Apparatus and method for the production of a particle foam part

Abstract

The present invention relates to an apparatus and a method for the production of a particle foam part. The apparatus has a mold 2 with a mold cavity 3, a steam generator 12 to generate steam for feeding into the mold cavity for the thermoplastic welding into a particle foam part of foam particles present in the mold cavity 3, a feed pipe 10, 11 for the feeding of steam to the mold, wherein a controllable steam valve 13, 14 is provided in the feed pipe, and a pressure sensor 15, 16 is located in the area between the steam valve and the mold, in order to measure the pressure of the supplied steam. A control device 23 controls pressure over time according to to a predetermined profile, wherein the profile has a ramp, in order to increase pressure gradually within a predetermined period of time from an initial value to an end value.

Claims

1. A method for the production of a particle foam part comprising the following: feeding foam particles into a mold cavity of a mold while applying a partial vacuum to the mold, wherein polyurethane-based (eTPU) foam particles are used; and thermoplasticly welding the foam particles in the mold to form a particle foam part, under a supply of steam, as the steam is introduced in the mold, a partial vacuum is applied, wherein the pressure of the steam is initially fed at low pressure, which facilitates flow through the mold cavity and the expulsion of air while continuing to introduce steam with a ramp having an increasing rate that allows welding of the inner zone of the foam part before skinning over of the foam part can occur.

2. The method according to claim 1, comprising the following: feeding foam particles into a mold cavity of a mold, wherein the foam particles are introduced into the mold either by crack split filling, pressure filling or counter-pressure filling; and thermoplasticly welding the foam particles in the mold to form a particle foam part, under a supply of steam, wherein the pressure of the steam is increased gradually.

3. The method according to claim 2, comprising the following: feeding foam particles into a mold cavity of a mold, wherein a mold is used which, in the closed state, has a volume of at least 0.5 m.sup.3.

4. The method according to claim 3, wherein the pressure of steam increased during the ramp is varied at a mean rate of between 0.01 bar/s and 2 bar/s.

5. The method according to claim 4, wherein a mold is used which has two mold halves, with each mold half being encompassed by a separate steam chamber, and with steam being fed into each steam chamber by means of a steam valve connected to a control device, and fitted in each steam chamber or in a corresponding feed pipe is in each case a pressure sensor, which is connected to the control device, and each steam chamber has a condensate valve to take steam away from the steam chamber, wherein firstly steam is fed at low pressure to the first of the two mold halves via the corresponding first steam chamber the steam is initially fed, which facilitates flow through the mold cavity and the expulsion of air while continuing to introduce steam at a rate that allows welding of the inner zone of the foam part before skinning over of the foam part can occur and at the second steam chamber the condensate valve is opened so that air expelled from the mold cavity may flow out and next, steam is fed to the second mold half via the second steam chamber the steam is initially fed, which facilitates flow through the mold cavity and the expulsion of air while continuing to introduce steam at a rate that allows welding of the inner zone of the foam part before skinning over of the foam part can occur and the condensate valve in the first steam chamber is opened so that air expelled from the mold cavity can flow away.

6. The method according to claim 5, wherein for crack steaming and/or for rinsing or cross-steaming of the mold cavity and/or for autoclaving of the foam particles present in the mold cavity, steam is fed to the mold cavity, with the pressure of the steam which facilitates flow through the mold cavity and the expulsion of air while continuing to introduce steam at a rate that allows welding of the inner zone of the foam part before skinning over of the foam part can occur.

7. The method according to claim 6, wherein the ramp is a linear rising ramp, a single or multiple curved ramp, a stepped, a parabolic or an exponentially rising ramp.

8. The method according to claim 7, wherein the foam particles are fed to the mold with the addition of water, in particular under a supply of steam.

9. The method according to claim 3, wherein the pressure of steam increased during the ramp is varied at a mean rate of between 0.01 bar/s and 2 bar/s.

10. The method for the production of a particle foam part according to claim 1, comprising the following: feeding foam particles into a mold cavity of a mold, wherein a mold is used which, in the closed state, has a volume of at least 0.5 m.sup.3.

11. The method according to claim 1 wherein a mold is used which has two mold halves, with each mold half being encompassed by a separate steam chamber, and with steam being fed into each steam chamber by means of a steam valve connected to a control device, and fitted in each steam chamber or in a corresponding feed pipe is in each case a pressure sensor, which is connected to the control device, and each steam chamber has a condensate valve to take steam away from the steam chamber, wherein firstly steam is fed to the first of the two mold halves via the corresponding first steam chamber, which facilitates flow through the mold cavity and the expulsion of air while continuing to introduce steam at a rate that allows welding of the inner zone of the foam part before skinning over of the foam part can occur and at the second steam chamber the condensate valve is opened so that air expelled from the mold cavity may flow out and next, steam is fed to the second mold half via the second steam chamber, which facilitates flow through the mold cavity and the expulsion of air while continuing to introduce steam at a rate that allows welding of the inner zone of the foam part before skinning over of the foam part can occur and the condensate valve in the first steam chamber is opened so that air expelled from the mold cavity can flow away.

12. The method according to claim 1, wherein for crack steaming and/or for rinsing or cross-steaming of the mold cavity and/or for autoclaving of the foam particles present in the mold cavity, steam is fed to the mold cavity.

13. The method according to claim 1, wherein the ramp is a linear rising ramp, a single or multiple curved ramp, a stepped, a parabolic or an exponentially rising ramp.

14. The method according to claim 1, wherein the foam particles are fed to the mold with the addition of water, in particular under a supply of steam.

Description

(1) The invention is explained in detail below, by way of example, with the aid of the drawings. The drawings show in simplified schematic form in:

(2) FIG. 1 an apparatus for the production of a particle foam part in a block diagram

(3) FIG. 2 a section through two steam chambers containing a mold

(4) FIG. 3 a section along the line A-A in FIG. 2

(5) FIGS. 4a-4d diagrams of different ramps, and

(6) FIG. 5 the course of a target value and actual value of the pressure with which the steam is supplied, in an apparatus according to the prior art.

(7) An apparatus 1 for the production of a particle foam part has a mold 2 made up of two mold halves 2/1 and 2/2 (FIG. 1). The mold halves 2/1 and 2/2 are generally a positive mold and a negative mold (not shown), in order to give a predetermined shape to the particle foam part to be produced. A mold cavity 3 is bounded by the mold 2 and the positive mold and negative mold located therein.

(8) Leading into the mold cavity 3 is a filling injector 4, by means of which foam particles from a material container may be fed via a pipe into the mold cavity 3. Provided at the material container and/or at the pipe is preferably a water or steam supply for wetting the foam particles to be conveyed to the mold. In this way, the conveyance properties of the eTPU foam particles may be significantly improved, and any blockage of the pipe or the filling injector is prevented. Connections may also be provided at several points along the conveyance path, in order to supply water or steam.

(9) The filling injector 4 has a connection 5 for the feeding of blowing air, with which the foam particles can be conveyed into the mold cavity (FIG. 2). An opening of the filling injector 4 leading into the mold cavity 3 may be closed by means of a punch 6.

(10) The two mold halves 2/1 and 2/2, on their sides facing away from one another, are respectively encompassed by a first steam chamber 7 and a second steam chamber 8. The mold halves 2/1 and 2/2 have several nozzles 9 which, from the inner part of the steam chambers 7, 8, open out into the mold cavity 3.

(11) The mold halves and the corresponding steam chambers may be moved together by a mechanism, and may be moved apart to open the mold cavity 3.

(12) The mold 2 may be in the form of a so-called crack splitting mold, which is not completely closed during filling with foam particles, but instead is closed completely only after filling, with the foam particle filling being compacted in the mold cavity 3. The mold 2 may however also be provided for so-called pressure-charging, in which the foam particles are fed into the mold under pressure, so that with a subsequent reduction in pressure, the foam particles expand in the mold.

(13) Each of the two steam chambers 7, 8 is connected by a feed pipe 10, 11 to a steam generator 12. The steam generator 12 provides dry saturated steam. Each of the feed pipes 10, 11 has a steam valve 13, 14, which may be used to control the supply of steam to the respective steam chamber 7, 8. In the area between the steam valves 13, 14 and the mold 2, there is in each case a pressure sensor 15, 16. In the present embodiment, the pressure sensors are provided in the feedpipes 10, 11. They may be similarly located in the first or second steam chamber 7, 8.

(14) FIGS. 2 and 3 show that the steam chambers 7, 8 have on the input side and the output side in each case a distribution channel 17, which extends over the entire length of the respective steam chamber 7, 8 and has several openings 18 distributed evenly over the length, so that the steam flow is distributed evenly over the length of the steam chambers 7, 8.

(15) On the output side, the distribution channels 17 lead in each case into a condensate pipe 19, 20, in each of which a condensate valve 21, 22 is provided.

(16) The steam valves 13, 14, the pressure sensors 15, 16 and the condensate valves 21, 22 are each connected to a control device 23 (FIG. 1).

(17) The operation of the apparatus 1 for the production of a particle foam part is explained below. Firstly the mold cavity 3 of the mold 2 is filled with foam particles via the filling injector 4. This may be effected by means of the crack split process or by pressure filling. After filling, the two mold halves of the mold are closed.

(18) Next, the steam chambers 7, 8 are rinsed with steam, by opening not only the steam valves 13, 14, but also the condensate valves 21, 22 simultaneously. In this way, air present in the steam chambers 7, 8 is forced out of the steam chambers into the condensate pipes 19, 20.

(19) After the two steam chambers 7, 8 have been rinsed with steam, all steam valves 13, 14 and condensate valves 21, 22 are closed.

(20) Next, the steam valve 13 of the feed pipe 10 to the first steam chamber 7, and the condensate valve 22 in the condensate pipe 20 of the second steam chamber 8, are opened. The steam therefore flows from the steam generator 12 into the first steam chamber 7, through the nozzles 9 of the first mold half 2/1 into the mold cavity 3, and through the nozzles 9 of the other mold half 2/2 into the second steam chamber 8 and from there into the condensate pipe 20. In this way, the mold cavity 3 is rinsed with steam. The opening of the steam valve 13 and of the condensate valve 21 is controlled by the control device 23 in such away that the pressure measured by the pressure sensor 15 in the feed pipe 10 to the first steam chamber 7 follows a predetermined ramp. In this way, the pressure of the steam in the mold cavity 3 is increased gradually. This rinsing of the mold, in which the steam flows from one steam chamber into the other steam chamber, is also described as cross-steaming. The duration of cross-steaming and the end value of the pressure reached at the end of the ramp are set according to the material and the size of the particle foam part. Typical end values of pressure for cross-steaming are 0.2 to 0.5 bar for ET polystyrol, 2 to 4 bar for ET-polypropylene, and 1.2 to 1.8 bar for ET-polyurethane. For small parts, cross-steaming lasts for around 3 to 5 seconds, and for large parts (several m.sup.3), around 10 to 20 seconds. For a large part, the duration of the ramp extends to around 10 seconds, while on the other hand, for a small part, the ramp is travelled over in around 1 to 2 seconds.

(21) The following parameters are suitable for the production of an E-polystyrol block with a volume of approx. 7 m.sup.3:

(22) End pressure 0.4 bar

(23) The duration of cross-steaming is 20 s, of which the ramp takes up 10 s. The mean variation in pressure during the ramp is therefore 0.04 bar/s.

(24) For the production of a small part made of E-polypropylene (approx. 15 cm.sup.3), the following parameters are suitable for the cross-steaming:

(25) End pressure 3 bar

(26) The duration of cross-steaming is 3 s, of which the ramp takes up 1.5 s. Here, the mean variation in pressure during the ramp is 2 bar/s.

(27) If the cross-steaming from the first steam chamber in the direction of the second steam chamber 8 is concluded, then all valves 13, 14, 21, 22 are closed again. A second cross-steaming is then carried out from the second steam chamber 8 through the mold cavity 3 into the first steam chamber 7, wherein the steam valve 14, by which steam is fed to the second steam chamber 8, and the condensate valve 21, are opened, by which steam is carried away from the first steam chamber 7. The opening of these two valves 14, 21 is again controlled by the control device 23 in such a way that pressure is increased gradually by a predetermined ramp (FIG. 4a-4d). In this second cross-steaming, the final pressure is generally slightly higher than in the first cross-steaming (around 0.1 to 0.5 bar more). This is expedient since, after the first cross-steaming, the foam particles are already partly welded, so that the flow resistance is greater.

(28) As an option, before cross-steaming, steam may be fed before or during the moving together and compaction of the foam particles. The steam is then supplied with the mold cavity initially open (crack-split), in order to force out the air present in the spandrel spaces. The steaming step is described as crack steaming.

(29) Steaming under partial vacuum in the mold (less than 0.5 bar absolute pressure) has turned out to be another advantageous steaming variant. For this purpose, by means of an additional pump (not shown), air is sucked out of the mold 2 through one or both condensate pipes 19, 20. The reduced air volume between the particles ensures good heat transfer. Due to the additional pressure gradient, it is also possible for steam to flow through foam particles which are already mechanically compressed (for example by crack split filling or counter-pressure filling). On account of the reduced pressure, the steam temperature remains low, so that the outer skin of the molded part is not welded gas-tight prematurely, before the inner zones are welded.

(30) FIGS. 4a-4d show different ramps, by which pressure may be increased at the start of cross-steaming. The ramp according to FIG. 4a has a circle-segment-shaped curve. The ramp according to FIG. 4b rises in a straight line. Both functions are continuously differentiable in the area of the ramp, i.e. there are no jumps and edges. Only at the start (FIG. 4a, 4b) of the ramp, as also at the end (FIG. 4b) is there intermittency in the first derivation. Such a continuously differentiable function may be controlled very precisely. This may be done for example using a simple proportional controller (P controller). Preferably however a proportional-differential controller (PD controller) and in particular a proportional-differential-integral controller (PID controller) is used.

(31) The ramp according to FIG. 4c has two opposite curves, with this ramp being continuously differentiable both at the start and at the end of the ramp. This is therefore a completely smooth function, which may be controlled very precisely.

(32) FIG. 4d shows a ramp with several steps. Control of this kind is in principle also possible. However, the individual steps are not continuously differentiable.

(33) At each step it is therefore possible for overswings to occur. Since the individual steps are distinctly smaller than in the prior art (cf. FIG. 5), the overswings are correspondingly smaller.

(34) All these ramps have in common the fact that, at the start, steam is fed at low pressure and therefore low temperature, which considerably facilitates flow through the mold cavity and the expulsion of air.

(35) The mean rate at which pressure is increased during the ramp is preferably less than 2 bar/s, in particular less than 1.5 bar/s and preferably less than 1 bar/s.

(36) After cross-steaming in both directions, the condensate valves 21, 22 are closed and the two steam valves 13, 14 are opened or held open. In this way, steam is fed through both mold halves of the mold 2 into the mold cavity 3, so that the particle foam contained therein is completely welded. This step is also described as autoclaving.

(37) During autoclaving, the set pressures are generally higher than for cross-steaming. Typical pressure values for autoclaving lie in the range 1-1.2 bar for E-polystyrol, in the range 3.5-5 bar for E-polypropylene, and in the range of 2.2-3.5 bar for E-polyurethane. The duration of the autoclaving stage depends on the volume of the particle foam part to be produced and the mass of the mold, and may lie between a few seconds and up to a minute.

(38) In principle it is also possible during autoclaving to increase pressure firstly using a ramp. Since, however, immediately before autoclaving, there should no longer be any air in the mold, and also the foam particles are pre-heated by cross-steaming, the effect of the ramp in autoclaving is much less pronounced than in the case of cross-steaming.

(39) In the alternative described above, that of crack steaming, i.e. the feeding of steam while the mold is still somewhat open, it makes a great deal of sense to allow pressure to rise according to a ramp, since at this stage there is much air in the mold.

(40) After autoclaving, the particle foam part produced is cooled down. This involves spraying of the mold halves with water. Through condensation of the steam present in the mold cavity, the volume of the steam and therefore the pressure on the particle foam part is reduced. In addition, a partial vacuum or vacuum may be applied, so that the evaporation of the condensed water leads to a further cooling effect. The mold is then opened and the particle foam part removed.

(41) The process of producing a particle foam part may then begin afresh.

(42) The method described above avoids the introduction of too much energy at once, in particular at the beginning when there is air in the mold, which may lead to skinning over of the foam part, even though there is still air in the inner zone and the foam particles in the inner zone are not yet welded. The method leads to a very efficient forcing of air out of the spandrel spaces. Due to the rapid and even distribution of steam in the mold cavity, heat is conducted quickly, resulting in the whole mold cavity having substantially the same temperature and leading to even welding. Partial scorching, in particular at the surface of the particle foam part, may thus be avoided reliably. In conventional methods, if skinning-over occurs, the steam cannot flow further. This is problematic especially if pressure and therefore temperature rise in this area, so that the surface of the particle foam part is partly scorched. Since, with the present invention, pressure and therefore temperature follow a defined function, these problems known from the prior art cannot occur.

LIST OF REFERENCE NUMBERS

(43) 1 apparatus

(44) 2 mold

(45) 3 mold cavity

(46) 4 filling injector

(47) 5 connection

(48) 6 punch

(49) 7 first steam chamber

(50) 8 second steam chamber

(51) 9 nozzle

(52) 10 feed pipe

(53) 11 feed pipe

(54) 12 steam generator

(55) 13 steam valve

(56) 14 steam valve

(57) 15 pressure sensor

(58) 16 pressure sensor

(59) 17 distribution channel

(60) 18 opening

(61) 19 condensate pipe

(62) 20 condensate pipe

(63) 21 condensate valve

(64) 22 condensate pipe

(65) 23 control device