Abstract:
The invention provides a method and apparatus for preparing precut steel fibers initially packed in bundles or occurring as closely packed lumps for mixing with concrete as a sprayed mass, the method comprising the steps of tumbling the bundles or lumps of fibers, dropping quantities of the fibers onto an inclined plane, subjecting the fibers to an air stream to cause said fibers to become parallel to each other, and mixing the fibers with a mass of concrete in the air stream.

Description:
The present invention refers to a method for preparing fibres in bundles or closely packed together lumps for aimed mixing into a sprayed concrete mass or the like as well as a device for performing the method. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     It is earlier known to add precut steel fibres to a concrete mass, which by means of concrete spraying is applied to the surface intended. The fibres have then been added in a concrete mixer or the like. The mixture thereupon has been placed in a spraying machine, whereupon it has been brought to an orifice and has been sprayed out onto a desired base. 
     It has proved itself that the above described type of addition of fibres to the concrete mass, limits the achievable fibre content in the mass to one or some percent of volume only, as the fibres during the mixing and the transport together with ballast and cement material has a tendency to ball or become packed together in lumps. It has therefore been necessary to use low fibre contents at the mixing, whereby the desired improvements regarding strength, fracture dispersion, deformation ability etc. cannot be achieved or will be achieved to a very limited extent only. The desired alignment of the fibres in mainly one direction is not obtained, but the fibres will randomly arrange themselves in three dimensions, whereby the reinforcing effect is essentially reduced. 
     It has earlier been proposed to supply the fibre material to the dry cement and ballast material in an air stream and this method has proved itself to be very successful. The steel or metal fibres are however available on the market only as short, cut pieces, which are packed together in lumps in such a manner that the fibres only with great difficulty can be separated from each other. 
     The purpose of the present invention is now to propose a method and a device for preparing the fibres so that they with elimination of the above mentioned drawbacks in a correct and controllable manner can be supplied to the material stream at concrete spraying. This problem has been solved thereby that the fibre bundles or fibre lumps, are disintegrated into separate fibres in a defibrating apparatus by being shredded, shaken, cut and/or tumbled in a sieve and/or a tumbler, that the separate fibres are dosed and that the separate fibres are aligned with the longitudinal direction of the fibres being essentially parallel to their direction of transport by means of unobstructed downfall upon an inclined surface followed by paralleling in an air stream in a transport duct. 
     This is achieved with a device comprising in combination a defibrating apparatus, designed mechanically to separate the fibres from each other, a dosing apparatus for feeding out the fibres in dosed quantities and an alignment unit for arranging the fibres in three planes and a transport duct connected to the alignment unit and provided with means for generating therein an air stream as a transport medium for the fibres. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will hereinafter be further described with reference to embodiments shown in the accompanying drawings in which like reference numerals are used to refer to equivalent parts in the various figures. 
     FIG. 1 shows a longitudinal section through a schematic device according to the invention, 
     FIG. 2 shows a similar section through a modified device according to the invention, 
     FIG. 3 shows a section through a device where the initial fibre material is a twisted wire, 
     FIG. 4 shows a section through a device where the initial fibre material is a number of threads, 
     FIG. 5 shows a further variant of the devices according to FIGS. 3 and 4, in which the threads also are shaped, 
     FIG. 6 shows in larger scale a section through the forming unit according to FIG. 5. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The device according to the invention consists in each illustrated embodiment of a defibrating apparatus 1, arranged mechanically to separate the fibres from each other, a dosing device 2 for controlling the quantity of fibres delivered by the defibrating apparatus, an alignment unit 3 and a transport duct 4. 
     The defibrating apparatus 1 in accordance with FIGS. 1 and 2 includes a tumbler having a drum 6, which is rotatable about a preferably somewhat sloping shaft supported in a housing 7 enclosing the drum. The drum is driven by a motor 8 at a variable and comparatively low speed. The drum 6 is open at one of its ends and this end is provided with a feeding hopper 9. The opposite end of the drum is closed by means of an end wall 10 and adjacent this end wall there is arranged one or more feeding-out openings 11 along the circumference of the drum. At the lower part of the housing 7 just in front of the feeding-out openings, there is also arranged a further opening 12. A cylinder 13 is fitted inside the drum in engagement with the internal surface of the drum 6 and said cylinder can be non-rotatably connected to the drum by means of a suitable locking means. The cylinder 13 is furthermore displaceable axially in the drum towards and away from the feeding-out openings 11, whereby the size of these openings can be adjusted. At the internal side of the cylinder 13 there is fitted a large number of radial pins 14, ridges or similar projections, which effect a further separation of the fibre lumps. The feeding-out openings 11 are preferably designed as exchangeable screens to prevent even small lumps of fibres from leaving the disintegrating apparatus. 
     The dosing effect in the example shown in FIG. 1 is thus accomplished by the feeding-out openings, the size of which can be adjusted and/or by varing the speed of the adjustable motor 8. 
     A very important detail is the alignment of the fibres and the alignment unit 3 of the device is designed as an inclined surface 15 arranged below the feeding-out openings 11 and 12 and comprising a smooth polished shute, which tapers in a direction against its lower outlet. The surface could preferably - but not necessarily - be vibrated by means of a vibrator 16. A pipe end is fitted to the lower end of the inclined surface 15 and this pipe end forms an elongation of the transport duct 4. An air stream with a heavy suction effect is generated in the pipe end by means of an ejector 17 comprising a conduit 18 for pressurized air arranged in the duct. Said air stream transports the fibres past the ejector and into the transport duct 4, where a heavy stream of pressurized air prevails. From the transport duct the fibres are transported to a spray mixer 40 (for convenience shown only in FIG. 2) where the fibres are mixed with a concrete mass. 
     The fibres thus will be defibrated, i.e. they will be separated from each other in the defibrator 1, which is designed as a tumbler and they will be fed out at a rate related to the rotational speed of the drum and of the size of the feeding-out openings in a desired quantity to the inclined surface 15 of the alignment unit 3, where the fibres are arranged in one plane by unobstructed downfall upon the smooth shute, whereupon the fibres are made parallel by being pulled by suction into the heavy air stream in the pipe end. 
     In order to obtain such a good as possible adherence between the fibres and the concrete mass the steel fibres can be provided with cams, which further will increase the tendencies of forming lumps and of packing together. In such cases it can be advantageous to arrange a further apparatus for rough defibration in front of the first mentioned defibrating apparatus as seen in the direction of fibre transport and by means of this further apparatus is it possible to loosen large segregations. The rough defibrating apparatus is on the drawing shown in dash and dot lines and it is designated 19. The apparatus comprises a reciprocating sieve 20, which is arranged in a charging hopper 21 located above the feeding hopper 9 of the defibrating apparatus 1. The sieve 20 is driven by a motor 22 and it is preferably provided with teeth adapted to shred the lumps of fibres. 
     In cases where a most exact dosing of the fibre material is wanted a dosing apparatus 23 is arranged preferably between the rough defibrating apparatus 19 and the fine defibrating apparatus 1, which dosing device feeds out the fibres to the transport duct for obtaining desired contents in relation to weight, quantity or volume. In FIG. 2 the device according to FIG. 1 is shown with such a dosing device located between the rough defibrating apparatus 19 and the fine defibrator 1. The dosing apparatus according to this embodiment comprises a device for volume measurement, designed as a rotor 24, connected to the charging hopper 21 and also to the feeding hopper 9, said rotor being provided with a number of vertical chambers 25. The rotor is indexable by means of a step motor 26 so that each one of the chambers successively can be brought to communicate with the charging hopper 21 and the feeding hopper 9. The chambers are thus filled with fibres from the reciprocating sieve 20 and are successively emptied in the feeding hopper 9. The step motor 26 is preferably controlled by photocells, which index the rotor one step when the chamber below the charging hopper has been filled to the predetermined height. 
     The dosing device can of course be formed as a weighing machine or the like instead of a volume measurement device. 
     At the embodiment shown in FIG. 3 the defibrating apparatus 1 includes a cutting device 30, adapted to cut up a twisted wire 31 which is wound on a roller 32 in short pieces when said wire is unwound and fed into the cutting device. The length of the pieces is determined by a feeding device 33, which in the example shown is formed as motordriven rollers. When the wire pieces are cut the separate threads, i.e. the fibres will be released and they are allowed freely to fall down onto the alignment device 3, i.e. the earlier mentioned inclined surface 15, whereon the fibres will be arranged in one plane and slide down to the transport duct 4. This motion may be improved by vibrating the surface 15. 
     At the embodiment according to FIG. 4 the initial material used is separate long threads 34, which are wound on cylinders 35. The apparatus comprises a thread collector 36, which can be designed to form the threads into a string, which preferably is at least somewhat twisted, which string in the same manner as the wire in FIG. 3 is supplied to the defibrating apparatus 1 by means of the dosing apparatus 2 by feed rollers 33 whereupon the string is cut into short pieces. The apparatus is in other respects equal to that of FIG. 3. 
     Also the variant shown in FIG. 5 does work with separate threads 34 as initial material, but these threads are not collected to a string but are fed into the apparatus one by one. The threads are supplied via a dosing apparatus 2 with feeding rollers 33 to a forming and cutting device 37, by means of which the thread pieces at their ends are provided with bends or the like. The formed and cut thread pieces are allowed unobstructedly to fall down onto the alignment device 3, wherefrom they are transported to the transport duct 4. The shaping of the threads are brought about by means of suitable shaping tools shown in FIG. 6 and comprising an upper and a lower die for cold upsetting the threads. Instead of upsetting the threads it is of course possible to use other types of shaping or coining devices but it is also possible to use form cutting or stamping from a strip of sheet metal. 
     The invention is not limited to the embodiments shown but a number of modifications are possible within the scope of the appended claims.