GB2219339A

GB2219339A - Builders shuttering for casting material such as concrete

Info

Publication number: GB2219339A
Application number: GB8812418A
Authority: GB
Inventors: Cedric Blackbourne; Robin Archer
Original assignee: BLACKBOURNE AND MCCOMBE
Current assignee: BLACKBOURNE AND MCCOMBE
Priority date: 1988-05-25
Filing date: 1988-05-25
Publication date: 1989-12-06
Also published as: GB8812418D0

Abstract

A method of and apparatus for moulding is provided wherein a plug (17) upstanding from a base (15) has a wall- bounding face of a mould cavity defined by a surface of a layer of lining material (21) which is sufficiently strong to resist deformation under hydraulic forces applied by the fluid casting material, but sufficiently yielding to allow separation of a cast article from the plug (17) without significant increase in separation force. <IMAGE>

Description

CASTING This invention relates to the casting of articles from a settable material such as concrete. The invention is particularly concerned with the manufacture of the hardened buildings described in co-pending Applications No.

and No. (code titles 3/4 and 2/4) filed herewith. When casting or moulding any article it is normal for walls thereof to be tapered to facilitate release of the article from its mould/shuttering after curing. If the shuttering/article are not tapered then it is necessary for the shuttering to be collapsible. Collapsible shuttering greatly adds to the cost of manufacture of cast articles and is usually only worthwhile when the higher cost of the product or some other feature makes it essential.

On most cast articles the tapering above mentioned leads to a variation in wall thickness from one end to another and in normal circumstances such variation can be tolerated. However, in certain concrete structures it is important that the wall thickness be maintained constant, for example in the hardened buildings described in the above co-pending applications, firstly to maintain a uniform degree of strength along the building and secondly so that when such buildings are used in combination with each other they produce a composite of uniform cross-section rather than meet at a step which would greatly hamper the union of adjacent units and create possible weak spots.

It is an object of the present invention to provide a method of and apparatus for casting whereby articles with parallel walls can be cast and removed from shuttering without the need for internal collapsible shuttering.

The invention provides a method of moulding comprising the steps of: providing a base; providing an internal plug, upstanding from the base, and having at least one inner wall- bounding face; constructing demountable shuttering around the plug to provide at least one outer wall bounding surfaces parallel to said at least one inner wall bounding surface on the plug, pouring settable material to fill a cavity defined by the plug, the base and the outer shuttering, allowing the material to set; removing the outer detachable shuttering; and lifting the cast article from the base, characterised in that the or each inner wall bounding surface, on the plug is constituted by an outer surface of a lining of yeildable material overlaying a body of the plug.

Preferably an inner surface of said lining and an outer surface of the body of the plug meet at a low friction interface and upon removal of the article from the plug the lining is removed from the plug with the article.

The lining can be removed from the interior of the article after its removal from the plug and can be re-used if its condition is satisfactory. If not, the lining is replaced for a next moulding operation.

The low friction interface between the lining and the plug body surface can be constituted by a smooth surface on the plug body cooperating with a natural surface on the yielding lining.

It is important to emphasize that the lining material although it must be capable of yielding to permit separation of the article from the mould, it must not be soft enough to permit deformation by hydraulic pressure of the settable material. Thus, a soft foamed material is not suitable. The material of the lining is preferably a rigid foamed material, for example expanded polystyrene of a minimum strength sufficient to withstand the hydraulic pressure of the settable material in the mould. This hydraulic pressure will depend upon the size of the mould and the strength of the lining will have to be selected accordingly.

A satisfactory low friction interface between the lining and the mould body can be achieved if each relevant surface of the plug body is smooth, flat and coated with a smooth substance such as paint, varnish, or a plastics coating material. If desired, an additional release agent can be applied to appropriate surfaces of the plug before application of the lining.

As mentioned, foamed polystyrene is a preferred substance for the lining, but sheets of rigid polurethane foam can be used, such sheets resisting compression during casting, but yielding during release. The lining can be a layer of material of corresponding properties but not of foamed plastic, for example a layer of corrugated material could be used, perhaps a multiple corrugated layer coated with wax on each side which is conventionally used as a relative cheap packaging material. Many other materials can be used for the lining provided that they are strong enough to resist the hydraulic force of the material being cast yet can yield upon removal of the cast article to reduce the separation load.

In cases where the shape of the cast article does not lend itself easily to being lifted, attachment points can be cast into the article to enable it to be engaged by a crane or the like to be lifted from the plug.

The invention also provides a method of moulding an article having at least one wall of constant thickness bounded by a pair of parallel surfaces, wherein a mould cavity is formed of which at least one wall-bounding surface is constituted by an outer face of a lining which is sufficiently strong to resist deformation under the hydraulic load of the material being cast, but which can yield upon withdrawal of a cast cured article from the cavity to reduce the separation load.

The material of the lining should not only be yielding in a direction transverse to its plane, but should also be significantly softer than the set material of the article so that in the event that any undercut is inadvertently formed, the force tending to withdraw the article from the mould can simply cause such an undercut to tear the material of the lining whithout adding significantly to the separation load.

The invention also provides apparatus for casting an article from settable material comprising a base, a plug upstanding from the base and shuttering spaced from the plug and defining with walling of the plug a cavity to form at least one wall of constant thickness, at least the wall-bounding surface of the plug being constituted by an outer face of a lining overlying a supporting body, the lining being sufficiently rigid to resist hydraulic forces applied by the casting material, but being yieldable to enable the cast article to be removed from the plug.

The invention also provides articles cast using the apparatus and/or method aforesaid.

The invention will be described further, by way of example, with reference to the accompanying drawings wherein Fig. 1 shows a building made up of a plurality of cast articles, each made by a method and apparatus of the invention; Fig. 2 is a sketch showing how a cast article for use in Fig. 1 is raised after having been cast, the article being shown in the configuration in which it is cast; and Fig. 3 is a cross-sectional view through a preferred casting apparatus of the invention illustrating the method of the invention.

Referring firstly to Fig.l, it will be seen that a building 10 comprises a plurality of units 11, each of which, considered in the direction the ridge 12, is of uniform cross-section. It will be appreciated that the wall thicknesses of the articles 11 must be constant in order that a number can be used together as in the building 10 to produce a uniform structure.

In particular in relation to hardened structures (as will be apparent from our co-pending applications No.

and No. code titles 3/4 and 4/4 filed herewith) the provision of a step at the junction between the two units 11 would be most undesirable as it would complicate their interconnection and would also provide a weak spot.

Fig. 2 shows how an article 11 is cast with its ridge and comparable angles vertical. In Fig. 2, the normal central core and surrounding shuttering have not been illustrated. However, four lifting lugs 13 cast into the material of the article 11 are attachable, upon lifting by cables 14 to a crane or the like. It will be appreciated that such cast concrete buildings are of significant weight and a crane of appropriate capacity must be used. If a parallel article 11 (or comparable article such as a section of a large diameter pipe or the like) is to be cast in the Fig. 2 configuration, the force between the surfaces of the cast article and the surfaces of any mould parts must be reduced or eliminated. If a full mould were left in contact with the article the separation force would be unduly high and severe mould damage might easily result.

In the casting of articles 11 in the Fig. 2 configuration is is relatively simple to use exterior demountable shuttering which can be removed after the article has set. However, to provide a central collapsible core is much more difficult, especially in the case where the upper end of the article is to be wholly or partially closed as is illustrated in Fig. 3.

Turning now to Fig. 3, it will be seen that a preferred apparatus of the invention is constructed on a base 15 of which portions 15a can bound a mould cavity. In using the described apparatus in accordance with the method of the invention, a core 17 is erected on the base 15. Core 17 includes a framework 18 lined with sheet material 19. The sheet material 19 can be of any convenient form, but will normally be of smooth plywood conventionally secured to the framework 18. The outer surfaces 20 of the sheeting 19 will be rendered smooth by either painting, varnishing or coating with an appropriate plastics lacquer or comparable material giving a smooth surface. There is next placed to overlie the surface 20 a lining 21 of a sheet material which has a rear face in contact with surface 20 and which can slide easily relative thereto.The lining21 is sufficiently rigid to resist significant compression under hydraulic forces applied by the casting material in its fluid state, but can yield during removal of the cast article 22 from the mould.

A suitable material for the lining 21 is expanded polystyrene having a thickness of about 25 mm.

However, a layer of rigid foamed material, for example, foamed polyurethane or other rigid foam can be used. As an alternative, a layer of corrugated material, such as corrugated cardboard could be used.

A multiple layer of waxed corrugated cardboard is suitable.

After construction of the core 17, reinforcement for the casting material (usually concrete) is placed around the core. In the present case, (as described in more detail in our co-pending application) No.

Case 4/4) (reinforcement consists of two steel sheets 23 which line one wall and the "roof" of the article in its casting position). These steel sheets are welded to a conventional arrangement of reinforcing mesh indicated at 24.

When the reinforcement and the steel plates have been installed, removable exterior shuttering 25 is mounted to have its upright walls at right angles to the surface of base 15 and parallel to the outer faces of the lining 21. The outer face of the lining and the inner surface of the shuttering 25 constitute wall bounding surfaces of the mould. Removable shuttering 25 is braced at 26 in conventional manner.

At this stage fittings to form lifting lugs 13 are disposed within the mould cavity defined between the core 17 and the outer shuttering 25. It will be seen that the height of the outer shuttering 25 extends above the top surface 20, 27 of the core thus allowing a horizontal wall 28 of the article 11 to be cast. The mould cavity formed between the core and the shuttering 25 is now filled with settable material, usually concrete of conventional nature.

The material is compacted and allowed to cure for say seven days.

Hereafter, the outer shuttering 25 is removed and cables 14 are attached to the lifting lugs 13.

Applying tension to the cables by means of a crane the article 11 is lifted from the mould. Where the concrete is in contact with the outer surface of the lining 21, a bond of significant strength develops and lifting of the article 11 would not normally easily break such a bond. However, the low friction boundary between the lining 21 and the body of the core 17 constituted by the sheeting 19 allows the lining 21 to be removed from the body of the core with the cast article. In the case of the sides of the article 11 which are provided with the steel sheets 23, it may be that the steel sheet will slide relative to the lining. In this case, the lining may fracture as the article is removed.However, the yieldable nature of the lining 21 is such that the engagement between the article and the lining does not add significantly to the separation force which has to be applied via the cables 14, usually by a crane.

A typical article 11 may weigh some 18 tonnes and the provision of the lining means that the lifting load on the crane is usually about from 19 to 21 tonnes. Without use of the yieldable lining a parallel mould surface, even reasonably smooth and coated with a release agent would possibly give lifting loads of between 25 and 30 tonnes, thus greatly increasing the chance of damage to the core, for example by tearing its components from the base 15, or putting an undue load on the crane, or requiring a much larger and therefore more expensive crane to be used.

The method and apparatus of the invention allow heavy, parallel sided articles 11 to be cast simply and economically.

The invention is not limited to the precise details of the foregoing and variations can be made thereto. For example, the material of the core can be varied considerably. If desired, the core itself could be a solid block onto which the lining is fixed. The material of the lining can be varied widely within the criteria mentioned above. By reducing the level of the casting material in the mould to the level of the top of the plug, or below, shorter, open-ended articles can be cast. Parts of the mould cavity between the core and the removable shuttering 25 can be filled by projections, mounted on shuttering 25 and forming after casting, openings in the article for doors, windows and the like.

Many other variations are possible within the scope of the following claims.

Claims

1. A method of moulding comprising the steps of: providing a base; providing an internal plug, upstanding from the base and having at least one inner-wall-bounding face; constructing demountable shuttering around the plug to provide at least one outer wall bounding face, parallel to said at least one inner-wall-bounding-face on the plug; pouring settable material to fill a cavity defined by the plug, the base and the outer shuttering; allowing the material to set; removing the outer detachable shuttering; and lifting the cast article from the base, characterised in that the or each inner wall bounding face, on the plug is constituted by an outer surface of a lining of yieldable material overlaying a body of the plug.

2. A method as claimed in claim 1, wherein an inner surface of said lining and an outer surface of the body of the plug meet at a low friction interface.

3. A method as claimed in claim 1 or 2, wherein the lining is removed from an interior of the article after its removal from the plug for re-use.

4. A method as claimed in claim 1 or 2, wherein the lining is renewed for each moulding operation.

5. A method as claimed in claim 2, wherein the low friction interface between the lining and the plug body surface is constituted by a smooth surface on the plug body cooperating with a natural surface on the yieldable lining.

6. A method as claimed in any preceding claim wherein the material of the lining is a rigid foamed material.

7. A method as claimed in claim 5, wherein the material is expanded polystyrene.

8. A method as claimed in claim 2, wherein the or each said surface of the plug body is smooth, flat and coated with a smooth substance.

9. A method as claimed in claim 8, wherein the smooth substance is paint, varnish, or a plastics coating material

10. A method as claimed in claim 9 wherein an additional release agent is applied to appropriate surface(s) of the plug before application of the lining.

11. A method as claimed in claim 8, wherein the lining is of rigid polyurethane foam or of corrugated material.

12. A method as claimed in any preceding claim, wherein attachment points are cast into the article to enable it to be lifted from the plug.

13. A method of moulding substantially as hereinbefore describd with reference to the accompanying drawings.

14. A method of moulding an article having at least one wall bounded by a pair of parallel surfaces, wherein a mould cavity is formed of which at least one wall-bounding surface is constituted by an outer face of a lining which is sufficiently strong to resist deformation under the hydraulic load of the material being cast, but which can yield upon withdrawal of a cast cured article from the cavity to reduce the separation load.

15. A method as claimed in claim 14, wherein the material of the lining is significantly softer than the set material of the article so that in the event that any undercut is formed, the force tending to withdraw the article from the mould can simply cause such an undercut to tear the material of the lining without adding significantly to the separation load.

16. Apparatus for casting an article from settable material, comprising: a base; a plug upstanding from the base; and shuttering spaced from the plug and defining, with walling of the plug, a cavity to form at least one wall of constant thickness, at least the wall-bounding surface of the plug being constituted by an outer face of a lining overlying a supporting body, the lining being sufficiently rigid to resist deformation under hydraulic forces applied by the casting material, but being yieldable to enable the cast article to be removed from the plug.

17. Apparatus as claimed in claim 16, wherein an inner surface of said lining and an outer surface of the body of the plug meet at a low friction interface.

18. Apparatus as claimed in claim 16 or 17, wherein the lining is adapted to be removed from an interior of the article after its removal from the plug for re-use.

19. Apparatus as claimed in claim 16 or 17, wherein the lining is adapted to be renewed for each moulding operation.

20. Apparatus as claimed in claim 17, wherein the low friction interface between the lining and the plug body surface is constituted by a smooth surface on the plug body cooperating with a natural surface on the yieldable lining.

21. Apparatus as claimed in any of claims 16 to 20 wherein the material of the lining is a rigid foamed material.

22. Apparatus as claimed in claim 20, wherein the material is expanded polystyrene.

23. Apparatus as claimed in claim 17, wherein the or each said surface of the plug body is smooth, flat, and coated with a smooth substance.

24. Apparatus as claimed in claim 23, wherein the smooth substance is paint, varnish, or a plastics coating material.

25. Apparatus as claimed in claim 24, wherein an additional release agent is applied to appropriate surface(s) of the plug before application of the lining.

26. Apparatus as claimed in claim 23, wherein the lining is of rigid polyurethane foam or of corrugated material.

27. Apparatus as claimed in any of claims 16 to 26, wherein attachment points are cast into the article to enable it to be lifted from the plug.

28. Moulding apparatus substantially as hereinbefore described with reference to the accompanying drawings.

29. A building made by the method of any of claims 16 to 28 or by the apparatus as claimed in any of claims 1 to 15.