IL46273A - Exapansible mold for the manufacture of plaster pieces - Google Patents

Abstract

1469847 Mould construction RHONEPROGIL SA 18 Dec 1974 [18 Dec 1973 29 Nov 1974] 54694/74 Heading B5A A plaster panel 7 (Fig. 2) (e.g. of phosphogypsum) having tongued and grooved edges, is cast in a mould comprising opposing vertical walls 2 sandwiching neoprene or silicone edge strips 3 and metal spacers 8. When a pressure force 5 is applied to the walls 2, the walls move relatively closer and the strips 3 are deformed to seal the mould; on removal of the pressure force 5 after casting, the strips 3 return to their original shapes to spring the walls 2 away from the plaster. The moulds are built up in banks (Fig. 4) on a fixed base 11, and stripping is aided by using walls 2<SP>1</SP> that are normally bowed, but are flat during moulding. The edge strips 3 can include polished metal inserts that define projections 4 (Fig. 2), or can comprise a sealed plastics jacket filled with a compressible fluid. Alternatively, two such jackets per strip are used, with one sealing the the walls 2 and the other forming the projection 4; the jackets are pneumatically or hydraulically inflated and deflated to effect moulding and springing apart of the mould walls. Finally the strips 3 can comprise a mechanic device deformable by a piston and cylinder. [GB1469847A]

Description

oas »oia is**V meoenn nan*3n n»aan EXPANSIBLE MOULD FOR TEE MANUFACTURE OF PLASTER PIECES This invention relates to an expansible mold for the manufacture of plaster pieces.

Usually the molding of plaster pieces is performed with the use of molds which can be disassembled or have movable parts which.are removed to allow removal of the plaster piece.

Nevertheless, the disadvantage of these molds principally consists of the fact that the assembly of the mold movable parts cannot be obtained with sufficient accuracy, thus thereby giving rise to dimensional errors in the finished product.

More particularly, this lack of accuracy is due to the clearances between the different movable parts and to the eventual insertion between these movable parts of plaster particles which prevent the mold being closed, to ita desired volume.

A second process, more particularly practiced for the molding of rectangular pieces, usually consists of using molds equipped with fixed side walls and a removable part, for instance for closing the upper side of the mold and slldable part for closing the lower side of the mold.

Then after disengagement of the removable upper part of the mold, the removal of plaster pieces can be carried out by displacing the slldable mold bottom part in the interior of the mold, for instance with the use of hydraulic cylinders, in order to force the plaster piece towards and out of the upper end of the mold. .

Such an operation, produces high stresses on the plaster piece and it is necessary that the internal faces of the mold are quite flat and smooth, in order to avoid any possibility of tearing up of the plaster surface and of abrasion of the mold surface.

This process, which requires molds having a very high degree of finish, is proving to be extremely expensive.

According to the present invention there is provided a mold' - for the manufacture of plaster pieces, comprising two opposed side walls which are spaced apart to define between them a mold, cavity, both of said opposed side walls or at least parts of said walls are relatively movable towards and away from one another between a casting position and a release position, two opposed spaced apart end wall forming members positioned between and in sealing engagement with the side walls, said end wall forming members being deformable, spacer members positioned between said side walls adjacent the outer 8ides of said end wall forming members for determining the spacing between the side walls when in the casting position, a feed opening communicating with the mold cavity for the introduction of cast material, and means for applying a pressure force to the side walls in a direction to cause said side walls to move relatively towards one another to said casting position in which they are spaced apart by a distance determined by said spacer members whereby the deformable end wall forming members are contracted in a direction normal to said side walls and expanded in the transverse direction end walls of the mold cavity and upon release of the pressure force expand in the direction normal to the ;> side walls to cause said side walls to move to their release position and retract in the transverse direction away from each other to release the article molded . in the mold cavity.

According to another characteristic of this invention, and in the case where the articles to be molded are parallelepiped and include molding on their side faces, both said parts include parallel flat walls, and the two deformable component parts include two rectangular surfaces. The extent of deformation of the deformable component parts is determined by interposing two metal parts between both said walls,said parts being positioned at the edges of the inside surface of the mold, and having a width equal to the desired thickness of the pieces to be molded.

An embodiment of the invention will be described hereinafter by way of non-restrictive example with reference to the accompanying drawings in which:- Figs. 1 and 2 are two horizontal secfcbnal views of a mold used for the manufacture of plaster pieces, respectively in positions of stripping (Fig. 1) or of molding (Fig. 2) ; Fig. 3 is a transverse elevation view of a set of molds identical to that represented in Figs. 1 and 2; Fig. 4 is a horizontal section of a mold according to one of the alternate methods, represented at the time of removal; and - - Fig. 5 is a vertical section of the same mold in the same phase of the manufacture showing another ~ alternate method.

With reference to Figs. 1 and 2, mold 1 on the one hand, involves two vertical and parallel walls 2 made of a material having a proper surface finish without particular hardness, and on the other hand, two deform-able incompressible component parts 3 made of an elastic material having two reciprocally opposite rectangular molding surfaces 4.

More particularly these component parts 3 can be made of elastomer, for instance of neoprene or of silicone, or of any other material having similar mechanical properties.

This elastomer has the property of being able to collapse in a direction (arrow 5) under the effect of a force applied in the same direction.

Owing to the fact that this elastomer is incompressible, its volume remains constant and the dimensional loss resulting from this collapse in the direction of arrow 5 is obtained with a directional increasing along the arrow 6.

The invention makes use of this property of the elastomer for enabling the removal of plaster pieces, the elastomer being subjected to a pressure at the time of casting the plaster and then relieved from any mechanical stress at the time of removal.

As represented in Fig. 2, the mold 1 is in molding position and the two internal faces of the walls 2, onto 46273/2 which the collapse forces of the elastomer are applied, are held in spaced relation at the thickness of the plaster piece 7 through the medium of two metal parts 8 arranged between the edges of said walls.

The component parts 3, tightly held between the walls 2 of mold 1, in the illustrated state of deformation, have molding surfaces 4, enabling the side molding of plaster piece 7 to be formed.

The removal of the plaster piece is effected by causing the release of the side collapse forces on walls 2 and consequently the release of the forces acting on the component parts 3.

This release simultaneously causes a gap between the walls 2 and the plaster and, in consequence of the retracting of elastomer component parts 3, also causes a delineatethe gap at surfaces 4 which gaps/thickness of the piece 7 (Fig. 1).

The piece 7 can be freely removed without stress or friction, without any slope having to be given to the mold walls in order to effect said removal and without gaps occurring which might result in the inclusion of particles which might subsequently be detrimental to the subsequent molding positioning.

With reference to Fig. 3, representing in section a set of molds 1 mounted in parallel in which the walls 2 internal to the set are common to two adjacent molds, the molding of the upper parts of pieces 7 is carried out by means of molding component parts 9 fixed on the side edges of walls 2, leaving openings 10 for the casting, the surfaces of said pieces corresponding to the openings 10. The molding of the lower part of pieces 7 is obtained by the use of a bottom 11 having moldings 12 for each of the molds 1 and on which the walls rest, this bottom being integral with a fixed base or even with the ground.

This arrangement of molds 1 makes evident an important advantage of the invention relating to the handling of plaster pieces 7 immediately after removal. According to the currently laamm processes, after removal it is known that it is necessary to carry out the conveying of the pieces up to a withdrawal station, storage station, drying station or a further storing station. This transport is particularly difficult owing to the fact that at the time of removal, the setting of the plaster has not been completed and the pieces have little mechanical strength. Consequently, it often happens that the plaster pieces are damaged during such conveying.

This disadvantage is particularly aggravated in the case where there are used non-homogeneous plasters whose setting time can vary considerably from one piece to the other, since for the same molding time, frequently the squares from the same casting are not all simultaneously transportable.

This invention eliminates this disadvantage. It avoids the use of any gripping means on the pieces such as handling pliers or the like, and enables the removal of pieces having very poor mechanical strength.

Thus it fits in with automation and permits very high molding capacities to be obtained, even when using non-homogeneous plasters, more particularly of hos ho sum.

According to an advantageous property of the invention, for this purpose there is carried out the transport of the whole molds themselves,, in which molds the pieces are partially hermetically sealed, the removal of the internal side of the pieces occurring at the time that tne set of molds is raised in the first phase of conveying, owing to the fact that the bottom 11 is fixed.

When said set of molds 1 has been brought to the withdrawal station, removal occurs by suppressing the forces which keep the component parts 3 compressed by lifting the molds from the loosened pieces 7, before returning the molds to the molding area. During this operation, the removal of pieces occurs through the lower part of the mold which remains open in the absence of bottom 11.

Of course, in the case where the set of molds 2 comprises a plurality of parallel disposed molds, as represented in Fig. 3, the compression of component elements 3 can be achieved by exerting a pressure on both outside walls of the set of molds, thus effecting the deformation of said component parts 3.

It is advisable to specify that the invention is not restricted to the use of component parts 3 made of elastomers or of materials which are deformable, incompressible and elastic.

These component parts 3 can be replaced by devices enabling the same results to be obtained.

By way of example, these component parts can involve a sealed jacket made of plastic having a molding surface filled with a non-compressible fluid or with smalls-sized 46273/2 The invention also includes a component part 3 in which both spacing operations (spacing of its own molding surfaces and spacing of both walls 2) are independent. Such a component part 3 can be achieved by the use of two sealed jackets/ each coupled with a hydraulic or pneumatic device, one of which jackets bears the molding surface and the other jacket being used only for forming the gap between walls 2 and said plaster pieces. The operating of the hydraulic or pneumatic device is such that: for the molding the molding surface bearing jacket is set under high pressure whereas the second jacket is set under a relatively low pressure; for the removal the second jacket is subjected to a higher pressure whereas the first jacket is subjected to lower pressure.

It is to be noted that this system albws spacings of molding surfaces greater than previously obtained.

The component part 3 can be composed of a mechanical device enabling the simultaneous spacing of the molding surfaces 4 and of the walls 2 under the effect of pressure for instance from a hydraulic or pneumatic cylinder.

At the time of removal, however, more particularly due to the pressure of a water film between the flat surfaces respectively of the mold and of the molded piece, it occurs that said molded piece separates only on one side from the mold and adheres on the other side onto one wall of this mold. In such instances it is difficult to loosen the piece from this wall of the mold without breaking the plaster. Furthermore the elastic component part of which a projection is engaged into the groove or hollow part which, having a reduced thickness, consequently splits or breaks, as observed on a number of ^ pieces.

An alternative method applied to the mold is such that the mold walls assembled by means of two deformable component parts are composed of plates which are flatter under the pressure exerted on said walls, enabling the mold to assume its molding position and to assume a non-flat shape when the mold is no longer subjected to the effect of these pressures at the time of removal.

With this latter alternative method of this invention, there is preferably also used a second means cooperating with the first and enabling avoidance of an injurious damage of the edges of the side faces said means having a middle recess for receiving the plaster molded piece, and which means is in turn deformed by the deformable component parts when, at the time of removal, a nonsymmetrical pressure is exerted during relaxation of the deformable component part on edges having a reduced thickness of the recesses of the side faces of said molded piece. It is beneficial to insert a rigid piece into the deformable component part which contributes to the molding of the side faces, said component part having a middle recess, said rigid part being without substantial elasticity and having a portion projecting out of the deformable component part which portion has the profile of the recess desired.

An embodiment of this invention comprising these alternative methods is described hereinafter to illustrate the same.

As seen in Fig. 4, two substantially vertical walls 2 rest on a horizontal bottom 11, to be fixed on a frameV^-work or the floor of a work-shop, said bottom being provided with reliefs 12 during the molding operation. In Fig. 5 walls 2' are represented in their equilibrium state, without external stress at the time of stripping. The curvature of these walls as shown in Fig. 4 is largely exaggerated, but is barely detectable with the naked eye. Metal parts 9, which are to be mounted on the upper edge of walls 2, give the desired shape to the upper edges of the pieces; a casting hole 10 is made between these parts for enabling the casting of th^e pourable plaster which spreads to form pieces. in Fig. 5 there is shown the walls 2, the molded piece 7, the deformable component parts 3 and 3' of which one 3 has a recess and whereas in the other 3' there is inserted a rigid piece 13, for instance made of polished metal whose external shape corresponds to that of the groove to which it has to conform. Metal parts 8 are used as braces for component parts 3 and 3' and maintain the spacing between the walls 2* at the time of removal.

Of course, the separate molds represented can be coupled in series as has been heretofore described, each mold being common to two adjoining molds, except those arranged at the ends of the set. The entire alternative methods or a part of the same described previously can be embodied in the improved mold of the present invention.

Fox performing the plaster molding , the molds are placed on their bottom 11 and on at least one of the walls there is exerted a pressure sufficient to bring the initially bent walls 2 to a substantially even plane, their spacing and their position being maintained by the bottom 11 and the different parts 9 and 6. This pressure can be exerted in a fairly homogeneous manner by a hydraulic or pneumatic transmission on a rigid flat plat (not represented) having a surface substantially equal to these of walls 2'. These walls, such as represented in the figures, are bent. The extent of deformation corresponding to the greatest distance between a point of the concavity of the bend and the position of the same point when in plane shape, is in the range of 1/1000 of the length of the flat faces of the pieces to be molded, or in dther words, for pieces having usual sizes from 3/10 to 8/10 of millimeter. These walls can be formed by disposing on an iron framework, two sheet iron plates having at least one smooth surface each and separated one from the other by a spacer having a constant thickness. At least two of the opposite sides of the framework are bent. Whenflattened:, under the effect of the pressure, these walls squeeze the deformable pieces and make them spread in the only unrestricted direction that is to say towards the interior of the mold. Then the plaster is cast, and afterwards when a sufficient degree of setting has been reached to make it non-deformable under the influence of its own weight, then the deformable component parts, by returning to their initial shape, push aside the walls which at the same time incurvate by allowing the air to penetrate between them and the plaster. The rigid inserted part 13 follows the general shrinkage direction in a translation according to the axial plane of the groove formed/ without exerting a non-symmetrical pressure on one or the other of the sides of this groove even if one of the vertical walls returned to its equilibration shape ore rapidly than the other or if a local adherence occurs.

Preferably the thickness of the walls 2' is selected in such a way that there is the necessary spacing between these pieces for effecting thaLr drying by air circulation propelled by an impeller. This spacing being made without difficulty by a single vertical displacement of the mold.

For instance this spacing is in the range from 20 to 30 mm for pieces of 30 mm in thickness.

Claims (12)

1. WHAT IS CLAIMED IS:- 1. A mold for the manufacture of plaster pieces, comprising two opposed side walls which are spaced apart to define between them a mold cavity, both of said opposed side walls or at least parts of said walls being relatively movable towards and away from one another between a casting position and a release position, two opposed spaced apart end wall forming members positioned between and in sealing engagement with the side walls, said end wall forming members being deformable, spacer members positioned between said side walls adjacent the outer sides of said end wall forming members for determining the spacing between the side walls when in the casting position, a feed opening communicating with the mold cavity for the introduction of cast material, and means for applying a pressure force to the side walls in a direction to cause said side walls to move relatively towards one another to said casting position in which they are spaced apart by a distance determined by said spacer members whereby the deformable end wall forming members are contracted in a direction normal to said side walls and expanded in the transverse direction towards each other to a casting position defining the end walls of the mold cavity and upon release of the pressure force expand in the direction normal to the side walls to cause said side walls to move to their release position and retract in the transverse direction away from each other to release the article molded in the mold cavity.

2. A mold as claimed in claim 1, in which said end wall forming members bear against an associated one of said spacer members and are formed of a resilient material which when pressure is applied thereto in one direction will contract in said one direction and will expand in a transverse direction.

3. A mold as claimed in claim 1, in which said end wall forming members bear against an associated one of said spacer members and are formed of a jacket of an elastic material filled with an incompressible fluid so that when pressure is applied to the jacket in one direction it will contract in said one direction and will expand in a transverse direction.

4. A mold as claimed in claim lf in which each of the end wall forming members consists of two sealed elastic members which can be supplied with fluid under pressure, one elastic member when subjected to fluid under pressure expanding in said transverse direction and the other elastic member when subjected to fluid under pressure expanding in the direction normal to the side walls.

5. . A mold as claimed in claim 1, in which each of the end wall forming members is mechanically movable towards the interior of the mold and back to its original position simultaneously with movement of said walls.

6. A mold as claimed in any preceding claim, in which said spacer apart side walls are flat and parallel.

7. A mold as claimed In any preceding claim, in which the side walls rest on a base surface provided ■ with a profile for forming a relief on an edge surface of the plaster piece.

8. A mold as claimed in any preceding claim, in which the side walls and end wall forming members can be bodily moved together with a molded plaster piece in the mold cavity before or after complete setting of the plaster to convey the molded plaster piece from a casting location to another location.

9. Molds as claimed in claim 1 which comprise a setof molds in which said molds are arranged in series, with said deformable members located in the inside of said set common to two adjacent molds.

10. Expansible mold for the manufacture of plaster pieces according to claim 1, wherein the mold walls are composed of curvilinear plates which become planar when displaced under pressure to define the mold space and return to curvilinear shape upon return to open position.

11. Expansible mold for the manufacture of plaster pieces according to claim 1, which includes a rigid part present as an insert in the deformable component part, said rigid part projecting outside of this component part towards the interior cf the mold and having a profile corresponding to that of the recess to be molded in the plaster piece.

12. A mold for the manufacture of plaster pieces substantially as hereinbefore described and with reference to the accompanying drawings.