Field of technology

Mineral wool production; Pneumatic transport; Turbomachinery Technical problem

The invention relates to an centrifugal device for producing mineral wool from fibers that are obtained from mineral melt by means of a centrifugal force, generated by one or more, usually four, cascading rotating cylinders and are pneumatically transported to an accumulation grid by an axial air flow generated by the blowing nozzles along the outer surfaces of the rotating cylinders. Technical problem addressed is failure to achieve good and uniform intertwining of the mineral fibers, good and uniform wetting of the mineral fibers by the binder, and tearing of the primary layer once deposited on the accumulation grid. Further technical problem is tearing-off molten chunks of material from rotating cylinder causing loss of material and decreasing the productivity.

State of the Art

Several devices for mineral wool production by means of the centrifugal force are known in state of the art and are referred to as spinning machines, rotating cylinders, or spinners. Typically, mineral melt is discharged from a melting furnace and poured onto a mantle surface of the first rotating cylinder where it is drawn in motion and forms a melt film. A part of the mineral melt is scattered into fibers under the action of centrifugal-force while-remaining-part-o^

rotating cylinder, where the process is repeated. This process is repeated until the last (usually fourth but by no means limiting - the centrifuge can also be comprised of two rotating cylinders) cylinder is reached, where the remaining portion of the mineral melt is fiberized. Blowing nozzles along the edge of each rotating cylinder produce a coaxial air flow (also known as the "blow-in flow") along the rotating cylinders which causes the fibers to be blown off, solidified in their definitive form and wetted by the binder which is injected into the coaxial air flow from the openings on the edges of the rotating cylinders. Said coaxial air flow directs the fibers being formed and wetted by the binder towards the accumulation grid that is positioned perpendicularly or at a certain angle to the direction of said air flow. This coaxial flow is referred to (for purposes of this application) as main coaxial air-fiber flow. Solid state, binder-wetted mineral fibers are deposited on the accumulation grid to form a primary layer of mineral wool. This basic principle of producing mineral wool by means of an centrifugal device is described in patents WO-A1-93/13025, WO-A1-95/14135, WO-Al -96/ 16912 and WO 99/59929.

Main challenge of described mineral wool production method is to attain a good and uniform intertwining of the mineral fibers, a good and uniform wetting of the mineral fibers by the binder and to prevent the mineral fiber layer, once deposited on the accumulation grid, from tearing which is induced by extremes of the coaxial air flow velocity near the accumulation grid. Patent WO-Al -93/13025 addresses uniformity of the mineral fibers deposit on the accumulation grid Patent WO-A1-95/14135 deals with the mineral fiber wetting by the binder; however, the problem of the tearing of the layer of mineral fibers, deposited on the accumulation grid is not addressed. Patent WO-Al - 96/16912 deals with the effect of the mineral melt viscosity on the mineral wool quality, solving it in terms of geometrical disposition and rotational speed of the rotating cylinders. It considers neither the problem of the mineral fiber wetting by the binder nor the problem of the mineral fiber layer tearing on the accumulation grid. Patent WO 99/59929 deals with 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 by directing part of axial flow of air against blow-in flow.

While the patent WO 99/59929 represents an important improvement in treatment of the issues related to the fiber intertwining and wetting with binder and also the tearing of the primary layer on the accumulation grid, the effect on the main coaxial flow direction and turbulent intensity is limited to the area downstream of the melt film on the rotating cylinders. Also, a small portion of the fibers transported with the blow-in flow may enter the recirculating flow induced by said radial fan mounted on the front side of the rotating cylinders and accumulate in the channels between the rotor blades of said fan, partially blocking the air flow through the channels. This may significantly reduce said positive effects of said radial fan on the quality of produced mineral wool.

Description of new invention

Method for producing mineral wool and device for carrying out this method solve above referenced technical problem by manipulating air flow around said rotating cylinder so air flows past backward facing edge of said rotating cylinder at an angle relative to axis of said rotating cylinder. This can be achieved either by shaping the edge of the rotating cylinders by chamfering the edge of the rotating cylinder facing upstream direction of air flow, or by adding a radial fan to the rotating cylinder, namely to side of the rotating cylinder facing upstream direction of air flow (hereinafter referred to as back side or backward facing side or backward facing direction of said rotating cylinder), Such a solution directs air flow coming from back side of the rotating cylinder in general direction of settling chamber (i.e. direction of forming mineral fibers) in such a way that a coaxial, conically-shaped air flow with a significant tangential (swirl) component, looking in the absolute reference frame is formed. Device for producing of mineral wool solves above referenced technical problem by shaping back side of at least one rotating cylinder (i.e. side which faces oncoming air flow, and is facing away from settling chamber) as a radial fan or attaching a radial fan to said back side of said rotating cylinder.

The present invention therefore represents a novel design of the rotating cylinders of the device for production of mineral wool. Said invention solves the technical problem of producing superior quality mineral wool by said process, it being recognized that the characteristics ^~ f ^"" the ^~ mineral ^— wool ^-" depend- on ^— the ^"~ geometrical ^~" an ^" d ^— mechanical ^" characteristics of the mineral fibers, their mean length, their mutual intertwining and their wetting by the binder. The quality of the mineral wool produced by said process proportionally depends on the homogeneity and on the isotropy of 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 mineral wool, produced by said process. Furthermore, the quality of the mineral wool produced by 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 mineral wool, produced by said process.

The objective of the invention is to design centrifugal device for production of mineral 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, an increase in the mean ligament length and reduction of the tearing of the layer of mineral fibers already formed on the accumulation grid. The design of said mineral wool production device must be robust, meaning that it allows said improvements in the quality of the produced mineral wool to be met for a wide range of operating parameters and that it is not sensitive to occurrences which could reduce its efficiency during prolonged periods of operation, e.g. the contamination by fibers and/or binder.

This is achieved by method of manipulating air field around the rotating cylinder in such a fashion that in position of air flow impacting on backward facing edge of said rotating cylinder (i.e. edge of said rotating cylinder facing incoming air flow) said air flow direction is not essentially parallel to axis of said rotating cylinder (i.e. flowing generally in parallel with surface of said rotating cylinder) when impinging on backward facing edge of said rotating wheel. Instead, air flow is in oblique direction to axis of rotating cylinder, i.e. coming at an angle relative to surface of said rotating cylinder. As a result, less molten material is torn off the surface of the rotating cylinder thus improving quality of fiber mat formed on the accumulation grid, this being surprising technical effect.

This method is comprised of the following steps:

- directing mineral melt onto at least one rotating cylinder in order to form fiber by means of centrifugal force causing mineral melt to be thrown from said rotating cylinder and forming fiber by elongating drops of mineral melt into fiber; - blowing air by means of at least one nozzle forming main blow-in air-fiber flow, said air flowing past said rotating cylinder thus forming air flow field around said rotating cylinder;

- manipulating air flow field by directing said air flow past backward facing edge of said rotating cylinder at oblique angle relative to axis of the rotating cylinder outward.

Manipulating of said air flow field can be achieved by further steps:

forming additional radial air flow component directed outward by a radial fan at the back side of said rotating cylinder;

- forming additional axial air flow component by said radial fan at the back of said rotating cylinder;

merging said flows to produce a coaxial, conically-shaped air flow with a significant tangential (swirl) component.

Alternatively, manipulating of said air flow field can be achieved by directing incoming air flow induced by either rotation of said cylinders or by other means (in state of the art by, for example, adding axial centrifugal devices) over rotating cylinder chamfered edge facing the direction of oncoming flow.

Method for producing of mineral wool may be further improved if said air flow direction is such that magnitude of relative velocity between said air flow and said fibers forming off said rotating cylinders is as low as possible.

In essence, air flow is formed by either nozzles or some other axial centrifugal device known in state of the art, or by even inducing air flow through rotation of said rotating cylinder. This air flow is directed by either chamfered backward facing edge of said rotating cylinder or by addition of radial fan to the backward facing side of said rotating cylinder, or by forming of said backward facing side of said rotating cylinder into blades resembling radian fan in such a way that flow no longer displays essentially axial flow field characteristics, but also some radial component thus resulting in air flow no longer flowing essentially parallel to rotating cylinder axis around said rotating wheel but at some angle relative to said rotating cylinder axis. This avoids current rate of entrainment of liquid melt by air field tearing-off chunks of it as experienced by using state of the art rotating cylinders. Of course, some entrainment will still be present even using herein described technical solution but it will be at much lower rate as it is with to-date designs known in state of the art where air flow field manipulation around said rotating cylinder was not considered an issue whereas in fact it was found to be of importance as shown and described herein.

As already stated, according to the invention, the problem described is solved by method of manipulating air flow which can be achieved either by chamfering back side of said rotating cylinder, or alternatively, by shaping back side of at least one of the rotating cylinders as a radial fan or by adding such radial fan to said back side of said rotating cylinder, said radial fan generating new radial air flow, directed outwards, and an axial air flow component, directed in the same direction as the main blow-in flow. Also, downstream of said blowing nozzles and upstream of said radial fan, a concentric, chamfered orifice plate is placed to optimally direct the air flow from said nozzles onto said radial fan. When combined, the axial air flow from the blowing nozzles and the additional axial and radial flow components generated by said radial fan produce a coaxial, conically-shaped air flow with a significant tangential (swirl) component, looking in the absolute reference frame. The air flow direction is such that the magnitude of relative velocity between said air flow and the fibers forming on said rotating cylinders is as low as possible. Also, the direction of said air flow is such that its absolute velocity makes a relatively shallow angle to the direction of local fiber orientation. By reducing the relative velocity magnitude and angle between said air flow and said fibers, aerodynamic force implied upon said fibers is reduced, resulting in a reduction of static and dynamic mechanical stress applied to said fibers. Consequently, fibers are elongated to longer lengths and thinned to lower diameters at the point of tearing from the mineral melt film on said rotating cylinder. The swirl component of the blow-in air flow determines an aerodynamically more stable and spatially more uniformly distributed fiber layer in the phase of pneumatic transport by said air flow, also resulting in a better and more uniform intertwining of said fibers and a more uniform mineral wool primary layer deposit on the accumulation grid. Also, the swirling component of the blow-in air flow improves the dispersion of the binder and subsequent wetting of the fibers by the droplets of said binder. Another advantage of said radial fanned version of rotating cylinders in comparison with the radial fan-less versions of rotating cylinders (with axial-only blow-in flow) is that as the radial and swirl components of the blow-in flow shall significantly reduce the spatial and temporal fluctuations and extremes in air flow velocity near the accumulation grid, thus reducing or even completely eliminating the tearing of the mineral fiber primary layer already formed on the accumulation grid. Consequently, the addition of the radial fan and orifice plate to said spinning machine results in a better quality of produced mineral wool.

Both embodiments for carrying out the method as described herein are further illustrated by means of the figures, these figures forming part of this patent application, and showing:

Figure 1 is a side view of the centrifugal device for producing mineral wool with an accumulation grid and with air flows traced out.

Figure 2 is a front view of the rotating cylinders of the centrifugal device for producing mineral wool with blowing nozzles and radial fan blades shown with a schematic sketch of the course of the mineral melt.

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

Figure ^" 4-shows ^" a ^" radial fan-shaped-as-a-ventilator-rotorr

Figure 5 shows a concentric, chamfered orifice plate located between the blowing nozzles and the ventilator rotor.

Figure 6 shows chamfered rotating cylinder showing also direction of air flow which is being manipulated by such arrangement. A centrifugal device 1 for producing mineral wool 8 comprises one or more, typically four cascading rotating cylinders 3 that each produce centrifugal force, at least one blowing nozzle 6 that generate axial air flow 12 in the duct 9 upstream of the rotating cylinders 2, chamfered orifice plate 5 located between said blowing nozzles and said rotating cylinders and an accumulation grid 2. Further, the back of at least one of the rotating cylinders is shaped so as to form a radial fan 4 that produces an additional radial-axial air flow 13 with outwards radial flow component and an axial flow component in the main axial flow 12 direction. This radial fan may be shaped as a ventilator rotor 4. Further, the body of said ventilator rotor 4 may be circular in form. Further, the body of said ventilator rotor 4 is thinner at the edge i.e., at the outer radius, thickening inwards i.e., towards the inner radius.

The invention thus relates also to centrifugal device 1 for producing mineral wool 8 from fibers 7 that are obtained from mineral melt 10 by means of a centrifugal force, generated by one or more, usually four, cascading rotating cylinders 3 and are pneumatically transported to an accumulation grid by the blow-in air flow 14 produced by the combination of axial flow 12 generated by the blowing nozzles along the outer surfaces of the rotating cylinders, and a radial-axial flow 13 generated by the ventilator rotor 4 of radial fan attached to the back side of at least one of the rotating cylinders 3. Additional effect on the air flow characteristics prior to entering the ventilator rotor 4 is provided by a concentric, chamfered orifice plate located slightly upstream of the rotor 4 blades 17. The invention solves a technical problem of improving the mutual intertwining of the mineral fibers, improving the wetting of the mineral fibers by the binder, increasing the fiber length and preventing the primary layer of mineral fibers from tearing once deposited on the accumulation grid.

Further, about the complete perimeter of said body of the ventilator rotor 4 there are blades 17 which extend to a radius greater than the outer radius 15 of the body of said rotor 4. On the part of blades 17 closer to the cylinder 3 rotation axis than said rotor 4 body outer radius 15, the blade working faces are parallel to the rotation axis of the rotating cylinders 3 and have a given inclination between 0° and 45° to the radial direction, and bend slightly in the direction opposite to the direction of rotation 18 of the rotating cylinder 3 toward the outer radius 16. Said part of said blades 17 may be uncovered or covered by a radial cover 27 attached to said blades. The section of blades 17 outwards from said rotor 4 body outer radius 15 is shaped so as to allow the optimal passing of axial flow 12, which may include a spatial curving of said blade 17 cross section about the radial axis as the distance from the cylinder 3 rotation axis is increased.

Further, a concentric, chamfered orifice plate 5 is positioned in the air duct 9 between the blowing nozzles 9 and the ventilator rotor 4 and may partially, or not at all overlap said rotor blades 17. The inner diameter 21 of said orifice plate 5 is between 50% and 99% of the duct 6 inner diameter 20 and greater than the blade 17 outer diameter. Said orifice plate 5 is chamfered at both inner edges with equal or different chamfer angles 23 and 24, respectively, each between 0° and 90° where angles 0° and 90° mean an un- chamfered orifice plate. The chamfer of both inner edges of said orifice plate 5 starts at the orifice inner diameter 21 and ends at the orifice outer diameter 20. Said orifice plate 5 may form a full circle or a partial circular section about the cylinder 3 rotation axis.

Figure 1 shows the centrifugal device 1 for producing mineral 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 back of each cylinder 3 is shaped as a radial fan in the form of a ventilator rotor 4 that generates the additional radial air flow directed outwards and axial air flow directed in the same direction as the main blow-in flow from the blowing nozzles 6 placed in a circular duct 9 behind the adjacent rotating cylinder 3. The rotor 4 has a typically radial rotor design at small radii and gradually transforms to an axial-like design at radii greater than the radius of the adjacent rotating cylinder 3. Further upstream of said rotor 4, a wide concentric orifice plate 5 with both sides chamfered at certain angles is located with the inner diameter 21 slightly smaller than the diameter 20 of the duct 9. The blowing nozzles 6 along the edges of the rotating cylinders 3 produce an axial air flow 12, which is mixed with the radial-axial flow component 13 generated by the rotor 4, to form the blow-in flow 14 which conveys the mineral fibers 7 to the accumulation grid 2. Out of the layer of mineral fibers, deposited on the accumulation grid 2, mineral wool 8 is formed. Together, the axial air flow 12 from the blowing nozzles 6 and the radial-axial air flow 13, generated by the ventilator rotor 4, also affect the definitive forming and solidification of the mineral fibers 7 from the mineral melt 10 and induce a better and more uniform mutual intertwining of the mineral fibers 7.

Figure 2 shows a front view of the four rotating cylinders 3 with radial fans 4 mounted on back sides (fan blades are only shown on the two rightmost cylinders), behind which the blowing nozzles 6 are situated. Between the cylinder radial fans 4 and blowing nozzles 6, the orifice plate 5 is installed. The mineral melt 10 is directed onto the mantle of the first (i.e., topmost) rotating cylinder 3. On the mantle of the rotating cylinder 3 a thin mineral melt film 19 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 blow- in air flow 14 from the blowing nozzles 6, whereas the remaining part of the mineral melt 1 1 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 back shaped as a radial fan in the form of a ventilator rotor 4. Behind the edge of the rotating cylinder 3 and the chamfered orifice plate 5 there are blowing nozzles 6 that ^~ gmeTate ^~ the ^~ axral ^~ a^

a coaxial, swirling blow- in air flow 14. Said orifice plate 5 can be placed behind the ventilator rotor 4, or it can partially overlap the rotor blades 17 in which case the ventilator rotor 4 outer diameter must be less than the inner diameter 21 of said orifice plate 5. Rotor blades 17 may be uncovered or partly covered by a radial cover 27 so that said cover is attached to said blades and does not extend beyond the outer diameter 15 of the ventilator rotor 4 body. The radial-axial air flow 13 is generated by the radial fan in the form of a ventilator rotor 4. The blow-in flow 14 transports the mineral fibers 7, previously torn by the centrifugal force off the film 19 of mineral melt. The swirling component of the blow-in air flow 14 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. Direction of air flow can be observed, said air coming to backward facing (upstream facing) edge of said rotating wheel at an angle relative to axis of said rotating wheel and not (as in state of the art) generally parallel direction.

Figure 4 shows an embodiment of the radial 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 (i.e., at the outer radius 15), thickening inwards (i.e., 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. The blades 17 extend beyond the outer radius 15 of the body of ventilator rotor 4 where they operate in a manner typical for axial radial fans. Said section of blades 17 which extends at the radius greater than the radial fan body outer radius 15 and lower than the duct inner radius 20 may be spatially curved around the radial axis to attain optimal aerodynamic efficiency of said ventilator rotor 4.

Figure 5 shows a concentric, chamfered orifice plate 5 located between the blowing nozzles and the ventilator rotor 4. The outer diameter 20 of said orifice plate is equal to the ^~ irm¾ridiam ^" eter ^" of ^" sardnduct

the outer diameter 20. Orifice plate length is denoted by position 22 while positions 23 and 24 denote the first and the second chamfer angle. Said orifice plate 5 is geometrically defined as a solid of revolution of the chamfered cross section 25 about the symmetry axis 26 for an angle of revolution greater than 0° and up to 360°, depending on the shaping of air duct 9. For said angle of revolution of 360°, the orifice plate forms a full circle as shown in Fig. 5 whereas for said angle of revolution of less than 360°, said orifice plate forms a partial circular section.

Figure 6 shows said rotating cylinder comprising backward facing chamfered edge i.e. chamfered edge facing upstream direction of air flow, said chamfered rotating cylinder in preferred embodiment comprising flow deflecting chamfer 28, inside part of the duct 29, flow deflecting chamfer angle 30, horizontal distance from end of the flow deflecting chamfer to the end of a duct 31 , back outside diameter of rotating cylinder 32, horizontal distance from back of the rotating cylinder to the start of the flow deflecting chamfer 33, inside diameter of outside part of a duct 34, outside diameter of inside part of a duct 35. Figure shows streaklines of air flow which are no longer parallel as known in state of the art to surface of said rotating cylinder at backward facing edge of said rotating cylinder but rather coming at an angle relative to axis of said rotating cylinder.