Milling method and milling device
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a milling method for pulverizing agricultural products, minerals, etc. 
     2. Description of the Related Art 
     Conventionally, the pulverization of agricultural products, in particular, cereals, has been performed by using a pulverizer called a mill, such as a ball mill, a vibrating mill, or a hammer mill. 
     The conventional milling method using such a mill requires the consumption of a large amount of energy and time for pulverization. Accordingly, the method is rather poor in terms of pulverization efficiency. Furthermore, the conventional method is limited in terms of processing capacity. 
     Moreover, the grain size distribution in the pulverized object is substantially determined by the mill used and is very difficult to change. 
     Further, the principal members of a mill, e.g., the balls, are extremely liable to wear. In addition, there is a problem that foreign matter generated as a result of wear may enter the pulverizer. 
     SUMMARY OF THE INVENTION 
     The present invention has been made with a view to eliminating the above problems in the conventional milling method using a mill. It is accordingly an object of this invention to provide a milling method and a milling device which provide a level of high pulverization efficiency, which allow an arbitrary setting of grain size distribution, and which help to avoid foreign matter intrusion into the pulverized object so that a high quality product can be obtained. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawing show a sectional view of a device in accordance with an embodiment of this invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention will now be described with reference to the drawing. 
     The device shown includes a body frame 1 equipped with a feeding inlet 2. The body frame 1 contains a first rotary blade 4 and a second rotary blade 5 which is opposed thereto. These rotary blades 4 and 5 define, together with upper and lower walls 1a and 1b of the body frame 1, a pulverizing chamber 3. 
     The first rotary blade 4, which is positioned inside the body frame 1 on the side of the feeding inlet 2, has at its center a drive shaft 6, which extends to the exterior of the body frame 1 to be joined to a driving device (not shown). The configuration of this first rotary blade 4 is so determined as to help introduce grain material supplied through the feeding inlet 2 into the pulverizing chamber 3 and to impart a whirling motion to the air in the body frame 1, i.e., in the pulverizing chamber 3. 
     The second rotary blade 5 has substantially the same configuration as the first rotary blade 4 and is equipped, at its center, with a drive barrel 7 which is in alignment with the drive shaft 6. This drive barrel 7 is slidably supported by a sleeve 8 provided on the body frame 1 and is joined to a driving device (not shown), so that the second rotary blade 5 can move toward and away from the first rotary blade 4, with the pulverizing chamber 3 communicating through this drive barrel 7 with a suction device (not shown). 
     When rotated by their respective rotating devices through the drive shaft 6 and the drive barrel 7, respectively, the rotary blades 4 and 5 impart a whirling motion to the air in the pulverizing chamber 3, thereby generating a vortex in the chamber. 
     The material a, fed in the above condition through the feeding inlet 2 into the body frame 1, is conveyed by the first rotary blade 4 into the pulverizing chamber 3, where it is moved around by the action of the vortex. In this process, a difference in speed is generated between the portion of the material in the central section of the vortex and that in the outer section of the vortex. This difference in speed causes friction between the material grains, thereby pulverizing the material. 
     When the suction device (not shown) is operated in this condition, the pulverized material, which is not so much under the influence of the centrifugal force generated by the vortex as it is under the influence of the sucking force of this suction device, is collected through the drive barrel 7. 
     By appropriately setting the correlation among the centrifugal force due to the vortex, the sucking force of the suction device, and the weight of the material particles, the device of this embodiment can help to obtain a fine powder with a substantially uniform grain size. 
     The degree of uniformity in grain size required depends on how the pulverized object is to be used. Generally speaking, a uniform fine powder can be obtained with this device as long as the material is such that it can be moved around by the air vortex generated in the pulverizing chamber 3. 
     The medium for whirling the material does not necessarily have to be air. It may also be a liquid such as water. 
     It is to be assumed that the difference in moving speed between different material portions, which is generated as the material is whirled, may be of different types, i.e., it may be a difference in speed in the radial, tangential, or axial direction of the vortex. While in the device of the above embodiment the difference in speed in the tangential direction of the vortex is utilized, it goes without saying that the difference in speed in any one of the above three directions may be utilized. It is also possible to obtain a pulverized product by operating the rotary blades after the material has been supplied into the pulverizing chamber, instead of operating the blades while the material is being supplied. 
     As a concrete example, a milling device was prepared, in which the diameter of the first and second rotary blades 4 and 5 was 250 mm; the distance between the blades was 40 mm; the rotating speed of the blades was 4500 rpm; and the inner diameter of the drive barrel 7 was 100 mm. Further, the sucking speed of the associated suction device was 10 m/s. By successively supplying wheat into the pulverizing chamber 3 of this milling device at a rate of 1 kg per minute, a pulverized product with an average grain size of 20 μm was collected. 
     In accordance with this invention, a material is whirled so as to generate a difference in moving speed between material portions, and this difference in moving speed causes friction between the material portions, thereby pulverizing the material. Thus, this invention provides a milling method which excels in pulverization efficiency and which allows arbitrary setting of grain size distribution, and a milling device which is economical in terms of energy consumption for pulverization and which avoid foreign matter intrusion.