IE55093B1 - Apparatus for producing fibres from thermoplastic material - Google Patents

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

The present invention relates generally to the fiberization of glass or other thermoplastic materials and relates more particularly to fiberization techniques vherein the molten material to be fiberized is centrifugally converted by a rapidly rotating spinner into a multiplicity of 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 24,708 2,984,864, 2,991,507» -2- 3.007,196, 3,017,663, 3,030,586; 3,084,381, 3,084,525, 3,254,977, 3,304,164, 3,819,345 and 4,203,745.

In carrying out this technique, substantial amounts of heat energy are required, first for heating 5 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 10 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 15 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 20 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 such a process. It accordingly follows that any improvement 25 in this technique would be of significant industrial -3- importance. As vfill be understood from the following disclosure, the present invention provides marked improvements in centrifugal blast attenuation fiberizing techniques with respect to product quality, production 5 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 10 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, 20 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, 25 in particular regarding the relatively short lifetime of this type of spinner, and the very high cost of -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 da}’ 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 mm.

Some improvement were attained, but the increase in diameter corresponds also to an increase in centrifugal acceleration. Although high centrifugal 5 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 10 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 20 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.

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 -7- the housing under a predetermined pressure. The reading of the air flovi through the sample depends on the fineness of the fibre. It is this measurement, obtained by means of a flow-measuring de\’ice, which is the "micronaire".

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 types Ci.e. micronaire 2.9 (5g)j average diameter 4 Jim) to relatively coarse types (i.e. micronaire 6.6 (5g)> average diameter 12 pn).

The insulating value of a blanket of fibres is not only dependent on the fibre fineness. The manner in which 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 thefibres are orientated perpendicular to the direction of heat transfer. Accordingly, -Βίο 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 fibres 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 mm 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 mm spinner to a 600 mm spinner, the rotational speed is reduced so as to confer centrifugal acceleration forces on the glass and on the spinner wall 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.

The present invention provides an apparatus for the production of fibres from a thermoplastic material, comprising a spinner rotating about an axis which is substantially vertical, and means to rotatably drive the said spinner, means 5 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 and forms filaments, and means to attenuate 10 the said filaments into fibres, these means comprising an internal combustion burner which delivers an annular gas blast adjacent to the external portion of the said peripheral wall and directed downwards, the said annular gas blast being at a high temperature and helping to maintain the filaments of the 15 material in a condition which permits them to be attenuated for a time sufficient for attenuation, wherein the diameter of the spinner is between 550 and 1500mm and the spinner is actuated by a rotational movement under conditions whereby its periphery is subjected to a centrifugal acceleration of 20 between 4000 and 20000 m/ss .

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.

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 way limiting.

Fig.l is a partial sectional elevational view shoving a spinner assembly and burner in accordance with the present invention; Fig. 2 is a schematic elevational view showing the operation of a conventional small diameter spinner and 10 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 view similar to Fig. 2 but employing 15 a large diameter spinner operating in accordance with the invention showing the relatively uniform distribution of fibres on the conveyor; Fig. k is schematic plan view showing a plurality of spinners and the arrangement of the spinners with 20 respect to an underlying conveyor; Fig. 5 is a schematic side elevational view of the apparatus shown in Fig. k; - 11 - Fig. 6 is a graph shoving the reverse of the mass per unit surface area of the mat formed against spinner diameter for fibres of various degrees of fineness; and Fig. 7 is a graph shoving energy consumption 5 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 with the present invention is illustrated including a spinner 10 having 10 a peripheral vail 12 and a neck portion 18. The spinner 10 is mounted by means of a huh portion 10 to a substantially vertical shaft 22, The shaft 22 is rotatably supported in a veil knovn manner by suitable bearings attached to a supporting frame and is driven in rotation 15 at a relatively uniform predetermined speed by an'electric motor and belt drive. The shaft support and drive details are com'entional and accordingly are not illustrated.

The shaft 22 is hollov, permitting a flov of molten glass 2k to pass dovnvardly therethrough into a 20 basket 26 supported beneath the lover end of the shaft by bolts 32. The basket 26 comprises a substantially cylindrical sidevall 34 having a plurality of orifices 36 through vhich the molten glass passes under the influence of centrifugal force in streams 38 vhich are directed onto 25 the interior of the peripheral spinner vail 12, A multi- 12 - plicity of orifices *»0 in tbe 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 tbe peripheral wall of the spinner and includes a nozzle 44 for forming the annular blast spaced above the spinner peripheral wall 12. The annular blast adjacent the spinner wall 12 entrains and attenuates the glass streams 41 issuing from the orifices 40. The burner 42 includes a metal casing 46 provided with a refractory liner 48 defining an annular combustion chamber 50 into which an air-fuel mixture is introduced. The blast nozzle 44 communicates with 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 which a cooling liquid such as water 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 below the spinner in concentric relation thereto. Its internal diameter is somewhat larger than the spinner to avoid interference with the downward flow of fibres entrained by the annular blast.

An auxiliary blast is generated by an annular bloving crovn 6¾ disposed outboard of tbe 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 68 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 thence deposited in the form of a blanket 7i on a foram-inous conveyor 72 as shown schematically in Figs. 2, 3 and 5. A suction box 7¾ 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 - an industrial installation the number of spinners directing fibres onto a conveyor might typically be six or more.

For operation of the described apparatus, the 5 spinner 10 including the basket 26 thereof is preheated in a well known manner utilizing the combustion of gases passing through passage 68, the heat of the burner 50 and heating ring 62 and such supplemental sources as may be necessary.

With 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 15 hollow 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 flows outwardly along the bottom of the basket under the influence of centrifugal force and passes through the 20 orifices 56 of the basket in the form of glass streams 38 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 25 the exterior of the peripheral wall in the form of a - 15 - multiplicity of streams 41 which 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 5 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, will 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 15 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. 3 and 5 is 20 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 flowing from the spinner, the rapid deceleration of the fibres within the receiving chamber produces a substantial expansion of the fibre veil and, for reasons discussed in more detail 25 - 16 - herebelow, 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 5 a more favourable orientation of the fibres during the formation of the fibre blanket w'ith 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 conven-10 tional 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 kOO mm. An increase in spinner diameter had not been deemed desirable, in particular because of the difficulties which could he 20 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.

Excellent results have been achieved utilizing a spinner of 600 mm diameter and substantially larger spinners can be used. The benefits of the invention can be attained with spinners having a diameter substantially 5 in excess of 500 mm and within 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 depart-IO ing from those conventionally utilized in smaller spinners, for example within the range of about 8,000 to 14,000 m/ε , the life would not be substantially affected.

The present invention contemplates a rotational speed of the spinner which, taking account of the preferred 15 range of spinner diameters as described above, would produce a centrifugal acceleration at the spinner peripheral wall within the range of about 4,000 to about 2 20,000 m/s . The centrifugal acceleration would preferably lie wdthin the range from about 6,000 to about 20 16,000 m/s2.

The graph of Fig. 6 illustrates the results obtained with spinners of various sizes, at a substantially 2 constant centrifugal acceleration of about 10,000 m/sec . The fibre, quality expressed by the reverse of the 25 mass of the fibre per unit surface area, for micronaires of 2.5, 3«0, 3.5 and 4.0 (under 5 grams), significantly - 16 - « improves as is graphically shown by the changes in the slope of the curve, at spinner diameters in excess of 500 mm.

The difference in weight for an insulating mat-5 erial 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 10 are finer.

For a micronaire of 2-5 to 5 g, the improvement is very substantial. It has thus been confirmed for example that by changing from a 400 mm spinner to. a 600 mm spinner, a reduction in weight of the 15 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 20 values, the increase in diameter is not accompanied by variations which are detectable or significant taking account of the degree of accuracy of the measurements.

Considering the preferred values of the diameters -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 which 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 which 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 -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.

The decrease in the burner pressure also results 10 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 15 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 20 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 -21- a diameter greater than 500 n, 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 4/5ths of the total. A reduction in this consumption 10 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 15 not the same. Thus, for conditions which allow the same quality of fibres 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 2o 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 17ΟΟ0 C, with a preferred temperature of about 1500° 25 -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 been taken on products obtained according to the prior art technique and products obtained according to the technique of 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 25 x 25 x 45 nun), 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 comparisors more convenient, there is calculated the variation Cv:-of the distribution with reference 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: Cy = 6.1% and that produced by the technique of the present invention Cy = 2.6%. The distribution of fibres in the samples analysed is therefore very substantially better in the products prepared in accordance with the invention.

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 5 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 of the reception hood 70 and are redirected towards the interior to give a blanket·71 having a relatively 10 uniform thickness. The deposit of fibres takes-place with a minimum of turbulence and thus the orientation of the fibres is largely parallel to the direction of the conveyor.

In contrast, an example of the prior art is 15 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 20 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 25 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.

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 5 transversely 2, 3j 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 10 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 15 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 20 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 25 located on the sides of the reception hood (U.S. Patent 3030659)) oscillating or alternating blowers or -25- deflector shutters for controlling the induced air (U.S. Patent 3255943); oscillating conduits for the fibre veil (U.S. Patent 3S3O636) and oscillation of the fiberisation machine (U.S. RE 30192). Although 5 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 10 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 15 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 20 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 25 spinner.

It can be seen that the form of the fibrous veil just beneath the spinner is more favourable -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 5pinner Diameter (mm) 400 600 800 1000 Pull rate per spinner (metric tons/day) 20 20 20 20 Burner nozzle width (mm) 7-7 7-7 7-7 6 Burner Pressure (mm water) 430 350 kOO 420 Burner temperature °C 1500 1500 1500 1500 Fineness (micronaire under 5g) 4.2 3-5 3-0 2 Density g/ra^ for R=2 at 2Q7°k 1180 990 880 720 Nominal Thickness (mm) 00 90 90 90 These examples show that for a same pull of 20 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 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,,

Claims (10)

1. Apparatus for the production of fibres from a thermoplastic material, comprising a spinner rotating about an axis which is substantially vertical, and 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 and forms filaments, and means to attenuate the said filaments into fibres, these means comprising an internal combustion burner which delivers an annular gas blast adjacent to the external portion of the said peripheral wall and directed downwards, the said annular gas blast being at a high temperature and helping to maintain the filaments of the material in a condition which permits them to be attenuated for a time sufficient for attenuation, wherein the diameter of the spinner is between 550 and 1500mm and the spinner is actuated by a rotational movement under conditions whereby its periphery is subjected to a centrifugal acceleration of between 4000 and 20000 m/sJ.

2. Apparatus according to claim 1 in which the spinner has a diameter between 600 and lOOOmm.

3. Apparatus according to claim 2 in which the spinner is rotated under conditions whereby the periphery of the spinner is subjected to a centrifugal acceleration of between 8000 and 14000 m/sJ. -29-

4. Apparatus according to one of the previous claims, wherein the internal combustion burner generates a gas blast of which the pressure at the outlet of the burner is between 100 and 900mm wafer column.

5. Apparatus according to claim 4 in which the burner pressure is within the range 200 to 600mm water column.

6. Apparatus according to one of the previous claims in which when it is put into operation, the thermal consumption of the burner for producing fibres having a micronaire from 10 3 (5g) is less than 1500 kcal per kg of fibres produced.

7. A device for producing fibres, substantially as herein described with reference to and as shown in Figure 1 of the accompanying drawings.

8. Apparatus for producing a blanket of fibres, 15 including one or more devices according to claim 7.

9. Apparatus for producing a blanket of fibres, substantially as herein described with reference to Figure 3 or Figures 4 and 5 of the accompanying drawings.

10. Fibres produced using an apparatus or device 20 according to any of claims 1 to 5 or 7. MACLACHLAN & DONALDSON Applicants' Agents 47 Merrion Square DUBLIN 2