Mold and method for forming plastic products

Mold (20) for manufacturing plastic products provided with a bottom and a sidewall, wherein the mold comprises at least a first (21) and second (22) mold part which jointly define at least partly at least one mold cavity (100) and are movable in a first direction, wherein the at least one mold cavity comprises at least one first, in particular bottom-forming part (101) and one second (102), in particular sidewall-forming part, wherein on the first mold part at least one fixed wall part (24) is provided which supports a first movable wall part (20) which is movable relative to the respective fixed wall part (24) in at least a second direction which includes an angle with the first direction, wherein in said first movable wall part a second movable wall part (35) is provided, on the side facing the mold cavity, which is movable between a forwardly moved position and a retracted position relative to the first movable wall part.

This application is the U.S. National Phase of, and Applicants claim priority from, International Application Number PCT/NL2005/000889 filed 23 Dec. 27, 2005 and Netherlands Patent Application bearing Serial No. 1027896 filed 27 Dec. 2004, which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The invention relates to a mold and apparatus for forming plastic products.

For forming plastic products, in many cases use is made of a mold having therein at least one mold cavity matching in shape and dimensions the products to be formed therein. During use, plastic is introduced into the respective mold cavity and allowed to harden through, for instance, solidification, chemical reaction or the like, after which a finished product can be taken out. Such molds are, for instance, injection molds or injection-compression molds.

For the purpose of forming products having for instance a bottom and a wall, such as containers, it is known to use a mold having a first and second mold part which, with the mold closed, define a mold cavity with a bottom-forming part and a sidewall-forming part. In order to make for instance openings or cavities in the sidewall of such a product, use is made of sliding parts which, during, before or after opening of the mold, can be retracted from a forwardly moved position, so that the product can be withdrawn. Incidentally, in a comparable manner, for other, non-withdrawable products molds with slides are used.

SUMMARY OF THE INVENTION

An object of the invention is to provide a mold for forming products, in particular from plastic, with which products can be formed in a particularly suitable manner.

In particular, though not exclusively so, an object of the invention is to provide such a mold with which container-like products can be formed.

A further object of the invention is to provide a method for forming products, for instance from plastic, using a mold.

In a first aspect, a mold according to the invention is characterized by at least a first and second mold part which jointly define at least partly at least one mold cavity and are movable in a first direction, wherein the at least one mold cavity comprises at least one first, in particular bottom-forming part and one second, in particular side wall-forming part, wherein on the first mold part at least one fixed wall part is provided which supports a first movable wall part which is movable relative to the respective fixed wall part in at least a second direction which includes an angle with the first direction, wherein in said first movable wall part a second movable wall part is provided, on the side facing the mold cavity, which is movable between a forwardly moved position and a retracted position relative to the first movable wall part.

In a mold according to the invention, use is made of a wall part which, with the mold closed, can define at least a portion of a mold cavity, which wall part is movable relative to a movable part of a mold part. Directions of movement of these parts include an angle with each other and/or with an opening and closing direction of the mold. In this way, a particularly great freedom of design is obtained for products to be formed in the respective mold.

In a second aspect, a mold according to the invention is characterized in that operating means for a first movable wall part and a second movable wall part movable relative thereto, which is movable along with the first movable wall part, are included at least partly in different mold parts. Upon opening of the mold, at least the first or second movable wall part is thereby separated from an operating means therefor. This enables complex movements of the respective movable wall parts.

The invention further relates to a forming apparatus provided with at least one mold having at least a first and second mold part which jointly define at least partly at least one mold cavity and are movable in a first direction, wherein the at least one mold cavity comprises at least one first, in particular bottom-forming part and one second, in particular side wall-forming part, wherein on the first mold part at least one fixed wall part is provided which supports a first movable wall part which is movable relative to the respective fixed wall part in at least a second direction which includes an angle with the first direction, wherein in said first movable wall part a second movable wall part is provided, on the side facing the mold cavity, which is movable between a forwardly moved position and a retracted position relative to the first movable wall part.

Such a forming apparatus provides the possibility of forming products in a particularly simple manner.

The invention furthermore relates to a method for forming products, in particular from plastic, using a mold having at least a first and second mold part which jointly define at least partly at least one mold cavity and are movable in a first direction, wherein the at least one mold cavity comprises at least one first, in particular bottom-forming part and one second, in particular side wall-forming part, wherein on the first mold part at least one fixed wall part is provided which supports a first movable wall part which is movable relative to the respective fixed wall part in at least a second direction which includes an angle with the first direction, wherein in said first movable wall part a second movable wall part is provided, on the side facing the mold cavity, which is movable between a forwardly moved position and a retracted position relative to the first movable wall part.

With such a method, products can be formed in a fast and simple manner.

In a further aspect of the invention, a method is given which utilizes adiabatic heat development in plastic in the mold, as a result of inter alia the speed of movement of the or each second and/or third moving wall part in the mold. Thus, compared with traditional injection molding with molds without movable wall parts, particular advantages can be achieved, such as, for instance, lowering of the required closing force and injection pressure, lowering of the required injection temperature, and shortening of the cycle time.

DETAILED DESCRIPTION OF THE INVENTION

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 wall3handles15are 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 first 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 first 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 first 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 first 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 first movable parts26, in the wall surface31a second movable wall part35is 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 second movable wall parts35can move in a fourth direction G which, for instance, are all approximately at right angles to the opening and closing direction S. Each second movable wall part35has a wall-forming part36on the side facing the core part29. On the opposite side, each second movable wall part35is provided with a first operating surface37. Seen from the core part29, behind each second movable wall part35, 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 second movable wall part35is pushed away from the first guide surface25. Since this second movable wall part35is guided by the first 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.

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 second movable wall part35two 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 rectangle49. Such means will be immediately clear to those skilled in the art.

A mold20according to the invention can be used as follows.

The mold20is closed, as shown inFIG. 3, with the first movable wall parts26in a forward position, in contact with the bottom plate23, and the second movable wall parts35in 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 second movable wall parts35. 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 third direction T. It will thereby carry along the slide39abutting against it, so that the respective second movable wall part35is 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 second movable wall parts35in 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.

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 first 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 fifth 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 second and third movable wall parts are 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.

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

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 second 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.

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.

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