Fibre delivery system for asphalt production

Abstract: Fibre delivery system comprising a hopper (2) for accomodating a bale (20) of fibrous material, and which is closed at its base by a plurality of rollers (8,9), each roller having on its surface a plurality of projections, and means (21) for forcing a bale (20) accommodated in the hopper onto the rollers (8,9).

Description: The use of fibrous materials as a means of increasing the wet film thickness of liquid coatings is well known. The use of such fibrous material in asphalt mixtures to increase the bitumen coating on the stone contained in the asphalt mix is also an established technique. There is also some evidence to support the idea that asphalt containing fibres are more resistant to rutting. Fibre-containing asphalt is normally produced as a hot thermoplastic material in a fixed blending plant, and then transported to site in an insulated vehicle. The hot thermoplastic asphalt is then applied to the substrate through conventional asphalt pavers. Recently an alternative method has been to produce the asphalt, in cold form, using bitumen emulsions, in a mobile blending, mixing and paving machine, which blends and mixes the material at the point of application. The addition of fibres to such a system has been found to enhance the surface texture, as well as impart the other aforementioned advantages. The fibre additions are generally between 0.1 % and 0.5 % and it has been found that only some types of fibres are suitable. The fibre size is usually between 2mm and 6mm long with a diameter ranging from 1 µ to 100 µ. The difficulty in handling tightly packed fibrous material is accepted. The feeding of such materials within acceptable limits to meet the demands of a continuous blending process is critical for the range of fibre materials likely to be encountered. Moreover to aid uniform distribution of the fibres throughout the material, requires that the fibre material is broken up prior to it being metered to the mixer with all the other asphalt components. To date, equipment used to deliver fibres into road composition manufacturing equipment has been designed to handle fibres which are supplied in palletised form. Alternatively the fibre metering equipment is designed to maintain the fibres in a loose form by containing them in an agitated hopper equipped with paddles or the like. The loose material is then metered into the road composition manufacturing equipment via a rotary valve device or screw arrangement. WO-A-92/010095 describes an apparatus for treatment of fibre material. This apparatus comprises a unit for loosening or opening the fibre material, and a unit for feeding the fibre material to the loosening unit. The feeding unit is designed to gradually feed the fibre material in the form of a compacted fibre body, especially a pressure-compressed bale, to simultaneous engagement with the teeth of two shredding rollers of the loosening unit. DE-A-24.16.944 discloses a device for opening and mixing fiber bales ; the fibers are transported by an infinite screw. US-A-4.126.913 discloses a fine opening mechanism for textile fibrous material which comprises a primary opening element such as a spiked beater roll and means for delivering a single undivided mass of textile fibres toward the primary opening element, and a plurality of feed elements are located between the primary opening element and the feeding means, the undivided mass of textile fibrous being divided into as many individual masses as there are pairs of feed rolls. The present invention concerns a fibre delivery system according to claim 1 which provides a compact storage and delivery system capable of accepting the fibrous material as high density packaged bales, and then breaking up the material into a loose form, and metering it in terms of mass-or-volume to ensure the correct dosing level. Variable mass means allow to provide a constant flow independent from the position of the means that force the bale onto the rollers that split the bale up. The whole assembly is suitable for integration into a mobile continuous mixing cold asphalt machine designed to mix asphalt materials and apply them as a road surfacing product. Details of the invention Reference to Figure 1 shows the essential components of the first embodiment. The container 1 is designed to accommodate one or more fibre bales 20 as well as form a structure to enclose and support the mechanism necessary for metering and delivering the fibres. Items 2 to 7 form a press mechanism which forces the bales, in a controlled manner, onto a set of contra-rotating spiked, or barbed, rollers 8 and 9. These spiked rollers tear and break up the material from the bale 20 and transport it into a void situated above the metering delivery auger 10. The drive system is by chains 12, 13, powered by an hydraulic or electric first motor 11 and tensioned by idle sprocket 14. Generally the auger is geared to rotate faster than the speed of the spiked rollers to prevent material jamming. Bearings 15, 16, 17 and 18 attached to the container 1 support the spiked rollers and auger. Auger 10 can be of progressive nature to avoid jamming. Material is delivered through duct 19. The metering rollers 8 and 9 are equipped with pointed spikes, typically of round cross-section, and up to around 10 mm, eg. 4-5 mm, long and up to 5 mm, eg. around 1.5mm, in diameter. They are preferably spaced at 5-15 mm, eg. 12 mm, centres both longitudinally and circumferentially. The feeding system consists of a platen 2, square guide tube 3 with slot 4 and guide plug 5 connected to platen 2 via gusset 6. Platen 2 and gusset 6 can be raised out of engagement of slot 4 and rotated through 180° to enable loading of fresh bales. To maintain a controlled feed, platen 2 can be weighted with mass 21. Figure 2A shows an electric second motor 30 driving a lead screw 31 which controls the feed rate of platen 2 via plug nut 33 which is constrained by guide tube 3 and slot 35. Figure 2B shows an hydraulic cylinder 40 which controls the feed rate of platen 2 through lead screw 42 contained in guide tube 3. In both cases the platen can be rotated 180° for loading when clear of container 1. Hinged lid 50 is designed to reduce the ingress of rain etc. It was discovered that not only can the auger vary the flow rate as would be expected from previous practice, but that material flow rate is dependent upon the speed of the spiked rollers 8 and 9 and can also be adjusted by varying the force between the bale of fibre and the spiked rollers. Table 1 shows the changes in output that can be achieved by either varying the spiked rollers speed or by changing the feeding force mass 21 applied to the bale 20 by variable mass means that are increasable in mass with travel down the hopper, for a variety of fibrous materials. It will be noticed, from Table 1, that the spiked roller speed is generally proportional to fibre flow rate, but that the weight applied to the bale to control the flow rate to meet a process target flow rate varies with the material type and its packing factor. Indeed, auger speed variations within certain limits resulted in little variation of feed rate. In the second embodiment the design has been changed to eliminate the auger metering device and use the spiked rollers only to meter the material as well as process the compacted material into a form suitable for admixing. All other aspects of the system are the same as for the first embodiment. Reference to Figure 3 shows the second embodiment with the fibrous material 20 contained in the hopper 1 which also forms the support structure for the spiked rollers 8, 9 which are geared together to give contra rotation. The drive system which can take the form of either an electric or an hydraulic motor 11 of variable speed. Chain and sprocket transmission 71 is capable of rotating the spiked rollers typically from 10 rpm to 300 rpm. The mechanism for pressing a bale onto the spiked rollers is not shown, but is the same as that used in the first embodiment. Fibrous material is delivered in suitable form from the base of the hopper and the delivery rate is proportional to the rotational speed of the spiked rollers and the force with which the compacted fibrous bale is applied to the roller. Hopper 1 is designed such that its height is sufficient to prevent human contact with the rotating spiked rollers. The metered and processed fibrous material can be delivered directly to the mixing facility by gravity, or, the metered and processed material issuing from the hopper can be deposited on a feeding means. In this particular case the endless conveyor belt 72 is an existing part of the surfacing machine, used to transport aggregate 73 to the mixing facility. The metered and processed fibrous material 22 is conveyed on top of the aggregate 73. The third and preferred embodiment is shown in Figure 4 and includes a method of replenishing the hopper unit with compressed fibre bales without interrupting the delivery of metered and processed fibre into the process. Essentially this embodiment consists of two hoppers similar to that described in the second embodiment, arranged to form a double hopper metering system with the spiked roller drive for each hopper organised such that only one hopper/roller assembly will deliver material at any one time. The roller drive is automatically switched to the other hopper roller assembly only when the first hopper is almost empty. In this way fibre bales can be replenished, as the processing time for each hopper is some 8 mins. The elevations, the plan and'the rear view show the fibre delivery system installed in an existing machine aggregate hopper 70. This enables a quick and effective addition of the facility to existing microasphalt road surfacing equipment. Reference to Figure 5 shows how the sequential switching is effected by using a detector switch 7 mounted in the wall of the fibre hopper 1 which is activated by the presence of platen 2 and so organised that only a small amount of fibre remains in the hopper once automatic changeover has occurred. This enables the empty hopper to be replenished with compacted bales of fibre ready for the next change over to occur and so on. Figure 6 shows a typical circuit diagram to control the automatic changeover operation. The independent roller hydraulic drive motors 11 are switched on and off by hydraulic change-over valve 63. The valve activation is controlled by detector switch 7 via change over relay 65. There is a need to deliver fibres only when other ingredients are being processed and this switching function is provided by switch 66. A manual over-ride system is also provided by switches 67, 68 which enable the fibre system to be run independently of other ingredients for calibration, or can be used to operate the process in event of component failure. An emergency stop 69 is provided in the event of the need to stop the process quickly.

Claims: Fibre delivery system comprising a hopper (1) for accommodating a bale (20) of fibrous material, and which is closed at its base by a plurality of rollers (8, 9), each roller having on its surface a plurality of projections, and means for forcing a bale (20) accommodated in the hopper (1) onto the rollers (8, 9), characterized in that the means for forcing the bale (20) onto the rollers (8, 9) comprise variable mass means (21) which are increasable in mass with travel down the hopper. A system according to claim 1, wherein the projections are in the form of spikes. A system according to claim 1 or claim 2, wherein adjacent rollers (8, 9) are arranged to rotate in opposite directions to one another. A system according to any preceding claim, which further comprises a delivery auger spaced apart and below the rollers (8, 9). A system according to any preceding claim, wherein the forcing means comprises a removable platen (2) which closes the upper end of the hopper (1) and which is movable down the hopper in a substantially horizontal plane, the movement of the platen (2) being controlled by the variable mass means (21). A system according to claim 5, wherein the platen (2) is pivoted about, or hinged at, one of its sides, so as to allow opening of the top of the hopper (1) for loading a bale (20) thereinto. A system according to any preceding claim, which comprises a plurality of hoppers (1) and associated forcing means (21), and switching means (7) responsive to the height of material in one hopper (1) for activating the rollers (8, 9), and auger when present, in another hopper. A mobile asphalt blending and laying machine comprising a blending unit, feeding into the blending unit a delivery system as defined in any preceding claim, and means for laying the material from the blending unit onto a substrate surface. A machine according to claim 8, which further comprises means for feeding aggregate (73) into the blending unit. A machine according to claim 9, which further comprises a conveyor (72) running into the blending unit, and wherein the aggregate feed means and the hopper (1) are arranged to deliver material onto the conveyor (72) for entry into the blending unit. A machine according to claim 10, wherein the hopper (1) is located after the aggregate feeding means, so that, in use, fibrous material (20) from the hopper (1) is laid on top of the aggregate (73) on the conveyor (72). Use of a system as defined in any of claims 1 to 7, for incorporating fibrous material (20) from bale form into an asphalt mixture for application to a substrate surface.

Inventors: KILNER DAVID NICHOLAS, KILNER, DAVID NICHOLAS
Applicants: COLAS SA, COLAS S.A.
Application year: 1997
Main classification: E01C19
IPC codes: E01C19, D04H1