GB2237222A - Bladed centrifugal pulveriser with rotatable feeder - Google Patents

Abstract

The pulveriser comprises a first (eg stator) disc 1, Figs 4 & 1 presenting on a main face thereof a plurality of concentric annular vanes 2, a second disc 4, Figs 6 & 1 presenting blading 8 on a main face thereof and disposed in spaced, coaxial relationship with the first disc so that the vanes of the first disc extend into notches 3, Fig 6 in the blading of the second disc whereby the said blading is intermeshed with the said vanes, and power means for causing relative rotation between the first and second discs about the axis of the discs, slots 7 Fig 4 being provided across the edges of the vanes facing the second disc, and an inlet aperture in at least one of the discs for the admission therethrough of material eg cellulose fibre material to be pulverised, and a rotatably mounted feeder 6, Fig 1 for feeding the material to be pulverised into the inlet aperture. <IMAGE>

Description

IMPROVEMENTS IN AND RELATING TO PULVERISERS This invention relates to pulverisers for wood products and other materials such as newsprint, wood fibres, hay and bark which are herein generally referred to as cellulose fibre materials and may be used as insulating and petroleum absorbent materials.

In my Canadian Patent No. 1045101, which is hereby incorporated in its entirety by reference, there is described and claimed a centrifugal pulveriser comprising a first disc presenting on a main face thereof a pluality of concentric annular vanes, a second disc presenting blading on a main face thereof, the first and second discs being disposed in spaced, substantially parallel, coaxial relationship with the vanes of the first disc extending into notches in the blading of the second disc whereby said blading is intermeshed with said vanes, and power means for causing relative rotation between the first and second discs about the axes of the discs, slots being provided across the edges of the vanes adjacent the second disc, and an axial aperture being provided in one of the discs for the admission therethrough of material to be pulverised.

In the pulveriser described in my Canadian Patent No. 1045101, the slots in the vanes are preferably so orientated relative to the blading of the impeller that, in use, a predominantly shearing action is created at the entrances and exists of the slots. The pedominant shearing action of my pulveriser contrasts markedly with other proposed pulverising and grinding machines which rely principally upon an impaction action or pulverising.

The pulveriser described in my Canadian Patent 1045101 permits continuous operation and, since interchangeable discs may be used together with a facility for adjusting the axial clearance between the discs, not only is the pulveriser suitable for use with a wide range of different materials but also permits a wide ranging control of final product specification including dimensional control of the pulverised material.

Conditions occurring at the inlet of the pulveriser are dependent upon various characteristics of the material including the particular size of the feed material, its moisture content, air borne density, air flow characteristics, circumferential feeding patterns as well as the radial and tangential components of velocity of the incoming feed material. Uncontrolled variations in the various characteristics mentioned may seriously impair the correct functioning of the pulveriser and lead to possible choking of the pulveriser. Such impairment may lead to over heating, loss of product, inconsistent final product specification or otherwise pulveriser malfunction. In the pulveriser according to Canadian Patent No. 1045101 the radially outermost blades of the impeller, that is, the second disc, create suction within the pulveriser.

Such suction has, however, been found in practice to be easily nullified if the inlet becomes blocked causing over heating and possibLe seizure of the pulveriser.

I have now found that operation by my pulveriser as described above is improved by additionally controlling the establishment of steady conditions existing during pulverisation of material. Further investigations have shown me that these steady conditions may be established and sustained by controlling those conditions prevailing at the inlet to the pulveriser.

Materials which may be satisfactorily ground in my pulveriser include not simply cellulose fibre materals such as wood products and paper but also tea, tobacco stalks, roots, vegetables, foam rubber and expanded polystyrene and other materials not normally susceptible to impact fracture.

Any impairment of the operation of a centrifugal pulveriser according to the present invention is at least reduced by admitting into the pulveriser, material to which at least a pre-rotational velocity component has been applied so as to assist introduction of the material into inlet spaces existing between adjacent blades of a rotating impeller.

The pre-rotational velocity component may be applied to the incoming material to the pulveriser by a rotably mounted feeder positioned in the region of the inlet to the pulveriser. Thus, according to the invention, a centrifugal pulveriser comprises a first disc presenting on a main face thereof a plurality of concentric annular vanes, a second disc presenting blading on a main face thereof and disposed in spaced coaxial relationship with the first disc so that the vanes of the first disc extend into notches in the blading of the second disc whereby the said blading is intermeshed with the said vanes, and power means for causing relative rotation between the first and second discs about the axis of the discs, slots being provided across the edges of the vanes facing the second disc, and an inlet aperture in at least one of the discs for the admission therethrough of material to be pulverised, characterised in that the pulveriser includes a rotatably mounted feeder for feeding the material to be pulverised in to the inlet aperture. Preferably, the feeder comprises a rotor including a plurality of vanes shaped to impart angular motion and, consequently, a velocity component to the material at least upon entry into the impeller. Conveniently, the rotor and vanes of the feeder are together shaped to impart radial, angular and axial motion to the material as it is fed between the discs of the pulveriser.

The function of the rotatable feeder, thus, produces a swirling motion to the material as it is fed into the pulveriser and may be regarded as a turbo prerotator which is driven in the same direction of rotation as the impeller of the pulveriser. The feeder may be driven either dependently or independently of the pulveriser per se. An independent drive is preferred in order to control a continuous or intermittent feed as required and dependent upon the nature of the cellulose fibre material to be pulverised as well as the desired characteristics of the final product.

The turbo pre-rotator serves to: i) induce and assist in maintaining air-flow and pressure at the inlet of the pulveriser; ii) impart a pre-rotational angular motion to the incoming feed material thereby reducing inlet shock conditions; iii) centrifugally feed the material as uniformly as possible around the circumferential region of the pulveriser inlet and thereby assist in the achievement of a steady state of inflowing material as rapidly as possible, and iv) improve fluidisation of the feed material when it is delivered directly into the initial stage of pulverisation away from the eyes of both the first and second discs which may be regarded as a stator and rotor respectively.

As indicated above, the centrifugal pulveriser described in my Canadian Patent No. 1045101 pulverises the feed material by impaction during passage of the material through a maze of vanes and annular blades situated on the rotor and stator respectively.

The consistency of the finished product depends upon the geometries of the inter-stage phases of the pulveriser presented to the material. These geometries are also dependent upon the speed of rotation of the rotor.

By modifying the profiles of the rotor, the resistance presented to the material to be pulverised may be varied between the extremes of 'high' or 'low' so as to obtain 'very rough' or 'very fine' cuts from a given feed. Preferably, the rotor and its associated stator profiles, are such as to permit a predominance of pulverisation by shearing action to occur at a particular energy level within the pulveriser; or in a particular sequential order. Such effects are desirable when localised temperature or moisture controls are essential to effect satisfactory pulverisation of plastics, rubbers, cardboard, newsprint etc.

According to a further aspect of my invention, I have found that by forming concentric and varying profiles and protrusions on the rotor blades with compatible complementary annular vanes on the stator, special effects can be produced during the pulverisation of the feed material. These profiles serve to direct the feed material into (or away from) predictable energy level regions within the pulveriser.

When considered in cross-section, the rotor may be formed to present a generally frusto-conically convex or concave arrangement of blades to the stator. If desired, according to the material to be pulverised as welt as the nature and degree of pulverisation required, the rotor may present a part conical, part convex and part planar blade carrying surface to the stator vanes.

The cross-section of the rotor blades may also be varied as hereinafter described.

The invention will no be described by way of example, with reference to the accompanying drawings in which: Figure 1 shows, schematically and in cross-section, a pulveriser according to the present invention; Figure 2 is a plan of the pulveriser shown in Figure 1; Figures 3A and 3F show six different second disc or rotor profiles for use with the pulveriser shown in Figures 1 and 2; Figures 4 and 5 show in plan and cross-section a first disc or stator of the pulveriser of Figures 1 and 2; Figure 6 shows the rotor of Figure 3A in plan, and Figure 7 shows the pulveriser mounted in a volute casing.

Referring to the drawings, the pulveriser has a volute casing C divided into two components A and B with inlet and outlet apertures indicated by arrows I and 0 respectively. A circular first disc (stator) 1 having on a main surface thereof a plurality of concentric vanes 2 is secured to the casing component A and the concentric vanes 2 have slots 3 cut across their free edges as shown in Figures 1, 4 and 5. A rotor 4 having concentric blades 8 is driven via a driving shaft 5 passing through the casing component B and is supported in bearings not shown. A pre-rotator 6 is centraLLy and coaxially supported relative to the concentric vanes 2 and blades 8 as well as the driving shaft 5. A thrust bearing 7 disposed between the pre-rotator 6 and the stator 1 serves to transmit thrust caused by incoming feed material to the volute casing C via the stator 1.

The pre-rotator 6 is generally cylindrcal having an outer shell 6A, an inner cone 68 and blades 6C. The inner cone 68 and the blades 6C together serve to impart axial, radial and angular components of motion to incoming feed material when it is fed from the prerotator 6 to the rotor 4. The pre-rotator 6 is driven from an electric motor M supported on casing component A via a spur gear 9 which is in engagement with gear teeth 11 cut on a flange formed on the outer shell 6A. Two freely rotatable stabilising pinions 12 in mesh with the gear teeth 11, serve to stabilise the pre-rotator 6.

Figures 3A to 3F show various forms of rotor and, although not illustrated an imaginary line joining the apices of the blades is reflected in the cross-sectional root shape of the stator 1 and from which the vanes 2 concentrically extend.

Reference has previously been made to driving the pre-rotator 6 by an electric motor M supported on the casing component A. Alternatively, the rotor driving shaft 5 may be tubular and an internal coaxial driving shaft may be used to drive the pre-rotator 6. In such an embodiment a single power-source may be used via appropriate drive-lines to drive both the rotor 4 and the pre-rotator 6.

Claims (7)

1. A centrifugal pulveriser comprising a first disc presenting on a main face thereof a plurality of concentric annular vanes, a second disc presenting blading on a main face thereof and disposed in spaced, coaxial relationship with the first disc so that the vanes of the first disc extend into notches in the blading of the second disc whereby the said blading is intermeshed with he said vanes, and power means for causing relative rotation between the first and second discs about the axis of te discs, slots being provided across the edges of the vanes facing the second disc, and an inlet aperture in at least one of the discs for the admission therethrough of material to be pulverised, characterised in that the pulveriser includes a rotably mounted feeder for feeding the material to be pulverised into the inlet aperture.

2. A pulveriser according to claim 1 characterised in that the feeder comprises a rotor including a plurality of vanes shaped to ;mpart angular motion to the material at least upon entry into the inlet aperture.

3. A pulveriser according to claim 1 or claim 2 characterised in that the vanes of the feeder are shaped to induce positive air-flow and pressure in the inlet aperture.

4. A pulveriser according to any preceding cLaim characterised in that the feeder extends into the inlet aperture.

5. A pulveriser according to claim 4 characterised in that the feeder includes an annular outlet for directing material to be pulverised into arcuately extending spaces between the vanes and blades of the first and second discs respectively.

6. A pulveriser according to any preceding claim characterised in that the vanes and blades of the respective first and second discs are divided into two or more concentric stages.

7. A pulveriser according to claim 6 characterised in that the vanes and the blades have different profiles in different stages.