WHITE, Ian, G. (Power-Sprays Ltd, Avonmouth WayAvonmouth, Bristol BS11 9YA, GB)
1. Apparatus for dispensing fibres comprising a dispensing drum rotatably mounted within a housing, the housing having a fibre inlet and a fibre outlet, and a fibre feed hopper mounted on the housing and in communication with the fibre inlet, wherein the dispensing drum has a plurality of dispensing brushes mounted thereon.
2. The apparatus of claim 1, wherein each dispensing brush extends along the length of the dispensing drum.
3. The apparatus of claim 2, wherein each dispensing brush follows at least a portion of a helical path.
4. The apparatus of claim 3, wherein the pitch of the helical path of each dispensing brush is greater than the circumferential spacing of adjacent dispensing brushes such that opposite ends of adjacent dispensing brushes circumferentially overlap.
5. The apparatus of claim 1, wherein each dispensing brush extends in a straight line from a first end of the dispensing drum to a point between the middle of the drum and the opposite end of the dispensing drum.
6. The apparatus of claim 5, wherein each dispensing brush extends at an angle relative to the longitudinal axis of the dispensing drum.
7. The apparatus of claim 6, wherein alternate dispensing brushes extend from opposite ends of the dispensing drum.
8. The apparatus of any preceding claim, wherein the dispensing drum and housing are co-axially aligned and are arranged so as to provide a uniform gap therebetween.
9. The apparatus of claim 8, wherein each dispensing brush extends radially from the dispensing drum by a distance greater than the thickness of the uniform gap.
10. The apparatus of any preceding claim, wherein the dispensing brushes are deformable.
11. The apparatus of any preceding claim wherein each dispensing brush comprises a plurality of bristles.
12. The apparatus of any preceding claim further comprising a variable speed motor arranged to rotatable drive the dispensing drum.
13. The apparatus of any preceding claim further comprising at least one load cell arranged to provide a signal indicative of the quantity fibres within the fibre feed hopper.
14. The apparatus of claim 13, wherein the apparatus further comprises a control unit arranged to receive the signal from the load cell and control the operation of the apparatus in response thereto.
The present application relates to an apparatus for dispensing reinforcing fibres, such as those used in fibre reinforced composites such as fibre reinforced concrete and fibre reinforced plastic.
Fibre reinforced concrete is the generic term for any cement-based composite that is reinforced with fibres, such as glass fibres or plastic fibres. The inclusion of the reinforcing fibres provides the reinforced concrete with high strength. This relative high strength and the ability to easily mould fibre reinforced concrete into, for example, thin, lightweight panels with a wide variety of shapes, forms and surface finishes makes fibre reinforced concrete a popular material in a construction of many buildings. Equally, its high strength to weight ratio also makes it a good choice for use in civil engineering applications.
Where relatively large quantities of the fibre reinforced concrete is required the preferred method of introducing the reinforcing fibres into the concrete-composite mix is by spraying. For example, the current applicants provide a spray gun that incorporates a system whereby reinforcing fibre is chopped and mixed with a sand/cement slurry at a single nozzle. This system ensures an even distribution of the reinforcing fibres in the composite mix. However, where smaller quantities of the fibre reinforced concrete are required spray mixing is not suitable and other methods of mixing the desired quantities of reinforcing fibres within a concrete mix are required.
Alternative apparatus for dispensing chopped fibres into the composite mix include apparatus comprising a rotatable dispensing cylinder mounted within an outer cylinder, the inner rotatable cylinder having one or more dispensing paddles formed on its outer surface, such that as the inner cylinder is rotated, for example by means of an electric motor, the dispensing paddles force a quantity of chopped reinforcing fibres that are located in a hopper directly above the inner and outer cylinder through the passage created between the inner and outer cylinders. However, this kind of dispensing apparatus commonly suffers the disadvantage of the cut reinforcing fibres becoming clogged or knitted together at the
interface between the hopper and the outer cylinder such that they are not fed in a controlled manner through the dispensing apparatus. The apparatus of the present application seeks to mitigate this disadvantage.
According to a first aspect of the present invention there is provided apparatus for dispensing fibres comprising a dispensing drum rotatably mounted within a housing, the housing having a fibre inlet and a fibre outlet, and a fibre feed hopper mounted on the housing and in communication with the fibre inlet, wherein the dispensing drum as a plurality of dispensing brushes mounted thereon.
The dispensing brushes preferably extend along the length of the dispensing drum and in preferred embodiments each dispensing brush follows at least a portion of a helical path, such that the dispensing brushes visually resemble the pattern of cutting blades on a rotary lawnmower.
Additionally, the pitch of the helical path of each dispensing brush is preferably greater than the circumferential spacing of adjacent dispensing brushes such that the opposite ends of adjacent dispensing brushes circumferentially overlap.
Additionally or alternatively, the dispensing drum and housing may be coaxially aligned with one another and are arranged so as to provide a uniform gap therebetween. Additionally, each dispensing brush preferably extends radially from the dispensing drum by a distance greater than the thickness of the uniform gap.
Additionally or alternatively, the dispensing brushes may be deformable. In preferred embodiments each dispensing brush comprises a plurality of bristles.
Additionally or alternatively, the fibre dispenser may further comprise a variable speed motor arranged to rotatably drive the dispensing drum.
In preferred embodiments the apparatus may further comprise at least one load cell arranged to provide a signal that is indicative of the quantity of fibres held within the fibre feed hopper. Additionally, the apparatus may further comprise a control unit arranged to
receive the signal from the load cell and to control the operation of the apparatus in response to the signal. In this way the amount of fibre to be dispensed can be automatically controlled.
Embodiments of the present invention are described, by way of illustrative example only, below with reference to the accompanying figures, of which:
Figure 1 schematically illustrates the arrangement of a fibre dispensing apparatus of the kind known from the prior art;
Figure 2 schematically illustrates the arrangement of a fibre dispensing apparatus according to an embodiment of the present invention; and
Figure 3 is a more detailed plan view of the fibre dispensing drum of the apparatus illustrated in Figure 2.
Examples of existing apparatus include fibre dispensers of the type illustrated in Figure 1. The apparatus comprises a substantially cylindrical drum 1 in which a set of rigid rotating dispensing paddles 3 are located, the paddles being arranged to rotate about the central axis of the drum 1, for example by means of an electric motor. An inlet aperture is provided in the upper surface of the drum 1 above which a fibre hopper 5 is located. A fibre outlet 7 is provided in the lower surface of the drum 1, diametrically opposed from the fibre inlet. In use, the fibre hopper 5 is at least partially filled with pre-chopped reinforcing fibres, or is placed in communication with a supply of fibres. To dispense a quantity of chopped fibres the dispensing paddles 3 are rotated with the intention of allowing a controlled flow of fibres to be dispensed out of the fibre outlet 7. However, this type of fibre dispenser rarely works well since the chopped reinforcing fibres tend to knit together and form a self supporting layer at a location in the fibre hopper 5 just above the high point of the passing dispensing paddles 3, indicated by the dotted line A-A in Figure 1. The self supporting layer of interwoven fibres prevents the passage of the reinforcing fibres through the dispenser. This problem has been found by the applicants to occur whenever the length of the chopped fibre exceeds approximately 2mm and/or the ratio of length to diameter of the chopped fibres exceeds approximately 2:1. Once the dispenser has become blocked by a
layer of interwoven fibres the apparatus must be stopped to allow the blockage to be manually cleared either by agitating the fibres either from the top of the fibre hopper 5, or less usually, from underneath via the outlet aperture 7. This is clearly extremely inconvenient and disadvantageous since not only does it require manual observation and intervention by an operator but also generates significant wastage of materials since the batch of fibre reinforced concrete into which the fibres were being dispensed at the time of blockage must be discarded since it is not possible to establish the exact quantities of fibres that were successfully dispensed into that batch.
Attempts have been made to alleviate the clogging/knitting problem by introducing one or more fibre agitators to the apparatus. These are typically located in the lower portion of the hopper 5 and in Figure 1 are represented by two additional rotating agitator blades 9. The agitator blades 9 are rotated in use, either in the same direction as one another or contra-rotating, in an effort to constantly agitate the chopped fibres within the hopper 5 so as to prevent the fibres from knitting together as previously described. However, the efficacy of such fibre agitators is minimal, since the fibres within the hopper 5 simply tend to knit together just above the agitators 9 in the same way that they knit together above the main dispensing paddle 3 when no agitators are included in the apparatus. Consequently, it is still necessary to periodically unclog the fibres within the hopper, even with the use of such agitators.
An apparatus for dispensing fibres according to an embodiment of the present invention is illustrated in Figure 2. As with the apparatus shown in Figure 1, the apparatus of the embodiment of the present invention shown in Figure 2 comprises an outer cylindrical housing 10 onto which a fibre feed hopper 12 is attached, the housing 10 having an aperture formed therein at the interface between itself and the hopper 12, thus allowing the passage of fibres from the hopper to the housing. Whilst the angle of the sides of the hopper 5 is not critical, generally the closer the sides are to being vertical the less the chance of any fibres knitting together. It has been found that if the sides of the hopper are sloped too gently, i.e. away from vertical, the chances of fibres knitting together is increased, especially for longer fibres. However, the closer the sides of the hopper 5 are to being vertical, the smaller the capacity of the hopper. The angle of inclination of the hopper sides is thus an operational compromise that may vary from embodiment to
embodiment. The housing 10 also includes a lower fibre outlet 14 that is diametrically opposed to the hopper 12. Located within the cylindrical housing 10 is a substantially cylindrical fibre dispensing drum 16, the central axis of rotation of the dispensing drum 16 being coincident with the central axis of the cylindrical housing 10, such that the drum and housing are coaxial to one another. The diameter of the dispensing drum 16 is less than the inner diameter of the housing 10, such that a uniform space is present between the outer surface of the dispensing drum 16 and the inner surface of the cylindrical housing 10.
Mounted on the external surface of the dispensing drum 16 are a number of dispensing brushes 18. Each dispensing brush 18 extends along substantially the complete length of the dispensing drum 16 so as to completely span the full length of the aperture formed between the hopper 12 and the cylindrical housing 10. Each dispensing brush 18 preferably comprises a plurality of individual bristles that extend radially from the outer surface of the dispensing drum 16, the bristles having a length that is greater than the spacing between the outer surface of the dispensing drum 16 and the inner surface of the cylindrical housing 10. The bristles of the dispensing brushes 18, which are preferably conventional brush material, are sufficiently resilient to deform as the dispensing drum 16 carries them past the cylindrical housing 10 during operation of the dispensing apparatus. In other embodiments the dispensing brushes may comprise a resilient material, such as rubber strips, rather than bristles.
As shown with reference to Figure 3, which illustrates a plan view of the dispensing drum 16, the dispensing brushes 18 are arranged on the outer surface of the dispensing drum in the manner of a series of partial helixes, in an analogous manner to the cutting blades of a rotary lawnmower. hi other words, each dispensing brush 18, when viewed in plan view, describes a curve along the length of the dispensing drum 16. As illustrated in Figure 3, the radius of curvature of the dispensing brushes 18 (the pitch of the helix) and their spacing relative to one another is such that opposite ends of adjacent brushes circumferentially overlap, shown by the arrow O in Figure 3.
hi operation, the dispensing drum 16 and dispensing brushes 18 are rotatably driven, for example by a motor 20 and driver belt or chain 22 as illustrated in Figure 2, within the cylindrical housing 10. The motor 20, which may for example be electrically or
hydraulically powered, may permit the dispensing drum 16 to be rotated at a variable speed, for example within a speed range of 0 to 50 rpm, so as to permit varying speeds of fibre dispensation. As the dispensing brushes 18 pass beneath the fibre hopper 12 the brushes come into contact with the fibres stored in the hopper 12 and propel them through the space provided between the outer surface of the dispensing drum 16 and the inner surface of the outer housing 10 until the fibre outlet 14 is reached, at which point the fibres exit the housing 10 by force of gravity. As the dispensing brushes 18 move through and past the reinforcing fibres located in the hopper 12 they provide an agitation of the reinforcing fibres that prevents them from knitting together or clogging. A proportion of the fibre agitation arises as a result of the resilience of the dispensing brushes 18. Since the dispensing brushes 18 are resilient they can deform as they pass through the reinforcing fibres in the hopper 12 and by virtue of this deformation the bristles of the fibre brushes 18 remain in contact with individual reinforcing fibres for a greater duration of time than would be the case with rigid dispensing paddles. Additionally, the dispensing brushes may deform slightly when passing against a clump of reinforcing fibres that are beginning to knit together and as the dispensing brush 18 moves past these reinforcing fibres the individual bristles of the dispensing brush 18 will tend to flick back to their natural undeformed state. As the dispensing brush bristles flick back they impart a further agitation action on adjacent reinforcing fibres. A further flicking action is generated as each dispensing brush 18 transitions from the space between the dispensing drum 16 and the outer housing 10, at which point the individual bristles of the dispensing brush 18 are bent away from the direction of rotation due to the spacing provided between the dispensing drum 16 and outer housing 10 being less than the natural length of the bristles of the dispensing brushes 18, since as they flick back to their natural state they impart an agitation action on the surrounding reinforcing fibres within the hopper 12. By virtue of the overlapping of adjacent dispensing brushes 18, as indicated and explained with reference to Figure 3, there is always at least a portion of a dispensing brush 18 in contact with the reinforcing fibres within the hopper 12, such that the agitation action is effectively continuous.
An alternative arrangement of the dispensing brushes on the dispensing drum according to a further embodiment of the present invention is illustrated in Figure 4. In contrast to the arrangement of the dispensing brushes shown in Figure 3, in the embodiment shown in
Figure 4 the dispensing brushes 418 extend along the outer surface of the straight line from an end of the dispensing drum 416 to a point between the mid-point of the drum's length and the opposite end of the dispensing drum. Each dispensing brush extends along the surface of the dispensing drum at an angle relative to the longitudinal axis of the drum, preferably less than 45°. In the preferred arrangement shown in Figure 4 the dispensing brushes 418 extend from opposite ends of the dispensing drum in an alternating manner, such that the ends of alternate brushes are 'interlaced' in the central region of the dispensing drum in an approximate chevron pattern. However, other arrangements, such as alternating pairs of brushes, may be envisaged and utilised in other embodiments.
The brushes are orientated such that when the dispensing drum revolves in the direction of normal use, the ends of the dispensing brushes nearest to the edge of the drum come into contact with the fibres stored in the hopper first. This tends to impart a sweeping force on the fibres urging them towards the centre of the dispensing drum. This reduces the possibility of a build up of fibres occurring at either end of the drum, which may occur with other arrangements of the dispensing brushes.
In some embodiments of the present invention, and independently of the arrangement of the dispensing brushes, the length of the bristles of each dispensing brush may vary. In particular within each brush there may be one or more portions having bristles that are longer than the remaining portions of the dispensing brush. These longer brush portions may be the same bristle material as the remainder of the dispensing brush or may be a different material, such as a rubber material. The purpose of the longer bristles is to impart an extra 'flicking force' to the fibres to be dispensed and thus further reduce the probability of the fibres clogging in the hopper.
To enable the amount of reinforcing fibre being dispensed from the apparatus to be accurately monitored and controlled, the dispensing apparatus is mounted on one or more load cells 24 that are located between the dispensing apparatus and a supporting frame 26. Consequently, the load imparted on the load cells 24 is directly in proportion to the weight of fibres held within the dispensing apparatus by means of an appropriate control unit. Consequently, by monitoring the change in weight of the apparatus and fibres contained therein during operation the weight of dispensed fibre can be monitored. The signals from
the load cells 24 can thus be used to control the operation of the dispensing apparatus. For example, by the provision of suitable control circuitry a desired weight of reinforcing fibres to be dispensed can be set in advance such that the operation of the dispensing apparatus is ceased automatically when this weight of fibres has been dispensed. In further embodiments the control circuitry may be arranged to vary the speed of the dispensing drum to improve the accuracy of the amount of fibres dispensed. For example, the rate of rotation of the drum may be reduced as the weight of dispensed fibres nears the target value, such that greater control can be exercised in dispensing the final amount The control strategy may vary depending on the different fibres being dispensed.