WO2019123371A1

WO2019123371A1 - Mold, molding equipment and method for making a tensioned membrane panel

Info

Publication number: WO2019123371A1
Application number: PCT/IB2018/060431
Authority: WO
Inventors: Enzo Renato BERTOLI
Original assignee: Stamber S.R.L.
Priority date: 2017-12-20
Filing date: 2018-12-20
Publication date: 2019-06-27

Abstract

The invention relates to an injection mold of plastic material for making a tensioned membrane panel, said mold comprising a fixed half-mold (10) and a movable half-mold (12) which jointly delimit, when the mold is closed, a mold cavity (16) suitable to receive the plastic material for forming the perimeter structure of the panel. In at least one of the two half-molds there is formed, around the mold cavity, a tensioning structure seat suitable to receive a frame (22', 22") of a tensioning structure which comprises the frame and the membrane (4) of the panel to be molded, held and tensioned by said frame. The invention also relates to a molding equipment comprising said mold and to a method for making a tensioned membrane panel by means of said mold.

Description

DESCRIPTION

"MOLD , MOLDING EQUIPMENT AND ME THOD FOR MAKING A

TENSIONED MEMBRANE PANEL"

[0001] The present invention relates to an injection mold, a molding equipment and a method for making a tensioned membrane panel, for example a filtering panel, i.e. a panel comprising a perimeter frame of plastic material and a membrane, for example a flat filtering element, such as a fabric, retained and placed in tension by the perimeter frame.

[0002] In some embodiments of these panels, the perimeter frame made of plastic material is overmolded on the membrane .

[0003] One of the most critical aspects in the construction of a membrane panel by overmolding is the tensioning of the membrane during the injection step of the plastic material .

[0004] Currently, in the case of panels for fabric filtering elements, the injection of the plastic material takes place externally to the fabric; the fabric then divides the flow of the plastic material and is subject to a high risk of breakage. But even when the fabric resists the flow of the plastic material, the result of the molding operation is a plastic part composed of two elements separated by the fabric. Therefore, the panel frame is composed of three structurally distinct parts, that is, plastic part, fabric, plastic part, and can break quite easily if subjected to transverse forces.

[0005] Furthermore, the mold must have adequate dimensions to accommodate the inlet point of the plastic material externally to the pattern.

[0006] In some embodiments, clamps are used to tension the membrane which hold the edges of the membrane and move in mutual distancing. On the one hand, this execution entails the risk of causing tears in the membrane, also due to the impossibility of tightening the membrane uniformly and not with constant control of the tensioning, on the other hand it makes it very complicated, if not impossible, to make undercuts in the perimeter frame of the panel because, due to the presence of the movable clamps, the dies which allow such undercuts to be made and which move substantially in the same plane as the clamps do not have space.

[0007] The object of the present invention is to provide an injection mold, an equipment and a method for making a tensioned membrane panel, for example a filtering panel, capable of overcoming the drawbacks described above with reference to the prior art.

[0008] Said objects are achieved with an injection mold according to claim 1, with a molding equipment according to claim 6, and with a method of manufacturing a panel according to claim 8. The dependent claims describe preferred embodiments of the invention.

[0009] The features and the advantages of the mold, equipment and method for making a tensioned membrane panel according to the invention shall be made readily apparent from the following description of preferred embodiments thereof, provided purely by way of a non limiting example, with reference to the accompanying figures, in which:

[0010] - figure 1 is a perspective view of the two separate parts of the injection mold according to the invention;

[0011] - figure 2 is a perspective view of the movable half-mold of the mold in figure 1;

[0012] figure 2a is a perspective view of a tensioning structure usable with the mold according to the invention;

[0013] - figure 3 is a perspective view of a part of the equipment according to the invention, comprising the movable half-mold of figure 2 on the extractors whereof, in an advanced extraction position, a tensioning structure is placed;

[0014] figure 4 is a perspective view of the equipment of the previous figure, with the extractors of the tensioning structure in a retracted position;

[0015] - figure 4a is a cross-section of the equipment in figure 4;

[0016] figure 5 is another cross-section of the equipment in figure 4;

[0017] figure 5a is a section of the equipment comprising the fixed half-mold closed on the movable half-mold and with the dies in an advanced position for making undercuts in the perimeter frame of the panel;

[0018] - figure 6 is a perspective view of the movable half-mold alone at the end of the overmolding step;

[0019] - figure 7 is a cross section of the movable half-mold in figure 6;

[0020] - figure 8 is a perspective view of the movable half-mold with the extractors in an advanced position for ejecting the panel;

[0021] figure 9 is a perspective view of the overmolded tensioning structure-panel assembly extracted from the mold; and

[0022] - figure 10 is a perspective view of the panel obtained by overmolding using the molding equipment according to the invention.

[0023] In said drawings, reference numeral 1 indicates as a whole an injection mold of plastic material for making a tensioned membrane panel 2, wherein said tensioned membrane panel 2 comprises a perimeter frame 3 made of plastic material and a membrane 4 held and tensioned by the perimeter frame 3.

[0024] For example, the membrane 4, made of fabric or synthetic material, produces a filtering element.

[0025] The mold 1 comprises a fixed half-mold 10 and a movable half-mold 12. The movable half-mold 12 is movable between an open mold position, in which it is spaced from the fixed half-mold 10, and a closed mold position, in which it is in contact with the fixed half-mold 10. For example, the movable half-mold 12 slides guided on guide columns 14 which extend from the fixed half-mold 10.

[0026] The two half-molds 10, 12 bound together, when the mold is closed, a mold cavity 16 adapted to receive the plastic material for forming the perimeter frame 3 of the panel 2.

[0027] According to an aspect of the invention, in one of the two half-molds 10, 12 there is formed, around the mold cavity 16, a tensioning structure seat 18 adapted to receive a frame 22 of a tensioning structure 20, illustrated in particular in figure 2a before its insertion into the tensioning structure seat 18.

[0028] This tensioning structure 20 comprises the frame 22 and the membrane 4 of the panel 2 to be molded, retained and tensioned by the frame 22. [0029] In other words, the tensioning structure 20 is also a tensioned membrane panel, with the membrane of extension greater than that of the panel to be made, so that the perimeter frame 3 can be overmolded on the membrane 4 placed in tension by the frame of the tensioning structure 22.

[0030] In one embodiment, the tensioning structure seat 18 is substantially complementary to the shape of the frame 22 of the tensioning structure 20, so as to form a shape coupling therewith.

[0031] As will be described further on, when the frame 22 of the tensioning structure 20 is positioned in the relative seat 18 and the mold is closed, the tensioning structure 20 is firmly coupled to the mold and tends the membrane 4 to the desired tension level. Therefore, no movable devices are required which translate between the two half-molds to stretch the membrane.

[0032] In the example illustrated in the drawings, the tensioning structure seat 18 is completely formed in the movable half-mold 12 to make room for dies and relative carriages of the mold, as will be described hereinafter. However, according to contingent requirements, the tensioning structure seat 18 could be partly obtained in a half-mold and partly in the other half-mold.

[0033] In one embodiment, the mold cavity 16 is formed by a first half-cavity 16 formed in a first flat portion 122 of a first surface 121 of the movable half-mold 12 facing towards the fixed half-mold 10, and a second half-cavity 16" formed in a second flat portion 102 of a second surface 101 of the fixed half-mold 10 facing the first surface 121. The tensioning structure seat 18 is formed in such a way that the membrane 4 of the tensioning structure lies on one of said first and second flat portions 122, 102.

[0034] In this way, when the mold closes, the membrane 4 is firmly held between the two flat portions 102, 122 facing the surfaces of the two half-molds facing each other.

[0035] In an embodiment which allows at least one undercut to be formed in the perimeter frame 3 of the panel 1, one of the two half-molds, for example the movable half-mold 12, is provided with dies 24 translatable transversely with respect to the translation axis of the movable half^¬ mold 12 for making at least one undercut in the perimeter frame 3 of panel 1.

[0036] For example, these dies 24 are mounted on respective carriages 26 movable between an inactive retracted position and an active advanced position, i.e. insertion of the ends of the dies 24 into the mold cavity 16.

[0037] In this embodiment, the tensioning structure seat 18 is completely formed in one of the two half-molds, for example in the movable half-mold 12, below the sliding plane of the dies.

[0038] Therefore, the presence of the tensioning structure 20 is not an obstacle to the movement of the dies 24.

[0039] One of the two half-molds, for example the movable half-mold 12, is provided with extractors 28 which can be actuated to engage the mold cavity 16 so as to eject the molded perimeter frame 3 therefrom.

[0040] More in detail, in a preferred embodiment, the movable half-mold 12 is provided with a first group of extractors 28 which can be actuated to engage the mold cavity 16 so as to eject the molded perimeter frame 3 therefrom, and a second group of extractors 30 which can be operated to engage the tensioning structure 18 to eject the frame 22 of the tensioning structure 20 therefrom when the mold is reopened.

[0041] In one embodiment, the two groups of extractors are actuated substantially simultaneously, so as to extract from the mold the assembly consisting of the tensioning structure 20 and the perimeter frame 3 overmolded on the membrane 4. For example, the two groups of extractors 28, 30 are connected to and moved by a single extractor drawer 29.

[0042] In one embodiment, the frame 22 of the tensioning structure 20 and the second group of extractors 30 are provided with mutual connecting means adapted to make the tensioning structure 20 and the extractors 30 integral with each other when the tensioning structure 20 is to be positioned in the respective tensioning structure seat 18.

[0043] In fact, when the tensioning structure seat 18 is recessed relative to the surface of the movable half-mold on which the membrane 4 rests, due to the presence of the tensioned membrane the frame 22 would not enter the tensioning structure seat without overcoming the resistance of the membrane. The second group of extractors 30, when it moves from the advanced extraction position to the inactive retracted position, then acts as a traction means of the frame 22 connected thereto.

[0044] For example, the free ends of the second group of extractors 30 are threaded, for example internally, and the frame 22 is crossed by holes 23 for inserting screws 23 for the connection between the frame and the second group of extractors 30.

[0045] In one embodiment, the mold 1 is provided with further tensioning means acting on the tensioning structure 20 to further increase the tension of the membrane 4 with respect to the tension imparted by the frame 22 of the tensioning structure 20.

[0046] It should be noted to this end that the frame 22 of the tensioning structure 20 forms a membrane plane in which the membrane 4 lies when the tensioning structure is out of the mold.

[0047] For example, the frame 22 of the tensioning structure is formed by two superimposed half-frames 22', 22". The membrane 4 is retained between said half-frames and the membrane plane is defined by the facing surfaces of the two half-frames between which a peripheral portion of the membrane is interposed.

[0048] In one embodiment, this increase in tension is obtained by making the frame tensioning structure 18 such that the membrane plane is substantially parallel but outside the mold plane in which the membrane 4 lies when the tensioning structure is positioned in the respective tensioning structure seat.

[0049] For example, as illustrated in particular in figures 5 and 7, the mold plane coincides with the plane identified by the flat portion 122 of the first surface 121 of the movable half-mold 12, which also coincides with the closing surface of the mold, and the tensioning structure seat 18 is an annular recess formed in the movable half-mold 12 and has a depth such that the membrane plane is retracted, or more internal, with respect to the mold plane.

[0050] In this case, the tensioning structure seat 18 is connected to said first flat portion 122 by means of a rounded corner 122' which prevents the creation of weakening lines in the membrane 4.

[0051] The tensioning of the membrane is therefore determined on the basis of the distance between the membrane plane and the mold plane.

[0052] The injection mold 1 and the tensioning structure 20 then form a molding equipment for making a tensioned membrane panel.

[0053] Another method of the invention is a method for making a tensioned membrane panel by means of the injection mold described above.

[0054] First of all, the method comprises making a tensioning structure 20 comprising a frame 22 and the membrane 4 of the panel 1 to be molded, retained and tensioned by the frame. The membrane 4 of the tensioning structure must have a surface greater than that of the panel 1 to be manufactured and is crossed by passage holes 25 suitable for allowing the passage of the plastic material through the membrane during the molding step. These passage holes 25, preferably subjected to a cauterization treatment, are made in positions corresponding to or in the vicinity of the points of injection of the plastic material in the mold cavity 16 of the mold which will use the tensioning structure 20 as tensioning means.

[0055] As can be seen in figure 5a, due to the presence of the passage holes 25, the mold is provided with injection plugs 27 and injection holes 21 communicating with the mold cavity 16 only in one of the two half-molds, for example in the fixed half-mold 10.

[0056] It should be noted that the passage holes 25 are the only means suitable for allowing the plastic material to pass through the membrane, since the meshes of the latter are too small to allow the passage of the plastic material .

[0057] Moreover, the passage holes 25 formed specifically in the membrane allow to prevent having to inject the plastic material laterally with respect to the membrane itself so that the plastic material is positioned above and below it without passing through it. It is clear that such a technical solution involves an increase in the dimensions and complexity of the mold.

[0058] With the mold open and the extractors 28, 30 in an advanced position, the tensioning structure 20 is connected, for example by screwing, to the ends of the second group of extractors 30 (figure 3) .

[0059] The retraction of the extractors is then controlled with the consequent insertion of the frame 22 of the tensioning structure 20 in the respective frame seat 18 (figures 4, 4a and 5) .

[0060] The mold is closed and, if present, the dies are moved into an advanced position (figure 5a) .

[0061] The plastic material is injected into the mold cavity, passing the plastic material through the through- holes 25 made in the membrane 4, so as to overmold the perimeter structure on the membrane (figures 6 and 7) .

[0062] The mold is opened and the extractors 28, 30 are advanced (figure 8) .

[0063] The assembly consisting of the tensioning structure

20 and the perimeter structure 3 overmolded on the membrane 4 of the tensioning structure is extracted from the mold, thus releasing the frame 22 from the second group of extractors 30. Figure 9 shows this assembly separated from the mold.

[0064] The excess membrane protruding from outside the perimeter frame 3 is cut so as to obtain the final panel 2 ( figure 10).

[0065] In one embodiment, in which the mold is provided with sliding dies for making at least one undercut in the perimeter structure and wherein the tensioning structure seat is completely formed in one of the two half-molds below the sliding plane of said dies, the dies are controlled to translate between an inactive retracted position and an active advanced position after insertion of the tensioning structure into the relative seat and before the step of injecting the plastic material.

[0066] In one embodiment, before the step of injecting the plastic material and after positioning the tensioning structure in the respective seat, the membrane is tensioned so as to increase its tension with respect to the tension supplied by the frame of the tensioning structure .

[0067] For example, as explained above, he further tensioning of the membrane is obtained by making the tensioning structure seat in such a way that the membrane plane is substantially parallel but external to the mold plane wherein the membrane lies when the tensioning structure is positioned in the respective tensioning structure seat.

[0068] As stated above, in one embodiment the frame 22 of the tensioning structure is formed by the coupling of two superimposed half-frames 22', 22", between which the membrane 4 is interposed.

[0069] For example, the two half-frames 22', 22" are screwed together or fixed by rivets.

[0070] Preferably, between the two half-frames 22', 22", a longitudinal bead 222 made of a yielding material is interposed so as to be at least partly flattened when the two half-frames 22', 22" are coupled together. A peripheral portion of the membrane 4 is held predominantly between this longitudinal bead 222 and the second half-frame 22".

[0071] For example, the longitudinal bead 222 consists of a protruding portion of a rod, for example having a circular section, partially housed in a rod seat 223 obtained in the first half-frame 22'.

[0072] The use of the longitudinal bead 222 allows making the frame 22 in two parts connected to each other with the interposition of the tensioned membrane 4.

[0073] In fact, the longitudinal bead 222 made of a yielding material allows reducing the crushing of the membrane between the two half-frames, and therefore preserving the integrity thereof, especially if made of fabric. With the longitudinal bead, the crushing of the membrane does not take place or occurs in a reduced manner as it is the bead itself that undergoes deformation .

[0074] Furthermore, the yieldable or deformable bead 222 allows compensating for any lack of coplanarity of the two contact surfaces of the two half-frames.

[0075] The use of the longitudinal bead 222 allows avoiding the use of means for gluing the peripheral portion of the membrane to the frame 22.

[0076] The use of a modular frame 22 allows, with respect to, for example, a frame overmolded or glued on the membrane, considerably reducing the manufacturing time of the tensioning structure and therefore having a reduced number of tensioning structures awaiting overmolding.

[0077] A man skilled in the art may make several changes, adjustments, adaptations and replacements of elements with other functionally equivalent ones to the embodiments of the injection mold, molding equipment and method for making a tensioned membrane panel according to the invention in order to meet incidental needs, without departing from the scope of the following claims. Each of the features described as belonging to a possible embodiment can be obtained independently of the other embodiments described.

Claims

1. Plastic injection mold for making a tensioned membrane panel, where said tensioned membrane panel comprises a perimeter structure made of plastic material and a membrane retained and tensioned by the perimeter structure, comprising a fixed half-mold and a movable half-mold which jointly delimit, when the mold is closed, a mold cavity adapted to receive the plastic material for forming the perimeter structure, characterized in that in at least one of the two half-molds a tensioning structure seat is formed around the mold cavity suitable to receive a frame of a tensioning structure which comprises the frame and the membrane of the panel to be molded, retained and tensioned by said frame.

2. Mold according to claim 1, wherein the mold cavity is formed of a first half-cavity formed in a first flat portion of a first surface of the movable half-mold facing towards the fixed half-mold, and of a second half cavity formed in a second flat portion of a second surface of the fixed half-mold facing the first surface, the tensioning structure seat being formed in such a way that the membrane of the tensioning structure lies on one of said flat portions.

3. Mold according to claim 1 or 2, wherein one of the two half-molds is equipped with dies which are translatable transversely with respect to the translation axis of the movable half-mold to make at least one undercut in the perimeter structure of the panel, the tensioning structure seat being completely formed in one of the two half-molds below the sliding plane of said dies .

4. Mold according to any one of the preceding claims, wherein one of the half-molds is provided with a first group of movable extractors between an inactive retracted position and an advanced position for extracting the perimeter structure from the mold cavity, and of a second group of movable extractors between an inactive retracted position and an advanced position for extracting the tensioning structure frame from the tensioning structure seat, said first and second group of extractors being controllable in a substantially simultaneous manner to extract from the open mold the assembly consisting of the panel and the tensioning structure joined by the membrane .

5. Mold according to the preceding claim, wherein the second group of extractors is suitable to be connected to the frame of the tensioning structure when it is in an advanced position so as to pull the frame inside the tensioning structure seat.

6. Mold according to any one of the preceding claims, wherein the injection of the plastic material into the mold cavity takes place only from one of the two half molds .

7. Molding equipment for making a tensioned membrane panel, wherein said tensioned membrane panel comprises a perimeter structure made of plastic material and a membrane retained and tensioned by the perimeter structure, comprising a mold according to any one of the preceding claims, and a tensioning structure comprising a frame and the membrane of the panel to be molded, retained and tensioned by said frame, the frame being suitable to be received in the tensioning structure seat before the mold is closed, the membrane being penetrated with through holes in the plastic material made at or near the injection points for the plastic material.

8. Molding equipment according to the preceding claim, wherein the tensioning structure seat is shaped in such a way as to achieve shape coupling with the frame of the tensioning structure.

9. Method for making a tensioned membrane panel by means of a mold according to any one of claims 1 to 6, where said tensioned membrane panel comprises a perimeter structure made of plastic material and a membrane retained and tensioned by the perimeter structure, comprising the steps of: - making a tensioning structure comprising a frame and the membrane of the panel to be molded, retained and tensioned by said frame, the membrane of said tensioning structure having a surface greater than that of the panel to be made and being penetrated by through-holes in the plastic material;

with the mold open, inserting the tensioning structure into the tensioning structure seat;

- closing the mold;

- injecting the plastic material into the mold cavity, passing the plastic material through the through- holes made in the membrane, so as to overmold the perimeter structure on the membrane;

- opening the mold;

- extracting from the mold the assembly consisting of the tensioning structure and the perimeter structure overmolded on the membrane of the tensioning structure;

- cutting off the excess membrane protruding from the perimeter structure.

10. Method according to the previous claim, wherein the mold is provided with sliding dies for making at least one undercut in the perimeter structure and wherein the tensioning structure seat is completely formed in one of the two half-molds below the sliding plane of said dies, and wherein the dies are controlled to translate between an inactive retracted position and an active advanced position after insertion of the tensioning structure into the relative seat and before the step of injecting the plastic material.

11. Method according to any one of claims 9 or 10, wherein, before the step of injecting the plastic material and after positioning the tensioning structure in the respective seat, the membrane is tensioned so as to increase its tension with respect to the tension supplied by the frame of the tensioning structure.

12. Method according to the preceding claim, wherein the frame of the tensioning structure forms a membrane plane wherein the membrane lies when the tensioning structure is out of the mold, and wherein the membrane is put under tension by making the tensioning structure seat in such a way that the membrane plane is substantially parallel but external to the mold plane wherein the membrane lies when the tensioning structure is positioned in the respective tensioning structure seat.

13. Method according to any one of claims 9-12, wherein the step of inserting the frame of the tensioning structure inside the tensioning structure seat comprises the sub-steps of:

bringing a group of tensioning structure extractors from the mold into an advanced position; - fastening the frame of the tensioning structure to the ends of the extractor assembly;

bringing the extractor group into a retracted position .