GB2151271A

GB2151271A - Fireproof panel

Info

Publication number: GB2151271A
Application number: GB8430793A
Authority: GB
Inventors: Christian Giraud
Original assignee: Everitube SA
Current assignee: Everite SA
Priority date: 1983-12-09
Filing date: 1984-12-06
Publication date: 1985-07-17
Also published as: GB2151271B; IT1179853B; DE3444707A1; GB8430793D0; IT8468222A0; BR8406276A; MX163176B; FR2556386A1; BE901237A; IT8468222A1; FR2556386B1

Abstract

A fireproof panel comprises a mixture of reinforcing fibres, a hydraulic binder and mineral fillers. The reinforcing fibres are cellulose fibres of coniferous trees obtained from a chemical paste of the bleached Kraft type. Panels having a thickness greater than 50mm may be prepared by suspending cellulose fibres in water and forming a aqueous paste containing the cellulose fibres, a hydraulic binder and mineral fillers. The moist paste is deposited continuously in a layer on a moving filter member, is partially dehydrated and wound around a roll until the desired thickness is obtained. The roll obtained is then cut and unrolled and the hydraulic binder is allowed to harden.

Description

SPECIFICATION Fireproof panel and its method of manufacture The present invention relates to a fireproof panel and more particularly to a panel composed of a mixture of fibres, hydraulic binder and mineral fillers as well as to its method of manufacture.

It is known to manufacture fireproof panels by mixing mineral fibres, a hydraulic binder and possibly mineral fillers with water, by moulding the said mixture after partial dehydration then by allowing the hydraulic binder to harden.

The fibres used under these conditions are generally asbestos binders and the panel manufactured in this way has at the same time adequate mechanical strength for the production of building components such as partitions for example and the fireproof nature required for respecting certain rules, in particular in the field of naval construction.

Other reinforcing fibres have appeared recently, which tend to supplant asbestos and the fibres are generally of synthetic material or vegetable origin. Henceforth, it is necessary to adapt the proportions of the various constituents in order to obtain the incombustibilityofthe product.

In addition, for economical reasons, manufacturers wish to use the same equipment as that which was suitable when using asbestos and in particular machines of the Hatschektype, by means of which an aqueous suspension of fibres and hydraulic binder is filtered on a screen. A single layer of cement fibres is thus deposited on the screen, which is discharged continuously by rotation of the screen and transferred to a fabric referred to as a felt, which is pressed into contact with the upper part of the screen by means of a couch-roll. After the superimposition of several successive layers on the felt, one proceeds with the transfer of the single layer to a forming roll, on which it winds until an accumulation of desired thickness is obtained.

When this thickness is reached, an automatic device cuts the roll of paste along one generatrix, so that the paste which is detached from the forming roll, is unrolled then carried away by an outlet belt.

However, when the mixtures used contain fibres of vegetable origin, such as cellulose, it becomes very difficult to manufacture fireproof panels of appreciable thickness on a Hatschek machine. In fact, the superimposition of the various single layers on the forming roll leads to the formation of a phenomenon referred to as splitting, in which, after hardening, the various layers lack cohesion and separate quite easily.

In addition, the fact of unwinding a thick layer from the forming roll causes the formation of cracks on the inner side, on account of the difference in the radius of curvature between the inner face and the outer face.

Finally, with the prospect of application to the manufacture of panels used in naval construction, it is necessary to aim at the lowest possible density in order to reduce the weight thereof to the maximum and to increase the fire resistance thereof.

The present invention obviates these drawbacks whilst making it possible to reconcile the various requirements of incombustibility, mechanical strength, low density and manufacture by winding on a machine of the type used in the asbestos-cement industry, although no asbestos fibre is used. It relates to a fireproof panel of the type constituted by amixture of reinforcing fibres, of a hydraulic binder and of mineral fillers, the reinforcing fibres being cellulose fibres, wherein the cellulose fibres are fibres of coniferous trees and are obtained from a chemical paste of the kraft type which is bleached.

The invention also relates to a method for the manufacture of fireproof panels containing reinforcing fibres, a hydraulic binder and mineral fillers, of the type according to which a moist paste is formed by placing the mixture in an aqueous suspension, the mixture is dehydrated and the hydraulic binder is left to harden, wherein for the manufacture of panels having a thickness of greater than 15mum, the moist paste is deposited continuously in the form of a layer on a movable filtering member, it is dehydrated partially, wound around a roll until the desired thickness is obtained, the roll obtained is cutr, it is unrolled and the hydraulic binder is left to harden.

Fireproof panels are thus obtained at a high production rate, the said panels having adequate mechanical strength and an appreciable thickness, for example greater than 15mum.

The hydraulic binder used is a cement or preferably the product of the reaction carried out in an autoclave of lime on silica, i.e. calcium silicate, the two constituents being added in equal parts, in a quantity comprised between 32.5% and 47.5% respectively by weight with respect to the total weight; the hydraulic binder thus represents 65 to 95% of the panel.

Cellulose fibres are added thereto in a quantity comprised between 2 and 5% by weight. Preferably, the cellulose used is obtained from a chemical paste of coniferous tree fibres, which are long, rather than from a mechanical paste which gives the finished product poor mechanical properties on account of the impurities which it contains. The chemical paste is a paste of the Kraft type, i.e. it is treated with soda; a paste treated with bisulphite does not make it possible to obtain thicknesses of the finished product greater than 15mum in a satisfactory manner, since beyond this a high number of cracks occur at the time of unrolling of the fresh paste. The paste is then bleached with chlorine or chlorinated derivatives.In the absence of bleaching, the silico-calcareous reaction takes place under less satisfactory conditions at the time of autoclaving.To summarise, it is thus preferable to use a cellulose prepared from a bleached Kraft paste of coniferous trees fibres.

Another important constituent of the mixture is represented by mineral fillers, such as perlite. The proportion of perlite, of at least 1% may reach 10% by weight; above 10%, the mechanical characteristics deteriorate. Up to 20% by weight of other known mineral fillers may be added thereto.

The bleached Kraft cellulose is preferably put in suspension in water, then an aqueous paste is formed containing the cellulose fibres, lime, silica, perlite, and possibly other mineral fillers, with a dilution of the order of 300 g/litre. A filtration adjuvant may also be added thereto in known manner, for example of the type constituted by diatomaceous silica which also participates in the silico-calcareous reaction; this addition is at the most equal to 4% by weight.

The moist paste thus formed is then introduced into a distributor where it is stirred continuously and from which it is deposited continuously and directly on a movable filtering member or felt, by being supplied positively. The felt is then subject to the action of vacuum boxes, with a view to brief dehydration of the paste, then it passes under a forming roll which collects the layer of paste thus formed. The superimposition of several layers gives a greater thickness of paste, which is cut along one generatrix after obtaining the desired thickness, unrolled, then discharged for cutting to the required dimensions of the final panel. The paste which is still fresh is then subject to autoclaving, the conditions of which allow the initiation of the silico-calcerous reaction, at a temperature of at least 120 C and under pressure.The panels obtained are then dried in an oven; they have a density of between 0.7 and 0.9.

According to one embodiment, a mixture of constituents is prepared under the following conditions: cellulose 4.59% by weight lime 44.47% by weight silica 42.54% by weight perlite 5.17% by weight filtration adjuvant 3.23% by weight After cutting of the roll on the forming cylinder, one obtained a thickness of 25 mm when fresh; unrolling took place without cracks forming.

When one wishes to obtain thicknesses of this magnitude by normal methods, one generally uses moulding, but the mechanical characteristics of the resulting products are less than those of the products obtained according to the invention by rolling; the following table summarises the bending strengths found on flat samples, which have been subjected to autoclaving and dried at 1 1 O"C for 24 hours (the bending strengths are given in the longitudinal direction Land the transverse direction T).

Method Thickness Bending Strength (mum) rNlmm2) By moulding 15 L: 5 T: 5 25 L: 5 T: 5 Byrolling 15 L:11 according to L: 8 the invention 25 L:10 L: 7 It will be ascertained that the rolling method according to the invention makes it possible to obtain better mechanical characteristics than the moulding method. It has the additional advantage of being able to be used continuously, without appreciable modification to existing installations.

It is thus possible to produce panels having considerable dimensions, such as 3 m x 1.3 m. These panels are fireproof according to the incombustibility test according to resolution A 270 (VEIL) adopted by the OMCI on November 20th 1973 and modified by resolution A 472 (Xli) adopted on November 19th 1981.

Claims

1. Fireproof panel, of the type constituted by a mixture of reinforcing fibres, a hydraulic binder and mineral fillers, the reinforcing fibres being cellulose fibres, wherein the cellulose fibres are fibres of coniferous trees and are obtained from a chemical paste, of the Kraft type which is bleached.

2. Panel according to claim 1, wherein the quantity of cellulose fibres is comprised between 2 and 5% by weight.

3. Panel according to claim 1, wherein the mineral fillers are constituted at least by perlite.

4. Panel according to claim 3, wherein the proportion of perlite is comprised between 1 and 10% by weight.

5. Panel according to claim 1, wherein the hydraulic binder is the product of the reaction carried out in an autoclave of lime on silica.

6. Panel according to claim 5, wherein lime and silica are added in equal parts, in a quantity comprised between 32.5% and 47.5% by weight each.

7. Panel according to one of claims 1 to 6, having a thickness greater than 15 mm and a density of between 0.7 and 0.9.

8. Method for the manufacture of a fireproof panel according to one of claims 1 to 7, wherein for the manufacture of panels having a thickness greater than 15 mm cellulose fibres are put in suspension in water, an aqueous paste is formed containing the said cellulose fibres, a hydraulic binder and mineral fillers, the moist paste is deposited continuously in the form of a layer on a moving filtering member, it is dehydrated partially, wound around a roll, until the desired thickness is obtained, the roll obtained is cut, it is unrolled and the hydraulic binder is left to harden.

9. Fireproof panel substantially as hereinbefore described.

10. Method for the manufacture of a fireproof panel substantially as hereinbefore described.