Man-made vitreous fibres

Abstract

The invention provides a method of manufacture of man-made vitreous fibers (MMVF) comprising: providing a fiberizing apparatus, wherein the fiberizing apparatus comprises: a set of at least three rotors each mounted for rotation about a different substantially horizontal axis; wherein each rotor has a driving means; rotating the rotors; wherein the first rotor rotates to give an acceleration field of from 25 to 60 km/s.sup.2 and the second and third rotors each rotate to give an acceleration field of at least 125 km/s.sup.2, providing a mineral melt, wherein the melt has a composition comprising the following, expressed by wt of oxides: SiO.sub.2 in an amount of from 33 to 45 wt %, Al.sub.2O.sub.3 in an amount of from 16 to 24 wt %, an amount of K.sub.2O and/or Na.sub.2O, an amount of CaO and/or MgO, wherein the ratio of the amount of Al.sub.2O.sub.3 to the amount of SiO.sub.2 is in the range 0.34-0.73, wherein the ratio of the total amount of K.sub.2O and Na.sub.2O, to the total amount of CaO and MgO, is less than 1; pouring the melt on to the periphery of the first rotor; wherein melt poured on to the periphery of the first rotor in the set is thrown on to the periphery of the subsequent rotors in turn and fibers are thrown off the rotors; and collecting the fibers that are formed. Man-made vitreous fibers (MMVF) can thus be formed having a median length of 100 to 300 m, a median diameter of not more than 2.5 m, and wherein the ratio of the median fiber length to median fiber diameter is 25 to 500.

Claims

1. A method of manufacture of man-made vitreous fibres (MMVF) comprising: providing a fiberising apparatus, wherein the fiberising apparatus comprises: a set of at least four rotors each mounted for rotation about a different substantially horizontal axis; wherein each rotor has a driving means; rotating the rotors; wherein the first rotor rotates to give an acceleration field of from 25 to 29 km/s.sup.2, wherein the second rotor rotates to give an acceleration field of about 125 km/s.sup.2, wherein the third rotor rotates to give an acceleration field of about 150 km/s.sup.2, wherein the fourth rotor rotates to give an acceleration field of about 225 to km/s.sup.2, providing a mineral melt, wherein the melt has a composition comprising the following, expressed by weight of oxides: SiO.sub.2 in an amount of from 33 to 45 weight %, Al.sub.2O.sub.3 in an amount of from 16 to 24 weight %, an amount of K.sub.2O and/or Na.sub.2O, an amount of CaO and/or MgO, wherein the ratio of the amount of Al.sub.2O.sub.3 to the amount of SiO.sub.2 is in the range 0.34-0.73, wherein the ratio of the total amount of K.sub.2O and Na.sub.2O, to the total amount of CaO and MgO, is less than 1; pouring the melt on to the periphery of the first rotor; wherein melt poured on to the periphery of the first rotor in the set is thrown on to the periphery of the subsequent rotors in turn and fibres are thrown off the rotors; and collecting the fibres that are formed; wherein the fibres that are formed have a range of variation of the fibre diameter less than 3.8 m, defined as the 84% quantile minus the 16% quantile.

2. A method according to claim 1, wherein the melt has a composition comprising the following, expressed by weight of oxides: SiO.sub.2 in an amount of from 33 to 45 weight %, Al.sub.2O.sub.3 in an amount of from 16 to 24 weight %, TiO.sub.2 in an amount of from 0 to 3 weight %, Fe.sub.2O.sub.3 in an amount of from 6 to 11 weight %, CaO and MgO in a total amount of from 23 to 33 weight %, and K.sub.2O and Na.sub.2O in a total amount of 1 to 6 weight %.

3. A method according to claim 1, wherein the fiberising apparatus comprises four rotors.

4. A method according to claim 1, wherein the axes of the first and second rotors are arranged such that a line drawn from the axis of the first rotor to the axis of the second rotor makes an angle of from 0 to 20, below the horizontal.

5. A method according to claim 1, wherein the ratio of the diameter of the last rotor to the diameter of the first rotor is from 1.1:1 to 1.5:1.

6. A method according to claim 1, wherein the first rotor has a diameter of 120 to 250 mm, and the final rotor has a greater diameter of 180 to 330 mm.

7. A method according to claim 1, further comprising providing a fiberising chamber and collector means comprising a conveyor in the base of the chamber; collecting the blown fibres as a web and carrying them away from the set of rotors.

8. A method according to claim 1, wherein the temperature of the surface of the periphery of the first rotor is at least 100 C. higher than the temperature of the surface of the periphery of the fourth rotor.

9. A method according to claim 1, wherein the melt is provided on to the periphery of the first rotor at a temperature of 1450 to 1575 C., preferably 1480 to 1550 C.

10. A method according to claim 1, further comprising the step of mixing the collected fibres with a binder composition and curing said binder composition, thereby forming a bonded MMVF product.

Description

(1) The invention is illustrated by reference to the accompanying drawings in which:

(2) FIG. 1 is a front view of a set of rotors assembled for use in the method according to the invention;

(3) FIG. 2 is a cross-section on the line II-II through the set of rotors in FIG. 1 and through the collecting chamber in which they are positioned in use; and

(4) FIG. 3 is a detail of the slot around one of the rotors.

(5) FIG. 4 is a front view of a number of fiberising means.

(6) FIG. 5 shows the fibre distribution of an Example of the MMVF of the invention.

(7) With reference to FIGS. 1-4 the apparatus includes a set 1 of rotors each mounted on the front face 2 of a housing 3. The set is positioned at one end of a chamber to receive melt from a melt furnace. Each rotor is mounted in conventional manner on a driven axle that allows it to be rotated at high peripheral speed. The set consists of four rotors, a first rotor 4 that rotates anti-clockwise, a second fiberising rotor 5 that rotates clockwise, a third fiberising rotor 6 that rotates anti-clockwise, and a fourth fiberising rotor 7 that rotates clockwise. The bearings and drive mechanisms are not shown. Air slots 8, 9, 10 and 11 are associated with, respectively, the rotors 4, 5, 6 and 7, each slot extending around part only of the rotor. Generally each slot extends around at least of the periphery of its associated rotor, generally around the outer part of the set of rotors. Generally it extends around not more than or of the periphery.

(8) Each slot leads from an air supply chamber within the housing.

(9) Molten mineral melt is poured on to the rotor 4 along the path illustrated and strikes the first rotor 4 at point A that is at a position such that the angle B (i.e., the angle that A makes with the horizontal towards the second rotor) is from 40 to 65 to the horizontal, often around 45 to 60 to the horizontal. The second fiberising rotor 5 should be positioned at or only slightly below the first rotor and so the angle C typically is from 0 to 20, often around 5 to 10.

(10) By this means, it is possible to ensure that melt that is thrown off the first rotor on to the second rotor impacts on the peripheral surface of the second rotor substantially at right angles (e.g., from 75 to 105 to the normal). Similarly, it is preferred that the sum of angles D, E and F should be as low as possible. F is the included angle between the horizontal and the line joining the axes of the third and fourth rotors, E is the included angle between the lines joining the axes of the third and fourth rotors and the second and third rotors, while D is the included angle between lines joining the axes of the first and second rotors with the axes of the second and third rotors. Preferably C+D+E+F is below 150 but should generally be above 120, and most preferably it is in the range 125 to 142, with best results being obtained at around 135 to 140.

(11) Some of the melt striking the first rotor 4 at A is thrown off the rotor 4 as fibres but some is thrown on to subsequent rotor 5. Some of the melt is fiberised off that rotor whilst the remainder is thrown along path 13 on to subsequent rotor 6. A significant amount of this is fiberised off rotor 6, mainly in the area where there is slot 9, but some is thrown along path 14 on to the subsequent rotor 7. A significant amount is fiberised in the general direction 15 but a large amount is also fiberised around the remainder of the rotor surface included within slot 10.

(12) Since the slots 8, 9, 10 and 11 do not extend around the entire periphery of each rotor, the air flow in the region of paths 12, 13 and 14 can be controlled and, indeed, can be substantially zero.

(13) In a preferred method, the first rotor 4 has a diameter of about 210 mm and rotates at about 5,000 rpm giving an acceleration field of about 29 km/s.sup.2. This compares with values for conventional apparatus in accordance with GB 1,559,117 which may be, typically, around 180 mm, 3,900 rpm and 15 km/s.sup.2 respectively. The second rotor (rotor 5) may have a diameter of about 280 mm and may rotate at a speed of 9,000 rpm or more, giving an acceleration field of around 125 km/s.sup.2 (compared to values for a typical apparatus in GB 1,559,117 of around 230 mm, 5,500 rpm and 39 km/s.sup.2 respectively).

(14) The third rotor (6) may have the same diameter 280 mm and may rotate at 10,000 rpm to give an acceleration field of around 150 km/s.sup.2, compared to typical values of 314 mm, 6,600 rpm and 75 km/s.sup.2 for typical apparatus according to GB 1,559,117.

(15) The fourth rotor (7) may again have a diameter of around 280 mm and may rotate at 12,000 rpm, giving an acceleration field of around 225 km/s.sup.2 compared to values of 330 mm, 7,000 rpm and about 89 km/s.sup.2 for typical apparatus according to GB 1,559,117.

(16) The air emerging through the slots preferably has a linear velocity, in the described example, of about 100-200 m/s. This air flow may have axial and tangential components, according to the arrangement of blades 25 within the slots.

(17) Within each slot blades 25 can be mounted at an angle, relative to the axial direction of the associated rotor, that can be predetermined at a value ranging, typically, from zero to 42. For instance, in slot 10 the angle in the region G to H can increase from 0 at G to about 20 at H and then the angle of the blades in the region H to I can be substantially uniform at 42. Similarly, in slot 10 the angle can increase from about zero at J up to about 20 at K and can then increase and be substantially uniform throughout the region K to L at an angle of about 42.

(18) In slot 8, it may be preferred to have a lesser angle, typically a uniform angle of around 15 to 30, often around 20 or 25.

(19) The inner edge 24 of each slot is preferably coaxial with the associated rotor and preferably has a diameter that is substantially the same as the associated rotor.

(20) Binder sprays 18 can be mounted as a central nozzle on the front face of each rotor and eject binder into the fibres that are blown off the rotor. Instead of or in addition to this, separate binder sprays may be provided, for instance beneath or above the set of rotors and directed substantially axially. The fiberising chamber comprises a pit 20 having a double screw 21 that collects pearls and other fibre that drops into the pit and recycles them to the furnace. A conveyor 22 collects the fibres and carries them away from the fiberising apparatuses. Air is forced through a secondary air ring, for instance a plurality of orifices 23 arranged around the front face of the housing 2 and/or in and/or beneath the front face of the housing 2. The secondary air ring provides an air stream to promote the axial transport of the fibres away from the rotors and to control their rate of settlement and the intermixing with binder.

(21) It will be seen from FIG. 3 that the inner edge 24 of the annular slot has substantially the same diameter as the outer edge of the periphery of rotor 6 and that the blades 25 are arranged substantially radially across the slot. Of course, if desired, they may be arranged at an angle. The leading edge of the blades is shown as 25, and the side face the blades is shown as 26. In FIG. 3, position X corresponds approximately to position I in FIG. 1, i.e., where the blades are arranged at about 42, position Y corresponds to position H, i.e., where the blades are arranged at around 20, and position G corresponds to position Z, i.e., where the blades are at 0 and thus promote truly axial flow of the air.

(22) Although only a single air inlet 23 is illustrated in FIG. 2, preferably there can be a plurality of individually mounted air slots that are mounted beneath the rotors and that direct air in a generally forward direction. Some or all of them are pivotally mounted so that they can be relatively horizontal or relatively vertical or otherwise inclined. Also they can have blades that control the direction of air from the slot. Also, the blades can be mounted for reciprocating motion in order that they can be reciprocated during use so as to provide a pulsating air stream. Generally the slots point upwards so as to direct air upwardly and forwardly. By appropriate choice of air streams, and their movement if any, it is possible to optimise fibre collection, binder distribution, and the properties of the final product since this leads to the formation of a wall jet when the air emerges from the slot parallel to the periphery.

(23) Although it is convenient to supply the air through true slots, a similar effect can be achieved by other means of providing a continuous curtain of air over the rotor surface, for instance a series of adjacent blast nozzles arranged around the wall rotor in the position shown in the drawings for the slots, and that will lead to the formation of a wall jet.

(24) In FIG. 4, the reference numbers indicate the same features of the apparatus as in FIGS. 1 to 3. Separate air chambers 35 are provided for each set of rotors and lead from the melt furnace.

(25) The invention leads to improved fiberisation of the melt, and in particular the amount of shot having size greater than 63 m in the final MMVF is reduced in the invention compared to the amount typically present when a conventional, relatively small, first rotor is used. The amount of large shot (above 250 m) is decreased.

(26) The invention is now illustrated by the following non-limiting examples.

EXAMPLES

Example 1

(27) The air flow resistivity of four MMVF substrates according to the present invention (Examples A to D) was compared to the air flow resistivity of five MMVF substrates not of the invention (Comparative Examples A to E). Each MMVF substrate contained approximately 1 wt % binder. The MMVF substrates of Examples A to D were made by the method of manufacture of the present invention and the MMVF were in accordance with the present invention. The MMVF substrates of Comparative Examples A to E were made by a different method of manufacture and the MMVF were conventional MMVF.

(28) The MMVF of Examples A to D were made on a spinner equipped with four rotors. The first rotor had a diameter of 210 mm and was driven at approximately 5,000 rpm (acceleration field 29 km/s.sup.2). The second to fourth rotor had a diameter of 280 mm and were driven at approximately 12,000 rpm (acceleration field 225 km/s.sup.2).

(29) The MMVF of Comparative Examples A to E were made on a conventional spinner equipped with four rotors. The first rotor had a diameter of 184 mm, and was driven at approximately 4,500 rpm (acceleration field 20 km/s.sup.2). The second rotor had a diameter of 234 mm and was driven at approximately 7,000 rpm (acceleration field 63 km/s.sup.2). The third rotor had a diameter of 314 mm and was driven at approximately 7,000 rpm (acceleration field 84 km/s.sup.2). The fourth rotor had a diameter of 332 mm and was driven at approximately 7,000 rpm (acceleration field 164 km/s.sup.2).

(30) The air flow resistivity is measured in accordance with EN29053. As shown in Table 1 below, the air flow resistivity of the Examples of the present invention is considerably higher than that of the Comparative Examples, at comparable density. This demonstrates that the MMVF substrates of the present invention have improved acoustic and heat insulation properties compared to the Comparative Examples.

(31) TABLE-US-00002 TABLE 1 Density Air Flow Resistivity (kg/m.sup.3) (kPa*s/m.sup.2) Example A 107 170 Example B 102 140 Example C 98 160 Example D 100 150 Comparative Example A 111 55 Comparative Example B 98 71 Comparative Example C 102 48 Comparative Example D 104 81 Comparative Example E 104 68

Example 2

(32) The diameter of a sample of MMVF of the present invention was compared to a sample of conventional MMVF. The MMVF of the present invention were made as described for Examples A to D. The conventional MMVF were made as described for Comparative Examples A to E. FIG. 5 shows that the spread of fibre diameters is much smaller for MMVF of the present invention than for the conventional wool. The range of variation is defined here as the 84% quantile minus the 16% quantile (+/1 standard deviation for the fibre diameter(logarithmic normal distribution)). This means that the probability is 68% of finding a given fibre diameter in the defined region. As shown in FIG. 5, there is far less variation in fibre diameter of MMVF of the present invention, than of conventional wool. In specific tests the range of variation for MMVF of the present invention was found to be 2.3-2.4 m at a median fibre diameter of 1.9 m to 2.2 m, where the range of variation for MMVF of conventional wool was significantly higher, such as 3.7 to 5 m at a median fibre diameter of 3.4 m to 4.3 m. This shows a further advantage of MMVF of the present invention as increased uniformity of fibre diameter means that MMVF substrates have greater uniformity, which has a positive influence on a number of characteristics of the MMVF, such as increased thermal performance and improved skin-friendliness.

Example 3

(33) The lambda values of four MMVF substrates of the present invention (Examples E to H) were compared to those of four MMVF substrates not of the invention (Comparative Examples F to I). The MMVF of Examples E to H were made as described for Examples A to D. The conventional MMVF of Comparative Examples F to I were made as described for Comparative Examples A to E. Lambda was measured in accordance with EN 12667. The density was measured in accordance with EN 1602. Each MMVF substrate contained approximately 1 wt % binder. The MMVF substrates of Examples E to H were made by the method of manufacture of the present invention and the MMVF were in accordance with the present invention. The MMVF in the MMVF substrates of Comparative Examples F to I were made by a different method of manufacture and the MMVF were convention MMVF. The density of each product is shown below. The lower the lambda value, the greater the resistance of the MMVF substrate to heat. As shown in Table 2 below, MMVF substrates according to the present invention have lower lambda values across the temperature range 50 to 650 C. The advantage of using the MMVF substrate of the present invention is particularly noticeable above 200 C.

(34) TABLE-US-00003 TABLE 2 Density of Example Temperature ( C.) Example kg/m.sup.3 50 100 150 200 250 300 350 400 450 500 550 600 650 Lambda HT Example E 85 37 n/a 48 n/a 62 n/a 77 n/a 100 n/a n/a 133 n/a 9 mW/mK Example F 95 36 n/a 47 n/a 58 n/a 73 n/a 97 n/a n/a n/a 150 Example G 96 37 42 48 55 n/a 71 n/a 90 n/a 112 n/a 138 n/a Example H 102 38 43 49 56 n/a 71 n/a 90 n/a 112 n/a 138 n/a Comparative 92 38 44 52 61 72 84 98 114 n/a 151 n/a n/a n/a Example F Comparative 83 39 43 49 57 66 76 88 102 n/a 134 n/a 172 193 Example G Comparative 100 39 44 50 58 68 80 93 108 n/a 144 n/a 186 205 Example H Comparative 104 38 44 51 59 n/a 81 n/a 108 n/a 142 n/a 181 n/a Example I

Example 4

(35) Fire tests were performed comparing a conventional MMVF substrate with an MMVF substrate according to the invention, both at a density of 100 kg/m.sup.3. The test was performed according to International Code for the Application of Fire Test Procedures (2010) Part 3. The test showed a substantial improvement of 14 minutes for the A 60 test of the MMVF substrate according to the invention (Example I) compared to the conventional MMVF substrate (Comparative Example J). The test showed an improvement for the A 30 test of 3 minutes of the MMVF substrate according to the invention (Example J) compared to the conventional MMVF substrate (Comparative Example K). The MMVF of Examples I and J were made as described for Examples A to D. The conventional MMVF of Comparative Examples J to K were made as described for Comparative Examples A to E.

(36) TABLE-US-00004 Construction Example result Example result Bulkhead A 30 Comparative Failed after Example I Failed after 50 mm on Example J 31 min At 34 min At level 30 mm avg. temp. Avg temp. on stiffener Deck A 60 Comparative Failed after Example J Failed after 50 mm on Example K 66 min At 80 min At level 30 mm Max. temp. Max. temp. on stiffener over a over a stiffener stiffener (TC no 6) (TC no 6) Avg temp Avg temp 134 K. 137 K.

Example 5

(37) Heat conduction tests were performed by Forshungsinstitut fr Wrmeshutz e.V. Mnchen on the MMVF substrate according to the invention. The MMVF of Example 5 were made as described for Examples A to D. Density of the tested products was 56-59 kg/m.sup.3, and the heat conduction at 10 C. found to be 0.0318 W/(m.Math.K) according to EN 12667.

Example 6

(38) For certain acoustic applications, the optimal flow resistivity for obtaining high sound absorption values is around 20-30 kN/m.sup.4. Experimental tests found that this value was obtained for an MMVF stone fibre substrate according to the invention at a density of around 40-50 kg/m.sup.3. For a stone wool MMVF substrate formed by a method not according to the invention, the optimal range was found to be 50-60 kg/m.sup.3. Thus the stone wool MMVF substrate made according to the invention can provide optimal acoustic properties at a lower density, and therefore using a lower amount of MMVF.