038356A (en) | 1978-09-12 |
Family
ID=3585476
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA205,049A Expired CA1038356A (en) | 1973-07-19 | 1974-07-18 | Mill, particularly tube mill or ball mill |
Country Status (4)
| Country | Link |
|---|---|
| AR (1) | AR202563A1 (en) |
| AT (1) | AT332199B (en) |
| CA (1) | CA1038356A (en) |
| ZM (1) | ZM11974A1 (en) |
-
1973
- 1973-07-19 AT AT635473A patent/AT332199B/en not_active IP Right Cessation
-
1974
- 1974-07-17 ZM ZM11974A patent/ZM11974A1/en unknown
- 1974-07-18 CA CA205,049A patent/CA1038356A/en not_active Expired
- 1974-07-18 AR AR25475674A patent/AR202563A1/en active
Also Published As
| Publication number | Publication date |
|---|---|
| ATA635473A (en) | 1975-12-15 |
| ZM11974A1 (en) | 1975-02-21 |
| AU7050574A (en) | 1976-01-08 |
| AT332199B (en) | 1976-09-10 |
| AR202563A1 (en) | 1975-06-24 |
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