EP0461995B1 - Fiber product recycling in a production line from fibers mat - Google Patents

Description

The invention relates to techniques for producing mineral fiber mattresses.

Industrially, these mattresses are obtained by a two-phase process, production of the fibers proper by stretching and freezing of a molten mineral material firstly, then, association of a very large number of fibers which are combined to constitute a mattress. Between the two phases, the glass or rock fibers are sprinkled with a binder which will be polymerized at the end of the second phase. Once the mattress is finished, it remains to finish the elaboration to constitute a ready-to-use product. In particular, the longitudinal edges of the ribbon must be cut so that they are clear. This operation produces a residue, the edges of the mattress, which we want to reuse. Likewise, certain falls resulting from the subsequent operation of the panels or rollers constitute by-products which it is advantageous to be able to recycle. Until now, the first operation, the recycling of the scraps coming from the banks is carried out, when it takes place, by shredding the scraps and returning the flakes upstream to the place where the mattress is created. This simple operation, however, has two drawbacks: on the one hand, the rate of falls reintroduced into the mattress is not regular, and on the other hand, as it is impossible to introduce falls whose density differs too significantly from that of mattress into which they are introduced, and that moreover the time which elapses between the moment when the falls are cut downstream of the line and the moment when they arrive upstream is very long, it is impossible to introduce the falls during a change of manufacture as soon as the difference in densities of the products produced exceeds a certain threshold. Likewise, with regard to the use of the scraps produced subsequently during the operation of the mattress during surfacing operations (possibly), longitudinal cutting, packaging and even shipping, it is very difficult and requires a great deal human intervention to prepare the waste, store it individually after flaking and then to make the decision to reintroduce it and finally execute it.

The object of the invention is to simplify, mechanize and generalize the recycling of all the fibrous scraps produced during the manufacture and exploitation of mineral fiber blankets or at least to reintroduce the maximum proportion thereof tolerated by the quality to produce and increase this limit compared to previous techniques.

The reintroduction of scraps from fibrous mattresses is a traditional practice, both on the production lines of rock fiber-based mattresses such as those produced according to the process described in patent EP-A-0059152 as on the production lines of glass fibers according to, for example, a process of the type described in patent EP-A-0091866. It consists in reintroducing the scraps in the form of flakes during the formation of the fibrous mattress. In the first process mentioned above which uses a single source of fibers, the scraps are in the form of flakes and are injected into the receiving hood, the flakes are sucked together with the new fibers on the conveyor which is a carpet perforated where the first mattress is formed. In the other method which uses several fiber production units in series, two techniques have been used, either the introduction of flake-like scraps above the conveyor, between two fiber production heads, or - according to the technique described in French patent FR 2 559 793 - directly in one or more of the receiving hoods. Apart from the requirement concerning the forming of flakes of the scraps, two other constraints are imposed, it is imposed on the one hand that the scraps before putting under flakes, have a density, that is to say a density which deviates as much as possible from the density of the mattress produced from a limit value which depends on the nature and use of the mattress. Furthermore, the quantity of recycled fibers must not exceed a certain rate. It also depends on the quality that we want to respect in the mattress produced. It is itself subject to technical criteria, such as for example the practical use for which the product is intended or commercial criteria such as, for example, the manufacture of a high or low-end product, etc. In any case, this rate must in most cases remain below 12%. It should also be noted that the more the density of the recycled fibers differs from that of the mattress, the lower the accepted rate. It can therefore be seen that the two values given above are only indicative, since they must be combined according to very diverse technical or commercial criteria.

As we have seen, the waste can have two origins, one systematic, the rectified edges of the mattress, the other random, the waste produced during the operation of said mattress, an operation which can provide waste under the conditions the most diverse: most are due to production difficulties: sometimes unsaleable products are made for one reason or another and the more the product is developed or the more sophisticated the packaging, the greater the risk. Thus the so-called "surfaced" products, that is to say on the surfaces of which a facing has been pasted, may exhibit detachments, tears, appearance defects, etc. It is then impossible to sell or even use the product panel or roll. In this case, there is only one alternative: either discard the finished product or recycle the essentials, that is to say the fibrous part. The first solution poses problems concerning the environment and that is why we try to reuse the fibers of such unsellable panels or rolls as much as possible. Various techniques have been proposed for separating the facing from the fibrous material and we assume that they have been implemented and that the panel or the bare fiber roll is available here. It is these fibers - as well as the fibers from the edges of the mattress - that we want to recycle. The invention proposes a process for carrying out this recycling.

Other known techniques such as those described in patents DE-A-22 23 683 or US-A-2 702 069 relate to the introduction of fibers of different nature in the manufacture of insulation masts.

According to the invention, the method of manufacturing the mineral fiber mat comprises the following steps: forming fibers from a molten material, drawing, entrainment by a stream of gas; the stream of fibers then being directed towards a conveyor which gathers them and drives them. Then, allogenic fibrous materials are added to the main flow of fibers, they have been selected according to their density and are driven at constant volumetric flow.

Preferably, the materials are formed into flakes.

Furthermore, the non-native fibrous materials were stored before their introduction into the main stream of fibers, their storage is done in silos where, in each, the fibers have a defined average density.

Allogenic fibrous materials are taken from stocks of different average densities in quantities such that the resulting average density is compatible with those of the fibers of the main stream. The invention therefore provides that weighings are carried out continuously at the outlet of each silo. In the same silo, the non-native fibrous materials are mixed according to their densities and their respective quantities and regardless of their origin.

In the manufacturing process according to the invention, between the exit from the silos and the introduction into the main flow of fibers, the non-native fibrous materials are mixed and then destructured.

A device is also proposed for implementing the manufacturing method of the invention, it comprises a constant level tank, a carpet with rising tips and two comb rollers in the upper part.

Furthermore, for a given belt speed, it is the first comb roller which defines the volumetric flow rate. The second is regulated so as to extract most of the fibrous materials that have reached it.

The process of the invention thus makes it possible to recycle the maximum of possible products, it therefore makes it possible to almost completely eliminate pollution of the environment by mineral fibers coming from fibrous mattresses, moreover this technique makes it possible to reduce the costs of production insofar as new fibers are replaced in the finished product by fibers which - otherwise - would have been lost.

• La figure 1 schématise les techniques de l'art antérieur,
• La figure 2 résume schématiquement l'ensemble des opérations préconisées par l'invention pour le recyclage des déchets sur une ligne de production de fibres minérales,
• La figure 3 présente sous forme schématique la machine utilisée pour la préparation et le dosage des flocons.

The description and the figures which follow will make it possible to understand the operation of the invention and its advantages.

• FIG. 1 schematizes the techniques of the prior art,
• FIG. 2 schematically summarizes all the operations recommended by the invention for recycling waste on a production line for mineral fibers,
• Figure 3 shows in schematic form the machine used for the preparation and dosing of the flakes.

In Figure 1, we see a production line of a mattress of mineral fibers, in this case glass fibers, here by the method using the centrifugation of a stream of liquid glass through the orifices of the wall d 'a rapidly rotating container. This process is described for example in patent EP-A-0091 866. In such a process, several sources of fibers are generally used which successively deposit plies which constitute, by their superposition, the fibrous mat. In the figure, four are shown. We see schematically in 1 the centrifuge device which projects a rain of fibers 2 which is deposited on the conveyor, in this case a perforated metal mat 3. Through the mat we suck air 4 so as to press the mattress 5 on the mat. Each centrifuge device 1 is isolated from the outside by a wall 6 which constitutes a suction hood. The fiber mat 5 is driven over a very long length in the direction of arrow 7. This length is most often a hundred meters. The system carrying the mattress is not shown. The device which in each extractor hood makes it possible to project a liquid binder onto the fibers, which is then dried and polymerized in the enclosure 8, has not been shown either.

The mattress 5 will then be cut to constitute either rolls or panels. The shaping of the mattress for the production of the finished product requires that previously the irregular longitudinal edges of the mattress be eliminated. Sure the production line, we therefore have to carry out a systematic longitudinal cutting of the selvedges. They are seen at 9 in Figure 1. They are driven to a shredder 10 which transforms them into flakes of fibers whose dimensions range from one to a few centimeters. These flakes, animated by the air supplied by a blower 11, are conventionally returned directly upstream, to the place where the fiber mat develops. There, they are reintroduced into the mattress, either between the extraction hoods, or in a more homogeneous manner, according to the technique described in patent FR 2,559,793, directly into the flow of fibers from each of the extraction hoods. . In FIG. 1, it is this technique of introducing the fibers into the extractor hood which is shown diagrammatically, the introduction is made at each layer of new fibers such as 2 by the conduits 12, two in number in each of the extractor hoods. Between the blower 11 and the conduits 12 the recovered fibers must therefore follow a long path 13 to a distributor 14 which directs identical recycled fiber flow rates over the four suction hoods shown. They thus pass through the four pipes 15 before arriving at the distributors 16 which also divide the flow intended for each of the conduits 12.

In a stabilized regime, that is to say when, for long periods, the same type of finished product is manufactured, that is to say with the same density and the same binder, the flakes from the edges 9 are easily inserted into the mattress 5.

However, it is obvious that the time which elapses between the production of a given mattress and the introduction of the scraps coming from this mattress into the extractor hoods is very long. Thus for example, on a line of the type of that of FIG. 1 with four fiber-drawing units at 15 tonnes per day and a mattress width of 1.20 m, we measure, in the case of the manufacture of a mattress with 60 kg / m ³ in 10 cm thickness, a delay of the order of 20 minutes between the production of a mattress and the reintroduction of its selvedges into the fiber mattress produced subsequently. During a stabilized production, this delay has no consequences, however, if we change manufacturing, with a significant difference in the densities of the two mattresses which makes it impossible to recycle the old fibers, there is then no other solution than a storage of large quantities (in the example chosen, 14 m ³ ) pending an identical future production or the disposal of the falls concerned. The solution of recycling the fibers in the glass or slag melting furnace can also be envisaged, but it is expensive (the fibers must be remelted) and it can disturb certain parameters of the melting such as the redox balance of the bath.

But in traditional production lines, we also want to recycle the scraps of fibrous materials produced offline, following, for example, poor workmanship. When we want to recycle such products after having rid them of allogenic elements such as materials used as facings for example, two cases arise, or they are compatible with the production of the moment (same binder and neighboring density) and then they can be added to the selvedges until constituting with them a defined fraction of the finished mattress, for example 10%, this limiting proportion being a function of the desired quality and the density of the mattress produced. On the other hand, when the materials are incompatible and we want to reuse the scraps, the only possibility outside of recycling in the oven is storage while waiting for the material whose density and / or quality to be produced again. obtaining will allow the reincorporation of the stored scraps.

Still in FIG. 1, there is the circuit for recycling finished products. 17 shows a shredder into which the panels 18 (or the rollers) are removed, stripped of their surface coating. The blower 19 propels the airborne flakes to the distributor 20 which - depending on the original density of the panel 18 (or of the roller) sends them through the pipe 21 to the storage silo 23 - reserved for example for products light, the others being transferred via line 22 to silo 24 reserved, he in the example, for the densest products.

Depending on the type of mattress 5 (density, target quality) that is in production, we will draw from the stock of light materials from silo 23 or from that of heavy materials from silo 25. In the traditional process to adjust the flow of recycled products at the target value which depends on the quantities to be recycled and the tolerable maximums, which themselves depend on the nature of the product in manufacture and on the quantities of flakes coming from the selvedges already reintroduced, a discontinuous scale 25 is used which is permanently responsible for flakes then empties when the load reaches a defined weight fixed in advance. The entire load is then poured onto the conveyor belts 26 and 27 to finally reach the circuit 13 thanks to a blower not shown. The path followed by this second family of waste is then the same as that of waste from the edges.

The waste recycling system which has just been described and which would make it possible, on a line devoted to a single type of manufacturing, to recycle the maximum amount of waste possible has, as we have seen, numerous drawbacks. Among these, some concern the recycling of the banks during campaign changes and have been extensively explained. qués above, they are very annoying because it happens that a campaign lasts less than an hour, the others concern the dosage and assimilation of waste from finished products. The first phase of the cycle, that which begins with the introduction of the panel 18 into the shredder 17 and ends with the storage of the flakes of light products in the silo 23 and of the dense flakes in the silo 24 generally goes very well. . It is the second part, between the sampling in the silos until the introduction into the distributor 14 which poses serious problems for the metering of waste.

Let us take as above, the example of a production of a mattress based on dense products with a width of 1.20 m with the four centrifuges represented figure 1. In the example, the cutting of the banks produces 8 % of waste which is permanently recycled using line 13. The production carried out is here intended for an end use which tolerates for example 12% of waste. It should therefore have been possible to introduce a maximum of 4% of waste from silo 24. The theoretical flow to be introduced is, given the parameters defined above, 1.6 kilograms per minute. The scales 25 operate in the following manner: a stabilized flake flow rate is established at the outlet of the silos approximately at the desired flow rate and at regular time intervals, the exact desired load is released and falls onto the conveyor belt 26. In the example in question, it is a load of 530 grams which falls every 20 seconds. Such a system thus provides the good average flow rate but a very variable instantaneous flow rate. In fact, during subsequent transport, the differences will slightly decrease, but there is nevertheless an oscillation of the overall quantity of recycled flakes around the target value. As we have the imperative not to exceed, for commercial reasons in this case the value of 12%, we are forced to reduce the quantity of flakes recycled from silo 24, for example to 10% to be sure of never exceed the maximum tolerance.

The traditional methods of recycling scrap from defective finished products are limited by the difficulties of assimilating flakes of non-native origin in the mattress. Indeed, the flakes that have been stored in silos 23 and 24 will be extracted then transported and finally mixed as such with the stream of new fibers. They therefore remain in the same form in the finished mattress where they constitute heterogeneities of notable size.

FIG. 2 represents the process of the invention for preparing, selecting, storing, dosing while destructuring then finally, distributing the wastes as well those coming from the edges on the line as those coming from the falls or workmanship, offline. Certain elements are the same as those in FIG. 1, in particular everything relating to the line proper, from the suction hoods 28 to the mattress 5 at the end of the line. The processing of longitudinal edges 9 uses shredders 10 and blowers 11.

• La rive, découpée par des scies, des disques ou des jets d'eau, s'engage dans un conduit horizontal suivi d'un conduit vertical ou oblique aboutissant au broyeur installé soit sous la ligne, soit de préférence dans la cave, ce qui facilite les opérations de maintenance et diminue le bruit. Il y a un broyeur par rive. La longueur minimum du conduit horizontal est de 500 mm. Sa section sera, par exemple, 340 x 350 mm.

The shredders are fed here as follows:

• The bank, cut by saws, discs or water jets, engages in a horizontal conduit followed by a vertical or oblique conduit leading to the crusher installed either under the line, or preferably in the cellar, which facilitates maintenance operations and reduces noise. There is one crusher per bank. The minimum length of the horizontal duct is 500 mm. Its section will be, for example, 340 x 350 mm.

Upstream of the horizontal duct, a motorized caster comes to lay the bank flat while pinching it. This prevents breakage of the edge downstream of the cutting saw. The length of the vertical or oblique part is approximately 2.5 m (depending on the depth of the cellar).

Depending on the width of the product, the distance between the horizontal conduits can be adjusted using two motors and two screw-nut assemblies.

The vertical conduits have at their upper end a cone which makes it possible to keep the vertical part fixed, despite the variation in distance between the horizontal conduits.

As a shredder, hammer mills are used. The mill consists of a 450 mm diameter rotor, a length of 400 mm, it comprises 90 hammers distributed over three rows, its rotation speed is of the order of 1500 revolutions per minute. The grid is made of manganese steel, dimensions 40 x 40 mm.

At the outlet of each shredder, a fan 11 ensures the evacuation of the flakes.

The characteristics of the fan are calculated in order to obtain a speed of 20 m / sec in the 200 to 250 mm diameter pipes, i.e. a flow rate 4 of approximately 3500 m ³ / h. The total pressure being calculated as a function of the pressure losses due to the installation of the pipes.

The materials used for the impeller and the scroll have good abrasion resistance.

At the outlet of the fans 11, there are here distributors 29 which are capable of orienting the flakes, either towards the duct 30 if, for example they are light, or towards the duct 31 if they are denser, they then join the main light 21 or heavy 22 circuit which directs them respectively to silos 21 or 24. The circuit of scraps or finished products from poor workmanship 18: shredder 17, blower 19, distributor 20 then channeled main tions 21 or 22 is itself made up of elements which are exactly the same as those which have just been described. It can be seen simply in FIG. 2 that the selvedge circuit has joined, after separation according to density, the circuit of falls and poor workmanship so as to constitute a single circuit, that of allogenic fibrous materials. Passage through silos such as 23 or 24 is therefore systematic. These silos are, for example, cylinders with a vertical axis with a capacity of 4 m ³ each. Each is surmounted by a capacitor (43, 44) which allows the separation of air and flakes. They are fitted with filters to remove dust before the air is recycled. In the figure only two silos have been shown, one 24 for dense products, the other 23 for light products. During the tests, the light products / heavy products border had been placed at a density of 20 kg / m ^3. The distributors 20 or 29, on each of the flake supply circuits are switched according to the density of the flakes which feed them either on the conduit 21 if their density is low, or on the conduit 22 if their density exceeds the fixed limit. This limit depends on the range of products produced on the lines (in the case of Figure 2, it can range from 8 to 110 kg / m ³ ) but it also depends on the respective quantities manufactured in the different densities, as well as it also depends on the proportion of additions of different density tolerated which is not the same according to the end uses of the product: a fiber intended to constitute a filler in a bitumen does not have the same requirements from this point of view as that which will constitute a roll intended for the insulation of roof spaces for example.

The number of silos shown in Figure 2 is two but it is obvious that a finer classification of the flakes to be recycled can be interesting. The number of silos is then multiplied, which makes it possible to refine the adequacy between the respective densities of the recycled flakes and the mattresses in production.

Following the route of the recycled flakes, at the exit of the silos (23, 24) is identical to that of FIG. 1, we find successively the scales 25, the conveyor belts 26 and the main conveyor belt 27. The element essential new in the circuit is machine 32. It is a machine called "ball breaker", its function is multiple. First of all the usual function of this type of machine which is to "break" the tangles of fibers. In fact, during the previous multiple manipulations, the flakes could have been packed, compacted, nested and it is necessary to try to restore them to their initial configuration, their integration in the new fibers will be all the better. We even want to go further: to destroy, to "burst" the original flakes to facilitate their integration in the flow of new fibers and therefore in the mattress. A second function of this machine, which is not usually required in bale breakers, is to homogenize flakes which have multiple origins: selvedges on the one hand and finished products on the other but also among these, flakes who have a different history from each other. A third completely new function is also fulfilled by this machine. The function is new because the problem posed here is not usual in the workshops where such machines are installed, it is a question of making constant the flow at the outlet of the scales, flow which varies periodically, as we have seen . It is necessary to "smooth" the cyclical variations so that the excess of flow compared to the average flow compensates for the deficiencies. This gives a constant volumetric flow.

The machine 32 is shown diagrammatically in FIG. 3. The product leaves the conveyor belt 33 which, for its part, is represented in FIG. 2, which has raised the flakes above the machine, on the left. The entry of the machine at 34 is in the form of a trough, the bottom of which is constituted by the conveyor belt 35. The latter is driven at constant speed, the flakes will therefore deposit there periodically as they are delivered by balance 25 in operation.

This conveyor belt 35 in turn feeds a conveyor belt 36 which constitutes the bottom of a tank at constant level, in fact, it is equipped with an ultrasound system not shown which allows the flakes of non-native fibrous materials which load it with water. '' occupy a constant thickness. As soon as the chosen level is reached, the drive motor of the treadmill 35 is blocked and the fiber supply is immediately stopped. In this way, the flakes occupy in the tank 37 a defined height which is chosen so that the fibers are entrained upwards at a constant flow rate which corresponds to the average weighing of the balance 25. The entrainment upwards is carried out using the spike belt 38 in translation at constant speed. This speed can be adjusted using a manual control, not shown.

At the top of the spiked carpet, the flakes reach the comb roller 39 which has four generators equipped with spikes and turns against the current, it drives down the excess flakes, thus ensuring a perfectly regular flow of fibers. Furthermore, the teeth of the combs penetrate into the flakes held by the tips of the carpet, causing the desired "destructuring". A second identical roller 40, which rotates in the direction of flow, performs a similar function and extracts all the fibers from the spiked apron and returns them on the inclined plane 41, towards the outlet 42 of the machine.

Below this outlet is the conveyor belt 45 which supplies a fan (not shown). This sends the regular flow of allogenic fibrous materials delivered by the machine 32 to the distributor 46 which feeds as many pipes as there are extractor hoods 28. Before the distribution in the distributors again, distributors 47 separate the flow of recycled fibers into two equal flows which supply the extractor hoods in pairs where they will be mixed with the main flow of fibers.

It can thus be seen that the use of the machine 32 makes it possible to deliver a constant and well-defined volumetric flow rate since it corresponds to the weighing carried out by the balance 25.

The invention therefore makes it possible to supply the production lines for rock fibers or glass fibers immediately after the fiberizing machines with a regular flow of open, destructured flakes. These two elements, regular feeding on the one hand, and destructuring of the flakes on the other, each contribute to facilitate the incorporation of allogenic fibers into the flow of new fibers. We can therefore always choose, if necessary, the maximum throughput of recycled fibers compatible with the quality criteria of the moment which are, as we have seen, dependent on the nature of the products produced, their final destination and the nature fibers to recycle.

The following examples will show how the storage of allogenic fibrous materials in silos where the average density is defined makes it possible to control the average density of the fibers reintroduced into the main flow of fibers.

Example 1

et dans le silo B :

La fabrication retenue pour l'exemple était celle d'un produit très dense d_f = 90 kg/m^3. Il se trouve qu'étant donné le marché auquel est destiné le produit et surtout ses conditions d'utilisation, uniquement en compression, il n'existe pas de problème de cohésion du matelas et la proportion de flocons légers tolérée est grande. Empiriquement, on a constaté qu'en utilisant les techniques de l'invention, cette proportion peut atteindre 8 % en volume avec un produit dont la densité est égale à celle du matelas en production, c'est-à-dire égale à d_f, mais qu'elle peut aller jusqu'à 15 % si sa densité moyenne est de 15 kg/m^3. Entre les deux une interpolation est possible, c'est-à-dire que par exemple, si l'on veut réintroduire des flocons de densité moyenne 30 kg/m³, on pourra en réintroduire 13,5 % et si leur densité est de 60 kg/m³, 11 %. Dans le cas concret de l'exemple, on a choisi cette dernière possibilité et on a donc pris l'intégralité des produits à recycler dans le silo B dont la balance a été ajustée pour délivrer en moyenne, 275 Kilos par heure. La machine 32 de la figure 2 est réglée de manière à assurer précisément le débit volumétrique constant de la quantité retenue. En faisant ce choix on fait légèrement baisser le stock de déchets contenus dans le silo B. En effet, la quantité horaire introduite (dans le silo B puisque sa densité, 90 kg/m³ est supérieure à la limite fixée, 30 kg/m³) correspond aux 8 % de la production tandis que la quantité extraite est de 11 %. Par ailleurs, la densité moyenne du stock s'accroît. Ce paramètre - gestion des stocks de déchets - s'ajoute à ceux déjà évoqués. Il fait partie des éléments à considérer avant de choisir la densité moyenne et la quantité à réintroduire.On a centrifuge glass fiber line comprising four fiberizing heads which produces 60 tonnes per day in 1.30 m of gross width, for a useful width of 1.20 m, we therefore have about 8% shoreline waste. The contribution of waste from finished products was zero that day. The line is equipped with two storage silos, silo A for light products and silo B for dense products. At the time of the example, the density limit between A and B was 30 kg / m ³ and the average density in silo A was:

and in silo B:

The manufacturing chosen for the example was that of a very dense product d _f = 90 kg / m ^3. It turns out that given the market for which the product is intended and especially its conditions of use, only in compression, there is no problem of cohesion of the mattress and the proportion of light flakes tolerated is large. Empirically, it has been found that using the techniques of the invention, this proportion can reach 8% by volume with a product whose density is equal to that of the mattress in production, that is to say equal to d _f , but it can go up to 15% if its average density is 15 kg / m ^3. Between the two an interpolation is possible, that is to say, for example, if one wants to reintroduce flakes with an average density of 30 kg / m ³ , we can reintroduce 13.5% and if their density is 60 kg / m ³ , 11%. In the concrete case of the example, we chose the latter possibility and we therefore took all of the products to be recycled in silo B, the balance of which was adjusted to deliver an average of 275 kilos per hour. The machine 32 of FIG. 2 is adjusted so as to precisely ensure the constant volumetric flow rate of the quantity retained. By making this choice, the stock of waste contained in silo B is slightly lowered. In fact, the hourly quantity introduced (in silo B since its density, 90 kg / m ³ is greater than the fixed limit, 30 kg / m ³ ) corresponds to 8% of production while the quantity extracted is 11%. In addition, the average stock density is increasing. This parameter - management of waste stocks - is in addition to those already mentioned. It is one of the elements to consider before choosing the average density and the quantity to be reintroduced.

Example 2

The glass fiber production line according to the method of European patent EP A 0091 866 comprises six centrifuge heads with a production of 120 tonnes / day. The net width is 2.40 m and shore waste constitutes 4% of production. Storage is done in three silos, A, B and C, the average densities of d _A = 12 kg / m ³ , d _B = 20 kg / m ³ and 50 kg / _m 3 respectively.

On the day of the example, the production was that of a mattress with a density of 30 kg / m ³ and the contributions of finished products to be recycled which had to be introduced into the silos consisted of a quantity of 200 m ³ per day with a density of 10 kg / m ³ . For production management reasons, we want to keep the same average density here in silo B, so we will introduce into it all the falls from the banks (200 kg, or 6.7 m ³ per hour) and l 'we will introduce the same volume of finished product scraps with a density of 10 kg / m ³ . The rest of the scraps of finished products will be stored in silo A where the average density will drop slightly. The product manufactured on the day concerned accepted 8% by volume of scrap but with an average density close to that of the product in production. A flow of 8.9 m ³ / h (178 kg) was therefore taken from silo B and silo C, 4.4 m ³ / h (220 kg), these quantities will be mixed and introduced, after equal distribution, into the receiving hoods of the 6 fiber production units.

On en déduit

et

But we might as well have taken a volume c from silo C and a volume a from silo A such that:

We can deduce

and

It is thus seen that there are many possibilities in the choice of parameters which, thanks to the invention, are offered to the production manager.

The technique of the invention therefore makes it possible not only to permanently reintroduce the falls originating from the banks of the mattress, whereas the prior techniques required this reintroduction to be interrupted during production changes, but in addition it allows recycling of waste whatever their origin and whatever the nature of their fibers. The only constraint is that there must be sufficient storage to allow waiting for production to be compatible with the nature of the fibers to be reintroduced.

The systematic recycling of fibers from finished products is particularly favorable for the preservation of the environment.

Furthermore, by making it possible to reintroduce the maximum tolerable quantity of recycled fibers, there is a significant saving on the cost of production. In fact, in the finished product, newly manufactured fibers are replaced by fibers which otherwise would have been thrown away and which cost nothing and made it possible to eliminate the costs which their elimination would have entailed. The additional cost is limited to that of transforming the finished product into flakes that can be stored in the silos and to a few subsequent handling operations.

We can thus see that the progress made in the field of environmental protection recalls that of the 1980s when industrialized countries recycled glass bottles.

Claims (9)

1. Method of producing a mineral fibre mat comprising forming fibres from a molten material, drawing them, entraining them by means of a stream of gas, subsequently directing the stream of fibres towards a conveyor which collects them and entrains them and in which foreign fibrous materials are added to the main fibre stream, characterised in that the foreign fibrous materials which are introduced are selected as a function of their density, and in that they are entrained at a constant volumetric rate.

2. Method of production according to Claim 1, characterised in that, before being introduced into the main stream of the fibres, the foreign fibrous materials are mixed and then destruc- tured.

3. Method of production of a fibre mat according to either one of Claims 1 or 2, characterised in that the foreign fibrous materials have been stored prior to their introduction into the principle stream of fibres.

4. Method of production according to Claim 3, characterised in that the storing is in silos and in that in each one of them the fibres have a clearly defined average density.

5. Method of production according to Claim 4, characterised in that the added fibrous materials are taken into stores of varying average densities, in quantities such that the resulting average density is compatible with that of the fibres in the main stream.

6. Method of production according to Claim 5, characterised in that weighing is performed continuously at the output of each silo.

7. Method of producing a mineral fibre mat according to Claim 4, characterised in that the foreign fibrous materials are mixed in the same silo as a function of their densities and their respective quantities and irrespective of their origin.

8. Device for the production of a mineral fibre mat comprising forming fibres from the molten material, drawing them, entraining them by means of a flow of gas, subsequently directing the stream of fibres towards a conveyor which collects them and entrains them and in which foreign fibrous materials are added to the main fibre stream, characterised in that it comprises in particular a blower (11, 19), a distributor (20, 29), compactors (43, 44), silos (23, 24), scales (25), a distributor (46) and machine (32) ensuring an entrainment at a constant volumetric rate.

9. Device according to Claim 8, characterised in that the machine (32) comprises a constant level tank (37), a spiked and ascending belt (38) and two comb rollers (39, 40) in the upper part.

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