Mold having independent movable walls

A method for manufacturing products using a mold having at least one mold cavity which is at least partly defined by at least two movable wall parts, wherein the mold is closed and the at least two movable wall parts (35A, 35B) are brought to a retracted position relative to the mold cavity, so that the volume of the mold cavity is enlarged relative to the volume required for a product to be formed, wherein at least partly molten material is introduced into the mold cavity and then in a first step a first one (35A) of the at least two movable wall parts is set into motion in the direction of a forwardly moved position and in a second step a second one (35B) of the at least two movable wall parts is set into motion in the direction of a forwardly moved position, wherein the movable wall parts are moved into said forwardly moved position for the formation of the product.

This application is the U.S. National Phase of, and Applicant claims priority from, International Application Number PCT/NL2005/000890 filed 23 Dec. 2005 and Netherlands Patent Application bearing Serial No. 1027910 filed 28 Dec. 2004, which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The invention relates to a method for manufacturing products. The invention relates in particular to a method for manufacturing products using a mold.

Mold-forming products provides the advantage that products can be manufactured relatively simply and reproducibly. Use can then be made, for instance, of injection molding technique. A disadvantage of this is that relatively high injection pressures are necessary to make the material spread throughout the mold cavity. Moreover, the injection temperature should be relatively high in order to prevent the material solidifying before the whole mold cavity has been filled. As a consequence, particularly high closing forces need to be applied to the mold, and stresses develop in the material and the product to be molded, which lead to an undesirably high degree of inaccuracy.

It has previously been proposed to make use of movable wall parts in the mold, so that flow paths for the material can be enlarged in cross section at least locally. As a consequence, the injection pressure can be lowered, as well as the injection temperature. In this technique, however, the control of the movable wall parts has to date been difficult.

An object of the invention is to provide a method for forming products using a mold with movable wall parts. In particular, an object of the invention is to provide a method for injection molding products, in which wall parts can be moved accurately and reproducibly.

SUMMARY OF THE INVENTION

In a first aspect, a method according to the invention is characterized in that the sequence of movement of the different movable wall parts is predetermined and is controlled, with the movable wall parts being moved in different steps. The steps have been chosen such that the movable wall parts are not set into motion all at the same time. Surprisingly, it has been found that in this way available energy for moving the wall parts can be utilized in a more accurate and more advantageous manner. Thus, it is possible to work more accurately.

In a second aspect, a method according to the invention is characterized in that different movable wall parts are set into motion at different times for displacing material, in particular plastic, in the mold cavity, such that the material is kept moving. It may then be advantageous that at least in a first step a movable wall part near a point where the material is introduced into the mold cavity is set into motion first and only then the or each further movable wall part.

In a further aspect, the invention is characterized in that a bottom-forming part and a wall-forming part are used, while in the bottom-forming part at least one movable wall part is provided and in the wall-forming part at least two movable wall parts are provided, and of the movable wall parts arranged in the wall-forming part, a movable wall part having the smallest surface is set into motion before the other movable wall part is set into motion. In that way, the available energy is used in a particularly advantageous manner.

In a still further aspect, the invention is characterized in that at least one and preferably each of the movable wall parts is moved from a retracted position to a forwardly moved position so fast that adiabatic heat development occurs in material in the mold cavity, so that the viscosity of the material is reduced. Preferably, the temperature in the material is raised, in particular such that the temperature is brought and/or held above the melting temperature of the material, at least until the respective movable wall part has been brought into the forwardly moved position.

In another aspect, the invention concerns a mold, provided with movable wall parts and a control unit therefor, with which the movable wall parts can be moved sequentially. Such a mold is particularly suitable for practicing a method according to the invention. With such a mold, products can be formed in a particularly simple and well-reproducible, accurate manner.

In yet another aspect, the invention concerns an operating device for a mold for forming products. This operating device comprises hydraulic and/or pneumatic means with a piston-cylinder assembly for different movable wall parts, as well as a pressure device for the supply and discharge of a pressure fluid under pressure to and from the piston-cylinder assemblies. Further provided is a control unit which is arranged such that the pressure fluid can be placed under high pressure, with pistons of one or more of the piston-cylinder assemblies being stationary, after which, using the built-up pressure, the or each respective piston can be set into motion instantaneously. In that way, the available energy is utilized in a particularly advantageous, accurate manner.

In this description, identical or corresponding parts have identical or corresponding reference numerals. Combinations of parts of the embodiments shown are understood to be represented herein as well. In this description, as an example, a crate, in particular a crate for bottles, will be described. However, the invention should not in any way be taken as being limited thereto. Many other holders, with or without compartmentation, having bottom surfaces of a variety of different shapes such as circular, rectangular, square, or any other shape, are possible within the framework of the invention. Also, holders can be formed with and without cavities in the sidewalls and/or bottom. Further, also other products can be manufactured in the same or a comparable manner, for instance partly hollow plate-shaped, bar-shaped, tubular or differently shaped products. The products can have a longitudinal wall or longitudinal walls extending at right angles to a bottom surface, but the or a longitudinal wall thereof can also be inclined relative to the bottom surface.

In a mold and method according to the invention, different materials, in particular different plastics, can be used, in particular thermoplastic plastics and blends. Also crystalline plastics and mixtures thereof have particularly good utility within the invention.

FIG. 1shows, in top plan view, a holder1according to the invention, in the form of a bottle crate, to which the invention is not limited.FIG. 2shows the holder1in cross-sectional side view. This holder1comprises a bottom surface2and a longitudinal wall3extending therefrom. The longitudinal wall3is substantially double-walled, which means that it comprises a first wall4, a second wall5and, located therebetween, a cavity or open space6. The wall thickness Dw is relatively small with respect to the dimensions A, B of the bottom surface2and the height H. The wall thickness can be, for instance, between some tenths of millimeters and some millimeters, depending on, for instance, the holder dimensions, intended use and the like. Between the walls4,5cross partitions7can be provided, preferably having a comparable wall thickness, for stiffening and increasing the bearing capacity. Within the longitudinal wall3and the bottom surface2, in an inner space8, a compartmentation9is provided by cross walls10. These reach to a point under the upper side11of the longitudinal wall3. The upper ends of the walls4,5are interconnected by a carrier edge12, preferably having a wall thickness comparable to that of the walls4,5. In the bottom surface2, openings13can be provided, being for instance circular, as shown at the bottom, right, or formed by cross bars14, as shown at the top, right. By providing openings, material and weight, cooling time and/or closing pressure can be limited. In the longitudinal wall3handles16are provided at opposite sides.

Hereinafter, a mold20and method will be described which can be used for a holder1according to the invention. It will be clear, however, that also a variety of other products can be manufactured with a comparable mold, for instance containers of a different kind, especially also single-walled holders.

FIGS. 3 and 4show a mold20in a closed and open condition, respectively. The mold20comprises a first part21and a second part22, which can move relative to each other in an opening and closing direction, indicated by the arrow S. To that end, for instance the first part21is included on a fixed table C and a second part22on a movable table D of a press (not shown) or like injection molding apparatus known per se. Incidentally, a variety of other means can also be used for opening and closing the mold20. The mold20comprises a mold cavity100with a first part101, being a bottom-forming part in the exemplary embodiment shown, and a second part102, being a wall-forming part in the embodiment shown.

FIG. 6schematically shows an elevation of the first part21, viewed in the direction S from the (removed) second part22. The first part21comprises a bottom plate23having thereon four fixed wall parts24upstanding from the bottom plate23, extending along the sides of a rectangle. The fixed wall parts24are provided, on the sides facing each other, with a first guide surface25which includes an angle α with the direction S. On each fixed wall part24, a movable wall part26is carried, of which a second guide surface27abuts against the first guide surface25and includes a same angle α with the direction S. First operating means28, as schematically drawn in as a piston-cylinder assembly inFIG. 5, are included in the first mold part21for moving the movable wall part26along the first guide surface25in a second direction Q, parallel to angle α.

As appears clearly fromFIGS. 3-6, the second mold part22is provided with a core part29which, with mold20closed, can be moved between the movable wall parts26, for forming for instance the inner space8, the partitions7and the like. In the drawing, for simplification, the core part29is drawn as a block, with sides having a draft angle β. As appears fromFIG. 3, with the mold closed, between the sides30of the core part29and the wall surface31of each movable wall part26that faces the core part29, a thin core32is included, mounted on the bottom plate23, for forming the cavity6in the walls of the holder1. These cores32can be omitted if for instance a holder1with solid walls is manufactured. As appears fromFIG. 4A, on the wall surface31a projection33may be provided which, with the mold closed, reaches into or through the core32, for instance as far as against the core part29, and can form a handle15or other opening or a deepened portion in the respective side of the holder1.

The mold20is provided, in the bottom plate23, with injection means34, at least injection openings34A, through which during use plastic or other material can be introduced into the mold20, for forming a product such as holder1shown. In the exemplary embodiment shown, the openings34A are provided near corners of the cores32.

In each of the movable parts26, in the wall surface31a first or second movable wall part35A, B is arranged, which is movable between a retracted position, as shown inFIG. 3on the left-hand side, and a forwardly moved position, as shown inFIG. 3on the right-hand side. To that end, these first or second movable wall parts35A, B can move in a direction G which, for instance, are all approximately at right angles to the opening and closing direction S. Each first or second movable wall part35A, B has a wall-forming part36on the side facing the core part29. On the opposite side, each movable wall part35A, B is provided with a first operating surface37. Seen from the core part29, behind each first or second movable wall part35A, B, against the first operating surface37, a second operating surface38has been laid which forms part of a slide39which is movable along the first operating surface37, in a third direction T. Each slide39has its opposite countersurface40supported against the first guide surface25and can move along it. Each slide39is slightly wedge-shaped, in the sense that the countersurface40and the second operating surface38slant towards each other in the direction of the bottom plate23. The first operating surface37includes an angle γ with the first guide surface25, which approximately corresponds to the wedge angle γ of the slide39. This means that if the slide39is moved in the third direction T towards the bottom plate23, the respective first or second movable wall part35A, B is pushed away from the first guide surface25. Since this first or second movable wall part35A, B is guided by the movable wall part26so as to be movable only in the fourth direction mentioned, it is forced in the direction of the core32and the core part29.

As appears clearly fromFIG. 6, the first movable wall parts35A are provided in the wall-forming parts arranged for forming the end walls4,5of the holder1, while the second movable wall parts35B are provided in the wall-forming parts arranged for forming the sidewalls3of the holder1. In the exemplary embodiment shown, the end walls have a smaller surface than the sidewalls.

For obtaining proper guidance, each slide39is slidable over or along a guide rod41which extends through the first movable wall part26in the direction T.

On the side remote from the bottom plate23, an end42of the slide39is situated in or near a partial surface43of the mold. InFIG. 6an embodiment is shown where for each first or second movable wall part35A, B two slides39are provided, whose ends42have been drawn in as ovals.

In the second mold part22, for each slide39an operating means44is provided, comprising a piston-cylinder assembly47with a piston rod45having a longitudinal axis46extending parallel to the third direction T. The piston rod can move in the direction of the longitudinal axis, and hence in the third direction T, driven by the piston-cylinder assembly47, for instance hydraulically, pneumatically or electrically. Of course, all kinds of other means, known per se, can be provided for driving the piston rod45in the third direction T. The piston rod45has a forward end48which, with mold20closed, can abut against the end42of the slide39, for moving same. As is clearly apparent, the piston rod45is not fixedly connected with the slide, so that the mold can be simply opened and closed.

In the exemplary embodiment shown, the piston-cylinder assembly47is driven by hydraulic means, schematically represented by the rectangle70. Such means will be immediately clear to those skilled in the art. A control unit60is provided for operating the different hydraulic means44, as will be discussed in more detail hereinafter.

A mold20according toFIGS. 3-6can be used as follows.

The mold20is closed, as shown inFIG. 3, with the movable wall parts26in a forward position, in contact with the bottom plate23, and the first and second movable wall parts35A, B in the retracted position, as shown on the left-hand side. The piston rods45are in a retracted position, with the ends42,48just butting against each other or at a slight distance. In this condition, plastic is introduced into the mold cavity via the openings34A, near the transition between the first and second part101,102of the mold cavity100. The plastic will largely fill the two parts101,102, though not completely so since the volume of plastic that is introduced into the mold cavity is virtually equal to the volume of the desired end product, whereas the volume of the mold cavity is greater as a result of the retracted first and/or second movable wall parts35A, B. After at least the greater part and preferably all of the plastic has been introduced into the mold cavity, the piston-cylinder assemblies47are energized, so that the piston rod is moved forcefully in the direction of the bottom plate23, in the direction T. It will thereby carry along the slide39abutting against it, so that the respective first or second movable wall part35A, B is moved in the fourth direction, to the forwardly moved position, as shown inFIG. 3on the right-hand side. Plastic between the respective second movable wall part and the opposite part of the core32or core part29will be displaced and the entire mold cavity is filled with the plastic. With all first and second movable wall parts35A, B in the forwardly moved position, the volume of the mold cavity100is substantially equal to that of the plastic introduced, while optionally after-pressure can be applied for compensation of shrinkage. In this condition the mold cavity moreover has the shape of the desired product.

Using the control apparatus60, the movement of the first and second movable wall parts35A, B is accurately driven. In a first step, each of the first movable wall parts35A is set into motion and only then, in a second step, each of the second movable wall parts35B. In this way, the plastic can be spread through the mold cavity100still better and optimum use is made of the available hydraulic energy. Preferably, the second step starts before the first movable wall parts35A have reached the forwardly moved position.

After in this condition the plastic has been allowed to solidify for some time, the mold20is opened for removal of the product1. To that end, the piston rods45are retracted substantially into the second part22of the mold20, as shown inFIG. 3on the left-hand side. Next, the second part22is moved away from the first part21, preferably simultaneously, or at least synchronized, with the movement of the movable wall parts26to a rearward position shown inFIG. 4A. In that position, the projections33have been pulled away, and the product1(not shown inFIGS. 4 and 4A) can be taken from the first mold part21. Next, the mold20can be closed again for a next cycle.

It is preferred that the second movable wall parts are moved to the forwardly moved position at high speed, preferably so fast that adiabatic heat development occurs at least in a part of the displaced plastic. It is advantageous in particular when the temperature in the displaced plastic and/or plastic to be displaced thereby obtains and/or keeps a temperature above the melting temperature of the respective plastic, so that the viscosity is reduced. The speed will then have to be chosen depending on for instance the plastic used, the desired wall thickness of the product at the respective positions, the total dimensions of the product, flow path lengths and cross sections, moving distance of the second movable wall parts. The suitable speed can be simply determined, for instance through experimentation with different speeds. As a consequence, the injection pressure of the plastic can be relatively low, and so can the closing pressure for keeping the mold closed. As a result, the properties of the plastic are not adversely affected and relatively stress-free products can be formed with particularly thin wall thicknesses and/or different wall thicknesses, and moreover relatively short cycle times are achieved. Moreover, as a result of the relatively low pressures, the advantage is achieved that relatively little material needs to be used for the mold, and cores, inserts and the like, if applicable, can be made of light and thin design. In this way, the freedom of design is enlarged still further.

In the embodiments shown, the angle α is for instance in the order of magnitude of between 5 and 30 degrees, more particularly approximately 15 to 20 degrees and the angle β between the closing direction S and the wall30is particularly small, in particular less than 5 degrees, for instance 1 to 2 degrees. The angle γ in the exemplary embodiment shown is smaller than the angle α and is between 1 and 10 degrees. This angle is for instance 2 to 6 degrees. These angles can in each case be chosen in a suitable manner on the basis of the desired speed of movement of the slide39and the second movable wall part35, the force required therefor and the distances to be traveled.

InFIG. 7an alternative embodiment of a mold20according to the invention is shown, which is broadly identical in structure to that according toFIGS. 3-6. These parts will not be further described here. In this embodiment, in the bottom-forming part, a third movable wall part50is provided. This wall part50, on its side remote from the mold cavity100, has two surfaces51sloping towards the middle. From two opposite sides, wedge-shaped slides52extend under the surfaces51, which wedges52rest on a bottom53of a slot54. Each slide52is drivable along the bottom53by means of a piston-cylinder assembly55or other earlier-discussed driving mechanism, in a direction K. InFIG. 7, the wall part50has been moved into a retracted position, that is, away from the core part29. In this condition, plastic can be introduced into the mold cavity100in the manner described earlier.

After the plastic has been introduced into the mold cavity100, the first, second and third movable wall parts35A, B and50are moved to the forwardly moved positions. To that end, the slides39and wedges52are moved in the third direction T and the fifth direction K, respectively. Thereupon, the product1can solidify and be taken out of the mold20in the manner described earlier.

With such a mold, the introduction of the plastic is simplified still further and the pressure can be kept low, also if a thin bottom wall and/or particularly long flow paths are used. With it, also ribs and the like can be provided in a simpler manner.

In this embodiment, using the control unit60, first the or each third movable wall part50is set into motion, next, in a second step, the or each first movable wall part35A, and then, in a third step, the or each second movable wall part35B. In this way, a particularly advantageous movement of the plastic through the mold cavity100is obtained. Since the plastic is introduced in relatively warm condition into a relatively large bottom-forming space101, relatively little energy will be needed to spread the plastic through this space101and to force it into the wall-forming parts102. Next, the plastic will be spread into the end wall-forming parts and eventually into the sidewall-forming parts. The second and third steps can start after the third movable wall part60has been brought into the forwardly moved position, but preferably at least the second step already begins before the or each third movable wall part has reached the forwardly moved position referred to. The third step preferably begins before the or each movable wall part35A has reached the forwardly moved position.

A holder1according to the invention can also be manufactured, for instance, in a mold20according toFIGS. 8 and 9. This mold20is included in an injection molding apparatus, at least press, known per se, of which are shown parts of a fixed table D and a table C, movable relative thereto in a first direction of movement S. The mold20comprises a first part21, arranged on the fixed table, and a second part22, movable relative thereto, mounted on the movable table C. The first direction of movement S, of course, can have any orientation, for instance vertical as shown inFIGS. 8 and 9, but also horizontal, by tilting the press.

The second part22comprises a central core part29, for forming the interior space8of the holder1. This central core part29is surrounded on all sides at a distance D1by a second core part32which is provided on the first part21of the mold20. The distance D1corresponds to the wall thickness D of the first wall4of the holder1. The second core part32corresponds in shape to the shape of the cavity6in the longitudinal wall3of the holder1. Optionally, pins32A may be provided in the upper side of the second core part32which fit into recesses in the second part22of the mold20, in support thereof. As a result, openings are formed in the edge12. Between a forward end of the central core part29and the first part22, a space101is provided for forming the bottom surface2. In this space101terminates a supply opening34A through which plastic can be introduced into the mold cavity100.

On the side of the second core part32remote from the central core part29, in the example shown on four sides, a first and second movable wall part35A, B, respectively, are provided in the form of a slide which is movable in a direction of movement C. The surface36facing the second core part32has the shape of the outer side of the respective part of the longitudinal wall3. Optionally, a projection33may be provided on the slide35A for forming the handle15, which projection, for that purpose, can reach through an opening in the second core part32. For simplicity, projection33and associated opening have been drawn only on the right-hand side.

In the position shown inFIG. 8, the slides35A, B are shown in a retracted position, that is, at a distance D2from the second core part32that is greater than the desired wall thickness D3of the second wall5. Accordingly, between the slide35A, B and the adjacent core part32, a relatively large, wide space102is provided, through which plastic can flow readily and without much resistance.

Provided on the rear side of the slide35A, B are inclined surfaces37, in the embodiment shown two surfaces37which are inclined in opposite directions. Furthermore, a flat running surface40is provided behind the slide, that is, on the side thereof remote from the second core part32. Provided between the inclined surfaces37and the running surface40are wedges39with correspondingly inclined surfaces38and running surfaces. The wedges39are connected with drive means44, inFIGS. 8 and 9constructed as piston-cylinder assemblies47, with which the wedges39can be moved from the first position shown inFIG. 8to a second position shown inFIG. 9and vice versa. Through movement of the wedges39to the second position, the slides35A, B are moved inwards, that is, towards the second core part32. As a result, the space102is reduced and hence plastic present therein is displaced and/or slightly compressed.

In top plan view, a mold20according toFIGS. 8 and 9is comparable to that inFIG. 6, in the sense that a pair of first movable wall parts35A are provided along the short end sides of the mold cavity100and a pair of second movable wall parts35B along the long sides of the mold cavity.

A mold20with press can be used as follows.

The mold20is brought into the closed position shown inFIGS. 8 and 9and held closed by the press with a relatively light closing pressure. The closing pressure is lower than is necessary for injection molding a similar holder using conventional injection molding technique and injection mold, which can conventionally be determined from, basically, the projected surface in the direction S, the flow paths, in particular the wall thicknesses, and the plastic used.

The slides35A,35B are brought into the retracted, first position, whereupon, using means suitable therefor, plastic is introduced via the or each supply opening34A into the space101, preferably in molten, at least substantially fluid form. From the space101, the plastic flows via the spaces between the central core part29and the second core part32over the second core part32into the spaces102. Since the plastic experiences substantially no resistance in the spaces102, it can easily flow into them without undesired pressure build-up and/or solidification of the plastic. Next, when substantially all necessary plastic has been introduced into the mold cavity100, the drive means44are energized using a control unit60. As a result, the wedges39are moved to the second position and the slides35A, B are forced in the direction of the second core part32. As a result, the plastic is forced further into the mold cavity100, in particular up to the end of the space102, so as to fill it completely.

The control unit60is then set such that the slides39, at least the first and second wall parts35A, B, are not moved all at the same time. In a first step, the first wall parts35A for the end walls4,5are moved, and next, in a second step, the third movable wall parts for the sidewalls3. As a result, the available energy is utilized in a suitable manner, and the plastic can moreover be set into motion and kept moving better. In general, preferably, in each case, first the or each movable wall part having a relatively small surface is set into motion and only then a part having a larger surface. The first and second steps can be carried out such that the second step does not begin until the first step has been carried out completely, which means that the first movable wall parts35A have been moved into the forwardly moved position completely. However, it is preferred that the second step is started sooner, that is, the second movable wall parts35A are set into motion while the first movable wall parts35A are still moving. In this way, a still better spread of the plastic can be obtained.

As the direction of movement C includes an angle with the direction of movement S, a favorable loading of the different parts is obtained. Since the plastic can flow into and through the mold cavity32without much resistance, relatively low pressures will suffice. This prevents, for instance, bending of the second core parts27and counteracts excessive wear. Moreover, partly as a result of this, the required closing force can be kept low.

After the slides have been moved forwards to a maximum, the plastic can solidify and, after optionally retracting the slides, and after opening the mold20, the holder1can be taken out. As a result of the relatively low injection pressure, the product will be virtually stressless.

InFIGS. 8 and 9the openings for forming the partition walls10are omitted for clarity.

The slides35of a mold20can be moved so fast that adiabatic heat development occurs in the plastic. As a result, the flow properties of the plastic can be further improved and any plastic which has solidified can be liquefied again. Alternatively, the slides34can also move slowly, so that the plastic is not heated, or is heated only to a very limited extent, and already solidifies to some extent during introduction. Also, it may be elected to move the slides in the direction of the second position (FIG. 9) already during introduction of the plastic, so that the plastic is kept moving continuously. This can be advantageous in particular with, for instance, crystalline plastics and plastics having a glass transition point and/or a low melt, or when product properties of the plastic are to be carefully preserved.

FIG. 10shows a diagram of an apparatus70for control and operation of at least a number of the operating means44for the movable wall parts35A, B and50. This apparatus70comprises a pressure device61, for instance a pump and/or accumulator, which communicates via a line system62with the different operating means44, in particular the piston-cylinder assemblies47. Between each piston-cylinder assembly and the pressure device extends a supply line63and a discharge line64. Each of the lines63,64includes a valve65,66. A control unit60is connected with the pressure device61and the valves65,66. Before a respective wall part35A, B or50is to be moved, at least the valves65in the supply lines are closed and using the pressure device pressure is built up in the section of the line63extending between the pressure device and the respective valve65. When this pressure is sufficiently high, for instance at a maximum, the valve65is controlled to open instantaneously, while the valve66in the discharge line64has been or is opened. As a result, the piston of the respective piston-cylinder assembly47will be moved instantaneously with very high speed, thereby operating the movable wall part35A, B,50. Next, using the discharge line, the piston is returned to the initial position and the valves are closed. The valves65,66, in particular the valves65in the supply lines, are arranged as closely as possible to the respective piston-cylinder assembly44, so that the line section63A between the valve65and the respective piston-cylinder assembly44is shorter than the section between the valve65and the pressure device, and preferably as short as possible. Surprisingly, it has been found that in this way the drive of the respective movable wall parts35A, B and50is possible still more accurately. Without wishing to be bound to any theory, this seems to be the result of the mass inertia of the fluid in the lines. By placing the greater part of the lines under a relatively high working pressure, only a small part of the fluid needs to be set into motion and/or placed under pressure after the valves65,66are opened, so that a much quicker response has been found possible. Moreover, in this way, the advantage is achieved that the movable wall parts can be driven more accurately. Preferably, for mutually associated movable wall parts, such as the pair of parts35A or the pair of parts35B, the line section63A between the respective piston-cylinder assembly and the associated valve is made of corresponding design in each case, such that a substantially equal amount of fluid is present in them. Thus, the accuracy is influenced still further. Using for instance PLCs, the valves can be set and driven in a particularly accurate manner.

FIG. 11shows an alternative embodiment, in which a double-acting piston47A is provided. Supply line63and discharge line64terminate on opposite sides of the piston47A. The control device is set such that prior to operation of a movable wall part35,50, on both sides of the piston the same high pressure prevails in the fluid, at least such pressures that the piston remains in a preselected position. When the respective wall part35,50is to be moved to the forwardly moved position, the valve66in the discharge line64is opened, so that the pressure on that side of the piston47A falls out and the piston is forced in that direction with force and high speed. In this way, in a particularly simple and accurate manner, the piston and hence the respective movable wall part35,50can be moved.

It will be clear that each of the apparatuses70as shown inFIGS. 10 and 11can be used with each of the molds20and methods as described earlier. Such apparatuses70can also be used for other moving parts in molds, whether or not according to the invention.

The invention is not limited in any way to the embodiments shown and described in the description and drawing. Many variations thereon are possible within the framework of the invention as outlined by the claims.

For instance, a plurality of mold cavities may be included within a mold according to the invention, both next to and above each other, for instance on opposite sides of the bottom plate. The first and second mold part can be interchanged, so that injection proceeds through or along the core part29. In-mold labels, inserts and the like can be used in a mold according to the invention. The mold cavity can have any desired shape. It will be clear that any desired number of first, second and/or third movable wall parts can be used, depending on the products to be formed. A product formed with a mold or method according to the invention can for instance have a fully closed bottom, single-walled sidewalls or parts thereof, a different compartmentation or none, and the like. Other operating means may be provided for moving the slides and wedges, for instance electric or pneumatic mechanical lever systems, linkages and the like. Optionally, the energy of injection of the plastic can be used at least partly for moving one or more movable wall parts, for instance to a retracted position. What is shown is a continuous wall of the product1. However, individual, mutually separated wall parts can naturally be used as well. The or each fixed wall part can be shaped and/or placed differently and can for instance carry the first movable wall parts on their sides.

In the embodiments shown, the operating means40are included in the second mold part. However, it is naturally also possible to include them at least partly in the plate D of the press. The second part22of the mold can then comprise the shafts45. In this way, a universal tool can be manufactured on which in each case a different mold20can be placed which can be made of particularly simple and light design since the relatively heavy and costly parts of the operating means44can be used again and again.

It will be clear that the directions of movement can also be chosen differently than shown. Thus, for instance, the slide39can be made to be movable parallel to the first direction S, with adaptation of the operating surfaces37,38, at least the angle thereof with respect to the direction S. Also, in principle, the operating means44for the movable wall parts35can be included in the first mold part21, with adaptation of the operating surfaces37,38, such that the slide39is moved in the direction of the second part22for moving the second movable wall part35to the forwardly moved position. Many variations thereof are possible and will be immediately clear from the description and drawings to those skilled in the art.

These and many comparable embodiments are understood to fall within the invention.