Gas separation – Specific media material – Fibrous or strand form
Reexamination Certificate
2001-03-27
2003-07-22
Smith, Duane (Department: 1724)
Gas separation
Specific media material
Fibrous or strand form
C055SDIG005, C425S008000, C264S008000, C264S211100, C065S459000, C065S460000, C065S521000, C065S522000, C065S524000, C065S525000, C065S528000, C428S221000, C428S325000, C428S332000
Reexamination Certificate
active
06596048
ABSTRACT:
The invention is concerned with the manufacture of mineral fibres of the type comprising glass fibres of fine diameter, especially of at most 3 &mgr;m, for the purpose of incorporating them into papers used more particularly for producing aerosol filters or battery separators.
Specifically, the patents EP-0,267,092 and EP-0,430,770 disclose fibre-containing papermaking sheets for such uses. These fibres are usually a mixture of too types of fibre: “fine” fibres having a mean diameter of the order of at least 2 to 3 &mgr;m, and “very fine” fibres having a diameter lower than 1 &mgr;m. The first are intended, more particularly, for reinforcing the paper mechanically and giving it the necessary “bulk”, whilst the second provide the porosity which gives it its filtration properties. As proposed in the two patents mentioned above, these two types of fibre may advantageously be obtained by means of a method called internal centrifuging which is widely used, moreover, for manufacturing fibres used to produced thermal or acoustic insulation products. In outline, this method involves introducing a stream of melted glass into a centrifuge, also called a fibre-forming disk, rotating at high speed and perforated on its periphery with a very large number of orifices, through which the glass is discharged in the form of filaments under the effect of the centrifugal force. These filaments are then subjected to the action of an annular drawing flow of high temperature and velocity which runs along the wall of the centrifuge and which thins them and converts them into fibres. The fibres formed are carried by this gaseous drawing flow towards a receiving device generally consisting of a gas-permeable band. This known method has undergone many improvements, including especially those taught in the patents BP-B-0,189,534 or EP-B-0,519,797.
For thermal or acoustic insulation, the fibres manufactured by means of such a method generally have a diameter greater than 3 &mgr;m, usually approximately 4 to 4.5 &mgr;m up to 12 &mgr;m: the method therefore cannot be used in its conventional operating parameters in order to obtain the “fine” or “very fine” fibres referred to above. Some adaptations are therefore necessary in order to obtain fine fibres by means of this method. Thus, the above mentioned patent EP-0,267,092 proposes, specifically, a particular selection of the velocity of the drawing gases in order to obtain the said fibres.
The object of the invention, then, is an improvement in the device and method for the formation of fibres by the internal centrifuging of fine mineral fibres of a diameter of at most 3 &mgr;m, the said improvement being aimed especially at the quality of the fibres obtained and/or the production yield of these.
The subject of the invention is, first of all, a device for the internal centrifuging of mineral fibres of a diameter below or equal to 3 &mgr;m, comprising a centrifuge equipped with a peripheral band perforated with orifices and which has a fibre-forming height below or equal to 35 mm, preferably below or equal to 32.5 or 30 mm, and, for example, between 16 and 32.5 mm.
Within the scope of the invention, the “fibre-forming height” of the centrifuge is defined by the distance separating the highest point of the peripheral band from the “lowest” orifices of the latter, “high” and “low” being understood with reference to the centrifuge arranged in the centrifuging position, that is to say along a substantially vertical axis (of rotation).
Conventionally, fibres of standard diameter for insulation are manufactured with the aid of centrifuges with a wide peripheral band having, to give an order of magnitude, a fibre-forming height of at least 40 mm. It is, in fact, expedient to select a considerable fibre-forming height, since this makes it possible to increase the number of orifices in the peripheral band and to have a large number of rows of orifices leading to an increase in the production capacity, often expressed by the “run-off” equal to the number of kg of glass fibres manufactured per day and per centrifuge. This reasoning has its limits, of course, since the production capacity is also linked to many other parameters and must not be obtained at the expense of too significant a quantity of unformed fibres, grains, risks of malfunctioning of the centrifuge, etc. Thus, it is also necessary, for example, to take into account the temperature gradients which may be established over the height of the peripheral band or the fact that the high-temperature drawing gases have or do not have the same impact on all the rows of orifices.
It became apparent that the quality of the so-called “fine” fibres, with a diameter of less than 3 &mgr;m, could be increased considerably by selecting a particular fibre-forming height below 35 to 30 mm or less, that is to say at values well below those used conventionally and those used hitherto to make so-called “fine” fibres of less than 3 &mgr;m. With such a type of centrifuge of lower height, it was possible to see that the “fine” fibres produced were much more stable dimensionally, with a much smaller quantity of defects of the type comprising unformed fibres/grains or of the type comprising amalgams of re-agglutinated fibres, and that they had highly satisfactory mechanical properties, especially in terms of yield strength under traction.
Moreover, the use of the centrifuge was simpler and less complicated than that encountered hitherto in the production of “fine” fibres. Furthermore, this increase in quality and this higher industrial feasibility were not obtained at the expense, of an economically unacceptable reduction in the production capacity, on the one hand because “fine” fibres of very particular use have a high added value and because it is also possible to have a production capacity a little lower than that obtained in the case of standard fibres, and, on the other hand, because it has been possible to limit at least partially the fall in production capacity by adjusting, especially increasing, the perforation density of the peripheral band.
Advantageously, the centrifuge according to the invention is selected with a mean diameter below or equal to 800 mm, especially of at least 200 mm, for example of approximately 200, 400 or 600 mm.
In order to obtain “fine” fibres with a diameter of at most 3 &mgr;m, it is preferable for the orifices of the centrifuge to have a diameter of at most 1.5 mm, for example at most 1.2 mm, especially in between 1.1 and 0.5 mm, for example between 0.9 and 0.7 mm (reference is made, here, to a “diameter”, since these orifices are usually all selected circular, but it is not ruled out that the orifices are not circular, in which case “diameter” must be understood as meaning “largest dimension”).
According to a preferred embodiment, the orifices of the peripheral band of the centrifuge are grouped in rows, conventionally rows arranged in concentric circles over the height of the band. In the invention, then, it is advantageous if at least two adjacent rows have orifices of different diameters, and, more precisely, if the rows, have decreasing orifice diameters from the top of the peripheral band downwards (usually, all the orifices of the same row have the same diameter). It is thus possible to provide, from the top downwards, n rows of orifices of a given diameter, then p rows of orifices of a smaller diameter, then t rows of orifices of an even smaller diameter, etc. With: n, p and t≧1.
An improvement in the fibre-forming quality was found when a kind of “gradient” decreasing from the top downwards in the size of orifices was established in this way. It was thus possible to reduce the differences in the way in which the filaments emanating from the highest rows were formed into fibres from those of the lowest rows; this “gradient” allows a development of the primary filaments at the outlet of the orifices and drawing which limits the path intersections, and therefore the impacts, between the fibres being drawn, which come from different rows of orifices, hence the increase in quality which
Guyot Daniel
Tuffal Guy
Greene Jason M.
Isover Saint-Gobain
Smith Duane
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