Several devices for producing rock wool by means of a centrifugal force are known, in which the mineral melt is poured onto the mantle of the first rotating cylinder, where, due to the centrifugal force, part of the mineral melt is scattered into fibers, whereas the remaining part of the mineral melt is accelerated by the first rotating cylinder and flung onto the second rotating cylinder, where the process is repeated. This process is repeated until the last cylinder is reached (usually it is the fourth), where the last remaining portion of the mineral melt is scattered into fibers. The blowing nozzles along the edge of each rotating cylinder produce an axial air flow along the rotating cylinders, which air flow causes the fibers to be blown off, solidified in their definitive form, and wetted by the binder which is injected into the axial air flow from the openings on the edges of the rotating cylinders, and directs the fibers being formed and wetted by the binder toward the accumulation grid that is positioned perpendicularly or at a certain angle to the direction of the axial air flow. Out of solid state mineral fibers, wetted by the binder and deposited on the accumulation grid, a layer of rock wool is formed. The basic principle of producing rock wool by means of an axial centrifugal device is disclosed in patents WO 93/13025, WO 96/16912 and WO 95/14135.

The difficulty with this method for producing rock wool is achieving a good and uniform intertwining of the mineral fibers, a good and uniform wetting of the mineral fibers by the binder, and preventing the layer of mineral fibers, once deposited on the accumulation grid, from tearing, which is provoked by extremes of the axial air flow velocity near the accumulation grid. The patent WO 93/13025 does not solve the problem of the wetting of the mineral fibers by the binder, it only deals with the uniformity of the deposit of the mineral fibers on the accumulation grid and with the reduction of the distance between the rotating cylinders and the accumulation grid.

The patent WO 95/14135 deals with the problem of the wetting of the mineral fibers by the binder; however, the process is complex and it is not related to the problem of the tearing of the layer of mineral fibers, deposited on the accumulation grid.

The patent WO 96/16912 deals with the problem of the influence of the mineral melt viscosity on the rock wool quality, solving it in terms of geometrical disposition and rotational speed of the rotating cylinders. It does not tackle the problem of the wetting of the mineral fibers by the binder, nor the problem of the tearing of the layer of mineral fibers on the accumulation grid. It follows from the foregoing that particularly the problem of the intertwining of the mineral fibers and their wetting by the binder and the problem of further reducing tearing of the layer of mineral fibers, deposited on the accumulation grid, have not been satisfactorily solved as yet.

The present invention solves the technical problem of producing superior quality rock wool by the said process, since the characteristics of the rock wool, produced by the said process, depend on the geometrical and mechanical characteristics of the mineral fibers, their mutual intertwining and their wetting by the binder. The quality of the rock wool, produced by the said process, proportionally depends on the homogeneity and on the isotropy of the said parameters. The more homogeneous and isotropic are the mutual intertwining of the mineral fibers and the distribution of the binder on the mineral fibers in the air flow before their deposition on the accumulation grid, the better is the quality of the rock wool, produced by the said process. Further, the quality of the rock wool, produced by the said process, depends on whether the already formed layer of mineral fibers, deposited on the accumulation grid, tears due to the extremes of the axial air flow velocity near the accumulation grid. The less the already formed layer of mineral fibers tears, the better is the quality of the rock wool, produced by the said process.

The object and scope of the invention is to design an axial centrifugal device for producing rock wool that will provide a better and more uniform wetting of the mineral fibers by the binder, a better and more uniform mutual intertwining of the mineral fibers, and reduce tearing of the layer of mineral fibers already formed on the accumulation grid.

According to the invention the problem is solved as stated in the characterizing portion of the first patent claim.

According to the invention the problem described is solved by shaping the front of the rotating cylinders as a fan which generates a new radial air flow, directed outwards, and a new axial air counter-flow, directed backwards. Together, the axial air flow from the blowing nozzles situated along the edges of the rotating cylinders, and the radial air flow, generated by the fans, produce a swirling air flow with a high turbulent kinetic energy, thus determining a better dispersion of the binder, a better and more uniform mutual intertwining of the mineral fibers, and a better and more uniform wetting of the mineral fibers by the binder. The axial air counter-flow, generated by the fans, modifies the velocity profile of the air flow near the accumulation grid so that the extremes of the axial air flow velocity near the accumulation grid are diminished, thus reducing tearing of the layer of mineral fibers already formed on the accumulation grid, or eliminating it altogether.

The axial centrifugal device according to the invention, having rotating cylinders with fronts shaped so as to form a fan that produces an additional air flow, has the following advantages: a higher and more uniform wetting of the mineral fibers by the binder, a higher and more uniform mutual intertwining of the mineral fibers, and smaller extremes of the axial air flow velocity near the accumulation grid, on account of which the tearing of the layer of mineral fibers already formed on the accumulation grid is reduced, and consequently the quality of the rock wool, produced by the said process, is increased.

The invention will now be described with reference to a sample embodiment illustrated in the following figures, in which: Figure 1 is a side view of an axial centrifugal device for producing rock wool with an accumulation grid and with air flows traced out.

Figure 2 is a front view of the rotating cylinders of the axial centrifugal device for producing rock wool with blowing nozzles for the axial air flow shown and with a schematic sketch of the course of the mineral melt.

Figure 3 is a section, taken along line A-A of Figure 2, of a rotating cylinder with its front shaped so as to form a fan, with air flows traced out.

Figure 4 shows a fan shaped as a ventilator rotor.

Figure 1 shows the axial centrifugal device 1 for producing rock wool 8 with a traveling accumulation grid 2. The rotating cylinders 3 generate a centrifugal force which causes the mineral melt 10 to scatter into fibers. The front of each cylinder 3 is shaped as a fan in the form of a ventilator rotor 4 that generates the additional radial air flow 13, directed outwards, and the axial air counter- flow 5, directed backwards. The blowing nozzles 6 along the edges of the rotating cylinders 3 produce an axial air flow 12, which conveys the mineral fibers 7 to the accumulation grid 2. Out of the layer of mineral fibers, deposited on the accumulation grid 2, rock wool 8 is formed. Together, the axial air flow 12 from the blowing nozzles 6 and the radial air flow 13, generated by the ventilator rotor 4, produce a swirling air flow 9 with a high turbulent kinetic energy that determines a better dispersion of the binder and a better and more uniform wetting of the mineral fibers by the binder. The swirling air flow 9 also affects the definitive forming and solidification of the mineral fibers 7 from the mineral melt 10 and induces a better and more uniform mutual intertwining of the mineral fibers 7.

Figure 2 shows a front view of the four rotating cylinders 3, around which the blowing nozzles 6 are situated. The mineral melt 10 is directed onto the mantle of the topmost (namely, the first) rotating cylinder 3. On the mantle of the rotating cylinder 3 a thin film of mineral melt is formed, out of which fibers are generated by the centrifugal force. Thus, part of the mineral melt 10 is scattered into fibers and blown off by the axial air flow 12 from the blowing nozzles 6, whereas the remaining part of the mineral melt 11 is accelerated by the first rotating cylinder 3 and flung onto the next rotating cylinder 3, where the process is repeated. This process is then repeated until the last rotating cylinder 3 is reached, where the last remaining portion of the mineral melt 10 is scattered into fibers. The topmost rotating cylinder 3 rotates anti-clockwise, the next one rotates in the opposite direction, i e clockwise, and each of the following cylinders rotates in the opposite direction to its predecessor. In the Figures 2 and 4, the direction of rotation of the rotating cylinders is denoted by the reference number 18.

Figure 3 shows a section, taken along line A-A of Figure 2, of a rotating cylinder 3 with its front shaped as a fan in the form of a ventilator rotor 4. Along the edge of the rotating cylinder 3 there are blowing nozzles 6 that generate the axial air flow 12 which, together with the outwards radial air flow 13, produces a swirling air flow 9. The outwards radial air flow 13 is generated by the fan in the form of a ventilator rotor 4. On the edges of the rotating cylinders 3 there are openings 14 through which the binder is conveyed into the swirling air flow 9. The swirling air flow 9 possesses a high turbulent kinetic energy that affects the definitive forming and solidification of the mineral fibers 7, previously torn by the centrifugal force off the film of mineral melt, formed on the rotating cylinders 3. The axial air flow 12 conveys the mineral fibers 7 being formed into the swirling air flow 9. The swirling air flow 9 determines a better dispersion of the binder, a better and more uniform wetting of the mineral fibers 7 by the binder, it affects the definitive forming and solidification of the mineral fibers 7 out of the mineral melt 10, and induces a better and more uniform mutual intertwining of the mineral fibers 7.

Figure 4 shows an embodiment of the fan in the form of a ventilator rotor 4. The body of the ventilator rotor 4 is circular in form and thinner at the edge, that is at the outer radius 15, thickening inwards, that is toward the inner radius 16. Throughout the perimeter of the body of the ventilator rotor 4 there are blades 17, the working faces of which are parallel to the rotation axis of the rotating cylinders 3 and have a given inclination between 0° and 45° to the radial direction. Toward the outer radius 15, the blades 17 bend slightly in the direction opposite to the direction of rotation 18 of the rotating cylinder 3.

It will be appreciated by those skilled in the art that the fan that is the object of the present invention is not to be limited to the specific embodiment in the form of a ventilator rotor, described herein, since, without departing from the spirit and scope of the invention, the object thereof may be embodied in many other ways that form part of the patent rights, covered by the appended patent claims.