GB1603749A - Cylindrical grinding drum - Google Patents

Description

(54) CYLINDRICAL GRINDING DRUM (71) I, HYOTARO SEGAWA, a citizen of Japan of 6-23, Otemachi, Noshiro, Akita-ken, Japan, do hereby declare the invention for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a cylindrical grinding drum for a grinding machine.

A grinding machine is herein defined as an industrial grinder having a horizontal drum which is charged with material (ores, stones, etc.) and a large number of iron balls or rods (hereinafter referred to as "grinding media") and is rotated at adequate speeds to grind or crush the material finely by the impacting and abrading interaction of the material, the grinding media, and axially extending drum-lining steel boards (hereinafter referred to as "liners") arranged around the inner circumference of the drum. An example is shown in Fig. 1, wherein right and left bearings 1, mounted on a base, support shaft portions of a drum 2 at opposite ends thereof. The drum 2 has a large gear 3 secured to the outer surface thereof at the left end to engage a small gear (not shown) which is located outside the large gear 3 and is rotated by a motor 4 installed on the base, thus rotating the drum 2.The drum has the cross-sectional configuration shown in Fig. 2. That is, the drum has a circumferential wall 5 the inside of which is covered with liners "a" arranged in mutually abutting relationship. Each liner "a" is fastened to the wall 5 by bolts 6 attached to the external surface of the drum 2 as shown in Fig. 1. The numeral 7 designates a manhole with a removable cover.

Liners generally may be classified, according to their shape, as for use with balls only or as for use with either balls and rods. The liners used in this invention are the latter ones, or those for balls and rods, and present such cross sections as shown in Figs. 2, 3 and 4, the latter two being enlarged views. The liner "a" shown in Fig.

3 is of the type which has so far been generally employed. A bulge 9 is formed on a central portion of a liner base 8, and a hole 10 for receiving a bolt 6 is formed from the vertex Q of the bulge 9 through the liner base 8. The head of the bolt 6 which is inserted in the hole 10 engages the liner base 8 and, with the lower bolt portion fastened, tightly affixes the liner base 8 to the drum wall 5. The bulge 9 acts to scrape the material and cooperates with the grinding media to grind the material, thus performing the most important grinding function.The present invention has observed that under the following grinding conditions; rotating speed of the drum 18 to 36 r.p.m.; the diameter of balls or rods as grinding media 50 to 125 millimeters; and the material to be ground glass, cement, fertilizer, or iron-making material, either wet or dry, as the grinding operation proceeds, as shown in Fig. 3, the vertex Q of the projection continues to shift downward and towards the trailing edge of the liner, in the direction opposite to the rotating direction (indicated by an arrow) of the liners secured to the drum, along with the decay of the bulge 9 as a whole.The retrogression of the vertex Q down to the point C on the chain line shown in Fig. 3 gives rise to a matter of vital importance with the liner "a" as follows: As the vertex Q retrogresses toward the point C following the line Q-C, the liner base 8 also wears like the bulge 9, decreasing in thickness, and the bolt receiving hole 10 also decreases in height at the same rate. Thus, the head of the bolt, 6, which is in engagement with the liner base 8 in the hole 10 so as to hold the base, appears on the liner surface and gradually wears so that its force it applies to hold the liner base 8 in position decreases.

When the liner base 8 begins to get loose from the drum wall 5, the grinding capability sharply decreases. The subsequent further separation of the base 8 from the drum wall 5 causes the grinding media to come into direct contact with the drum wall S and thus damage the wall.

Therefore, when wear of the head of the bolt 6 begins, liner replacement is required though the liner base 8 has a remaining thickness sufficient for grinding. Because, (i) the liners are made of a high quality steel material which is higher in hardness than the material of the drum wall S and thus more expensive and (ii) replacing the liner requries interruption of the grinding oper'ation and the operator's entry into the drum 2 through the manhole 7, it is economically important problem to extend the endurance of the liners.One attempt at solving this problem is disclosed in our (Japanese Patent No. 574,843 in which rod mill liners are provided each having such cross-sectional configuration that a curved bulge (projection 9) having a height within the range from the radius of grinding media to the diameter thereof and a base length within the range from the diameter of the grinding media to three times the diameter is positioned on a liner base (8) in such a manner as to locate a centered vertex (Q) of the bulge in advance of the position of a hole (10) for a liner fastening bolt in the rotating direction of the liner by a distance within the range from the radius of the grinding media to the diameter thereof. The bracketed reference characters in the above description of the basic invention are added for reference to the corresponding elements shown in the conventional liner of Fig. 3.

However, individual practical liner shapes to be employed are determined in accordance with various elements given by users, such as rod diameter, drum size, material properties, and other factors, so that precise designing is required within the disclosure of the aforesaid Japanese Patent.

According to the present invention we provide a cylindrical drum for a grinding machine, the drum comprising a lining formed by a plurality of part cylindrical liner segments each of which comprises a part cylindrically curved base and a bulge which is of curved cross section in a radial plane through the drum, and liner fastening bolts connecting the liner segments to the drum casing and positioned in respective holes in the said liner segments; the drum containing grinding media of circular cross section; and wherein: i) the curved bulge has a height from the bottom surface of the respective liner segment within the range of from the radius of the grinding media to the diameter thereof; ii) the length of each said liner segment in the circumferential direction is within the range from the diameter of the grinding media to three times the diameter thereof; iii) the vertex of the bulge is positioned in advance of the position of the fastening bolts in the rotating direction of the respective liner segment by a distance within the range of from the radius of the grinding media to the diameter thereof; iv) each said liner segment is such that (i) the rate of regression of the vertex due to wear in use of the drum is in the range of from 3 to 5 times the rate of increase in distance between the leading edge of the bulge and the leading edge of the liner segment; and (ii) the rate of decrease in height of the vertex during use of the drum is 1.8 to 2.0 times the rate of increase in distance between the leading edge of the bulge and the leading edge of the liner segment; v) the curvature of the bulge increases during use of the drum 1.3 to 1.7 times the initial curvature thereof;; vi) the locus of each bolt head during rotation of the drum can be expressed in a rectangular system of coordinates of X-X and Y-Y axes as x2+(y-r)2=(r-h)2 (1) and a locus of shifting of the vertex as y=-mx+H' (2) in which the Y axis is an imaginary line passing diametrically through the grinding drum and with which line the longitudinal axis of the respective fastening bolt coincides during rotation of the drum and the X axis is an imaginary line perpendicular to the Y axis and tangential to the inner surface of the drum;; wherein r stands for the inner radius of the drum, h for the height of the bulge at a time limit of use, m for the amount of descent of the vertex divided by the amount of retrogression of the vertex and H' for the height of the bulge from the liner bottom surface before use, and the vertex, before use of the liner, segment, being positioned in advance of the fastening bolt by a distance 'x' determined by resolving said two equations.

In the drawings:- Figure 1 is a front view of an exemplary grinding machine.

Figure 2 is a sectional view of a drum included in the grinding machine shown in Figure 1, depicting an arrangement of liners embodying the present invention.

Figure 3 is a front view of a conventional liner.

Figure 4 is a front view of a liner embodying the invention.

Generally speaking the specifications of the liners for use in a grinding machine are as follows: A drum diameter and length are selected according to the required processing capacity, and the width of each liner segment is determined in dependence on the diameter of the drum. Also, the size, hardness and other properties of material particles are taken into account in selecting a rod or ball diameter. These factors determine the height of the curved bulge 9 as a lifter, the curvature of the bulge, and so on. It has been the practice hitherto, in view of these factors, to position the curved bulge 9 in the center of the liner and to set the liner fastening bolts also in the central position. The positioning of the curved bulge 9 ahead of the liner bolts has also been proposed. However, the forward position of the curved bulge, height etc.

have been limited or determined merely on an experimental basis, not by an appropriate calculation method, resulting in the drawback described hereinbefore in connection with Figure 3, so that the designed liners cannot be used over a satisfactorily long period. Conventionally, in order to comply with specified time limits of liner endurance, appreciable improvements have been achieved mainly in liner material and heat treatment for example. Nevertheless, it has been impossible to prevent the aforementioned endurance time loss due to vertex retrogression along the line Q-C.

The aforesaid disadvantage is minimised or eliminated by using a grinding drum in accordance with the present invention in the design of which the following criteria are used:- (the amount of descent) 1.8-2.0 (the amount of retrogression) 3--5 =m (A) Referring to Figure 3, for the liner, a central point 0' (which coincides with the central point of the drum) is given in a rectangular coordinate system of X-X and Y-Y axes as defined above. Thus, the central point O' is fixed on the Y-Y axis so that & =r (radius), where 0 is the origin, that is, the point of intersection of both axes.In use of the drum as the wear of the liner proceeds, the vertex Q shifts downward and rearward from the initial position at the rate (m) of the above formula (A). We now let "h" refer to the height of the projection at the time limit of endurance of the bolts fastening the conventional liner. Then, the vertex C of the projection at said time limits can be obtained from equations (i) and (ii) set forth above.In addition, the bottom surface of the liner base in the plane including the X-X and Y-Y axes is expressed as: x2+(y-r)2=r2 A typical design calculation for determining the position of vertex C is as follows: If h=30 mm, r=900 mm, m=2/3 and H'=90 mm in the equations (i) and (ii), we obtain 3+90-900)t=(90e30)2 -1080+1321.7 x= 2.88 Taking the positive value for X, then: 241.7 x= =84 2.88 This means that the distance S from the initial vertex Q to the final vertex C in the direction of the X-X axis should be 84 mm.

In this way, the equations (i) and (ii) are used to determine the point C, and thus the distance S between the points Q and C is obtained. The method for geometically contructing the design will now be described by reference to Figure 4. The central point 0' of the liner is positioned on the Y-Y axis in the X-X and Y-Y rectangular coordinate system so that OO=r.

An arc is then drawn about the central point 0' with the radius of r-h (the radius r of the liner minus the height h of the projection at the time limit of use, i.e. when the bolt has just lost its capability for tightly affixing the liner to the drum wall) in such a way that the arc intersects a straight line Y'-Y', which is drawn in parallel with the Y-Y axis, but is spaced therefrom by the vertex transfer distance S. The point of intersection is represented by C'.An arc is then drawn about the central point 0', taking r-H' (the radius r minus the sum of the thickness of the liner base and the height of the projection over the base) as its radius, and a straight line connecting the points 0' and C', thus obtaining, as vertex Q', the point of intersection of the arc and the straight line O'-C'. Further, we draw an arc about the central point 0', taking r-H" (the radius r minus the thickness H" of the liner base) as its radius. In contact with this arc and the arc R, arcs of a radius R' are drawn to complete the shape of the bulging projection.Next, in order to set the leading end of the liner, we draw a straight line passing through the point 0' and the point of contact, P, between the arc of radius rHY and that of radius R' on the leading side, and an arc of radius r, thus obtaining the point of intersection, P', of the straight line and the arc r, the line P-P' defining the leading end surface of the liner.

With reference to the intersection point P', we put a Point P" on the arc r so that 77F=W. Then, the straight line connecting the point 0' and P" defines the trailing end surface of the liner. It should be noted here that the radii R and R' are determined by the diameter of the rods and/or balls employed which is conventionally determined by the diameter and length of the drum.

In the liner thus designed, the central point of an upper portion of the bolt head lies on the arc of radius r-h. It is now assumed for the sake of comparison that the novel liner is used until the limit of endurance of the conventional liner shown in Fig. 3 is reached. In such a case, there will be a further gain in the time of endurance which gain corresponds to the height h-h'. Generally, when the liner base reaches its limit of use, the vertex Q' will retrogress down into the bolt receiving hole, thus increasing the time of endurance.In use of a drum in accordance with the invention we have found that generally the grinding ratio (the amount of ores of a fixed particle size contained in ground ores discharged from the grinding machine divided by the amount of the discharged ores) is fairly high, and below and above the specified range, the amount of coarse particles of 40 to 60 meshes (Tyler standard) is in a large proportion while the amount of fine particles of 80 to 100 meshes (Tyler standard) is in a large proportion.

WHAT I CLAIM IS: 1. A cylindrical grinding drum for a grinding machine, the drum comprising a lining formed by a plurality of part cylindrical liner segments each of which comprises a part cylindrically curved base and a bulge which is of curved cross section in a radial plane through the drum, and liner fastening bolts connecting the liner segments to the drum casing and positioned in respective holes in the said liner segments; the drum containing grinding media of circular cross section; and wherein: i) the curved bulge has a height from the bottom surface of the respective liner segment within the range of from the radius of the grinding media to the diameter thereof; ii) the length of each said liner segment in the circumferential direction is within the range from the diameter of the grinding media to three times the diameter thereof; iii) the vertex of the bulge is positioned in advance of the position of the fastening bolts in the rotating direction of the respective liner segment by a distance within the range of from the radius of the grinding media to the diameter thereof iv) each said liner segment is such that (i) the rate of regression of the vertex due to wear in use of the drum is in the range of from 3 to 5 times the rate of increase in distance between the leading edge of the bulge and the leading edge of the liner segment; and (ii) the rate of decrease in height of the vertex during use of the drum is 1.8 to 2.0 times the rate of increase in distance between the leading edge of the bulge and the leading edge of the liner; v) the curvature of the bulge increases during use of the drum 1.3 to 1.7 times the initial curvature thereof;; vi) the locus of each bolt head during rotation of the drum is expressed in a rectangular system of coordinates of X-X and Y-Y axes as x2+(y-r)2=(r-h)2 and a locus of shifting of the vertex as y=-mx+H' in which the Y axis is an imaginary line passing diametrically through the grinding drum and with which line the longitudinal axis of the respective fastening bolt coincides during rotation of the drum and the X axis is an imaginary line perpendicular to the Y axis and tangential to the inner surface of the drum; ; wherein r stands for the inner radius of the drum, h for the height of the bulge at a time limit of use, m for the amount of descent of the vertex divided by the amount of retrogression of the vertex and H' for the height of the bulge from the liner bottom surface, before use, and the vertex, before use of the liner segment, being positioned in advance of the fastening bolt by a distance 'x' determined by resolving said two equations.

2. A cylindrical grinding drum, substantially as described herein with reference to Figure 4 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (2)

**WARNING** start of CLMS field may overlap end of DESC **. we put a Point P" on the arc r so that 77F=W. Then, the straight line connecting the point 0' and P" defines the trailing end surface of the liner. It should be noted here that the radii R and R' are determined by the diameter of the rods and/or balls employed which is conventionally determined by the diameter and length of the drum. In the liner thus designed, the central point of an upper portion of the bolt head lies on the arc of radius r-h. It is now assumed for the sake of comparison that the novel liner is used until the limit of endurance of the conventional liner shown in Fig. 3 is reached. In such a case, there will be a further gain in the time of endurance which gain corresponds to the height h-h'. Generally, when the liner base reaches its limit of use, the vertex Q' will retrogress down into the bolt receiving hole, thus increasing the time of endurance.In use of a drum in accordance with the invention we have found that generally the grinding ratio (the amount of ores of a fixed particle size contained in ground ores discharged from the grinding machine divided by the amount of the discharged ores) is fairly high, and below and above the specified range, the amount of coarse particles of 40 to 60 meshes (Tyler standard) is in a large proportion while the amount of fine particles of 80 to 100 meshes (Tyler standard) is in a large proportion. WHAT I CLAIM IS:

1. A cylindrical grinding drum for a grinding machine, the drum comprising a lining formed by a plurality of part cylindrical liner segments each of which comprises a part cylindrically curved base and a bulge which is of curved cross section in a radial plane through the drum, and liner fastening bolts connecting the liner segments to the drum casing and positioned in respective holes in the said liner segments; the drum containing grinding media of circular cross section; and wherein: i) the curved bulge has a height from the bottom surface of the respective liner segment within the range of from the radius of the grinding media to the diameter thereof; ii) the length of each said liner segment in the circumferential direction is within the range from the diameter of the grinding media to three times the diameter thereof; iii) the vertex of the bulge is positioned in advance of the position of the fastening bolts in the rotating direction of the respective liner segment by a distance within the range of from the radius of the grinding media to the diameter thereof iv) each said liner segment is such that (i) the rate of regression of the vertex due to wear in use of the drum is in the range of from 3 to 5 times the rate of increase in distance between the leading edge of the bulge and the leading edge of the liner segment; and (ii) the rate of decrease in height of the vertex during use of the drum is 1.8 to 2.0 times the rate of increase in distance between the leading edge of the bulge and the leading edge of the liner; v) the curvature of the bulge increases during use of the drum 1.3 to 1.7 times the initial curvature thereof;; vi) the locus of each bolt head during rotation of the drum is expressed in a rectangular system of coordinates of X-X and Y-Y axes as x2+(y-r)2=(r-h)2 and a locus of shifting of the vertex as y=-mx+H' in which the Y axis is an imaginary line passing diametrically through the grinding drum and with which line the longitudinal axis of the respective fastening bolt coincides during rotation of the drum and the X axis is an imaginary line perpendicular to the Y axis and tangential to the inner surface of the drum; ; wherein r stands for the inner radius of the drum, h for the height of the bulge at a time limit of use, m for the amount of descent of the vertex divided by the amount of retrogression of the vertex and H' for the height of the bulge from the liner bottom surface, before use, and the vertex, before use of the liner segment, being positioned in advance of the fastening bolt by a distance 'x' determined by resolving said two equations.

2. A cylindrical grinding drum, substantially as described herein with reference to Figure 4 of the accompanying drawings.