WO1992012839A1

WO1992012839A1 - Moulds for making articles out of synthetic materials

Info

Publication number: WO1992012839A1
Application number: PCT/BE1992/000001
Authority: WO
Inventors: Philippe Julien
Original assignee: Philippe Julien
Priority date: 1991-01-24
Filing date: 1992-01-24
Publication date: 1992-08-06

Abstract

A mould is provided in an apparatus for making articles out of synthetic materials in which a molten material is injected into a mould. The mould comprises a separable wall which may consist of a plunger (3) movable in a cylinder (13) and preferably provided with a spring (10) which counters the pressure of injected material. The mould further comprises a movable wall (12) which moves to allow the article to be removed from the mould. The movement of the wall (12) is controlled by a plunger (16) moving in a cylinder (15) which is coupled with the cylinder (13).

Description

DESCRIPTION

Molds for the manufacture of plastic products

The present invention relates to molds for the manufacture of plastic products using an extruder or other means, which injects a melt into a mold. The synthetic material can be any plastic or similar material, such as thermoplastic resins as well as materials for recycling plastic products, which are homogeneous, heterogeneous and even polluted, or mixtures of these materials with other materials. The invention applies to any installation using one or more molds; the invention will however be preferably used in installations comprising a plurality of molds.

An example of such an installation is described in the Belgian patent published under the number 1 001 848. This installation is equipped in particular with an extruder and a carousel comprising several molds and which, by rotation, brings each mold into functions successive allowing filling, consolidation, cooling and demoulding.

To date, installations comprising several molds have always used molds for parts of the same length, this in particular following the principles of detection of filling and evacuation of the product formed from the mold.

An economic disadvantage is that all parts of a production batch must be the same length. Indeed, if we want to use an installation at its optimal capacity, it you need a complete set of molds of the same length, but if the manufacturing campaign requires products of various dimensions, you have to work length by length and replace a set of molds of the same length with another set of molds of different length annuity. The investment in molds for each type of product is therefore significant and the performance of the installation is not optimal.

To this end, the invention proposes to perfect the principle described in French patent 1,216,466 and to equip the mold inside a separable wall. Another drawback of the molds used to date lies in the field of demolding and evacuation of the products formed; indeed, the dimensions and / or the shape of a product can be such that demolding and removing the product is difficult. Difficult demolding, however, affects the good production and reliability of the installation.

In addition, some products cannot be manufactured with existing equipment. This is the case when the shape of the product is such that when it solidifies the product shrinks and stalls on one or more surfaces of the mold, automatic demolding becomes almost impossible. An example of this type of product are parts whose surface is complex, for example embossed.

In order to avoid demoulding difficulties, the mold is equipped with one or more walls which can be made mobile during demolding.

According to a characteristic of the invention, the separable wall is a piston, or a part attached to the piston, which can exert a pressure opposing the melt. Preferably, the pressure exerted by the piston can be made adjustable, for example, using a spring, the preload of which can be adjusted. In addition to an improvement in the uniformity and the state of the surface of the product produced, the demolding of this product is facilitated by the displacement of the piston and / or the relaxation of the spring.

In addition to a separable wall, the mold according to the invention comprises one or more walls which can be made mobile during demoulding. To this end, the invention proposes to actuate the movement of this or these walls by means of a piston moving in a cyhndre.

According to an advantageous form of application of the invention, there will be coupling and / or interaction between the displacements of the piston controlling the separable wall and the piston actuating the movable wall or walls.

According to a preferred form of application of the invention, the piston actuating the separable wall moves inside a cyhndre towards the end of the remphssage of the mold under the effect of the injected material, against d 'a spring, which opposes the force exerted by the injected material. Advantageously, the displacement of the piston is limited by a stop and actuates means which detect the end of the remphssage of the mold. It should be noted that the term "separable wall", as used in this text must be understood in a broad sense. This term "separable wall" means a wall which can be separated and then be replaced by another wall or also a separate wall and then changed place. In this text, separable wall therefore means a movable, replaceable, exchangeable, interchangeable wall, etc. .

Other characteristics and advantages of the invention will emerge from the description of several examples of applications given below by way of non-limiting reference with reference to the attached drawings which represent:

- Figure 1: a schematic cross section of a mold according to a form of implementation of the invention;

- Figure 2: a section along line A- A of Figure 1; - Figure 3: a schematic cross section of a mold according to another form of implementation of the invention;

- Figure 4: a section along line AA of Figure 3; - Figure 5: a schematic cross section of a mold according to yet another form of implementation of the invention. Referring to Figure 1, it shows a mold with a separable wall so as to be able to produce parts of different length and of which another wall can be moved during demolding. The product to be produced according to the example has a U-shaped section and tends to stall on the mold due to its shrinkage during cooling. The figure shows a mold 1 with the injection orifice 2 on the front side (injection side). The body of the mold 1 consists of an outer part 11 and an inner part 12 which together determine the shape of the product to be produced. On the rear side opposite to the feed, the mold 1 is equipped with a piston 3 which constitutes the rear face of the mold 1 and which can move axially in the body of the mold. This piston 3 comprises on the rear side a rod 4 fitted with a finger 5. The position of the rod 4 relative to the piston 3 is adjustable using a thread on the rod and a locking nut 6- The bottom 7 of the mold body has a stop 8 placed around the rod 4. The stroke of the piston 3 is limited, on the one hand, by the contact of the lock nut 6 against the stop 8 and, on the other hand , by the contact of the finger 5 against this stop 8. Advantageously, the separable wall will not be the piston 3, proper, but a part 9 fixed on the piston 3. Between the piston 3 and the bottom 7 of the mold, a spring 10 tends to move the piston towards the supply side. By adjusting the spring preload we can determine the resistance opposed by the piston to the molten material at the end of filling. This resistance influences the quality and the homogeneity of the product formed as well as the condition of the surface of this product. The spring 10 also allows the piston 3 to automatically return to its rest position.

Using the mold is simple. The injection orifice 2 is applied against the extruder head. The molten material is injected and pushes the piston towards the bottom 7 of the mold body. When the resistance caused by the piston 3 is overcome and the piston is in its extreme position, that is to say the lock nut 6 against the stop 8, the position of the finger is detected by any signal, (mechanical , electric or electronic) and the remphssage is interrupted. We can also detect the contact between lock nut 6 and stop 8 to interrupt the remphs¬ wise of the mold.

The chamber formed by the rear face of the piston 3 and the bottom 7 of the mold is divided into two compartments, a compartment 13 on the piston side and the compartment 14 on the bottom side 7 of the mold body. In communication with the compartments 13 and 14 is a chamber 15, fitted with a piston 16 provided with a spring 17. The piston 16 can move axially in the chamber 15 and the spring 17 exerts pressure on the piston 16 to maintain it in an end-of-travel position, that is to say that the piston 16 is pushed on the stop 18 fixed on the bottom 7 of the mold body. The compartment 14 is in communication via an opening 19 with the space between the stop 18 and the bottom of the piston 16. The compartment 13 is in communication via an orifice 20 with the space formed by the chamber 15 when the piston 16 is in an end position.

Outside the chamber 15, the piston 16 is connected with the wall (or internal part) 12 by means of a connecting rod 21, fixed, on the one hand, via the articulation 22 to the piston 16 and, on the other hand, to the wall 12 using a bolt 23 or any means of fixa¬ tion.

The wall 12 also includes one, two or more slides 24, each equipped with one or more rollers 25, fixed to the wall 11. When the piston 16 moves, this movement is transmitted via the connecting rod 21 to the wall 12, which moves as a result of the movement of the rollers 15 in the ghssières 24.

When the mold is filled, it is cooled before the product is discharged. For the evacuation of the compressed air is injected into compartment 14, the compressed air passes through the opening 19 and acts on the piston 16 which moves towards the supply side of the mold. This displacement causes the displacement of the wall 12 which emerges from the product produced. When the piston 16 has passed the orifice 20, the compressed air injected will pass through this orifice 20 into the compartment 13 and act on the piston 3.

The compressed air moves the piston 3 towards the supply side of the mold and the spring 10 will relax. Therefore, the finished product gets rid of the mold and can be evacuated through the feed side. As soon as the piston is stopped in its rest position, the evacuation of the manufactured product continues with the air jet which escapes through the clearance 29 formed by the slot between the piston 3 and the walls 11 and 12 of the mold 1.

The blow caused by the start of the displacement of the piston on the product produced is one of the advantages of the mold according to the invention, since it contributes to the effort necessary to undo the product from the mold. This effort is all the more important as the shape of the product produced is difficult to remove from the mold.

As soon as the injection of compressed air is stopped, the pres¬ sion inside the chamber 15 and the compartments 13 and 14 will drop and the spring 17 will push the piston 16 towards its rest position causing via the connecting rod 21 the wall 12 which will also return to the rest position (filling position).

According to a variant of this form of application appli¬ described we can provide a mold in two parts, a first part (supply part) conventional and a second part equipped with a set of pistons according to the invention. A mold made up of two parts can have additional advantages and in particular to avoid a multiplication of molds when it comes to products to be manufactured having at least one identical part. Figures 3 and 4 show a slightly different implementation mode than that illustrated in Figures 1 and 2. The part to be manufactured having an embossed surface 30, the movement of the movable part 12 of the mold must be perpendicular to the 'axis of the mold. To this end, the mobile part 12 is connected to an element 31 which carries the rollers 25 which can move in the slides 24. The element 31 which is connected to the piston 16 moves in a translational movement using rollers 32 which roll in grooves 33 parallel to the axis of the mold and formed in the outer wall 11. The shape and inclination of the ghssières 24 determine the movement of the wall 12 allowing the release of the manufactured part.

FIG. 5 shows an implementation mode according to which the piston 3 and the piston 16 are arranged coaxially. For the simplicity of the text, in FIG. 5, the elements corresponding to those described in FIGS. 1 to 4 have been designated by the same reference numbers.

FIG. 5 shows that the piston 3 and the piston 16 are arranged coaxially and are actually located one inside the other. The separable wall (bottom of the mold), in the previous examples, part 9, in this embodiment is part of the piston 3 and includes a valve 41. The orifice 20 between the chamber 15 and the compartment 13 (in the preceding figures) is replaced by lights 42 in the piston 3 which is hollow inside and which constitutes an enclosure 43. During demolding the compressed air is injected into the compartment 14 and acts directly on the piston 16 which moves towards the supply side mold. This movement causes via the connecting rod 21, the movement of the wall 12 of the mold and thus frees the produced part. When the piston 16 has passed the lights 42, the compressed air will pass through these lights 42 in the enclosure 43 inside the piston 3 and will also push it towards the mold supply side. Under the effect of compressed air, the valve 41 in the part 9, forming an integral part of the piston 3, opens and the compressed air enters the mold and acts on the object produced. The advantages of the invention clearly emerge from the description. An additional advantage lies in the fact that the piston-spring system continues to act on the part produced and contributes to controlling the shrinking thereof during its cooling. It is clear that the invention is not limited to the examples described above, but that multiple variants are possible without departing from the scope of the invention. Thus, for example, one can determine the stroke of the piston 3 by other elements than the nut 6, the finger 5 and the stop 8. Also the detection of rem¬ phssage of the mold can be done by other means than those described.

As regards the movable walls, the examples have illustrated forming molds with a single wall which could move; it is obvious that the displacement, simultaneous or not, of two or more walls can be considered. Also the use of slides and rollers is only one example and many other mechanical solutions can be considered. In the above description, the piston part with or without spring is described as being part of the mold, which itself can be made in one or more parts. One can also consider using a piston-spring system which is not part of the mold but which is part of another element, for example the mold holder of the installation. Although the invention can be advantageously applied to an installation comprising an extruder and a carousel, it will bring the same advantages to any other installation using injection means and equipped with one or more molds. The mold may include other elements which are useful for the envisaged installation, thus, for example, the mold may be fitted with an automatic water evacuation device, if the installa¬ tion includes a cooling bath. containing water.

Similarly, the mold according to the invention can be used for the manufacture of hollow products by combining the piston with a retractable or deformable core.

Claims

1. Mold for installation for manufacturing products of synthetic or similar material, equipped with means for injecting material at least partially melted and comprising at least one separable wall (9) making it possible to manufacture parts of different forms and at least a movable wall (12) allowing the demou¬ lage of the manufactured parts, characterized in that the movement of these walls is controlled by means coupled together.

2. Mold according to claim 1, characterized in that these means are pistons (3-16) moving in cyhndres.

3. Mold according to claim 2, characterized in that the separable wall (9) is actuated by a piston (3) which can move in a cylinder (13) and that the movable wall is actuated by a piston (16) which can move into a chamber (15) and in that the cyhndre (13) is in communication with the chamber (15).

4. Mold according to claim 2, characterized in that the piston (3) actuating the separable wall (9) is coaxial with the piston (16) actuating the movable wall (12).

5. Mold according to claim 4, characterized in that the piston (3) actuating the separable wall moves partially inside the piston (16) actuating the movable wall (12).

6. Mold according to claim 2, characterized in that the piston (3) actuating the separable wall moves inside the cyhndre (13) at the end of the remphssage of the mold under the effect of the injected material, and that a spring (10) acting on the piston (3) opposes the force exerted by the injected material, and that the displacement of the piston (3), limited by a stop (8), actuates means which detect the end of the remphssage of the mold.

7. Mold according to claim 2, characterized in that the piston (3) acts on the separable wall by means of a part (9) which can be a retractable or deformable core.

8. Mold according to one or more of claims 1 to 7, characterized in that the displacement of the movable wall (12) connected to the piston (16) by means of a connecting rod (21) is carried out using at least one roller (25) rolling in at least one slide (24) formed in the wall (12).

9. Mold according to one or more of claims 1 to 8, characterized in that during the release of the compressed air first actuates on the piston (16) moving the movable wall (12), before actuating on the piston (3) moving the separable wall (9).

10. Mold according to claim 9, characterized in that the action sequence is obtained by means of the orifice (20-42)

11. Mold according to one or more of the preceding claims, characterized in that it is used in a multiple station installation such as an installation equipped with a carousel.