WO1988005342A1

WO1988005342A1 - Abrasive medium mill

Info

Publication number: WO1988005342A1
Application number: PCT/GB1988/000030
Authority: WO
Inventors: Michael Edward Hampshire; Gordon Peter Pearson
Original assignee: Yorkshire Chemicals Plc.
Priority date: 1987-01-17
Filing date: 1988-01-18
Publication date: 1988-07-28
Also published as: GB8700984D0; AU1105888A

Abstract

A cylindrical bead mill has a metal drum (10) with an inlet pipe (12) at one end. A shaft (14) with spaced-apart agitating discs (16) is rotatably mounted within the drum (10), and as the shaft rotates it agitates abrasive medium (18) within the drum. At the opposite end of the mill to the inlet (12) is a filter assembly (20). The assembly is in the form of a rectangular exit conduit (22) extending upwardly from the drum within which a filter portion (24) is releasably securable. The filter portion is also in the form of a rectangular conduit, but its lower open face (26) is provided with a filter screen in the form of a plurality of aligned wedge wires (30). When in position in the mill, the filter (28) partially surrounds an agitator (16a). The presence of the agitator (16a) in the vicinity of the filter (28) provides a cleaning action for the filter, thereby reducing the frequency with which the filter has to be maintained. The provision of the filter as one end of a conduit (24) which fits within another conduit (22) allows the filter to be removed very easily.

Description

DESCRIPTION ABRASIVE MEDIUM MILL The present invention relates to mills containing an abrasive medium, and in particular, but not exclusively, to bead or sand mills used in the manufacture of dyestuffs .

Abrasive medium mills are used to reduce the size of the particles suspended in a liquid which is fed through the mill. There are different types of such mills, but they all consist of an elongate drum containing an abrasive medium, e.g. glass beads or sand. The liquid to be treated is fed in at one end and passes out of the opposite end. By agitating the abrasive medium, the size of the particles in the liquid is reduced as the liquid passes through the mill. One way of agitating the abrasive medium is to provide a rotatable shaft along the longidutinal axis of the drum, the shaft being provided with a number of spaced-apart discs, whereby rotation of the shaft also causes the discs mounted thereon to rotate and thereby agitate the medium.

Obviously it is necessary to filter the liquid emerging from the tank to remove any particles of abrasive medium from the liquid, lest they contaminate the finished product. One such filter, which is used particularly with the agitator arrangement described above, extends into the drum and comprises two spaced-apart discs of filter material (e.g. perforated metal) joined by a short tubular wall, thereby forming a filter in the form of a very short drum with circular ends of filter material. The liquid is extracted from a pipe leading from the internal space defined by the two filtering walls and the tubular wall, so that all liquid leaving the mill passes through the filter. The above-described f lter, in common with all filters, requires cleaning or replacement after a while in- order to remove any material trapped in the filter. The above filter suffers from the disadvantage that it is very heavy and- requires lifting device such as a block and tackl^'e to remove it from the bead mill. For this reason, the filter must normally be removed and replaced by a trained fitter and an assistant rather than by an operator of the mill, and this increases the running costs of the mill. -Also, it takes a long time to replace the filter, which increases the downtime of the mill and again increases running costs.

It is an object of the present invention to provide an abrasive medium mill whose filter requires changing or cleaning less frequently than known mills. In accordance with a first aspect of the present invention, an abrasive medium mill comprises a drum for housing an abrasive medium, a plurality of agitators for agitating the medium, an outlet from the drum and a filter through which the outlet communicates with the interior of the drum, characterised in that the filter at least partially surrounds an agitator.

The presence of the agitator in the vicinity of the filter provides a cleaning action for the filter, thereby reducing the frequency with which the filter has to be maintained.

Preferably, the filter is arcuate, and in a preferred embodiment the radius of curvature of the filter is substantially identical to that of the drum. Preferably, the filter is situated generally above the agitator, and preferably the filter is positioned above the level of the abrasive medium in the drum. In a preferred embodiment, the mill comprises a rotatable shaft positioned within the drum and the agitators comprise discs mounted on the shaft.

Preferably, the filter is releasably securable in a conduit communicating with the interior of the drum. This may be achieved by positioning the filter across one end of a tube or pipe which is shaped to fit within the conduit. This makes removal, cleaning and replacement of the filter a very simple task which need not be undertaken by a skilled fitter. Preferably, the filter is in the form of a screen comprising a plurality of aligned wires, e.g. wedge wires.

The abrasive medium may, for example, comprise beads, e.g. glass beads, or may comprise sand.

It is a further object of the present Invention to provide a filter for use in an abrasive medium mill, which filter may be easily and quickly replaced.

In accordance with a second aspect of the present invention, a filter assembly for use in an abrasive medium mill is characterised by a first conduit which communicates with the interior of the mill and extends upwardly from the mill and a second conduit shaped to fit within the first conduit and having a filter medium across one end, whereby when the second conduit is positioned within the first conduit, material emerging from the bead mill is filtered through the filter.

Preferably, the first conduit extends substantially vertically upwardly from the mill.

In a preferred embodiment, the filter is arcuate, and preferably the first and second conduits are rectangular in cross-section.

Preferably, the filter is in the form of a screen comprising a plurality of aligned wires, e.g. wedge wires. In a preferred embodiment, the filter is shaped to partially surround an agitator in the drum, when the filter is in position on the bead mill .

By way of example only, a specific embodiment of the present invention will now be described, with reference to the accompanying drawings, in which:-

Fig. 1 is a longitudinal cross-section of an embodiment of bead mill in accordance with the present invention; Fig. 2 is a cross-section looking in the direction of arrows II-II in Fig. 1;

Fig. 3 is an exploded perspective view of the filter section of the embodiment of Fig. 1; and

Fig. 4 is a detailed perspective view, partly in cross-section of a portion of the filter of the embodiment of Fig. 1.

A bead mill comprises a cylindrical metal drum 10 having an inlet pipe 12 through which liquid to be treated is fed. A shaft 14 is rotatably mounted within the mill, with its axis of rotation coincident with the longitudinal axis of the drum. The shaft is rotat ble by means of conventional drive means (not illustrated) situated outside the drum, and carries a plurality of evenly-spaced agitator discs 16, the plane of each disc being normal to the axis of rotation. The drum is filled to about two-thirds of its depth with very small glass beads 18 which are used, as will be explained, to reduce the size of particles in the liquid to be treated.

The bead mill 10 has a filter and exit portion 20 situated at the end of the drum remote from the Inlet 12. The filter and exit portion comprises a rectangular exit conduit 22 extending vertically upwardly from the uppermost portion of the drum 10, within which a removable filter portion 24 is ° securable. The filter portion 24 also comprises a rectangular conduit, but two opposed walls are each provided with a recess 26 in the shape of an arc of a circle of the same radius as that of the drum 10. An arcuate wedge wire filter screen 28 of the same radius 5 of curvature as the recesses 26 is attached to the four planar walls of the conduit 24, thereby forming the base of the filter portion 24. Also, two bars 29 extend between the opposed walls, to assist in lifting the filter portion 24. ^Q The composition of the wedge wire screen is better illustrated in Fig. 4, from which it can be seen that the screen comprises a plurality of spaced-apart aligned wires 30, each of which has a cross-section in the form of a trapezium, such that the gap between ⁵ adjacent wires widens as the fluid (represented by wavy arrows) flows therethrough, such that the narrowest portion of the gap is approximately 0.007 inches (0.01778 cm) wide but the spacing is selected according to the size of the particles of the abrasive medium. It can be seen from Figs. 2 and 3 that a plurality of reinforcing wires 32 extend across the screen 28.

In use, the filter portion is placed within the exit conduit 22, and the wedge wire filter screen and in this position the wedge wire filter^' screen 28 extends approximately down to the drum 10 such that the screen partially surrounds the end agitator disc 16a. Thus, the screen 28 conforms approximately to the shape of the portion of the drum which has been removed to allow the positioning of the exit conduit 22. The position of the filter portion 24 within the exit conduit 22 is dictated by co-operating peripheral flanges 34, 36 respectively, which limit the degree of entry of the filter portion 24 into the exit conduit 22. A rectangular cover 38 having an exit pipe 40 is placed on top of the filter portion 24, and the cover 38 and filter po tion 24 are secured to the exit conduit by means of bolts 42 passing through aligned holes in the cover and in the flanges of the filter portion and exit conduit. In practice, gaskets are inserted between the cover and the flange 34, and between the flange 34 and the flange 36 to provide a fluid-tight seal, but these have been omitted from the drawings for the sake of clarity.

The liquid to be treated, e.g. dyestuff, is fed Into the bead mill via the inlet 10, and the shaft 14 and discs 16 thereon are rotated by activating the drive means. The rotation of the actuating disc causes the beads and the liquid to be intimately mixed, and the abrasive nature of the beads breaks down the particles suspended in the liquid into smaller particles.

The treated liquid is passed, by means of pressure on the liquid, through the wedge wire filter screen 28, thereby removing glass beads and large, unwanted particles from the treated liquid. Any liquid passing out -of the outlet pipe 40 must necessarily first pass through the filter screen 28.

It can be seen from Fig. 1 that the end disc 16a is situated directly beneath, and concentrically with, the arcuate wedge wire filter screen 28, and that the wedge wire screen partially surrounds the end agitator disc 16a. The close proximity of the rotating disc to the filter results in less clogging of the filter, due to the scouring action of the disc 16a, thereby reducing the frequency with which the filter must be inspected, cleaned and replaced. Also, the arcuate • filter screen is aligned with the curved drum 10, as best seen in Fig. 2, and the distance between the tip of the end disc 16a to the filter screen is the same (to about 1cm) as the distace between the other discs and the interior surface of the drum.

When it becomes necessary to remove the filter , the mill is drained of liquid as much as possible and the shaft is stopped. The bolts 42 and the cover 40 are removed and the filter portion 24 may be lifted out using the bars 29. The filter is much smaller than those presently used, and is easily removable and replaceable by one man. The wear rate is substantially improved, and therefore the useful life of the sieve is greatly extended. Since no complicated assembly is required, the task may be performed by an unskilled person and need not be carried out by a trained fitter.

Claims

C LA IMS

1. An abrasive medium mill comprising a drum (10) for housing an abrasive medium (12), a plurality of agitators (16) for agitating the medium, an outlet (20) from the drum and a filter (28) through which the outlet communicates with the interior of the drum, characterised in that the filter (28) at least partially surrounds an agitator (16).

2. A mill as claimed in claim 1, wherein the filter (28) is arcuate.

3. A mill as claimed in claim 2, wherein the drum (10) is cylindrical, the radius of curvature of the filter (28) ^'being substantially identical to that of the drum (10).

4. A mill as claimed in any of the preceding claims, wherein the filter (28) is positioned generally above the agitator (16) which it partially surrounds.

5. A mill as claimed in claim 4, wherein the filter (28) is positioned above the level of the abrasive medium (18) in the drum (10).

6. A mill as claimed in any of the preceding claims, wherein the mill comprises a rotatable shaft (14) positioned within the drum (10) and the agitators (16) comprise discs mounted on the shaft.

7. A mill as claimed in any of the preceding claims, wherein the filter (28) is releasably securable in a conduit (22) communicating with the interior of the d r um .

8. A mill as claimed in claim 7, wherein the filter (28) is positioned across one end of a tube or pipe (24) which is shaped to fit within the conduit (22).

9. A mill as claimed in any of the preceding claims, wherein the filter (28) is in the form of a screen comprising a plurality of aligned wires (30).

10. A mill as claimed in claim 9, wherein the aligned wires (30) comprise wedge wires.

11. A mill as claimed in any of the preceding claims, wherein the abrasive medium (18) comprises beads .

12. A mill as claimed in any of the preceding claims, wherein the abrasive medium (18) comprises sand.

13. A filter assembly (20) for use in an abrasive medium mill, characterised by a first conduit (22) which communicates with the interior of the mill and extends upwardly from the mill and a second conduit (24) shaped to fit within the first conduit and having a filter medium (28) across one end, whereby when the second conduit (24) is positioned within the first conduit (22), material emerging from the bead mill is filtered through the filter (28) .

14. An assembly as claimed in claim 13, wherein the first conduit (22) extends substantially vertically upwardly from the mill.

15. An assembly as claimed in claim 13 or claim

14, wherein the filter (28) is arcuate.

16. An assembly as claimed in any of claims 13 to

15, wherein the first and second conduits (22, 24) are rectangular in cross section.

17. An assembly as claimed in any of claims 13 to

16, wherein the filter (28) is in the form of a screen comprising a plurality of aligned wires (30).

18. An assembly as claimed in claim 17, wherein the aligned wires (30) comprise wedge wires.

19. An assembly as claimed in any of claims 13 to 18, wherein the filter (28) is shaped to partially surround an agitator (16) in the mill when the filter (28) is in the position on the mill.