Roll crusher and crushing method in use for the roll crusher

Abstract: A roll crusher having a pair of rolls facing each other, in which feed material to be crushed is fed into a space or a crushing chamber formed in between these rolls, and the pair of rolls rolls up the material to compress and crush. During the process of crushing, the crushing clearance of rolls is set to 0.6 to 2.4 times 80% passing size of feed material, and feed rate is limited so that passing rate of the material ranges 0.5 to 0.8 times the theoretical throughput capacity of the crusher, which remarkably increases the actual throughput of the roll crusher.

Description: Technical Field The invention relates to a crushing method used in a roll crusher for crushing rocks and ores, etc. Background Art From GB-A-690 640, GB-A-2 135 211, EP-A-0 084 383 and DE-A-1 757 093 there has been known a basic type of roll crusher, as shown in Figs. 5 and 6, in which a pair of rolls 2 and 3 respectively facing each other and rotating in adverse direction to each other is provided, feed material such as rocks and ores to be crushed is supplied through the supply port 5 into the crushing chamber 6, that is, a space formed in between the pair of rolls, and the feed material supplied is crushed by compression while being rolled with said pair of rolls 2 and 3. The type of roll crusher has a crushing chamber 6 (a region indicated by chain line) as shown in Figs. 7a and 7b, whose longitudinal side faces 6a and 6b are formed respectively by the outer surfaces of the pair of rolls 2 and 3, and whose end faces 6c and 6d coincide with the openings formed in between the end faces 2a and 2b as well as 3a and 3b of said pair of respective rolls 2 and 3. But the crushing chamber shown is an example for explanation, therefore not necessarily limited to the shape, but varying to a convenient space region depending on crushing condition. On the other hand, some roll crusher according to the prior art is provided with side plates called cheek plates to prevent crushed stock from flowing out from the end openings 6c and 6d of the crushing chamber 6. During the process of crushing by the rolls 2 and 3, this type of roll crusher has no capability sufficient to prevent material being crushed from being pushed out of the crushing chamber 6 through the lower end portions of the end openings 6c and 6d (higher pressure applied on material to be crushed here), thus resulting in higher pressure applied on the rolls 2 and 3 at the roll center, and in lower pressure at both ends. Repeated crushing with such different pressures distributed on the rollers may cause partial wear of the rolls 2 and 3, as shown in Fig. 8, thus resulting in an ununiform shape with the smaller middle section and the larger end sections. Such partial wear cannot maintain a constant axial crushing clearance between rolls. Therefore, in crushing material with a relatively small clearance in such case as making crushed sand, crushing clearance at the middle section is too large, although the rolls come into a close contact with each other with zero clearance at both ends. This partial wear of rolls has been long well known as the worst defect of the roll crusher, which causes a failure of effective crushing, thus necessitating laborious repair work to abrade the roll surface for a uniform axial crushing clearance between rolls. Heretofore, in crushing rocks or ores by the roll crusher, to have a large crushing ratio, roll clearance is adjusted to be equal to or smaller than the particle size of desired products. Particularly for fine particle products, to have a large fraction of fine particles in crushed products, it was common for roll clearance to be adjusted to about 1/2 particle size of desired products. Crushing mechanism according to the prior art may be described as follows, referring to Fig. 14. A clearance between a pair of opposing rolls 2 and 3, that is, crushing clearance S is smaller than particle diameter F of feed material to be crushed, and equal to or smaller than the particle diameter P of desirable products. Particles of material to be crushed are subjected to a continuously increasing compressive load and are eventually broken from the time when they come into contact with the surfaces of the pair of the opposing rolls to the time when they pass between the closest positions of the two opposing rolls. As stated above, the roll crusher according to the prior art has a small crushing clearance S, thus limiting the throughput capacity of feed material through the crushing chamber, resulting in a low productivity of products. Especially, the smaller the particle size of desirable products, the smaller the crushing clearance, thus further restricting the productivity. And, because feed material to be crushed is pressed by the roll 2 and 3 from the left and right sides of the drawing, the size and shape of broken particles are regulated as regards the horizontal direction, but no regulation cannot be expected as regards other two directions such as vertical and perpendicular to the paper surface of the drawing. Therefore, products according to the prior art include a large fraction of particles having sizes larger than the crushing clearance S, and it is well known that they contain a lot of flat or slender particles. Concerning the setting of the crush clearance and the limiting of the feed rate of material no specific values are given in the cited documents representing the prior art. Only in GB-A-690 640 it is disclosed to restrict the output of a servo-motor driving the crusher rolls to a range of 60-80 per cent of the maximum capacity. Object of Invention The object of the invention is to provide an enhanced productivity in making products, particularly of finer particles by roll crusher, and a high acceptance factor of products with particles of round shape. Disclosure of Invention To achieve the object of the invention, the invention provides a crushing method by a roll crusher in which a pair of rolls facing each other is provided, feed material is supplied into a space formed in between these two rolls or a crushing chamber, and the feed material to be crushed is compressed for crushing while being rolled up with aforesaid pair of rolls, being characterized by a limited crushing clearance in between the rolls, which is 0.6 to 2.4 times a mesh aperture through which 80% in weight of feed material passes, and a limited feed rate in a range of 0.5 to 0.8 times the theoretical throughput of the crusher, defined by the mathematical product of the parameters roll width, roll peripheral speed, crushing clearance of the rolls and true specific gravity of the feed material. Brief Description of the Drawings Fig. 1 is a sectional side view of a roll crusher; Fig. 2 is a sectional plan view of Fig. 1 taken along line II-II; Fig. 3 is a top view of the roll crusher as shown in Fig. 1; Fig. 4 is a sectional view of Fig. 1 taken along line IV-IV; Figs. 5 and 6 are sectional views of the roll crusher according to the prior art; Figs. 7a and 7b are perspective views showing the crushing chamber; Fig. 8 is a view showing partial wear of rolls in the roll axial direction; Fig. 9 is a sectional view showing an example of the roll driving device; Fig. 10 is a sectional view showing another example of the roll driving device; Fig. 11 is a view showing the gear train for use in the device in Fig. 10; Fig. 12 is a sectional view showing other example of the roll driving device; Fig. 13 is a view showing an interparticle crushing method; Fig. 14 is a view showing the crushing method according to the prior art; and Figs. 15 and 16 are graphs showing particle size distributions of feed material and crushed products. Best Mode for carrying out the invention Figs. 1 and 2 show an example of a roll crusher. In these drawings, the same members as the roll crusher according to the prior art shown in Fig. 5 are given by the same numerals. In the roll crusher according to Fig. 1 and 2 there are block members or cheek plates 11 which prevent feed material to be crushed from flowing out of a crushing chamber 6 by blocking end surface openings 6c and 6d in the crushing chamber 6 (Fig. 7b), and flanges 12 which prevent the feed material to be crushed from being pushed out of the crushing chamber 6 through lower end portions under high pressure applied to the feed material to be crushed in the end surface openings 6c and 6d. The flanges 12 are fixed to end faces of one roll 3 for rotating together with the roll 3. The radius of the flange 12 is at least a crushing clearance in between the rolls larger than that of the roll 3. Because the flange 12 rotates integrally with the roll 3, there is little relative dislocation thereof to feed material to be compressed and crushed in between the rolls 2 and 3 under high pressure. As a result, there is little wear on the flange 12, permitting preservation of the function of the flange 12 to maintain the axially uniform pressure applied to the rolls 2 and 3 even under the progress of the wear of the rolls 2 and 3 after long service, thus preventing partial wear of the rolls 2 and 3, and maintaining a desirable interparticle crushing effect. A fixed plate 7 and a slide gate 8 are provided in a supply port 5 of feed material. A rod 9 is connected to the slide gate 8 as shown in Fig. 3. The movement of the rod 9 as shown in Arrow AA' can adjust the spacing between the fixed plate 7 and the slide gate 8, which in turn adjusts the amount of material to be fed into the crushing chamber from the supply port 5. The leading edge of the slide gate 8 is curved so that the section of the supply port 5 is wider in the end portions than the middle portion, which is to compensate short supply of material to the side wall portions of the supply port 5 (that is, both end portions of the crushing chamber 6) due to friction and to supply feed material uniformly over the length of the crushing chamber 6. The longitudinal length L of the supply port 5, as shown in Figs. 3 and 4, is designed essentially equal to the spacing between both flanges 12 of the roll 3 and slightly longer than the axial length L' of the roll 2. This, together with the curvature of the leading edge of the slide gate 8 as described above, is to supply feed material uniformly over the length of the rolls 2 and 3. Sign BE in Fig. 2 is bearings for supporting the rolls 2 and 3. A roll crusher shown in Fig. 1 uses the less worn flanges 12 to prevent feed material from being pushed out of the crushing chamber 6 in the axial direction of the rolls 2 and 3 by the compression force of the rolls 2 and 3, thus resulting in a uniform distribution of the pressure applied to the rolls 2 and 3 as well as of the compression force of particles of material to be crushed acting on each other, over the whole area of the longitudinal direction (roll axial direction) for a long period of service. As a result, partial wear of the rolls can be prevented for long, thus maintaining a desirable interparticle crushing effect. Fig. 9 shows a driving device to drive for rotation of particularly a pair of rolls 2 and 3. The roll 3 on the right side of the drawing is supported on a frame 1 with bearings BE1 and connected to a drive power such as the output shaft of a motor 10 through a coupling 19. The motor 10 drives the roll 3 for counterclockwise rotation in Fig. 1. The roll 2 on the left side of the drawing is supported with bearings BE2 rotatably (can be rotated freely). In crushing, first one roll 3 is rotated by the motor 10 counterclockwise in the Fig. 1. Then the other roll 2 is rotated clockwise in the drawing through the material being crushed in the crushing chamber 6. As a result, the stock is broken while being rolled up in between the rolls 2 and 3 rotating adversely to each other. Because the follower roll 2 follows the driving roll 3 and rotates at a nearly same speed as the driving roll 3, crushing is positively performed without any trouble. Here, only one driving power is used for the rolls 2 and 3, thus resulting in a simple configuration of the whole roll crusher, leading to cost reduction. Incidentally, it is desirable that with a roll crusher the relative positions of the rolls can be varied, that is, the rolls is brought closer or removed away, in order to adjust particle size of crushed products or to compensate wear of the rolls 2 and 3 to maintain a constant clearance of the rolls. For this purpose, the bearing BE2 supporting the follower roll 2 according to the invention is so fixed to the frame 1 that the bearing BE2 can be moved as shown by Arrow AA'. In this case, because the roll 2 is rotating freely without any motor or other driving means provided, the movement of the bearing BE2 or the roll 2 is easily made, thus permitting a simple adjustment of crushing clearance of rolls. Fig. 10 shows another example of the driving device for the rolls 2 and 3. In this drawing the same members as those shown in Fig. 9 are given by the same numerals. The follower roll 2 is connected to the driver roll 3 through a gear train 20, which transmits the rotational force of the driver roll 3 to the follower roll 2. The gear train 20 consists of, for instance, four gears 21, 22, 23 and 24 meshing with each other as shown in Fig. 11, and further a one-way clutch 25 is provided between the last gear 24 and the shaft 2a of the follower roll 2. The gear train 20 is so designed that the follower roll 2 rotates at a speed at least 5% slower than the driver roll 3. The one-way clutch 25 is installed to transmit the clockwise rotation of the last gear 24 (Fig. 11) to the roll shaft 2a, but not to transmit the adverse rotation. In crushing, first, the motor 10 rotates the driver roll 3 counterclockwise in Fig. 11, at this time the follower roll 2 rotates clockwise at a speed at least 5% slower because of the gear train 20. Supplied in between the rolls 2 and 3 under this condition, the material to be crushed are rolled up in between the rolls 2 and 3 which have started rotation. Once the material is rolled up in between rolls, the interference of the material adds up the rotation speed of the follower roll 2 nearly to that of the driver roll 2, then the one-way clutch 25 functions to allow the free rotation of the follower roll 2 without restricted by the rotation of the last gear 24 or the driver roll 3. At that time, each gear in the gear train 2 makes so-called racing. With the embodiment in Fig. 9, because the follower roll 2 does not rotate together with the driver roll 3 at first, it may happen that, when entering feed material includes coarser particles, the coarser particles cannot be nipped, in other words, effective "nip angle" (the maximum nipping angle which allows crushing in between rolls) becomes smaller. On the contrary, with the embodiment in Fig. 10, in which the follower roll 2 rotates at a lower speed from the beginning, there is no such chance as stated above. Besides, the gear train 20 intends only to tansmit rotation during no load or light load, and only races during crushing. Therefore, it does not be required to transmit large torque and to have much strength, thus reducing additional cost. As described above, it is desirable that at least one of the rolls 2 and 3 can be moved for adjustment of the crushing clearance of rolls. In the case of Fig. 11, the position of the roll 2 can be shifted by rocking the idle gears 22 and 23 about the roll shaft 3a as shown by Arrow EE'. Fig. 12 shows a further different embodiment for the driving device, in which the follower roll 2 of the embodiment in Fig. 9 is provided with an auxiliary motor 30 to drive. The auxiliary motor 30 can be turned ON or OFF as required by a controller (not shown). Switching the auxiliary motor 30 OFF allows the follower roll 2 to be rotated freely. Alternatively, a clutch can be introduced between the auxiliary motor 30 and the follower roll 2. ON or OFF of the clutch can switch the follower roll 2 to be rotated by the auxiliary motor 30 or freely. The rotational speed of the follower roll 2 by the auxiliary motor 30 may be the same as that of the driver roll 3 by the motor 10. Both speeds are not necessary the same, but, as in the case of Fig. 10, the follower roll 2 may be driven by the auxiliary motor 30 through a one-way clutch so that the rotation speed of the follower roll 2 is at least 5% slower than that of the driver roll 3. When the rolls 2 and 3 are rotating under no load or light load, the auxiliary motor 30 is switched ON to rotate the follower roll 2, at this time, the driver roll 3 has already been driven by the motor 10. Under this condition, feed material is supplied in between the rolls 2 and 3, and crushing starts. Once crushing starts the auxiliary motor 30 is turned OFF, and since then the follower roll 2 is brought into free rotation or rotating while following the driver roll 3 through material being crushed. Further crushing operation is performed under this conditions. As stated above, under no load or light load, the auxiliary motor 30 is energized to rotate the follower roll 2, but since this rotation does not require large torque, a very inexpensive motor can be used for the auxiliary motor 30, thus contributing no noticeable increase in cost. Therefore, as compared with the case when the rolls are independently driven, cost is lowered. At the same time, since the follower roll 2 is rotated beforehand under no load, as with the case in the device shown in Fig. 10, coarse particles of feed material can be crushed, in other words, a large effective nip angle can be maintained. According to the invention there is an advantageous method for crushing feed material using a roll crusher as follows: According to the method, in Fig. 13, crushing clearance S between the rolls 2 and 3 is adjusted to 0.6 - 2.4 times 80% passing size of feed material as well as the feed rate is controlled in a range of 0.5 to 0.8 times the theoretical throughput capacity of the crusher. The "80% passing size of feed material" refers to a square mesh aperture of a sieve just in case, when a given particle distribution of feed material is put through the sieve, 80% in weight passes the sieve and the rest 20% remains on the sieve. And, the "theoretical passing capacity of crusher" refers to an amount expressed by roll width x roll peripheral speed x crushing clearance of rolls x true specific gravity of feed material. So far, in crushing rocks or ores by a roll crusher, as shown in Fig. 14, crushing clearance S has been set smaller than the diameter F of feed particles to be crushed and equal to or smaller than the diameter P of particles of desirable products. Such narrower crushing clearance S as with the roll crusher according to the prior art limits the throughput capacity, thus resulting in a low productivity of products. Especially, the smaller the desirable particle size of products, the narrower the crushing clearance, therefore the more remarkably the productivity falls. Furthermore, because feed material to be crushed is pressed from both of the right and left directions in the drawing by the rolls 2 and 3, the size and shape of particles are limited as regards only the right and left directions but for other two directions such as a vertical direction and a perpendicular direction to the paper. As a result, the products may include an amount of particles larger than the crushing clearance S, and notorious shapes of flat or slender particles. On the contrary, according to the invention, the new method forms a spacious crushing chamber by widening the crushing clearance S, which permits a multiple layer of stock particles to pass through two opposing rolls, thus resulting in an remarkable increase in throughput capacity. With wider crushing chamber, much more feed material can be fed into the crushing chamber to cause individual particles to apply pressure on each other, thus introducing what is called interparticle crushing. This extent of mutual interference generated between particles of feed material is called the interparticle crushing effect. It is the invention that remarkably increases the productivity of a roll crusher and realizes an excellent compressive crushing, by controlling the interparticle crushing effect. "The control of feed rate so that the throughput of feed material ranges 0.5 to 0.8 times the theoretical throughput capacity" is made to maintain an optimization of aforesaid interparticle crushing effect. By this control, feed material is positively crushed to finer particles than limited by a crushing clearance S, thus resulting in an efficient production or an increased throughput even with finer particles of products. Further, once interparticle crushing takes place, individual particles of feed material are subjected to pressure from every direction for crushing, the most part of crushed particles are desirable or round cubic, and less are flat or slender. If the crushing clearance S should be widened larger than 2.4 times 80% passing size of feed material, the crushing naturally produces a larger throughput capacity, but fails to obtain a sufficient interparticle crushing effect, thus resulting in coarser particles of products, i.e. losing practical crushing. Even though the crushing clearance S is within 0.6 to 2.4 times 80% passing size of feed material, if the feed rate should be so high that the feed rate exceeds 0.8 times the theoretical throughput capacity, the crushing causes the feed material to be overcompacted in the course of compression of the feed material in the crushing chamber (K, L, M and N in Fig. 13), thus resulting not only in overloading but also in grinding rather than crushing and in producing much more fine powder. Therefore, in order to ensure an adequate interparticle crushing effect and to prevent excessive consolidation, it is indispensable to maintain the crushing clearance S of rolls between 0.6 and 2.4 times 80% passing size of feed material, and to limit the feed rate to such that the throughput ranges 0.5 to 0.8 times (preferably 0.6 to 0.7) the theoretical throughput capacity. Crushing experiments were made using the crushing method according to the invention (Fig. 13) and the prior art (Fig. 14). The difference in the effect of both methods is described as follows: Crushed stone S - 5 (5 - 2.5 mm fraction) of porphyrite was used as feed material to be crushed. The particle size distribution of the material is shown by the curve L in Fig. 15; 20 weight percent contains particles larger than particle size of 4.8 mm, while 80 weight percent smaller. Crushing of the material was made aiming at acceptable products smaller than particle size of 2.1 mm. The particle size distribution of crushed products obtained by the crushing method (Fig. 13) according to the invention is shown by the curves ℓ1 in Figs. 15 and 16, while one by the crushing method (Fig. 14) according to the prior art is shown by the curves ℓ2 in both Figures. The results are tabulated in Table 1. Invention Prior Art Roll Clearance S / mm 6.4 2.1 Throughput t/Hr 13.1 1.3 Ratio to theoritical capacity 0.67 0.20 Production of minus 2.1 mm t/Hr 7.3 0.95 Power consumption KW 18.8 4.6 Percentage of absolute volume 59.8 57.5 Note: Table includes the results of percentage of absolute volume to evaluate grain shape of manufactured sand based on JIS-A5004, to indicate the difference in grain shapes of products obtained by both methods. The curves ℓ1 and ℓ2 in Figs. 15 and 16 verify that the particle size distribution according to the invention and the prior art is essentially similar. But, as shown in Table 1, as regards production rate and power consumption per unit product, the method according to the invention is far better than one according to the prior art. And, based on the percentage of absolute volume for the grain shape evaluation (Table 1) and visual observation of crushed products, the grain shape of porducts obtained by the method according to the invention is mostly cubical, while products obtained by the method according to the prior art include much more of flat or slender particles.

Claims: A crushing method for use in a roll crusher having a pair of rolls (2, 3) facing each other, in which feed material to be crushed is continuously fed into a crushing chamber (6) formed in between these rolls (2, 3), and the pair of said rolls (2, 3) rolls up the material by adverse rotations to each other to compress and crush, comprising the steps of: setting a crushing clearance (S) of said rolls (2, 3) to 0.6 to 2.4 times a mesh aperture through which 80% in weight of feed material passes, and limiting a feed rate of material so that a passing rate of the material ranges from 0.5 to 0.8 times the theoretical throughput capacity of the crusher, which capacity being defined by the mathematical product of the parameters roll width, roll peripheral speed, crushing clearance (S) of rolls (2, 3) and true specific gravity of the feed material.

Inventors: TAKAGI FUMIO, TAKAHASHI NOBUHIRO, TAKAGI, FUMIO, TAKAHASHI, NOBUHIRO
Applicants: NITTETSU MINING CO LTD, NITTETSU MINING CO., LTD.
Application year: 1988
Main classification: B02C4
IPC codes: B02C4