GB1589077A

GB1589077A - Moulding process and apparatus

Info

Publication number: GB1589077A
Application number: GB2607277A
Authority: GB
Original assignee: Societe Europeenne des Produits Refractaires SAS
Current assignee: Societe Europeenne des Produits Refractaires SAS
Priority date: 1976-06-29
Filing date: 1977-06-22
Publication date: 1981-05-07
Also published as: IT1081105B; FR2356488A1; CH614884A5; NL7707246A; DE2729197A1; DE7720274U1; CS200220B2; BE856206A

Description

(54) MOULDING PROCESS AND APPARATUS (71) We, SOCIETE EUROPEENNE DES PRODUITS REFRACTAIRES, (S.E.P.R.) 67, boulevard du Chateau, 92201 Neuilly S/Siene, France, a body corporate organised under the Laws of France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a process for obtaining, from fibrous suspensions, high precision moulded articles having very complex shapes and varying thicknesses.

The present invention also relates to an apparatus for carrying out such a process.

For many years, the refractory industry has sought to develop processes for obtaining moulded articles which resist thermal impact without bursting, breaking or becoming damaged in the operating conditions.

These processes have been based on known industrial processes which were applied in other fields. The processes used in the paper industry have enabled more or less rigid panels, sheets or envelopes to be made of refractory or other materials. The process involves forming an aqueous suspension of mineral products and flowing the suspension onto flat racks provided with holes which ensures that the liquid flows away and the dispersed mineral products remain on the racks. Articles having simple shapes can be prepared in the same manner.

It has been suggested that moulded materials of constant thickness could be made of refractory fibres by collecting an aqueous suspension of these fibres in filtering moulds of relatively simple shape such as cones, truncated cones, parallelepiped elements and hemispherical elements which allow the moulded article to be removed very easily from the mould.

However, these simple shapes do not cover all needs. The users of these moulded refractory products wanted more and more elaborate and complex shapes and precise dimensions to accommodate the technical requirememts of certain specific industries, such as those using refractory materials as mountings for means of producing thermal energy such as resistance mountings and burner mountings.

Conventional processes for producing such articles could not be adapted to complete manufacture by simple moulding procedures. It was necessary to follow the moulding step by a machining step to give the article the required dimensions. Machining represented a high manufacturing cost.

Although it is technically feasible to machine moulded articles made from refractory compounds, it is vastly more difficult to apply this principle to articles moulded from fibrous suspensions.

It has been found practically impossible to make fibrous products having complex shapes, variable thicknesses and precise dimensions without carrying out machining after moulding and thus increasing the cost of production.

We have sought to provide a process for manufacturing moulded fibrous material of variable thickness and of high precision without the need for machining to a final shape.

Accordingly, the present invention provides a process for moulding an article having a complex shape of variable thickness and having a part or parts where relatively high precision of moulding is required and which does not require machining to a final shape, which comprises introducing into a mould a suspension containing fibres dispersed in a liquid phase, and moulding the article by eliminating the liquid phase from the suspension through drain holes pierced in the mould, the concentration of drain holes per unit surface area of mould varying over the surface of the mould and being relatively great in the area or areas corresponding to the part or parts of the article requiring relatively high precision, so that the liquid phase is eliminated predominantly from the said part or parts.

The present invention also provides an apparatus for use in a process as defined above, which comprises a mould having a filtering surface provided with pierced drain holes and having at least one core including an area in which the concentration of drain holes per unit surface area is greater than in the rest of the filtering surface.

Thus, the moulds used for making complex shapes are provided with more filtering drains in the areas of high precision moulding compared with the areas of simple geometric shapes.

These drains are generally composed of ducts of very small diameter which are pierced in the mould itself and which may be capillaries. The density of distribution of the ducts is related to the degree of complexity of the article to be moulded. The density is preferably higher in the areas which are most hollowed or most in relief or the areas with sharp edges, that is in all areas where the dimensions of the moulded article must be of higher precision.

Thus, the permeability of the filtering section is preferably greater in the areas of highest precision.

The diameter of the drains is always greater than the diameter of the fibres but smaller than the length of the fibre itself, so that the latter may be placed across the orifice of the drain, resting on the edges.

These drains may also be in the form of narrow cylindrical rings, comprising hollow cylinders formed in the mould, cylindrical cores of smaller diameter being introduced into these drains. This drain type is used particularly when fibre-based moulded pieces are to be produced which have a large number of bores passing through them, such as tubes or even cavities for receiving additional elements, such as electrical resistances and thermometric probes.

The cores themselves may be solid or hollow and may be provided with outlet drains which therefore form a denser filtering surface in the areas of the mould with particularly complex shapes. The hollow cores may act as drains for eliminating the liquid phase from the suspension.

The mould itself, comprises at least one wall which is a filter and at least one wall which has an opening for the supply of fibrous suspensions.

The fibrous suspension used in the process of the invention comprises fibres of known types or mixtures of fibres of known types, dispersed in a liquid phase, possibly in the presence of charges of organic or mineral origins. This process is particularly suitable for the manufacture of moulded articles from natural or synthetic refractory fibres such as rock fibres, kaolin fibres and alumina-based fibres.

But the process is also applicable to the manufacture of non-refractory moulded articles from tedtile or paper fibres of natural, artificial or synthetic origin as well as to manufacturing moulded articles from fibres such as carbon fibres and metallic fibres.

The fibres may be used alone in the form of a suspension in a liquid phase, but they may also be used with large charges such as those formed from bentonites, aluminas, silicas and cements which may comprise up to 90 parts by weight of the substances introduced for at least 10 parts of fibrous material. The quantity of the charges in the suspension is generally very notably greater than that used in former processes.

The fibres and charges are dispersed in a liquid phase which may be water or organic or mineral diluents, a mixture or a dispersion of them, in order to obtain a concentration of this suspension and a viscosity which promote homogeneous and rapid filtration of the liquid phase during moulding.

The suspension, maintained in a state of agitation is introduced into the mould by a suitable means and, once the mould is full, a difference of pressure is established between the area for supplying the mould with suspension and the area for evacuating the liquid dispersant phase for a period which varies according to the size and the complexity of the article to be made, and the concentration of the suspension used.

The volume of fibrous suspension introduced into the mould is firstly accurately measured and determined in relation to the volume of the article to be produced and to the concentration of dry substance in the suspension.

The difference in pressure may be obtained either by supplying the mould under a pressure above atmospheric pressure or by causing a drop in pressure downstream of the mould, or by simultaneously combining the application of an over-pressure at the inlet of the mould and a drop in pressure at the outlet of the mould.

This difference in pressure is generally between 0 and 25 atmospheres. It is preferably between 0 and 1 atmosphere in the case of relatively simple shapes which give relatively thin moulded materials. On the other hand, it is preferably between 5 and 25 atmospheres when moulded materials having particularly complex shapes and great thickness are produced. This difference in pressure may be achieved by the mechanical action of a piston, for example, by hydrostatic action or by any means known to the skilled man.

The moulded articles which have no particular limitation in size may also have metallic or other elements such as electrical resistances positioned in the mould before the fibrous suspension is introduced and which are included in the article itself once the mould is removed.

Once a substantial amount of the liquid phase has been eliminated, this moulded material is mechanically removed from the mould then dried thermally.

By the process of the present invention high precision articles which are moulded on several faces may also be produced easily from fibrous suspensions.

The process of the present invention may be carried out discontinuously equally as well as continuously.

The invention is further illustrated by the accompanying drawings wherein: Figure 1 is a perspective view of a simple mould provided with cores, for producing a parallelepiped element comprising five regular channels and having a precise diameter, after removal from the mould.

Figure 2 is a perspective view of a ring shaped mould having a detachable filtering core.

Figure 3 is a vertical section of the article produced using the mould shown in Figure 2, along the axis of symmetry.

Figure 4 illustrates moulding a tube or cylinder-shaped article having relatively thick walls.

Figure 5 is a vertical section of a mould for applying the process of the present invention.

Figure 6 is a perspective view of an article moulded in the mould of Figure 5.

Figure 1 is a perspective view of a mould for moulding articles made of fibrous elements, having a relatively simple shape but comprising five channels. The mould is composed of five fixed faces 2,3,4,5, and 6 and a movable face 7 acting as a piston and transmitting a mechanically exerted pressure to the fibrous suspension which has previously been introduced into the mould. The hollow cores 8 form an integral part of the face 5 while movable face 7 slides with a slight clearance over the cores 8 by means of holes 9. The faces of the mould are provided with drains for evacuating the liquid phase from the suspension as shown by 10,11,12,13,14 and 15. The distribution density of the drains is higher in the high precision areas such as, the corners or edges.

The hollow cores 8 are provided with drains 16 densely distributed and adapted for suction.

Figure 2 represents a more complex ringshaped mould having a cylindrical external wall 21 and an internal wall comprising two portions shaped as truncated cones 22 and 23, and a cylindrical portion 24 connecting the two truncated cones. The hollow core formed by the three aforesaid portions 22, 23 and 24 is detachable. The mould is fed through upper face 25.

The liquid phase is evacuated through drains comprising either the high density filtration areas 26 or low density filtration areas 27. Thus, the filtering drains are densely distributed along edges 28, 29 and 30 for example, but less densely in the areas having continuous surfaces 27.

Figure 3 is a section throug the mould of Figure 2.

Figure 4 is a section of a means 42 for supplying mould 41. The liquid phase is eliminated through mould base 43 by means of drains 44 and 45. The lateral wall of the mould 41 comprises drains 46 and 47, the density of drains 46 corresponding to a high precision part being greater.

Figure 5 illustrates a mould for moulding a fibrous article as shown in Figure 6, of complex shape and comprising numerous channels.

The mould of Figure 5 comprises a detachable cylindrical wall 51, a base 52 provided with drains 53 and 54, and an element 55 upon which hollow cores 56 are fixed. The liquid phase from the suspension introduced into the mould is evacuated essentially through drains 53 and 54 and through high precision cores 56 provided with a relatively large number of drains.

Figure 6 shows a fibrous article after removal from the mould comprising a shoulder 61 and channels 62.

A difference in pressure is established between the upper part and the lower part of the mould as previously mentioned.

The invention is further illustrated by the following Examples.

EXAMPLE A complex fibrous article having many holes as illustrated by Figure 6, was produced according to Figure 5. This article had a useful diameter of 100 millimetres and comprised 943 truncated conical holes with diameters of 1.7 mm and 2 mm over a height of 30 mm.

The overall diameter was 130 mm while the overall height was 33 mm.

The suspension of refractory fibres used has a dry substance concentration of 3% representing 90 parts by weight of fibres and 10 parts of a mineral binding agent of a known type (sodium silicate or aluminium phosphate), the liquid phase was water.

The volume of fibrous suspension introduced into the mould was measured accurately and determined in relation to the volume of the article to be produced and the dry substance concentration of the suspension. This volume of suspension was transformed into a weight of suspension which is expressed in relation to the weight of the finished article (knowing its volume and its density in the finished state) and to the dry substance concentration of the suspension. A difference of pressure of 0.5 atmosphere was then applied between the lower part and the upper part.

After eliminating the liquid phase, the article was removed from the mould and dried.

By applying the process according to the invention, the moulded article had very regular side and sharp edges, making machining unnecessary.

WHAT WE CLAIM IS: 1. A process for moulding an article having a complex shape of variable thickness and having a part or parts where relatively high precision of moulding is required and which does not require machining to a final shape, which comprises introducing into a mould a suspension containing fibres dispersed in a liquid phase, and moulding the article by eliminating the liquid phase from the suspension through drain holes pierced in the mould, the concentration of drain holes per unit surface area of mould varying over the surface of the mould and being relatively great in the area or areas corresponding to the part or parts of the article requiring relatively high precision, so that the liquid phase is eliminated predominantly from the said part or parts.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. accompanying drawings wherein: Figure 1 is a perspective view of a simple mould provided with cores, for producing a parallelepiped element comprising five regular channels and having a precise diameter, after removal from the mould. Figure 2 is a perspective view of a ring shaped mould having a detachable filtering core. Figure 3 is a vertical section of the article produced using the mould shown in Figure 2, along the axis of symmetry. Figure 4 illustrates moulding a tube or cylinder-shaped article having relatively thick walls. Figure 5 is a vertical section of a mould for applying the process of the present invention. Figure 6 is a perspective view of an article moulded in the mould of Figure 5. Figure 1 is a perspective view of a mould for moulding articles made of fibrous elements, having a relatively simple shape but comprising five channels. The mould is composed of five fixed faces 2,3,4,5, and 6 and a movable face 7 acting as a piston and transmitting a mechanically exerted pressure to the fibrous suspension which has previously been introduced into the mould. The hollow cores 8 form an integral part of the face 5 while movable face 7 slides with a slight clearance over the cores 8 by means of holes 9. The faces of the mould are provided with drains for evacuating the liquid phase from the suspension as shown by 10,11,12,13,14 and 15. The distribution density of the drains is higher in the high precision areas such as, the corners or edges. The hollow cores 8 are provided with drains 16 densely distributed and adapted for suction. Figure 2 represents a more complex ringshaped mould having a cylindrical external wall 21 and an internal wall comprising two portions shaped as truncated cones 22 and 23, and a cylindrical portion 24 connecting the two truncated cones. The hollow core formed by the three aforesaid portions 22, 23 and 24 is detachable. The mould is fed through upper face 25. The liquid phase is evacuated through drains comprising either the high density filtration areas 26 or low density filtration areas 27. Thus, the filtering drains are densely distributed along edges 28, 29 and 30 for example, but less densely in the areas having continuous surfaces 27. Figure 3 is a section throug the mould of Figure 2. Figure 4 is a section of a means 42 for supplying mould 41. The liquid phase is eliminated through mould base 43 by means of drains 44 and 45. The lateral wall of the mould 41 comprises drains 46 and 47, the density of drains 46 corresponding to a high precision part being greater. Figure 5 illustrates a mould for moulding a fibrous article as shown in Figure 6, of complex shape and comprising numerous channels. The mould of Figure 5 comprises a detachable cylindrical wall 51, a base 52 provided with drains 53 and 54, and an element 55 upon which hollow cores 56 are fixed. The liquid phase from the suspension introduced into the mould is evacuated essentially through drains 53 and 54 and through high precision cores 56 provided with a relatively large number of drains. Figure 6 shows a fibrous article after removal from the mould comprising a shoulder 61 and channels 62. A difference in pressure is established between the upper part and the lower part of the mould as previously mentioned. The invention is further illustrated by the following Examples. EXAMPLE A complex fibrous article having many holes as illustrated by Figure 6, was produced according to Figure 5. This article had a useful diameter of 100 millimetres and comprised 943 truncated conical holes with diameters of 1.7 mm and 2 mm over a height of 30 mm. The overall diameter was 130 mm while the overall height was 33 mm. The suspension of refractory fibres used has a dry substance concentration of 3% representing 90 parts by weight of fibres and 10 parts of a mineral binding agent of a known type (sodium silicate or aluminium phosphate), the liquid phase was water. The volume of fibrous suspension introduced into the mould was measured accurately and determined in relation to the volume of the article to be produced and the dry substance concentration of the suspension. This volume of suspension was transformed into a weight of suspension which is expressed in relation to the weight of the finished article (knowing its volume and its density in the finished state) and to the dry substance concentration of the suspension. A difference of pressure of 0.5 atmosphere was then applied between the lower part and the upper part. After eliminating the liquid phase, the article was removed from the mould and dried. By applying the process according to the invention, the moulded article had very regular side and sharp edges, making machining unnecessary. WHAT WE CLAIM IS:

1. A process for moulding an article having a complex shape of variable thickness and having a part or parts where relatively high precision of moulding is required and which does not require machining to a final shape, which comprises introducing into a mould a suspension containing fibres dispersed in a liquid phase, and moulding the article by eliminating the liquid phase from the suspension through drain holes pierced in the mould, the concentration of drain holes per unit surface area of mould varying over the surface of the mould and being relatively great in the area or areas corresponding to the part or parts of the article requiring relatively high precision, so that the liquid phase is eliminated predominantly from the said part or parts.

2. A process as claimed in Claim 1, wherein

the diameter of the drain holes is greater than the diameter of the fibres in the suspension but less than the length of the fibres.

3. A process as claimed in Claim 1 or 2, wherein the liquid phase is eliminated in a free space between a wall of a core and a plate of a mould in order to produce a tubular moulded article.

4. A process as claimed in Claim 1 or 2, wherein the liquid phase is eliminated through hollow cores provided with outlet drains in order to produce a multitubular moulded article.

5. A process as claimed in any of Claims 1 to 4, wherein a difference in pressure of between 0 and 25 atmospheres is established between an inlet and an outlet of the mould.

6. A process as claimed in any of Claims 1 to 5, wherein the quantity of fibrous suspension is determined before introduction into the mould.

7. A process as claimed in any of Claims 1 to 6, wherein the fibrous suspension comprises up to 90 parts by weight of an inert charge and at least 10 parts of fibres.

8. A process as claimed in Claim 1 substantially as herein described with reference to the accompanying drawings and/or the Example.

9. An article whenever moulded by a process as claimed in any of Claims 1 to 8.

10.. An apparatus for use in a process as claimed in Claim 1 , which comprises a mould having a filtering surface provided with pierced drain holes and having at least one core including an area in which the concentration of drain holes per unit surface area is greater than in the rest of the filtering surface.

11. An apparatus as claimed in Claim 10, substantially as herein described with reference to the accompanying drawings.