WO2007099445A2

WO2007099445A2 - Mold with shut-off wall which is pushed by the expanding material to close conduit

Info

Publication number: WO2007099445A2
Application number: PCT/IB2007/000501
Authority: WO
Inventors: Piero Enrico Gilardi
Original assignee: Toscana Gomma S.P.A.
Priority date: 2006-03-03
Filing date: 2007-03-02
Publication date: 2007-09-07
Also published as: ITTO20060159A1; WO2007099445A3

Abstract

A mold (1), for molding articles of foam material, has a hollow bottom portion (2) for receiving a mass (3) of expandable material; and a top portion (4) which is movable between an open position and a closed position, and supports at least one relief device (6) for allowing air out of the mold; the relief device (6) has at least one conduit (7) connecting the inner cavity (5) of the mold to the outside and formed through the top portion; and a shut-off wall (9) located inside the cavity and movable between a withdrawn rest position, in which it connects the cavity to the outside, and a forward work position, in which it is pushed by the expandable material onto an inner surface of the top portion (4) to close the inlet of the conduit (7) in fluidtight manner.

Description

MOLD FOR MOLDING ARTICLES OF FOAM MATERIAL

TECHNICAL FIELD The present invention relates to a mold for molding articles of foam material. BACKGROUND ART

Articles of foam material are known to be produced using molds which, after being sprayed with a release agent, are filled with a given mixture of initially liquid expandable material which reacts to form gas and, ultimately, foam. As the material reacts, the foam increases in volume to fill the mold completely and form the desired article. Since the expansion time of the foam is only a few tens of seconds, it is important at this stage to allow the air inside the mold to escape as fast as possible. An increase in pressure inside the mold caused by trapped air, in fact, would impair normal expansion of the foam, thus increasing the minimum density of the finished article.

For this reason, where the movable part of the mold contacts the fixed part, relief conduits are normally formed, with a flat cross section of a few tenths of a millimetre in width, and a length varying according to the number of conduits, the type of mold, and the type of foam used. The size of , the relief conduit section is carefully calculated so that the foam closes the conduits as soon as it reaches them, to prevent collapse of parts of the foam inside the mold.

Alternatively, or in conjunction with the above relief conduits, molds are provided in the top with relief devices, also in the form of flat conduits which, like the above conduits, are closed by the foam. Unlike the conduits formed directly inside the mold, when the article is removed, the relief devices must be periodically removed, cleaned, sprayed with release agent, and reassembled, thus adding further running cost to the initial manufacturing cost.

Flat relief conduits, however, are functionally unsatisfactory, on account of the counterpressure inevitably formed inside the mold, and which - impairs free expansion of the foam, and varies principally according to the cleanliness, arrangement, and number of the conduits .

As an alternative to foam-closed flat relief conduits, a large-section relief opening is also known to be formed in the mold, and is associated with a powered closing device controlled by a sensor for determining the presence of foam close to the inlet of the opening, or by a timed device calibrated according to the assumed foam expansion rate. Though effective in keeping foam out of the relief openings, such systems are relatively complex, expensive, and not always reliable.

DISCLOSURE OF INVENTION It is an object of the present invention to provide a mold for molding articles of foam material, designed to provide a straightforward, low-cost solution to the aforementioned drawbacks.

According to the present invention, there is provided a mold for molding articles of foam material, as claimed in Claim 1.

BRIEF DESCRIPTION OF THE DRAWINGS

A non-limiting embodiment of the invention will be described by way of example with reference to the accompanying drawings, in which:

Figure 1 shows a schematic section of a preferred embodiment of a mold in accordance with the present invention;

Figure 2 shows a larger-scale detail of Figure 1; Figure 2a is similar to and shows a variation of a detail in Figure 2;

Figure 3 shows a view, with parts removed, in the direction of arrow B in Figure 2;

Figure 4 shows a variation of the Figure 2 detail; Figures 5a and 5b show a further variation of a detail in Figure 1 in two different operating positions.

BEST MODE FOR CARRYING OUT THE INVENTION

Number 1 in Figure 1 indicates a mold for molding articles of foam material. Mold 1 comprises a hollow bottom portion 2 for receiving a mass 3 of expandable foam-producing material; and a top portion 4 which, together with bottom portion 2, defines a mold cavity 5. Top portion 4 is movable between an open position shown in Figure 5b and by the dash line in Figure 1, and a closed position shown in Figure 5a and by the continuous line in Figure 1.

With reference to Figures 1 and 5, mold 1 comprises a relief device 6 for allowing air to escape from mold cavity 5. Device 6 comprises a conduit 7 connecting cavity 5 to the outside, and formed through top portion 4 with a flow section conveniently ranging between 100 and 2000 square millimetres; and a plate- or flap-like appendix 9 for closing conduit 7. Appendix 9 is housed inside cavity 5, is made of elastically deformable material, conveniently a preferably fluorinated or silicone elastomer, or Teflon, and, depending on the application, is of more or less constant thickness, or varies in thickness from point to point, so that each portion of appendix 9 has a desired elastic performance.

With reference to Figure 1 and, in particular, Figures 2 and 3, appendix 9 comprises a fastening end portion 11 connected directly to top portion 4, e.g. by screws 12; a movable shut-off portion 13; and an intermediate portion 14 defining a virtual hinge 15. Shut-off portion 13 functions in the same way as a shutter, and is movable between a withdrawn rest position (Figures 1 and 2), in which cavity 5 communicates with the outside via conduit 7, and a forward work position (shown by the dash line in Figure 2) , in which it rests against an inner surface A of top portion 4 surrounding the inlet of conduit 7, to close the inlet 7a of conduit 7 in fluidtight manner.

In the Figure 2 embodiment, surface A is substantially flat. In the Figure 2a embodiment, surface A is at least partly corrugated or grooved, and comprises two or more adjacent projections 14a defining between them the outlet of a respective known narrow channel 15b extending along portion 4 to collect any air still inside the mold when the mold is almost completely filled with foam. Channels 15b have a conveniently V-shaped cross section, and define a mesh or web for conducting air to the relief conduits. In the Figure 2a example, channels 15b are defined by grooves formed directly in top portion 4. Alternatively, in a variation not shown, channels 15b are defined by contoured parts applied to portion 4. With reference to Figure 2, when shut-off portion 13 is in the withdrawn position, appendix 9 is curved with its concavity facing the bottom of bottom portion 2 of mold 1.

In a variation not shown, inlet 7a of conduit 7 is closed by a movable shutter, which comprises an elastically deformable sealing portion cooperating with surface A, and is connected to top portion 4 by an ordinary hinge to rotate about a fixed hinge axis between said withdrawn and forward positions.

With reference to Figure 1 and, in particular, Figures 2 and 3, relief device 6 also comprises a grille 16 locked inside a seat 17 formed in inlet 7a of conduit 7 and defining, in use, an extensive support for shut-off portion 13 of appendix 9. Alternatively, as shown in Figure 4, the single relief conduit 7 and grille 16 are replaced by a number of parallel, side by side relief conduits 18 extending through top portion 4 and defining a total flow section comparable with that of grille 16. In this solution, too, portion 13, in the forward position, closes the inlets of all conduits 18 in fluidtight manner.

With reference to Figure 5, relief device 6 also comprises a mechanical push device 21 for moving shut-off portion 13 into the rest position when top portion 4 of mold 1 is in the open position (Figure 5b) .

Push device 21 comprises a push rod 22 movable inside conduit 7; and an oscillating weight 24 for moving push rod 22 between a push position, in which push rod 22 acts on shut-off portion 13 when top portion 4 is in the open position (Figure 5b) , and a detached position detached from shut-off portion 13 when top portion 4 is in the closed position (Figure 5a) . In the embodiment described, weight 24 and push rod 22 are fitted to the free ends of the arms 25, 26 of a rocker arm lever 27, which is substantially V-shaped, with its concavity facing outwards, and is hinged to top portion 4 to rock, with respect to top portion 4, about a horizontal axis 28. Arm 25 is also associated with an adjustable screw- nut screw type angular positioning device 29 for adjusting the position of push rod 22, in the detached position (Figure 5a), with respect to shut-off portion 13.

In a variation not shown, mechanical push device 21 is replaced by a pneumatic push device having a blower unit for blowing air into the mold through conduit/s 7, 18 to detach the appendix from top portion 4. Air is conveniently blown into the mold before portion 4 is moved into the closed position.

In actual use, once mass 3 of expandable material is fed into portion 2 of mold 1, and top portion 4 is closed, appendix 9, by virtue of its own weight or its initial curved configuration, remains in the rest position, thus allowing air to escape freely through relief conduit/s 7, 18 as the foam expands. This continues until the foam reaches shut-off portion 13 of appendix 9, from which point on, the foam gradually deforms appendix 9 and moves portion 13 towards top portion 4, thus gradually closing conduit/s 7, 18. Deformation of appendix 9 continues until the foam fills the whole of cavity 5 and pushes portion 13 against top portion 4 to close conduit/s 7, 18 in fluidtight manner. If surface A is corrugated or grooved, appendix 9 first comes to rest on projections 14a (as shown by the dash line in Figure 2a) , thus still allowing air to escape through the outlets of narrow channels 15b, and then deforms further to also close narrow channels 15b and so completely cut off access to relief conduit/s 7, 18.

Once the foam is cross-linked, the mold is opened and the finished article extracted. Once the article is extracted, appendix 9, no longer subjected to pressure by the article, returns automatically to its undeformed position. If, for any reason - e.g. excessive pressure exerted by the foam or insufficient spraying of the mold with release agent before feeding in the expandable material - shut-off portion 13 sticks partly to top portion 4 of the mold, weight 24, as top portion 4 is opened to extract the article, rotates rocker arm lever 27 anticlockwise in Figure 5 to push push rod 22 inside conduit 7 and detach shut-off portion 13 from inlet 7a of conduit 7 and move it into the detached rest position. Alternatively, appendix 9 is detached by the air blown in by the blower unit.

As will be clear from the above description, in mold 1 described, the foam inside cavity 5 never enters the relief conduits, which thus remain clean at all times. In addition, the ample air flow section allows the air to flow out freely with no localized load losses along the conduits, and until the foam fills cavity 5 completely. As a result, on the one hand, expansion of the foam is in no way obstructed, thus obtaining articles of low minimum density, and, on the other, collapse of the foam, caused by the relief conduits not being closed in time, is prevented. To further reduce resistance encountered by the foam, the outlet/s of conduit/s 7, 18 are fitted with a vacuum device 30 (Figure 1) for creating a vacuum in cavity 5 and so obtaining lighter, softer articles for a given amount of foaming gas in the initial mixture, and at lower cost as compared with articles produced in the absence of a vacuum.

Relief device 6 described is also extremely simple to produce, highly effective and reliable, and cheap to both produce and maintain. This is substantially due to the design and operating mode of the appendix, which is always completely coated with the release agent sprayed initially inside the mold, and therefore does not stick to the mold and remains clean at all times . Being elastically deformable, the appendix rests on the mold in such a manner as to ensure fluidtight sealing at all times, even on less than perfectly flat supporting surfaces. With either grille 16 or a number of conduits 18, i.e. in ramified support conditions, shut-off portion 13 may be extremely thin to improve performance of appendix 9, and without the thrust exerted by the foam extruding shut-off portion 13 locally inside the conduit/s .

Clearly, changes may be made to mold 1 as described herein without, however, departing from the protective scope defined in the accompanying Claims. In particular, the mold may be provided with a number of devices 6 arranged on the top portion; and appendix 9 may be made of material other than that indicated by way of example, and may be replaced with other equivalent plate-like closing members.

Claims

1) A mold for molding articles of foam material, the mold comprising a hollow bottom portion for receiving a mass of expandable material; a top portion which, together with the bottom portion, defines a mold cavity, and is movable between an open position and a closed position; and relief means for allowing air out of said cavity; said relief means comprising at least one conduit connecting the cavity to the outside and formed through said top portion, and closing means for closing said conduit; the mold being characterized in that said closing means for closing said conduit comprise a movable wall movable, inside said cavity, between a withdrawn rest position, in which it connects the cavity to the outside, and a forward work position, in which it is pushed by said expandable material onto an inner surface of said top portion to close an inlet of said conduit in fluidtight manner. 2) A mold as claimed in Claim 1, characterized in that said movable wall is an elastically deformable, plate-like wall.

3) A mold as claimed in Claim 1 or 2, characterized in that said relief means also comprise hinge means connecting said movable wall to said top portion.

4) A mold as claimed in Claim 3, characterized in that said relief means comprise a plate-like appendix, in turn comprising a fastening end portion connected directly to said top portion; a shut-off end portion defining said movable wall; and a flexible intermediate portion defining a virtual hinge.

5) A mold as claimed in Claim 4, characterized in that said appendix, when in said withdrawn rest position, is curved with its concavity facing downwards.

6) A mold as claimed in any one of the foregoing Claims, characterized in that said relief means comprise a grille located inside said inlet to define a support for said movable wall.

7) A mold as claimed in any one of the foregoing Claims, characterized in that said relief means comprise a number of said conduits formed side by side directly inside said top portion; said movable wall, when in said forward work position, closing all said conduits in fluidtight manner.

8) A mold as claimed in any one of the foregoing Claims, characterized by also comprising push means for moving said movable wall into said withdrawn rest position when said top portion is in the open position.

9) A mold as claimed in Claim 8, characterized in that said push means comprise a push member movable inside said conduit; and an oscillating weight fitted to said top portion to move said push member between a contact position contacting said movable wall when said top portion is in the open position, and a detached position detached from said movable wall when said top portion is in said closed position. 10) A mold as claimed in Claim 9, characterized in that said push means also comprise a rocker arm lever hinged to the top portion and fitted on one end with said push member, and on the opposite end with said weight. 11) A mold as claimed in Claim 10, characterized in that said rocker arm lever is substantially V-shaped with its concavity facing outwards; angular positioning means being provided to adjust the position of said push member with respect to said movable wall when the push member is in the detached position.

12) A mold as claimed in Claim 9, characterized in that said push means comprise blow means for blowing air into said mold through said conduits.