GB2108897A

GB2108897A - Orienting the fibres during the casting of fibre-reinforced concrete

Info

Publication number: GB2108897A
Application number: GB08229320A
Authority: GB
Inventors: Ronald Leslie Attwell
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-10-14
Filing date: 1982-10-14
Publication date: 1983-05-25
Also published as: IE812406L; GB2108897B

Abstract

An apparatus for moulding cementitious material and in particular glass fibre reinforced cement comprises a vibrating table (3) for receiving a mould (8). An eccentric weight vibrator (6) is mounted on the underside of the table (3) and is either rotated in a circular mode or oscillated in an arc in a horizontal plane to produce vibrations perpendicular to the table (3). The frequency of vibration used is at or near to the natural or harmonic frequency of the cementitious material being moulded. The apparatus is used for casting cementitious materials with glass reinforcing fibres (10) and the vibrations orientate the fibres (10) into a desired plane parallel to the table (3) which gives a finished article of particularly high mechanical strength. <IMAGE>

Description

SPECIFICATION A method and apparatus for casting a fibre reinforced cementitious mixture This invention relates to a method and apparatus for casting a fibre reinforced cementitious material.

Cementitious materials are used in the manufacture of building products such as cladding members, paving slabs, kiosks, ceiling tiles and the like. With conventional cementitious materials these products are manufactured by pouring a wet cementitious mixture into a mould and vibrating the mould to form a densely packed finished product.

More recently fibre materials, for example, glass or steel fibre materials have been used as reinforcing in such products. One such reinforced cement is glass reinforced cement which allows very much thinner sections to be mounded whilst retaining or improving on the mechanical strength of the finished product. To maintain or improve on the strength of these products it is essential that the reinforcing fibres lie in the plane in which it is desired that the product should have its maximum strength. Normally this plane is randomly in the horizontal plane.

In moulding fibre reinforced cementitious material conventional vibration techniques are unsuitable in that they normally cause the fibres to be orientated to lie in a plane at right angles to the desired plane and do not enable moulds of intricate sections to be adequately filled.

One method which is particularly used with glass fibre reinforced cement includes the step of spraying the cementitious mixture together with a stream of reinforced fibres into a mould. Voids in the matrix are removed by hand rolling to ensure compliance of the mould face and removal of entrapped air. This method suffers from the disadvantage of being labour intensive.

There is therefore, a need for a method and apparatus for casting a fibre reinforced cementitious mixture so that the reinforcing fibres are orientated to lie in a desired plane.

Additionally, there is a need for a method and apparatus which ensures that the matrix does not contain voids and the apparatus is capable of fluidising the mixture so that it will flow into all areas of intricate moulds.

The present invention is directed towards providing such a method and apparatus.

According to the invention there is provided a method of casting a fibre reinforced cementitious material so that the fibres are orientated in a desired plane including the steps of introducing the cementitious mixture into the mould and vibrating the mixture, the vibrations being directed in a plane parallel to the desired plane.

In one embodiment of the invention the frequency of the vibration is at or close to the harmonic frequency of the cementitious material.

Preferably, the cementitious material is vibrated by vibrating the mould.

In one embodiment of the invention the vibrations are developed by rotational motion.

Preferably the rotational motion is in a horizontal plane. In this embodiment of the invention typically the vibrations are in a circular mode.

In an alternative embodiment of the invention the vibrations are developed by an oscillating motion. Preferably, in this embodiment of the invention the oscillating motion describes an arc in a horizontal plane. Usually the length of the arc of oscillation is dependent on the mass of cementitious material being moulded.

The invention also provides apparatus for carrying out the method including a table vibrator having an eccentric weight, the weight being capable of rotation or oscillation about an axis perpendicular to a predetermined desired plane.

Usually the eccentric weight is movable at variable speeds.

Advantageously the axis of rotation of the eccentric weight is perpendicular to the surface of the table.

The invention will be more clearly understood from the following description of some embodiments thereof given by way of example only with reference to the accompanying drawings in which: Fig. 1 is a typical sectional view of an apparatus according to the invention, Fig. 2 is a sectional view through a fibre reinforced cementitious mixture in a mould, before being subject to a method according to the invention, Fig. 3 is a sectional view through the cementitious mixture similar to Fig. 2, after the mixture has been subjected to the method.

Referring to the drawings and initially to Fig. 1 there is provided an apparatus indicated generally by the reference numeral 1 for moulding an article and in this case a flat sheet of glass fibre reinforced cement. The apparatus 1 comprises a vibrator 2 having a vibrating table 3 for receiving a mould, in this embodiment the invention a flat sheet mould 8. The table 3 is mounted by rubber vibrating mounts 4 on a base 5, portion of which is shown in the drawing. An eccentric weight 6, diagrammatically illustrated in Fig. 1, is mounted on the underside of the table 3. The eccentric weight 6 is movable by a motor (not shown) in the direction of the arrow A about an axis 7 perpendicular to the surface of the table 3.The weight 6 may be rotatable about the axis 7 to describe a full circle in which case the vibrations are in a circular mode or may be movable in an oscillating motion through a range of arcs in the same horizontal plane. In the case of the circular mode the frequency of vibration is harmonised to the cementitious mixture in the mould. In the case of the oscillating motion the arc of oscillation is related to the mass of material in the mould and the frequency of oscillation is related to the harmonic frequency of the material being moulded.

It has been found that when a cementitious mixture having reinforcing fibres is vibrated at or near the harmonic or sympathetic frequency of the material the reinforcing fibres orient themselves into a plane parallel to the plane in which the vibrations are directed. In this case the reinforcing fibres orient themselves into a plane parallel to the surface of the table 3.

To manufacture a flat sheet a cementitious mixture of sand and cement including glass reinforcing fibres 10, is placed in the flat sheet mould 8 with the reinforcing fibres 10 randomly distributed and directed as shown in Fig. 2. The mould 8 is placed on the table 3 of the vibrator 2 and vibrated either by rotating the eccentric weight in a horizontal plane parallel to the table 3 or by oscillating the weight through an arc in the same horizontal plane. Because the vibrations generated by the eccentric weight 6 are in a plane parallel to the surface of the table 3 the reinforcing fibres 10 are orientated into a plane parallel to the table 3 and in turn parallel to the plane of the flat sheet.

The speed of rotation of the eccentric weight or the length of the arc described by the weight in the oscillating mode is related to the harmonic frequency of the material being moulded. For a larger mass of material the speed of rotation or the length of the arc of oscillation is increased.

The flat sheet produced by this particular method could be used for many purposes, for example, a paving slab or a sheet of cladding for a building.

Although this method and apparatus has been described for use in the casting of a flat sheet it will be appreciated that it could have been used for casting any product from a fibre reinforced cementitious mixture, for example, structural elements for buildings and the like.

it will also be appreciated that where it is desired to have the reinforcing fibres orientated into a plane perpendicular to the table of the vibrator, the axis of rotation of the eccentric weight is arranged to be parallel to the table. Any other orientation of the reinforcing fibres may be achieved by suitably altering the angle of the axis of the eccentric weight to the vibrating table.

It will also be appreciated that any conventional vibrating mounts may be used as an alternative to rubber mounts, for example, springs. The principal advantage of the invention is that it provides a method for moulding fibre reinforced cementitious materials which provides building products with a high structural strength and relatively thin wall thickness.

The invention is not limited to the embodiments hereinbefore described which may be varied in both construction and detail.

Claims

1. A method of casting a fibre reinforced cementitious material so that the fibres are orientated in a predetermined desired plane including the steps of: introducing the cementitious mixture into the mould, and vibrating the mixture, the vibrations being directed in a plane parallel to the desired plane.

2. A method as claimed in claim 1 in which the frequency of the vibrations is at or close to the harmonic frequency of the cementitious material.

3. A method as claimed in claim 1 or 2 in which the cementitious material is vibrated by vibrating the mould.

4. A method as claimed in claim 1, 2 or 3 in which the vibrations are developed by rotational motion.

5. A method as claimed in claim 4 in which the rotational motion is in a horizontal plane.

6. A method as claimed in claim 4 or 5 in which the vibrations are in a circular mode.

7. A method as claimed in claim 1, 2 or 3 in which the vibrations are developed by an oscillating motion.

8. A method as claimed in claim 7 in which the oscillating motion describes an arc in a horizontal plane.

9. A method as claimed in claim 8 in which the length of the arc of oscillation is dependent on the mass of cementitious material being moulded.

10. A method as claimed in any of claims 1 to 9 in which the vibration is effected by a vibrator including an eccentric weight capable of oscillation or rotation about an axis perpendicular to the desired plane.

11. A method as claimed in any preceding claim in which the cementitious material is glass fibre reinforced cement.

12. Apparatus for performing the method of any of claims 1 to 11 including a table vibrator having an eccentric weight, the weight being capable of rotation or oscillation about an axis perpendicular to a predetermined desired plane.

13. Apparatus as claimed in claim 12 in which the axis of rotation or oscillation of the weight is perpendicular to the surface of the table.

14. Apparatus as claimed in claim 12 or 13 in which the eccentric weight is movable at variable speeds.

1 5. An article of cementitious material produced in the apparatus as claimed in any of claims 12 to 14.

1 6. A method as claimed in any of claims 1 to 11 substantially as hereinbefore described with reference to and as illustrated in Figs. 1 to 3 of the accompanying drawings.

1 7. Apparatus as claimed in any of claims 1 2 to 1 5 substantially as hereinbefore described with reference to Fig. 1 of the accompanying drawings.