IE42700B1 - Improvements in and relating to the manufacture of fibrous artefacts - Google Patents

Abstract

1521482 Board TAC CONSTRUCTION MATERIALS Ltd 26 May 1976 [30 May 1975] 23536/75 Heading D2B A process for making a fibrous board or sheet comprises forming said board or sheet on a rotary sieve from an aqueous slurry containing ¢ to 20% by wt. vitreous fibres, (based on the finished product), an inorganic binder, and a minor proportion of non- asbestos fibres having a Canadian Standard Freeness of 20-300‹. The latter fibres may be a cellulosic pulp. The vitreous fibres may be glass and/or mineral wool fibres. The inorganic binder may be ordinary Portland cement and may include pulverised fuel ash. Perlite, china clay and/or diatomite may be added to the slurry to regulate the density of the final product, and free silica containing materials may also be added to react with any lime released with the binder sets.

Description

This invention relates to the manufacture of fibrous artefacts such as boards and sheets byprocesses including the step of forming a layer on the surface of a rotary sieve from an aqueous slurry.

Such processes have hitherto been carried out using a slurry including asbestos fibre and cement, optionally with modifying agents,fillers and the like, which serve to control the density of the final product.

In the most commonly used processes, asbestos and cement are mixed and beaten with a large proportion of water to form a thin slurry, which is then stored while being agitated in a container known as a stuff-chest. This constitutes a reservoir from which supplies of a slurry are taken, diluted with water and fed to one or more vats in each of which a sieve cylinder is rotated. Each of these cylinders picks up the slurry as a continuous , thin wet layer, excess water draining through the meshes of the sieve, and the layer is applied to an endless conveyor belt by which it is carried to a rotating cylinder to which it is transferred and on which it is wound. The coating on the cylinder builds up layer by layer until the required thickness is reached. To make a flat sheet, the layered product on the cylinder (which is then usually known as a forming bowl) is cut - 3 axially when it has reached the required thickness.

However, attempts to completely replace the asbestos fibre with vitreous fibre have been unsatisfactory because the physical characteristics of vitreous fibre are so very different from those of asbestos, making the formation of a coherent sheet on the rotary sieve extremely difficult, if not impossible.

According to the present invention, we provide a process for producing a fibre-reinforced board or sheet product from an aqueous slurry by forming a layer on the surface of a rotary sieve, from which the layer is subsequently removed, the process including the step of forming the aqueous slurry from water, an inorganic binder and from to 20% by weight of vitreous fibres (referred to the finished product) together with a minor proportion of auxiliary non-asbestos fibres having a Canadian Standard Freeness in the range 20 to 300°. The percentage of vitreous fibre is referred to the finished product. The expression Canadian Standard Freeness (CSF) in the present context refers to the standard sheet forming test as commonly applied throughout the papermaking industry and wherein, for example, raw cellulose pulp exhibits a CSF of 700-900° and a very highly opened papermaking cellulose pulp exhibits a CSF of about 300°.

The vitreous fibre may be glass fibre,or mineral wool, or a mixture of these. The term mineral wool includes both slag and rock wool. Where glass fibre is used, the staple length is preferably 2¾ cm or less, 1¾ cm being especially preferred. The mineral wool may be pretreated to reduce its staple length, if necessary, for example by subjecting it to a milling treatment.

The inorganic binder may be a hydraulic binder such as Ordinary Portland (O.P.) cement and in such a case it is preferred that the vitreous fibre be either alkali-resistant or at least treated to reduce its susceptibility to alkaline attack. The binder may also include a pulverised fuel ash. 43700 - 4 The- auxiliary non-asbestos fibre is preferably cellulosic and will usually be in the form of a pulp; if so the process may include a preliminary refining treatment to confer upon the pulp the desired degree of openness equivalent to a Canadian Standard Freeness value in the range 20° to 300°, 150° being very suitable in practice. It will be appreciated that in a conventional papermaking process CSF values of less than 300° are generally regarded as very low. In contrast, we find that the Iq present process operates Well with CSF values of 150° or even lower. However, provided that the surface area char- . acteristics of the auxiliary non-asbestos fibre are at least similar to those of asbestos or cellulosic fibre, other materials may be used in the present process. 2_5 Although minor proportion includes up to 49% by weight, other requirements, for example, non-combustibility requirements, may limit the proportion to a very much smaller figure, say to 5 or 10% by weight, based on the weight of the finished product. 2Q Optionally, the process may also include the step of adding to the slurry density modifying fillers or agents such as perlite, china clay and/or a diatomite, so as to bring the density of the finished artefact into the range appropriate for a particular end use.

It is also possible to add free silica-containing materials for the specific purpose of reacting with substantially all of any free lime released when the binder sets. This is particularly relevant to processes using hydraulic cement as the binder and where the binder is caused to set by autoclaving. Free lime would of course tend to degrade the vitreous fibre component of the artefact if no attempt to minimise its effects was made.

Material stripped from the rotary sieve is naturally in a wet condition and the process will normally include causing the binder to set, for example, by air drying , autoclaving or stoving, i.e. heating in an oven to produce the finished product. Optionally, the wet products may be profiled and/or cut or trimmed prior to causing the binder to set. After setting the binder, the boards or sheets may be sanded or otherwise prepared for sale and/or use.

The invention also includes board or sheet products 5 made by a process according to the invention.

Xn order that the invention may be better understood, three preferred embodiments of it will now be described by way of example.

Example 1 An aqueous slurry was made from a furnish comprising:% by Weight Alkali resistant glass fibre (1¾ cm staple length 2 Alkali resistant mineral wool fibre (pretreated by milling) 10 Bleached kraft pulp (refined to 130-150° CSF) 5 Ordinary Portland cement 50 Diatomite 13 Perlite 10 China Clay 10 The furnish was mixed with water in a pilot plant scale Hollander beater, 125 litres of water being needed for 27 kg. beater charge. The mixing time was of the order of 10-15 minutes, including 5 minutes after adding the glass fibre to the other ingredients. This was to ensure thorough dispersion of the glass fibre. The water temperature was in the range of 30-35°C.

The slurry was then run on a vat machine and pro30 cessed into boards which were air matured for seven days and oven dried at 100°C for 24 hours. The average Modules of Rupture (M0R) (at a standard density of about o 720 Kg/m ) figures obtained from all the runs on this 2 basic furnish varied from 5-5-5.8 N/mm depending upon the machine running conditions used. These figures met the British Standard Specification 3536 for Insulation Boards.

The impact strength Of the boards exhibited significant increases over conventional asbestojfs-based boards but the interlaminar bond and stiffness of the boards were not so good. Equivalent or improved performances were obtained in tests for Freeze/Thaw Stability, Water Absorption and Dimensional Stability.

Example 2 Fiat sheets were made as just described, using a furnish comprising; 1.2 cm staple length alkali resistant glass fibre Kraft pulp (130-150° CSF) Ordinary Portland Cement 1.5% (bywt.) % 93.5% The products had a density of 1250 Kg/nr* and a 2 modulus of rupture of 17.1 MN/m .

Example 3 Partition boards were made by the same method from a furnish comprising:1.2 cm staple length alkali resistant glass fibre 2.0 % (by wt.) Kraft pulp (130-150° CSF) Ordinary Portland Cement Pigment 8.0% 89.66% 0.34% The products had a density of 1095 Kg/m and a modulus of rupture of 22.2 MN/m^.

Claims (14)

1. CLAIMS:1. A process for producing a fibre-reinforced board or sheet product from an aqueous slurry by forming a layer on the surface of a rotary sieve, from which the layer is subsequently removed, the process including the step of forming the aqueous slurry from water, an inorganic binder and from % to 20% by weight of vitreous fibres (referred to the finished product) together with a minor proportion of auxiliary non-asbestos fibres having a Canadian Standard Freeness in the range 20-300°.

2. A process according to Claim 1 wherein the auxiliary non-asbestos fibres are cellulosic.

3. A process according to Claim 1 or Claim 2 including a preliminary step of opening the auxiliary non-asbestos fibres to a Canadian Standard Freeness of 20-300° before forming the slurry.

4. A process according to Claim 1, 2 or 3 wherein the vitreous fibres are glass fibres having a staple length of 2.5 cm or less. 5. 10. A process according to any preceding claim including the step of adding to the slurry a density-modifying filler or agent.

5. A process according to Claim 4 wherein the glass fibres have a staple length of 1.25 cm.

6. A process according to Claim 3 wherein the vitreous fibres are of mineral wool.

7. A process according to Claim 6, including the preliminary step of pretreating the mineral wool fibres to reduce their staple length,

8. A process according to any of Claims 1 , 2 or 3 wherein the vitreous fibres are a mixture of glass and mineral wool fibres. 270 0 - 8

9. A process according to Claim 8 wherein the glass fibres have a staple length according to Claim 4 or Claim 5 and the mineral wool fibres are pretreated according to Claim 7 to reduce their staple length.

10. The layer from the surface of the rotary sieve.

11. A process according to any preceding claim including the step of causing the binder to set after removing

12. A process according to Claim 11 wherein the binder is caused to set by autoclaving the wet product.

13. A process for producing an asbestos-free board or sheet product substantially as hereinbefore described 15 with reference to the Examples.

14. Asbestos-free board or sheet products made by a process according to any preceding claim.