FI75556B - ANORDING FOR FRAMING OF MINERAL FIBER UTGAOENDE FRAON ETT 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

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This invention relates to an apparatus for producing mineral fibers from a thermoplastic material, the apparatus having a centrifuge rotating about a substantially vertical axis, apparatus for rotating the centrifuge, apparatus for directing a flow of molten material in a towed space to the centrifuge in this, through which holes the molten material passes to form strands, and means for drawing the strands into fibers, the apparatus comprising a burner blowing an annular jet adjacent the outer surface of the circumferential wall and a downward high temperature gas jet to help retain the strands.

Fiber making equipment of this type has been used in industry for many years to make insulation products made of mineral fibers, and a significant portion of the insulation products of this type manufactured today are produced using this technology. Details of various embodiments of this method are described, for example, in U.S. Patent Nos. RE 24,708, 2,984,864, 2,991,507, 3,007,196, 3,017,663, 3,020,586, 3,084,381, 3,084,525, 3,254,977, 3 304,164, 3,819,345 and 4,203,745, and in SE patent 412,378 and FI patents 47,658, 54,097 and 69,447.

These devices require a large amount of thermal energy, firstly to melt the glass and secondly to produce a jet of pulling gas. Uncertainty in energy supply and high prices have created a growing demand for fiberglass insulation products, while the same factors have led to a sharp rise in the cost of production of these products.

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Therefore, every effort has been made to improve the yield of the fiber production method described above or to use other, alternative methods. In recent years, for example, a method of manufacturing mineral fibers has been developed in which the fiber is pulled only by centrifugal action, mainly to avoid the energy consumption required for gas jet drawing.

However, the production of fibers by centrifugation as described above, and in addition by gas jet drawing, is considered a preferred method both because of the excellent quality of the nonwoven produced in this way and because a large portion of the insulation industry currently has equipment to use this method. Therefore, any improvement to this method is very important for the industry. It will be apparent from the following description that the present invention represents clear improvements in fiber production methods using centrifugation and gas jet drawing, both in terms of product quality and production volume and cost.

Since the production of fibers is in practice a very complex method, which is characterized by a very large number of variable parameters, it is not necessary here to discuss many details of these known methods, let alone refer to previously known patents. However, let us consider here some aspects of the previously known methods, in particular those factors for which the present invention differs clearly from the previously known practice.

Of the many variables worthy of consideration, the structure of the centrifuge is particularly important for the satisfactory completion of the production of fibers by centrifugation.

The temperature and speed of the gas jet, as well as the arrangement of the gas jet blowing nozzles and the direction of the jet relative to the walls of the centrifuge 3 75556, are also important factors in order to obtain the best possible drawing of the fibers. The service life of the centrifuge is an important factor especially considering the relatively short service life of these types of centrifuges and the very high cost of replacing the centrifuge. Other features relating to the quality of the products are set forth below in the description of embodiments of the invention.

The centrifuges used as the first fiber drawing devices by centrifugation and gas jet were about 200 mm in diameter. It was later found that in a centrifuge of a certain type of manufacture and of a certain diameter, no yield, i.e. the amount it draws, which is normally expressed in tonnes of finished fibers per day, could be added without a corresponding deterioration in fiber quality. It was further found that the practice also set limits on the flow rate per hole in order to keep the fiber quality good. However, the economic necessity to increase the production of a given line has usually resulted in an increase in flow rate despite the deterioration of the product quality. "Quality" in this context means the weight of the product per unit area when the thermal resistance and specific thickness of the product are determined. Thus, a lower quality product is heavier - although it has the same insulating ability - than a better quality product. Thus, a product of inferior quality is of inferior quality because it requires, in particular, a higher amount of glass per area given and, therefore, of course, this product is more expensive to manufacture.

Attempts to increase the flow rate have focused in particular on increasing the centrifuge diameter to 300 mm first and only 400 mm.

Improvements have been made, but at the same time increasing the diameter means increasing the centrifugal acceleration. Although high centrifugal forces are necessary to provide a flow of molten material from the holes in the centrifuge and thus to form pre-filaments, high centrifugal forces shorten the life of the centrifuge.

Since the service life of the centrifuge actually changes inversely with the centrifugal acceleration forces to which the centrifuge is exposed, it has hitherto been considered appropriate not to increase the diameter of the centrifuge too much in order to extend its service life.

Another important factor for these methods is the fineness (average diameter) of the finished fibers. It is known that the thinner the fibers at a given fiber density per unit area of fiber mat, the better the thermal resistance of the mat. An insulation product made of thinner fibers can thus be thinner - while maintaining its insulation capacity as a thicker product made of thicker fibers. Or, the density per unit area of a product made of equally thinner fibers may be lower than that of a product made of thicker fibers of the same thickness and still have the same insulating capacity.

Because insulation products are usually sold with guaranteed minimum thermal insulation (value R), the thinness of the fibers is an important factor in determining the density of the product per unit area, known as basis weight. Insulation made of thinner fibers has a lower basis weight and therefore requires less glass to manufacture, which in turn means savings in production costs.

From an economic point of view, however, the fineness of the fibers, like other factors, is usually a trade-off. Namely, it is known that finer fibers are obtained at higher jet speeds and / or by using harder glass compounds, i.e. those which are suitably flowable at lower temperatures. Increasing the blowing speed of the gas jet immediately causes an increase in energy costs, and harder glasses are characterized by the fact that they contain materials that are expensive and, in addition, usually polluting the environment.

The fineness of the fibers, which can be expressed as the diameter of the fibers in microns and which represents the arithmetic mean of the diameters of the fibers measured, is also conveniently expressed by the fineness index of the fiber, referred to as the "micronair". The micronaire is measured as follows. A predetermined amount of the sample to be measured, for example 5 g of fibers, is placed in a chamber of a certain volume so as to form a barrier through which air flows through this chamber at a given pressure. The amount of air flowing through the test sample depends on the fineness of the fiber. It is this measurement value obtained with a flow meter that is the micronaire (thinness in microns) of the fiber.

In general, the finer the fibers, the greater the obstacle they place on the flow of air in the test sample. In this way, the average fineness of the fibers in the test sample is determined. For example, fibers with a mean diameter of 4 micrometers have a micronaire of about 2.9 to 5 g of fibers and fibers with a mean diameter of 12 micrometers have a micronaire of about 6.6 to 5 g of fibers.

The non-fibrous insulation value does not depend solely on the fineness of the fibers. The way in which the fibers are deposited on the receiving conveyor, above all the uniformity of their distribution, as well as the direction of the fibers in the insulation product also play an important role.

The thermal resistance of the fiber mattress varies depending on the direction in which the fibers are relative to the measured heat flow, with greater resistance when the direction of the fibers is perpendicular to the direction of heat flow * Thus, to maximize the thermal resistance of the insulating mattress, the direction of the fibers should be as parallel as possible to the receiving conveyor Due to the strong turbulence generated above the receiving conveyor 6 75556, it is difficult to control the direction of the fibers. In this zone, the main aim is to make the fibers relatively evenly distributed in the width direction of the conveyor. However, in order for the fibers to settle parallel to the conveyor, it is preferred that the fibers be long.

For example, the above-mentioned patent FI-69 447 describes the use of centrifuges with a diameter of 400 mm (or can be mentioned as up to 500 mm, although no more detailed examples of this are given), the specific purpose of which is to increase production.

The object of the present invention, despite the difficulties described above, is to improve the properties of the fibers, in particular the non-fibrous thermal insulation, under conditions which are not unfavorable for the service life of the manufacturing equipment.

To achieve this object, the invention is characterized in that the centrifuge has a diameter of between 550 and 1500 mm and that the device has drive means which drive the centrifuge at such a speed that the centrifuge circumference is subjected to a centrifugal acceleration 2 of between 4000 and 20,000 m / s, preferably 2 6 000-16,000 m / s.

When moving from a 400 mm diameter centrifuge to a 600 mmm centrifuge, the rotational speed is reduced so that the centrifugal acceleration forces on the glass and the centrifuge wall are within normal limits, so that the stresses applied to the holes and the wall structure are not much different from the prior art.

According to the invention, the diameter of the centrifuge is preferably 600-1000 mm. In addition, it is preferred if the burner nozzle is shaped and sized to blow a gas jet having an outlet pressure of between 100 and 900 millimeters of water, preferably 200 to 600 millimeters of water.

The following is a detailed explanation of the equipment used to improve performance, as well as an explanation of some of the features of the finished product.

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Although every effort has been made to identify the main factors contributing to the improvement in the performance of a larger diameter centrifuge, it has not been possible to draw complete and precise conclusions to date.

The theoretical explanations set forth in this specification are to be considered as one of the most widely attempted experiments to elucidate this matter and are not intended to limit the invention.

Figure 1 is a partial vertical sectional view of an assembly of a centrifuge and a burner according to the invention.

Fig. 2 is a schematic vertical sectional view showing the operation of a conventional small diameter centrifuge and fiber receiving conveyor; this image is longitudinal to the conveyor and shows that the fibers are unevenly distributed and land in a random direction on the conveyor in the absence of a fiber distribution control system.

Figure 3 is a view similar to Figure 2, but showing a larger diameter centrifuge operating in accordance with the invention and showing that the fibers are relatively evenly distributed on the conveyor.

Fig. 4 is a schematic plan view showing several centrifuges and their position relative to the conveyor.

Figure 5 is a schematic side view of the device of Figure 4.

Fig. 6 is a graph showing how the density of the finished fiber felt per unit area changes inversely with respect to the centrifuge diameter at different finenesses.

Fig. 7 is a graph showing energy consumption relative to centrifuge diameter when fibers are fabricated by constant centrifugal acceleration.

The drawings, and in particular Figure 1, show a defibering zone according to the invention comprising a centrifuge 10 having a circumferential wall 12 and a neck portion 18 of the centrifuge 8. The centrifuge 10 is arranged with a body 20 on a vertical shaft 22. The rotatable shaft 22 is supported in a manner known per se by bearings speed is provided by an electric motor and a belt drive. Shaft mounting and actuators are known per se and are therefore not shown here.

The shaft 22 is hollow, so that the molten material stream 24 can flow through it into the basket 26, which is fastened under the lower end of the shaft with nuts 32.

The basket 26 comprises a cylindrical wall 34 provided with a plurality of holes 36 through which molten glass penetrates by centrifugal force in the form of strands directed against the inner surface of the circumferential wall 12 of the centrifuge. A large number of holes 40 in the circumferential wall 12 of the centrifuge convert the molten glass into a plurality of strands 41 as the molten material penetrates through the holes by centrifugal force.

A burner 42 is arranged above the wall of the centrifuge, in which combustion takes place inside the burner, and comprises a nozzle 44 which forms an annular jet above the circumferential wall 12 of the centrifuge. An annular gas jet adjacent the wall 12 grabs and stretches the glass strands 41 from the holes 40. The burner 42 comprises a metal body 46 having a refractory jacket 48 within it which defines an annular combustion chamber 50 into which a mixture of air and fuel is introduced. The nozzle 44 communicates with the combustion chamber 50 and is formed by the inner and outer edges 54 and 56 of the tube 54. These edges 54 and 56 comprise internal and external cooling circuits 54a and 56a, respectively, to which a coolant, such as water, is supplied.

In order to keep the temperature of the centrifuge and the fibers constant during drawing, a high-frequency induction heater 62 is arranged just below and concentric with the centrifuge. Its inner diameter is slightly larger than that of the centrifuge to prevent it from contacting the downwardly entrained gas jet.

The auxiliary jet is provided by an annular blow ring 64 fitted outside the burner edges and connected to a source of compressed gas such as an air, steam or fuel source.

The hollow shaft 22 has a plurality of concentric fixed tubes. The innermost of these pairs of tubes defines an annular cooling passage 66 in which coolant flows, while the outermost pair defines an annular passage 68 in which the fuel mixture can pass and ignite to preheat the basket 26 prior to starting the centrifuge.

The fibers formed by the centrifuge and the gas jet enter the receiving space or receiving cabinet 70 and from there they land as a mattress 71 on the perforated conveyor 72, as schematically shown in Figures 2, 3 and 5. The suction box 74 below the conveyor shows a large amount of gas passing through the conveyor in the conventional manner.

As shown in Figures 4 and 5, a plurality of fiberizing machines, each with a centrifuge 10, are used in a conventional manner to form a fiber mattress 71, and according to a preferred arrangement according to the invention, these devices are arranged in a row along the longitudinal axis of the conveyor 72. In equipment used in industry, there are usually six or more centrifuges that direct the fibers to the conveyor.

With respect to the operation of said apparatus, the centrifuge 10 comprising the basket 26 is preheated in a conventional manner by utilizing the combustion gases coming through the duct 68, the heat of the burner 50, the heating ring 62 and similar additional sources as may be required.

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When the centrifuge rotates at a predetermined speed and the burner is adjusted to provide a pressure in the chamber that gives the gas jet sufficient speed to provide the desired degree of stretch and fineness of the fibers, the molten stream 24 enters the centrifugal hollow shaft 22 from the preheater or any other from a source of molten glass placed above the centrifuge. As the molten glass stream enters the basket 26, it flows to the bottom of the basket under centrifugal force and penetrates through the holes 36 in the basket as glass streams 38 directed toward the circumferential wall 12 of the centrifuge.

As a result of the stronger centrifugal force on the wall 12, the glass penetrates outside the wall from the many small holes 40 of the circumferential wall in the form of a plurality of strands 41 directly from a gas jet directed outside the wall, where combustion takes place inside the burner. Due to the high temperature of the gas jet, the glass fibers 41 remain in a stretchable state long enough to become drawn fibers. The fineness of the drawn fibers is adjusted in particular by adjusting the speed of the gas jet, which in turn depends on the burner pressure. Increasing the burner pressure and the gas blowing speed results in stronger stretching and thus finer fibers.

It should be noted, however, that increasing the tensile strength does not necessarily mean an overall improvement in the quality of fiber products. When the stretching caused by the gases is too strong, the quality of the fibers is usually poorer.

In addition to the flow of drawn fibers, large amounts of air are directed to the receiving space or cabinet 70, as indicated by the arrows at the top of the receiving chamber. The introduction of air into this space and the rapid deceleration of the speed of the fibers within the receiving space cause the fiber curtain to expand strongly and for the reasons explained in detail below, they provide a better distribution of fibers within the finished product and the width of the conveyor. In addition, it is found that the turbulence in the conveyor zone is reduced, as a result of which the orientation of the fibers remains better in the non-fibrous formation stage, whereby the non-fibrous thermal insulation properties are improved. The binder is sprayed on the drawn fibers from the top of the receiving space in a conventional manner. To simplify Figures 2-5, the equipment required for applying the binder has been omitted.

The diameter of the centrifuge is an important factor in this method.

The diameters of the largest centrifuges used in industry, in which the fibers are drawn by means of a centrifuge and a gas jet, have hitherto been in the order of 400 mm. Increasing the diameter of the centrifuge has not been considered advantageous, in particular because of the difficulties it could cause, above all in terms of the service life of the centrifuge.

It has now been found that by significantly increasing the diameter of the centrifuge, better quality insulating felts can be produced without significantly reducing the life of the centrifuge.

Excellent results have been obtained using a 600 mmm centrifuge and even larger diameter centrifuges can be used well. The advantages according to the invention are obtained with centrifuges with a diameter of more than 500 mm and about 550 to 1500 mm. The most preferred range is 600 to 1000 mm.

When the speed of the centrifuge is chosen to be such that it produces centrifugal acceleration forces which do not differ too much from the speeds normally used in connection with smaller centrifuges (for example 8000 to 14,000 m / s), the service life of the centrifuge does not change much.

The present invention contemplates a centrifugal rotation speed which, taking into account the best diameter range described above, provides a centrifugal acceleration to the circumferential wall located in 2 ranges of about 4,000 to 20,000 m / s. The centrifugal acceleration 2 is preferably located in the range of about 6000 to 16,000 m / s.

Figure 6 shows the results obtained with centrifuges of different lengths at a constant acceleration of about 1000 m / s. The quality of the felt, expressed here as the inverse of the fiber densities per unit area, with a micronair of 2.5, 3.0, 3.5 and 4.0 (in a 5 g sample) is clearly improved when the centrifuge diameter is more than 500 mm, as shown in the graphical diagram by a clear change in the steepness of the curve.

The difference in basis weight while maintaining the same insulation capacity is greater in products made with large diameter centrifuges, the finer the fibers, i.e. the smaller the micronaire F. Thus, the finer the fibers are, the more advantageous the use of centrifuges with a diameter of more than 500 mm.

When the microcaire is 2.5 in a 5 g sample, the improvement is very noticeable. It is stated, for example, that when moving from a 400 mm centrifuge to a 600 mm centrifuge, a reduction of 5% to the square meter weight is already obtained.

Figure 6 further shows that these improvements were not predictable based on the results obtained with previously known centrifuges. Namely, the curves only rise substantially after 400 mm. For lower values, the increase in diameter does not result in changes that could be observed or that would be significant given the accuracy of the measurements.

Taking into account the above-mentioned most preferred diameters and centrifugal acceleration values, the circumferential speed of the centrifuge is preferably about 50-90 m / s. Preferably, the circumferential speed is 55-75 m / s.

Another factor of great importance in the production of fibers is the burner pressure, the adjustment of which directly affects the fineness of the fiber and on which the energy consumption required by the process also depends.

When the burner of Figure 1 is used, the pressure of the burner is preferably in the range of about 100 to 900 millimeter millimeters, and more preferably 200 to 600 millimeter millimeters of water. It has now been found that, for reasons which have not yet been fully elucidated, the burner pressure required to produce a fiber of a given fineness decreases as the centrifuge diameter increases, even if the centrifugal acceleration does not increase. This may be one of the reasons for the observed improvement in fiber quality when using larger-pitch centrifuges. The lower burner pressure actually reduces the risk of the fiber breaking due to the pull gas flow.

It is also conceivable that in a weaker gas flow, the risk of collisions or gluing of the fibers would be lower. According to the invention, longer and more regular fibers would then be obtained.

Thus, as mentioned above, the improvement in fiber quality could be due to the fact that a lower basis weight is required to achieve a given insulation property and fineness.

In addition, the reduction in burner pressure results in less energy being consumed per the same amount of fiber.

The results of studies on this subject, shown in Figure 7, show a sharp decrease in energy consumption as the centrifuge diameter increases. The curve in this graph is obtained under conditions with a constant acceleration of 10,000 m / s. In these experiments, the density of the holes in the centrifuge wall, the diameters of the holes, the flow per hole, and the fineness of the finished fibers are the same.

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The graphical diagram in Figure 7 corresponds to the preparation of very fine fibers (micronaire 3 in a 5 g sample). In particular, it is noted that under the conditions of the invention, i.e. using centrifuges with a diameter of more than 500 mm, the heat consumption is less than 1500 kcal / kg when it is, for example, 1750 kcal / kg of fibers produced with a 300 mm centrifuge.

It should be noted that the heat consumption required to provide a traction gas jet represents the most significant part of the energy consumption in the manufacture of fibers. It accounts for almost four-fifths of total energy consumption. The reduction in this consumption is therefore very significant in terms of production costs.

It should be emphasized once again that even if the same heat consumption values give the same quality of fiber, the production volumes are not the same. Thus, under conditions where fibers of equivalent quality are obtained, centrifuges with a diameter of 300 mm, 400 mm and 600 mm produce 10, 13.5 and 20 tonnes of fiber per day, respectively. The savings in energy consumption therefore come in addition to the savings that come from increasing production.

The width of the burner nozzle opening 44 is preferably about 5-20 mm and more preferably about 8 mm. The temperature of the burner is preferably about 1300-1700 ° C and most preferably about 1500 ° C.

When using the centrifuges referred to in the invention, it has been found that they can be used to distribute the fibers more evenly on the conveyor and likewise the direction of the fibers in the fiber mat is better with these centrifuges.

Various measurements were performed on products prepared according to previously known methods and, on the other hand, on products prepared by the method of the present invention.

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The distribution of fibers within a finished product can be measured in several different ways. One of the simplest methods of measurement is to cut the product into small parallelograms or "cubes" (e.g. 25 x 25 x 45 mm) which are weighed separately. The different weights, which can be expressed as local mass densities relative to the center of gravity of each "cube," provide a three-dimensional picture of the fiber distribution. To make the comparison more comfortable, the coefficient of variation of the distribution is calculated from the ratio of the square deviation (square root of the mean squares of the deviations) to the mean of the weights of the "cubes".

Thus, for example, a very significant discrepancy was observed between products prepared by previously known methods (Cv = 6.1%) and products prepared by the method according to the invention (Cv = 2.6%). The distribution of the fibers in the samples examined is thus quite substantially better in the products prepared under the conditions of the invention.

With respect to the example of the invention shown in Figure 3, the relatively large temperature of the centrifuge provides a layer of fibers that spreads well before it enters the conveyor. When the conveyor is not very wide in the embodiment shown in the figure, the fibrous layer covers the entire width of the conveyor. The fibers at the edge of the layer collide with the side walls of the receiving cabinet 70 and redirect inward, resulting in a relatively uniform thickness of mat 71. The fibers descend only with very little vortex and, as a result, their direction is largely the same as the direction of the conveyor.

In contrast to the previous one, Figure 2 shows an example of previously known methods. Under conditions other than the centrifuge diameter being the same, the fiber layer is too narrow to extend into the walls of the cabinet. The fibers settle largely in the middle of the conveyor. A carpet is created which is not 16 75556 flat but thick in the middle and thin at the edges. On the other hand, in contrast to the use of a large diameter centrifuge, as in Fig. 3, here a strong vortex is generated in the edge portions of the fibrous layer near the conveyor; as a result of this vortex, the fibers land on the conveyor completely randomly and the direction of the fibers is clearly less the same as that of the conveyor than it was when using the device and method according to the invention.

The above-mentioned difficulties in fiber distribution are common, and various methods have been proposed in the past to improve the distribution.

If wide conveyors are used, two, three and more defibering devices can be arranged transversely to the conveyor, but even if this arrangement theoretically allows even distribution, a significant disadvantage is that when one unit has to be stopped, for example during a centrifuge change, this stop that the product manufactured by all other entities during the suspension of this measure will have to be rejected in its entirety. Therefore, the defibering units are preferably arranged in a single row parallel to the direction of movement of the conveyor, since stopping one unit does not cause significant changes in fiber distribution and manufacturing can be continued without interruption, with production reduced for only one stopped unit.

In connection with the defibering units arranged in this way, various auxiliary devices are used in an attempt to make the distribution of the fibers more even. These means include, for example, fans arranged on the sides of the receiving cabinet (U.S. Pat. No. 3,030,659), pendulum or alternating fans or control valves without inlet (U.S. Pat. No. 3,255,943), pendulum standards for fiber 75556 17 gauze (U.S. Pat. 638) and the reciprocating trajectory of the defibering device (US RE 30 192). Even if these devices cause the fibers to be better distributed, they usually generate more vortex in the receiving space, making the orientation of the fibers in the fiber mat even worse. Since the orientation of the fibers is extremely important in an insulating material made of fibers, since the best insulating properties are obtained if the fibers are parallel to the direction of movement of the conveyor, it is advisable to refrain as much as possible from using these distribution-enhancing accessories. Therefore, according to the invention, the wider fiber ash obtained by using larger centrifuges is an important factor in obtaining the best possible non-fiber. In addition, the present invention makes it possible to reduce or, if narrow fiber mats are made, to completely eliminate the accessories which improve the distribution of the fibers and thus to save their operating costs.

The extent of the fibrous gauze at the conveyor level is considerably larger than the extent that could be thought to result solely from an increase in the diameter of its initial plane, i.e., the diameter of the centrifuge.

It can be seen that the shape of the fibrous gauze immediately below the centrifuge is more advantageous in Figure 3 than in Figure 2, as the gauze of Figure 3 shrinks relatively little under the centrifuge, whereas the gauze of Figure 2 is substantially narrowed in this zone.

The following table summarizes examples of various embodiments of the invention. Example I, which does not correspond to the conditions of the invention, is a comparative example therein.

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Example no

I II III IV

Diameter of centrifuge (mm) 400 600 800 1000

Yield of centrifuge (t / day)

Burner cam width (mm) 7.7 7.7 7.7 6.5

Burner pressure (water column millimeters) 430 350 400 4 20

Burner temperature (° C)

Fineness (micronaire in a 5 g sample) 4.2 3.5 3.0 2.5 2

Weight per square meter in g / m when R = 2 nr ° K / w 297 ° K 1180 990 880 720

Specific thickness (mm) 90 90 90 90 These examples show that with the same yield of 20 tons / day, the products according to the invention are substantially better.

Comparing Examples I and II, it is found that when the heat resistance is the same, the basis weight is lower in the products made according to the invention, and also that the pressure and thus also the energy consumption are also lower.

Example III corresponds to similar conditions as Example II, but with an even larger centrifuge diameter. In this example, the fibers are even finer and at the same time the basis weight is still lower.

Example IV is another example in which the centrifuge diameter is even larger. The fineness and basis weight of the products made according to this example are particularly low, i.e. the fibers are very fine and the fiber density required to provide a given thermal resistance is very low.

Claims (4)

An apparatus for producing mineral fibers from a thermoplastic material, comprising a centrifuge (10) rotating about a substantially vertical axis (22), means for rotating the centrifuge, means for conducting a stream (24) of molten material in pullable state to the centrifuge and feeding it to the inner surface of the peripheral wall of the centrifuge, a large number of openings (40) through the peripheral wall through which the molten material passes and forms filaments (41), and means for drawing these filaments to fibers having means comprising a burner which emits a downwardly directed annular gaseous jet adjacent the outer portion of the peripheral wall, said gas jet having an elevated temperature which contributes to maintaining the filaments in a drawable state for sufficient time for drawing, characterized by: that the diameter of the centrifuge ranges between 550 and 1500 mm and that the device has drive means which drive the centrifuge at such a speed that the periphery of the entrifuge is subjected to a centrifugal acceleration upward, 2 tili between 4000 and 20,000 m / s, preferably 6,000-16,000 m / s. Device according to claim 1, characterized in that the centrifuge (10) has a diameter of 600-1000 mm. Device according to claim 1 or 2, characterized in that the nozzle of the burner is of the shape and size such that it produces a gas jet whose output pressure rises to 100-900 millimeters of water column, preferably 200-600 millimeter of water column. 4. Apparatus according to any preceding claim, characterized in that the heat consumption of the burner for the production of fibers, whose micro-nutritional value is 3 in 5 g of sample, is less than 1500 kcal per kg of fiber products.