Device and method for producing a particle foam part

Abstract

The invention relates to an apparatus and a method for the production of a particle foam part, wherein a mould cavity (5) is filled with foam particles, the foam particles are welded into a particle foam part and the particle foam part is cooled down in the mould. The foam particles are heated by means of a ceramic body (17) with integrated resistance heating and by the application of electromagnetic waves.

Claims

1. Apparatus for producing a particle foam part comprising: a mould for bounding a mould cavity for holding foam particles; a heating device for welding the foam particles into a particle foam part, the heating device including: a ceramic body with an integrated resistance heating wire made from electrically conductive ceramic components or semi-conductive ceramic components for heating the mould; and a generator to supply the mould cavity with electromagnetic waves.

2. The apparatus according to claim 1, wherein a cooling body with channels through which a cooling medium may be fed is connected to the ceramic body.

3. The apparatus according to claim 1, wherein the mould has two mould halves, wherein the ceramic body is connected to a first mould half or the ceramic body forms the one mould half.

4. The apparatus according to claim 3, wherein a second mould half is made of a plastic body and has a capacitor plate adjacent to the second mould half, wherein the plastic body may be of materials with differing permittivity and/or varying thickness and/or provided with electrically conductive bodies and/or the capacitor plate may be contoured so as to form an electrical field of the electromagnetic waves.

5. The apparatus according to claim 3, wherein the first mould half to which the ceramic body is connected is made of metal.

6. The apparatus according to claim 1, wherein the mould has two mould halves, wherein both mould halves are connected to one such ceramic body, or two ceramic bodies each form one of the mould halves.

7. The apparatus according to claim 1, wherein two cooling bodies of an electrically conductive material are provided, and are connected to the generator to apply electromagnetic waves to the mould cavity.

8. The apparatus according to claim 1, wherein the conductive or semi-conductive ceramic components have metal-like carbides (ZrC, TiC) or nitrides ((TiN, TaN) or silicon carbide, boron carbide or titanium sub-oxide.

9. The apparatus according to claim 1, wherein the mould is a crack gap mould.

10. The apparatus according to claim 1, wherein a mould half is a plastic body made of a plastic which is substantially transparent to electromagnetic waves.

11. The apparatus according to claim 1, wherein the ceramic body is substantially transparent to electromagnetic waves.

12. The apparatus according to claim 1, wherein a mould half of the mould is a plastic body made of a plastic which is substantially transparent to the electromagnetic waves.

Description

(1) The invention will be explained in detail by way of example with the aid of the drawings, which show in:

(2) FIG. 1 a schematic view of an apparatus for the production of a particle foam part, in which a mould of this apparatus is arranged in a crack gap position

(3) FIG. 2 the apparatus of FIG. 1, with the mould arranged in an end position, and

(4) FIG. 3 a schematic view of an apparatus for the production of a particle foam part, in which a mould is provided with two mould halves, each made of plastic.

(5) An apparatus 1 for the production of a particle foam part comprises a mould 2, a material container 3 and a pipe 4 leading from the material container 3 to the mould 2. Through the pipe 4, foam particles may be fed to the mould 2 and are introduced into a mould cavity 5 bounded by the mould 2 (FIGS. 1, 2).

(6) The mould 2 is made of two mould halves 6, 7, designated below as the quality mould half 6 and the functional mould half 7. In FIGS. 1 and 2, the quality mould half 6 is arranged below the functional mould half 7. The arrangement of the mould halves may however also be switched or rotated as desired (for example rotated through 90°).

(7) The functional mould half 7 is made of a metal body with a base 8 and a continuous side wall 9. Formed in the side wall 9 are through holes 10, 11, which serve to feed the foam particles into the mould cavity 5 or to vent the mould cavity 5. One through hole 10 is connected to the pipe 4 leading from the material container 3.

(8) The base 8 and the side wall 9 bound a hollow space and the mould cavity 5 respectively. The surface of the latter is in the form of the quality surface 12. In the present embodiment, the quality surface 12 is milled and has a very smooth surface.

(9) The functional mould half 7 is a plastic body made of a plastic which is substantially transparent to electromagnetic waves, such as e.g. polytetra-fluoroethylene (PTFE), polyethylene, in particular UHMWPE, polyether-ketone (PEEK) and other materials transparent to RF radiation. The plastic body may be a monolithic plastic body. It may however also be made of several plastics, in particular of several plastic layers. In particular it is expedient to make the surface of the functional mould half 7 which faces the quality mould half 6 out of a plastic layer which absorbs electromagnetic waves and by this means is heated.

(10) The functional mould half 7 forms a punch, which is able to dip a short distance into the hollow space bounded by the quality mould half 6 and closes flush with the upper and free edge 21 of the continuous side wall 9 of the quality mould half 6. A gap formed between the free edge of the continuous 9 and the opposite surface of the functional mould half 7 facing this edge is smaller than the smallest foam particles usually fed to the mould cavity 5, so as to ensure that no foam particles can escape from the mould cavity 5.

(11) Formed at the side of the functional mould half 7 facing away from the quality mould half 6 is a continuous collar 13 which, with full insertion of the functional mould half 7, lies on top of the quality mould half 6 at the upper edge of the side wall 9 of the quality mould half 6 (FIG. 2).

(12) In the area of the collar 13, a continuous metal ring 14 is integrated in the functional mould half 7. In the present embodiment, the metal ring 14 is continuous. It may however extend over one or more circumferential segments or be omitted altogether.

(13) Located on the side of the functional mould half 7 facing away from the quality mould half 6 is a capacitor plate 15. In the present embodiment, the capacitor plate 15 is permanently connected to the functional mould half 7.

(14) The capacitor plate 15 and the quality mould half 6 are each connected to a generator 16 for the generation of electromagnetic waves. The generator 16 is designed to generate RF radiation at a frequency of 27.12 MHz.

(15) The metal ring 14 shortens the distance between the electrically conductive quality mould half 6 and the capacitor plate 15, thereby leading to a compression of the electrical field. By this means, greater energy density is created in the edge area of the mould cavity 5, leading to correspondingly more powerful melting of the foam particles. This results in good edge formation on the finished particle foam part.

(16) Connected to the side of the quality mould half 6 facing away from the functional mould half 7 is a ceramic body 17 with integrated resistance heating wiring. The resistance heating wiring is connected to a power source 18 so that the ceramic body may be heated electrically and can form resistance heating wiring.

(17) Provided on the side of the ceramic body 17 facing away from the quality mould half 6 is a cooling body 19 which has several cooling channels 20, through which may flow a cooling medium such as for example water.

(18) The operation of the apparatus 1 in producing a particle foam part is explained below.

(19) The mould 2 is firstly arranged with its two mould halves 6, 7 in a crack gap position (FIG. 1), in which the functional mould half 7 closes flush with the free edge 21 of the quality mould half 6, but the two mould halves 6, 7 are far enough apart from one another that the through holes 10, 11 open out freely in the mould cavity 5.

(20) Foam particles are fed from the material container 3 through the pipe 4 to the mould cavity 5.

(21) When the mould cavity 5 is completely filled with foam particles, then the two mould halves 6, 7 are pressed together into the end position (FIG. 2). For this purpose a press (not illustrated) is used. The two mould halves 6, 7 are held in the end position by the press. In the end position the two through holes 10, 11 are covered by the functional mould half and therefore closed.

(22) By means of the generator 16, RF radiation is then applied to the mould cavity 5 and at the same time, by means of the power source 18, the ceramic body 17 and with it the quality mould half 6 are heated. Since the ceramic body 17 and the quality mould half 6 made of metal are each good heat conductors, the foam particles in contact with the quality mould half 6 are heated with similar rapidity, like the foam particles in the interior of the mould cavity 5, which are heated especially by the electromagnetic radiation. Very even heating is therefore obtained at the interface with the quality mould half 6 and in the interior of the mould cavity 5. This results in a very homogenous welding of the foam particles and a particle foam part of high quality.

(23) It is also possible for the quality mould half 6 to be heated for a short time to a temperature which lies above the temperature of the foam particles in the rest of the mould cavity 5. This leads to melting of the foam particles and of the particle foam part respectively at the surface in contact with the quality mould half 6.

(24) After the heating process, the mould 2 is cooled down. For this purpose the electromagnetic radiation produced by the generator 16 and the heating current generated by the power source 18 are switched off, and cooling medium is fed through the cooling channels 20 of the cooling body 19. By this means, the quality mould half 6 in particular is cooled down very rapidly, since the metal quality mould half 6 and the ceramic body 17 are good heat conductors, so that heat can be conducted away quickly through the cooling body 19. If during the heating phase, the surface of the particle foam part adjacent to the quality mould half 6 was melted, then it solidifies quickly and takes exactly the shape of the surface of the quality mould half 6. In this way a particle foam part is produced which has a high quality surface and is made exactly complementary to the surface of the quality mould half 6.

(25) In principle, due to the layered structure of the quality mould half 6, the ceramic body 17 and the cooling body 19, heat may be conducted away from the mould cavity 5 very quickly, making it possible to produce large-area and large-volume particle foam parts efficiently. In addition, a temperature profile may be implemented very precisely in the particle foam part, making it possible to produce particle foam parts from plastic materials with very specific temperature requirements.

(26) Moreover, in such an apparatus, the foam particles may be heated to high temperatures of for example above 150° C., above 190° C., above 200° C. and in particular above 250° C. Because of this it is possible to use plastic materials which melt only at high temperatures and are corresponding thermally-stable. The particle foam parts made from these materials have correspondingly high thermal stability and may undergo further processing steps in which they are subjected to high temperatures which foam particles of polystyrol or polypropylene could not withstand.

(27) After cooling down of the mould, the two mould halves 6, 7 are moved apart from one another and the finished particle foam part is removed.

(28) A second embodiment of an apparatus 1 for the production of a particle foam part will be explained below. Identical parts are given the same reference number as in the first embodiment. Unless otherwise stated below, the statements made for the first embodiment apply equally for the same parts of the second embodiment.

(29) The apparatus 1 for the production of a particle foam part again includes a mould 2, a material container 3 (not shown) and a pipe (not shown) leading from the material container to the mould 2. The mould 2 has two mould halves 7/1 and 7/2, each made of plastic. They may each be in the form of a monolithic plastic body. Preferably though, they are made of different plastic bodies. For example the surface bordering a mould cavity 5 may be made of a plastic material which absorbs electromagnetic waves, and the remaining area of the mould halves 7/1, 7/2 of a material which does not absorb electromagnetic waves. By this means, the mould halves 7/1, 7/2 are heated at their edge areas adjoining the mould cavity 5 when electromagnetic waves are applied.

(30) In this embodiment, a ceramic body 17/1, 17/2 is connected to each of the two mould halves 7/1, 7/2. The ceramic bodies 17/1, 17/2 are designed just like the ceramic body 17 of the first embodiment and are connected to a power source 18. By applying a suitable current, the ceramic body 17/1, 17/2 may be heated by means of resistance heating. In the present embodiment a common power source 18 is provided for both ceramic bodies 17/1, 17/2. It is however also possible to provide two independent power sources, so that the two ceramic bodies 17/1, 17/2 may be heated independently of one another.

(31) At the side of the ceramic bodies 17/1, 17/2 facing away from the mould halves there is in each case a cooling body 19/1, 19/2 with cooling channels 20. The cooling bodies are designed exactly as in the first embodiment and are made of an electrically conductive material, such as e.g. aluminium or copper or a corresponding metal alloy. The cooling bodies 19/1, 19/2 are connected to a generator 16. The generator 16 is designed to generate RF radiation at a frequency of 27.12 MHz. The cooling bodies 19/1, 19/2 thus act as capacitor plates, in order to apply an electromagnetic field to the mould cavity 5.

(32) The second embodiment may be used in the same manner as the first embodiment.

(33) In the present second embodiment, the cooling bodies 19/1, 19/2 are located outside the ceramic bodies 17/1, 17/2 with reference to the mould cavity 5. In the context of the invention it is possible for the arrangement of the cooling bodies and the ceramic bodies to be exchanged, so that the cooling body is closer to the mould cavity 5 than the respective ceramic body. If the ceramic body is arranged closer to the mould cavity, then heating of the foam particles may be effected more quickly than if the ceramic body is located outside the cooling body. If the cooling body is arranged closer to the mould cavity 5 than the ceramic body, then the cooling down of the mould may be effected more rapidly than if the cooling body is located outside the ceramic body. Depending on whether it is more important for the heating of the foam particles in the mould cavity 5 to take place more quickly or for the cooling to be effected more quickly, the ceramic body or the cooling body is to be arranged closer to the mould cavity 5.

(34) In principle it applies that the representation of FIGS. 1 to 3 is not true to scale. If the mould halves are made of plastic, then it is advantageous for them to be as thin-walled as possible, so that the heat conduction path between the mould cavity 5 and the ceramic body is as short as possible.

(35) Each of the ceramic bodes of the present embodiment has integrated resistance heating wiring. The ceramic bodies are insulating in their peripheral area, so that the resistance heating wiring is electrically insulated from the adjacent cooling body. If the whole of the ceramic body is electrically conductive, then it may also be expedient to provide a separate insulating layer between the cooling body and the ceramic body.

(36) In a further alternative embodiment, the ceramic body or bodies may also form the relevant mould halves. The ceramic bodies then have a complementary shape on one side, corresponding to the particle foam part to be produced.

(37) The cooling bodies 19/1, 19/2 which are connected to the generator 16, may be cooled by water which, as cooling medium, is fed through the cooling channels 20. It may however also be expedient to use cooling media based on oil, which is electrically insulating to avoid discharging electrical charges in an undesired manner.

LIST OF REFERENCE NUMBERS

(38) 1 apparatus 2 mould 3 material container 4 pipe 5 mould cavity 6 mould half (quality-) 7 mould half (functional-) 8 base 9 side wall 10 through hole 11 through hole 12 quality surface 13 collar 14 metal ring 15 capacitor plate 16 generator 17 ceramic body 18 power source 19 cooling body 20 cooling channel 21 free edge