JP2695733B2 - Operating method of horizontal dry mill - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for operating a horizontal dry continuous pulverizer for producing ultrafine powder.

[0002]

2. Description of the Related Art FIG. 10 is a system diagram showing an example of a conventional method for operating a dry ultrafine grinding mill capable of continuous discharge. The crushed material (raw material) is continuously supplied from a raw material hopper (11) to a mill (13) via a feeder (12). The pulverized material is discharged out of the mill by the carrier air sent into the mill (13) by the blower (14), and is then discharged to a classifier (cyclone or the like) (1).
It is sorted by 5). The coarse particles are stored in the product tank (1
6) The fine particles are collected in a dust collector (eg, bag filter).
After (17) , it is collected in the product tank (16) .

[0003]

In the above-mentioned conventional mill operation method, a large amount of conveying air is required to discharge the pulverized material out of the mill. Therefore the blower (14)
And a cyclone for collecting powder from the air (1
5), a bag filter (17) and the like were required. That is, in addition to the mill, many additional facilities and their installation space were required, and power for operating these facilities was also required.

[0004]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an outer cylinder having a plurality of agitating blades projecting from an inner wall surface and a plurality of agitating blades projecting from an outer surface. Using an inner cylinder arranged coaxially in the outer cylinder and rotating around an axis, the raw material is placed at one end of a crushing chamber having an annular cross section formed between the outer cylinder and the inner cylinder and filled with crushing balls therein. And discharging the finely pulverized material from the other end, when the inner diameter of the outer cylinder is D (m), the rotation speed of the inner cylinder is 42.3D.
^-1/2 (rpm) (i.e., critical rotation speed) or more, and the ratio of the bulk volume of the crushed balls to the internal volume of the crushing chamber (i.e., ball filling ratio) is 30% or more and 90% or more.
% Of the dry type dry mill is proposed.

[0005]

In the method of the present invention, the range of the number of rotations and the ball filling rate of the horizontal dry mill is appropriately selected, so that the stirring blades attached to the inner and outer cylinders of the mill and the crushing balls forcedly moved by the stirring blades are used. As a result, a compressed flow is periodically generated.
The pulverized material is continuously discharged outside the mill by this compressed flow. Since the mill itself has a continuous discharge function, no conveying air is required.

[0006]

1 is a longitudinal sectional view showing one embodiment of a horizontal dry mill used in the method of the present invention, and FIG. 2 is a sectional view taken along the line II-II of FIG. As shown in FIG. 1, the horizontal dry mill (10) of the present embodiment has an outer cylinder (1) having a plurality of stirring blades (3) protruding on an inner wall surface and a plurality of stirring blades (4) on an outer surface. And an inner cylinder (2) arranged coaxially in the outer cylinder (1) and rotating around an axis. A grinding ball (6) is filled in a grinding chamber (5) having an annular cross section formed between the outer cylinder (1) and the inner cylinder (2).
Raw material input port (7) in outer cylinder (1) at one end of crushing chamber (5)
As shown in FIG. 2, the other end communicates with the discharge port (9) through an aperture plate (8) with a slit (8a).

The crushed material continuously supplied from the raw material inlet (7) is crushed in the crushing chamber (5) with the rotation of the inner cylinder (2). FIGS. 3 and 4 are views showing the movement of the grinding ball (6) when the inner cylinder (2) is rotated within the fixed outer cylinder (1). First, as shown in FIGS. 3A and 3B, a stirring blade (4) fixed to a rotating inner cylinder (2).
The crushing ball (6) repeatedly compresses and relaxes in the direction of the rotation axis with the approach and separation of the stirring blade (3) fixed to the outer cylinder (1). The movement of the grinding ball (6) generates a compressed flow. Next, in FIG. 4, the crushing ball (6) is gradually scraped up in the rotation direction by the stirring blade (4) fixed to the inner cylinder (2). Along with this, the ridge line (dotted line in the figure) of the accumulation of the crushed balls (6) becomes steeper as shown in FIG. 4 (a) to FIG. 4 (b). When the inclination reaches the criticality, the accumulation of the crushed ball (6) collapses as shown in FIG. 4 (c), and the crushed ball (6) falls until the state shown in FIG. 4 (d) is reached. The falling causes a compressed flow.
The powder is conveyed by the compressed flow generated by these two actions, and the outlet (9) provided at the other end of the outer cylinder (1)
Is continuously discharged from

FIG. 5 is a system diagram showing a system incorporating the horizontal dry mill of this embodiment. The raw material is supplied from the raw material hopper (11) to the horizontal dry mill (10) by the feeder (12), and is pulverized. The powder continuously discharged from the horizontal dry mill (10) is classified into coarse particles and fine particles by a vibrating sieve (18), and the fine particles are guided to a product tank (16). The coarse particles are again fed into the horizontal dry mill (10) and pulverized by the belt conveyor (19). Therefore, this system does not require any ventilation / dust collection system.

The ratio of the bulk volume of the crushing ball (6) to the internal volume of the crushing chamber (5) (that is, the ball filling ratio) is 3
0% or more and less than 90%. The inner cylinder (2)
The rotation is performed at a rotation speed not less than the critical rotation speed N _C defined by the following equation.

[0010]

(Equation 1)

The grounds for such limitation will be described in detail below. In the case of pulverizing by a horizontal dry mill, the pulverizing balls (6) filled in the pulverizing chamber (5) are filled in the inner cylinder (2).
As shown in FIG. 4 (a), the liquid is gradually scraped up in the rotating direction as shown in FIG.
It collapses and falls as shown in (c). Due to the drop impact, the raw material is crushed and a compressive force is generated, thereby conveying and discharging the powder. However, when the rotation speed of the inner cylinder (2) is too low, the crushed ball (6) is hardly lifted. That is, the ridgeline shown by the dotted line in FIG. 4 hardly tilts, and the grinding ball (6) repeats only a small range of vertical movement. Therefore, in this case, not only the pulverizing performance is significantly reduced, but also no pressure is generated.

FIG. 6 is a diagram showing the fluctuation of the pressure in the mill.
FIG. 7 is a diagram showing the relationship between the internal pressure fluctuation width and the critical rotational speed ratio (the ratio of the actual rotational speed N to the critical rotational speed N _C. Hereinafter, only the rotational speed ratio) shown in FIG. . FIG. 8 is a graph showing the relationship between the rotation speed ratio and the discharge characteristics.
From these figures, it can be seen that, at a rotational speed ratio of 1.0 or more, the internal pressure fluctuation width becomes sufficiently large and good discharge becomes possible.

FIG. 9 is a graph showing the relationship between the ball filling ratio and the crushable particle size. Looking at FIG. 9 and FIG.
It can be seen that the ball filling ratio has an upper limit and a lower limit. That is, in FIG. 8, when the ball filling rate is increased to 90% or more, the discharge amount with respect to the supply amount is extremely reduced. This is because if the ball filling ratio is too large, the free space in the mill is reduced, so that the above-mentioned collapse movement of the crushed balls does not occur, and no compressed flow is generated, so that discharge becomes impossible. is there. In FIG. 9, when the ball filling rate is less than 30%, the pulverizing energy given to the material becomes insufficient and the number of short passes increases, so that the average particle diameter (D _{50 in the} figure) increases and the amount of coarse particles (FIG. 9) increases. It can be seen that the so-called pulverizability becomes poor, for example, the medium D ₉₀ ) increases. Therefore, the appropriate range of the ball filling rate is limited to 30% or more and less than 90%.

Next, specific examples of the method of the present invention will be described. The inner cylinder was rotated at an absolute rotation speed of about 70 rpm using a steel ball having a ball diameter of 10 mm in a mill having an outer cylinder inner diameter of 800 mm, and as a raw material to be pulverized, a 50% average particle size of 1.5 mm and a grindability index of HGI35. Was crushed to obtain ultrafine silica having a 50% average particle size of 1.8 μm, and was continuously discharged.

[0015]

In the method of the present invention, a compressed flow is generated in the crushed material and the stagnant layer of the ball by the movement of the stirring blade in the mill and the accompanying movement of the ball. By the discharging action using the compressed flow, the mill itself can continuously discharge the finely pulverized material. Therefore, since no equipment or power for conveying air is required, the cost is greatly reduced as compared with the conventional dry-type continuous pulverization system, and the installation space for the equipment can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing one embodiment of a horizontal dry mill used in the method of the present invention.

FIG. 2 is a cross-sectional view taken along the line II-II of FIG.

FIG. 3 is a view showing movement of a grinding ball in a mill in a rotation axis direction.

FIG. 4 is a view showing a circumferential movement of a crushed ball in a mill.

FIG. 5 is a system diagram showing a system incorporating the horizontal dry mill of FIG. 1;

FIG. 6 is a diagram showing a pressure fluctuation state in a mill.

FIG. 7 is a diagram showing a relationship between a pressure fluctuation width in a mill and a rotation speed ratio.

FIG. 8 is a diagram showing a relationship between a discharge characteristic of a mill and a rotation speed ratio.

FIG. 9 is a diagram showing a relationship between a crushable particle size and a ball filling rate.

FIG. 10 is a diagram showing an example of an operation method of a conventional dry ultrafine grinding mill.

[Explanation of symbols]

 (1) Outer cylinder (2) Inner cylinder (3), (4) Stirring blade (5) Crushing chamber (6) Crushing ball (7) Raw material input port (8) Opening plate (8a) Slit (9) Discharge port ( 10) Horizontal dry mill (11) Raw material hopper (12) Feeder (13) Mill (14) Blower (15) Classifier (cyclone) (16) Product tank (17) Dust collector (bag filter) (18) Vibrating sieve ( 19) Belt conveyor

Continued on the front page (72) Inventor Katsuyuki Ueda 1-1, Akunoura-cho, Nagasaki-shi Inside Mitsubishi Heavy Industries, Ltd. Nagasaki Shipyard (72) Inventor Amano Olympic Circle 1-1, Akunoura-cho, Nagasaki-shi Mitsubishi Heavy Industries, Ltd. (56) References JP-A-2-99151 (JP, A)

Claims (1)

(57) [Claims] 1. An outer cylinder having a plurality of agitating blades protruding from an inner wall surface and an inner cylinder having a plurality of agitating blades protruding from an outer surface and disposed coaxially within the outer cylinder and rotating about an axis. Use, in the method of introducing a raw material into one end of a grinding chamber having an annular cross section filled with grinding balls formed between the outer cylinder and the inner cylinder and discharging finely pulverized material from the other end, The inner diameter of the outer cylinder is D
(M), the rotation speed of the inner cylinder is set to 42.3D ^-1/2
(Rpm) or more, and the ratio of the bulk volume of the grinding balls to the internal volume of the grinding chamber is 30% or more and 90% or more.
%, And a method for operating a horizontal dry mill.