GB2183172A - Apparatus for grinding suspensions - Google Patents

Abstract

An apparatus is proposed for grinding and dispersing suspensions of brittle materials having a hardness of up to 4 Mohs hardness scale. The apparatus comprises a housing (1) having an inlet (8) and an outlet (9), and disks (2,3) arranged coaxially inside the housing (1) for rotation therein. The outlet (9) occupies the central area of the disks (2,3). The disks (2,3) have pins (4) secured to the sides thereof facing each other. One of the disks (2) has a sleeve (5) arranged about its outer diameter and embracing the other disk (3) about its circular periphery to form an annular passage (6). One of the walls of the passage (6) has a helical groove (7). <IMAGE>

Description

SPECIFICATION Apparatus for grinding suspensions This invention relates to apparatus for wet grinding, and more particularly to apparatus for grinding suspensions.

The apparatus according to the invention can find application for grinding and dispersing suspensions of brittle materials having a hardness of up to 4 Mohs hardness scale.

The apparatus of the invention can also be used for classification accompanied by postgrinding of large-size particles of materials, that is for conditioning the product to the required characteristics.

The present-day practice of grinding is characterized by rigid requirements as to the granulometric omposition of materials, particularly with respect to large-size particles retained on the sieve.

It is well known that a product ground in any apparatus has a wide range of particle size. In order to narrow this range with respect to coarse fraction, use is made, as a rule, of classifiers ganged with grinders, whereby the facility becomes bulky and inefficient because, along with large-size particles, a certain amount of fine particles is returned for regrinding.

There is known an apparatus (crusher) (cf., Sidenko P.M. "lzmelchenie v khimicheskoi pro myshlennosti"-Grinding in The Chemical Industry, in Russian, the "Khimiya" Publishers, Moscow, 1968, pp.155 to 157) which comprises a housing having inlet and outlet tubes, a rotatable disk and a hinged cover plate, the disk and cover plate having pins secured thereto about concentric circles with the rows of pins on the cover plate being disposed between the rows of pins on the disk.

There is also known a disintegrator comprising a housing, two disks secured on coaxial shafts to be rotatable in the opposite directions and having pins secured thereon about concentric circles, each row of pins of one disk having a small clearance between the two rows of pins of the other disk.

Inherent to the aforedescribed prior art apparatuses is a disadvantage in that they fail to ensure obtaining a product of homogeneous composition.

A device which bears the closest resemblance to the one proposed in the present invention is described in a publication by Sidorenko P.M. "lzmelchenie v khimicheskoi promyschlennosti" in Russian, the "Khimiya" Publishers, Moscow, pp.248 and 249. This apparatus comprises a rotor in the form of a disk member fitted onto a shaft and provided with rows of pins arranged about concentric circles, and beaters secured in the center of the disk. A cover plate is further provided having rows of pins secured thereto in concentric circles arranged between the rows of pins on the rotor.

However, this device is inherently disadvantageous because of the failure to obtain a granulometrically homogeneous material and due to excessive amount of power consumed fdr regrinding.

During operation of the above device the material to be ground is fed to the central part of the rotating disk for centrifugal forces to throw it toward the periphery. Grinding is effected through the travel of the material from the center to the periphery.

Accordingly, centrifugal forces of greater magnitude act on the large-size particles to cause them to move at a higher speed, whereby their residence time in the grinding zone is shorter than that of the smaller particles, although the large-size particles, naturally, require grinding for a greater length of time.

In view of the foregoing, all the prior art grinding apparatuses suffer from a common disadvantage resulting in grain size non-uniformity of the end product.

Consequently, repeated grinding of the coarse fraction calls for extra expenditures.

It is therefore an object of the present invention to provide an apparatus which would be capable of producing homogeneous material in terms of its grain size.

The aim of the invention is attained by that in an apparatus for grinding suspensions comprising a housing having an inlet and an outlet, disks coaxially arranged inside the housing for rotation of at least one of such disks, the disks being provided with pins secured about concentric circles on the sides of the disks facing each other, one of the disks has a sleeve occupying its outer diameter and embracing the other disk about its circular periphery to form an annular passage, at least one of the walls of this annular passage having a helical groove, whereas the outlet occupies a space in the central area of the disks.

The provision on one of the walls of the annular passage of the helical groove makes it possible to convey the suspension from the periphery of the disks toward the center, that is toward the zone where centrifugal forces are at their maximum.

Conveying the material to the zone of maximum centrifugal forces promotes classification during which fine particles of the material are delivered to the center of the apparatus under the action of the flow of liquid, whereas large-size particles of the material are retained by the centrifugal forces at the periphery of the grinding members to progressively move toward the center in the course of grinding and result in a reduction of their size. This prevents the penetration of the particles of coarse fraction to the end product.

Preferably, the helical groove is provided on two walls of the annular passage, the grooves on the walls of the annular passage being cut in the opposite directions. Such an arrangement of the helical grooves on the walls of the annular passage makes it possible to increase pressure head at which the suspension is delivered and, accordingly, improve the production efficiency of the apparatus.

Advisably, the helical groove is a multistart cut groove. Such multistart grooves enable to still further increase the pressure head produced thereby, because the head is directly proportional to the number of groove starts. An increase in the head ensures higher efficiency of the apparatus at a higher magnitude of centrifugal forces, whereby it becomes possible to separate finer particles of the product being ground.

Other objects and advantages of the invention will become more fully apparent from a more detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings, in which: Figure 1 is a general view of an apparatus for grinding suspensions.

Figure 2 is a section taken along the line ll-ll in Fig. 1.

The proposed apparatus for grinding suspensions comprises a housing 1, disks 2 and 3 arranged coaxially inside the housing 1 for rotation of at least one of such disks and provided with pins 4 secured about concentrical circles on the sides of the disks 2 and 3 which face each other. A sleeve 5 is disposed about the outer diameter of the disk 2 to embrace the disk 3 circumferentially and form an annular passage 6. Helical grooves 7 are provided on the walls of the passage 6, i.e., on the inside surface of the sleeve 5 and outer end face of the disk 3 embraceable by the sleeve 5. Such grooves 7 may be provided only on one of the walls of the passage 6.

The helical grooves 7 on the two walls of the passage 6 may be cut in a similar or opposite directions. The helical grooves 7 are generally multistart cut grooves.

The housing 1 comprises inlet and outlet indicated at 8 and 9, respectively, the outlet 9 being arranged in the central zone of the disks 2 and 3. A drive shaft is rigidly connected to the disk 3.

The apparatus operates in the following manner. The disk 3 is rotated and the suspension to be ground is fed to the interior of the housing 1 through the inlet 8. The provision of the passage 6 with the grooves 7 on its wall ensures a pressure differential necessary to overcome the centrifugal force and convey the suspension to the working interior between the disks 2 and 3 traversed by the movable pins 4. The grooves 7 tend to entrain the suspension and produce a pressure head, which enables to force the ground suspension against the centrifugal force toward the center of the apparatus.

The suspension is thus ground, whereas particles of predetermined size are conveyed by the flow of liquid to the center of the disks 2 and 3 to be evacuated from the apparatus via the outlet 9, whereas large particles are retained by the centrifutal forces at the periphery of the disks 2 and 3 until they are reduced to the required size, whereafter they are carried by the liquid to the center of the disks 2 and 3.

The structure of the helical grooves 7 (viz., the groove cross-section, groove pitch and number of groove starts) is selected proceeding from operating conditions of the apparatus. Factors to be taken into consideration include grinding capacity of the apparatus, particles size at the inlet to and outlet from the apparatus, and the required degree of separation.

Example 1 Pumped from a buffer mixer having a stirrer to a crusher unit for grinding was a sulphur suspension having grain size up to 0.5 mm.

The crusher unit capacity at a solid-to-liquid phase relationship of 1:1 was 200 I/h. Active power consumed by the crusher unit was registered by a metering equipment. Quintuple circulation of the suspension through the crusher was carried out. Results of the trials are represented in Table 1.

Example 2 A sulphur suspension was fed from a pressure tank to the apparatus according to the invention operating at the same circumferential velocities as the prior art crusher unit in a manner substantially similar to one described in Example 1. The end product characteristics are also represented in Table 1.

The number and shape of the grinding pins 4 in both trials were the same (10 mm in dia., 68 pcs. in number). Table 2 shows the amount of power consumed for the trial operation by the prior art and proposed apparatuses.

Table 1 Nos Content of fractions, per cent In the prior art apparatus +0.14 mm -0.14+ -0.074+ -0.040+ +0.074 mm +0.040 mm +0.01 mm 1 2 3 4 5 1. 2.3 17.2 48 23.4 2. 1.7 13.2 52.3 28.1 3. 0.8 7.2 41.4 42.4 4. 2 2.7 37.3 57.7 5. - 0.2 33 61.8 Table 1 (Cont.) Content of fractions, per cent In the proposed apparatus Nos +0.14 mm -0.14+ -0.074+ -0.040+ +0.074 mm +0.040 mm +0.01 mm 1 6 7 8 9 1. - - 10.3 86.2 2. - - - 3. - - - 4. - - - 5. - - - Table 2 Nos Parameter 1 2 1 Power consumption for one circulation, kW 2 Number of circulations 3 Overall consumption of power for grinding, kW Table 2 (Cont.) Example 1 Example 2 1 3 4 1 5.5 7.6 2 5 1 3 27.5 7.6

Claims (4)

1. An apparatus for grinding suspensions comprising a housing having inlet and outlet; disks arranged inside the housing for at least one of such disks to be capable of rotation; the outlet being disposed in the central area of the disks; pins being secured about concentric circles on the sides of the disks facing each other; a sleeve arranged about the outer diameter of one of the disks to embrace the other disk about its circular periphery and define an annular passage; a helical groove provided at least on one of the walls of the annular passage.

2. An apparatus as claimed in claim 1, in whidh the helical groove is cut on both walls of the annular passage, the grooves on the walls of the annular passage being cut in the opposite directions.

3. An apparatus as claimed in claims 1 and 2, in which the helical groove is a multiple start cut groove.

4. An apparatus as claimed in any of the preceding claims substantially as disclosed in the description and represented in the accompanying drawings.