Pulverizer

Abstract: A pulveriser has a shell (1) having an inlet port for air and the material (6) to be pulverized and a discharge port (7) for the pulverized product. The shell is filled with a pulverizing medium such as steel balls. A vertical screw shaft (2) having a screw blade (10) is rotatably mounted in the shell. It is hollow and provided at the bottom end thereof with an outlet port (3) for a carrier fluid. The outlet port (3) is located behind the screw blade with respect to the direction of rotation of the screw shaft. A fluid supply box (11) is provided at the bottom of the screw shaft so as to extend from the screw shaft to the outer edge of the screw blade (10). The outlet port (3) is formed in the fluid supply box. A scrape plate (12) is provided to protrude downwards from the bottom end of the screw shaft. Three or more screw blades may be provided.

Description: This invention relates to a pulverizer for producing powdery or particulate products of the type as defined in the pre-characterizing part of claim 1. Prior art pulverizers of this type are known from EP-A-0 217 977 and are also shown in Fig. 16 and 17. As shown in Fig. 17, a pulverizer of this type has a vertical shell 1 and a hollow screw shaft 2 extending vertically in the shell. The shell 1 is filled with pulverizing medium b such as steel balls. Material a to be pulverized is introduced into the shell 1 from top end thereof with the screw shaft 2 rotating to pulverize the material by friction between the particles of the material and between the particles of the material and the pulverizing medium b . The powdery product c thus produced is carried out of the shell 1 by an upward flow of carrier fluid d such as air or water passing through the shell 1. In this type of pulverizers, there is provided means for introducing carrier fluid d into the shell. It is in the form of outlet ports 3 provided at the bottom of the screw shaft 2. Carrier fluid d may be supplied to the outlet ports 3 through the hollow screw shaft 2 as shown in Fig. 17. Heretofore, the outlet port 3 was either a mere opening formed in the bottom end of the screw shaft 2 as shown in Fig. 16 or a plurality of vertical slits formed in the bottom end of the screw shaft 2 as shown in Fig. 17. In other words, the outlet port was formed in the screw shaft 2. In this arrangement, since the fluid d reaches only the area near the screw shaft 2, that is, only the central part of the shell 1, an upward current is also formed only in the central part. This causes only the pulverized product c in this area to be discharged, with the product in the outer peripheral part of the shell 1 remaining in the shell for a long time and pulverized too finely. Thus, it was difficult to pulverize the material in the shell uniformly. Also, since the bottom opening in the screw shaft 2 is liable to get clogged by the pulverizing medium and the material to be pulverized, fluid d has to be fed into the shell 1 with a sufficient force to push them aside. This causes loss of power. For example, if the fluid d is air, a fan with a large capacity is required. Further, if the slits 5 are formed in the screw shaft 2, the number and thus the sectional area thereof cannot be increased so much. Thus, a considerable power is necessary to feed a sufficient amount of fluid. Also, since the pulverizing medium is always in contact with the bottom end of the screw shaft 2 and the slits 5, the screw shaft 2 tends to be worn remarkably at the bottom edge thereof or at the surrounding area of the slits 5. In the pulverizer shown in Fig. 16, the inner diameter of the shell 1, the outer diameter of the screw blades 10 and the revolving speed of the screw shaft 2 are determined taking into consideration the diameter of the pulverizing medium and the inclination of the screw blades. But the screw blades and the liners tend to be worn severely. If the revolving speed is reduced in order to reduce wear of the liners, the efficiency of pulverization will drop. It is an object of the present invention to provide a pulverizer which allows smooth and uniform supply of the carrier fluid into the shell and can reduce wear at the outlet port and which obviates the abovesaid problems of the prior art. In order to solve these problems, the pulverizer according to this invention has outlet ports for the carrier fluid provided behind the screw blade at bottom of the screw shaft with respect to the direction of rotation thereof, and fluid supply boxes are provided to extend from the screw shaft to the outer periphery of the screw blade. In this case, the above-described outlet ports are formed in the fluid supply boxes. The fluid supply boxes should preferably have an outer peripheral surface tapered toward the screw shaft and rearwardly with respect to the direction of rotation. Further, it should preferably have a bottom surface tapered upwardly and rearwardly with respect to the direction of rotation. Further, downwardly protruding scrape plates are provided on the bottom of the screw shaft. They should preferably be slant or skewed rearwardly with respect to the direction of rotation. In the pulverizer according to this invention, the material is pulverized by turning the screw shaft in the known manner and the pulverized product is discharged out of the shell. During this operation, the pulverizing medium is scraped up by the screw blades, creating air gaps behind the screw blades with respect to the direction of rotation thereof, the gaps extending over the entire length of the screw blade, i.e. from the outer periphery of the screw shaft to that of the screw blade. Since the outlet port for the carrier fluid is located near the air gaps, the fluid is smoothly blown radially in all the directions in the shell and flows up. In the arrangement wherein the outlet port for the carrier fluid is formed in the fluid supply box, the fluid supply box serves to feed the carrier fluid more smoothly. The box may have its peripheral surface tapered with respect to the direction of rotation. The tapered surface, which forms a relief angle with respect to the flow of pulverizing medium, serves to reduce wear to the box. Also, by the provision of the scrape plates, the pulverizing medium located near and under the screw shaft is scraped together, thus creating an air gap behind each scrape plate with respect to the direction of rotation. The scrape plates should preferably be slant or skewed rearwards with respect to the direction of rotation so that the pulverizing medium will move outwards. This serves to increase the size of the air gaps near the screw shaft, thus allowing the carrier fluid to be blown out more smoothly into the gaps. We observed the range within which the pulverizing medium is moved by the screw blades in this type of pulverizer, namely the range within which the pulverizing medium is affected by the turning force of the screw blades when they turn for a predetermined time period. As a natural result, we found that the higher the revolving speed is, the larger the range of influence. This fact suggests that by moving the pulverizing medium in the area outside the range of influence with extra screw blades, the range of influence can be kept large even if the revolving speed is low. In another arrangement, the screw shaft is provided with an increased number of blades, so that the number of blades in any given horizontal plane increases. Thus, even if the area of influence of each blade is narrowed as a result of reduction in the revolving speed of the screw shaft, the area of influence of all the blades covers substantially the entire area in the shell. Also, we found that the pulverizing medium is in frictional contact with the upper surface of the screw blades. We thought that such friction can be reduced if part of the pulverizing medium can be kept staying on the upper surface of the blades. In still another arrangement, the ribs are provided to prevent movement of the pulverizing medium on the blades, thus causing it to stay on the blades. As a result, the moving medium is brought into frictional contact with the medium staying on the blades and not directly with the blades. Thus, no large frictional force will act on the blades. According to this invention, the material can be pulverized uniformly and the pulverized product in the shell throughout the entire area can be smoothly carried out. Since the product can be carried out smoothly, no large power is necessary to discharge them. The peripheral surface of the box may be tapered to protect the box and the outlet port against wear. In another arrangement, wear of the screw blades can be reduced. This improves the durability of the blades and thus reduces the maintenance cost and makes a long continuous operation possible. Other features and objects of the present invention will become apparent from the following description taken with reference to the accompanying drawings, in which: Fig. 1 is a schematic sectional view of the first embodiment of the pulverizer according to this invention; Figs. 2 and 3 are perspective views of portions of the embodiment of Fig. 1; Fig. 4 is a partially cutaway plan view of Fig. 1; Fig. 5 is a sectional view of a portion of the embodiment of Fig. 1 showing how it operates; Fig. 6 is a schematic view of the second embodiment; Fig. 7 is a partially cutaway plan view of Fig. 6; Fig. 8 is a sectional view of a portion of the embodiment of Fig. 6 showing how it operates; Figs. 9 and 10 are sectional views of portions of other embodiments; Fig. 11 is a schematic sectional views of a third embodiment; Fig. 12 is a partially cutaway plan view of Fig. 11; Fig. 13 is an enlarged perspective view of a portion of Fig. 11; Fig. 14 is an enlarged perspective view of a portion of a still further embodiment; Fig. 15 is a view showing the area of influence of the pulverizing material in the embodiment shown in Fig. 11; and Fig. 16 and 17 are sectional views of portions of prior art pulverizers. [EMBODIMENT 1] As shown in Fig. 1, a pulverizer has a vertical shell 1 and a hollow screw shaft 2 rotatably mounted in the shell. The shell 1 is filled with pulverizing medium b such as steel balls. Material a to be pulverized is introduced into the shell 1 from its top end with the screw shaft rotating to pulverize the material by friction between the particles of the material and between the particles of the material and the medium b . The powdery product c thus produced is carried out of the shell 1 by an upward flow of carrier fluid d such as air or water passing through the shell 1. First, as shown in Fig. 1, an inlet port 6 for the material a to be pulverized and a discharge port 7 for the pulverized products c are provided at the upper part of the shell 1. A rotary valve 6a is provided in the inlet port 6 to feed the material a into the shell 1 while keeping air-tightness. The discharge port 7 is connected to a suction fan 9 through a product collector 8 such as a bag filter or a cyclone. The fan 9 serves to form an air circulation flow extending through the hollow screw shaft 2, shell 1 and a collector 8. Air supply boxes 11 are provided at the bottom end of the screw shaft 2 so as to extend from the shaft 2 to the outer edge of a screw blade 10 formed on the shaft. Each box 11 has outlet ports 3 in the form of slits defined by a grid 3a to prevent inflow of the pulverizing medium b . The number, shape and size of the ports 3 should be determined according to the desired flow rate of fluid (air). The end surfaces of the air supply boxes 11 extending along the outer periphery of the blade 10 and their bottom surface are tapered rearwardly with respect to the direction of rotation as shown in Figs. 3 and 4, forming relief angles α and β , respectively, which serve to lessen friction with the pulverizing medium b . The relief angle α and β are determined through experiment taking into account the degree of friction. In the figure, numeral 13 designates a liner laminated on the inner surface of the shell 1. When the fan 9 is activated, a circulation passage of air (fluid) is formed. By turning the screw shaft 2 in this state, the material is pulverized in the shell 1 into the product c in the conventional manner. The product c thus pulverized is carried up by an upward current of air out of the shell 1 and collected in the collector 8. While the material is being pulverized, the pulverizing medium b is scraped up by the screw blade 10, so that air gaps are formed behind the screw blade. Air d is blown out of the shaft 2 into the air gaps and flows up uniformly over the entire periphery in the shell. The product can be smoothly carried out by this upward air current. [EMBODIMENT 2] In this embodiment shown in Fig. 6, scrape plates 12 are used to blow out air d smoothly. Such scrape plates 12 are provided at the bottom end of the screw shaft 2. They extend downwardly from the bottom of the shaft 2 and are slant or skewed rearwardly with respect to the direction of rotation so that they will be partially inside of the shaft 2. The number, position and downward protrusion of the scrape plates are determined according to the scraping requirement. As the screw shaft 2 rotates, the pulverizing medium b near and under the screw shaft 2 will be pushed outwardly by the scrape plates 12. Thus air gaps are formed behind the scrape plates 12 with respect to the direction of rotation. The air d is blown smoothly into the air gaps and flows up in the shell 1. Also, since the scrape plates 12 partially protrude into the screw shaft 2 as shown in Fig. 7, the material in the screw shaft 2 can be pushed out of the outlet port 3, forming an air gap in the screw shaft 2. Thus, air flows out smoothly. In either of the first and second embodiments, fluid d may be supplied through a separate pipe 4 as shown in Figs. 9 and 10. The scrape plates 12 of the second embodiment may be added to the structure of the first embodiment e.g. at the bottom of the screw shaft 2. Further, the carrier fluid d may be a gas other than air or a liquid such as water. [EMBODIMENT 3] In this embodiment, the screw shaft 2 is provided with three screw blades 20 as shown in Figs. 11 and 12. As shown in Fig. 12, the blades 20 are arranged at equal angular intervals as viewed from top. The horizontal component of the counterforce from the pulverizing medium b acts uniformly on the blades 20, allowing the screw shaft 2 to rotate smoothly in good balance. As shown in Fig. 13, ribs 21 in the form of thin plates may be welded to the upper surface of the blades 20. A liner 22 is bolted to each blade 20 to extend along the entire edge thereof. The height and intervals of the ribs 21 should be determined according to the diameter and the desired degree of staying of the pulverizing medium. The liner 22 and the ribs 21 may be mounted on the blades 20 by fixing them first to a sub-board 23 and then welding or bolting the sub-board 23 to the blades 20 as shown in Fig. 14. In Fig. 11, numeral 13 designates a liner laminated on the inner surface of the shell 1. In operation, as shown in Fig. 15, since there are provided three blades 20 on the shaft 2, even if the turning speed of the screw shaft 2 is low, the influence of the blades 20 covers substantially the entire area in the shell 1. This allows smooth pulverization in the shell. Namely, the pulverizing efficiency scarcely drops even if the turning speed is low. Generally, as the turning speed of the screw shaft increases, the blades 20 wears at a rate higher than the increase rate of the turning speed. By increasing the number of blades 20, the area of wearing surface increases. Therefore, the turning speed can be reduced. This leads to reduction in wear as a whole, thus allowing a prolonged continuous operation compared with a conventional structure. The ribs 21 serve to prevent movement of the pulverizing medium on the blades 20, so that it will stay longer on the blades. Thus, the moving medium is brought into frictional contact with the medium staying on the blades. Thus, the frictional force from the pulverizing medium scarcely acts on the upper surface of the blades 20. Namely, the pulverizing medium staying on the blades acts for self-lining. This reduces wear of the blades 20, thus allowing a prolonged continuous operation. In this embodiment, three blades 20 are provided. But four or more blades will also have a similar effect. In any case, the blades should be arranged at equal intervals as viewed from top.

Claims: A pulverizer comprising a vertical shell (1) having an inlet port (6) for the material (a) to be pulverized and a discharge port (7) for the pulverized product (c), said shell (1) being filled with a pulverizing medium (b), a vertical screw shaft (2) rotatably mounted in said shell (1) and having a screw blade (10) formed thereon, said screw shaft (2) being hollow and provided at the bottom end thereof with an outlet port (3) for a carrier fluid, (d), characterized in that said outlet port (3) is located behind said screw blade (10) with respect to the direction of rotation of said screw shaft (2), and at least one fluid supply box (11) is provided at the bottom of said screw shaft (2) so as to extend from said screw shaft (2) to the outer edge of said screw blade (10), said outlet port (3) being formed in said fluid supply box (11). A pulverizer as claimed in claim 1, wherein said fluid supply box (11) has its outer peripheral surface tapered rearwardly toward said screw shaft (2) with respect to the direction of rotation of said screw shaft (2). A pulverizer as claimed in claim 1, wherein said fluid supply box (11) has its bottom, surface tapered upwardly rearwards with respect to the direction of rotation of the screw shaft (2). A pulverizer as claimed in any of claims 1 - 3, further comprising at least one scrape plate (12) protruding downwards from the bottom end of said screw shaft (2) and extending substantially diametrically of said screw shaft (2). A pulverizer as claimed in claim 4, wherein said scrape plate (12) is skewed rearwardly with respect to the direction of rotation of said screw shaft (2). A pulverizer as claimed in any of claims 1 - 5, wherein said vertical screw (2) shaft has at least three screw blades (20) formed thereon. A pulverizer as claimed in claim 6, further comprising radial ribs (21) provided on the upper surface of said screw blades (20) at equal intervals in the longitudinal direction of said screw blades (20).

Inventors: IHARA YOSHITAKA C O KYUHOJI FA, IKEBUCHI IWAO C O KYUHOJI FACT, ISHIKAWA HIDEMASA C O KYUHOJI, KAWABATA SHIGETOSHI, TAKEI HISASHI C O KYUHOJI FACT, IHARA, YOSHITAKA, C/O KYUHOJI FACTORY, IKEBUCHI, IWAO, C/O KYUHOJI FACTORY, ISHIKAWA, HIDEMASA, C/O KYUHOJI FACTORY, KAWABATA, SHIGETOSHI, TAKEI, HISASHI, C/O KYUHOJI FACTORY
Applicants: KUBOTA KK, KUBOTA CORPORATION
Application year: 1991
Main classification: B02C17
IPC codes: B01F7, B02C17, B01F3, B01F13