HRP970033A2 - Improvement to devices for manufacturing mineral fibres by free centrifuging - Google Patents

Description

The invention relates to a device for the production of mineral fibers by centrifugation from extractable material.

Procedures called free centrifugation are known, and according to them, the material for fibrillation is brought in a molten state from the outside to the rim of the fibrillation rotors and, caught by the rotors, is forcibly separated from them in the form of fibers due to the action of centrifugal force.

In this process, generally 3 or 4 centrifugal rotors are used, located close to each other. The molten material is poured onto the first rotor, accelerated and taken to the next rotor. The material, which can be drawn into threads, passes from one rotor to another, with each rotor turning some of the material into fibers and sending them to the next rotor.

These procedures are especially used for the industrial production of stone wool from basalt glasses, slag from blast furnaces and more generally from any material with a high melting point.

Many improvements have been proposed for these processes, and special mention should be made of the improvement described in European patent EP-B2-0,059,152.

Centrifugal rotors are exposed to high temperatures due to their contact with molten material. However, these high temperatures do not have to be such that they lead to deformation and/or wear that would be detrimental to the position of these rotors. Therefore, the conventional devices described in the above-mentioned patent application include cooling means consisting in particular of the flow of a current of water through the rotor shaft and also through the inner surface of the peripheral part of the rotor.

Two types of cooling are known, with recycling liquid or with liquid that is lost. That is, in the latter case, the liquid is generally water, which, after passing through the rotor, is ejected from it through the holes. The method according to the invention belongs to this second method of cooling.

In document EP-B-0,195,725 the cooling water after contact with the rim of the centrifugal ring is evacuated (possibly in the form of steam) through holes arranged on both sides of the rotor. The fact that the cooling water is ejected, and that it is done close to the hottest point of the centrifugal rotor, has many advantages. Firstly, the fluid flow, which goes in one direction, is therefore greatly simplified and, secondly, the exiting water can evaporate, which, due to the very high latent heat of evaporation, results in much more efficient cooling.

The European patent EP-B-0,195,725 shows in detail the system for supplying cooling water to the centrifugal rotor, which also has a supply of binder inside the rotor, which ensures mutual cohesion within the grid they form. In the case of water supply, a pipe is installed, concentric with the axis of the rotor, with which the water is drained, which ends in the plane of symmetry of the rotor in an expanded nest from which the water exits through the cavities and enters the inner space of the rotor and is then directed by means of centrifugal force to the holes that they come out on each side of the side surfaces.

The cooling system in general in the two previous documents fulfills its role perfectly and enables a significantly longer service life of the centrifugal rotors. However, although the cooling is generally effective, large temperature gradients exist at the rim, where the liquid vitrified material is deposited. Because of this, the material is deposited and retained on the belt, which has a certain thickness, before it is discarded in the form of fibers or in the form of droplets thrown onto the next rotor. If the relative position of the ejected jet from the melting part and from the rotor remains the same, a large temperature difference occurs between the substrate in the center of that strip, which is very hot, and the area immediately to its edges; in the place where the thickness of the molten material is smaller, the substrate remains cooler, because the mass is greater, while the surface for heat exchange with the outer side is essentially the same. This favors the reduction of that gradient, as it is a source of wear due to the stress introduced into the fibrillation rotor.

In patent application WO 95/07243, a centrifugal rotor intended for the production of mineral fibers is proposed, with a very different construction from the previous one. It has the shape of a drum rather than a ring, its thickness along the axis being generally greater than its greatest diameter. Additionally, the diameter in the area covered with the fibrillation material may be different. The molten material is deposited at one end of the drum, at a place of smaller diameter, and progressively, along the axis of the fiber formation area, at the other end of a larger diameter. In the last area, holes are made on the rim of the drum that allow water to escape in the form of steam. The purpose of the introduction device is to obtain fibers that differ very little from each other in diameter.

As for the temperature gradient, at the external joint of the drum according to WO 95/07243 it is slightly increased, not decreased compared to the prior art, because the molten material cools mainly during its progress from one end of the joint to the other. It seems that the function of the dimples, through which the steam escapes, is not primarily a cooling one, because in the hottest area, where the molten material is deposited, there are no dimples, while the task set was to avoid contact with the metal opposite each dimple and, therefore, very locally , the formation of a series of pimples in the molten material, each pimple originating from a fiber.

Although this is not their primary function, the holes that allow steam to escape facilitate the cooling of the fibrillation material, which covers the holes as well as the layer itself in that area. Since the material for fibrillation is the coldest at that point, the effect of steam escaping through the holes increases the thermal gradient at the joint.

The aim of the invention is to reduce the thermal gradient in the axial direction of the rim of centrifugal rotors.

The invention provides a rotor for fibrillation that is part of a plant for the production of mineral fibers by external centrifugation, where the rotor includes a rim on the outside of which the molten material for fibrillation is fed from the dividing rotor, or from another rotor for fibrillation. The rotor includes an internal liquid circulation with holes for draining the liquid. The holes are located on the rim on the part of the fibrillation rotor where the fibrillation material is fed.

This arrangement of cooling holes allows the temperature to be reduced in the hottest part of the substrate. The result is a lowering of the corresponding temperature gradient.

Preferably, the holes are arranged on the rims in at least two rows in parallel planes and, advantageously, the rotor includes two rows that are symmetrical with respect to the plane of symmetry of the rim.

The arrangement in parallel rows, especially when they are centered symmetrically to the rotor of the invention, enables cooling of the center of the area where the molten material is deposited.

The invention therefore provides a means for distributing the liquid, which enables the feeding of each row of holes and, usefully, the dividing means for feeding the holes is a series of dividing cavities located in a plane parallel to the plane in which the row of holes is located.

The result of this is that all rows of holes are finally powered. One way to achieve this result is to make a series of holes, separated from each other by a continuous partition, each series of cavities thus feeding the series of holes and not affecting the adjacent series of holes.

In the embodiment of the rotor according to the invention, which is preferred, a two-part chamber for the supply of liquids is made for this purpose, one part of the chamber serves for the supply of liquids, and the other part is a distribution chamber, where they are then connected by means of distribution cavities. In general, the distribution cavities have a total cross-section smaller than the total cross-section of the rim holes. In general, as far as both chambers are concerned, they are designed so that the flow rate of liquid to the rotor can be adjusted so that a supply of liquid is created in the feed chamber.

To ensure optimal cooling of the inside of the rotor, it is useful that the separation cavities are arranged in two rows in the same planes, on each side of the two surfaces with rows of holes on the rim. The same is done for the inner wall of the rotor, which is located on the side where the fibers are ejected, and on the opposite side, going from the inside of the rotor, it approaches the rim, so that the liquid goes from the separation cavities and, as it progresses towards the holes on the rim, it sprays out through them.

Thus, before it exits, the liquid extracts maximum heat from the rotor.

In the case of cooling on the fiber extraction side, at the place where air heated by passing over the molten material is blown, which passes by the rotor and also heats it up, the rotor according to the invention has direct exit holes arranged in a circle and centered on the axis of the rotor, and they are located on side of the rotor where the fibers are ejected, and the direct exit cavities primarily feed the circular groove of a large radius. In this case, it is useful that the total cross-sectional area of the direct exit cavities is of the same order of magnitude as the cross-sectional area of the dividing cavities, with the fact that the latter can be usefully larger. These direct side cavities are generally located on the flange that forms the side wall of the rotor.

Such a choice of an equal flow rate of the liquid coming out of the rim and the liquid coming out of the side of the rotor, the latter being however less heated with the molten material, shows the effectiveness of the main cooling system according to the invention at the hottest point.

The description and the following figures will enable the invention to be understood and its advantages to be assessed.

Figure 1 shows a fibrillation machine with two fibrillation rotors, figure 2 shows a section through a fibrillation rotor according to the invention and figure 3 shows the temperature distribution curves on the surface of the rim determined on the same rotor.

Figure 1 shows a type of fibrillation device used in accordance with the invention, which includes three centrifugal rotors 1, 2 and 3, where two successive rotors rotate in opposite directions. A device of the same type with 4 centrifugal rotors is also generally used. The material for fibrillation 4 is in a molten state and is poured through the outlet 5 or from the hole of the stabilizing tank onto the first centrifugal rotor 1, which is also called the dividing rotor, since it does not really produce fibers, but its function consists mainly in accelerating and distribution of the material for fibrillation 4 on the next rotor 2. The material therefore comes to the rotor 2 and partially adheres to it. The glued molten material is separated from the rotor 2 by the action of centrifugal force and then the fibers are formed which relate to the gas stream created by means of the holes on the fan ring 6 and/or on the extraction lips, while the unglued material goes on to the next centrifugal rotor 3 for production, in the same way, further fibers.

The gas stream carrying the fibers is directed transversely to the direction of ejection of the fibers from the rotor. By the action of the element 7 for ejecting the binder into the gas stream, the binder is centrifugally ejected in the form of droplets. The gas stream finally blows up the binder droplets so that the resulting fibers are uniformly coated with the binder.

These centrifugal rotors are water cooled, primarily with the amount of cooling water flow adjusted for each rotor depending on the desired equilibrium temperature. Normally, going from the first rotor 1 towards the end rotor 3, the temperature of the rotor in contact with the molten material decreases.

The invention relates to centrifugal rotors and their cooling system with circulating liquid.

Conventional centrifugal rotors, similar to those described in patent EP-B-0,195,725, usually consist of a shaft through which fluids - cooling water and binder - are fed, from a rim to a rim on which the molten material fibrillates, which is divided in the molten state, and two flanges on either side of the rotor, which are connected on one side to the shaft and on the other side to the rim, thus forming a kind of inner chamber (the rotor is hollow), through which the coolants flow before being expelled through the holes that are generally located on the flanges. Fibrillation rotors also, in addition, in their central part, on the side of fiber extraction, generally include an element 7 for ejecting the liquid binder (see patent EP-B-0,059,152), which will not be discussed here.

This is a cooling system for centrifugal rotors of the above type, which can be improved with the invention.

Unlike the system of the earlier type, the centrifugal rotor according to the invention has holes on the rim of the rim itself for the exit of the coolant - water in most cases. These holes are marked 8, 9 in Figure 2, and they were drilled through the rim in areas 10, 11 that were specially thinned. Such a configuration enables very efficient cooling of the central part of the rim, at the point where the most heat is supplied with the fibrillation material. These holes emerge on the surface of the rim, which has a normal structure. In the figure the rim is marked with circular ribs 12 which are in a plane perpendicular to the axis of the rotor, but any other structure useful for good fibrillation is compatible with the invention.

Figure 2 shows a preferred embodiment of the invention, i.e. the rows of holes are separated by some kind of partition 30, which on the one hand enables separate feeding of each row of holes, and on the other hand divides the hollow part inside the rotor into two chambers, the feeding chamber 13 and the distribution chamber 14. The two chambers 13, 14 are connected to the connecting cavities 15, 16. The supply chamber 13 receives the coolant in the usual way via the motor shaft, which is not shown. Due to the action of centrifugal force, the liquid is ejected to the periphery of the chamber 13, at the place where the cavities 15, 16 are located. also over the inlet rim of the chamber 13. At the outlet cavities 15, 16, the liquid is ejected by centrifugal force along the axis of these cavities and first of all hits the walls of the separation chamber, i.e. 17, 18, which go all the way up to the rim of the rotor and thus enable the coolant to advance - again by the action of the centrifugal force - towards the holes 8, 9, "mourning" the walls 17, 18, which are thus cooled before the liquid goes from the inside of the rotor to the rim. The "partition" 30, between the two rows of holes, guarantees the power supply of each of the two rows. The two chambers are shown in the picture as closed boxes. This is not necessary since the centrifugal force systematically drives the water in a radial direction parallel to the plane of symmetry of the rotor.

In the prototype rotor with a diameter of 350 mm, holes 8, 9 form two circular arrays with 120 cavities, each of which had a diameter of 1.2 mm. The first row 8 lies on one side of the plane of symmetry of the rotor, and the second row 9 lies symmetrically on the side of the fiber extraction. The wall, which separates the two chambers 13, 14, is itself drilled with two circular series of cavities 10, each of which has a diameter of 0.9 mm. Thus, a series of holes on the rim with a total cross-sectional area of 271 mm2 was obtained, while they are fed by the action of connecting cavities 15, 16 of a much smaller total cross-section, namely 12.7 mm2. The choice of these sections prevents the retention of the coolant in the distribution chamber where there is a risk of heating, and the possible formation of steam can increase these problems. Creating a supply of liquid in the feed chamber by adjusting the flow rate of the liquid allows for a safe continuous supply.

Two chambers, namely the feeding chamber 13 and the dividing chamber 14, form one embodiment of the invention. The arrays of holes 8, 9 can also be fed directly from the area 10, 11 which is separated by the partition 30, by placing feeding cavities which act in the same way as the cavities 15, 16, but which are located on a tube concentric with the axis of the rotor, compare the document EP-B-0,195,725.

Other tests were performed with rows of holes on the rim, which were distributed asymmetrically with respect to the plane of symmetry of the rotor. The results were equally satisfactory.

Figure 2 shows a cavity 19 which forms part of a circular array of direct outlet cavities and provides additional cooling of the outer wall of the fibrillation rotor, on the fiber withdrawal side. The holes 19 in the prototype have a diameter of 0.9 mm and are marked with the number 10. Their total cross-sectional area is thus 6.4 mm2, which is less than the total cross-sectional area of the connecting cavities 15, 16 (12.7 mm2), but the difference is not large . As can be seen in the picture, a circular channel 32 is made above the cavities 19 in which the liquid coming out of the cavity 19 is collected and distributed over a wider area. Similarly, the cavity 19 projects rearwardly behind the channel 32 and above all in relation to the edge of the rim, allowing the fluid to extract heat from a large area of the side of the rotor before exiting the rotor.

Compared to a conventional cooling system (where cavities lying in the flange on each side of the centrifugal rotors are used), the system according to the invention, as just described, is much more efficient and allows the use of only 250 liters of water per hour, instead of the usual 350 - 400 liters .

Figure 3 shows a possible temperature profile on the rim surface. It is very difficult to measure the actual temperature profile of the metal on the surface of the rim, which is located directly next to the molten material. This here is an estimate, the most likely, and is fully compatible with the results of experiments on centrifugal rotors according to the invention produced in production, the results of which will be discussed below.

Two curves are shown:

22: temperature distribution curve under operating conditions in the case of conventional centrifugal rotors;

23: curve of temperature distribution on the rotor rim according to the invention.

With the old system, the cooling is less effective in the center of the rim, between the borders 20, 21, between which the molten material is deposited. On the other hand, it is much more efficient on the side of the ring where the circumferential blowing takes place (on the plant side) and works identically on the side of fiber extraction.

The temperature gradient in the area 20, 21 is marked with 24 and 25 for the earlier method, i.e. for the invention, where the latter temperature gradient is significantly smaller than the earlier one.

Comparative tests were carried out with common compositions that are normally used for rock wool fibrillation, and also with special compositions that are much more fluid, have a steeper viscosity curve and/or a narrower "working area".

Conventional masses that can be fibrillated for the production of stone wool had the following mass composition:

SiO2 50%

Al2O312%

CaO 28%

MgO 6%

Fe2O3 2.5%

various oxides 1.5%

Compositions of the above type, which can be fibrillated, show a very slow change in viscosity as a function of temperature. Thus, the viscosity goes from log10η = 1 at the point where the temperature is 1493°C to log10η = 3 at a temperature difference of approximately 380°C. The operating range is considered to be the temperature range that divides the temperature at which the viscosity corresponds to log10η = 1 from the temperature of the liquidus, at the moment of the start of vitrification. That second temperature in this case is 1230°C, so it can be said that the working range has a range of 260°C. Such a composition, which can be fibrillated on centrifugal rotors according to the invention, makes it possible to obtain mainly longer fibers than with conventional rotors. Further, during endurance tests for 40 hours, with rotors according to the invention driven at a speed of 6000 revolutions per minute, fiber elongation was observed such that it was possible to reduce the surface density of the primary warp from 300 g/m2 to 220 g/m2 with equal by the amount of binder for a given index of fineness ("shaping"). Extending the fibers also allows for a reduction in the amount of binder.

"Fazoning" is a measure used by all stone wool producers, and which allows for the evaluation of the overall fineness and length of the fibers. It is measured using a so-called "shaping" device, for example a device from the company AVIATEST NIEBERDING, Germany. The test sample is a strand of mineral wool, without binder or oil, of a certain mass, which may contain non-fibrous ingredients (slag, sand, etc.) conditioned by certain fibrillation processes. This is prevented in a cylindrical chamber of previously determined volume. A stream of gas - dry air or nitrogen - passes through the test sample. The gas flow rate is kept constant, and the pressure drop across the test sample is measured using a water column graduated in conventional units.

Primary weave is a stage in production when weaves are produced in two stages: first, the primary weave is formed from fibers and a liquid binder (this weave is as thin as possible) and then several thicknesses of the primary weave are arranged in a zigzag, perpendicular to the end axis mess. The characteristics of the final weave are better the greater the number of primary weaves, i.e. when all things are equal, and only the individual surface density is lower. Normal production is limited due to the low ultimate surface density of the primary weave (below this minimum value the weave tears and voids are visible), but with this invention it is possible under the same production conditions to easily go down to lower values, which significantly improves the ultimate quality mess. It can also be said that for a given quality, i.e. for a given number of folds of the primary weave in the final hesura, the amount of binder can be reduced, because the binder, which ensures the cohesion of the primary weave, is liquid.

Other tests were carried out with a composition that is much more fluid in the liquid state. It is a product that includes a high proportion of blast furnace slag with a low iron content, which makes it possible to obtain clean fibers that are desirable for some applications, especially for spraying. A typical mass composition is for example:

SiO2 44%

Al2O311%

CaO 38%

MgO 5%

Fe2O3 <1%

various oxides >1%

The temperature difference, which corresponds to the viscosity η so that log10η = 1 and the liquidus, in that case is 90°C, which corresponds to a narrow "working area". To work properly, it is necessary to keep the molten material during fibrillation within a very narrow temperature range. With centrifugal rotors according to the invention, it has been found that the plant can be maintained much more easily under proper production conditions.

Some compositions of rock wool are particularly difficult to fibrillate. This is especially the case with those that dissolve much faster in biological fluids.

Such a typical mass composition:

SiO2 52%

Fe2O30.5%

Al2O3 2%

CaO 31.5%

MgO 9.5%

Na2O 4%

miscellaneous 0.5%

has a particularly narrow working area, which makes it very difficult to control fibrillation conditions with conventional rotors. Therefore, the temperature for log10η = 1 is equal to 1360°C, and the liquidus is at 1340°C, which gives a working range of 20°C. In plants equipped with rotors where the coolant exits from the side flanges, it is really impossible to stabilize the plant, which constantly oscillates between material that fibrillates and is too hot to fibrillate or too cold, so devitrification occurs. The rotors according to the invention made it possible to stabilize the plant and fibrillate for hours without interruption. They thus provide a solution to a major problem affecting health and the environment.

Even more, the above three cases, regardless of whether it is a conventional composition or a composition that is more difficult to fibrillate, a lower wear of the centrifugal rotors that have to be replaced at a working time that is approximately 20% longer is observed.

Thus, it can be seen that the device according to the invention, acting by lowering the temperature gradient on the rim of the centrifugal rotor under the molten material for fibrillation, enables significantly improved production conditions, in both senses, in terms of production quality (fiber length and prevention of quality reduction due to rotor wear) and from the point of view of stability conditions (especially with a composition with a very narrow working area), or from the point of view of equipment wear.

Claims (14)

1. The fibrillation rotor, which is part of the plant for the production of mineral fibers by external centrifugation, has a rim on the outer side to which the material to be fibrillated is fed in a molten state either from the separation rotor or from another fibrillation rotor, the rotor also includes an internal liquid circulation with holes for the exit of the liquid located on the rim of the rotor, characterized by the fact that the holes (8, 9) lie in that part of the rim where the material to be fibrillated is fed. 2. Fibrillation rotor according to claim 1, characterized in that the holes (8, 9) are arranged on the rim in at least two rows lying in parallel planes. 3. The rotor for fibrillation according to claim 2, characterized in that it includes two rows that lie symmetrically in relation to the plane of symmetry of the rim. 4. A rotor for fibrillation according to claim 2 or claim 3, characterized in that the means for distributing the liquid enables the feeding of each series of holes. 5. A rotor for fibrillation according to claim 4, characterized in that the means for distribution feeding the series of holes is a series of distribution cavities arranged in a plane parallel to the series of holes. 6. Fibrillation rotor according to claim 5, characterized in that the rows of holes (8, 9) are separated from each other by a continuous partition (30). 7. Fibrillation rotor according to claim 5 or claim 6, characterized in that it includes a two-part liquid supply chamber, a supply chamber (13) and a distribution chamber (14) and that they are connected to distribution cavities (15, 16). 8. Fibrillation rotor according to one of claims 5 to 7, characterized in that the dividing cavities have a total cross-sectional area smaller than the total cross-sectional area of the holes on the rim. 9. Rotor for fibrillation according to claim 7, characterized in that the speed of liquid inflow to the rotor is adjusted so that a supply of liquid is created in the supply chamber (31). 10. Fibrillation rotor according to one of claims 2 to 9, characterized in that the dividing cavities are arranged in two rows in the planes on each side of the two planes of the rows of holes on the rim. 11. Fibrillation rotor according to claim 10, characterized in that the inner walls (17, 18) of the rotor, which are located on the side where the fibers are ejected, and also on the opposite side, approach each other going from the inside of the rotor towards its circumference, and the liquid, which comes out of the distribution cavities, is sprayed over them, advancing towards the holes on the rim. 12. Fibrillation rotor according to one of claims 1 to 11, characterized in that on the side it has direct outlet cavities (19) arranged circularly centered on the axis of the rotor, and located on the side of the rotor where the fibers are ejected. 13. Rotor for fibrillation according to claim 12, characterized in that the circular groove (32) with a larger radius is fed from the direct outlet cavities (19). 14. Rotor for fibrillation according to claim 12 or claim 13, characterized in that the total cross-sectional areas of the direct outlet cavities (19) and the dividing cavities are of the same order of size, but the latter are preferably larger.