GB2294236A - Curvable felt of fibrous materials with random orientation - Google Patents

Abstract

To permit the curvature of felts of crimped mineral wool fibres, ie. those in which the orientation of the fibres, instead of being parallel to a plane, is quasi-random, in a temporary or permanent manner, they are provided on the convex side with a surfacing sheet, the rupture resistance of which is greater than 300 kPa such as, for example, a kraft paper of a surface mass which is greater than 60 g/m<2>. <IMAGE>

Description

CURVABLE FELT OF FIBROUS MATERIAL WITH RANDOM ORIENTATION The invention relates to mineral wool felts, and, more particularly, to felts called "crimped", ie. in which the orientation of the fibres is quasi-random in place of being parallel in one plane.

Crimped felts are intended for various usages, in particular if it is desired either to exert a pressure thereon without causing too much crushing, or to exert a traction perpendicular to the surface without causing delamination.

However, in contrast to usual layered felts, they are very sensitive to flexion and as soon as they are arched, even slightly, they crack, perpendicular to their surface. This phenomenon substantially restricts the area in which the crimped felts may be used. It is desired to be able to enlarge this area.

Traditionally, the mineral fibre felts are layered, they are formed in a continuous manner by depositing on the conveyor fibres which are transported by gaseous currents. The conveyor retains the fibres and allows the gases to pass through.

Before they are disposed on the conveyor, the fibres are coated with a resinous composition intended to bind the fibres to one another, thus providing a cohesion of the formed felts. The resinous composition is applied in liquid form and cross-linked by a heat treatment which is performed on the felt which has previously been brought to the desired thickness and volumetric mass.

The traditional methods of forming felt result in products the properties of which do not fulfil perfectly all the conditions which are required for certain particular applications. In addition to insulating qualities which are generally required, it is also sometimes necessary for the products which are used to have very specific mechanical properties. This is, for example, the case with products which support masonry elements and which must, in consequence, resist strong compressions, such as products acting for the insulation of roof terraces which are accessible to traffic. This is also the case for products which are used for exterior insulation and which, in particular, must be able to resist tearing forces.

To obtain products having these particular properties, the traditional processes for forming felts must be modified.

In the traditional process, the felts are formed by depositing the fibres on the receiving conveyor or on a similar member leading to a tangling which is not homogenous in all directions. It has been found by experimentation that the fibres have a strong tendency to locate themselves parallel to the surface of reception.

The longer the fibres, the more this tendency is accentuated. This fibre structure is favourable to the insulating properties thereof and also to the resistance to traction in the longitudinal direction. A structure of this type is, consequently, advantageous for numerous applications. However, it will be understood that a structure of this type is not the most suitable when, for example, the product needs to resist compression or tearing in the direction of the thickness thereof.

Methods are known which provide quasirandom orientation of fibres. Thus, European patent application EP-A-0 133 083 proposes that the fibre felts collected on the receiving organ be compressed continuously in the longitudinal direction, optionally after having been subjected to a compression in the direction of thickness, ie. been compressed continuously in their longitudinal direction by passing from one pair of conveyors driven at a certain speed to a pair of conveyors working at a slower speed than the first pair. Higher compression rates may be achieved when the compression is performed in several successive stages, in particular in the case of felts in which the compression without the formation of folds is the most difficult to obtain.Likewise, in the case of the same final compression rates, the properties of the products obtained may be improved when the compression is conducted in several stages.

In another document, the European patent application EP-A-O 434 536, there is proposed a mineral fibre felt with improved properties where the fibres have quasi-random orientations, which felt is formed of fibres having, in the case of the great majority of them, a diameter of between 2.5 and 4.5 zm and a length of 2 to 15 cm, and which have a volumetric mass which is no greater than 40 kg/m3. In this application, it is envisaged that the mats may have a surfacing, ie.

be covered with one or more adhesive sheets of paper, aluminium, polyethylene or PVC.

The crimped mineral fibre mats obtained by methods which will be described are generally transported and used in the form in which they are manufactured, ie. as flat panels. It would, however, be advantageous to be able to curve the crimped mats - temporarily or permanently optionally even with small radii of curvature.

The advantage of being able to roll up the crimped mats to permit the transport and long term storage thereof without using too much space is obvious. In the area of industrial applications of crimped mats, the insulation of large channels or cylindrical cisterns on which it must be possible to walk is an application in which the permanent curvature of a crimped mat would be very useful.

Still with reference to the field of the prior art of felts of crimped mineral wools, European patent EP-B-0 472 532, which proposes a method for manufacturing a crimped plate covered with a surfacing sheet on a single side, is known.

According to this method, after having performed the crimping in the usual manner, a glass fibre cloth is disposed on the two surfaces of the mat prior to the thermal treatment of the resin which forms the binder. At the outlet, the mat is split along its thickness to obtain two identical mats which are surfaced on one side. This method permits there to be obtained a plate which may be curved by leaving the glass fibre cloth on the concave side. The document clearly shows that the flexion in the other direction (glass fibre cloth on the convex side) is impossible. In effect, the intermediate product with the cloths on the two faces thereof is described as rigid, but, after splitting, the fibres of the free side "are not subjected to tension and compression forces in the direction of the fibres when the plate is curved but perpendicular to the fibres.Thus, the plate produced by this method curves well owing to the absence of horizontal binders at the rear. The convergence of these two phenomena, the rigidity of the plate covered on its two surfaces, and the flexibility of the plate divided along its thickness shows that it is in traction that the glass fibre cloth is not deformable and that the curvature can only be realised in the case of covering of the concave side. The mounting method described in the document, with the edges of the ceiling plate "supported on profiled sections in the form of a T" as in the case of an arch, confirms this.

The object of the invention is to provide a product, a crimped fibre mat, which may, without deterioration, be rolled up in order to permit the transport and storage thereof. It is also an object of the invention to permit the use of a crimped mineral fibre mat on curved surfaces without any loss in the properties thereof, in particular insulation.

To obtain these results, the invention proposes a crimped mineral wool felt, provided on at least one of its faces with a surfacing sheet and intended to be subjected to a temporary or permanent curvature, the face of which which is intended to be convex being equipped with a surfacing sheet the resistance of which to cracking is greater than 300 kPa.

This sheet is advantageously based on kraft paper. In order to obtain, by itself, the necessary resistance to cracking, this kraft paper must have a surface mass which is greater than or equal to 60 g/m2.

For rolling easily about itself and to retain all its properties when it is used on a curved surface, the crimped felt according to the invention preferably has a crimping rate of between 4 and 5 and a surface mass of less than 2 kg/m2.

An advantageous variant of the product according to the invention has, on the face opposite that which is covered with a surfacing sheet according to the invention, fibres which are practically perpendicular to the surface. An arrangement of this type is ensured if the crimped mineral wool felts is produced in particular from the separation, along the thickness, of a thicker felt, the surface opposite the one which is covered with the surfacing sheet according to the invention being the product of the separation.

The Figures and the description which follow will permit the invention to be understood and the advantages thereof to be known.

In the Figures, Figure 1 shows the result of a curvature imposed on a crimped mat of the prior art, Figure 2 shows a mat according to the invention before curvature and Figure 3 shows a mat according to the invention after curvature.

The crimped fibres which are in question here are formed from mineral wools, glass wools or wools called rock wools. These products are most often formed from fibres obtained by centrifuging methods, in this case with passage through the apertures of a centrifuge or simply by ejection from the surface of rollers rotating at high speed.

The fibre-forming installation comprises, firstly, one or more machines of the above type, which are fibre generators. The ejected fibres are collected in the base part of the machines by aspiration on a conveyor belt forming the base of a receiving chamber.

Inside the chamber, the devices spray a liquid binder composition onto the fibres.

Traditionally, it is sought to perform this in such a manner that the distribution of the binder on the fibre is as uniform as possible in order that the binder is subsequently distributed in a very homogeneous manner through the whole of the felt.

The felt leaving the chamber is usually relatively light. The average volumetric mass thereof is low in relation to a substantial thickness. Furthermore, owing to the method of producing the felt, the fibres are principally directed in directions which are parallel to the conveyor.

In traditional installations for manufacturing mineral fibre felts, the felt coming from the reception chamber enters immediately into the heat treatment furnace which permits the binder to set.

In compensation, when a crimped felt is being produced, a supplementary operation is performed after the setting of the binder: this is to modify the dominant orientation of the fibres.

Several methods are possible. Thus, for example, the felt may be "worked on" using needles which, by their action, direct the fibres perpendicular to the surface of the felt. Another method permits, by means of a series of modifications, the felt to be brought to a very greatly increased volumetric mass and to a different orientation of the fibres.

The modifications, according to this last method, preferably comprise a compression of the felt in the direction of the thickness thereof.

This compression is obtained, for example, in passing the felt between two conveyors, the distance separating the conveyors reducing in the direction of the progression of the felt.

The felt formed in this manner passes between two other pairs of conveyors, the speed of each pair being less than that of the preceding pairs of conveyors, which brings about a continuous longitudinal compression of the felt.

During the series of modifications, the felt is permanently restricted to prevent it returning, at least in part, to its initial volume, it is subsequently introduced directly into the furnace where the heat treatment ensures the cross-linking of the binder and the stabilisation of the product.

When a sample of the crimped felt obtained according to one of the preceding methods is subjected to a flexion, the product is usually damaged, even if the radii of curvature are very large. Fissures which occur between the fibres on the convex surface extend into the interior of the product. Figure 1 shows an illustration of this phenomenon. Fissures of this type destroy the lateral stability of the product and the cohesion thereof is severely damaged. In effect, the tearing of the connection between the fibres on either side of the crack is irreversible: these are chemical bonds which are established in the binder during the cross-linking thereof, which no longer exists. The effect of the phenomenon which will be described is that it is impossible to curve a crimped felt, even temporarily, without damaging the properties thereof.It is for this reason that if, for example, a glass wool crimped felt with a volumetric mass of 16 kg/m3 and a thickness of 120 mm is used to insulate a cylindrical cistern of a diameter of 1 meter which is located horizontally - the use of the previously crimped material making it possible to produce a good continuous insulation - fissures appear in the convex side, identical to those shown in Figure 1, and these considerably damage the thermal insulation of the crimped felt covering.

Working on the same principle, if it is wished to market a crimped felt of a width of 1.20 m and a length of 10 m with a volumetric mass of 30 kg/m3 and a thickness of 30 mm, it is advantageous to be able to condition the product when the felt is rolled up. In a case of this type, even if the external convolutions of the roll have a large radius of curvature which only causes shallow fissures on the convex side, this is different at the centre of the roll where the radii of curvature are of the same size as the thickness of the felt and thus scarcely greater than 30 mm. There, the damage is unacceptable.

It is, in all cases, particularly advantageous to be able to arrange the existing crimped felts in rolls, this having an indefinite length because, in the workplace, it is possible to cut a slice of exactly the size which is needed without producing scraps which constitute waste.

The inventors have thus had the idea of providing one of the surfaces of the product with a surfacing sheet, the essential function of which is to avoid an extension of the convex face of the produce which is to be subjected to a curvature.

Tests have been performed using numerous different materials: plastics material (polyethylene) films, films of metals (aluminium), and various papers (kraft) have been used. Either single films or composite materials are used.

These latter are in the form of sandwiches such as, for example, an aluminium film associated, on the entire surface thereof, with a polyethylene film, ie. in the form of a single reinforced film.

Kraft papers reinforced with reinforcing networks of glass or polyester threads have also been tested.

By way of example, there is described hereinbelow an operation which permits a solution to be provided for the problem which is posed. On a glass wool production line where the fibres are obtained by forcing them to pass through the apertures of a centrifuge, there is introduced, between the crimped felt and the conveyor belt which supports it, prior to the heat treatment installation where the cross-linking of the binder is performed, a surfacing sheet of kraft paper of a surface mass of 90 g/m2. This is adhered to the felt in the conditioning furnace and stays with it permanently, the product obtained being shown in Figure 2. The felt has a volumetric mass of 43 kg/m3 and a thickness of 60 mm.The crimping rate, ie. the longitudinal concentration of the fibres produced during the crimping operation, is 4.5 (this is also the ratio of speeds at the inlet and at the outlet of the crimping zone; it is also the increase in the volumetric mass produced). The tests of rolling up the felt which is thus equipped were performed taking care to leave the kraft paper on the convex side. After having kept the roll restrained for one week, it was flattened out again and it was thus established that, once returned to being flat, the felt has no memory; once flattened, it remains so. Finally, a destructive test in which the kraft paper was separated from the surface of the felt, showed no fissures: the product has not altered in any way by being rolled up.

An attempt to roll the paper up in the other direction, the paper being on the concave side, produces felt with the appearance of Figure 1, having a multitude of fissures which, given an average thickness of the felt, pass right through it in several places.

On the other hand, if the paper is on the convex side, the result is that in Figure 3 where it is seen that the felt only works under compression of the single concave side.

A comparative test performed with a paper which was identical but of a lower surface mass (60 g/m2) resulted in failure: in the course of rolling up the felts, the paper has torn in several places.

The tests performed with different materials used as the surface sheet have finally shown that a necessary condition for the good operation of the invention is that the resistance to tearing of the sheet must be greater than a certain threshold: 300 kPa. In an entirely surprising manner, it has appeared that this limit does not depend on the characteristics of the felt: from the moment where the crimping rate is greater than 4: whatever the thickness of the volumetric mass of the felt, it is capable of being subjected to strong curvature, which may include rolling up, providing that the surfacing sheet is placed on the convex side and provided that it has a resistance to tearing which is in excess of 300 kilopascals.

The resistance to rupture is of a level which is characteristic of the solidity of fine films intended for packaging. The measurement is performed according to DIN standard 53 113 (June 1990).

The only limits established were the large thicknesses of the felts associated with large volumetric masses. The results became less certain when, for example, a felt of 60 kg/m3 had a thickness of 120 mm. It is thus still possible to impose a curvature on a felt intended to insulate a curved support, but the rolling up of the felt, no space being left at the centre of the roll, is impossible. It has been established that, provided the volumetric mass of the product multiplied by the thickness remains within certain limits, rolling up is always possible. If the volumetric mass in kg/m3 multiplied by the thickness in metres (ie. the surface mass) remains at a maximum of 2 kg/m3) rolling up the product according to the invention is always possible, even with a crimping rate of greater than 4.

Claims (5)

1. Felt of crimped mineral fibre, provided on at least one of its surfaces with a surfacing sheet, and intended to be subjected to a temporary or permanent curvature, characterised in that the face which is intended to be convex is provided with a surfacing sheet, the resistance of which to rupture is greater than 300 kPa.

2. Felt of mineral wool according to Claim 1, characterised in that the surfacing sheet is based on kraft paper.

3. Felt of mineral wool according to Claim 2, characterised in that the surfacing felt is formed of a kraft paper of a surface mass which is greater than or equal to 60 g/m2.

4. Mineral wool felt according to any one of Claims 1 to 3, characterised in that the crimping rate thereof is greater than 4 and the surface mass thereof is less than 2 kg/m2 and in that it is rolled up to form a roll.

5. Mineral fibre wool according to any one of the preceding claims, characterised in that it is produced by the separation, as regards thickness, of one thicker felt.