WO2004069510A1

WO2004069510A1 - Molding apparatus for the production of polyurethane articles and relative method

Info

Publication number: WO2004069510A1
Application number: PCT/IB2003/004732
Authority: WO
Inventors: Mario Damo
Original assignee: G.M.P. Spa
Priority date: 2003-02-05
Filing date: 2003-10-27
Publication date: 2004-08-19
Also published as: ITUD20030028A1; AU2003274438A1

Abstract

Molding apparatus and method for the production of polyurethane articles (14) covered with a film (22), the apparatus comprising a matrix element (11) and a mating punch element (12). The matrix element (11) has a concave configuration with a lowered cavity able to contain in height the whole form of the article (14) to be made. The apparatus also comprises an annular element (28) able to be arranged above the matrix element (11) and including a raised peripheral edge (29) to contain splashes of material.

Description

"MOLDING APPARATUS FOR THE PRODUCTION OF POLYURETHANE ARTICLES AND RELATIVE METHOD"

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FIELD OF THE INVENTION The present invention concerns a molding apparatus for the production of polyurethane articles, covered with an aesthetic and decorative film. The invention is applied particularly, but not exclusively, for articles obtained starting from polyurethane reinforced and/or enriched with fibrous material such as glass fiber, carbon fiber or fiber from other suitable material.

The molding apparatus according to the invention is of the type that can be selectively opened to cooperate with a mixing head suitable to introduce the substantially liquid mixture of polyurethane and glass fiber into the cavity defined between the two elements of the mold, and in particular to distribute said mixture onto the surface (s) of the mold covered or not by the aesthetic film.

The invention is applied in the field of molding articles having high aesthetic and mechanical characteristics, in particular to make components for farm machines, earth moving machines and automobiles, hoods, panels, doors, etc.

The invention also concerns a method for molding polyurethane articles using said apparatus.

BACKGROUND OF THE INVENTION Molding apparatuses of the "open-mold" type are known and are used to mold articles, covered or not, starting from a polyurethane raw material possibly enriched and loaded with structural reinforcement fibers, particularly but not exclusively long glass fibers. Such molding apparatuses are normally equipped with a heating circuit using water, diathermic oil or other, and include means to create a vacuum.

Molding apparatuses as normally used comprise a matrix element and a punch element, with one or more impressions. The two elements can be selectively opened, one with respect to the other, to allow the close-up insertion of a mixing head by means of which the mixture of polyurethane and glass fiber is distributed onto the surface (s) of the mold, covered or not by the film. A press is also used which supports 'and moves the elements of the mold and by means of which the molding operations are carried out until the article is obtained and discharged. Although researchers in this field have been searching for a long time to achieve a method which gives uniform and industrially usable results, due to the presence of the thin film of the type indicated, it has not been possible so far to obtain satisfactory results due to the plurality of problems connected to this type of production.

In fact, molding apparatuses as used at present are subject to a plurality of problems and disadvantages that until now have prevented an industrial application of the open-mold technology.

A first disadvantage derives intrinsically from the open-mold method to distribute the liquid mixture that, apart from being difficult to access, generates splashes and spurts outside the elements of the mold, which dirty the mold, the joint parts of the mold, and the area and equipment surrounding the mold.

Another disadvantage is that it is difficult to distribute, in a manner coherent with the requirements of the finished form, the polyurethane mixture on the surface of the matrix, in order to completely fill the ribs and ridges with the material. A further disadvantage concerns the times and difficulties required to maintain and change the mold, and also to modify the format, and possibly the type, of the segment of covering film.

Other disadvantages are connected to the problems of achieving the aesthetic undercuts of a variable form and size along the perimeter of the article, and the problem of guaranteeing an efficient and uniform coupling with the means to transport and position the covering film.

Another disadvantage is that in known molding apparatuses the closing perimeter between the punch and the matrix, which defines the profile of the shape of the article to be made, generally coincides with the upper edge of said matrix, which therefore often has an irregular conformation, not plane; this creates problems if an annular element, for example used to transport and transfer a covering film, has to rest, at least during one step of the thermoforming and molding cycle, on said matrix.

Examples of such molding apparatuses which include one and/or the other of the disadvantages identified above can be found in documents US-A-5.238.640, EP-A-0.033.116, WO-A- 95/27604 and EP-A-1.249.329.

Applicant has devised, tested and embodied the present invention to overcome all these shortcomings and to obtain other advantages .

One purpose of the invention is to achieve a molding apparatus of the "open-mold" type, suitable to be used in a repetitive manner, with limited costs and in short times, and with high and uniform quality, in the production of polyurethane articles covered on at least one face with at least an aesthetic and decorative film. The aesthetic and decorative film preferably has a thickness of between 0.2 and 1.4 mm, but it is not excluded that films of a greater thickness may be used, even 3 mm and more . A further purpose is to achieve a basic, at least partly standardized molding apparatus, which can be configured easily, quickly and economically in a different way to at least partly modify the figure and/or perimeter of the article.

Another purpose of the invention is to achieve a molding apparatus suitable to cooperate effectively with means of the type with a plane or frame to transport and transfer a covering film, and also suitable to contain the sprays of polyurethane mixture during the introduction thereof, to prevent dirtying the area and equipment around the mold.

SUMMARY OF THE INVENTION The present invention is set forth and characterized in the main claims, while the dependent claims describe other characteristics of the main solution.

The molding apparatus according to the invention comprises at least a matrix element and a relative punch element that define, in the closed working condition, a molding cavity able to define the shape of the article to be made .

The two elements of the mold can be selectively opened, one with respect to the other, to allow the close- up positioning of a mixing head that distributes the mixture of polyurethane and glass fiber in the molding cavity.

According to the invention, the matrix element has a "basin-type" concave configuration, with a lowered cavity able to contain in height at least all the form to be made, even having a shape with a perimeter profile which is not plane; said matrix element also has a perimeter edge that is plane at the upper part and able to couple with frame means to delimit the perimeter that achieve a substantially plane outer supporting and closing surface.

To be more exact, in the molding apparatus according to the invention, the perimeter closing profile between the matrix element and the punch element, which defines the perimeter profile of the article to be made, lies on a plane that is always below the upper edge of the matrix element or of elements associated with it; thanks to this characteristic, for example at the start-of-cycle step, elements of the type with a plane or of the type with a frame, used to transport and transfer the covering film, are able to rest on the matrix element.

Thanks to the presence of the plane coupling surfaces, the transfer of the film from the transport element to the matrix element can occur using vacuum systems that guarantee an optimum grip and tensioning of the film in all the steps, preventing the formation of wrinkles and creases .

Moreover, the "basin-type" concave configuration of the matrix element, together with the presence of the frame means, considerably facilitates the skimming step of the polyurethane mixture and guarantees an efficient containment of the splashes of material during the introduction step, containing the leakage thereof from the mold and allowing to introduce the mixing head in depth. Thanks to this concave configuration the substantially liquid polyurethane mixture tends to go downwards in the mold closure step. The pressure exerted progressively takes the liquid masses on the surface to the thickness of the molded form, with the result that said masses expand towards all the cavities of the figure both due to the closing pressure and also due to the possible expansion of the polyurethane mixture, even when there are inserts, cavities, ribs, or suchlike present. If a transport plane is used, whether heated or not, which positions the segment of aesthetic film on the outer edge of the matrix, the presence of a plane, outer supporting surface allows to use, also for said transport plane, a universal element, not specialized according to the type and size of said segment.

Moreover, in the mold closure step, the presence of an outer supporting surface, still substantially plane irrespective of the shape of the article to be made, gives the possibility of guaranteeing high and uniform closing pressures .

In this way we prevent any thickening of the liquid mixture, the formation of holes, depressions, irregularities or other disadvantages that occur when the closing pressure of the mold is discharged onto surfaces that couple with each other in a non-plane manner.

According to a characteristic of the present invention, the molding apparatus comprises an annular element, for example made of metal sheet or other suitable material, with a raised perimeter edge, able to be arranged in cooperation with the perimeter of the matrix element, or of any other annular element arranged above the matrix.

A first function of the annular element is to contain the splashes of polyurethane material during casting. A second function of the annular element is to exert a retaining function on the film when the film is transferred to the mold, in order to clamp it mechanically in position when the transport plane which has transferred the film onto the matrix moves away from the mold in order to allow the subsequent operations of casting and closing the mold. A further function of the annular element is to maintain the vacuum in the matrix element, creating an airtight perimeter seal and preventing losses of vacuum during all the subsequent steps after the transport plane of the film has moved away, up to the closing of the mold.

According to another characteristic of the present invention, the molding apparatus comprises a first group of basic and standardized components, which are not replaced as the figure and the perimeter profile of the article vary, and a limited group of specific and specialized components, interchangeable according to the type of article to be made. This solution simplifies construction and considerably reduces the costs of the specific molding components, since a large portion of the plant part (vacuum means, conditioning means, movement devices) is provided on the standardized basic components. Moreover, this solution greatly reduces the times and activities required for the change-of-mold operations, and also for replacement and repair interventions. It is also possible to make lateral undercuts of a complex form without entailing complications to the specific elements of the mold. All this allows to make even small series of pieces, with limited costs and without increases in time and manpower, maintaining a high level of repeatability and uniformity of the results obtained and a high quality both in terms of forming the aesthetic film, particularly corners and edges, and also in terms of structural conformation of the article.

According to another characteristic, the suction holes and fissures which achieve the vacuum at least during the step to form the aesthetic film are arranged outside the figure of the article, for example in the coupling zones between the base components and the specific components. This fact also allows to reduce the costs of the specific components and to prevent, when the article is finished, signs or residues of the suction on the surface of the article itself.

BRIEF DESCRIPTION OF THE DRAWINGS These characteristics and advantages will become apparent from the following description of the preferential form of embodiment, given as a non-restrictive example with reference to the attached drawings wherein:

- fig. 1 is a perspective view of the molding apparatus according to the invention associated with the transport plane of the aesthetic film;

- fig. 2 shows a section of the molding apparatus in fig.

1 in the open condition;

- fig. 3 shows the matrix element and the relative support and containing elements in a section along the plane A of fig. 1 in the step subsequent to the thermoforming of the film;

- fig. 4 shows the components of fig. 3 in the step to distribute the mixture of polyurethane and fibers; - fig. 5 shows the closed mold during the molding step in a section according to the plane B of fig. 1;

- fig. 6 shows the open mold during the step when the molded article is removed;

- figs. 7a and 7b show respectively the specific parts and the basic standardized parts of the molding apparatus in fig. 1.

DESCRIPTION OF THE DRAWINGS

With reference to the attached figures, the reference number 10 denotes generally a molding apparatus of the "open-mold" type for the production of polyurethane articles 14, covered by a decorative film 22 (figs. 2, 3 and 6) .

The molding apparatus 10 comprises, in the embodiment shown here, a matrix element 11 and a mating punch element 12 able to define, in the closed condition (fig. 7a) , a molding cavity 13 that defines the shape of the polyurethane article 14 to be made. The matrix 11 and the punch 12, in known manner, have channels 27 that define, together with corresponding inlet and outlet channels 127 made in the relative support components 15 and 16, a heating circuit using water, diathermic oil or suchlike. Matrix 11 and punch 12 are associated with plane support plates, respectively 15 and 16, of a basic and standardized type, that is, able to cooperate respectively with matrixes 11 and punches 12 of an interchangeable type that can be replaced by other of a different type, shape and size in the step to prepare the configuration of the article 14 to be made.

The use of standardized support plates 15 and 16 allows to considerably reduce the times and costs required for preparing the mold 10 during the change-of-figure step. The molding apparatus 10 comprises lateral shoulders 17, also of a basic standardized type, which serve to create suction chambers 25 that connect to the cavity 13 by means of channels 26 and/or fissures located in positions such as to remain outside the • figure of the article 14, so as not to leave marks on the molded piece.

The suction chambers 25 are connected to the means to generate a vacuum by means of pipes 126 made at least in the standardized plate 15.

The vacuum is created at least in the step of forming the film 22 and of its adhesion to the inner surface of the matrix element 11.

The support plates 15 and 16 are able to cooperate with a mating press element, not shown here and which can be of the traditional type or of the tilting type as described in a parallel patent application in the name of the present Applicant.

The matrix element 11, as can be seen in the figures, has a concave conformation suitable to contain the various heights of the figure of the article 14 to be obtained. On the upper lateral edge 23 of the matrix element 11, which is at least partly plane on the upper part, blocks 18 are able to be associated, which can be of the movable type 18a and of the fixed type 18b, so as to cover substantially the whole perimeter of the matrix element 11, constituting a raised edge thereto.

To be more exact, as can be seen in fig. 7a, thanks to this lowered "basin-type" conformation of the matrix element 11, the closing profile between the matrix element 11 and the punch element 12, which defines substantially the perimeter profile of the article to be made, rises at most to a horizontal plane Pi which is always below the horizontal supporting plane P2 defined by the upper surface of the blocks 18.

In this way, as can be seen in fig. 2, on said horizontal supporting plane defined by the blocks 18 it is possible, as we shall see later, to rest operational elements of the mold, such as a ring-nut 21, or elements to transport the film 22, such as a hot plane 24, guaranteeing an optimum coupling and effective transfer, for example using pneumatic means, without risks of wrinkles or creases forming on the film.

The blocks 18 are replaceable and interchangeable and cooperate with the mold elements 11 and 12 during the reciprocal closure so as to define an aesthetic profile of the article 14 with an undercut (see the detail in fig. 2) . The movable block 18a can be moved, in this case, by means of a jack 19 whose rod 20 is introduced into a suitable hole present in one of the shoulders 17.

The combination of the concave configuration of the matrix element 11 and the presence of the lateral blocks 18a and 18b defines a "basin-type" containing zone for the liquid mixture which greatly reduces the possibility that splashes or spurts of polyurethane leak from the mold during introduction and dirty the surrounding areas .

Above the block 18 and resting on the lateral shoulders 17 a universal ring-nut 21 is able to be positioned, as we said before, which defines on the upper part a plane supporting surface for the support plate 16' of the punch element 12.

The presence of the universal ring-nut 21 that achieves a plane supporting surface also allows an easy coupling with frame elements 24 of transport planes, heated or not, suitable to position the segment of film 22 above the matrix 11.

In this case, the frame 24 of the transport plane can also be made universal and mating with the shape of the ring-nut 21 for any type of article 14 to be made and film 22 to be used.

After the film 22 has been positioned, an annular element 28, for example made of metal sheet or other suitable material, with a raised perimeter edge, 29, is positioned above the ring-nut 21.

A first function of the annular element 28 is to further contain, in an efficacious manner, the splashes of polyurethane material during casting. A second function of the annular element 28 is to exert a retaining function on the film 22 as the vacuum action exerted on it passes between the matrix 11 and the ring-nut 21, in order to retain it in position when the transport plane which has transferred the film 22 onto the matrix 11 moves away to allow the subsequent operations of casting and closing the mold.

A further function of the annular element 28 is to maintain the vacuum in the matrix element 11, creating an air-tight perimeter seal and preventing possible losses of vacuum during all the subsequent steps after the transport plane of the film 22 has moved away, up to the closing of the mold. Fig. 7a shows the specific elements of the molding apparatus 10 which are changed when the figure of the article 14 is modified, that is, the matrix 11, the punch 12 and at least part of the movable blocks 18a.

Fig. 7b shows the basic or universal elements, which remain the same even when the figure of the article 14 is changed, that is, support plates 15, 16, shoulders 17, ring-nut 21 and annular element 28.

Claims

CLAIMS 1. Molding apparatus of the type suitable for introducing material into an open mold for the production of polyurethane articles (14) covered with a film (22), comprising at least a matrix element (11) and a mating punch element (12) defining in the closed working condition a molding cavity (13) able to define the shape of the article (14), said matrix element (11) having a concave configuration with a lowered cavity able to contain in height the whole form of the article (14) to be made, characterized in that it comprises at least an annular element (28) able to be arranged above said matrix element (11) and including a raised peripheral edge (29) to contain splashes of material.

2. Molding apparatus as in claim 1, characterized in that said annular element (28) has the function of mechanically clamping the perimeter of said film (22) onto the matrix element (11) .

3. Molding apparatus as in claim 1 or 2 , characterized in that said annular element (28) functions as a perimeter seal to prevent losses of vacuum from the matrix element (11) at least after the thermoforming of said film (22).

4. Molding apparatus as in claim 1, characterized in that said matrix element (11) comprises an upper supporting surface defined by the upper edge of block elements (18a, 18b) able to be arranged in cooperation with an upper lateral edge (23) of said matrix element (11) .

5. Molding apparatus as in any claim hereinbefore, characterized in that it comprises a first group of components (15, 16, 17, 21, 28) of a basic or universal type, which are not replaced as the figure and perimeter profile of the article (14) change, and a limited group of specific and specialized components (11, 12, 18), comprising at least said matrix element (11) and said punch element (12), of the interchangeable type, according to the type of article (14) to be made.

6. Molding apparatus as in claim 5, characterized in that said basic and universal components comprise standardized support means (15, 16) respectively for said matrix element (11) and punch element (12), and peripheral column means (17) able to define, together with at least part of said specific components (11, 18), vacuum chambers (25) connected to said molding cavity (13) through channels and fissures (26) arranged outside the figure of the article (14) to be made.

7. Molding apparatus as in claim 6, characterized in that said channels and fissures (26) are connected to the means to create a vacuum by means of pipes (126) made in said standardized support means (15, 16).

8. Molding apparatus as in any claim from 5 to 7 inclusive, characterized in that said basic and universal elements comprise at least a ring-nut element (21) able to be arranged above said matrix element (11) or said block elements (18a, 18b) to define a substantially plane upper supporting surface.

9. Molding apparatus as in claim 6 or 7, characterized in that said support means (15, 16) comprise inlet and outlet means (127) for a heating fluid able to be circulated in circulation channels made in said matrix element (11) and punch element (12) .

10. Molding apparatus as in claim 4 or 5, characterized in that said upper surface of said ring-nut element (21) or of said annular element (28) is able to cooperate with transport and positioning means (24) , of the universal type, of a segment of said film (22) to be arranged in cooperation with the inner face of one of said elements of the mold ( 11 , 12 ) .

11. Molding method for the production of polyurethane articles (14) covered with a film (22), wherein a mixture of polyurethane material is cast by means of a casting head into a molding apparatus comprising at least a matrix element (11) having ring-nut means (21) on the upper part and a mating punch element (12), characterized in that it provides a first step wherein, in a position outside the molding apparatus, said film (22) is clamped and at least heated by transport and positioning means comprising at least frame means (24) , a second step wherein said frame means (24) of said transport and positioning means rest on the plane upper edge of said ring-nut means (21) in order to locate said film (22) above said matrix element (11), a third step wherein vacuum means present at least in said matrix element (11) are activated in order to thermoform the film (22) on the inner surface of said matrix element

(11) , a fourth step wherein an annular element (28) is located above said film (22) to retain it at least on the perimeter, and a fifth step wherein the vacuum is also activated between said matrix element (11) and said annular element (28) made of metal sheet, said annular element (28) exerting a retaining function on the film (22) and perimeter sealing of the vacuum at least when said transport and positioning means move away from the matrix element (11) .