PRODUCT BASED ON MINERAL FIBERS AND PROCESS FOR OBTAINING IT

Abstract

A thermal insulation product based on mineral wool, characterized in that the fibers have a micronaire of less than 10 1/min, preferably less than 7 1/min and especially between 3 and 6 1/min, and in that the material has a thermal conductivity of less than 31 mW/m.K, especially less than 30 mW/m.K. The parameters for obtaining this product are in particular the pressure of the burner, the rotation speed of the fiberizing spinner and the daily fiber output per spinner orifice.

Claims

1. (canceled)

2. In an internal centrifugation fiberizing process for producing a thermal insulation product with an internal centrifugation device comprising (1) a spinner capable of rotating about an axis X which has its peripheral band drilled with a plurality of orifices for delivering filaments of a molten material, (2) a high-temperature gas attenuating unit in the form of an annular burner which attenuates the filaments into fibers, (3) a receiving belt for receiving the fibers, and (4) a conveyor for the fibers that extends the receiving belt; the improvement wherein the conveyor conveys the fibers at speed greater than the speed of the receiving belt by more than 10% and the process produces a thermal insulation product having at least 75% of its fibers aligned approximately parallel to the longer dimensions of the planes of the thermal insulation product, meaning a parallelism to within plus or minus 30° with respect to the planes formed by the longer dimensions of the product.

3. In the internal centrifugation fiberizing process for producing a thermal insulation product according to claim 2, the improvement wherein the conveyor conveys the fibers at speed greater than the speed of the fiber-receiving belt by more than 15% and the process produces a thermal insulation product having at least 80% of its fibers parallel to the longer dimensions of the planes of the thermal insulation product.

4. The improved internal centrifugation fiberizing process for producing a thermal insulation product according to claim 2, wherein the improvement additionally comprises maintaining the pressure of the burner between 450 and 750 mmWC, maintaining the rotation of the spinner at a speed greater than 2000 revolutions/minute, and maintaining the daily fiber output per spinner orifice at no more than 0.5 kg.

5. The improved internal centrifugation fiberizing process for producing a thermal insulation product according to claim 2, wherein the improvement additionally comprises maintaining a throughput of molten material entering the spinner at less than 18 tonnes/day for a spinner having at least 32,000 orifices.

6. The improved internal centrifugation fiberizing process for producing a thermal insulation product of claim 2, wherein the improvement additionally comprises a spinner having a diameter of between 200 and 800 mm, and adapting the fiber output per orifice to the diameter of the spinner.

7. The improved internal centrifugation fiberizing process for producing a thermal insulation product of claim 2, wherein the improvement additionally includes a spinner having an orifice-perforated band height of at most 35 mm.

8. The improved internal centrifugation fiberizing process for producing a thermal insulation product of claim 2, wherein the improvement additionally includes the diameter of the spinner orifices of between 0.5 and 1.1 mm.

9. The improved internal centrifugation fiberizing process for producing a thermal insulation product of claim 2, wherein the improvement additionally comprises orifices of the spinner distributed in several annular zones, rows of orifices of different diameter in each zone, and the diameter of the offices per annular row decreases, in a centrifugal position, from a top of a peripheral band of the spinner toward the bottom.

10. The improved internal centrifugation fiberizing process for producing a thermal insulation product of claim 9, wherein the improvement additionally comprises varying the distance between centers of neighboring orifices in each annular zone and varying the distance from one zone to another by at least 3%, and in the centrifugal position, the distance between centers of the neighboring offices in each annular zone decreases from the top of the peripheral band of the spinner toward the bottom is between 0.8 mm and 2 mm.

Description

[0045] Other advantages and features of the invention will now be described in greater detail with regard to the appended drawings in which:

[0046] FIG. 1 illustrates a schematic vertical cross-sectional view of a fiberizing installation according to the invention; and

[0047] FIG. 2 illustrates a schematic vertical cross-sectional view of the fiberizing device of the installation.

[0048] FIG. 1 shows schematically a cross-sectional view in a vertical plane of an installation 1 for forming a mineral wool blanket.

[0049] The installation 1 comprises, in a known manner from upstream to downstream, or from the top down, along the direction of flow of the attenuable material in the molten state, an internal centrifugation device 10 that delivers filaments of an attenuable material, an attenuation device 20 delivering a gas stream that converts the filaments into fibers, which fall in the form of a web 2, an annular inductor 30 placed beneath the centrifugation device 10, a binder supply device 40, and a belt 50 for receiving the fibers, on which the fibers accumulate so as to form the blanket. The blanket is then conveyed to an oven in order to cure the fibers and the binder by means of a conveyor belt that extends the receiving belt 50 in the same plane.

[0050] FIG. 2 illustrates the devices 10, 20 and 30 of the fiberizing installation in greater detail.

[0051] The centrifugation device 10 comprises a spinner 11, also called a fiberizing dish, rotating at high speed, having no bottom in its lower part, and pierced around its peripheral wall 12 by a very large number of orifices via which the molten material is ejected in the form of filaments owing to the centrifugal force.

[0052] The bottomless spinner 11 is fastened to a hub held on a vertically mounted hollow shaft 13 rotating about an axis X, the shaft being driven by a motor (not shown).

[0053] A basket 14 with a solid bottom is connected to the spinner, being placed inside the spinner, so that its opening faces the free end of the hollow shaft 13 and its wall 15 is substantially away from the peripheral wall or band 12.

[0054] The cylindrical wall 15 of the basket is perforated by a small number of relatively large orifices 16, for example having a diameter of around 3 mm.

[0055] A stream of molten glass feeds the spinner, passing through the hollow shaft 13 and flowing out into the basket 14. The molten glass, by passing through the basket orifices 16, is then delivered in the form of primary streams 16a directed toward the inside of the peripheral band 12, from where they are expelled in the form of filaments 17a through the spinner orifices 17 owing to the centrifugal force.

[0056] The attenuation device 20 consists of an annular burner that delivers a high-temperature high-velocity gas stream, said stream hugging the spinner wall 12. This burner serves to maintain the high temperature of the spinner wall and contributes to the attenuation of the filaments so as to convert them into fibers.

[0057] The attenuating gas stream is generally channeled by means of a surrounding cold gas sheath. This gas sheath is produced by a blowing ring 21 that surrounds the annular burner. Said cold gas sheath also helps to cool the fibers, the strength of which is thus improved by a thermal quenching effect.

[0058] The annular inductor 30 heats the underside of the centrifugation device so as to help to maintain the thermal equilibrium of the spinner 11.

[0059] The binder supply device 40 consists of a ring through which the web of fibers 2 flows. The ring includes a multiplicity of nozzles that spray the web of fibers with binder. Usually, the binder that helps to provide mutual cohesion of the fibers includes anti-dust agents, of the oily type, and antistatic agents.

[0060] The mineral material that is converted into fiber is preferably glass.

[0061] Any type of glass convertible by the internal centrifugation process may be suitable.

[0062] It may for example preferably be a lime-borosilicate glass containing significant amounts of boron.

[0063] According to the invention, fine fibers are obtained by regulating various parameters, in particular: [0064] the pressure of the burner 20; [0065] the rotation speed of the spinner 11; and [0066] the daily output of fibers delivered by each spinner orifice 17.

[0067] The annular burner 20 is of standard design. The temperature of the gas jet at its outlet is between 1350 and 1500° C., preferably around 1400° C.

[0068] According to the invention, the pressure of the burner is set between 450 and 750 mmWC (it will be recalled that 1 mmWC=9.81 Pa) so as to generate an attenuating gas jet best suited to the desired fiber fineness, in combination with the other aforementioned parameters. Although usually the pressure of a burner is 500 mmWC, it is possible according to the invention to choose to increase the pressure so as to make thinner fibers. However, this requires more energy. There has to be a compromise between the various abovementioned parameters in order to obtain the desired product depending on the economic and energy factors to be taken into account.

[0069] According to the invention, the rotation speed of the spinner is more rapid than the usual 1900 revolutions per minute (rpm). The spinner of the invention rotates at a speed of greater than 2000 rpm, for example 2200 rpm.

[0070] According to the invention, the fiber output per spinner orifice is at most 0.5 kg/day and preferably does not exceed 0.4 kg/day. The daily fiber output per orifice corresponds to the throughput of molten material passing through each orifice per day.

[0071] This output is of course dependent on the throughput of molten material delivered upstream of the spinner and on the number of orifices drilled in the spinner. According to the invention, the throughput of molten material does not exceed 19 tonnes per day (t/day) and preferably does not exceed 14 t/day. In comparison, the usual output of a furnace delivering molten glass is generally around 23 to 25 tonnes per day. The spinner itself has at least 32 000 orifices, preferably at least 36 000 orifices, and therefore a larger number than in a standard spinner, which is generally 31 846.

[0072] The spinner has a diameter of between 200 mm and 800 mm, the number of orifices and the output of molten material delivered being adapted accordingly. The fiber output delivered by a spinner will be lower the smaller the diameter of the spinner. The diameter is preferably 600 mm.

[0073] The spinner contains two or more annular zones superposed one above the other, each zone being provided with one or more annular rows of orifices. Certain particular features relating to the spinner can also help to obtain fine fibers.

[0074] The perforated band height of the spinner—the height over which the orifices are spread—does not exceed 35 mm.

[0075] The spinner orifices have, from one zone to another, rows of orifices with different diameters, and the diameter per annular row decreasing, in the centrifugation position, from the top of the peripheral band of the spinner downward. The diameter of the orifices is between 0.5 and 1.1 mm.

[0076] The distance between the centers of neighboring orifices in the same annular zone is essentially constant throughout an annular zone, this distance varying from one zone to another by at least 3%, or even at least 10%, and decreasing, in the centrifugation position, from the top of the peripheral band of the spinner downward, in particular with a distance of between 0.8 mm and 2 mm.

[0077] According to the invention, the metered amount of binder delivered by the ring 40 is advantageously between 5 and 8% and preferably between 5 and 7%. The amount of binder customarily necessary in the usual products and in proportions of 8%, or higher, is here replaced by the amount of fiber; the product thus has a higher weight of fiber, leading to an increase in the thermal conductivity λ.

[0078] Finally, the lowering of the thermal conductivity λ is also dependent on the arrangement of the fibers in the blanket. More than 75%, or even more than 85%, of the fibers are arranged so as to be approximately parallel to the long dimensions of the product. For this purpose, the run speed of the conveyor belt 60 is, according to the invention, faster than the speed of the receiving belt 50 by more than 10% and preferably by at least 15%.

[0079] This change in speed with acceleration makes the fibers lie as flat as possible in the run plane of the belts, being therefore oriented substantially parallel to the longest dimensions of the fiber blanket obtained, i.e.

[0080] horizontally to the plane of the belts to within plus or minus 30°.

[0081] An example of a product according to the invention obtained in accordance with the method of the invention is presented below.

[0082] The installation comprised a fiberizing spinner 600 mm in diameter with 36 000 orifices, having an arrangement of orifices and diameter of the orifices as described above.

[0083] The daily output per orifice was 0.4 kg. The rotation speed of the spinner was 2200 rpm.

[0084] The pressure of the burner was 500 mmWC.

[0085] The speed of the conveyor 60 was 15% higher than that of the receiving belt.

[0086] The product obtained had the following characteristics: [0087] a fiber fineness index of 5.5 1/min; [0088] more than 65% of the fibers had an average diameter of less than 1 μm; [0089] a thermal conductivity of 29.6 mW/m.K, measured at 10° C. according to the ISO 8301 Standard; [0090] a density of 45 kg/m.sup.3; [0091] a binder content of 5% by weight of the product; [0092] a thickness of 45 mm; and [0093] more than 80% of the fibers were substantially parallel to the long dimensions.

[0094] The orientation of the fibers was determined in the following manner: several (especially at least six) parallelepipedal specimens, of the same size and with the same thickness as the product, were removed from said product. They were cut by means of a cutting instrument, such as a blade producing a sharp cut without dragging fibers in the cutting direction, thus not disturbing the fiber arrangement forming the product before cutting. Each specimen was observed edge-on, the observed surface was divided into small unitary areas, the fibers being detected visually in each unit area, the angle made between the fiber direction and a horizontal direction parallel to a long dimension of the product was recorded and the average angle in each of the areas was calculated. An image acquisition tool coupled to image processing software was used for this purpose. For each specimen, the fraction of fibers having an angle of orientation falling within a given angular sector was thus determined. The average of the data for each specimen was then averaged so as to express the orientation of the fibers in the product. In this example, it was found that 80% of the recorded angles lay within the 0°-30° and 150°-180° sectors (horizontal fibers), whereas 15% of the recorded angles lay within the 30°-60° and 120°-150° sectors (oblique fibers) and 5% of the recorded angles lay within the 60°-90° and 90°-120° sectors (vertical fibers).

[0095] Stable production of this product is obtained under conditions meeting the requirements of the EN 13162 Standard, the stated thermal conductivity value expressing the limit representing at least 90% of the production, determined with a 90% confidence level.

[0096] It is also possible to obtain a product with an even lower micronaire of 3.4 1/min with the burner pressure increased to 750 mmWC.

[0097] This product may be compared with a product obtained in a more standard fashion using the same 600 mm spinner, but one having 31 846 orifices and a daily fiber output per orifice of 0.7 kg, the burner pressure being 500 mmWC and the spinner rotation speed being 1900 rpm.

[0098] The comparative product produced had the following characteristics: [0099] a fiber fineness index of 2.8 under 5 g, which represents a value of greater than 10 1/min; [0100] an average fiber diameter of 2 μm; [0101] a thermal conductivity of 34 mW/m.K; [0102] a density of 50 kg/m.sup.3; and [0103] a thickness of 50 mm.

[0104] To provide a thicker product, for example with a thickness of 90 mm or more, thus giving a thermal resistance of 3 or more, the invention proposes to assemble at least two layers of the product that has just been described. This superposition of layers may be achieved before crosslinking the binder, by combining two plies between reception and the oven, especially between the conveyor belt 60 and the oven. Cohesion of the two plies is provided by the sharing of the uncrosslinked binder present at the interface between the two plies and by crosslinking the binder throughout the product in the oven.

[0105] Consequently, the configuration of the fiberizing installation according to several specific features, dependent most particularly on the rotation of the fiberizing spinner, on the burner and the fiber output, and additionally dependent on the receiving belt and on the conveyor following it, have made it possible, in a non-obvious manner, to obtain the thermal insulation product of the invention, which hitherto has not existed.

[0106] The product of the invention, because of its very fine fibers, offers the advantage of a softer feel, making it much less disagreeable to handle.

[0107] The product, through its considerably lowered thermal conductivity, provides even better thermal insulation and achieves an optimum thermal resistance for reasonable thicknesses.

[0108] Finally, the product of the invention, through its density preferably greater than 30 kg/m.sup.3, takes the form of relatively rigid sheets which furthermore, because of a standard thickness, can thus be easily handled and can be easily cut and positioned as required against the walls to be insulated. In addition, as may be seen in the case of the comparative example, it is possible to reduce the density of the product, the product therefore being lighter, to reduce its thickness and to achieve a better thermal conductivity.