Moulding tool for manufacturing parts from expandable plastic beads and method for using said moulding tool

Abstract

A moulding tool for manufacturing parts from expandable plastic beads that comprises a first half with a first cavity plate and a second half with a second cavity plate, both made from a metal material, and a filler; the first half comprises a first block arranged to form a first chamber, heating means comprising a first conduit and cooling means comprising a second conduit, both in the first block; and / or the second half comprises a second block arranged to form a second chamber, heating means comprising a fourth conduit and cooling means comprising a fifth conduit, both in the second block; the first block and the second block being made from a material that has low thermal conductivity, equal to or less than 2 W / mK. The method for using said moulding tool includes purging, filling, introduction of steam and retention, cooling and ejection.

Description

[0001]MOLDING TOOL FOR MANUFACTURING PARTS FROM EXPANDABLE PLASTIC BEADS AND METHOD OF USING SAID MOLDING TOOL FIELD OF THE INVENTION The present invention falls within the field of molding tools for manufacturing parts that include two halves that configure a cavity with the shape of the part to be molded, specifically parts formed by expandable plastic beads. BACKGROUND OF THE INVENTION Conventional molding tools, also called molds, for parts formed by expandable plastic beads, such as expandable polypropylene (EPP) or expandable polystyrene (EPS), include two halves that together form a mold cavity into which expandable plastic beads are introduced and given the desired final shape of the part by directing steam heat to fuse the external surface of the beads, so that they can stick together. At least half of the molding tool includes a steam chamber near a cavity plate,which is the part of the mold that makes up the mold cavity, also includes through holes to distribute the steam in said mold cavity with a significant distribution depth in order to achieve uniform heating and distribution of the steam to the cavity to fuse the beads homogeneously. Each half of the molding tool is usually made of a resistant metal and with sufficient thickness to withstand the steam pressure and pressure to shape the beads, also being thermally conductive. A typical process consists of introducing a certain amount of plastic beads into the mold cavity, then steam is introduced to heat them to a temperature of about 140 ° C, then another steam phase is produced by directing steam from at least one of the halves until the beads are fused and the forming process is completed, in a final step, the molding tool is cooled to reduce the temperature of the molded piece before releasing it,This is typically done by spraying significant amounts of cold water onto the inner back of each half, i.e., into the steam chamber, avoiding direct projection of water onto the beads, to reduce their temperature to around 60 to 70°C. In this typical process, a large amount of steam is required to heat the molding tool and fill the steam chamber. This amount is substantially greater than the steam required to fuse the beads due to the size of the steam chamber and the mass of the molding tool to be heated; the same applies to cooling the molding tool. Consequently, large amounts of steam and cooling water are required.which leads to an extremely unfavorable energy balance of known devices and also places special demands on the installation site of the molding machines due to the large quantities of water involved. Known patent with publication number DE2936273A1 discloses a two-half metal mold for producing molded parts from pre-foamed plastic granules, another name for plastic beads. The metal walls of said mold are double-layered and spaced from each other by means of spacers, cavities being formed within the double layers, allowing a heating / cooling medium in one half and the passage of steam into the mold cavity in the other half. The disadvantage of this mold is that each heating / cooling and steam passage acts on only one half, so that the parts that can be produced can only be made thin-walled.since otherwise the temperature cannot be guaranteed nor can the steam penetrate adequately; then the mold is, therefore, only suitable for a limited range of applications, not being suitable to be a universal or widely used molding tool. Also known is patent with publication number US3837769A which discloses a molding tool in which heat exchange chambers are provided behind each wall of each half that forms the cavity, i.e. each cavity plate, which are crossed by steam channels that conduct the steam to the mold cavity, allowing for better temperature management of the tool. However, the design of the tool and the arrangement of the through holes for steam directly to the part to fuse the beads are subject to narrow structural limits and the surface is not permeable to condensate,which leads to some quality problems on the surface of the formed parts. Also known is patent publication number EP3088153A1, which describes a single-piece molding tool made from sintered metal, with the inner wall of each half formed with a large number of capillary channels extending from an inner surface facing the molded part in the cavity to an outer surface facing a steam chamber. In this way, with a compact, thin-walled tool, the thermal management of the tool can be achieved with a fluid conducted between both walls, and steam can be conducted from the steam chamber to the cavity. This allows for efficient thermal management and reduced cycle times. However, this tool concept is limited by the requirements of the sintering process, particularly the size and cost of the process. In the case of tools with multiple cavities,having independent cavities to configure this tool, each cavity having its heating and cooling inlets and outlets, results in a high cost and a significant tool size and long tool changeover times on the same machine, making this molding suitable for high volume production. DESCRIPTION OF THE INVENTION The present invention is set forth and characterized in the independent claims, while the dependent claims describe further features thereof. The object of the invention is a molding tool that overcomes the drawbacks of the state of the art, provides efficient thermal management with reduced steam consumption, is cost effective and the method of using said molding tool provides a reduced cycle time and can also provide faster tool changeover. The present invention is a molding tool for manufacturing expandable plastic bead parts comprising two halves,a first half and a second half, the first half comprising a first cavity plate and the second half comprising a second cavity plate, both cavity plates being made of a metallic material and configuring a mould cavity when the moulding tool is in a closed state, the first half comprising a filler arranged to allow expandable plastic beads to be introduced into the mould cavity through a second orifice, the first half and the second half each including heating means and cooling means, as is known in the art. The moulding tool is characterised in that the first half also comprises a first block arranged to configure a first chamber to the first cavity plate, the first block including a recess arranged to allow the filler to pass through it,the heating means of the first half comprise a first conduit in the first block arranged to reach the first chamber to accommodate the steam to be introduced into the mold cavity through a first hole in the first cavity plate, the cooling means of the first half comprise a second conduit in the first block arranged to provide a cooling fluid to the mold cavity, the second half also comprises a second block arranged to configure a second chamber to the second cavity plate, the heating means of the second half comprise a fourth conduit in the second block arranged to reach the second chamber to accommodate the steam to be introduced into the mold cavity through a third hole in the second cavity plate,the cooling means of the second half comprise a fifth conduit in the second block arranged to provide a cooling fluid to the mold cavity; the first block and the second block being made of a material with low thermal conductivity, equal to or less than 2 W / km / h, understood in the sense of being the core or main portion of each block, that is, said material being an alloy, metal, plastic, any other or any combination thereof, which for reasons of the aforementioned thermal conductivity may have a limited property, for example mechanical resistance, it being convenient to include some small different portions, for example being stronger like metal (a corner, a washer, ...), which represent a very small amount compared to the material that constitutes each block. Either the first block or the second block may be included. When only the first block is included,If the marks from the second filler hole are on the same side as the first steam introduction hole, the formed part may include all the visual marks on one side, leaving a clean surface on the opposite side. Conversely, depending on the specific configuration of the part to be formed, it may be interesting for the second plastic bead introduction hole to be on the opposite side of the first steam introduction hole for heating and cooling reasons, then only the second block is included. And when the heating and cooling requirements must be maximum in terms of steam penetration - especially for thick parts -, surface uniformity - especially for large parts or those with complex surfaces - or similar conditions, both the first and second blocks are included. The first and second blockswithstand the stresses driven by steam pressure and compression of the expandable plastic beads, supporting the mold cavity plates, whereby said cavity plates can be designed with reduced thickness, thus also improving their heat capacity and the need for steam and chilled water to heat and cool the cavity, together with the low thermal conductivity of any of the blocks, gives efficient thermal management with reduced steam consumption and cycle time of the method of using the molding tool, as mentioned below. Another advantage is that the conduits arranged to provide a cooling fluid to the mold cavity provide adequate mold cooling for optimized cycle time and avoid the cost and complexity of additional circuits to the molding tool since it remains integrated in the blocks. The invention is also a method of using a molding tool as described above,characterized in that it comprises the following steps in sequence: - purging air from the mold cavity: 1-2 seconds, - filling the mold cavity with expandable plastic beads through the filler that crosses the first block and the second hole: 8-12 seconds, - introduction of steam through the first conduit in the first block and the first hole and / or through the fourth conduit in the second block and the third hole in the mold cavity: 13-17 seconds, - maintenance of steam in the mold cavity: up to 20 seconds,-introduction of a cooling fluid into the mold cavity through the second conduit in the first block and / or the fifth conduit in the second block: up to 55 seconds; -ejection of the thus formed part: 2-4 seconds. The configuration of the molding tool allows these steps to provide an optimized cycle time of approximately 20% less than the time known in molding tools of the prior art. Further advantages with respect to the features of the dependent claims can be found below in the detailed description. BRIEF DESCRIPTION OF THE FIGURES This document is complemented by a set of exemplary drawings to illustrate the preferred embodiment,and which in no way limit the invention. Figure 1 is a section through a prior art molding tool. Figure 2 is a section through a molding tool of the present invention. Figure 3 is a section through one half of the molding tool of Figure 2 showing the block without a filler and including steam holes. Figure 4 is a partial section through the cavity plate and block showing the steam chamber. Figures 5 and 6 are details of the partial section of Figure 4 which also includes thermal insulating liners. Figure 7 is a partial section through the cavity plate and block showing the steam ducts,cooling and condensation and the chamber. Figure 8 is a top view of a block with three ducts. Figure 9 is a diagram of a block section with internal void areas and three ducts. Figure 10 is a top view of several blocks arranged in a contiguous arrangement configuring a 2x2 matrix. DETAILED EXPOSURE OF THE INVENTION Figure 1 represents a section of a molding tool of the state of the art, the piece, partially represented by sets of expandable plastic beads, is molded in a mold cavity (100), symmetrically doubled in the disclosed embodiment, each defined by two cavity plates (101,102) with a significant thickness to withstand the molding pressure to compress the expandable plastic beads introduced by the fillers (103) and the steam introduced under pressure to heat the mold cavity (100) and fuse the plastic beads. The usual wall thickness of these cavity plates (101, 102) in aluminum is in the range of 15 mm. The steam is conducted through steam chambers (104,105) and then through diffusers (106) or holes (107) located in at least one of the cavity plates (101,102), said introduction of steam being represented by small arrows. Each steam chamber (104,105) must be large enough to allow a homogeneous distribution of the steam. The metal cavity plates (101,102) also allow rapid heat conductivity to have a homogeneous temperature but due to their thickness and the mass of the support frames (108,109) require a significant amount of heat to reach the desired melting temperature of about 140°C. Typical thermal conductivity values ​​expressed in W / Km for metals are in the range of 20 for stainless steel or 100 for aluminum. In order to release the parts, they need to be cooled and this is done by projecting cold water through a circuit with a cooling duct with nozzles (110), which again requires a significant consumption of water to capture the thermal energy from the cavity plates (101,102) and support frames (108,109) and results in a long cycle time. The molding tool of the present invention is shown in Figures 2 to 4. Figure 2 represents a section of a molding tool for manufacturing parts from expandable plastic beads, represented by assemblies, comprising two halves, a first half (1) and a second half (2), the first half (1) comprising a first cavity plate (1.1),and the second half (2) comprises a second cavity plate (2.1), both cavity plates (1.1,2.1) of a metallic material and configuring a mold cavity (3) when the molding tool is in a closed state, as shown in figure 2, the first half (1) comprises a filler (4) arranged to allow the expandable plastic beads to be introduced into the mold cavity (3) through a second hole (1.12), in the embodiment two fillers (4) are shown; the first half (1) and the second half (2) each include heating means and cooling means as described below. The first half (1) also comprises a first block (1.3), figure 2, arranged to configure a first chamber (1.4) to the first cavity plate (1.1), the first block (1.3) includes a recess (1.31) arranged to allow the filler (4) to pass through it,the heating means of the first half (1) comprise a first conduit (1.2) in the first block (1.3) arranged to reach the first chamber (1.4) to accommodate the steam to be introduced into the mold cavity (3) through a first hole (1.11) in the first cavity plate (1.1), in figure 2 several first holes (1.11) are shown to have a uniform introduction, the cooling means of the first half (1) comprise a second conduit (1.5) in the first block (1.3), figure 7, arranged to provide a cooling fluid to the mold cavity (3). The second half (2) also comprises a second block (2.3), figure 3, arranged to configure a second chamber (2.4) to the second cavity plate (2.1),the heating means of the second half (2) comprise a fourth conduit (2.2) in the second block (2.3) arranged to reach the second chamber (2.4) to accommodate the steam to be introduced into the mold cavity (3) through a third hole (2.11) in the second cavity plate (2.1), several third holes (2.11) are shown in Figure 3 to have a uniform introduction, the cooling means of the second half (2) comprise a fifth conduit (2.5) in the second block (2.3), Figure 7, arranged to provide a cooling fluid to the mold cavity (3); the first block (1.3) and the second block (2.3) being made of a material with low thermal conductivity, equal to or less than 2 W / Km. The alternative in figure 3 is represented alone, configuring the second half (2) of the molding tool, but it is understood that it can be implemented with the first half (1) of figure 2 and then having the option "and" of two blocks, first (1.3) and second (2.3),in a molding tool. Any combination or intermediate solution is possible in the sense that, fulfilling the requirement of any of the blocks (1.3, 2.3), explained here, the other half (1, 2) of the molding tool can include any possible configuration, as in figure 1 where the second half (2) includes the fourth duct (2.2) arranged to reach the second chamber (2.4) to house the steam, which is not to be introduced into the mold cavity (3), there is no third hole (2.11) in the second cavity plate (2.1), since steam is used to heat said second cavity plate (2.1), which is not introduced into it, as is known in the state of the art. A specific characteristic about the thickness is that when the first block (1.3) is included, the first cavity plate (1.1) has an average thickness equal to or less than 6 mm; when the second block (2.3) is included,the second cavity plate (2.1) has an average thickness equal to or less than 6 mm. This thickness is approximately half of the molding tools of the prior art. In order to receive steam and / or condensed water from the mold cavity (3) at the end of the manufacturing process of a part, the first (1.2) and / or fourth steam conduit (2.2) can also operate in the reverse direction, represented by a double arrow in dashed lines in Figure 7. However, an alternative, when the first block (1.3) is included, it may include a third conduit (1.6), Figures 7-10, arranged to receive steam and / or condensed water from the mold cavity (3); when the second block (2.3) is included, it may include a sixth conduit (2.6), Figures 7-10, arranged to receive steam and / or condensed water from the mold cavity (3). Said circuits (1.6,2.6) avoid the cost and complexity of an additional circuit to the molding tool, as it is integrated into the blocks (1.3, 2.3). In short, this provides the advantage of including all the conduits normally required in this type of molding tool in a single block (1.3, 2.3), which is easier to manufacture and manage. As shown in Figures 7 and 8, each duct of the first block (1.3), first (1.2), second (1.5) and third (1.6), includes a main duct, first (1.21), second (1.51) and third (1.61) respectively, connected to an auxiliary duct, first (1.22), second (1.52) and third (1.62) respectively, any of the main ducts (1.21,1.51,1.61) being parallel to the mold cavity (3) and any of the auxiliary ducts (1.21,1.51,1.61) being perpendicular to the main ducts (1.21,1.51,1.61) and to the mold cavity (3), which is a usual configuration according to mold machining,but which is not limiting since any of the ducts, first (1.2), second (1.5) and third (1.6), could be a single duct being transversal to the mold cavity (3) or including more than two ducts or any other possible configuration. The same occurs with each duct of the second block (2.3), fourth (2.2), fifth (2.5) and sixth (2.6), with their respective main ducts, fourth (2.21), fifth (2.51) and sixth (2.61), connected to the respective auxiliary ducts, fourth (2.22), fifth (2.52) and sixth (2.62). Figure 8 shows the ducts (1.2,1.5,1.6,2.2,2.5,2.6) in top view, section at the height of the second (1.5) and fifth duct (2.5) -in continuous line-, showing that their route can be designed, for each of the blocks (1.3,2.3), to avoid any collision between them, also to balance the forces exerted by the fluids in their passage through the ducts. Another option, Figure 9,is that the first block (1.3) and / or the second block (2.3) include first internal void areas (1.8) or second internal void areas (2.8) respectively, in order to improve their insulating properties and reduce the material used and therefore the weight of the molding tool, also being more economical since less material is used and heat transmission is reduced since the void areas (1.8,2.8) are not heat conductors, thus acting as thermal insulation areas. Due to the complexity, additive manufacturing, such as 3D printing, could be suitable. The first cavity plate (1.1) and the first block (1.3) may be directly in contact with each other, not shown in the figures. Another option is that a first support rib (1.7), figures 2, 4-7, 9, and / or a second support rib (2.7), figures 2-7, 9, are arranged respectively between the first cavity plate (1.1) and the first block (1.3) to create the first chamber (1.4),between the second cavity plate (2.1) and the second block (2.3) to create the second chamber (2.4). This provides a support to withstand mechanical stresses, such as bending resistance, which also creates the chambers (1.4,2.4) to house the steam, the cavity plates (1.1,2.1) can be thinner, having a higher surface area / own volume ratio, which improves their thermal behavior, having faster heating and cooling. A support rib (1.7,2.7) is a minimum amount to provide support, however, as shown in the figures, several support ribs (1.7,2.7) can be included depending on the specific application. The support ribs (1.7,2.7) can be separate elements placed between the cavity plates (1.1,2.1) and the corresponding blocks (1.3,2.3), figure 2, 3, or integrated to any of these, for example to the corresponding cavity plate (1.1,2.1), figures 4-7, 9, being advantageous for the integration itself,which can be obtained by making the cavity plates (1.1,2.1) by laser sintering. One option, figures 5 and 6, on an insulating layer that prevents excessive heating of some surfaces that would limit the choice of materials to be used, is that when the first block (1.3) is included, said first block (1.3) includes a layer of a first heat-insulating coating (1.32) arranged to be in contact with the first support rib (1.7) or the first support rib (1.7) includes a second heat-insulating coating (1.71) arranged to be in contact with the first block (1.3); when the second block (2.3) is included,said second block (2.3) includes a layer of a third heat-insulating coating (2.31) arranged to be in contact with the second support rib (2.7) or the second support rib (2.7) includes a fourth heat-insulating coating (2.71) arranged to be in contact with the second block (2.3). The first block (1.3) provides sufficient support to the molding tool to be fixed directly to a machine platen, reducing the weight of the molding tool and the components associated with it; a possible drawback is the number of conduit connections, as many as circuits, that must be connected-disconnected when changing the molding tool. However, another option is that the molding tool may comprise a first frame (1.100,1.101,1.102) arranged to contain the first block (1.3). This provides the advantage of reducing the cost of the molding tool since said frame (1.100,1.101,1.102) can be used with different first blocks (1.3) and the cycle time for changing them is reduced since it only involves extracting a first block (1.3) with the cavity plate (1.1) and inserting another, making connections of ducts to the frame (1.100,1.101,1.102), not being necessary the connection-disconnection of the same when changing a molding tool. This also applies to the second block (2.3), in which the molding tool also comprises a second frame (2.100,2.101,2.102) arranged to contain the second block (2.3). Another option, Figure 10, which shows a diagram of the conduits (1.2,1.5,1.6,2.2,2.5,2.6) in Figure 8, is that when the first block (1.3) is included, several first blocks (1.3) are arranged together in a matrix arrangement, the first conduits (1.2) and the second conduits (1.5) arranged to provide continuity of conduction between adjacent first blocks (1.3); and / or when the second block (2.3) is included,a plurality of second blocks (2.3) are arranged together in a matrix arrangement, the fourth ducts (2.2) and the fifth ducts (2.5) arranged to provide conduction continuity between adjacent second blocks (2.3). Furthermore, this also applies to the third (1.6) and sixth ducts (2.6), when a plurality of first blocks (1.3) are arranged, it includes third ducts (1.6) arranged to receive steam and / or condensed water from the mold cavity (3) and to provide conduction continuity between adjacent first blocks (1.3); and / or when a plurality of second blocks (2.3) are arranged, it includes sixth ducts (2.6) arranged to receive steam and / or condensed water from the mold cavity (3) and to provide conduction continuity between adjacent second blocks (2.3). This provides a single inlet and outlet for each circuit, shown by arrows on the left of Figure 10,while offering the advantage of manufacturing a larger molding tool in a simple way by having a single block design (1.3,2.3) and repeating it as much as necessary. In order to close branches of ducts (1.2,1.5,1.6,2.2,2.5,2.6) that are left open and that lose some fluid, first plugs (1.9) can be included at the end of said branches for the first blocks (1.3) and second plugs (2.9) can be included at the end of said branches for the second blocks (2.3). A specific characteristic is that the distance (D), figure 4, between the center of two consecutive first holes (1.11) and / or two consecutive third holes (2.11) is between 4 and 6 mm. This is the proven range that provides a good steam distribution while maintaining a sufficient structural rigidity to have a robust and durable molding tool. Another specific characteristic is that the height (H), figure 4,of the first chamber (1.4) and / or the second chamber (2.4) is between 25 and 35 mm. This range is approximately half the height of prior art molding tools, a height that contributes to thermal efficiency since less steam volume is needed. Another detail is that the material of the first block (1.3) and / or the second block (2.3) is a polymer selected from polyetherimide (PEI) and polyetheretherketone (PEEK). These polymeric materials with high temperature resistance allow the molding tool to be easily manufactured with any of the aforementioned ducts (1.2, 1.5, 1.6, 2.2, 2.5, 2.6), and any internal void areas (1.8, 2.8), and also at a reduced cost, in contrast to metallic materials; as a preference, additive manufacturing methods, such as 3D printing, can be used with the inherent advantages; also a standard plastic injection procedure,whereby it can be manufactured on a large scale and at reduced costs or a combination of both if manufactured in different sections. The invention is also the method of using a molding tool as described above, comprising the following steps in sequence: - purging air from the mold cavity (3): 1-2 seconds, - filling the mold cavity (3) with expandable plastic beads through the filler (4) passing through the first block (1.3) and the second hole (1.12): 8-12 seconds, - introducing steam through the first conduit (1.2) in the first block (1.3) and the first hole (1.11) and / or through the fourth conduit (2.2) in the second block (2.3) and the third hole (2.11) in the mold cavity (3): 13-17 seconds, - maintaining steam in the mold cavity (3): up to 20 seconds,-introduction of a cooling fluid into the mold cavity (3) through the second conduit (1.5) of the first block (1.3) and / or the fifth conduit (2.5) of the second block (2.3): up to 55 seconds; -ejection of the piece thus formed: 2-4 seconds.,

Claims

CLAIMS 1.–Moulding tool for manufacturing parts from expandable plastic beads, comprising two halves, a first half (1) and a second half (2), the first half (1) comprising a first cavity plate (1.1), and the second half (2) comprising a second cavity plate (2.1), both cavity plates (1.1,2.1) of a metallic material and configuring a mould cavity (3) when the moulding tool is in a closed state, the first half (1) comprising a filler (4) arranged to allow the expandable plastic beads to be introduced into the mould cavity (3) through a second orifice (1.12); the first half (1) and the second half (2) each include heating means and cooling means; characterized in that the first half (1) also comprises a first block (1.3) arranged to configure a first chamber (1.4) to the first cavity plate (1.1), the first block (1.3) includes a recess (1.31) arranged to allow the filler (4) to pass through it, the heating means of the first half (1) comprise a first conduit (1.2) in the first block (1.3) arranged to reach the first chamber (1.4) to accommodate the steam to be introduced into the mold cavity (3) through a first hole (1.11) in the first cavity plate (1.1), the cooling means of the first half (1) comprise a second conduit (1.5) in the first block (1.3), arranged to provide a cooling fluid to the mold cavity (3); and / or the second half (2) also comprises a second block (2.3), arranged to configure a second chamber (2.4) to the second cavity plate (2.1), the heating means of the second half (2) comprise a fourth conduit (2.2) in the second block (2.3) arranged to reach the second chamber (2.4) to accommodate the steam to be introduced into the mold cavity (3) a. through a third hole (2.11) in the second cavity plate (2.1), the cooling means of the second half (2) comprise a fifth conduit (2.5) in the second block (2.3), arranged to provide a cooling fluid to the mold cavity (3); the first block (1.3) and the second block (2.3) being made of a material of low thermal conductivity, equal to or less than 2 W / Km 2. ​​Molding tool according to claim 1 wherein when the first block (1.3) is included, the first cavity plate (1.1) has an average thickness equal to or less than 6 mm; when the second block (2.3) is included, the second cavity plate (2.1) has an average thickness equal to or less than 6 mm.

3. Molding tool according to claim 1, wherein when the first block (1.3) is included, it includes a third conduit (1.6), arranged to receive steam and / or condensed water from the mold cavity (3); when the second block (2.3), this includes a sixth conduit (2.6), arranged to receive steam and / or condensed water from the mold cavity (3).

4. Molding tool according to claim 1 wherein, when the first block (1.3) is included, it includes first internal empty areas (1.8); when the second block (2.3) is included, it includes second internal empty areas (2.8) 5. Molding tool according to claim 1 wherein, when the first block (1.3) is included, a first support rib (1.7) is arranged between the first cavity plate (1.1) and the first block (1.3) to create the first chamber (1.4); when the second block (2.3) is included, a second support rib (2.7) is arranged between the second cavity plate (2.1) and. the second block (2.3) to create the second chamber (2.4).

6. Molding tool according to claim 5 wherein the first support rib (1.7) is an integral part of the first cavity plate (1.1).

7. Molding tool according to claim 5 wherein the second support rib (2.7) is an integral part of the second cavity plate (2.1).

8. Molding tool according to claim 5 wherein, when the first block (1.3) is included, said first block (1.3) includes a layer of a first heat-insulating coating (1.32) arranged to be in contact with the first support rib (1.7) or the first support rib (1.7) includes a second heat-insulating coating (1.71) arranged to be in contact with the first block (1.3); When the second block (2.3) is included, said second block (2.3) includes a layer of a third heat-insulating coating (2.31) arranged to be in contact with the second support rib (2.7) or the second support rib (2.7) includes a fourth heat-insulating coating (2.71) arranged to be in contact with the second block (2.3).

9. Molding tool according to claim 1, when the first block (1.3) is included, it also comprises a first frame (1.100,1.101,1.102) arranged to contain the first block (1.3); when the second block (2.3) is included, it also comprises a second frame (2.100,2.101,2.102) arranged to contain the second block (2.3).

10. Molding tool according to claim 1 wherein, when the first block (1.3) is included, it.

11. Molding tool according to claim 10, wherein when several first blocks (1.3) are arranged together in a matrix arrangement, the first ducts (1.2) and the second ducts (1.5) arranged to provide continuity of conduction between contiguous first blocks (1.3); when the second block (2.3) is included, several second blocks (2.3) are arranged together in a matrix arrangement, the fourth ducts (2.2) and the fifth ducts (2.5) arranged to provide continuity of conduction between contiguous second blocks (2.3).

11. Molding tool according to claim 10, wherein when several first blocks (1.3) are arranged, it includes third ducts (1.6) arranged to receive steam and / or condensed water from the mold cavity (3) and to provide continuity of conduction between contiguous first blocks (1.3); when several second blocks (2.3) are arranged, it includes sixth ducts (2.6) arranged to receive steam and / or condensed water from the mold cavity (3) and to provide continuity of conduction between adjacent second blocks (2.3).

12. Molding tool according to claim 1 wherein the distance (D) between the center of two consecutive first holes (1.11) and / or two consecutive third holes (2.11) is between 4 and 6 mm.

13. Molding tool according to claim 1 wherein the height (H) of the first chamber (1.4) and / or the second chamber (2.4) is between 25 and 35 mm.

14. Molding tool according to claim 1 wherein the material of the first block (1.3) and / or the second block (2.3) is a polymer selected from polyetherimide (PEI) and polyetheretherketone (PEEK).

15. Method of using a molding tool according to claim 1, characterized in that it comprises the following steps in sequence: - purging air from the mold cavity (3): 1-2 seconds, - filling the mold cavity (3) with expandable plastic beads through the filler (4) that passes through the first block (1.3) and the second hole (1.12): 8-12 seconds, - introduction of steam through the first conduit (1.2) in the first block (1.3) and the first hole (1.11) and / or through the fourth conduit (2.2) in the second block (2.3) and the third hole (2.11) in the mold cavity (3): 13-17 seconds, - maintenance of steam in the mold cavity (3): up to 20 seconds, - introduction of a cooling fluid into the mold cavity (3) through the second conduit (1.5) of the first block (1.3) and / or from the fifth duct (2.5) of the second block (2.3): up to 55 seconds; - ejection of the piece thus formed: 2-4 seconds.

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