Method and apparatus for producing a cellular molded body

Abstract

In a method and apparatus for producing a molded body made of foamed plastic from thermoplastic granules expanded in a mold cavity (4), which are blown under pressure into a mold cavity via filling injectors (6) and are subjected to steam and / or heated, causing the plastic granules to expand and fuse into a cellular molded body that completely fills the mold cavity, it is provided that the expanding plastic granules are blown in by a separate time- and / or volume-controlled activation of the at least two filling injectors (6), wherein the activation includes actuating valves (11, 15) in the compressed air supply (13) and / or in the nozzle outlet (8) of the filling injectors (6). Preferably, only one of the at least two filling injectors (6) is activated at any given time.

Description

[0001] The present invention relates to a method and a device for producing a molded body made of foamed plastic from thermoplastic granules expanded in a mold cavity, which are blown into a mold cavity under pressure via filling injectors and are exposed to steam and / or heated, so that the plastic granules expand and weld together to form a cellular molded body that completely fills the mold cavity.

[0002] Common filling injectors utilize the Venturi effect, which reduces the static pressure in a flowing fluid forced through a constriction in a pipe. A suction port at the constriction of the Venturi nozzle allows a secondary fluid to be drawn in. The plastic granules, preferably compressed in a storage container, are fluidized at the container outlet, enabling them to be drawn in by the filling injector and mixed with compressed air. For the production of large-volume and / or branched body structures, several continuously operated filling injectors are used, each fed sequentially with plastic granules from a storage container via a rotating perforated disc.

[0003] The object of the invention is to improve the method and the apparatus in such a way that delicate foam bodies, especially made of EPA (polyamide), can be manufactured flawlessly.

[0004] This problem is solved according to the invention in a method according to the preamble of claim 1 by blowing in the expanding plastic granules by means of a separate time- and / or volume-controlled activation of the at least two filling injectors, wherein the activation includes actuating valves in the compressed air supply and / or in the nozzle outlet of the filling injectors. In a device according to the preamble of claim 5, a control device is provided which activates the at least two filling injectors separately in a time- and / or volume-controlled manner, wherein valves in the nozzle outlet and / or the compressed air supply of the filling injectors are actuated. It should be expressly mentioned here that the invention is not limited to filling injectors based on the Venturi principle.

[0005] The invention is based on the understanding that when filling with multiple filling injectors, which are successively fed with plastic granules, those filling injectors that are temporarily not injecting particles not only introduce unladen air into the mold cavity, but also a higher air pressure than the filling injector that is simultaneously filling the mold cavity with particles. At the same time, the number and arrangement of vent openings through which air present in and injected into the mold cavity can escape are limited in the case of intricate mold cavities. The resulting overpressure slows the flow velocity of the particles, so that particles with a higher density, such as EPA (polyamide), can no longer reach the branched areas of intricate mold cavities, particularly away from the injection point.

[0006] Because the temporarily deactivated filling injectors do not introduce compressed air, the particles injected during this time can reach and fill even remote areas, particularly in complex mold cavities. Especially delicate areas, where the thinnest wall thicknesses are comparable to the particle size of the plastic granules, can be flooded by the high-speed flowing particles. The particles are elastically deformed and forced into the narrow gaps, sometimes even through them. This also results in lower compressed air consumption.

[0007] By separately activating the filling injectors based on time and / or volume, it is possible to selectively influence the filling of the mold cavity, so that certain areas are prioritized and / or a defined filling sequence and thus filling profile can be set. A subgroup of filling injectors can be formed and controlled together.

[0008] Preferably, during activation, the valves in the nozzle outlet of the filling injectors are actuated. This prevents any particles from being flushed from the mold cavity into the granulate feed through a deactivated injector.

[0009] In a preferred further embodiment, it is provided that at least one of the at least two filling injectors is always deactivated.

[0010] In a preferred embodiment, only one of the at least two filling injectors is activated at any given time. This ensures that the filling injectors do not interfere with each other. Preferably, the at least two filling injectors are activated alternately multiple times.

[0011] The filling process can also be precisely controlled by making the operating pressure and / or flow rate of at least two filling injectors separately adjustable and / or controllable. Operating pressure refers to the pressure at which the compressed air is applied to the inlet of the filling injector.

[0012] In a preferred further embodiment, it is provided that the activation also includes the actuation of valves in the granule supply of the filling injectors.

[0013] The claim concerns a molded body produced according to the method of any one of claims 1 to 5 and / or with a device according to claim 6 or 7 from foamed plastic made of thermoplastic polymer granules expanded in a mold cavity. In particular, it is produced from an expanded polyamide (EPA). Specifically, the molded body is a cellular displacement body which reduces the flow space and / or the filling volume for a fluid in a fluidic system.

[0014] Further advantages and details of the invention can be found in the following description of the figures. Individual technical features of the embodiment described below can also be combined with previously described embodiments as well as the features of the independent claims and any further claims to form objects according to the invention. Where appropriate, functionally equivalent elements are provided with identical reference numerals. The figures show... Fig. 1 schematically a device for producing a molded body from foamed plastic; Fig. 2 a cellular displacement body.

[0015] The device 1 comprises a storage container 2 for expandable plastic granules such as EPS (polystyrene), EPP (polypropylene), EPE (polyethylene), EPA (polyamide), ETPU (thermoplastic polyurethane), a molding tool 3 that defines a mold cavity 4, and several lines 5 that lead from the storage container 2 to the molding tool 3.

[0016] The plastic granules, which can be fluidized in the storage container 2 by air nozzles (not shown), reach the suction connection 9 of three filling injectors 6 via the lines 5, which lead into injection points 12 of the mold 3.

[0017] The filling injectors 6 are connected to a compressed air source 14 via compressed air lines 13. The compressed air entering the inlet 7 of the filling injectors 6 flows through a constriction 10 and, according to the Venturi effect, creates a vacuum at the suction port 9, so that plastic granules are drawn in, mixed with the compressed air and finally blown into the mold cavity 4 via the injection points 12.

[0018] The filling injectors 6 have a valve 11 in the outlet 8, in the form of a needle valve system. A valve 15 is also located in each of the compressed air lines 13. The valves 11 and 15 are connected to a control unit 16, which activates the filling injectors 6 separately according to time and / or the volume of particles injected by opening and closing the valves 11 and 15 accordingly. Specifically, the filling injectors 6 are activated sequentially, so that of the three filling injectors 6, only one injector is activated at any given time to inject a defined partial volume of plastic granules. Fig. In step 1, the middle filling injector 6 is activated, as indicated by the open valves 11 and 15, while the other two filling injectors in outlet 8 and their associated valves 15 are closed and thus deactivated. Once the filling process at the mold 3 is complete, the valves 15 in the compressed air lines 13 close with a time delay relative to the valves 11 in outlet 8 of the filling injectors 6, allowing the compressed air to flush particles from the filling injectors 6 and lines 5 back into the reservoir 2.

[0019] After filling, the introduced plastic granules are exposed to hot steam, which is supplied to the mold via steam lines 17 from a steam generator 18. This causes the plastic to swell and fuse to form the desired molded part. For uniform circulation and purging, the steam is directed into an additional chamber (not shown) surrounding the mold cavity, which is connected to the mold cavity 4 via small air-permeable openings. Air present in the mold cavity 4 and air blown in, followed by the steam, escapes through these openings. The flow in and out, particularly to maintain steam pressure, is controlled by valves 19.

[0020] Fig.Figure 2 shows a section of a cellular displacement body 20, which can be produced from expanded polyamide (EPA) using the device 1 and according to the claimed method. This polyamide exhibits higher strength and resistance compared to conventional foam plastics such as EPS (polystyrene), EPP (polypropylene), or EPE (polyethylene) and is therefore better suited for technically demanding applications. The highly branched, filigree displacement body 20 has fully formed areas with a thin wall thickness of less than 1 mm. The displacement body 20 is used in battery modules to at least partially fill the space between axially parallel and spaced-apart circular cylindrical battery cells. This allows for savings in temperature control fluid. Reference symbol list 1 Device 2 storage containers 3 Forming tool 4 Mold cavity 5 lines 6 Filling injector 7 Admission 8 Outlet 9 Suction port 10 Narrowing 11 valve 12 Injection point 13 Compressed air line 14 Compressed air source 15 valve 16 Control unit 17 Steam pipe 18 Steam generator 19 valve 20 displacement bodies

Claims

[1] Method for producing a molded body from foamed plastic from thermoplastic plastic granules expanded in a mold cavity (4), comprising the steps: • Blowing an expandable plastic granulate under pressure into the mold cavity (4) via at least two filling injectors (6), • Applying steam to the filled mold cavity (4) and / or heating the plastic granules, • wherein the plastic granules expand and weld together to form a molded body that completely fills the mold cavity (4), • wherein the air present and blown into the mold cavity (4) as well as the water vapor flow out through at least one opening (19) leading to the outside, characterized by , • that the expanding plastic granules are blown in by a separate time- and / or volume-controlled activation of the at least two filling injectors (6), • wherein the activation includes actuating valves (11, 15) in the compressed air supply (13) and / or in the nozzle outlet (8) of the filling injectors (6). [2] Method according to claim 1, characterized by , that of the at least two filling injectors (6) at least one filling injector is always deactivated. [3] Method according to claim 1 or 2, characterized by , that only one of the at least two filling injectors (6) is activated at any given time. [4] Method according to any one of claims 1 to 3, characterized by , that the operating pressure and / or the volume flow of the at least two filling injectors (6) is separately adjustable and / or controllable. [5] Method according to any one of claims 1 to 4, characterized by , that the activation includes actuating valves in the granule supply of the filling injectors (6). [6] Device (1) for producing a molded body made of foamed plastic from thermoplastic plastic granules expanded in a mold cavity (4), comprising • a molding tool (3) with at least one mold cavity (4), • which can be filled under pressure with expandable thermoplastic polymer granules via at least two filling injectors (6), • wherein the filled mold cavity (4) can be exposed to steam and / or heated to heat the plastic granules in order to cause expansion and welding of the plastic granules, • wherein the mold cavity (4) has at least one opening (19) leading outwards through which the air present and blown into the mold cavity (4) and the water vapor can escape, characterized, • by a control device (16) which activates the at least two filling injectors (6) separately in a time- and / or volume-controlled manner, • wherein valves (11, 15) in the nozzle outlet (8) and / or the compressed air supply (13) of the filling injectors (6) are actuated. [7] Device according to claim 6, characterized by , that the control unit (16) always activates only one of the at least two filling injectors (6). [8] Molded body which is produced according to the method of any one of claims 1 to 5 and / or with a device according to claim 6 or 7 from foamed plastic made from thermoplastic plastic granules expanded in a mold cavity (4). [9] Molded body according to claim 8, characterized by that the molded body is made of expanded polyamide (EPA). [10] Molded body according to claim 8 or 9, characterized by , that the shaped body is a cellular displacement body (20) which reduces the flow space and / or the filling volume for a fluid in a fluidic system.

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