A METHOD AND APPARATUS FOR MOULDING AN ARTICLE

Abstract: The invention provides a method and apparatus for mould­ ing articles. The invention solves the problem of the moulding of ce­ mentitious materials in moulds in that it reduces the time taken to mould the article, increases the inherent strength, and addi­ tionally provides moulded articles that are much lighter than has heretofore been possible. Essentially, the method involves forming the cementitious material in a mould (1, 2) and during or after the introduction of the cementitious material into the mould (1, 2) introducing an inflatable core member (6). When the mould is closed the inflat­ able core member (6) is used to pressurise the cementitious material thus expelling water and also forming a hollow core to lead to not only a stronger moulded article but also one that is considerably lighter than heretofore.

Description: Method and Apparatus for Moulding an Article and Article when so moulded The invention relates to a method of moulding an article of cementitious material in a mould comprising the steps of: mixing a water-setting cementitious mixture with water; filling the mould; closing the mould; and applying pressure to the cementitious mixture within the mould to expel water therefrom. Additionally the invention provides a moulding apparatus for moulding an article of cementitious material of the type comprising a mould, having a mould cavity for moulding the article. The term cementitious material in this specification embraces not only conventional concrete formed from portland or other cement, sand and aggregate but also for example, a fibre reinforced cement or any plaster. It generally includes any water settable mixture which has for workability more water than required for setting. It has long been appreciated that the use of glass fibre reinforced cement (GRC) which is a mixture of portland cement, silica sand and water mixed with alkaliresistant glass fibres is particularly suitable for the production of many articles because it has a high strengthweight ratio so that it can be used for many applications where conventional concrete is too heavy and costly. One of the major problems in moulding such articles whether from GRC or conventional concrete is to produce an adequate surface finish and the necessary strength. The purpose of de-watering is to remove excess water which is required in the moulding process to ensure adequate workability. However, since not all is necessary for the chemical reaction of the cement it has a diluting effect on the strength of the cement binder. Thus, the more water that is used in a concrete mix design the weaker the strength of that design. There is -also a marked increase in drying skrinkage of the moulded component where excess water is used. Thus, to achieve a good surface finish it is well known that it is necessary to have a considerable amount of water in the mix and then when moulded to dewater or extract the excess water by pressing or vacuuming or both. This de-watering also leads to increased strength. Conventionally, the excess water is often forced to pass through a membrane of some kind which permits the water to pass through while holding back the solids forming the slurry of the cementitious mixture. Using fibre reinforced cementitious material it is possible to obtain a moulded article having a high structural strength and a good surface finish. GRC is particularly suitable for the moulding of articles having elongate portions whose transverse dimensions are small relative to their lengths. Such portions can generally also be described as relatively narrow portions and hereinafter in the specification are referred to as elongate portions. Particularly suitable articles for moulding with GRC are, for example, though not exhaustively, window frames, door frames, both internal and external incorporating a door saddle, decorative wall units, shop front frames and the like articles hereinafter referred to as frames. It will be readily appreciated that if a complete window or door frame can be moulded that the building time then required to place it in situ is much less than with more conventional methods of building. While this refers specifically to GRC substantially the same comments apply to more conventional cementitious mixtures. Problems have been encountered with the use of split moulds for GRC particularly where, if the two filled moulds are vibrated before being joined,the two subsequently mating surfaces, do not adequately join together to form a coherent article, the joint forming a plane of weakness. An object of the invention to provide a method of moulding an article of cementitious material which would be more efficient than heretofore known methods. A further object of the invention is to provide such articles which will be lighter than heretofore without sacrificing any great strength. A still further object of the invention is to provide a method of moulding an article of cementitious material in a split mould which will not suffer from the disadvantages inherent in the previously known methods. Another object of the invention is to provide a method of moulding an article of cementitious material which will allow the moulded article to be removed from the mould quicker than heretofore thus, increasing the utilisation of the mould. These and other objects are achieved in accordance with the present invention in that the pressure is applied to the cementitious mixture by an inflatable core member introduced into the mould cavity and then inflated after the mould is closed, forming on setting of the cementitious material a hollow core in the moulded article. Because the water is expelled from the mould once it has been utilised for workability the inherent strength of the article is increased. In one method according to the invention, the mould is partly filled with a cementitious mixture before the core member is introduced. This has the added advantage of allowing intricate shapes to be moulded. In another method according to the invention the cementitious mixture is partly set before the core member is inflated. This is advantageous in that it avoids the leaching of the cement or the like material. In another method according to the invention the cementitious mixture is set the core member is deflated and withdrawn from the hollow core. This has the advantage of allowing the core members to be re-used. In another method of the invention the cementitious mixture is set the core member is deflated and left in the hollow core. The advantage of this is that it obviates the necessity to withdraw cores, clean them etc., and is obviously advantageous when the core member is manufactured of a relatively cheap and therefore, disposable material. In another method according to the invention the hollow core is filled with an infill material. The advantage of the use of an infill material will be readily apparent as there are many advantages from, as this is the case, heat insulation or sound insulation. In another method according to the invention the core member is inflated by hot water which is circulated through the core member to cure the cementitious mixture. The advantage of using hot water is that the cementitious mixture is cured quicker than it would be if hot water was not used. The core thus facilitates the heating of the concrete which is not possible with more conventional moulds. In another method according to the.inentioh the core member is inflated by means of a settable infill material introduced under pressure into the core member. This settable material may be heat insulation material. The advantage of using a settable infill material is that it obviates the necessity to inject the infill material after the article has been formed. o In another method according to the invention the core member is inflated by introducing the two reactable material which on reaction produce a gas and hence an internal pressure in the core member. The advantage of this is that it obviates the necessity to provide separate pressurising equipment. In carrying out the methods of the present invention it has been found advantageous to use glass fibre reinforced cement. The manner in which the glass fibre orientate themselves within the mould has been found particularly advantageous. 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 perspective cut-away view of portion of a window frame and sill moulded in accordance with the invention, Fig. 2 is a front plan view of the top half of a mould forming part of a moulding apparatus according to the invention, Fig. 3 is a perspective view of the bottom half of the mould, Fig. 4 is a typical cross-sectional view through an enclosed mould, Fig. 5 is a plan view of the bottom half of the mould showing a core member according to the invention in position, Figs. 6 to 8 are diagrammatic views showing different arrangements of core member according to the invention, Fig. i is a cross-sectional view of a connector according to the invention, rtion of a mould Fig. 10 is a plan view of portion of a mould according to the invention, Fig. 11 is a cross-sectional view of another construction of mould according to the invention, and Fig. 12 is a cross-sectional view of portion of an article moulded according to the invention. Referring to the drawings and initially to Figs. 1 to 5 thereof there is provided a moulding apparatus for moulding-an article of cementitious material in this instance a window frame of which portion of the -bottom, an upright and the window sill is illustrated in Fig. 1 the cross-section of one portion being shown in Fig. 4. The moulding apparatus includes a mould formed from a bottom mould half indicated generally by the reference numeral 1 a top mould half, indicated generally by the reference numeral 2, which forms a closure member for the mould, the mould being essentially an enclosed mould. The top mould half 1 and the bottom mould half 2 have half mould cavities 3 and 4 respectively. The bottom mould half 1 includes a removable bottom plate 5 so that the sill can be formed. The necessity of this will be readily apparent from an examination of Fig. 1 where it will be appreciated that if the bottom plate 5 is not removable from the mould the window sill could not be released. The mould is essentially a conventional mould and any suitable form of mould may be used. The top mould half 2 is provided with holes 7, 8 and 9 to allow lengths of tubing 6 form a core member which projects outside a closed mould. Each length of tubing 6 is a sealed tube having an air inlet 10. A suitable air supply and auxiliary supply lines for delivering air into each length of tubing 6 is provided but is not shown as it is again of conventional construction. In use, a cementitious mixture, in this embodiment glass fibre reinforced cement (GRC), is placed in the two mould halves 1 and 2. When the mould halves 1 and 2 are filled they are vibrated. A former to the approximate external shape of the tubing 6 is pressed into the top of the GRC in one of the mould halves. The tubing 6 is then placed in this recess and put -into the GRC as illustrated in Fig. 5. The mould halves are again vibrated slightly to allow the GRC to compact somewhat and the mould halves are brought together and the mould is assembled. The assembled mould is again vibrated slightly. Air is introduced into the mould at a pressure of at least 50 psi. The GRC is compressed and water is expelled from the mould as the tubing 6 is inflated. When the cementitious mixture has set there is formed a moulded article having a hollow core. The tubing 6 may then be deflated and withdrawn. Referring to Fig. 6 there is illustrated an alternative construction of core member manufactured from the one piece of tubing to form a simple rectangular frame. Needless to say, such a core member would generally be formed from a disposable cheap material such as a plastics material and would be left in the hollow core after use. Removable core members may be manufactured from any flexible -impermeable material such as rubber. Fig. 7 shows an arrangement similar to Fig. 6 except that now two separate removable core members are used. In Fig. 8 there is illustrated a still further arrangement in which the core member is formed from a tube which in turn is formed from a plurality of lengths of tubing interconnection means 11 being provided between the lengths of tubing. The interconnection means 11 is illustrated in more detail in Fig. 9 and is simply a push-on pull-of fitting having a male part 12 and a female part 13. This allows the tubing to be removed easily after the mixture has set. While in the embodiment above the de-watering was achieved through the joint between the two mould halves it could equally well be achieved by any form of dewatering apertures or the like. A typical example of de-watering apertures would be a plurality of holes formed in either mould half such as the holes 14 in a mould wall 15 as illustrated in Fig. 10. Referring to Fig. 11 an alternative construction of mould wall 16 is illustrated having a plurality of holes 17. The inside of which are covered by a de-watering membrane 18. Needless to say, such a de-watering membrane 18 can form, if necessary, portion of the mould walls. It has been found that when using a relatively flexible tubing for the core member and a GRC material that the tubing on inflation tends to take up the shape of the mould as it were mirroring the inner shape of the mould thus producing an article with a hollow core somewhat of the shape illustrated in Fig. 12. While the method and apparatus described above has been for moulding GRC it will be appreciated that the invention is not limited to this material. It has, for exampl,e been found that the method and apparatus according-to the invention can be used for the moulding of conventional concrete articles such as those having an aggregate. Many other materials which require excess liquid for working but not for subsequent setting may be used with the present invention. Ideally, the glass fibre should be of the so-called alkali resistant type. In the embodiment above the mould was almost completely filled with cementitious mixture before the core member was introduced. Needless to-say, the core member may be placed in position before all the cementitious mixture has been introduced. Similarly, it has been found that it may in certain cases be advantageous to allow the cementitious mixture to partially set before the coremember is inflated. In the embodiment described above when the cementitious material was set the core member was deflated and withdrawn from the hollow core. Needless to say, as mentioned above, the core member need not be withdrawn from the hollow core on deflation but may remain within the hollow core. This is particularly advantageous where the core member is manufactured from a disposable cheap material such as light plastics tubing. When the article has been moulded the hollow core may be filled by an infill material. A suitable infill material needless to say, would be a heat insulation material particularly for articles such as window frames. One rather surprising result has been achieved with the present i-nvention is that it has been found that there has been no.reduction in strength when a split mould has been used and that indeed there has been an improved surface finish. It has been found that where instead of a split mould a mould has been used for example, with a top cover plate or the like, that the surface of the moulded article corresponding to where the cover or closure plate had been placed is not as good as the surface finish on the remainder of the article. However, this problem does not appear to arise when the mould is a split mould. It has however, been found that the interior surface of the core is not finished to as high a finish as would be expected and it appears, though it has not as of yet been proven conclusively, that a certain amount of the entrained air in the cementitious mixture, and this is particularly the case with GRC, is entrained around the sides of the core member and is not expelled out of the mould. It will be readily appreciated by those skilled in the art that it is surprising that the surface finish with a split mould should be better thanthat for example, with a top filling mould. A particularly suitable method of inflating the core member is to inflate it with hot water which hot water can be left some time in the core to cure the cementitious mixture. Ideally, the hot water should be continuously circulated. It has also been found that the core member may be inflated by means of a settable infill material introduced under pressure into the core member. Such suitable materials include for example, foamed plastics materials and ideally such a settable material is a heat insulation material. It has further been found that the core member may be inflated by introducing two reactable materials which on- reaction produce a gas and hence an internal pressure in the core member. Such reactable material is set and are'left in the core. For example, it is known that if aluminium powder and a rubber laytex solution or polyvinyl-chloride mixture is mixed with lime and water that the mixture will produce hydrogen by a reaction with the aluminium. We have found that the core member should be inflated to ideally 50 psi or more but very low pressures may be used. It will be appreciated that the present invention is particularly suitable for the manufacture of elongate narrow parts. Such elongate parts include frames in general and include long interconnecting and o intersecting parts. It will be appreciated that in accordance with the present invention in addition to obtaining the advantages heretofore known in providing for example, windows and window frames and the like from GRC or other cementitious material that there are certain particular advantages with the present methods of-moulding. In addition to the improvement in surface finish it had been found that because, particularly with GRC, the core tends to mirror the outer shape of the article that a reduction in the amount of material normally required may be achieved thus reducing the weight of the article. In addition to this saving of material it will be appreciated that the core, being hollow can act itself as a heat insulator or alternatively may be filled with an infill material thus further improving the heat insulation properties of the article. It has additionally been found that when the invention is used to produce, for example, simple window frames and door frames for buildings that in addition to a reduction in costs of the article and the provision of a superior article there were added advantages in that the time taken to build is considerably reduced. For example, in the setting of a window frame into an opening at the present moment the procedure is somewhat as follows. When the wall has been built to a certain height the window sill is placed in position using a conventional damp-course.in concrete. Then the rest of the wall is built up until the lintel is placed in position. When the lintel has been placed in position a wooden or metal window frame is placed in the opening and cemented and plastered into position. With the present invention it is a simple matter to place the window frame down, built the wall around the window frame and across the top of it without any problems whatsoever. It has also been found that with more conventional concrete articles that a considerable reduction in material can be achieved without any great loss and strength. It is envisaged that in certain instances the window frame both interior and surround may be assembled prior to bringing on site: this is particularly the case with vertical sash, horizontally pivoted e.g. half way down the frame, or non-opening windows. Windows may be glazed or doors hung off site thus leading to increased efficiency on and off site together with better quality control.

Claims: CLAIMS 1. A method of moulding an article of cementitious material in a mould comprising the steps of: mixing a water-setting cementitious mixture with water; filling the mould; closing the mould; and applying pressure to the cementitious mixture within the mould (1,2) to expel water therefrom; characterised in that the pressure is applied to the cementitious mixture by an inflatable core member (6) introduced into the mould cavity (3,4) and then inflated after the mould is closed, forming on setting of the cementitious material a hollow core in the moulded article. 2. A method as claimed in claim 1 characterised in that the mould (1,2) is partially filled with the cementitious mixture before the core member (6) is introduced. 3. A method as claimed in claim 1 or 2 characterised in that the cementitious mixture is partially set before the core member (6) is inflated. 4. A method as claimed in any of claims 1 to 3 characterised in that when the cementitious mixture is set the core member (6) is deflated and withdrawn from the hollow core. 5. A method as claimed in any of claims 1 to 3 characterised in that when the cementitious mixture is set the core member (6) is deflated and left in the hollow core. 6. A method as claimed in claim 4 or 5 characterised in that the hollow core is filled with an infill material. 7. A method as claimed in claim 6 characterised in that the infill material is a heat insulation material. 8. A method as claimed in any preceding claim characterised in that the core member (6) is inflated by hot water which is circulated through the core member (6) to cure the cementitious mixture. 9. A method as claimed in claim 5 characterised inthat the core member (6) is inflated by means of a settable infill material introduced under pressure into the core member (6). 10. A method as claimed in claim 9 characterised in that the settable material is a heat insulation material. 11. A method as claimed in claim 5 characterised in that the core member (6) is inflated by introducing tworeactable materials which on reaction produce a gas and hence an internal pressure in the core member (6). 12. A method as claimed in any preceding claim characterised in that the cementitious material is a glass fibre reinforced cement. 13. A method as claimed in any preceding claim characterised in that the core member (6) is inflated to at least 5 psi. 14. A method as claimed in claim 13 characterised in that the core member (6) is inflated to at least 50 psi. 15. A method as claimed in any preceding claim in which the cementitious material is concrete. 16. A method as claimed in any preceding claim characterised in that prior to the introduction of the core member (6) into the mould cavity (3,4) a former to the approximate external shape of the core member (6) is inserted into the mould cavity (3,4) to form a void for reception of the core member (6). 17. A cementitious article produced by the method of any preceding claim. 18. A moulding apparatus for moulding an article of cementitious material of the type comprising a mould (1,2) having a mould cavity (3,4) for moulding the article characterised in that an inflatable core member (6) is provided for introduction into the mould and in that the mould has a de-watering aperture (14) and a closure member (2). 19. Apparatus as claimed in claim 18 characterised in that at least part of the mould cavity (3,4) forms an elongate narrow cavity and the core member extends the length of the cavity. 20. Apparatus as claimed in claim 19 characterised in that at least part of the mould cavity (3,4) forms two interconnecting elongate narrow cavities, the core member (6) extending through both cavities. 21. Apparatus as claimed in claim 18 characterised in that the mould cavity (3,4) forms at least one frame cavity the core member (6) extending substantially around the whole frame cavity. 22. Apparatus as claimed in any of claims 19 to 20 characterised in that the core member (6) is a rubber tube. 23. Apparatus as claimed in any of claims 18 to 20 characterised in that the core member (6) is a plastics tube. 24. Apparatus as claimed in claim 22 or 23 characterised in that the tube (6) is formed from a plurality of lengths of tubing interconnection means (11) being provided between the lengths of tubing. 25. Apparatus as claimed in claim 24 characterised in that the interconnection means (11) is a push-on pulloff connector (12,13). 26. Apparatus as claimed in any of claims 22 to 25 characterised in that the tube (6) includes a plurality of inlet valves (10) for a pressurising fluid, said inlet valves projecting outside the mould and being fed from a common supply line. 27. Apparatus as claimed in any of claims 18 to 26 characterised in that the de-watering aperture (14) is formed in the mould (1,2) along a joint formed between it and its closure member (2). 28. Apparatus as claimed in any of claims 18 to 26 in which the mould is a split mould formed from a pair of mould halves (1,2) the joint between the mould halves forming the de-watering aperture (14). 29. Apparatus as claimed in any of claims 18 to 26 characterised in that the de-watering aperture (14) is formed by a plurality of holes (14) interconnecting the mould cavity (3,4) and the exterior of the mould (1,2). 30. Apparatus as claimed in any of claims 18 to 26 characterised in that the de-watering aperture (14) is formed by a water permeable membrane (18) incorporated in the mould. 31. Apparatus as claimed in any preceding claim characterised in that a former corresponding approximately to the external shape of the core member (6) is provided for insertion into the mould cavity to form a void for reception of the core member. 32. A cementitious article produced in the moulding apparatus as claimed in any of claims 18 to 31. 33. A frame having integral elongate inter-connecting portions manufactured from a cementitious material characterised in that the portions include interconnecting hollow cores.

Inventors: PRICE, ARTHUR, PRICE, JAMES CYPRIAN, PRICE, JOHN FRANCIS
Applicants: INSTITUTE FOR INDUSTRIAL RESEARCH AND STANDARDS
Application year: 1981
Main classification: B28B7
IPC codes: B28B3, B28B7, B29D12