Mould for injecting thermoplastics and method for using said mould
Mould for producing plastic items obtained by the injection of thermoplastic material of the “hot melt” or polyamide type, the mould being made of flexible vulcanised silicone, rubber or other elastomers, the mould being formed by two parts which, when facing each other and attached, generate a series of compartments and channels that allow for the introduction of the melted thermoplastic material and the filling of the cavities with the shape of the item desired, and, in turn, allow for a vacuum to be generated, also removing the inside air from the mould by means of a series of conduits and channels; and a method or methodology for producing said plastic items by means of said mould, allowing for the reproduction of short and medium series of items produced with plastic materials, and in which a control system and a mould incorporating a means to be identified can be added to the method.
1. A mould for injecting thermoplastics, subjected to a pressure injection, wherein the mould is formed by an upper mould or lid, and a lower mould or base, wherein the mould is made of flexible vulcanised silicone, rubber or other elastomers with a Shore A hardness between 30 and 90, and wherein, when the upper mould and the lower mould are facing each other and attached by fasteners or brackets, a distribution chamber for melted thermoplastic material is generated which is supplied by a central, a reinforced pass through opening on the upper mould with a sealed coupling to sealingly couple to an injection system, and a plurality of distribution channels exit from the distribution chamber, which are connected to cavities by feeders with the shape of the item that is to be manufactured, and wherein tiny slots emerge from each cavity, which are connected to a perimetral vacuum channel having a vacuum outlet pass through opening on the lower mould, with a sealed coupling to sealingly couple to a vacuum system, wherein air is removed via the tiny slots that have a miniscule cross-section such that melted thermoplastic material cannot pass through the tiny slots but the air can pass through the tiny slots to the vacuum channel.
2. The mould according to claim 1 , wherein the upper mould or lid has a reinforcement flange on the central part of the external side designed for the sealed coupling to an injection system.
3. The mould according to claim 1 , wherein the lower mould or base has a central reinforcement area on the external side designed for the sealed coupling to an injection system.
4. The mould according to claim 1 , wherein the slots have a variable cross-section, wherein the variable cross-section increases along the slot between the cavity and the vacuum channel.
5. The mould according to claim 1 , wherein the mould incorporates a code or other elements in order for said mould to be able to be identified by a control system.
6. The mould according to claim 1 , wherein the reinforced pass through opening and the vacuum outlet pass through opening are on the same part of the two parts that make up the mould.
7. The mould according to claim 1 , wherein the two parts of the mould are asymmetrical.
8. A method for using a mould for injecting thermoplastics in a pressure injection process for the manufacturing of plastic items, the method comprising:
introducing a thermoplastic material into a process supply unit;
heating the thermoplastic material to a melt temperature of the thermoplastic material;
placing and attaching a flexible mould between two platforms of a pressure injection system, via a sealed coupling, wherein the two platforms close said mould by a pressure closure, wherein this pressure closure is variable and determined by a control system;
injecting the thermoplastic material into the mould through an injection nozzle that introduces the thermoplastic material as a melted material from a reservoir into an internal reception chamber of the mould;
whilst the mould is being filled with the melted material, and also prior thereto, removing inside air from the mould by a vacuum system, which comprises a vacuum conduit that connects, via a sealed coupling, a vacuum outlet point of the mould to an external vacuum pump of the vacuum system, wherein the air is removed via tiny slots that have a miniscule cross-section such that the melted thermoplastic material cannot pass through the tiny slots but the air can pass through the tiny slots to the vacuum conduit;
once the mould has been filled, opening and relieving pressure that closes the mould, allowing the free mould to cool down;
separating the mould by separating an upper mould or lid, from a lower mould or base, and removing parts generated in cavities;
wherein the method further comprises:
controlling, by the control system:
the injection pressure of the thermoplastic material into the flexible mould;
stopping injection into the mould when the stipulated pressures, the closing pressure of the mould closing system, and/or the pressure of the resistance of said flexible mould, are exceeded;
controlling a device for heating the thermoplastic material,
controlling the operation of the vacuum system, before and during the injection process,
controlling velocity or flow of the material and the temperature of the mould,
controlling the mould closing system and the minimum solidification times until said closing system are opened,
performing a manual or automatic regulation of:
the injection pressure,
the material inlet rate,
the temperature to which the thermoplastic material is heated, and
the temperature at which the mould is heated,
the operation of the vacuum system,
the closing pressure of the flexible mould, and
the time during which the flexible mould will remain closed for the solidification of the thermoplastic material.
9. The method for injecting thermoplastics, according to claim 8 , wherein injecting the thermoplastic material comprises injecting the thermoplastic material such that a temperature of the injected thermoplastic material ranges between 180° C. and 250° C.
10. The method for injecting thermoplastics, according to claim 8 , wherein allowing the free mould to cool down comprises allowing the free mould to cool down to room temperature.
11. The method for injecting thermoplastics, according to claim 8 further comprising incorporating a mould identification phase in order for the control system to be able to determine the characteristics of the mould.
12. The method for injecting thermoplastics, according to claim 8 further comprising implementing an automatic introduction of selected moulds by an automated carousel system that takes the selected moulds to an injection position in a selected order.