WO2006106212A1

WO2006106212A1 - Mould for lost casting patterns

Info

Publication number: WO2006106212A1
Application number: PCT/FR2006/000701
Authority: WO
Inventors: Jacques Mourey
Original assignee: Knauf
Priority date: 2005-04-04
Filing date: 2006-03-30
Publication date: 2006-10-12
Also published as: FR2883780A1; FR2883780B1

Abstract

The invention relates, in particular, to a mould provided with at least one cavity for producing at least one part which is made of a foam material obtained from expandable polymer balls and is used in the form of a lost pattern for producing a casting. Said mould comprises channels which penetrate through the wall thereof, are open into the cavity and outside of the mould and are embodied in the form of slots extending in a substantially parallel manner two-by-two along the mould cavity contour. Said channels make it possible to discharge the air contained in the mould cavity during the filling thereof with said balls, to uniformly introduce a saturated steam into the mould, wherein said steam enables said balls to be tied to each other and uniformly laminate the surface of said part.

Description

MOLD FOR LOST MODELS OF FOUNDRY

The present invention relates to a mold for producing pieces of cellular material which are each intended to serve as a lost model for the creation of a casting.

The invention also relates to a use of the mold for the production of at least one of these pieces of cellular material, and a method of producing said pieces of cellular material implementing said mold.

In order to produce complex parts in a precise manner, it is customary to make a model of said piece of wax or cellular material, for example polystyrene, to embed this model in sand in a formwork, and to cast metal in fusion in the formwork.

The liquid metal melts the cellular material and replaces it in all the space it occupies in the sand. After cooling and demolding, we obtain a metal part having exactly the shape of the model initially made of expanded polystyrene which is called "lost model".

To make these models, there are several methods.

One of these methods is to make the model by machining it directly into an expanded polystyrene block.

This process is slow to implement. It is therefore considered to be expensive.

A second method consists in molding the model.

The mold used according to this second method can be produced:

- by machining a block of metal,

by molding a metal alloy,

- by electroerosion of a porous material, by stacking on the field of metal slats whose final shape is obtained by machining.

The choice of the technique for producing the mold depends on the shape of the model to be produced.

Although these molds are profitable since they make it possible to create between 500 and 1 million pieces, they have certain disadvantages.

These disadvantages reside in particular in the surface state of the models obtained.

Indeed, the molds which are composed of a superposition of lamellae produce polystyrene models, for example, which have as many surface defects as lamellas stacked on top of each other composing the mold.

As for the models obtained with the other molds, they always have surface defects.

These defects are due to the introduction of filters, consisting of small cylinders in holes passing right through the wall of the molds.

Indeed, during the molding, the filters leave a mark on the surface of the model.

These defects can also be simply due to the holes made in the wall of the mold.

These filters or these holes are however essential because they ensure:

the evacuation of the air during the filling of the cavity formed in the mold with balls of cellular material, the introduction into the mold of water vapor to enable the balls of material to be welded or bonded together and to plasticize the material at the surface, and

- The evacuation of residual water vapor and pore-forming agents that are contained in the material balls and which allow them to swell and bind together, before unmolding the model.

The invention provides the industry with a substitution variant for existing production methods.

It relates to a mold having at least one cavity for the production of at least one piece of cellular material obtained from expandable polymer beads, which is intended to serve as a lost model for the manufacture of a casting. The mold has channels that pass through its wall, opening on the one hand into the cavity and on the other hand outside the mold, and which are made in the form of slots extending substantially parallel two by two and at least partially according to the contours of the mold cavity.

The channels allow, on the one hand, the escape of the air contained in the cavity of the mold during its filling by the said balls and, on the other hand, the introduction into the mold of saturated steam in a uniform manner, the steam allowing to bind the balls together and to laminate the surface uniformly on the surface.

According to a first variant embodiment, the channels have a width of between 0.1 mm and 0.2 mm, preferably of 0.15 mm.

According to a second variant embodiment, two substantially parallel channels are separated by a distance of between 3 mm and 10 mm. Preferably, the distance is 8 mm.

Advantageously, each of the channels has a length of between 20 mm and 150 mm. According to one embodiment, the mold has a thickness of between 5 and 10 mm.

In the context of an embodiment which will be described and illustrated subsequently, at least one of the channels of the mold according to the invention extends in a rectilinear direction.

According to another embodiment, at least one of the channels extends in a curvilinear direction.

According to yet another embodiment, the ends of the channels at least partially delimit bosses located in the mold cavity.

According to another embodiment, the channels extend in discontinuous lines.

Advantageously, the channels are made equidistant from each other to allow uniform bonding of the balls together and a uniform surface state of the workpiece.

According to one embodiment, it is provided that the mold is designed in a non-oxidizable metal by water vapor.

In the context of this embodiment, the mold is preferably made of aluminum alloy or cuprous alloy.

The invention also relates to a use of a mold having at least one of the previously exposed characteristics or a combination of these characteristics, for producing a lost model of cellular polymer material from polymer beads made of expandable material. Advantageously, it is expected that the cellular material consists of expanded polystyrene, polymethylmethacrylate alveolar, or a copolymer of polystyrene and polymethylmetacrylate.

In the context of a preferred mode of use, the mold is enclosed in an airtight chamber.

In the context of this embodiment, to bind said beads together, saturated water vapor is advantageously introduced into the chamber until the pressure around the mold is of the order of 1 to 2 bar and the temperature is of the order of 12O ⁰ C, said vapor entering the mold through said channels.

To cool the part, it is advantageous to spray cold water around the mold in the sealed chamber, at the rear of the mold, until the temperature inside the chamber is of the order of 50 ⁰ C.

In the context of an advantageous mode of use, a vacuum of approximately 0.3 bar is applied inside said chamber so as to eliminate through said channels the residual water which has served to cool said part, as well as a pore-forming agent included in the polymer beads and allowing the beads to swell and bind to each other.

The invention also relates to a method for producing a mold having at least one of the previously discussed characteristics or a combination of these characteristics, according to which the channels are made by means of a laser.

According to another embodiment of the method according to the invention, the channels are made by means of a jet of water under pressure.

According to yet another mode of implementation, the channels are made by wire EDM. In the latter case, it is advantageous to use a wire which has a diameter of 1/10 mm.

Advantageously, and in order to facilitate cutting in the mold by the wire, a hole is made to introduce the wire into the thickness of the mold, before the production of the channels.

In addition, the drilling is preferably closed by an insert of the same nature as that in which the mold is made, after the production of the channels. This makes it possible to limit the stresses to which the mold is subjected during the molding of the piece of cellular material.

Other objects and advantages of the invention will become apparent from the description which follows, made with reference to the appended figures in which:

- Figure 1 illustrates, in top view, a mold according to the invention according to a first embodiment;

- Figure 2 shows, in profile view, a mold according to the invention according to a second embodiment;

- and Figure 3 shows schematically, in sectional view, part of the tooling to implement in a molding process according to the invention.

It should be understood that the invention is in no way limited to molds whose shapes are shown in Figures 1 and 2, and that it extends to all molds that have the characteristics of the invention, they do not matter their shapes or their dimensions.

FIG. 1 represents, in top view, the half-mold 1 (half-shell) according to a first embodiment of a mold according to the invention. The half mold 1 is designed to produce two pieces of cellular material which are each intended to serve as a lost model for the manufacture of a casting.

The cellular material used to make these parts consists of expanded polystyrene, polymethylmethacrylate alveolar or a copolymer of polystyrene and polymethylmetacrylate.

For this purpose, the mold half 1 comprises two cavities 11 and 12 which are hollowed out in its thickness.

These two indentations 11 and 12 each have recesses 13 and bosses 14.

As shown in Figure 1, the mold half 1 has channels 2, illustrated by lines in each of the indentations 11 and 12.

The channels 2 allow in particular the escape of the air contained in the cavity of the mold when it is filled with balls of cellular material and the introduction into the mold of saturated vapor, for binding the balls together and for plasticizing in said surface uniformly, as will be detailed later, when describing the molding process using a mold according to the invention.

To allow the circulation of water vapor or air through the wall of the mold, the channels 2 are made through opening opening on the one hand in the cavity 11 or 12, and on the other hand outside of the mold.

The channels 2 are made in the form of slots extending substantially parallel to each other in pairs and at least partially in the contour of the cavity 11 or 12 half mold 1. S

As can be seen in Figure 1, some channels 2 have ends 21 which at least partially delimit some bosses 14 located in the cavity of the mold.

In addition, among the channels 2, channels 22 extend in rectilinear directions, and channels 23 extend in curvilinear directions.

Moreover, the channels 2 are made in the form of discontinuous lines.

The embodiment in the form of discontinuous lines makes it possible to preserve the physical properties of the mold, particularly as regards its resistance to deformation during the molding of the part.

Thus, the mold has a longer life than if the channels were made in the form of continuous lines.

Figure 1 also shows that the channels are made equidistant from each other, which allows a substantially uniform distribution of the channels in the mold half cavity.

It will be understood that "equidistantly" means:

that the distance separating two channels extending on the same is always substantially the same, and / or that the distance D separating two channels is always substantially the same.

In this way, the flow of air or steam is uniformly in the cavity of the mold, which allows for homogeneous parts, the surface condition is also uniform.

In the context of the presently described embodiment, the channels have a width of between 0.1 mm and 0.2 mm, preferably of 0.15 mm. The channels 2 are separated by a distance D which is between 3 mm and

10 mm.

It should be understood that the distance D corresponding to the distance separating two substantially parallel channels, measured between a first point belonging to the line on which a first channel extends, and a second point belonging to the line on which extends over the neighboring channel, this second point being obtained by crossing the perpendicular to the line of the first channel at the first point considered, and the line of the second channel.

On average, in the context of the exemplary embodiment illustrated in FIG. 1, the distance D between two channels is of the order of 8 mm.

The channels have a length of between 20 mm and 150 mm.

Regarding the mold, it consists of two half molds that are identical or not, depending on whether the part to be produced has a plane of symmetry or not.

The mold is made of a non-oxidizable metal by water vapor, for example aluminum alloy or cuprous alloy.

Figure 2 shows a half mold the (half shell) according to the invention. The half-mold has an imprint 15 of substantially cylindrical shape, of oval section, having a bottom 16 substantially flat.

Channels 24 axially crisscross the side wall of the cavity 15 of the half-mold 1a.

The channels 24 have substantially the same dimensions as those of the channels 2 of the mold half 1 shown in FIG.

A flat flange 17 makes it possible to fix the half mold 1 in a box 3 specific to the molding tooling which will now be described with reference to FIG. The molding tool shown in Figure 3 allows to connect one of the two mold half 1 (or the) to a machine whose utility will be detailed later.

The molding tool comprises a box 3 which is fixed on a frame 4 of the machine, a plate 5 on which the half-mold 1 (or the half-mold 1) is fixed and a bottom plate 6.

The half-mold 1 (or the) can be fixed on the plate 5 by fixing screws implanted in the aluminum of the half-mold with intervis sockets, or by means of a sliding system making it possible to easily dismount the half-mold to change, for example.

It is understood that the half-mold 1 (or the) is centered on the plate 5 before being attached thereto.

The bottom plate 6 and the walls of the interior of the box are equipped with material injectors, are provided with openings allowing the passage of saturated water vapor, and means for cooling the half mold 1 (or the ').

Injectors, orifices and cooling means are known to those skilled in the art. They have not been shown in the figures for ease of reading.

To limit the steam consumption, it is necessary to use a box 3 having a depth P which is the lowest possible.

Also, in the context of the embodiment described here, the box 3 has a depth P of between 50 and 250 mm.

To constitute an entire mold, two boxes 3 each carrying a half-mold are placed facing each other in a plane parallel to that of the plate 5. The two boxes 3 are centered relative to one another by means of three centering pins 7 which they present, one of the boxes having male centering studs, and the other box having female centering studs. .

To promote the molding of the part and reduce the time of completion of a part, each box 3 advantageously has a seal (not shown), so that when the boxes are positioned and fixed one in front of the other, there can be no exchange of air or steam with the outside.

The two boxes 3 thus define a hermetic chamber in which the mold is enclosed.

It should be noted that in the context of the example shown, the box is an insert on the machine. It should be understood, however, that the box could just as well constitute a part of the machine, without this limiting the use of the mold according to the present invention.

The hermetic nature of the chamber is important in the molding process. Indeed, and in particular for molding a piece of cellular material such as polystyrene, for example, it is necessary to bind the balls together by a supply of saturated steam (a dry vapor is less supported by the material which collapses under the action of heat). To promote this, it is preferable that there is no air inlet in the chamber in which the mold is located.

When closing the mold, the two plates 5 carrying the half molds 1 (or the) are positioned relative to each other with three bacon bits.

These three bacon are known to those skilled in the art. They have not been shown to facilitate reading of Figure 3.

The alloy in which the mold is designed has undergone appropriate heat treatments so that the mold can withstand abrupt temperatures, of the order of 70 ⁰ C in a few minutes, significant pressures, of the order of 7 bar, and voids of the order of 0.3 bar.

In order to enlighten the reader, the molding process of a part will now be described.

Once the two boxes 3 positioned opposite each other, they seal the mold hermetically.

The alveolar material, which is initially in the form of beads, is introduced into the mold by any known means until the mold is completely filled.

To facilitate the introduction of the balls into the mold, it is intended to apply a vacuum in the sealed chamber until the mold is completely filled with balls.

This operation allows a homogeneous distribution of the balls in the mold. This makes it possible to obtain a part having a homogeneous density.

To favor the vacuum in the mold, a groove is made at the junction of the two half-molds, at their joint plane, through which it is possible to suck the air contained in the cavity, or molding volume .

The thickness of the groove is substantially between 0.1 and 0.15 mm and its depth is of the order of 5 to 10 mm.

The support of the two half-molds is effected in zones to allow fluid passage from the cavity to the chamber surrounding the mold and vice versa. The bearing surface is calculated according to closing forces and material qualities. A saturated steam is introduced into the chamber until the pressure around the mold is of the order of 1 to 2 bars and the temperature is of the order of 120 ^° C.

This pressure ensures the introduction of saturated steam into the mold, through the channels.

Each ball of cellular material comprises an amount of pore-forming agent which, under the effect of saturated water vapor, swells the ball and the soda (or dregs) with the balls that surround it. In this way, all the balls contained in the mold are welded together.

In addition, the saturated water vapor allows to plasticize the piece surface, by contact between the surface of the balls and the wall of the mold cavity.

This operation only lasts a few minutes.

At the moment when the blowing agent binds the balls together, the pressure measured inside the mold is of the order of 2 bars.

A second step is to cool the mold in the sealed chamber, so as to cool the room.

To do this, it is common to spray cold water on the back of the mold in the sealed chamber, until the temperature inside the chamber is of the order of 50 ⁰ C.

Finally, once the part and the mold have been cooled, a vacuum of the order of 0.3 bar is applied inside the chamber so as to eliminate the residual water that has served to cool the mold (and the part) , as well as the blowing agent that allowed the beads to swell and bind to each other.

The residual water and the blowing agent are removed from the mold through the channels 3 (or 24) under the effect of the vacuum applied in the chamber. It is clear from the above description that the exchanges between the inside and outside of the mold are through the channels 3 (or 24).

The channels provide a uniform distribution of water vapor entering the mold, which allows to obtain a good surface condition of the molded part.

The channels 3 or 24 are made in the thickness of the mold by means of a laser, a jet of pressurized water or by the wire electroerosion method.

In the latter case, a wire of diameter substantially equal to 1/10 mm is preferably chosen.

In order to introduce the wire into the thickness of the mold, before the production of the channels, a drilling having a diameter of between 2 and 3 mm is carried out beforehand.

After completion of the channels, the hole is closed by an insert of the same type as that in which the mold is made.

This makes it possible to better preserve the physical characteristics of the mold during its successive uses.

It will be understood that the molding technique which has just been described is not limited exclusively to the production of lost foundry models.

By extension, it is applicable to the production of all molded pieces of cellular material for applications such as packaging, the production of molded parts for the building, and technical parts such as shock absorbers in the automotive industry.

This technique is also applicable to the production of packaging parts for the food industry.

Claims

1. Mold comprising at least one impression for the production of at least one piece of cellular material obtained from expandable polymer beads, which is intended to serve as a lost model for the manufacture of a casting, characterized in that it has channels that pass through its wall, opening on the one hand into the cavity and on the other hand outside the mold, and which are made in the form of slots extending substantially parallel to each other. two and at least partially according to the contours of the mold cavity, said channels allowing on the one hand the escape of the air contained in the cavity of the mold during its filling by said beads and on the other hand, introduction into the mold of saturated steam uniformly, said steam to bind said beads together and to plasticize said surface uniformly said surface.

2. Mold according to claim 1, characterized in that the channels have a width of between 0.1 mm and 0.2 mm, preferably 0.15 mm.

3. Mold according to claim 1 or 2, characterized in that two substantially parallel channels are separated by a distance (D) of between 3 mm and 10 mm.

4. Mold according to claim 3, characterized in that the distance (D) is equal to 8 mm.

5. Mold according to any one of the preceding claims, characterized in that each of the channels has a length of between 20 mm and 150 mm.

6. Mold according to any one of the preceding claims, characterized in that at least one of the channels extends in a rectilinear direction.

7. Mold according to any one of the preceding claims, characterized in that at least one of the channels extends in a curvilinear direction.

8. Mold according to any one of the preceding claims, characterized in that the ends of the channels at least partially delimit bosses located in the cavity of the mold.

9. Mold according to any one of the preceding claims, characterized in that the channels extend in discontinuous lines.

10. Mold according to any one of the preceding claims, characterized in that the channels are made equidistant from each other.

11. Mold according to any one of the preceding claims, characterized in that it is designed in a non-oxidizable metal by water vapor.

12. Mold according to claim 11, characterized in that it is made of aluminum alloy or cuprous alloy.

13. Mold according to any one of the preceding claims, characterized in that it has a thickness of between 5 and 10 mm.

14. Mold according to any one of the preceding claims, a groove is formed at the junction of the two half-molds forming said mold, at their joint plane, by which it is possible to suck the air contained in the 'footprint

15. Use of a mold according to any one of the preceding claims, for producing a lost model of cellular polymer material from polymer beads made of expandable material.

16. Use according to claim 15, characterized in that said cellular material consists of expanded polystyrene

17. Use according to claim 15, characterized in that said cellular material consists of alveolar polymethylmethacrylate.

18. Use according to claim 15, characterized in that said cellular material consists of a copolymer of polystyrene and polymethylmetacrylate.

19. Use according to any one of claims 15 to 18, characterized in that the mold is enclosed in a sealed chamber.

20. Use according to any one of claims 15 to 19, characterized in that a vacuum is applied in said sealed chamber until the mold is completely filled with balls.

21. Use according to claim 19 or 20, characterized in that, to bind said beads together, saturated water vapor is introduced into said chamber until the pressure around the mold is of the order of 1 to 2 bar and the temperature is of the order of 120 ⁰ C, said vapor entering said mold through said channels.

22. Use according to claim 21, characterized in that, to cool said room is circulated cold water around the mold in the sealed chamber, until the temperature inside the chamber is of the order of 50 ^° C.

23. Use according to claim 22, characterized in that a vacuum of about 0.3 bar is applied inside said chamber so as to eliminate through said channels the residual water having served to cool said room, and a porogenic agent included in the polymer beads and allowing the beads to swell and bind to each other.

24. A method of producing a mold according to any one of claims 1 to 14, characterized in that said channels are made by means of a laser.

25. A method of producing a mold according to any one of claims 1 to 14, characterized in that said channels are made by means of a jet of water under pressure.

26. A method of producing a mold according to any one of claims 1 to 14, characterized in that said channels are made by wire EDM.

27. A method of producing a mold according to claim 26, characterized in that said wire has a diameter of 1/10 mm.

28. A method of producing a mold according to claim 26 or 27, characterized in that a bore is made to introduce the wire into the thickness of the mold, before the production of the channels.

29. A production method according to claim 28, characterized in that the hole is closed by an insert of the same kind as that in which the mold is made, after the production of the channels.