GB2331941A

GB2331941A - Mixing machine

Info

Publication number: GB2331941A
Application number: GB9815584A
Authority: GB
Inventors: Geoffrey Ashley Greenwood
Original assignee: COCKSEDGE ENG Ltd
Current assignee: COCKSEDGE ENG Ltd
Priority date: 1997-07-23
Filing date: 1998-07-20
Publication date: 1999-06-09
Also published as: GB9715410D0; GB9815584D0; GB2331941A9

Abstract

A mixing machine, especially for liquids, in which the material to be mixed is fed under pressure between two relatively rotatable abrasive elements (24, 26), one having a central aperture to enable the material to be worked upon in a gap (41A, 41 B) between the two elements, the size of said gap diminishing from the central aperture to the periphery of the elements from which the mixed material emerges.

Description

2331941 Mixing Machine This invention relates to a mixing machine. The

machine is especially although not exclusively intended for mixing materials which are at least predominantly liquids, and the term "mi)ijng" includes homogenising and, in the case of some possible materials, liquidising.

According to the invention, there is provided a mixing machine comprising, within a region of the machine through which material is fed under pressure, two relatively rotatable elements at least one of which has an abrasive surface, one said element having a central feed aperture to enable material to be worked upon to be fed into a gap between the two relatively rotatable elements, said gap being greater in the central region of the elements around the feed aperture than at the g- peripheries of said elements.

The two relatively rotatable elements are preferably a matching disc and annulus and while for some applications only one of these elements may possess an abrasive surface, in general both elements will preferably possess abrasive surfaces, facing each other across the gap between the two elements. These abrasive surfaces may be provided by layers applied to the surfaces of the two elements, but preferably both elements are made of a solid grinding material such as carborundum.

Preferably, one element is held stationary and the other driven in rotation. If only one element has an abrasive surface, it is this element which will be rotatably driven. The element driven in rotation will preferably be the disc, the annulus having the feed aperture being held stationary.

Thus, in a preferred arrangement, the machine has a vertical axis about which the abrasive disc is driven in rotation below the stationary abrasive annulus having the feed aperture. The output shaft of an electric motor may drive the abrasive disc from below, while an impeller, preferably driven by the same motor output shaft, may be mounted at the bottom of an inlet above the said aperture in the annulus, through which material is driven down into the gap between the two elements, in order for said material to be mixed as it is driven radially outwards by centrifugal action to emerge at the periphery of the gap.

The abrasive elements are therefore preferably housed within a collecting chamber having a bottom surface inclined downwards towards an outlet, at which the mixed material emerges from the machine.

Means are preferably provided for adjustment of the width of the gap between the two relatively rotatable elements, in order to suit different applications of the machine. Preferably, the gap between the two elements is uniform radially outwards of a central narrowing zone around the feed aperture. Typically, this uniform gap region may be adjustable from zero up to about 0.4 mm.

Means such as an inverter are also preferably provided for adjustment of the speed of the electric drive motor. From the motor, the output shaft preferably extends vertically upwards to the disc drivable in rotation, passing through bearings and a liquid seal immediately below the rotatably driven disc.

Preferably, in order to pressurize the material to be mixed, it is delivered to the machine inlet by a pump, and the outlet from the machine includes a restrictive control valve lin-dting the rate of delivery of the mixed material(s). The material is thus subject to back pressure within the region of the machine between the inlet and the outlet in which the aforesaid two relatively rotatable elements are located. The control valve is preferably adjustable, and possibly can be shut, to enable the back pressure to be varied. The region of the machine where the material(s) is i pressurized is both pressure resistant and sealed.

The described pressurization of the material minimises aeration and possible foaming.

In view of the pressurization, leakage of material through the aforesaid seal and bearings immediately below the rotatably driven disc is preferably prevented by use of two pairs of seals in tandem. These may be separated by a chamber with which connects a leakage pipe leading to the exterior of the machine. The operator is thereby warned, by evidence of exit of material at the leakage pipe, that at least the first (upper) pair of seals, subject to the greater pressure, require replacement. Alterenatively, two sealing units having an internal water purge on the seal running faces may be employed, in which case a leakage pipe may be unnecessary.

The bearings on the remote side of the seals from the relatively rotatable elements preferably comprise back-to-back angled contact ballraces.

Two embodiments of mixing machine in acordance with the invention are now further described with reference to the accompanying drawings, in which: Figure 1 is a perspective view of the machine; Figure 2 shows the machine interior; Figure 3 shows the scaling and bearing assembly in detail; and Figure 4 shows the interior, including the sealing and bearing assembly, of the modified machine.

The machine shown in Figure 1 is an industrial mixer, typically standing about 1 m high. It has a base flange by which it can be bolted down.

Referring also to Figure 2, the machine has a lower housing 10 accommodating an electric motor 12, start/stop switch 14, speed sensor 16, speed controller 18, and digital speed indicator 20. The speed control 18 is operative through an external inverter 13.

The machine also has an upper, circular, sealed and pressure-resistant housing 22, bolted to the lower housing 10. This upper housing 22 accommodates two relatively rotatable abrasive elements 24, 26, preferably solid abrasive elements of carborundum, of a grade suited to the application of the machine.

A motor output shaft 28 extends vertically upwards from the lower housing 10 into the upper housing 22, whereby to drive the lower abrasive element, abrasive disc 24, in rotation. The upper abrasive element, abrasive annulus 26, is held fixed against rotation by carrier 30, but the latter can be adjusted in position axially, by use of gap adjusting handle 32, gap indicator scale 34 and a lock nut 36. The gap is observable through window 37.

The annular form of upper abrasive element 26 provides a feed aperture 38 through which material under pressure, generally material of liquid form, to be mixed can be pumped downwardly through an infeed 39 into a gap between the two abrasive elements 24, 26. Within the entire upper housing 22, the material to be mixed is under pressure.

It is to be observed that the (,rap between the two abrasive elements has an inner zone 41A around the feed aperture 38 at which said gap narrows in the radial outwards direction to an outer zone 41B of uniform gap size. By means of the aforesaid gap adjustment means 32, 34, 36, the size of the uniform zone of the 0 1 i gap may be adjustable from zero up to about 0.4 mm, to suit different applications of the machine. compensation for wear.

The gap adjustment means also enables Material forced under pressure into the gap at the feed aperture is spun outwardly by centrifugal action through the narrowing inner gap zone 41A into the uniform outer gap zone 41B to ernere at the periphery of the gap. In use, a thorough mixing or homogenising action, and in some cases a liquidising action, takes place as the material is ground, abraded and swirled round between the two relatively rotating abrasive elements 24, 26. A typical speed of relative rotation may be up to 2600 r.p.m. Pumping the material through the abrading elements 24, 26 under pressure minimises aeration and possible foaming.

As the mixed material has to be collected on emergence from the periphery of the gap 41A, 4113, the two relatively rotatable abrasive elements 24, 26 are housed within a collecting chamber 42 forming part of the upper housing 22. This chamber 42 has a sloping base 44 leading to an outlet passage 46. Where the motor output shaft 28 extends upwardly through the base of the collecting chamber 42, a sealed bearing assembly 48 is provided, immediately below a carrier 50 for the lower rotatable abrasive element 24. Clamping of the carrier 50 and element 24 to the output shaft 28 is effected by lock nuts 52.

As already indicated, mixing takes place within a pressurized region of the machine. Pressurization is created by a back pressure generated between a pump 60 which delivers the material to be mixed to the infeed 39 and an adjustable flow-restrictive valve 62 provided in a delivery pipe 64 connected to the machine outlet passage 46.

The sealing bearing assembly 48, shown in detail in Figure 3. is thus important for preventing leakage of material.

This bearing assembly 48 thus includes two pairs of annular seals 66, 66A and 68, 68A in tandem, above a bearing which consists of back-to-back angled contact ball races 70, 70A. Between the pairs of seals 66, 66A and 68, 68A an annular chamber 72 is provided, with which communicates a leakage pipe 74 leading to the exterior of the machine.

In use, the leading pair of seals 66, 66A are subject to the greater pressure and more likely to wear, and the operator is warned that these seals need replacement by evidence of material appearing at the exit of the leakage pipe 74.

One principal application of the machine is the homogenisation of a chemical mixture to be used for the coating of de-husked sugar beet seed. For this purpose, a gap of about 0.03 to 0.05 mm between the abrasive elements 24, 26 will usually be appropriate. However, the machine may alternatively be applied to such applications as the manufacture of tomato puree or mustard paste, in which cases a larger gap will generally be appropriate. In the last-mentioned applications, an amount of liquidisation will take place, in addition to mixing and homogenisation.

Figure 4 shows the interior of a modified machine. Here, instead of the sealing and bearing assembly of Figure 3, a sealing and bearing assembly generally referenced 76 is employed. This assembly incorporates two sealing units 78, 80 above the ball race bearing 70, 70A, which is the same as that shown in Figure 3.

The two sealing units 78, 80 have an internal water purge on the seal running faces, the water inlet being indicated at 82 and the water outlet at 84.

Additionally, the upper sealing unit 78 has fluorocarbon/silicon antiabrasive seal facings. The use of these two sealing units 78, 80 obviates the need for the leakage pipe 74 of Figure 3.

1 The sealing units 78, 80 are of greater wdal length than the tandem seals of Figure 3, so that the ball race bearing 70, 70A is relatively lower down within the machine. For this reason, an additional bearing 86 for the shaft 28 is introduced to increase the stability of the shaft. This bottom bearing 86 is located just above an adaptor 88 for the drive motor 12, which also occupies a position lower in the machine housing than the motor in Figure 2.

Additionally, an overpressure switch may be incorporated, for example in the top wall of the sealed housing 22.

Claims

1. A mixing machine comprising, within a region of the machine through which material is fed under pressure, two relatively rotatable elements at least one of which has an abrasive surface. one said element having a central feed aperture to enable material to be worked upon to be fed into a gap between the two relatively rotatable elements, said gap being greater in the central region of the elements around the feed aperture than at the peripheries of said elements.

2 A nii)dng machine according to claim 1, wherein the two relatively rotatable elements are a matching disc and annulus.

3. A mixing machine according to claim 2, wherein at least one of said disc and annulus has an abrasive surface facing the other element.

4. A mixing machine according to claim 3, wherein the facing surfaces of both the disc and the annulus are abrasive.

5. A mixing machine according to claim 4, wherein both elements are made of a grinding material.

6. A mixing machine according to claim 5, wherein the grinding material is carborundum.

7. A mixing machine according to any of claims 1 to 6, wherein one element is fixed and the other rotatable.

8. A mixing machine according to claim 7 when appendant to claim 2, wherein the stationary element is the annulus, which has the feed aperture, and the I 1 element driven in rotation is the disc.

9. A mixing machine according to claim 8, wherein the axis of the machine is vertical and the abrasive disc is driven in rotation below the stationary abrasive annulus having the feed aperture.

10. A mixing machine according to claim 9, wherein the abrasive disc is driven from below by the output shaft of an electric motor.

11. A mixing machine according to claim 10, wherein the output shaft of the motor also drives an impeller mounted at the bottom of an inlet above the said aperture in the annulus, through which material is driven down into the gap between the two elements, in order for said material to be mixed as it is driven radially outwards by centrifugal action to emerge at the periphery of the gap.

121. A mixing machine according to any of claims 1 to 11, wherein the abrasive elements are housed within a collecting chamber having a bottom surface inclined downwards towards an outlet, at which the mixed material emerges from the machine.

13. A mixing machine according to any of claims 1 to 12, wherein means are provided for adjustment of the width of the gap between the two relatively rotatable elements, in order to suit difierent applications of the machine.

14. A mixing machine according to claim 13, wherein the n-p between the two elements is uniform radially outwards of a central narrowing zone around the feed aperture.

15- A mixing machine according to claim 14, wherein the uniform cap region is adjustable from zero up to substantially 0.4 mm.

16. A mixing machine according to any of claims 10 to 15, having means for adjusting the speed of the drive motor.

17. A mixing machine according to any of claims 10 to 16, wherein the output shaft of the motor extends vertically upwards to the disc drivable in rotation, passing through bearings surmounted by a liquid seal immediately below the rotatably driven disc.

18. A mixing machine according to any of claims 1 to 17. having means for adjustment of the speed of the motor.

19. A mixing machine according to any of claims 1 to 18, wherein, in order to pressurize the material to be mixed, it is delivered to the machine inlet by a pump, and the outlet from the machine includes a restrictive control valve limiting the rate of delivery of the mixed material(s).

20. A mixing machine substantially as hereinbefore described with reference to the accompanying drawings.

20. A mixing machine according to claim 19, wherein the control valve is adjustable to vary the applied pressure.

21. A mixing machine according to claim 19 or claim 20, wherein the pressurized region of the machine is both pressure resistant and sealed.

221. A mixing machine substantially as hereinbefore described with reference to the accompanying drawings.

i 1 i Amendments to the claims have been filed as follows 1. A mixing machine comprising, within a sealed, pressure resistant region of the machine established between a machine inlet through which material to be mixed is fed into the machine and a machine outlet from which mixed material is delivered from the machine and through which region the material to be mixed is fed under pressure, two relatively rotatable elements at least one of which has an abrasive surface, one said element having a central feed aperture to enable the material to be mixed to be fed into a gap between the two relatively rotatable elements which is greater in the central region of the elements around the feed aperture than at the peripheries of said elements, the mixed material emergent from between the element peripheries passing to the machine outlet, wherein the sealed pressure resistant region of the machine is established between a pump for delivering the material to be mixed through the machine inlet and a restrictive control valve for limiting the rate of delivery of the mixed material through the CP machine outlet.

2. A mixing machine according to claim 1, wherein the control valve is adjustable to vary the applied pressure.

3. A mixing machine according to claim 1 or claim 2, wherein the two relatively rotatable elements are a matching disc and annulus.

4. A mixing machine according to claim 3, wherein at least one of said disc and annulus has an abrasive surface facing the other element.

5. A mixing machine according to claim 3, wherein the facina surfaces of both t> 0 the disc and the annulus are abrasive.

1 t 6. A mixing machine according to claim 5, wherein both elements are made of a grinding material.

7. A mixing machine according to claim 6, wherein the grinding material is carborundum.

8. A mixing machine according to any of claims 1 to 7, wherein one element is fixed and the other rotatable.

9. A mixing machine according to claim 8 when appendant to claim 3, wherein the stationary element is the annulus, which has the feed aperture, and the element driven in rotation is the disc.

10. A mixing machine according to claim 9, wherein the axis of the machine 0 is vertical and the abrasive disc is driven in rotation below the stationary abrasive annulus having the feed aperture.

11. A mixing machine according to claim 10, wherein the abrasive disc is driven from below by the output shaft of an electric motor.

12. A mixing machine according to claim 11, wherein the output shaft of the Z' motor also drives an impeller mounted at the bottom of an inlet above the said aperture in the annulus, through which material is driven down into the gap between the two elements, in order for said material to be mixed as it is driven radially outwards by centrifugal action to emerge at the periphery of the gap.

13. A mixing machine according to any of claims 1 to 12, wherein the abrasive elements are housed within a collecting chamber having a bottom surface inclined downwards towards an outlet, at which the mixed material emerges from the machine.

1 14. A mixing machine according to any of claims 1 to 13, wherein means are provided for adjustment of the width of the gap between the two relatively rotatable elements, in order to suit different applications of the machine.

15. A n-dxing machine according to claim 14, wherein the gap between the two elements is uniform radially outwards of a central narrowing zone around the feed aperture.

16. A mixing machine according to claim 15, wherein the uniform gap region is adjustable from zero up to substantially 0.4 mm.

17. A mixing machine according to any of claims 11 to 16, having means for adjusting the speed of the drive motor.

18. A mixing machine according to any of claims 11 to 17, wherein the output shaft of the motor extends vertically upwards to the disc drivable in rotation, passing through bearings surmounted by a liquid seal immediately below the rotatably driven disc.

19. A mixing machine according to any of claims 1 to 18, having means for t> adjustment of the speed of the motor.