Melt-Formed Inorganic Fibres

Abstract

A needled blanket is provided comprising melt-formed inorganic fibres having an overall composition in weight percent SiO.sub.2: 47 to 65%; AI.sub.2O.sub.3: 35 to 53%; the blanket having a shot content, of shot >45 m, of less than 51 wt %, a specific surface area [BET)>0.25 m.sup.2.Math.g.sup.1. also disclosed are fibres for producing such blankets, and self-supporting products made from such fibres.

Claims

1. A needled blanket comprising melt-formed inorganic fibres having an overall composition in weight percent SiO.sub.2: 47 to 65% Al.sub.2O.sub.3: 35 to 53% the needled blanket having a shot content, of shot >45 m, of less than 51 wt %, a specific surface area (BET)>0.25 m.sup.2.Math.g.sup.1.

2. A needled blanket as claimed in claim 1, in which the amount of SiO.sub.2 is greater than 52%.

3. A needled blanket as claimed in claim 2, in which the amount of SiO.sub.2 is greater than 53%.

4. A needled blanket as claimed in claim 3, in which the amount of SiO.sub.2 is greater than 54%.

5. A needled blanket as claimed in claim 4, in which the amount of SiO.sub.2 is greater than 55%.

6. A needled blanket as claimed in claim 5, in which the amount of SiO.sub.2 is greater than 56%.

7. A needled blanket as claimed in claim 6, in which the amount of SiO.sub.2 is greater than 57%.

8. A needled blanket as claimed in claim 1 in which SiO.sub.2+Al.sub.2O.sub.3>98%.

9. A needled blanket as claimed in claim 1 having a shot content of less than 45 wt % or less than 44 wt % or less than 43 wt %.

10. A needled blanket as claimed in claim 1, in which the needled blanket has a tensile strength to density ratio of >0.39 kPa/kg.Math.m.sup.3 or >0.43 kPa/kg.Math.m.sup.3 or >0.45 kPa/kg.Math.m.sup.3.

11. A needled blanket as claimed in claim 1, in which the specific surface area is in excess of 0.3 m.sup.2.Math.g.

12. A needled blanket as claimed in claim 1, in which the inorganic fibres have an arithmetic mean diameter <2.5 m.

13. A needled blanket as claimed in claim 1, in which the inorganic fibres have an arithmetic mean diameter <2.25 m.

14. A mass of melt-formed inorganic fibres having a shot content, of shot >45 m, of less than 51 wt %, a specific surface area (BET)>0.25 m.sup.2.Math.g.sup.1. and suitable for needling to form a blanket as claimed in claim 1.

15. A self-supporting insulating body other than a needled blanket, formed of fibres as claimed in claim 14 and having a shot content, of shot >45 m, of less than 51 wt %, a specific surface area (BET)>0.25 m.sup.2.Math.g.sup.1.

16. A self-supporting insulating body as claimed in claim 15, in the form of a monolithic refractory fibre module having a shot content, of shot >45 m, of less than 51 wt %, a specific surface area (BET)>0.25m.sup.2.Math.g.sup.1.

17. A needled blanket comprising melt-formed inorganic fibres having an overall composition in weight percent SiO.sub.2: 47 to 65% Al.sub.2O.sub.3: 35 to 53% the needled blanket having a shot content, of shot >45 m, of less than 51 wt %, and a specific surface area (BET)>0.25 m.sup.2.Math.g.sup.1, wherein SiO.sub.2+Al.sub.2O.sub.3>98%.

Description

DESCRIPTION OF DRAWINGS

[0083] FIG. 1 is a schematic illustration of a conventional fibre forming machine

[0084] FIG. 2 is a schematic illustration of a fibre forming machine suitable for forming fibres in accordance with the present invention

[0085] FIG. 3 is a schematic diagram showing dimensions of a typical fibre forming machine

[0086] FIG. 4 shows fibre diameter distributions for an aluminosilicate fibre (RCF) produced by blowing and spinning respectively.

[0087] FIG. 5 shows the values of thermal conductivity for a number of different fibres.

[0088] FIG. 6 shows apparatus for measuring tensile strength of blanket

[0089] FIG. 7 shows schematically lines and planes used in defining the apparatus suitable for forming fibres in accordance with the present invention.

[0090] FIG. 8 shows schematically a plan view of a rotor.

[0091] FIG. 9 shows schematically a side view of the rotor of FIG. 10 and delivery of melt from a melt source to a region proximate the rotor

[0092] FIG. 10 is a summary of trials on an RCF composition

DETAILED DESCRIPTION

The Fibre Forming Process

[0093] As stated above, a known process for the manufacture of inorganic fibres is to supply a stream of a molten material of the desired chemical composition to a high-speed rotor (with or without blowing air around the rotor), such that fibres are flung off the rotor and collected for subsequent processing.

[0094] The process is hypothesised to work by a droplet of molten material being flung off the rotor and drawing a tail of molten material that forms the fibre. The droplets form part at least of the shot.

[0095] For the process to work the viscosity of the molten material must be appropriate.

[0096] The molten material is typically held in a container having heating/insulation means to keep the molten material at a suitable temperature.

[0097] As viscosity depends upon temperature, control of the temperature of the molten material is advisable. For each material a different range of temperatures will provide the optimum viscosity. Ideally the molten material as it hits the rotor should be within 150 C. preferably within 100 C., and more preferably within 50 C. of the optimum temperature for the molten material concerned. It is advantageous to monitor the temperature of the stream of molten material [e.g. using a pyrometer] as it leaves the container [and ideally as it hits the rotor] and to use this to control supply of heat to the molten material.

[0098] To ensure best performance, the stream of molten material should be uninterrupted for as long as possible during the fibre forming process. This means that the pour rate of the molten material should be sufficiently high to provide a continuous stream and not so low as to break up into droplets of molten material.

[0099] FIG. 1 shows fibre forming apparatus in which a motor arrangement 1, drives a rotor 2 housed in a fibre forming region 3 delimited at an end remote from the rotor by a barrier 4. Beyond the barrier 4 is what is conventionally known as a wool bin 5 where in use fibres settle onto a conveyor 6 to form a fleece of loose fibres 7 that may then be passed on to further processing [e.g. by needling to form a blanket]. Extractors 8 remove air from below the conveyor assisting draw down of fibre from the wool bin to the conveyor.

[0100] The apparatus also comprises a blower 9 that passes air [typically at 50 kPa or less above atmospheric] through an air ring into the fibre forming area behind the rotor 2.

[0101] The rotor arrangement which comprises two rotors 2, although a single rotor or more than two rotors may conventionally be used. As is conventional, one rotor is displaced from and placed slightly above the other, the appropriate angle of displacement and separation between the rotors 2 being a matter of design. Suitable angles and displacements are discussed, for example, in WO92/12939 and WO2015/055758 but typically the rotors have a separation of [2-10 mm] and the angle between horizontal and a line connecting the axis of one rotor to the axis of the other rotor is in the range [0-15 (typically) and 2-10 (preferred)]. The entire assembly of rotors may be displaced from the vertical as in U.S. Pat. No. 4,238,213. One or more of the rotors may be mounted at one end of a drive shaft with at least two spaced bearings supporting the drive shaft within a direct drive mechanism, which may be mounted with shock absorbers in a mount.

[0102] Fibre is produced as melt is flung from the peripheries of the rotors; once it has been made it needs to be moved away from the rotors into the wool bin. This is done partially by the residual velocity of the fibre and shot, and partly by the use of gas (usually air) moving generally perpendicular to the travel of the fibres which are then transported into the wool bin. The equipment used is generically referred to as air rings or stripper rings; the name ring comes from the shape, which forms part circles around the outside of the spinning rotors. The air ring typically comprises holes in metal blocks (typically 50-100 holes per block) with the air supply charged by a blower.

[0103] Preferably the air rings extend around as much of the periphery of the rotor as possible without disrupting the melt stream. For example, for a given rotor the air ring may extend around >180, >200, >220, or >240 of the rotor periphery.

[0104] In operation melt drops as a melt stream from a source of molten material 25 [FIG. 11] onto the rotor 2 and is spun off to form fibres, fibre formation being assisted in part by the air flow from blower 9. Melt sources can comprise any type appropriate to the nature of the material being melted. This is conventional technology and exemplified, for example, in US2012/0247156.

[0105] Typically melt sources comprise a chamber for melting and holding molten the constituents of the melt and a tapping hole in the base of the chamber to permit the melt to be released when required. In practice, point-like precision of impact of the melt on the rotor is not possible, and cone 26 from the source 25 to the region 23 indicates a range of possible melt stream paths, such that the melt can land on the rotor over a region 23. The melt stream is shown schematically as a dotted line 20 representing a vertical line through the region 23. The vertical line 20 may pass anywhere through region 23, for example through the centroid of region 23 on the rotor, and where melt is delivered vertically from an orifice 27 in the source of molten material 25, the vertical line 20 may conveniently pass through the centroid of the melt delivering orifice 27.

[0106] In practice, since the melt stream may lie off this vertical line anywhere within the region 23, it may prove necessary to arrange for the rotor to be movable to ensure the melt stream falls on the optimum position for the melt in question. Typically, the melt is preferred to impinge on the first rotor it meets, on the front half of the rotor [e.g. between and the depth of the rotor from the front (conveyer facing) face of the rotor and to impinge within 0-90, typically 18-72 (e.g. 18-30) of a vertical plane including the rotor axis either in advance or behind the direction of rotation of the rotor. The size of the region 23 will depend upon the geometry of the source 24 and its position relative to the rotor.

[0107] Fibres produced from the melt are carried by the stream of gas from the rotors to pass over the upper edge of the barrier 4 towards the conveyer 6; while shot and short fibre falls back from the lip of the barrier 4 to a waste chute 10 (sometimes called the shot pit) from which the waste shot and fibre passes to a granulator which breaks up the waste preparatory for disposal or re-use.

[0108] The applicant previously considered the slope from the upper edge of the barrier 4 to the waste chute 10 to be a region where further shot and fibre separation could occur, with the fibre being blown up the slope to the upper edge of the barrier 4.

[0109] Such apparatus typically produces fleece with a shot content of 45-50% assuming all other parameters (e.g. tap stream temperature and pour rate are optimal).

[0110] A problem with this apparatus is that the use of a low pressure air system implies high volumes of air to strip the fibres from the rotor and this leads to turbulence and eddying within the waste chute 10 such that some shot initially stopped by the barrier 4 can be blown up the slope of the barrier 4 and into the wool bin 5.

[0111] The applicants have realised that by lowering the upper edge of the barrier relative to the rotor and shortening the distance from the rotor to the barrier, there is a lower chance of eddying such that shot and short fibre falling from the barrier towards the waste chute is less likely to be blown back over the barrier.

[0112] FIG. 2 shows fibre forming apparatus in accordance with the present invention in which like integers carry the same reference signs as FIG. 1.

[0113] In this apparatus rather than a blower 8, compressed gas under high pressure [typically >100 kPa above atmospheric] is supplied to a series of flat spray nozzles distributed in a ring around the rotors 2. This provides more efficient separation of the fibre and shot so that more fibre goes into the wool bin 5 and more shot drops down into the waste chute 10. A secondary blowing device is also provided under the rotors, this provides further separation of fibre and shot, but also improved flow of fibre off the barrier, and prevents fibre laden shot returning back up the ducting into the wool bin.

[0114] Suitable spray nozzles are for a flat spray pattern without hard edges. They come with several spray angles.

[0115] This process typically allows a shot content of 30-45% to be achieved for alkaline earth silicate fibres without deshotting.

[0116] FIG. 3 shows the construction of FIG. 1 with dimensions, and shows schematically the angle , the determination of which is shown in greater detail in FIG. 7

[0117] FIG. 7 shows the axis of rotation 16 of a rotor and a vertical plane 17 including axis 16.

[0118] Plane 17 intersects orthogonal vertical plane 18 along line of intersection 19, and vertical plane 18 includes vertical line 20 which passes through the region 23 on the rotor to which melt is delivered.

[0119] Line 21 lies within plane 17 and extends from the intersection of axis of rotation 16 with plane 18 to the upper edge of the barrier 4.

[0120] Horizontal line 22 lies within plane 17 and meets the intersection of axis of rotation 16 with plane 17. [When the axis of rotation 16 is horizontal, lines 16 and 22 are identical]. The angle is the angle between line 21 and horizontal line 22,

[0121] FIG. 8 shows schematically in plan the rotor 2 positioned by the back 24 of the apparatus and the barrier 4. The region 23 may lie in advance or behind top centre in the direction of rotation of the rotor 2.

[0122] Table 1 compares the apparatus of FIG. 1 with the apparatus of FIG. 3.

TABLE-US-00004 TABLE 1 Apparatus of Apparatus of Dimension FIG. 1 FIG. 2 A - Length from end to end 9030 mm 10600 mm B - Height of barrier below roof 1183.8 mm 1400 mm C - Height of conveyor below 3790 mm 3900 mm roof D - Length of conveyor internal 6467.2 mm 9350 mm of wool bin E - Distance from conveyor to 1353.7 mm 750 mm mouth of waste chute F - Width of base of waste 825.8 mm 525 mm chute G - width of mouth of waste 1166.3 mm 525 mm chute H - Height of rotor axis below 435 mm 435 mm roof J - Distance of barrier from 1817.4 mm 600 mm rotor end of apparatus K - Distance from vertical line 275 mm 275 mm through centre of region 23 to back end of apparatus B-H - Height of rotor centre 748.8 mm 965 mm above barrier 26.8 74.6 Gas stream velocity 16-17 m .Math. s.sup.1 55-100 m .Math. s.sup.1

[0123] The principle difference between the designs is the increase in the angle from below 30 to above 40 and the higher air velocity (above 40 m.Math.s.sup.2). This difference results in a lower shot content for fibres of a given chemistry produced on the Apparatus of FIG. 2 than the Apparatus of FIG. 1.

[0124] In addition, the increased angle can be achieved by bringing the upper edge of the barrier closer to the rotor and in consequence permits a longer conveyor to be used for a given overall length of the wool bin. This longer conveyor improves uniformity of lay down of fibre.

[0125] The improvements achieved for a given chemistry, tap stream temperature, and rotor speeds are indicated below with reference primarily to alkaline earth silicate fibres but similar improvements will apply to other chemistries [including, without limitation, aluminosilicate chemistries, alkali metal aluminosilicates]. The following indicates some of the relevant variables that need to be considered in providing optimal fibre production.

Tap Stream Temperature.

[0126] The optimal value is chemistry dependent.

[0127] For the present aluminosilicate chemistries the tap stream temperature is preferably in the range 1950-2200 C.

Pour Rate.

[0128] The optimal pour rate depends upon the capacity of the rotor to convert the tap stream into fibre and ensuring a stable tap stream. For 20 cm (8) rotors good results are typically obtained with a pour rate between 250 kg/hr and 800 kg/hr. Below 250 kg/hr the tap stream tends to break up, and the resultant splatter creates damaging shot. Preferably, for such rotors, the pour rate is 400-750 kg/hr.

Rotor Speed.

[0129] For 20 cm (8) rotors this is preferably 15000-17000 rpm [equivalent to accelerations of about 250-320 km.Math.s.sup.2] although higher rotational speeds can result in finer fibre. This is substantially greater than 12000 rpm, which is the usual speed for making alkaline earth silicate fibres and equivalent to about 160 km.Math.s.sup.2. Results for alkaline earth silicate fibres when speed is below 10000 rpm [equivalent 110 km.Math.s.sup.2] are less beneficial; although aluminosilicate fibre (RCF) is typically made at 10,000 rpm.

[0130] Blankets formed using fibres produced under these spinning conditions using the apparatus claimed possess lower thermal conductivity and shot content than fibres produced at slower linear speeds and retain acceptable mechanical properties such as tensile strength. As an indication, Table 2 shows typical tensile strengths and shot contents of blankets of various density formed from specified fibres:

TABLE-US-00005 TABLE 2 Alkaline earth silicate fibre (calcium magnesium silicate fibre of SUPERWOOL Composition Aluminosilicate fibre PLUS composition) Blown or spun Blown Spun Spinning apparatus N/A Apparatus of FIG. 1 Apparatus of FIG. 2 Spinning speed [all with N/A 12,000 rpm 15,000 rpm 20.3 cm (8) rotors]) Tensile Density of 17 kPa >25 kPa >25 kPa >25 kPa 25 kPa strength blanket 31 kPa >45 kPa >40 kPa >40 kPa 55 kPa 64 kg/m.sup.3 44 kPa >60 kPa >50 kPa >50 kPa 55 kPa 96 kg/m.sup.3 128 kg/m.sup.3 Average shot >45 m* 50% 50% 50% 35-38% 28-35% typical typical typical typical Typical arithmetic mean <2 2.5-3 2.5-3 2.5-3 <2 fibre diameter [m] Typical thermal 0.30 0.34 0.38 0.29 0.21 conductivity at 1000 C. [W .Math. m.sup.1 .Math. K.sup.1] *Under ISO guidelines 10635 for fibre making provide that the testing party may declare what value they are using. For the purpose of this application, shot comprises any particulate material that is over 45 m in size

[0131] As can be seen from the table: [0132] the tensile strength for spun fibre blankets are significantly higher than for blown fibre blanket, this significantly helps in handling [0133] moving from Apparatus of FIG. 1 to Apparatus of FIG. 2 results in a major drop in shot content and correspondingly lower thermal conductivity [0134] increasing the spinning speed results in a much lower thermal conductivity since fibres of diameter comparable with blown fibres can be achieved with a lower shot content.

[0135] Further details are set out in the following examples and comparative examples.

[0136] The products of Comparative Examples 1 and 2 are claimed in applicant's previously filed application PCT/EP2017/050506 and do not form part of the present invention.

Comparative Example 1

[0137] Calcium magnesium silicate fibres of chemistry indicated in Table 3 were produced in apparatus as shown in FIG. 2 with the dimensions given in Table 1 using a tap stream at a temperature of 145050 C. directed to on 20.3 cm [8 ] diameter rotor rotating at a speed of 15,000 rpm. Table 3 compares the chemistry of Example 1 with typical composition of SUPERWOOL PLUS and shows typical measured properties:

TABLE-US-00006 TABLE 3 Example 1 SUPERWOOL PLUS Component Amount in wt % CaO 30.1 27-31 MgO 5.4 4-7 SiO.sub.2 64.6 64-66 Property Arithmetic mean diameter 1.85 m .sup.3-3.5 m Cumulative total for shot 29-33% .sup.35-38% 45 m or above

[0138] The thermal conductivity for a blanket, formed from the fibres of Example 1, with density 125.4 kg.Math.m.sup.1.Math.K.sup.1 is shown in Table 4 and is a significant improvement over SUPERWOOL PLUS blanket which has a typical value at 1000 C. of 0.25-0.29 W.Math.m.sup.1.Math.K.sup.1.

TABLE-US-00007 TABLE 4 Commercial Temperature SUPERWOOL PLUS % ( C.) Sample (datasheet values) difference 200 C. 0.04 0.05 20% 400 C. 0.06 0.08 25% 600 C. 0.10 0.12 17% 800 C. 0.15 0.18 17% 1000 C. 0.21 0.25 16% 1100 C. 0.24 n/a

Comparative Example 2

[0139] Calcium magnesium silicate fibres of chemistry indicated in Table 5 were produced in apparatus as shown in FIG. 1 with the dimensions given in Table 1 using a tap stream at a temperature of 1680-1730 C. directed to on 20.3 cm [8 ] diameter rotor rotating at a speed of 15,000 rpm. Table 5 compares the chemistry of Example 2 with typical composition of SUPERWOOL HT and shows typical measured properties:

TABLE-US-00008 TABLE 5 Example 2 SUPERWOOL HT Component Amount in wt % CaO 24.68 22.2-26.sup. Al.sub.2O.sub.3 1.18 0.9-1.4 K.sub.2O 0.77 0.5-0.8 MgO 0.6 0.4-0.8 SiO.sub.2 72.72 .sup.73-74.5 Property Arithmetic mean diameter 1.85 m .sup.3-3.5 m Cumulative total for shot 33.24% 38.25% 45 m or above

[0140] The thermal conductivity for a blanket with density 117.5 kg.Math.m.sup.1.Math.K.sup.1 is shown in Table 6 and compares well with a typical value at 1000 C. of 0.34 W.Math.m.sup.1.Math.K.sup.1 for SUPERWOOL HT.

TABLE-US-00009 TABLE 6 Conductivity (W/m .Math. K) Commercial Temperature SUPERWOOL HT % ( C.) Example 2 (datasheet values) difference 200 C. 0.04 0.04 0% 400 C. 0.07 0.08 13% 600 C. 0.11 0.14 21% 800 C. 0.18 0.23 22% 1000 C. 0.26 0.34 24% 1200 C. 0.37 0.48 23%

[0141] It is known that the thermal conductivity of a blanket also depends on density of the blanket, and FIG. 5 shows the commercial literature values of thermal conductivity against blanket density for SUPERWOOL PLUS and SUPERWOOL HT and the blown and spun RCF fibres described above, together with the experimental values for Examples 1 and 2.

[0142] As can be seen the fibres produced using the apparatus of FIG. 2 with a rotor giving an acceleration of about 250 km.Math.s.sup.2 produces significantly lower thermal conductivities than commercial product and indeed lower than blown RCF.

[0143] The fibres can be used to produce an insulating blanket of thermal conductivity <0.21 W.Math.m.sup.1.Math.K.sup.1 at 1000 C and 128 kg/m.sup.3 density. This is possible due to the properties of the fibresfine, low shot, with extremely low thermal conductivity in their own right.

[0144] Density of a blanket also correlates with the thermal mass of the blanket, which is of particular importance in cycling conditions. By providing a required thermal conductivity with a lower density blanket than a conventional blanket of equivalent composition, the present invention reduces the thermal mass of the blanket.

[0145] If the lines for SUPERWOOL PLUS and SUPERWOOL HT respectively in FIG. 5 are extrapolated to the thermal conductivities shown for Examples 1 and 2 respectively, densities of 20 kg/m.sup.3 or more above those of Examples 1 and 2 would be indicated as necessary for the same thermal conductivity.

[0146] Prior to the development of the apparatus disclosed herein production of such blankets was impossible: whilst shot could conceivably be removed from fibres produced via another method, the shot cleaning operation shortens the fibres, making them unsuitable for the production of a blanket.

Example 3

[0147] An aluminosilicate fibre was trialled on spinning apparatus as shown in FIG. 2 using pairs of 20 cm (8) rotors, and the rotor speed increased stepwise from 9000/9500 rpm (one rotor at 9000, the other at 9500 rpm) through to both rotors running at 15,000 RPM. Fibre diameter and shot content were measured and the results and fibre composition are set out in FIG. 10.

[0148] With increasing rotor speed both fibre diameter and shot content decreased to provide, at higher speeds, fibres having fibre diameters similar to blown RCF, but shot content similar to or significantly less than spun RCF.

[0149] In light of the results of Example 3 the applicants have compared: [0150] aluminosilicate materials made with the presently claimed apparatus using the rotor configuration of Example 3 and high rotor speeds (both rotors at 14,500 rpm); with, materials made using the presently claimed apparatus using lower rotor speeds [0151] commercially available materials.

Example 4

[0152] A standard spun refractory ceramic fibre has a typical composition in weight percent: [0153] Alumina 46-48% [0154] Silica 52-54%
and is exemplified by Cerablanket (a trademark of Morgan Advanced Materials plc). Such a material has a shot content >45 m of about 50%.

[0155] A material of the same composition made using the high rotor speeds (both rotors at 14,500 rpm) has a shot content >45 m of 43-46%.

[0156] Comparative results for thermal conductivity for a 128 kg/m.sup.3 blanket measured by ASTM-C201 expressed in W/mK are shown in Table 7.

TABLE-US-00010 TABLE 7 Thermal Conductivity (W/m .Math. K) Temperature Example Morgan Cerablanket % ( C.) 4-14500 rpm RCF (data sheet) difference 200 0.06 0.06 0% 400 0.08 0.1 20% 600 0.12 0.15 20% 800 0.17 0.2 15% 1000 0.23 0.27 15%

Example 5

[0157] Blown fibres tend to be finer than spun fibres, and to hence provide lower thermal conductivity. However blown fibres tend to be shorter than spun fibres and blankets are difficult to make from blown fibres. Blown fibres also tend to have more shot than spun fibres. Typically blown RCF has a shot content >45 m of above 50%, and above a spun fibre of like composition.

[0158] High alumina (HA) RCF fibre is known for meeting higher temperature applications than standard RCF fibre and is normally blown, as it has proven difficult in the past to spin or make into blanket.

[0159] HA fibres have typical compositions in weight percent:

TABLE-US-00011 Alumina 50-53% Silica 47-50%

[0160] Comparative results for thermal conductivity for a 128 kg/m.sup.3 blanket measured by ASTM-C201 expressed in W/mK are shown in Table 8, which compares: [0161] A. a spun HA fibre with composition based on

TABLE-US-00012 Alumina 50-52% Silica 48-50% [0162] made using the high rotor speeds (both rotors at 14,500 rpm) having a shot content >45 m of 43-46%. [0163] B. a standard blown refractory composition [Kaowool a trademark of Thermal Ceramics, Inc.] with composition in weight %

TABLE-US-00013 Alumina 46-48% Silica 52-54% [0164] With some substitution of up to 3% alumina by iron and titanium oxides. [0165] C. a commercial HA product with composition based on Alumina 53%, Silica 46%, balance impurities.

[0166] As can be seen, spun fibres of a high alumina composition RCF produced on the apparatus of the present invention, are superior in thermal conductivity to blown RCF fibres whether of standard or high alumina composition.

TABLE-US-00014 TABLE 8 Thermal Conductivity (W/m .Math. K) A B High speed Kaowool C % % Temperature HA spun standard RCF Commercial difference difference C. fibre blown blanket blown blanket from B from C 200 0.05 0.05 0.07 0% 29% 400 0.08 0.1 0.11 20% 27% 600 0.13 0.15 0.17 13% 24% 800 0.19 0.2 0.24 5% 21% 1000 0.27 0.3 0.33 10% 18% 1200 0.36 0.39 0.44 8% 18%

[0167] A factor that is important for making blanket is its tensile strength. For a given composition, short fibres make weaker blanket than long fibres. The applicants have made needled blankets at a density of about 128 kg.Math.m.sup.3 from a range of RCF compositions as indicated in Tables 9 & 10 below.

TABLE-US-00015 TABLE 9 Experiment/Comparative Experiment 1 C-1 2 C-2 C-3 Chemistry Alumina (%) 42.28 45.97 50.22 49.85 48.95 Silica (%) 57.23 53.77 49.24 49.31 50.44 Spinning speed (rpm) 15000 12500 14500 13000 13000 Shot content 45 m 40.8 51.6 50.6 60.2 57 Tensile strength (kPa) 71.7 71 26.9 20 27.6 Tensile strength/density 0.56 0.55 0.21 0.16 0.22 kPa/kg .Math. m.sup.3 Diameter (m) 2.1 2.8 2.8 3.7 3.1 SSA (BET) 0.317 0.220 0.254 0.201 0.237 Thermal 200 C. 0.05 0.05 0.05 0.05 0.05 conductivity 400 C. 0.08 0.07 0.08 0.08 0.08 (W/mK) 600 C. 0.12 0.12 0.13 0.13 0.13 800 C. 0.16 0.17 0.19 0.19 0.19 1000 C. 0.22 0.25 0.27 0.27 0.26

TABLE-US-00016 TABLE 10 Sample reference C-4 3 Chemistry Alumina (%) 34.7 35.0 Silica (%) 64.3 64.7 Spinning speed (rpm) 12000 13500 Shot content 45 m 35.7 32.6 Tensile strength (kPa) 137 138 Tensile strength/density 1.12 1.18 kPa/kg .Math. m.sup.3 Diameter (m) 3.63 3.61 SSA (BET) 0.232 0.296 Thermal 200 C. 0.05 0.06 conductivity 400 C. 0.08 0.08 (W/mK) 600 C. 0.14 0.13 800 C. 0.22 0.20 1000 C. 0.32 0.29

[0168] It is a feature of the tensile strength test used that blankets having a sufficient proportion of long fibres (sufficient to span the 150 mm clamping distance) show a higher tensile strength than blankets without such long fibres. The significant drop from 70 kPa for experiment 1 and comparative experiment C-1 to less than 30 kPa for experiment 2 and comparative experiments C-2 and C-3 shows that these latter fibres, with a silica content below 52 wt %, are significantly shorter than the former fibres, with a silica content in the 53-58 wt % range.

[0169] Likewise, the tensile strength of experiment 3 and comparative experiment C-4, with a silicate content of 64 wt % indicate a further increase in tensile strength.

[0170] The blankets/fibres within the scope of the present invention (experiments 1 to 3) demonstrate that use of high spinning speeds (at a specific fibre composition) results in both lower shot and generally finer fibres, with the process providing a higher specific surface area compared to fibres produced at lower speeds as indicated in comparative experiments C-1 to C4).

[0171] As indicated in the Tables 9 & 10, an increase in silica content is accompanied by a decrease in shot levels. The specific surface area was able to be maintained at different compositions, with the fibre diameter generally increasing with silica content (at the comparable spinning speeds), particularly for silica contents greater than 52 wt %.

[0172] Therefore, the compositions of the present invention are able to provide an advantageous balance of strength and thermal insulation through converting a high portion of the molten aluminosilica glass to fibre rather than shot.

[0173] The applicants have shown that a variety of aluminosilicate fibres (e.g. refractory ceramic fibres [RCF] also known as aluminosilicate wool [ACW]) can be made using the methods and apparatus described herein to provide fibre masses of fibre diameter comparable to blown fibre, with fibre length comparable to spun fibre, and with low shot content. Such materials will be useful in many applications, including in automotive applications as further mentioned below.

[0174] One application to which such fibres may be applied is to monolithic refractory modules, for example the product known as PYRO-BLOC which is a needled body of lubricated fibres with typical densities of the order of 160-240 kg.Math.m.sup.3. Such modules are used in a variety of applications. Fibres of a nature suitable to form blankets as now claimed, particularly blankets having a tensile strength to density ratio of >0.39 kPa/kg.Math.m.sup.3, enables monolithic refractory modules to be made having [0175] a shot content, of shot >45 m, of less than 51 wt %, [0176] a specific surface area (BET)>0.25 m.sup.2.Math.g.sup.1
or even better; for example having [0177] a shot content, of shot >45 m, of less than 45 wt %, and/or having [0178] a specific surface area (BET)>0.26 m.sup.2.Math.g.sup.1, >0.27 m.sup.2.Math.g.sup.1, >0.28 m.sup.2.Math.g.sup.1, >0.29 m.sup.2.Math.g.sup.1, >0.30 m.sup.2.Math.g.sup.1, or >0.31 m.sup.2.Math.g.sup.1

[0179] Tensile strength for such monolithic refractory modules need not (and is not) be as high as for blanket. Tensile strengths in excess of 5 kPa, or 10 kPa, or 20 kPa, or 30 kPa are expected to give functional modules and even lower may work in some applications. Measurement may be by cutting a sample of like size to blanket (as indicated below under test methods) and with a thickness of 25 mm with general fibre alignment in the plane of the sample; burning off lubricant at, say, 650 C., and measuring as below.

Test Methods

Shot Content

[0180] Shot content is measured by a jet sieve method using a Hosokawa Micron Air Jet Sieve (from Hosokawa Micron Powder Systems).

[0181] To ensure that the fibres pass through the sieve, the sample has to be prepared by crushing, this breaks the fibres to short lengths which are no longer tangled together in clumps that otherwise might be mistakenly measured as shot. The jet sieve then uses ultrasonic energy to agitate the fibres and align them with the mesh of the sieve. Suction then pulls the fibres through and collects them in a high efficiency particulate arresting (HEPA) filter. By measuring the weight of the sample before and after sieving, the proportion of shot can be calculated.

[0182] In detail:

Heat Treatment of Sample

[0183] To avoid moisture, or lubricants or other organic materials causing fibres to aggregate into lumps; preheating to an appropriate temperature for the sample [e.g. to 650 C.) to dry and/or burn off any lubricant/organic is appropriate if the sample is not known to be free of such materials.

[0184] Some materials may be too tough to be readily crushed in the following step, if so, heat treating to embrittle the fibres may be required.

[0185] The need for such heat treatment may be assessed by attempting the following steps and viewing the sample after sieving to determining whether sufficient fibrous material is retained in the sieve to affect the outcome of the measurement by more than the desired level of precision.

Crushing

[0186] Samples need to be crushed to break up the fibre tangles and to separate the shot from the fibre as well as to make the sections short enough to pass through the sieves' mesh. This has to be done in a manner that provides efficient shortening of the fibres without affecting the nature of the shot significantly.

[0187] Samples (typically 50-100 g or whatever size is appropriate for the die used) are crushed three times in a die at a minimum of 10 MPa (preferably at about 12 MPa). Between crushes the samples are well stirred to break up lumps and compacts so that the subsequent pressing can work on any uncrushed material.

[0188] Most samples will be crushed sufficiently by this process, but further repetition may be required for obstinate samples. The need for further repetition for a particular material, or higher crushing pressures, can be assessed by viewing the sample after sieving to determining whether sufficient fibrous material is retained in the sieve to affect the outcome of the measurement by more than the desired level of precision.

Weighing

[0189] A balance is used that meets or exceeds the following specification (e.g. Sartorius MSE1202S-100-DO) [0190] Readability 0.01 g [0191] Repeatability 0.005 g [0192] Linearity 0.02 g [0193] Range 0-800 g

[0194] The balance pan must also have a diameter > the sieve diameter and must be placed on a solid base to minimise vibrations.

[0195] The lid and sieve used (see below) are first weighed and then an appropriate amount of crushed sample is added, typically 200.5 g, measured to the nearest 0.01 g.

Sieving

[0196] Suitable apparatus comprises a Hosokawa Micron air jet sieve and lid; a Nilfisk GD930 vacuum cleaner; and a Stainless steel test sieve (BS410) designed for air jet sieve. For determining shot content as reported herein a 45 micron sieve was used. Any suitable jet sieve may be used.

[0197] Sieving with this apparatus comprises the steps: [0198] putting the lid on to the sieve, [0199] placing the sieve on the jet sieve unit, and sealing thereto [0200] using a sieving time of 180 seconds under a reduced pressure of at least 4.7 kPa (19 inches of water),
during the sieving, if necessary, stopping sieving to brush off any material adhering to the lid through static electricity

[0201] After sieving the sieve, lid, and retained shot are measured together and the amount of shot determined by difference.

Tensile Strength

[0202] Tensile strength is measured by a modification of ISO 10635:1999(E). The parting strength of a blanket is determined by causing rupture of test pieces at room temperature.

[0203] Samples are cut using a template (2305 mm752 mm). The samples are dried at 110 C. to a constant mass, cooled to room temperature and then measured and tested immediately.

[0204] The width is measured using a steel rule to a 1 mm accuracy across the middle of the piece and the thickness of the sample is measured on each sample (at both ends of the sample) using the EN1094-1 needle method.

[0205] Samples for each test are taken along the direction of manufacture.

[0206] The samples are clamped at each end by clamps comprising a pair of jaws having at least 40 mm75 mm in clamping area with serrated clamping surfaces to prevent slippage during the test. These dimensions give an unclamped span of 1505 mm to be tested. The clamps are closed to 50% of the sample thickness (measured using a Vernier caliper or ruler).

[0207] The clamps are mounted in a tensile testing machine [e.g. Instron 5582, 3365 using a 1 kN load cell, or a machine of at least the equivalent functionality for testing tensile strength]

[0208] The crosshead speed of the tensile testing machine is a constant 100 mm/min throughout the test.

[0209] Any measurement with the sample breaking nearer to the clamp jaw than to the centre of the sample is rejected. FIG. 8 shows the sample before and after testing for a good test.

[0210] The maximum load during the test is recorded to allow strength to be calculated.

[0211] Tensile strength is given by the formula:

[00001]$R\left(m\right)=\frac{F}{Wt}$

Where:

[0212] R(m)=Tensile Strength (kPa) [0213] F=Maximum Parting Force (N) [0214] W=Initial Width of the active part of the test piece (mm) [0215] T=Initial Thickness of test piece (mm)

[0216] The test result is expressed as the mean of five tensile strength measurements together with the bulk density of the product.

Fibre Diameter

[0217] Fibre diameter can be measured in a variety of ways. A suitable method, used in determining the values presented herein comprises:

Sample Dispersion

[0218] Homogeneously dispersing a suitable quantity of fibre sample onto a 25 mm carbon tab (a carbon based electrically conductive adhesive disc, frequently referred to as a Leit tab) mounted on a 32 mm aluminium SEM stub. Dispersion is preferably by a dry method to reduce agglomeration. A convenient product to use is a Galai PD-10 powder disperser which uses a vacuum to such fibre into a chamber, from where it deposits onto the stub surface. By suitable quantity is meant sufficient to provide a uniform coating on the stub, but not a coating so dense as to make measurement problematic [e.g. 0.03 to 0.3 grams].

Sputter Coating

[0219] Coating the sample with a conductive material (e.g. metal or carbon).

Imaging

[0220] Using a scanning electron microscope (SEM) to take a number of images from regions of the sample [e.g. 50, 100, 200 or more images], the images comprising a number of fibres. Typically anywhere from 100 to 300 fibres would be measured. For the purpose of reproducibility, 300 fibres from at least 50 different images may be measured.

Image Analysis

[0221] For each image any fibre that is in focus, has an aspect ratio (length/diameter) of at least 3:1 and touches a reference line placed across the image, the diameter is measured by measurement from the SEM image.

[0222] This part may be semi-automated using image analysis software linked to the SEM. such as the Scandium system available from Olympus Soft Imaging Solutions GmbH.

[0223] From the accumulated fibre measurements calculate the arithmetic mean diameter.

[0224] Because the diameter is measured only for fibres intercepting a line, and the probability of interception depends on fibre length, this method provides a length weighted arithmetic mean diameter.

Specific Surface Area

[0225] An alternative measure that correlates with fibre diameter (and is quicker to use) is to look to the specific surface area.

[0226] The lower the shot content, the better the correlation between SSA and fibre diameter.

[0227] There are various methods of measuring specific surface area, the most commonly applied being the Brunauer, Emmett and Teller (BET) method. Specific surface areas mentioned in this disclosure were measured using a Micrometrics TriStar 3000 apparatus. Samples were preheated to 650 C. to burn off any lubricant or other volatile material that might impede measurement. Samples were degassed at 350 C. in a nitrogen atmosphere.

Density

[0228] Using a dried sample (as provided for measurement of tensile strength above), the width is measured using a steel rule to a 1 mm accuracy across the middle of the piece and the thickness of the sample is measured on each sample (at both ends of the sample) using the EN 1094-1 needle method. Length is measured end-to-end using a steel rule to a 1 mm accuracy and volume calculated from length, width and thickness. The blanket is weighed and density taken as measured mass divided by calculated volume.

Potential Uses

[0229] The fibres of the present invention can be used, subject to meeting relevant performance criteria, for any purpose for which fibrous inorganic materials, and particularly alkaline earth silicate and aluminosilicate materials, have been used heretofore; and may be used in future applications where the fibre properties are appropriate. In the following reference is made to a number of patent documents relating to applications in which the fibres may be used, subject to meeting relevant performance criteria for the application. The fibres of the present invention can be used in place of the fibres specified in any of these applications subject to meeting relevant performance criteria. The fibres may be used as made or in processed form [for example as chopped fibres] to meet the demands of the application concerned.

[0230] For example, the fibres may be used as: [0231] bulk materials; [0232] in a mastic or mouldable composition [WO2013/080455, WO2013/080456] or as part of a wet article [WO2012/132271]; [0233] as a constituent in needled or otherwise entangled [WO2010/077360, WO2011/084487] assemblies of materials, for example in the form of blanket, folded blanket modules, or high density fibre blocks [WO2013/046052]; [0234] as a constituent of non-needled assemblies of materials, for example felts, vacuum formed shapes [WO2012/132469], or papers [WO2008/136875, WO2011/040968, WO2012/132329, WO2012/132327]; [0235] as a constituent (with fillers and/or binders) of boards, blocks, and more complex shapes [WO2007/143067, WO2012/049858, WO2011/083695, WO2011/083696]; [0236] as strengthening constituents in composite materials such as, for example, fibre reinforced cements, fibre reinforced plastics, and as a component of metal matrix composites; [0237] in support structures for catalyst bodies in pollution control devices such as automotive exhaust system catalytic converters and diesel particulate filters [WO2013/015083], including support structures comprising: [0238] edge protectants [WO2010/024920, WO2012/021270]; [0239] microporous materials [WO2009/032147, WO2011019394, WO2011/019396]; [0240] organic binders and antioxidants [WO2009/032191]; [0241] intumescent material [WO2009/032191]; [0242] nanofibrillated fibres [WO2012/021817]; [0243] microspheres [WO2011/084558]; [0244] colloidal materials [WO2006/004974, WO2011/037617] [0245] oriented fibre layers [WO2011/084475]; [0246] portions having different basis weight [WO2011/019377]; [0247] layers comprising different fibres [WO2012065052]; [0248] coated fibres [WO2010122337]; [0249] mats cut at specified angles [WO2011067598]; [0250] [NB all of the above features may be used in applications other than support structures for catalytic bodies] [0251] in the form of an end cone [e.g. U.S. Pat. Nos. 6,726,884, 8,182,751] [0252] as a constituent of catalyst bodies [WO2010/074711]; [0253] as a constituent of friction materials [e.g. for automotive brakes [JP56-16578]]; [0254] for fire protection [e.g. WO2011/060421, WO2011/060259, WO2012/068427, WO2012/148468, WO2012/148469, WO2013074968]; and optionally in combination with one or more intumescent materials, endothermic materials, or both intumescent and endothermic materials [0255] as insulation, for example; [0256] as insulation for ethylene crackers [WO2009/126593], hydrogen reforming apparatus [U.S. Pat. No. 4,690,690]; [0257] as insulation in furnaces for the heat treatment of metals including iron and steel [U.S. Pat. No. 4,504,957]; [0258] as insulation in apparatus for ceramics manufacturing.

[0259] The fibres may also be used in combination with other materials. For example the fibres of the invention may be used in combination with polycrystalline (sol-gel) fibres [WO2012/065052] or with biosoluble fibres [WO2011/037634].

[0260] Bodies comprising the fibres may also be used in combination with bodies formed of other materials. For example, in insulation applications, a layer of material according to the present invention [for example a blanket or board] may be secured to a layer of insulation having a lower maximum continuous use temperature [for example a blanket or board of alkaline earth silicate fibres] [WO2010/120380, WO2011133778]. Securing of the layers together may be by any known mechanism, for example blanket anchors secured within the blankets [U.S. Pat. No. 4,578,918], or ceramic screws passing through the blankets [see for example DE3427918-A1].

[0261] The unique control of shot content and fibre diameter provided by the method and apparatus disclosed provides fibre masses that with little or no need for post-formation deshotting, enable products to be made with lower thermal conductivity than current comparable products on the market.

[0262] The above disclosure is by way of example and the person skilled in the art will readily be able to find a multiplicity of uses for the fibres produced on the disclosed apparatus or by the disclosed methods.