HRP970032A2 - Process and device for the free centrifuging of mineral fibres - Google Patents

Description

The invention relates to the process for the so-called external centrifugation or the free centrifugation process for the production of mineral fibers, and more specifically to the blowing intended for removing the fibers and supplying the binder that joins them together.

The invention relates to the process of producing stone wool, which is used as, for example, the basic material for thermal and/or sound insulation of products. More particularly, the invention relates to an improvement in the process of fibrillating high-melting material that can be drawn into strands, comprising, for example, basalt glass and blast furnace slag or other equivalent materials, by which the fibrillation material is poured in a molten state onto a circumferential strip centrifugal, rotating rings, they accelerate it, it separates from them and partially turns into fibers due to the action of the centrifugal force, the gas stream, which goes tangentially towards the circumference of the rings, separates the fibers from the non-fibrillated material, and the fibers thus formed lead to the receiving unit.

The fibrillation process briefly described above is known, for example, from European patent applications 59 152 and 195 725, it is called only the free spin process, from which it is not seen that the molten glass is divided into series of individual strips (internal spin) nor that it is exposed gas-induced extraction, using high-velocity, high-temperature gas. This fibrillation process is very useful, especially since, for all intents and purposes, it alone can be used under economically interesting conditions for materials such as basalt slag, which are characterized by significantly higher melting points than ordinary glasses containing sodium oxide.

In this process of fibrillation, the fibers are guided away from the nearest fibrillation machine by means of a tangential stream of gas, which comes along the periphery of the centrifugal rings, in a direction which is generally parallel to the edges of the rings; the acceleration caused by the centrifugal rings gives the still unfibrillated particles, present between the fibers, a speed sufficient for the peripheral gas stream to significantly affect the path of these particles, which leads to the separation of the fibers that are otherwise removed due to their lower relative density and lower speed.

The invention relates to a device in accordance with that described in European patent EP-B 439 385. This device includes a series of centrifugal rings arranged in an assembly which brings their peripheral surfaces close to each other, these rings being rapidly rotated by means of a motor which located on one side, outside the assembly formed by a series of centrifugal rings, and which drive said rings by means of a mechanical transmission located in such a way that the area in the middle of the series of centrifugal rings is clean. In the path of the material to be fibrillized, two consecutive rings rotate in opposite directions, and the unit for supplying the molten material is mounted so as to allow the said material to be poured onto the outer surface of the first centrifugal ring; the first fan creates a gas stream around a series of centrifugal rings, parallel to the axis of rotation of said centrifugal rings, and the second fan creates an auxiliary gas stream slightly offset from the centrifugal rings and mostly in the same direction as the main gas stream.

Devices of the above type are equipped with a system for supplying a liquid binder designed to mechanically connect the fibers to each other after drying and/or polymerization and to obtain a fibrous mesh.

An important problem is the distribution of the binder within the hasure. Several procedures have been recommended for supplying the binder and for its equal distribution among the fibers. Thus, the European patent EP-B-59 152 recommends feeding the liquid binder into the center of the centrifugal rings and ejecting it by centrifugal force from the circular gap at the same distance from the ring's rim. thus radially ejected binder droplets meet fibers that are themselves ejected parallel to the axis of the ring. that system is very effective, but it also has its limitations. On the other hand, the utilization is not maximal, so it can be said that the percentage of binder actually used is generally less than 100. This is because the fibers have not yet been created and drawn over the inlet rim of the centrifugal rings - in general, they only take up three quarters of the rim at most . Binder ejected over the remaining quarter has a very low chance of meeting the fibers. Another limitation of this procedure is the very short time during which the binder droplets are likely to encounter one or more strands. While the two foil-like currents, that of the binder droplets and that of the threads, are vertical and thin, the area where they intersect occupies a very small volume. The task of the invention is to improve the process described in patent EP-B 59 152.

European patent EP-B-439 385 describes a process of free centrifugation by which an auxiliary stream of gas, which emerges in particular from a ring with nozzles, is added to the main stream of gas emerging from circular slits, which partially cover the periphery of the centrifugal rings. This procedure is very useful for very precise control of the transport conditions of the threads to the receiving part, which has the effect of improving the quality of the insulation material obtained from two points of view: reducing the amount of non-fibrillated particles and increasing the thermal impedance. However, the study of the separation of the spent binder, due to centrifugation, from the circular gap on the face of the surface of the centrifugal ring is not presented in that document. The aim of the invention is to improve this distribution.

Procedures have been proposed to control the distribution of the binder in the various layers that form the fiber tow.

European patent application EP-A-374 112 proposes that the source of the binder in the center of the rotor be added to pipes located in certain special places so that certain areas of the "suspension of threads formed during the process", which correspond to individual layers in the mesh, receive special amounts or special types of binders, causing the appearance of uneven distribution of the binder in the hashura, whereby certain layers, especially on the outside of the hashura, for example, are coated with a larger portion of the binder, while other parts, such as the central part, receive less binder. The aim of the invention is to achieve the opposite of that in EP-A-374 112, because this refers to achieving the maximum possible uniform distribution of the binder throughout the entire thickness of the grid.

In general, if the binder distribution in the so-called stone or glass mineral fiber screed is not uniform, it leads to a decrease in quality from two points of view - appearance quality and mechanical quality.

Resins are used that are generally colored and they give each product a special manufacturer's color, even more, they allow observing the distribution of the binder between the fibers during production.

If the distribution is not satisfactory, lighter areas can be seen in the finished hashura, which correspond to groups of unconnected strands. This represents an obvious disadvantage which, however, in certain cases can have technical consequences: in places where the lack of binder is the greatest, the thread cohesion is insufficient and there is a greater risk for the hasura to delaminate easily. The aim of the invention is to improve the uniform distribution of the binder in the harus.

In order to achieve this, the invention proposes a process for the formation of mineral fibers, by which molten material is cast on the rim of centrifugal rings, which have mainly horizontal axes, where the fibers are formed by centrifugation and then ejected, in a direction mainly parallel to the axes, by the action of the main gas belt over at least part of the circumference of the ring, in which an auxiliary gas stream is created, generally in the same direction as the main gas stream, and by which the liquid binder is ejected onto the fibers, and wherein the auxiliary gas stream consists of individual streams, of which special some rotating currents.

These rotating currents mainly improve the distribution of the binder ejected from the wall of the centrifugal rings on the casing and through its thickness, as well as the actual structure of the casing.

First of all, the rotary auxiliary gas currents are directed convergently in relation to the axis of the rotor.

In order to obtain an even better distribution, the invention additionally enables the introduction of a liquid binder especially in some of the rotary auxiliary gas streams. However, the main part of the liquid binder is introduced primarily into the center of the centrifugal rings and is divided by centrifugal force, while approximately 30% of the liquid binder is introduced via internal auxiliary gas streams, and the rest goes through the center of the centrifugal rings.

The invention also proposes a device for carrying out the procedure. It is a device for forming mineral fibers, which includes centrifugal rings having mainly horizontal axes. The molten material is poured onto the rim of the rings. The device then includes a range on the periphery of the ring which is fed, at least locally, by a gas source and nozzles, also fed with a gas source, located around the gap, while the binder supply system ejects the binder radially into the center of the centrifugal rings. Some of the nozzles of the device, which are specifically located around the gap, include a rotary guide.

Three examples of guides are given, which can be either rotary screws or can be made from a helical rod or can even include a rotary driven vane.

Also provided is a binder supply tube built into the rotary guide.

The invention also proposes a process for the production of mineral fibers, by which the molten material is cast on the periphery of centrifugal rings, which have mainly horizontal axes, whereby the fibers are formed by centrifugation and then, in a direction which is generally parallel to the axes, they are ejected by the main stream of gas over at least part of the circumference of the ring, in which an auxiliary gas stream is created in substantially the same direction as the main gas stream and with which the liquid binder is ejected onto the fiber, whereby the binder is supplied with the auxiliary gas stream.

The delivery of the binder with an auxiliary gas stream advantageously takes place mainly under the centrifugal rings which form the fibres. However, it is useful to introduce the bulk of the binder in the center of the centrifugal rings and distribute it by centrifugal force. Even more, approximately 30% of the liquid binder is introduced with the internal auxiliary gas stream and the rest goes through the center of the centrifugal rings.

The description and figures will facilitate an understanding and appreciation of the advantages of the invention. Thereby

figure 1 shows an external centrifugation machine according to the invention,

figure 2 shows the device for supplying the binder, i

Figure 3 shows the same device with an additional blowing device according to the invention.

A plant for the production of mineral fibers by free centrifugation generally includes the following elements: a furnace for melting the raw material, from which one or more vertical strips of molten vitreous material exit, one or more fiber extraction devices, from which a strip of melt is introduced into each device, and a device in which fibers are formed and burst with a liquid binder. The fibers are caught on a conveyor belt and, if a tangle is formed, they go into a furnace where the binder hardens.

A smelting furnace is usually a cupola furnace that is filled with natural stone and industrial products such as blast furnace slag. Glass is formed in this dome furnace at a temperature of approximately 1500ºC. Current flows into the fibrillation device in Figure 1 and drips onto the first centrifugal ring 1, from which the molten material is ejected towards ring number 2. The first ring, like the others, is surrounded by a gap 3 on the device itself, through which the gas escapes. It serves to cool the ring 1. The ring 2 captures part of the molten material and repels it from its surface using the air current coming out of the gap 4 and forms fibers that are thrown in a direction that is generally parallel to the axis of the centrifugal ring 2. The remaining material, which not converted into fibers, it is ejected towards the centrifugal ring 5, and so on. Like ring 2, each of rings 5 and 6, respectively 7 and 8, has a gap, through which gas is expelled tangentially to the periphery of the ring to draw out and discard the fibers, the velocity of the gases being approximately 100 m/sec. These gases around the centrifugal rings 2, 5 6 form the main gas stream that takes the fibers to the conveyor belt, where they are collected and form a base of fibers. This base of fibers forms the final hasura, or at least one part of it.

In Figure 1, the number 9 shows the nozzles from which the gases that create the auxiliary gas stream blow. these nozzles form a ring and, as explained in the patent EP-B-439 385, the auxiliary gas stream makes it possible to achieve a good distribution and a good orientation of the fibers on the receiving belt.

The binder intended - when hardened - to mechanically join the fibers together, is usually ejected from the centrifugal rings themselves through the central slits. 10, 11, 12.

The device according to the invention is used in nozzles 9. This device includes two elements, each of which successively contributes to the result. These are rotary guides and they feed the binder.

Let's consider the latter first. These are pipes that are mostly concentric with one of the nozzles of the 9 rings by means of a gas stream. Figure 2 shows such a nozzle equipped with a binder supply tube. The nozzle 13 is mounted with its end 14 on the fibrillation machine. The pipe has a diameter of, for example, 40 mm and gases are ejected from it at a speed of approximately 70 m/sec. The tube 16, preferably on the axis of the outlet 15 of the nozzle, enables the supply of binder in the middle of the gas stream flowing through the nozzle 13.

Experiments were carried out to bring the binder to different places in the ring using the gas stream in Figure 1. It was observed that the distribution of the binder in the fiber bundle is significantly improved if the secondary supply of the binder is made below the rotors 2, 5 and 6, which form the fibers, especially below the first 2 and the second 5. Such binder supply, which is connected to some of the nozzles in the ring, does not serve to supply the secondary binder. It was observed that the best conditions are those when only 30% of the binder is applied to the ring, and the rest is ejected in a conventional way from the center of the rings 10, 11, 12.

Figure 3 shows a nozzle equipped with its own binder supply and with a rotary guide. These two devices are independent and each works independently. The rotary guide is intended for the rotation of the auxiliary gas stream coming out of the nozzle such as the one 9 in Figure 1. The system shown in Figure 3 belongs to the "corkscrew" type, that is, a metal rod 17 in the form of a spiral is placed inside the nozzle concentrically with the latter. When the gases flow through the nozzle they meet the spiral rod at high speed (for example 70 m/s), and they rotate around the axis of the nozzle. Other equivalent devices were also tested, in particular a rotating screw, whose axis coincides with the axis of the nozzle, and even a system that included a blade that rotated around the axis of the nozzle, whereby the blade had a slight spiral shape, which allowed it to rotate when the speed of the gas stream stabilized. All of these rotary devices enable the rotation of at least some of the auxiliary gas streams.

To evaluate the effectiveness of the above means, many comparative experiments were conducted. For each means, the rotary guide on the one hand, and the central supply of binder, on the other hand, as well as for the combination of both means, large quantities of stone wool were produced under the same conditions and the results were compared.

The essential production parameters that must be reflected equally in the two experiments intended for comparison were: the degree of extraction, the density of the final weave, the amount of binder and the features, the diameter and the length of the individual fibers.

The tests intended to evaluate the distribution of the binder in the final product, that is to compare the test results, were of two types, one of which was a visual observation and the other was a tear test.

The visual appearance was evaluated by measuring the color on the surface of the finished hasura. The color was measured using the trichromatic coordinates L*,a*, b*. The colorimeter measuring the reflectance on a circular surface with a diameter of 8 mm was a CR 100 type from the MINOLTA company. 30 evenly spaced measurement points were selected on a 1 m x 1 m panel. Since the binder produces a yellow product, only the L* (luminance) and b* (blue) coordinates were measured. The measurement consists in calculating the percentage of measured points for which L* is greater than 0.62 and b* is less than 0.20. These boundaries are those that separate the area where there is no binder ("white strip") and the area where the binder is laid normally. The calculated percentage gives the "white bar content".

The tear test serves to determine the tensile strength of the end product perpendicular to the surface of the grid and is carried out in accordance with the CEN/TC 88 standard. From the width of the production line, 16 samples of 10 x 10 cm were taken, uniformly distributed over the entire width. 10 mm thick preparation connected with glue on each side. Then, when the glue had hardened, the samples were placed one by one in an INSTRON strain gauge and the yield force was read. At the same time, one side of the sample was fixed, while the other side was pulled.

Breaking strength in kN/m2, σ, j:

σ = 10-3 F/S

where F is the force measured in newtons, and S is the area (0.01 m2).

The measurement of the "white band content" was performed on three different samples and on a comparative sample. The production mesh had a density of 45.5 kg/m2, the amount of binder in the final product was 3.1%, and the content of white tape was 22%.

Under the following conditions, three experiments were carried out in accordance with the invention

1.) The rotation itself

All nozzles in the ring were equipped with a rotary guide consisting of a spiral rod in Figure 3, the binder was fed conventionally through the center of the centrifugal rings 10, 11 and 12.

2.) Supply of binder to the nozzles

None of the nozzles 9 had a rotary guide. The binder supply pipes were fixed in all nozzles located between the eighth and fifteenth and between the twenty-third and twenty-fifth nozzles, which are numbered in the positive direction in Figure 1 starting from the top left of the figure. 70% of the binder was supplied through the center of the centrifugal rings, and 30% through the nozzles.

3. Rotation and supply of binder to the nozzles

It is a combination of the two above means; all nozzles were equipped with a rotary guide and nozzles 8 to 15 and 23 to 25 had binder feed tubes (same dimensions as above).

The results are listed in the table.

[image]

These results show that each of the two proposed means, rotation and outsourcing, is effective on its own (improvement of 32% and 41%, respectively), and that their combination gives a further improvement (actual disappearance of "white bands").

Even more, the excellent results obtained with the combination of the two systems were confirmed by performing tear tests in the following experiments, in which the density was twice the above.

The results are also summarized in a table.

[image]

In the tear test, an improvement of 16% was observed.

By carrying out the procedure according to the invention, a significant improvement was obtained in both appearance (white strip content) and mechanical properties (tear).

This better distribution of the binder, in addition to the mechanical behavior of the finished hashura, has another advantage: it gives a shaped hashura with better cohesion. This is especially useful, if the hems are produced in two stages, by making the primary weave, as thin as possible, and then placing several thicknesses of the primary weave, zig zag, perpendicular to the axis of movement of the hem. The higher the number of primary weaves, all other things being equal, the smaller the individual thickness and the better the final weave properties.

these experiments showed that where, in the case of the surface density of the primary weave, the normal production of hasura was limited to a low result, (below this minimum value the weave tears and cavities are formed), under full production conditions the invention very easily allows a reduction to values that are at least 30% lower, that is, the primary weave is thinner by 30%, and enables a significant improvement in the quality of the finished hasur.

Claims (10)

1. A process for the production of mineral fibers, by which the molten material is cast on the rim of centrifugal rings, having generally horizontal axes, the fibers being formed by centrifugation and then thrown with the main gas stream in a direction generally parallel to the axes, at least over a part the circumference of the rings in which an auxiliary gas stream is created, mostly in the same direction as the main gas stream, and with which the binder is thrown onto the fibers, indicated by the fact that the binder is fed into the auxiliary gas stream. 2. The method according to claim 1, characterized in that the binder is fed into the auxiliary gas stream mainly close to the centrifugal rings that form the fibers. 3. The method according to claim 1 or claim 2, characterized in that the main part of the binder is brought to the center of the centrifugal rings and is divided by centrifugal force. 4. The method according to claim 3, indicated by the fact that approximately 30% of the liquid binder is supplied by means of internal auxiliary gas streams, and the rest is supplied through the center of the centrifugal rings. 5. The method according to any of the preceding claims, characterized in that the auxiliary gas flow consists of individual flows, some of which are rotary in particular. 6. A device for the production of mineral fibers comprising rings, having generally horizontal axes, on the periphery of which the molten material is poured, goes into a gap on the periphery of the rings, at least in places by means of gas and nozzles, which are also fed from a gas source, located around the gaps, while the binder supply system, in the center of the centrifugal rings, ejects it radially, indicated by the fact that some nozzles, which are located around the gaps, include pipes for supplying liquid binder. 7. Device according to claim 6, characterized in that some nozzles include special rotary guides. 8. Device according to claim 7, characterized in that the guides are made in the form of a spiral rod. 9. Device according to claim 7, characterized in that the guides are rotating screws. 10. Device according to claim 7, characterized in that the guide includes a blade with a rotary drive.