NZ203666A

NZ203666A - Centrifugal production of fibres using spinner with diameter greater than 500mm

Info

Publication number: NZ203666A
Application number: NZ203666A
Authority: NZ
Inventors: J Battigelli; M-P Barthe; F Bouquet
Original assignee: Saint Gobain Isover
Priority date: 1982-04-06
Filing date: 1983-03-23
Publication date: 1986-03-14
Also published as: FI831145A0; PT76510B; ZA832336B; GR78517B; CA1221512A; FI75556C; KR900007334B1; IS2796A7; DK143983D0; BR8301731A; TR21774A; KR900009019B1; IL68303A0; IE55093B1; IS1524B; EP0091381B1; NO831182L; ATE24882T1; FI75556B; DE3369117D1

Abstract

1. Apparatus for producing fibres from a thermoplastics material and comprising a centrifuge (10) revolving about a substantially vertical axis (22), means for driving the said centrifuge with a rotary motion, means of conveying a stream (24) of material molten to the drawable condition into the centrifuge and carrying it onto the inner surface of the peripheral wall of the said centrifuge, a large number of orifices (40) in the peripheral wall through which the molten material passes to form filaments (41), end means of drawing the said filaments (41) into fibres, said means comprising an internal combustion burner delivering an annular gaseous jet adjacent to the outer part of the said peripheral wall which is directed downwardly, the said annular gaseous jet being at an elevated temperature contributing to maintaining the filaments of material under drawable conditions for a period of time sufficient for drawing, characterised in that the diameter of the centrifuge is between 550 and 1500 mm and in that the centrifuge is driven with a rotary movement under conditions in which its periphery is subject to a centrifugal acceleration comprised between 4000 and 20,000 m/s2.

Description

<div class="application article clearfix" id="description"> 2 03 6 6 6 Priority Date(s): G ;ft. Complete Specification Filed: &3.?. Class: ii4MAKW" Publication Date: 7 P.O. Journal, No: c / No.: Date: NEW ZEALAND PATENTS ACT, 1953 COMPLETE SPECIFICATION IMPROVEMENTS IN TECHNIQUES FOR THE FORMATION OF FIBRES BY CENTRIFUGING AND GAS ATTENUATION ^We, ISOVER SAINT-GOBAIN, a French Company of 18 avenue d'Alsace, 92400 COURBEVOIE, FRANCE hereby declare the invention for whichX'/ we pray that a patent may be granted to g»p/us, and the method by which it is to be performed, to be particularly described in and by the following statement: - - 1 - (followed by page la) 2 036 66 IA The present invention relates generally to the ft ^ r fiberization of glass or other thermoplastic materials and relates more particularly to fiberization techniques wherein the molten material to be fiberized is centrifugally converted by a rapidly rotating spinner into a multiplicity f ' or glass streams which are attenuated into fibres by a concentric annular gaseous blast from an internal combustion burner adjacent the periphery of the spinner directed perpendicularly to the centrifugal stream, such a fiberization technique being herein referred to as "centrifugal blast attenuation". The fibres. after being sprayed with a binder, are collected on a foraminous conveyor in the form of a blanket or mat, which is then passed through a curing oven. The centrifugal blast attenuation glass fiberization technique generally described above has been used industrially for many years in the production of glass fibre insulation products, and a substantial percentage of glass fibre insulation manufactured at the present time is produced utilising this technique. Details of various forms of this process are disclosed for example in U.S. Patents RE 24,70S 2,9S4>864> 2,991j5073 -2- 203666 3,007,196, 3,020,586, 3,084,381, 3,084,525, 3,254,977, 3,819,345 and New Zealand patent specifications 115981, 137399, 192341, 192342 and 192343. In carrying out this technique, substantial amounts of heat energy are required, first for heating the glass to a molten state, and secondly for producing the attenuating blast. The uncertain availability and high cost of energy have created an increasing demand for glass fibre insulation products, while the same factors have caused a substantial increase in the cost of producing such products. Efforts have accordingly been made to improve the efficiency of the described fiberization process or to utilize alternate fiberization techniques. For example, some glass fibre production has in recent years been carried out utilizing a purely centrifugal fibre attenuation, primarily to avoid the energy requirements of the blast attenuation technique. Centrifugal stream formation coupled with blast attenuation as generally described above remains a preferred technique however, both because of the excellent quality of the fibre blanket obtained therewith as well as the fact that a substantial portion of the industry is equipped at present with apparatus for carrying out , ~ 'V such a process. It accordingly follows that any improvemef?^\ in this technique would be of significant industrial n/ .if importance. As will be understood from the following disclosure, the present invention provides marked improvements in centrifugal blast attenuation fiberizing techniques with respect to product quality, production rate, and operating costs. Inasmuch as glass fiberization is in practice an extremely complex technique characterised by a large number of variable parameters, many of the details of known techniques need not be included herein, reference being made to the above patents for such disclosures. However, certain limited aspects of the prior art will be considered, especially concerning those factors respecting which the present invention departs substantially from prior practice. Among the many variables to be considered, the construction of the spinner is of particular importance in successfully carrying out a centrifugal fiberization process. The temperature and the velocity of the blast, as well as the arrangement of the nozzles which provide the gaseous blast, and the direction of the blast with reference to the walls of the spinner, are also important factors in optimising the attenuation of the fibres. The length of life of the spinner is an important factor, in particular regarding the relatively short lifetime of this type of spinner, and the very high cost of ' 2 03 6 6 6 -4- replacement, thereof. Other characteristics which affect the quality of the product are brought out in the description of examples of method of carrying out the invention. The spinners used in early centrifugal blast attenuation equipment were typically of a diameter of about 200 mm. It was realised that for a spinner of given size and construction, the output or pull rate, conventionally expressed in terms of the weight in tons per day of produced fibre, could be increased only at the expense of a corresponding decrease in fibre quality. It was further perceived that there were practical limits to the pull rate per spinner orifice for maintaining acceptable fibre quality. Nonetheless, the economic demands for increasing production of a given line usually resulted in an increase in pull rate despite the resulting deterioration in product quality. The term "quality" in this sense refers to the product weight per unit of area for a given thermal resistance and nominal product thickness. A lower quality product would hence be a heavier product although with the same insulating value as the better quality product. The lower quality product is thus lower in quality because it requires more glass for a given surface area, and is thus more costly to manufacture. In an effort to increase the pull rate, the diameter of the spinner was increased, first to 300 mm -5- and then more recently to 400 nun. 203666 Some improvement were attained, but the increase in diameter corresponds also to an increase in centrifugal acceleration. Although high centrifugal forces are necessary to produce a flow of molten material through the spinner holes and thus to form the primary stream, high centrifugal forces reduce the life of the spinner. Assuming that the life of the spinner varies f effectively inversely in relation to the centrifugal acceleration forces to which the spinner is submitted, it has up to now been judged desirable not to increase the diameter of the spinner too much in an attempt to prolong its life. A further factor is of importance, namely the fineness (average diameter) of the fibres. It is well established that for a given density of fibre mat layer, the finer the fibres, the greater the thermal resistance ^ ' of the layer. An insulating product comprising finer fibres can accordingly be thinner with the same insulating value as a thicker product of coarser fibres. Likewise, a product of finer fibres can be less dense than one of coarse fibres of the same thickness and have the same insulating value. 2 03 6 6 -6- Since sales of insulation products are usually based on a guaranteed thermal resistance (R value) at a nominal thickness, the fibre fineness is an important factor determining the relative weight of the product per unit of area, known as the basis weight, a product of finer fibres having the lower basis weight and hence requiring less glass and enjoying manufacturing economies. From an economic standpoint, however, fibre fineness, as with other factors, is normally considered to be a compromise. It is known that finer fibres can be obtained from higher blast velocities and/or from the use of softer glass compositions, i.e. glass for which an adequate viscosity is attained at lower temperatures. Increasing the blast velocity results in a direct increase in energy costs, and softer glasses typically require ingredients which are expensive and which, further, usually have undesirable pollutant characteristics. Fibre fineness, which can be expressed in terms of fibre diameter, in microns, of a fibre representing the arithmetic mean value of measured fibre diameters, is also conveniently expressed on the basis of a fibre fineness index, known as a "micronaire" determination. The "micronaire" is measured as follows. A predetermined mass or sample for example 5 grams of the fibres, is positioned within a housing of a given volume so as to form a permeable barrier to air passing through 2 036 6 6- the housing under a predetermined pressure. The reading 3 of the air flow through the sample depends on the fineness of the fibre. It is this measurement, obtained by means of a flow-measuring device, which is the "mi cronaire". In general, the finer the fibres the higher is the resistance offered to the passage of air through the sample. In this manner an indication is given of the average fibre diameter of the sample. The fineness of typical blast attenuated centrifugal glass fibre insulation products ranges from fine tj'pes (i.e. micronaire 2.9 (5g).: average diameter 4 u.m) to relatively coarse types (i.e. micronaire 6.0 (5g)- average diameter 1 2 ) . The insulating value of a blanket of fibres is not only dependent on the fibre fineness. The manner in vhicn the fibres are laid down on the collecting conveyor, especially evenness in the distribution of the orientation of the fibres in the insulation product. also has a significant effect. The thermal resistance of a fibre blanket will vary depending on the direction of orientation of the fibres to the measured heat flow, the resistance being greater when thcfibres are orientated perpendicular to the direction of heat transfer. Accordingly, w w -S- to maximise the thermal resistance of an insulating blanket, the fibres should be oriented to the maximum degree possible in an attitude parallel to the collecting conveyor and the plane of the blanket formed thereon. Because of the extreme turbulence generated above the collecting conveyor by the decelerating fibres and gaseous currents, control of the orientation of the fibres is difficult. Most efforts in this area of the fiberizing process being directed towards achieving a relatively uniform distribution of fibres across the width of the conveyor. Nevertheless it is useful to obtain long fibre.0 to arrange for the fibres to be deposited parallel "to the conveyor. The inventors have confirmed that unexpected improvements can be obtained with still larger spinners, particularly 600 nun in diameter and greater. The reason for these improvements are not entirely clear, especially those that relate to the quality of the felts prepared. In passing from a 400 nun spinner to a oOO mm spinner, the rotational speed is reduced so as to confer centrifugal acceleration forces on the glass and on the spinner wal1 within the conventional limits so that the supply to the orifices of material to be converted into fibres, as well as the strain on the structure of the wall, do not greatly exceed those of the prior art. 2036 -Ci- In general terms, the present invention concerns means for producing fibres and an insulating fibrous mat from such fibres. The invention in particular concerns spinners having a diameter greater than 500 mm and preferably from 550 to 600 mm, up to about lfOO mm. Further, the means according to the invention include a system which supplies a stream of molten material to the spinner and an internal combustion burner which supplies a downwardly-directed annular blast, adjacent to the wall of the spinner, to attenuate the streams of material discharged from the spinner to form fibres. The fibres thus formed are directed into a reception hood or chamber and are accumulated on a horizontal perforated conveyor arranged at the bottom of the reception chamber. Below is given a detailed description of means used to obtain the improvement in performance as well as a description of some of the properties of the product obtained. Although all efforts have been made to distinguish the principal factors which are responsible for the improvements in performance of the larger-diameter spinner, these efforts have not yet permitted a complete and precise conclusion to be reached. 203666 -10-. The theoretical explanations such as are given in this description may be considered to be an attempt, which is to be submitted to further experimental verification, but are in no wav limiting. Fig.1 is a partial sectional elevational view ^- shoving a spinner assembly and burner in accordance vith the present invention; Fig, 2 is a schematic elevational viev showing f the operation of a conventional small diameter spinner and fibre collecting conveyor, the view being taken transversely through the conveyor and illustrating the uneven distribution and random orientation of fibres on the conveyor in the absence of fibre distribution means; Fig. 3 is a viev similar to Fig. 2 but employing a large diameter spinner operating in accordance vith the invention shoving the relatively uniform distribution of fibres on the conveyor; Fig. h is schematic plan view shoving a plurality of spinners and the arrangement of the spinners with respect to an underlying conveyor; Fig. 5 is a schematic side elevational vievof the apparatus shown in Fig„ k; __ . ^' - 11 - Fig. 6 is a graph showing the area of the mat formed against of various degrees of fineness; 203666 reverse of the mass per unit suri.zcc spinner diameter for fibres and Fig. 7 is a graph shoving energy consumption plotted against spinner diameter for fibres produced at a constant centrifugal acceleration. Referring to the drawings and particularly Fig. 1, a fiberizing station in accordance vith the present invention is illustrated including a spinner 10 having a peripheral vail 12 and a neck portion IS. The spinner 10 is mounted by means of a hub portion 20 to a substantially vertical shaft 22. The shaft 22 is rotatablv supported in a veil known manner by suitable bearings attached to a supporting frame and is driven in rotation at a relatively uniform predetermined speed by an electric motor and belt drive. The shaft support and drive details are conventional and accordingly are not illustrated. The shaft 22 is hollow, permitting a flow of molten glass 2k to pass downwardly therethrough into a basket 26 supported beneath the lover end of the shaft by bolts 32e The basket 26 comprises a substantially cylindrical sidewall J>k having a plurality of orifices 36 through which the molten glass passes under the influence of centrifugal force in streams 38 which are directed onto the interior of the peripheral spinner wall 120 A^ult.i- 2 03 6 6 6 plicitv of orifices 40 in the peripheral vail 12 of the spinner serve to form a multiplicity of molten glass streams 41 as the molten glass is forced through the orifices "by a centrifugal force acting thereon. An annular internal combustion burner 42 is disposed above the peripheral vail of the spinner and includes a nozzle 44 for forming the annular blast spaced above the spinner peripheral vail 12. The annular blast adjacent the spinner vail 12 entrains and attenuates the glass streams 41 issuing from the orifices 40. The burner 42 includes a metal casing 46 provided vith a refractory liner 4S defining an annular combustion chamber 50 into vhich an air-fuel mixture is introduced. The blast nozzle 44 communicates vith the combustion chamber 50 and is formed by inner and outer nozzle lips 54 and 56. These lips 54 and 56 respectively include internal cooling channels 54a and 56a into vhich a cooling liquid such as vater is introduced,, In order to maintain the thermal balance of the spinner and fibres during attenuation, a high frequency induction heating ring 62 is provided just belov the spinner in concentric relation thereto,, Its internal diameter is somevhat larger than the spinner to avoid interference vith the dovnvard flov of fibres entrained by the annular blast. - 13 - 20366 An auxiliary blast is generated by an annular bloving crown 64 disposed outboard of the blast nozzle lips and connected to a source of pressurized gas such as air, steam or combustion products. The hollow shaft 22 includes several fixed concentric tubes. The innermost pair of these tubes defines an annular cooling passage 66 through which cooling water is circulated while the outer-most pair defines an annular passage 6S through which a combustible mixture can be passed and ignited to preheat the basket 26 prior to startup of the spinner. The fibres generated by the spinner and the blast pass into a receiving chamber or hood 70 and are a thence deposited in the form of a blanket 71 on a form-inous conveyor 72 as shown schematically in Figs* 2, 3 and 5. A suction bos 74 beneath the conveyor withdraws the high volume of gases passing through the conveyor in a conventional manner. As shown in Figs. 4 and 5, a plurality of fiberizing stations each having a spinner 10 are employed in the conventional manner for the production of the blanket 71 and in the preferred form of the invention are arranged in a longitudinal row vertically aligned with the longitudinal centre line of the conveyor 72. In - 14 - 2 0366 an industrial installation the number of spinners directing fibres onto a conveyor might, typically be six or wore„ For operation of the described apparatus, the spinner 10 including the basket 26 thereof is preheated in a veil knovn manner utilizing the combustion of gases passing through passage 6S, the heat of the burner 50 and heating ring 62 and such supplemental sources as may be necessary. Vith the spinner rotating at a predetermined speed and the burner adjusted to provide a combustion chamber pressure resulting in a blast velocity sufficient to provide the desired attenuation and fineness of the fibres, the molten glass stream 24 is introduced into the hollov spinner shaft 22 from a forehearth or other source of molten glass disposed above the spinner assembly. The stream of molten glass upon reaching the basket 26 flovs outvardly along the bottom of the basket under the influence of centrifugal force and passes through the orifices 56 of the basket in the form of glass streams 3S which are directed towards the spinner peripheral wall 12. Under the influence of the stronger centrifugal force on the peripheral wall, the glass passes through the multiplicity of small orifices 40 and issues from the exterior of the peripheral vail in the form of a - 15 - 2 036 66 multiplicity of streams 41 vhich are immediately subject to the attenuating effect of the blast from the internal combustion burner 50 directed downwardly across the exterior of the spinner wall. The glass streams 41 are maintained in an attenuable condition by the elevated •temperature of the blast for a time sufficient to effect attenuation thereof. The fineness of the attenuated fibres is regulated primarily by the control of the blast velocity which in turn is a function of burner pressure. An increase in burner pressure and blast velocity vill result in a greater attenuation and hence a finer fibre product. It should however "be noted that an increase in this attenuation does not necessarily correspond to a general improvement in the resulting products. "When attenuation by the blast becomes too violent, the quality of the fibres is normally inferior. The flow of attenuated fibres into the receiving chamber or forming hood 70 as shown in Figs. 5 and 5 is accompanied by the induction of substantial amounts of air as shown by the arrows at the top of the receiving chamber. Although the induced air tends initially to restrict the expansion of the veil of fibres flowTing from the spinner, the rapid deceleration of the fibres vithin the receiving chamber produces a substantial expansion of the fibre veil and, for reasons discussed in more detail - 16 - 2 03 6 6 herebelov, provides a relatively uniform distribution of the fibres across the width of the conveyor. Furthermore. due to a diminution of the turbulence usually present in the conveyor region, the invention produces a more favourable orientation of the fibres during the formation of the fibre blanket with a resultant improvement of the thermal properties of the blanket. A binder spray is applied to the attenuated fibres at the top of the receiving chamber in a conventional manner. The apparatus for applying the binder has however been omitted in the schematic views of Figs„ 2-5 to simplify these views. The diameter of the spinner is an important factor in the present technique. The largest spinners in industrial use in centrifugal blast attenuated processes have heretofore had a diameter on the order of 400 mm. An increase in spinner diameter had not been deemed desirable, in particular because of the difficulties vhich could he caused as regards the life of the spinner. The inventors have discovered that substantial increases in spinner diameter can confer better properties on mats without resulting in a substantially shortened life of the spinner. - 1? - 203666 Excellent results have been achieved utilizing a spinner of 600 mm diameter and substantially larger spinners can be used. The benefits of the invention car-be attained vith spinners having a diameter substantially in excess of 500 mm and vithin the range of about 550 mm * to about 1500 mm. The preferred range of spinner diameter is 600 mm to 1000 mm. By selecting a spinner rotational speed providing centrifugal acceleration forces not significantly departing from those conventionally utilized in smaller spinners, for example vithin the range of about 8,000 to 14,000 m/s , the life vould not be substantially affected. The present invention contemplates a rotational speed of the spinner vhich, taking account of the preferred range of spinner diameters as described above, vould produce a centrifugal acceleration at the spinner peripheral vail vithin the range of about 4,000 to about Q 20,000 m/s . The centrifugal acceleration vould preferably lie vithin the range from about 6,000 to about 16,000 m/s2. The graph of Fig. 6 illustrates the results obtained vith spinners of various sizes, at a substantially 2 constant centrifugal acceleration of about 10,000 m/s.ec . • ^ ' ' The fibre quality expressed by the inverse of the „'<v f * mass of the fibre per unit surface area, for mi of 2.5, 5-0, 3.5 and 4.0 (under 5 grams), significantly ^ - is - improves as is graphically shown by the changes in the slope ol the curve, at spinner diameters in excess of 500 mm. The difference in weieht. for an insulating material of the same quality is all the more sensible than the fibres obtained using large diameter spinners are finer, in other words than the micronaire F is smaller. Thus, the use of spinners having a diameter greater than 500 mm is still more advantageous as the fibres produced are finer. For a micronaire of 2.5 to 5 s, the improvement is very substantial. It has thus been confirmed for example that by changing from a 400 mrr. spinner to a 600 mm spinner, a reduction in weight of the order of 5% can be attained. Figure 6 again shows that these improvements are not•predictable from the results obtained using prior art spinners. In fact, the curves begin to increase substantialy only above 400 mm. For lower values, the increase in diameter is not accompanied by variations which are detectable or significant taking account of the degree of accuracy of the measurement s . Considering the preferred values of the diameters 2 03 6 -19- and of the centrifugal acceleration described above, the peripheral velocity of the spinner is preferably within the range of about 50 to about 90 m/s. The peripheral velocity is more advantageously within the range of about 55 m/s to about 75 m/s. Another factor which has a great influence on the production of fibres is the burner pressure, adjustment of vhich directly affects the fineness of the fibres and on which also depends the energy consumption of the process. Using a burner of the type such as shown in Figure 1, the preferred range of burner pressures is between about 100 and 900 mm water, with a preferred pressure of 200 to 600 mm water. For reasons which are not totally understood, the inventors have discovered that the burner pressure necessary to produce a fibre of a certain fineness decreases as a function of the increase in the diameter of the spinner, even if the centrifugal acceleration is not increased. This factor may be one of the reasons for the improved quality of the fibre vhich has been noted when larger spinners are used. In fact, a weaker burner pressure reduces the danger of breaking the fibres under the effect of the gaseous attenuating blast. In a less violent gaseous current it can be 2 036 £ -20- considered that the risks of collision or of sticking together of fibres would be reduced. In the products according to this invention this results in longer fibres^ and also more regular ones. The improvement in the quality of the fibres mentioned above, might account for the reduction in the weight necessary to achieve given insulating properties and fineness. f' ' The decrease in the burner pressure also results in a decrease in the consumption of energy for the production of a given mass of fibres. The results of the research carried out by the inventors on this subject, and which is summarised in Figure 7, shows a great decrease in the energy consumed when the diameter of the spinner increases. The curve shown on this graph is for a constant acceleration of 10,000 m/s". In these experiments the density of the orifices on the spinner walls, the dimensions of the orifices, the pull per orifice and the fineness of the fibres produced are identical. The graph of Figure 7 corresponds to the production of very fine fibres (micronaire 3 - 5 g)- It is established in particular that under the conditions of the invention, in other words with spinners having 2 036 -21- a diameter greater than 500 mm. the consumption of heat is less than 1500 kcal/kg whereas it is for example 1750 kcal/kg with fibres produced using a spinner with a diameter of 300 mm. It should be noted that the heat consumption for the formation of the gaseous attenuating blast represents the greater part of the energy consumed in producing the fibres. It represents at least 4/5^hs of the total. A reduction in this consumption therefore has a very substantial effect on the production cost. It is necessary to emphasise once again that if the thermal consumption values correspond to the same quality of fibres, the quantities produced are not the same. Thus, for conditions which allow the same quality of fibr_es to be.obtained, spinners 300, 400, and 600 mm in diameter produce respectively 10. 13.5 and 20 metric tonnes of fibres per day. The economies in consumption are therefore added to the economies made by the increase in production rate. The width of the burner lips 44 is preferably within the range of about 5 to 20 mm with a preferred width of about 8 mm. The temperature of the burner is preferably within the range of about 1300° to 1700° C, with a preferred temperature of about 1500°c. 2 0 36 6 -22- Kith the spinners under consideration in the present invention, an improved distribution of fibres on the mat has been observed,, as well as an improved orientation of the fibres on the blanket. Measurements have bee according to the prior art te according to the technique of n taken on products obtained chnique and products obtained the present invention. Several methods exist for measuring the distribution in the interior of a product. One of the simplest consists in cutting up the product into a series of little parallelepipeds or cubes (for example having the dimensions -5 x 25 x 45 mm), which are weighed individually. The different weights, which may be expressed in local weights per unit volume with reference to the centre of gravity of each "cube" gives a three dimensional picture of the distribution. To make the comparisore more convenient, there is calculated the variation C .-of the distribution with reference v to the standard deviation (square root of the mean of the squares of the deviations) at the mean value of the weights of the "cubes". Thus for example a very significant deviation has been found in a product made by the prior art technique: = 6.1% and that produced by the technique of the present invention C = 2.6%. The distribution of fibres in the samples v analysed is therefore very substantially better in the products prepared in accordance with the invention. ^ _23_ 2 03 6 66 ... - Concerning the example of the invention shown in Figure 3> the relatively large diameter of the spinner gives a veil of fibres which spread out well before reaching" the mat. In the form shown,, the conveyor being fairly narrow,, the veil covers the whole of the width of the mat. The fibres at the edge of "the veil come up against the lateral walls f*''' of the reception hood 70 and are redirected towards the interior to give a blanket 71 having a relatively uniform thickness. The deposit of fibres takes place with a minimum of turbulence and thus the orientation J" _ or the fibres is largely parallel to the direction of the conveyor. In contrast, an example of the prior art is given in Figure 2. Under the same conditions apart from the dimensions of the spinner, the veil of fibres is too narrow to reach the walls of the hood. The greater part of the fibres is deposited on the centre of the conveyor. A blanket is formed which is not uniform, thick in the centre and thin at the sides. Furthermore, contrary to that which is produced when a large spinner such as is shown in Figure 3 is used, substantial turbulence is developed around the edge of the veil near to the conveyor, this turbulence causes a chaotic deposition of fibres, the orientation of the fibres being substantially less parallel to the conveyor than the orientation produced with the apparatus and method of the present invention. 2 036 6 -24- The difficulties in distributing fibres mentioned above are well known and various methods to improve the distribution have been previously proposed. For very wide conveyors it is possible to arrange transversely 2, 5; or more, fibre assemblies in a transverse direction on the conveyor, but although theoretically this arrangement permits uniform distribution it in fact has the major disadvantage that any interruption to one of the assemblies, for example to change the spinner, the disturbance to the distribution caused by this interruption causes the rejection of the products formed by all the other assemblies during the whole duration of the interruption. For this reason it is generally preferred to arrange the fibring assemblies in a single line in the longitudinal direction of the conveyor, because in this case any interruption in one assembly does not have any noticeable effect on the distribution and it is possible to continue production, production only being decreased of that corresponding to the assembly which has been stopped. With assemblies disposed in this manner, various auxiliary distributing means are used in an attempt to obtain a better distribution of fibres. Among these distribution means, there are for example blowers located on the sides of the reception hood (U.S. Patent 3030659); oscillating or alternating blowers or "25" 203666 deflector shutters for controlling the induced air (U.S. Patent 3295943), oscillating conduits for the fibre veil (U.S. Patent 3230635) and oscillation of the fiberisation machine (U.S. RE 30192). Although these devices can provide a better distribution of the fibres, in general they introduce greater turbulence into the receiving chamber, thus conferring on the fibres in the blanket an inferior' orientation. Given that the orientation of the fibres is extremely important for a fibrous insulating medium, the orientation of the fibres parallel to the conveyor giving the best characteristics of thermal insulation, it is preferred to restrict as much as possible, use of "the auxiliary distributing means. For this reason a very large veil produced by large spinners in accordance with the invention is an important factor in optimising the quality of the fibrous blanket. Further, with the present invention it is possible to reduce or, in the case of narrow felts, do away with the auxiliary-distribution means and the cost of operating them. The increase in the width of the veil at the level of the conveyor is greatly superior to that which results simply from its original dimension, in other words the increase in the diameter of the spinner. It can be seen that the form of the fibrqji-^ veil just beneath the spinner is more f avourabl^^ r-O ''' F r V 2 036 6 6 -26- in Figure 3 than in Figure 2. the veil in Figure 3 contracting a relatively small amount beneath the spinner while that shown in Figure 2 is substantially contracted in this zone. Examples of different methods of operating in accordance with the invention are shown in the following table. Example 1, which does not correspond to the conditions of the invention, is for comparison purposes. Example No. I II III IV Spinner Diameter (mm) 400 600 SCO 1000 Pull rate per spinner (metric tons/day) 20 20 20 20 Burner nozzle width (mm) 7 • 7 7 • 7 7 • 7 0 Burner Pressure (mm water) 430 350 400 420 Burner temperature °C 1500 1 500 1500 1500 Fineness (micronaire under 5g) 4- 2 3 • 5 3 • 0 0 Density g/m~ for R=2 at 297 °k 1180 990 CO CO 0 720 Nominal Thickness (mm) 3D 90 90 90 These examples show that for a same pull of 20 • 5 metric tons per day, the products obtained according to the invention are substantially superior. In comparing Examples I and II, it can be seen that for the same thermal resistance, the density is smaller * 2 0 3 6 6 6 -27- according to the invention and also the pressure and thus the consumption of energy are also less. Example III is analogous to example II with a larger spinner diameter. The fineness and the mass per unit area are still improved. Example IV is another example in which the dimension of the spinner is further increased. The fineness and the density of the products obtained according to this example are particularly low. in other words the fibres are very fine and the mass of fibres necessary to obtain a given degree of thermal insulation is greatly reduced. </div>

Claims

<div class="application article clearfix printTableText" id="claims"> -25- IVHAT WE CLAIM IS: 2 036 66

1. Apparatus for the production of fibres from a thermoplastic material, comprising a spinner L rotating about an axis which is substantially vertical, and having a diametei" greater than 500 mm. means to rotatably drive the said spinner, means to conduct a stream of molten material in an attenuable state into the spinner and to conduct it onto the inside surface of the peripheral wall of the said spinner, a plurality of orifices in the peripheral wall through which the molten material passes in the form of filaments and means to attenuate the said filaments rf'into fibres, these means comprising an internal combustion burner vhich delivers an annular blast adjacent to the external portion of the said peripheral wall and directed downwards, the said annular blast being at a temperature which is sufficiently high to maintain the filaments of the material in a condition which permits them to be attenuated for a time sufficient for attenuation.

2. Apparatus according to Claim 1 in which the spinner ^J^frT^has a diameter between 550 and 1 500 nun.

3. Apparatus according to Claim 1 in which the spinner ^i-C'T'^has a diameter between oQO and 1000 mm.

4. Apparatus according to Claim 1. characterised in that the internal combustion burner generates a gas blast of _;0_ 2C3666 ^ y which the pressure at the outlet of the burner is between 100 and ?00 mm water column.

5. Apparatus according to Claim 4 in which the burner pressure is within the range 200 to 600 mm ^ater C°1umn• m

6. Apparatus for producing a blanket of mineral fibres comprising a reception chamber with lateral walls T^on each side of a perforated conveyor £v-2"jT^for receiving the fibres, suction means on the conveyor, a spinner having a diameter greater than 500 irm situated at a distance above the conveyor, the said spinner having a perforated peripheral wall and being rotatably mounted about a substantially vertical axis, means to conduct molten material in a drawable state to the internal surface of the peripheral wall, causing centrifugal discharge of filaments J^rT~~of molten material, means to attenuate the discharged filaments to form fibres comprising an internal combustion burner with means to generate an annular gaseous blast around the peripheral wall of the spinner and directed downwardly, towards the conveyor Tthe burner creating an annular jet at an elevated temperature which contributes to maintaining the filaments in an attenuable state and which carries JAItQfi <5 h .;'c, 203686 the attenuated fibres towards the conveyor JrT where they are deposited, characterised in that by virtue of the dimensions of the spinner the thermal consumption of the burner for producing fibres having a maximum micronaire of 3 (5g) is less than 1500 kcal per kg of fibres produced.

7. Apparatus as claimed in any one of the preceding claims for the production of fibres frccn a thermoplastic material substantially as herein described with reference to figures 1 and 3 to 5 of the drawings. dated this>^day of 19 tc A. J. &_^oN agents for the a??ucants </div>