GB2062715A

GB2062715A - Mats of Metallic Fibres, Apparatus for Manufacturing Such Mats, and Methods of Manufacturing Articles Incorporating Such Mats

Info

Publication number: GB2062715A
Application number: GB8034504A
Authority: GB
Original assignee: HANDELSBOLAGET SCANOVATOR
Current assignee: HANDELSBOLAGET SCANOVATOR
Priority date: 1979-10-29
Filing date: 1980-10-27
Publication date: 1981-05-28
Also published as: DE3039586A1; SE7907637L; JPS5679752A; IT1134096B; BE885764A; IT8025646A0; FR2468674A1

Abstract

A mat of metallic (e.g. steel) fibres comprises fibres which are either continuous or have a certain length within a range defined by the length/diameter ratio (L/d) 100 to 2000. The mat is held together by the length and surface structure of the fibres, and also by the application of a bonding agent. The mat has a variety of uses, mainly as a reinforcement in cement and concrete technology where it is of particular benefit in manufacturing thin, double-curved shells, and also in the reinforcement of rubber, plastics and other materials. A technique for manufacturing the mat utilises thin wire which is applied to a surface either continuously or as short fibres. The fibres may be distributed in a uniform or random manner in the mat. <IMAGE>

Description

SPECIFICATION Mats of Metallic Fibres, Apparatus for Manufacturing Such Mats, and Methods of Manufacturing Articles Incorporating Such Mats This invention relates to mats of metallic fibres, apparatus for manufacturing such mats, and methods of manufacturing articles incorporating such mats.

Examples of products whose basic material comprises metallic fibres include the familiar wire netting and steel wool, which comprises fibres produced by a turning process. Sintered fibre mats are a further example of such products, which are manufactured with the aid of methods used in the textile industry. It is, however, difficult and expensive to produce certain types of fibre mat, especially if seeking to achieve an even quality.

According to the invention there is provided a mat of metallic fibres, which has been formed by more or less evenly distributing the fibres with random or other orientation over a surface, the fibres being of sufficient length that they become interwoven during application and thus bind together.

The following description discloses mats of metallic fibres embodying the invention. It also discloses apparatus for manufacturing such mats, methods of manufacturing the mats, and industrial methods for producing thin-walled articles wherein such mats are used as reinforcing mats. A mat of short, metallic fibres (e.g. steel) embodying the invention can be manufactured by a random and even distribution of the fibres upon a surface. When sufficiently many fibres have been thus distributed, and if they are of sufficient length, they will become interwoven and bind together. A mat embodying this invention may thus comprise previously evenly distributed and randomly oriented fibres of such quantity and length that they bind together sufficiently to be movable as a body and without any greater change in appearance continue to constitute a generally cohesive mat.

A similar type of mat embodying this invention may be produced by random distribution of short and/or continuous fibres upon a surface until an evenly thick layer is obtained.

Cohesion may be improved by roughened surfaces of the fibres and/or by the shape of the fibres. Further, the fibres may be flattened so as to produce depressions either at intervals or along the whole lengths of the fibres before the fibres are distributed on the surface. A further improvement in cohesion may be achieved by application of a bonding agent. Such an agent can be applied as a finely dispersed spray over the whole of the mat to lock the fibres together as a well intertwined mat. A preferred bonding agent contains a large proportion of water-glass. The bonding agent may additionally serve as a surface treatment against corrosion. The bonding agent may, for example, cover the fibres with a layer whose thickness is less than 20% of the thickness (e.g. diameter) of the fibres.Other types of bonding agent can be distributed in continuous 'strings' which bond the mat together along their length. US Patent No. 3,047,444 describes a technique for glueing non-woven material for use in the textile industry. A further method which can be used to bind the fibres together into a mat is the use of binding wires which are sewn or woven into the mat and hold it together by locking the fibres in the vicinity of the binding wires.

Principles for attaching the fibres together to form a mat having improved cohesion can be divided into the following main groups: (a) glueing by spraying or dipping; (b) glueing by the application of 'strings' of glue; (c) heating or fusing of an applied material; (d) tacking (sewing) or weaving of binding wires; (e) application of material to the fibres for later reaction with solvents; (f) enclosing within a mould; and (g) rolling and spot or seam welding.

In accordance with (c), one possible method comprises mixing a certain proportion of plastics fibres, for example polypropylene, into the metallic fibre mat and locking these by heating them under light pressure.

A mat produced in accordance with this invention can advantageously be applied to a foil of plastics, paper or similar material, which stabilises the mat and holds it together. With foil as a backing material, a fibre mat can usually be rolled up in a number of turns on a reel, possibly followed by further packing. A fibre mat with oriented fibres can be manufactured by passing a stream of fibres between two flat, containing walls which converge as a chute into a long, narrow opening through which the fibres can travel oriented in the same direction as the opening. By placing a coil in a suitable position the fibres can be oriented magnetically when current is passed through the coil. In order to improve the technique the fibres can be vibrated mechanically or electromagnetically.By forming layers of parallel fibres in different directions, the orientation can be optimised as desired. A mat can be preformed at manufacture into the general shape intended for a product.

In order to ensure an even distribution of the fibres, in one technique of manufacturing a mat in accordance with the invention a wire is fed and cut at a fairly high rate to form the fibres. In one practical example, a feed rate of between 8 and 40 m/s is used for drawn steel wire, which is cut with rotating knives into desired lengths. Because of the pliability and length of the wire the fibres are interwoven spontaneously into a mat which can withstand a certain amount of handling. An indentation or deformation of the wire makes it possible for the mat to tolerate rougher handling.

An even distribution is facilitated by direct production of the fibres on a surface where they form a mat.

There are considerably greater difficulties involved in using a method comprising storing fibres in bulk, feeding them into a separating device such as a rotating drum provided with holes or radially mounted studs on the inside, and then discharging them onto a surface. A technique of this nature is described in UK Patent Specification No. 1,383,123. This specification indicates that mainly short, straight fibres with a length/diameter (lid) ratio of up to 50 or thereabouts are usable in practice. According to preferred techniques of manufacturing mats embodying this invention, here is no such limit and fibres having a ratio L/d=100 to 2000 are fully usable. Certain products are dependent on the use of such long-fibre mats.

A completely different method is to heap or stack the fibres in the same direction and store them in a container for later discharge onto a surface. This method makes use of good interweaving of the fibres and can also separate long fibres during temporary storage for even distribution onto a surface.

Production equipment for fibre mats embodying the invention may comprise one or more fibre machines which employ chutes to spray fibres onto a foil which can be moved as the mat is built up, a bonding agent being sprayed on and the mat and foil rolled up together or,in accordance with an alternative technique, the fibre machine(s) and spraying equipment can move over a backing surface on which the mat is built up. An increased drying/hardening rate may possibly be introduced into the process, for example through the use of some form of heating.

The fibres can be packed loosely in air with various volume concentrations depending partly on their L/d ratio and partly on their orientation.

Randomly oriented fibres and an L/d ratio of 300 have an air content of approximately 98%, while a fibre mat comprising two layers each with a uniform orientation and disposed perpendicularly to each other can be made more compact and have a corresponding air content of approximately 95 to 96%. Since the normal bulk density of the fibre coincides quite well with the desired volume proportion in a composite material, it has become apparent that fibre mats embodying this invention have a number of practical applications.

In concrete technology, mats of steel fibres are very useful in manufacturing thin-walled articles, especially those with double curved surfaces.

Other important applications are reinforcement of rubber and plaster, earth foundations, erosion protection, construction of winter roads over ice by freezing in fibre mats and in reinforcement of asphalt. Mats embodying the invention can be used in these applications.

The following describes an industrially practical method for producing thin-walled articles such as slabs, cladding panels, screens, culverts, ships' hulls, storage tanks and the like with the aid of a reinforcing mat embodying this invention. The method involves placing the fibre mat in a singlesided or double-sided mould and impregnating it with concrete material. A preferred technique of impregnation is spraying or pumping. However, other techniques for impregnation with concrete can be used; the simplest is manual application where the concrete is pressed in with a trowel, spreading knife or the like. It is known from other fields of technology, such as glass fibre reinforced plastics, to impregnate a glass fibre mat in the same way by spraying the mat with resin.

However, since both the reinforcing mat and the matrix in reinforced concrete technology are inorganic materials, the particles in the matrix are a considerably greater size, and single fibres are used which are longer and thicker than those used in reinforced plastics, the technique differs greatly. The volume proportion of glass fibre in the case of plastics is approximately 1 5 to 60%, while in the case of concrete the fibre proportion is approximately 1 to 10%.

Another method of manufacturing articles incorporating mats embodying this invention comprise a vacuum treatment of a mould which can be single-sided or double-sided. By applying mould surfaces, or a membrane and mould surface respectively, which may be a relatively impermeable plastics sheet over a permeable undersheet, to the article and then evacuating the air so that the concrete mass is simultaneously compressed, superfluous water is drained off thereby improving the quality of concrete. In addition, the matrix material and the reinforcing mat are pressed together whereupon any trapped air is removed and any expansion of the strong steel fibre mat during its initial curing is prevented. In the case of sloping or vertical walls or the application to an overhead surface, the evacuation will assist retention of the material in position.

In moulding against a single-sided mould an impermeable plastics foil can, in some cases, be pressed against the newly moulded surface. The air between the concrete and the foil can then be worked out by using rollers or vibrating tools.

With this method any fibres protruding from the concrete can be effectively pressed down. The foil is then allowed to remain on the surface and serves as a moisture barrier while the concrete is curing.

Vibration improves removal of air from the concrete and also the compaction of the concrete around each individual fibre. This is of decisive importance for the strength of the material, which has been shown to have very high values through use of the above method. A flexural strength which, prior to failure, exceeds the compressive strength of concrete, has been achieved. The reinforcing technique is simple to perform; insertion of the reinforcing mat demands considerably less skill than reinforcement with conventional bars or mesh.

One particularly advantageous technique, which is especially useful for sealing concrete while protecting the mould surface when making ships' hulls and tanks, is carried out in the following way. A mould surface is coated or sprayed with a gel coat of a plastics material such as epoxy resin which, when it has gelled somewhat, is scattered or flocked with short fibres such as polypropylene or glass fibres (or steel fibres) electrostatically charged to stand up over the whole surface. The steel fibre mat may then be pressed into the gel coat. When the gel coat has hardened, the matrix (e.g. concrete) is moulded against the gel coat; with concrete as a matrix it may be possible to use polymers for increased adhesion.

An alternative technique for achieving increased adhesion between a gel coat and concrete is to coat a single-sided mould with a conventional surface of a thermosetting plastics material such as an epoxy or polyester resin. The plastics material is pigmented for the desired colour. In this way an external, impermeable, coloured (and shiny) layer is obtained. When this has hardened, a new layer of plastics material is applied which receives, prior to hardening, a binding material. A steel fibre mat is pressed against the surface of the plastics material. The concrete is then applied by, for example, spraying until good impregnation of the reinforcing mat is achieved, possibly followed by vacuum treatment and vibration.An alternative procedure to obtain good bonding between the concrete and a gel coat involves spraying a thin layer consisting mainly of mineral compounds or polymers onto the gel coat surface before casting the concrete.

If a fabric of polypropylene or other suitable material is applied before laying down a vacuum mat when casting against a single-sided mould and if this is followed by the normal upper and lower sheet for the vacuum, a second surface will be obtained which is free of protruding steel fibres and which generally raises the quality of the product. It has been found that the finished product with a surface containing polypropylene fabric and a base of steel fibre has a strength and hardness-a resistance to cracking-of large value in loading tests.

The products and methods to which the invention can be applied are not limited to those mentioned above. Thus, for example, additives, light ballasts, pozzolanas and such can be used.

The fibre mat can be manufactured and fibres oriented in the direction of the main stresses in loadings which determine dimensioning. Products can be manufactured in sections with single or double-sided moulds. In highly mechanised processes, vacuum treatment, pressing, vibration and concrete impregnation can be carried out with special, permanent equipment built up into a processing plant.

With a suitable bonding agent, metallic mats can be used for a number of different purposes, such as filters, electrodes for electrolysis, acoustic panels, heat exchangers, silencers, etc.

The invention will now be further described, by way of illustrative and non-limiting example, with reference to the accompanying drawings, in which: Figure 1 shows one form of fibre which can be used to form a mat of metallic fibres embodying the invention; Figure 2 is a schematic perspective view of apparatus for manufacturing a mat embodying the invention; Figure 3 shows another mat embodying the invention, the mat comprising oriented fibres bound with wires which are tacked; and Figure 4 shows a further mat embodying the invention, the mat comprising continuous fibres and simultaneous tacking.

Mats of metallic (e.g. steel) fibres embodying the invention can be formed from various kinds of fibres and by various methods and apparatuses, as outlined hereinabove.

Figure 1 shows one form of fibre that can be used to make such mats. The illustrated fibre is so shaped as to contribute to cohesion of the fibres into the mat. The shape permits snap-iocking between the fibres.

Figure 2 illustrates a method of manufacturing mats which has been outlined above. Fibres 1 are produced by one or more fibre machines 2 (four such machines are shown in the drawing) by drawing and cutting wires 3 (e.g. of drawn steel) from storage means 4. The fibres pass downwardly through a chute 5 onto the upper surface of the foil, web or belt 6 which is unwound from a reel 7 by means (not shown) so as to pass beneath the mouth of the chute. The chute 5 comprises two flat converging walls which converge to form a long narrow opening through which the fibres 1 travel, oriented in the same direction as the opening. The fibres 1 thus become evenly distributed in a random orientation on the upper surface of the foil 6 and because of their pliability and length become spontaneously interwoven and thus bind together into a mat. A roller 8 presses the fibres 1 together.

The fibres then pass beneath spray heads 9 which spray a bonding agent on to them to improve cohesion of the fibres, by further binding them together, as explained above. The fibres next pass beneath infra-red heating means 10 which dries the bonding agent to form a fibre mat 11 which is wound into a roll 12 together with the foil 6.

In a modification of the apparatus of Figure 2, at least the items 2, 4 and 5 are movable over a stationary surface on which the mat is to be formed.

Figure 3 shows another mat embodying the invention in which oriented metallic fibres 30 are bound together by sewing or tacking binding wires 32 into them as shown.

Figure 4 shows a further mat embodying the invention in which continuous fibres 40 are bonded together by sewing or tacking binding wires 42 into them as shown.

Claims

1. A mat of metallic fibres, which has been formed by more or less evenly distributing the fibres with random or other orientation over a surface, the fibres being of sufficient length that they become interwoven during application and thus bind together.

2. A mat according to claim 1, wherein the fibres are bound together as a consequence of their possessing rough surfaces and/or a shape that interlocks them more firmly.

3. A mat according to claim 1 or claim 2, wherein the fibres are flattened so as to produce depressions either at intervals or along the whole length of the fibres before the fibres are distributed on the surface.

4. A mat according to claim 1, claim 2 or claim 3, wherein the fibres are bonded together by a bonding agent.

5. A mat according to claim 4, wherein the bonding agent also constitutes a surface treatment against corrosion.

6. A mat according to claim 4 or claim 5, wherein the bonding agent convers the fibres with a layer whose thickness is less than 20% of the thickness of the fibres.

7. A mat according to claim 4 or claim 5, wherein the bonding agent has been distributed in thin strings.

8. A mat according to claim 4 or claim 5, wherein the bonding agent contains water-glass.

9. A mat according to claim 4 or claim 5, wherein the bonding agent comprises a material suited to the matrix formed by the fibres.

10. A mat according to claim 1, claim 2 or claim 3, wherein the fibres are bonded together by welding, soldering or heating.

11. A mat according to claim 1, claim 2 or claim 3, wherein the fibres are bonded together by binding wires which are sewn or woven into the mat.

12. A mat of metallic fibres, the mat being substantially as herein described with reference to Figure 2, Figure 3 or Figure 4 of the accompanying drawings.

1 3. Apparatus for manufacturing a mat of metallic fibres according to any one of claims 1 to 11, comprising means for manufacturing the fibres and means to direct an even stream of the fibres to cover said surface.

14. Apparatus according to claim 13, wherein said means to direct the fibres is operative to direct the stream of fibres onto a foil or belt, the apparatus comprising means to continuously drive the foil or belt continuously beneath the stream of fibres, and means to wind up the foil or belt to form a roll of mat with the fibre mat thus produced lying between the turns.

1 5. Apparatus according to claim 13, arranged to be movable over a surface on which the fibre mat is to be continuously manufactured.

1 6. Apparatus according to any one of claims 13, 14 and 15, comprising means for applying a bonding agent to the fibres on said surface.

1 7. Apparatus according to claim 16, comprising means for hardening bonding agent applied, in use, to the fibres.

1 8. Apparatus according to claim 17, wherein the hardening means is operative to effect hardening by warming or by the addition of a hardener.

1 9. Apparatus according to any one of claims 1 3 to 18, wherein the means to direct the fibres comprises a chute operative to direct a stream of oriented fibres onto said surface, the chute comprising at least two guiding walls which terminate just above the surface in such a way that the stream of fibres is directed onto the surface.

20. Apparatus according to any one of claims 1 3 to 19, including an electric coil operative to influence the fibres in such a way that the fibres are uniformly oriented.

21. Apparatus according to claim 20, wherein the electric coil is operative also to vibrate the fibres.

22. Apparatus for manufacturing a mat of metallic fibres, the apparatus being substantially as herein described with reference to Figure 2 of the accompanying drawings.

23. A method of manufacturing a thin-walled article incorporating at least one mat according to any one of claims 1 to 12, wherein the one or more mats are placed in a single-sided or doublesided mould, to serve as a reinforcing mat or mats, and sprayed or otherwise impregnated with concrete.

24. A method according to claim 23, wherein the steps of mats placement and impregnation with concrete are repeated so that the article is built up in layers.

25. A method according to claim 23 or claim 24, wherein a mould surface or membrane is placed over the cast article, after which evacuation of air and water takes place with simultaneous vibration.

26. A method of manufacturing an article incorporating a reinforcing mat of steel fibres according to any one of claims 1 to 3, comprising coating a wall of a mould with a plastics material, such as epoxy resin, hardening a layer of such gel coat, then applying a new layer of plastics material and, before this has hardened, applying the reinforcing mat to the layer of liquid plastics and embedding it therein, spraying concrete until impregnation of the mat is achieved, applying a mould surface or membrane to the concrete, and effecting evacuation of air and water and vibration.

27. A method of manufacturing a thin-walled article incorporating a reinforcing mat of steel fibres according to any one of claims 1 to 3, comprising coating a wall of a mould with a plastics material, such as epoxy resin, hardening a layer of such gel coat, then applying a new layer of plastics material and, before this has hardened, applying a binding material to the layer of liquid gel coat, and then embedding the mat in the binding material and impregnating the mat with concrete.

28. A method of manufacturing thin-walled articles incorporating a mat of metallic fibres according to any one of claims 1 to 5, wherein a gel coat is applied to a surface of a mould after which short fibres or flock are sprayed onto the mould surface and raised by electrostatic charging over the entire mould surface, more or less perpendicularly to the mould surface.