TITLE

A MICRO-MEDIA AGITATOR MILL FIELD OF THE INVENTION

The present invention is related to a micro-media agitator mill to reduce particle size and disperse the particulate matter in slurry such as pigment in slurry. BACKGROUND AND PRIOR ART OF THE INVENTION

A new era in particle size reduction and dispersion started when Du Pont de Nemours introduced a vertically positioned "sand mill" that had an axially revolving shaft with several media discs spaced equally along its length revolving within a stationary grinding cylinder charged with sand as a grinding media.

Over the coming years many other vertical and subsequently, horizontal mills were developed with better designs and wear-resistant materials. Advanced machining techniques led to the development of more efficient more radical designs of the mills with very high power densities and consequently very high outputs.

Presently available micro-media agitator mills comprise of a vertical or a horizontal cylinder with a rotating shafts with a series of equally spaced agitator discs mounted on the shaft. The cylinder is charged with the micro- bead grinding media 60% to 80% of its volume, depending upon the type of mill and the product to be milled. The rotating shaft and the discs rotate at a high speed and generate a centrifugal force proportional to the peripheral speed, which is generally above 10 m/s at the edge of the discs.

The US patent No. 6000646 discloses a double barrel chamber for a media mill where the media mill is used to grind and disperse pigments for paint, coating, ink products, and other pigment-vehicle fluids, as well as grinding and dispersing other particulate matter. Centered in each barrel is a rotatable shaft. On each shaft are a number of horizontally spaced discs. The shafts are parallel and arranged such that the edges of the discs overlap to cause major impacting and mixing in the central portion of the chamber when the shafts are rotated in a common direction. Also it is disclosed a coiled cooling water jacket system for cooling the cylinder. The system allows 100%, or near 100% recovery of cleaning solvent, limits potential damage to a pumping system and allows slurry-feeding flexibility. A special bearing seal section is disclosed which allows use of a diaphragm pump. The pump in conjunction with the spinning discs force the pigment slurry up from the bottom of the chamber and out through a specially designed discharge screen, which is also disclosed. A bump feature on each disc is disclosed. The bump feature increases pumping and impact of media in the media mill.

However, the retention time of the slurry in the mill claimed in US Patent No. 6000646 is not sufficient and therefore requires multiple circulation of the slurry through the mill to obtain required size reduction and a narrow range of distribution of the particles in the slurry.

Moreover, there is a problem of accumulation of grinding media or bead packing due to high through put of the slurry in the horizontal mill. This leads to the uneven grinding and high wear and tear of the beads, even crushing in severe conditions.

Besides, existing mills have more disadvantages such as high peripheral speed of the rotating discs leading to impacting of the beads on the cylinder of the mill resulting in high wear and tear of the mill internals, excessive attrition and impact lead to high temperature difference between the slurry input and output necessitating efficient jacket cooling leading into the lost of the energy.

Hence, there is a need and for an micro-media agitator mill which provides sufficient retention time for the slurry and can provide multiple circulation of the slurry through the mill to obtain required size reduction and a narrow range of distribution of the particles in the slurry.

Another need is to device a micro-media agitator mill that can reduce the wear of the internal parts of the micro-media agitator mill to the minimum. Further, studies on existing mill have shown that only a small percentage of the power input to the mill is actually used to do the work of particle size reduction and dispersion; this needs to be changed so as to increase the efficiency of energy conversion. SUMMARY OF THE INVENTION

It is an object of the present invention to provide a micro-media agitator mill that overcomes all the problems associated with existing mills as described above.

According to the one of the embodiment of the present invention, a micro- media agitator mill for particle size reduction and dispersion of particulate size matter, comprises a cylinder having inlet and outlet; atleast one rotating shaft adapted centrally to the cylinder; a series of equally spaced rotating discs having a series of concentric inner openings near its axis of rotation;

an inner spacer adapted between the two discs to separate the shaft and the inner openings of the rotating discs; an outer spacer adapted between the rotating discs such that inner spacer and outer spacer forms an annular space between the cylinder and shaft forming an annular passage extending from one end to other end of the mill in combination with the inner openings of the rotating discs; and a turbine adapted on the shaft for sucking the slurry and grinding media through the annular passage formed between the cylinder and shaft from one end to the other end of the mill thereby reduces the accumulation of the grinding media near the outlet of the mill and allowing re-circulation of the slurry within the mill.

According to the another embodiment of the present invention, a micro- media agitator mill for particle size reduction and dispersion of particulate matter, said micro-media agitator mill comprises a cylinder having inlet and outlet for slurry, wherein inner surface of cylinder has bellows-like deflectors; atleast one rotating shaft adapted centrally to the cylinder; a series of rotating discs adapted on the shaft, wherein each disc have an outer opening for passing of the slurry; and a deflector provided on the rotating shaft between the two rotating discs matching with the deflectors provided on the cylinder wherein deflectors in combination with the two rotating discs form a compartment between the two disc and directs the slurry and grinding media to circulate within the compartment improving attrition between the grinding media and increasing the retention time of the slurry in the mill. According to the present invention, the deflectors mounted between discs and provided on the inner wall of the cylinders are concave for circulation of the slurry within the compartment.

According to further embodiment of the present invention, a rotating disc or impeller for a micro-media agitator mill, having a central opening for mounting of the shaft, said disc comprises atleast two sets of concentric openings adapted at different radial positions from the central hole, wherein a set of concentric inner openings near to the rotational axis of the disc is tapered so as to create a suction force on slurry and grinding media while rotating in the micro-media agitator mill.

According the present invention, said inner openings and outer openings are of any shape and preferably they are kidney shape. BRIEF DESCRIPTION OF DRAWINGS

The foregoing objects and advantages will be better understood from the following description with reference to the accompanying drawings, in which: Fig 1 shows the cross sectional view of a micro-media agitator mill of the present invention having single shaft. Fig 2 shows a magnified view of W marked on Fig 1.

Fig 3 shows the cross sectional view of a micro-media agitator mill of the present invention having two shafts.

Fig 4 shows a top view of the rotating disc of the present invention. DETAILED DESCRIPTION OF THE PRESENT INVENTION: Fig 1 and Fig 3 shows micro-media agitator mills of the present invention comprising single shaft and two shafts respectively.

Referring to Fig 1 and 2, the micro-media agitator mill (100) of the present invention for particle size reduction and dispersion of particulate size matter in slurry comprises a cylinder (10) having inlet (12) and outlet (14) for the slurry in which particulates are required to be size-reduced and dispersed, a

rotating shaft (20) adapted centrally to the cylinder (10), a series of equally spaced rotating discs (30) having a series of concentric inner openings (32) near its axis of rotation, an inner spacer (40) adapted between the rotating discs (30) to separate the shaft (20) and the inner openings (32) of the rotating discs (30), an outer spacer (50) adapted between the rotating discs (30) and a turbine (60) adapted on the shaft (20).

The inner spacer (40) and the outer spacer (50) are preferably cylinders having diameters such that an annular space (P) forms between the inner spacer and outer spaces. This annular space (P) in combination with the rotating discs (30) forms an annular passage (45) extending from one end to other end of the mill. The inner spacer (40) acts as a partition by avoiding contact of the grinding media with the shaft (20) thereby prevents the wear and tear of the shaft (20). A turbine (60) adapted on the shaft (20) sucks the slurry and grinding media through the annular passage (45) from one end to the other end of the mill (100). Generally, the turbine (60) is adapted at the end of the annular passage (45) and preferably near the inlet (12) of the cylinder (10) for slurry. According to the present invention, the inner openings (32) on the rotating disc (30) are tapered so as to produce pumping action on rotation. The rotating disc (30) is mounted on the shaft (20) in such a way that the inner tapered openings (32) pushes the slurry and the grinding media from one annular space to the other annular space as shown in Fig 2 along the annular passage (45) helping the turbine (50) to re-circulate the slurry and also prevents accumulation of the grinding media at the outlet of the mill (100).

The cylinder (10) of the present invention may have any cross section shape such as circular, oval or a shape claimed in US 6000646 depending on the number of the shafts adapted in the cylinder such as the cylinder for single shaft mill has preferably circular cross section. According to the present invention, the cylinder (10) has plurality of the deflectors (16A) arranged like bellows on the inner surface (not shown) and similarly the present invention provides deflectors (16B) on the outer surface of the outer spacers (50). Further, The rotating disc (30) may have series of outer openings (34) near periphery to allow passage of the slurry. The deflectors (16B) on the outer spacers (50) and the deflectors (16A) on the inner surface of the cylinder (10) are adapted in such a way that the deflectors (16A, 16B) are like a mirror images of each other. The deflectors (16A ₁ 16B) have preferably concave surface. These deflectors (16A, 16B) in combination with the rotating discs (30) form at least one compartment (70) between the two rotating discs (30) and the outer openings (34) act as inlets and outlets of the compartments (70). The deflectors (16A, 16B) as showed in Fig 1-3 form two compartments (60) between the two discs (30). It is already known in the present art that the rotating discs rotate the slurry and grinding media and push it towards the inner wall of the cylinder by centrifugal force. In the present invention, the deflectors (16A, 16B) which form compartments (70) in the mill (100) in combination with the rotating discs (30) direct the slurry and grinding media, which are pushed towards them to circulate as shown in Fig 2 within the compartments (70). The deflectors circulate the slurry, which is in contact with the upper surface of the rotating disc (30) in a direction υ1 ' while the slurry which is in contact

with the lower surface of the rotating discs (30) in a direction υ2" causing in increase in the differential velocity (d) between grinding media. This improves attrition and shear forces generated between the grinding media between the grinding media. Further, as the rotational disc (30) allows passage of the slurry and the grinding media through the outer openings (34) from one compartment to other compartment through the outer openings (34) provided on the rotating disc (30) in a direction T i.e. towards the outlet (14) of the mill (100) that helps the circulation of the slurry along with grinding media in each compartment (70). The circulation of the slurry in each compartment increases the retention time of the slurry in the mill (100). The turbine (60) with the help of the inner openings (32) on the rotating discs (30) sucks the slurry and grinding media reached at the outlet (12) of the cylinder (10) in a direction (X) and re-circulates the grinding media and partial or total amount of slurry within the mill (100) thereby prevents accumulation of the grinding media at the outlet of the mill (100) and increases the retention time of the slurry in the mill (100). The micro-media agitator mill (200) as shown in Fig 3 comprises two shaft (2OA, 20B) adapted off-centrally and plurality of rotating discs (30) adapted on the shafts partially overlapped with each other wherein the deflectors (16B) mounted on the shafts (2OA, 20B) form compartments (70 A) between rotating discs (30) of the shafts (10A, 10B) in addition to the compartments (70) that are formed by the deflectors (16B) mounted on the shaft with the deflectors (16A) provided on the inner wall of the cylinder (10). The shafts (10A, 10B) of the mill (100) rotate in the same clock/anticlockwise direction

thereby achieving exceptionally high differential velocity in the compartments (70A) form by overlapping of the rotating discs (30).

The present invention also provides the mill having compartments only for circulation of the grinding media and slurry within the compartments i.e. the mill may not have annular passage for re-circulation of the slurry and grinding media within the mill or the mill having only annular passage to re- circulate the grinding media and slurry i.e. the mill may not have compartments. Though figures of this mill are not shown, a person skilled in the art can easily understand from Fig 1 and 3. The rotating discs have only outer opening for the mills having only compartments for the passage of the slurry from one compartment to another compartment whereas the rotating discs adapted in the mill having inner passage have only tapered inner openings for re-circulation of grinding media and slurry within the mill. The micro-media agitator mill of the present invention can be operated vertical or horizontal with necessary modifications. The mills (100) shown in the Fig 1 and 3 are the horizontal mills.

As shown in Fig 4, the present invention also provides a rotating disc (30) for a micro-media agitator mill. The rotating disc (30) has a central opening (36) for mounting on the shaft (20). According to the present invention, the rotating disc (30) comprises atleast two sets of concentric openings (32, 34) adapted at different radial positions from its axis of rotation (W). An inner set (32) of concentric openings, which is near to the axis of rotation (W) is tapered so as to create a pumping action on slurry and grinding media in the micro-media agitator mill as described earlier.

The dimensions of the concentric openings depend upon the throughput of the slurry required through the micro-media agitator mill. The concentric openings are any shape and preferably of kidney shape as according to the inventor, kidney shape openings provide larger area for slurry to circulate through the disc.

A system of separation provided at the outlet of the micro-media agitator mill to separate the grinding media from dispersed slurry depends on dimensions of the grinding media and the field of the application of the micro-media agitator mill. The system of separation shown in the Fig 1 and 3 is a centrifugal separator (90). However, the separator means can be any type of separator like screen, gap separator etc. The mill may have cooling arrangement (15) as shown in Fig 1-3.

The mill of the present invention increases the amount of hydraulic shear developed and also enhances the forces of attrition within the grinding media suspended in the slurry in each compartment. Each compartment of the micro-media agitator mill acts as a separate micro-media agitator mill. As the differential velocities and shear forces generated by the cross flows within the circulating slurry are several times higher than in conventional mills, the conversion of energy input to the mill is far more efficient, thus allowing the shafts and discs to be rotate at a considerably lower peripheral speeds, hence reducing the wear and tear of the mill internals. In spite of this, prototypes have demonstrated that this mill is more than three times more efficient as compared to conventional mills existing today. Also as the micro-media agitator mill of the present invention provides re-circulation of the slurry and the grinding media within the mill though the annular passage,

one can easily achieve the required size reduction of the particles and dispersion in the slurry with one pass of the slurry through the mill of the present invention. The mill of the present invention reduces the particle size can be used to reduce the particle size substantially below sub-microns i.e. below 1 micron with less power input and wear and tear of the mill.

The mill of the present invention enables the processing of slurries with high solid content and high viscosities in spite of running the mill at relatively low peripheral speeds thus achieving very high efficiency. The mill of the present invention therefore increases the amount of energy conversion for the purpose of de-agglomeration, particle size reduction, and dispersion with an additional advantage of greatly reducing wear and tear of mill internals due to the employment of relatively lower peripheral speeds of the shafts of the mill of the present invention. The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to person skilled in the art, .the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.