GB2081382A - Fans provided with cutting knives - Google Patents

Abstract

A fan includes a screen 40 which divides a housing outlet 27 into two parts, so that oversize material chopped by cutting knives 13 on the blades 12 of an impeller 10, is separated from small chopped material and can be returned to the housing inlet 25. Chopped material can be kept away from a rotary bearing 30 carrying the impeller 10 by providing blades 16 to draw air away from the bearing or by designing the bearing as a forced air bearing. Large agglomerates in the inlet 25 and resting against the blades 12 can be stirred by pins mounted on the impeller plate 11 or by arranging for two of the blades 12 to project further towards the inlet 25 than do the other four blades 12. <IMAGE>

Description

SPECIFICATION Chopper fan This invention relates to a chopper fan especially, although not exclusively, to a chopper fan for cutting plastics flash material, recovered from an automatic record press, into smaller pieces suitable for recycling.

Chopper fans are known, see for example British Patent 1,167,338, but these suffer from the disadvantage that the output material thereof may be of widely varying dimensions and may be too large for subsequent reuse.

According to one aspect of the present invention, there is provided a chopper fan, comprising housing means having inlet means for receiving material for chopping, and an impellar rotatably mounted within the housing means at a location appropriate for drawing material through the inlet means and including blades arranged to chop said material, said housing means including filtering means for intercepting chopped material exceeding a predetermined size and for directing such material to first outlet means of said housing means, any material which passes through said filtering means being directed towards second outlet means of said housing means.

According to another aspect of the present invention, there is provided a chopper fan, comprising housing means having inlet means for receiving material for chopping and outlet means for chopped material, and an impeller rotatably mounted within the housing means at a location appropriate for drawing material through the inlet means and including blades arranged to chop said material, and protruding means of said impeller arranged to stir any large agglomerates of said material in said inlet means and bearing against said blades.

According to a further aspect of the present invention, there is provided a chopper fan, comprising housing means having inlet means for receiving material for chopping and outlet means for chopped material, an impeller rotatably mounted within the housing means at a location appropriate for drawing material through the inlet means and including blades arranged to chop said material, a bearing whereby said impeller is rotatably mounted within said housing means, and means for producing a gaseous flow tending to keep said material away from said bearing.

In order that the invention may be more readily understood and carried into effect embodiments thereof are now described, by way of example only, by reference to the accompanying drawings, in which Figure 1 shows an exploded view of a chopper fan, Figure 2 shows a front view of an impeller of the fan, Figures 3a and 3b show respective side and perspective views of the housing of the fan, and Figure 4 shows a side elevation of a modified version of the impeller.

Referring to the exploded view of Figure 1, the fan comprises an impeller 10 mounted for rotation in a housing 20, shown in broken outline.

The housing comprises respective front and back plates 21 and 22 which are spaced by an intervening wall member 23, and this construction is shown more clearly in Figure 3b which illustrates the rear view of the housing looking towards plate 22.

As shown in Figure 1, the front plate 21 includes a circular inlet port 24 (of 17.25" minimum internal diameter in this example) having an inwardly projecting funnel 25 and whose extreme inner edge acts as a static, annular cutting blade. The housing also has an outlet port 27.

The impeller 10, which is also shown in the front view of Figure 2, comprises a circular radial plate 11 supporting a plurality of upstanding, symmetrically spaced planar radial blades 12; in this example six blades are used. The impeller is mounted for rotation by a rotary bearing 30 shown in Figure 1,so that the upstanding blades 12 face the inlet port 24 and, on rotation of the impeller, can act to draw material into the housing 20 for chopping. Each blade 12 includes a flat, cutting knife 13 securely attached to the edge thereof facing the inlet. The impeller 10 is supported within the housing so that the knives 13 lie in a common plane parallel to, but offset from, the plane of the static cutting edge so that during rotation of the impeller each knife co-operates with the static blade to slice through interposed material in a scissor-like cutting action.

The spacing between the knives and the static cutting edge may be chosen to suit a particular application, a relatively large spacing being chosen for use with relatively bulky material. In this example of the invention the axis of the funnel 25 is slightly offset from the axis of the impeller so that during each rotation thereof each knife 13 engages the static cutting edge along a substantial portion of the length of the knife. This arrangement serves to reduce wear of the cutting surfaces and results in a more effective cutting action.

In operation of the fan, material drawn into the housing by the action ofthe impeller 10 is thrown radially outwards and is chopped into relatively smaller pieces in the above-described manner. The impeller which typically rotates at about 1,500 r.p.m.

induces an air flow, in the same sense as the rotation, in the region between the wall 23 of the housing and the surface defined by the extreme edges E of the blades 12, the housing being shaped to direct chopped material towards the outlet 27. As shown in the side and perspective views of Figures 3a and 3b respectively the spacing between the wall 23 and the said surface (represented by the dashed line E in Figure 3) increases smoothly as the outlet is approached.

A problem encountered with an arrangement of the kind described thus far is that some material emitted at the outlet may have been insufficiently chopped by the cutting blades and may be unsuitable for further use. Therefore, a filter 40 in the form of a curved screen is located within the housing and extends between the opposed front and back plates 21 and 22. The position of the filter is indicated by the dot-dash line F in Figures 3a and 3b and it serves to intercept substantially all material exceeding a predetermined size governed by the mesh size of the filter. In this case a mesh size of 1/4" in diameter or alternately 1/4" square is used which is sufficient to intercept material of up to about 3/16" maximum dimension.As shown in Figures 1 and 3b the screen 40 is positioned within the housing to divide the outlet into two parts, OP1 and OP2, and extends into the housing, suspended between the opposed plates 21 and 22, to meet the wall 23 at a point P. Figure 3a is a reduced scale drawing, and shows the position of the filter 40 within the housing 20. Material conveyed towards the outlet by the induced airflow is intercepted by the screen if it exceeds a predetermined size and is directed towards one part OP1 of the outlet. Material passing through the screen, however, is directed to a separate part OP2 of the outlet for collection. The material directed to part OP1 of the outlet may be collected for disposal; alternatively, however, in another embodiment, this material may be conveyed by a duct (not shown in the drawings) back to the inlet for recycling through the fan.

At the middle of the plate 11 among the blades 13 are boss portions 14 of a convex shape (e.g. a frusto-conical shape) as shown in Figure 2. This shaping tends to increase the radial outward airflow on rotation of the fan and, moreover, the boss portions reinforce the blades to deter bending of the blades. It has also been found that agglomerates of the material in the inlet may simply bear against the blades 12 without being chopped by them. This can be mitigated by the use of bolts or pins 15, upstanding from the surface of the plate 11, which serve to stir and thus promote chopping of the agglomerates. This arrangement involves a risk that the bolts or pins 15 may break off and damage the fan. To avoid this risk and still achieve a stirring of the agglomerates, one or more, in this case two of the blades 12 can project further towards the inlet than do the other blades 12. This is illustrated in Figure 4, where the knives 1 3a of the diametrically opposed blades 12a (of which only one is seen) protrude about " forwards beyond the knives 13 of the other four blades 12.

It is also found in operation that the rotary bearing 30 may become fouled by the presence of chopped material which migrates to behind the impeller. This problem has been mitigated in one embodiment of the invention by the use of a forced air bearing as the bearing 30, the air emitted in operation of the bearing serving to deflect the material from the vicinity thereof. Aiternatively, the impeller may include relatively short blades 16 on the side of the plate 11 facing the bearing 30, thereby drawing air away from the bearing and preventing progression of material thereto.

Claims (18)

1. A chopper fan, comprising housing means having inlet means for receiving material for chopping, and an impeller rotatably mounted within the housing means at a location appropriate for drawing material through the inlet means and including blades arranged to chop said material, said housing means including filtering means for intercepting chopped material exceeding a predetermined size and for directing such material to first outlet means of said housing means, any material which passes through said filtering means being directed towards second outlet means of said housing means.

2. Afan as claimed in claim 1, and further comprising conveying means arranged to convey to said inlet means the material received by said first outlet means.

3. A fan as claimed in claim 1 or 2, wherein said first and second outlet means are respective parts of an outlet which extends approximately tangentially away from the periphery of an imaginary solid of rotation of said impeller and are separated by said filtering means in the form of a screen.

4. A fan as claimed in claim 3, wherein said screen extends in a curve from a location on an internal surface of a curved peripheral wall of said housing means to said outlet means.

5. Afan as claimed in any preceding claim, wherein said impeller further comprises a radial plate to one face of which said blades are fixed, said inlet means extends axially of said impeller along to said blades and there are centrally among said blades convex boss portions facing said inlet means.

6. A fan as claimed in any preceding claim, and further comprising protruding means of said impeller arranged to stir any large agglomerates of said material in said inlet means and bearing against said blades.

7. Afan as claimed in claim 6, wherein said protruding means comprises pin-like members.

8. A fan as claimed in claim 6 or 7, wherein said protruding means comprises portions of other blades of said impeller which blades project towards said inlet means further than do the first-mentioned blades.

9. Afan as claimed in any preceding claim, and further comprising a bearing whereby said impeller is rotatably mounted within said housing means, and means for protruding a gaseous flow tending to keep said material away from said bearing.

10. Afan as claimed in claim 9, wherein said bearing is a forced air bearing, and said means for producing a gaseous flow serves to force air into said bearing.

11. Afan as claimed in claim 9 or 10, wherein said means for producing a gaseous flow comprises further blades of said impeller arranged to draw air from said bearing towards said impeller.

12. A chopper fan, comprising housing means having inlet means for receiving material for chopping and outlet means for chopped material, and an impeller rotatably mounted within the housing means at a location appropriate for drawing material through the inlet means and including blades arranged to chop said material, and protruding means of said impeller arranged to stir any large agglomerates of said material in said inlet means and bearing against said blades.

13. Afan as claimed in claim 12, wherein said protruding means comprises pin-like members.

14. Afan as claimed in claim 12 or 13, wherein said protruding means comprises portions of other blades of said impeller which blades project towards said inlet means further than do the first-mentioned blades.

15. A chopper fan, comprising housing means having inlet means for receiving material for chopping and outlet means for chopped material, an impeller rotatably mounted within the housing means at a location appropriate for drawing material through the inlet means and including blades arranged to chop said material, a bearing whereby said impeller is rotatably mounted within said housing means, and means for producing a gaseous flow tending to keep said material away from said bearing.

16. Afan as claimed in claim 15, wherein said bearing is a forced air bearing, and said means for producing a gaseous flow serves to force air into said bearing.

17. A fan as claimed in claim 15 or 16, wherein said means for producing a gaseous flow comprises further blades of said impeller arranged to draw air from said bearing towards said impeller.

18. A chopper fan, substantially as hereinbefore described with reference to Figures 1 to 3b, or Figure 4, of the accompanying drawings.