GB2093758A

GB2093758A - Producing moulded articles from foamable thermoplastic synthetic material

Info

Publication number: GB2093758A
Application number: GB8126637A
Authority: GB
Original assignee: Haendle & Soehne Maschf Karl
Current assignee: Haendle & Soehne Maschf Karl
Priority date: 1981-02-28
Filing date: 1981-09-02
Publication date: 1982-09-08
Also published as: IT1153449B; DE3107697A1; FR2500788A1; IT8219746A0

Abstract

Moulded articles of a foamable thermoplastic synthetic material are produced by introducing the material into a mould (3), steam treating the moulded material (20) and then stabilizing the moulded article by the application of a vacuum thereto immediately after the steam threatment with no intermediate treatment by a stabilizing medium. Apparatus for performing the method comprises the mould (3) which is located within a steam chamber (2) which has inlets (9) to which are connected a steam delivery pipe (19), a compressed air supply pipe (30) for use in discharging the moulded article, and a vacuum pipe (21) for application of the vacuum. <IMAGE>

Description

SPECIFICATION Method of producing moulded articles from foamable thermoplastic synthetic material and apparatus therefor.

The invention relates to a method as well as to an apparatus for carrying out this method.

German OS 15 04 360 describes a method in which cooling water is introduced in the stabilizing phase and then a vacuum is applied. After cooling of the moulded article by the cooling water, the moulded article is ejected by vacuum.

In a method of this type (German OS 29 1 1 120), after foaming of the moulded article, compressed air is introduced as a stabilizing medium, in order to make the cell structure of the moulded article permeable to the trapped propellant and foaming agent. However, due to this the moulded article has a rougher surface than when stabilized with water.

Therefore, in order to smooth the surface, a vacuum is applied at the end of the stabilizing phase, during which the structure of the moulded article becomes compacted.

The stabilizing media used for cooling, namely cooling water or compressed air necessitate not only stages of the method which involve a great deal of work and are time-consuming for the introduction of these media, but also necessitate a special construction of the apparatus serving for carrying-out the method. Furthermore, the application of the vacuum is necessary as a further stage of the method in order to obviate the drawbacks caused by the stabilizing medium.

Despite these complicated measures, subsequent foaming of the moulded article cannot be prevented, because the propellant present in the moulded article cannot be cooled sufficiently quickly or the moulded article has such a cell structure that the propellant can only escape slowly.

The object of the invention is to develop the method of this type so that further subsequent foaming is prevented due to the abrupt removal of the propellant.

The invention provides a method for the production of moulded articles from thermoplastic synthetic material which is capable of foaming, in which the synthetic material is introduced into a foaming mould, the moulded article is steamtreated in a steam chamber and then is stabilized, and in which before removing the moulded article from the foaming mould, a vacuum is produced on the moulded article, characterised by the fact that the vacuum is applied directly after foaming without the intermediate addition of a stabilizing medium such as water, air or the like whereby the moulded article is stabilized exclusively by the application of the vacuum and the propellant located in the foaming mould is removed.

In this method the use of a particular stabilizing medium, such as water or air, for cooling the foamed moulded article is dispensed with and instead of the latter evacuation takes place directly after the steam treatment. When applying the vacuum, a strong sudden suction occurs, which abruptly carries along all the propellant and the steam present, so that the moulded article is cooled quickly and therefore subsequent foaming is effectively prevented. As a result of this method according to the invention the moulded article has a smooth surface, as is otherwise achieved solely in the case of water-cooled moulded articles, without additional stages of the method being required. The surface of the moulded article can be smoothed still further in that water is sprayed into the steam during the steam treatment.This produced a cooling effect which leads to higher moisture and thus better welding together of the particles of synthetic material which are in the form of granulated material. Thus, with the method according to the invention, neither stabilizing media nor special measures are required for introducing and removing a stabilizing medium of this type, so that the method according to the invention can be carried out in a substantially cheaper and simpler manner by saving on material, the expenditure of energy and time. Since no water is used for cooling, the mould and the moulded article are virtually free from moisture when they are removed, so that subsequent drying can be largely dispensed with.

Finally, the economy is improved still further due to the fact that the operating temperature is substantially maintained during evacuation, so that the mould does not need to be reheated for the next foaming operation.

Further features of the invention will become apparent from the claims, description and drawings.

The invention is described in detail hereafter with reference to a foaming apparatus for carrying out the method according to the invention, illustrated in section in the drawing.

The foaming apparatus 1 comprises a steam chamber 2, in the central region of which a foaming mould 3 is arranged in the upper and lower foaming mould wall so that the steam chamber is divided into an upper and lower heating chamber 2' and 2". A filling injector 5 passes through the upper heating chamber 2' and opens into an inlet opening 31 in the upper wall 32 of the foaming mould 3. Two or more uniformly distributed nozzle apertures 4 are located in the upper and lower walls 32 and 30 of the foaming mould, on both sides of the filling injector 5. Two openings 9 to 1 1 are respectively located in the side walls 6 and 7 of the chamber and in the bottom wall 8 of the chamber. The openings 9 in the right-hand side wall of the chamber are inlet openings into which lines 12 and thus connected steam delivery pipes 12 open.

Arranged one behind the other in the supply lines 19 in the direction Z in which steam is supplied are two open plunger valves 13 and 14, by which the supply of steam from a container (not shown) for saturated steam located outside the apparatus can be controlled. The rear valve 14 is connected to a control valve 1 5 for this purpose. Provided in the left-hand side wall 7 are two outlet openings 10, which like the inlet openings 9 open respectively into one of the heating chambers 2' and 2". For the drainage of the chambers, the outlet openings 10 are connected to open plunger valves 1 6, through which the condensate can be directed to drain channels (not shown). The two otheropenings 11 in the bottom 8 of the chamber are connected to open control valves 17 for venting the chamber.The pipes 12 are connected by way of a valve line 21 to a vacuum system, which consists of a vacuum pump 22 and located one after the other in the suction direction A of the pump, an open plunger valve 29, a cyclone separator 27 with an outlet valve 28 for condensate, a pressure gauge 26, a cut-off 25, a vacuum-limiting or rear control valve 24 for adjusting the vacuum, and an inspection glass 23 as a checking part.

The method according to the invention can also be carried out with a steam chamber in which no steam, but water is supplied. In this case, close to the inner side of the lower and upper chamber walls, a heating element in the form of an electric heating plate is provided and a water spray pipe is respectively located between the heating plates and the opposite chamber wall, the openings in which pipe are directed towards the heating plates.

The required quantity of synthetic material is introduced by the filling injector 5 into the foaming mould 3 which is pre-heated to a temperature of approximately 85 to 10006. In the apparatus 1 illustrated, the foaming mould is preheated and kept at the desired temperature by introducing steam through the openings 9. With a chamber comprising heating elements and water spray pipes, pre-heating and mainta#ining the temperature are achieved by introducing water into the spray pipes and subsequent spraying and the temperature is maintained by the heating plates.

For introducing steam into the heating chambers 2' and 2", the valves 13 and 14 in the steam delivery pipe 19 are opened, whereas the control valve 29 of the vacuum system is closed.

At the same time a compressed air valve 18 in a compressed air line 30 is closed, which is likewise connected to the pipes 12 for ejecting the moulded article 20. After the steam supplied in this way has penetrated the foaming mould 3 through the nozzle apertures 4, the synthetic material, such as polystyrene for example, located inside the foaming mould foams. Water can be sprayed into the saturated steam for cooling and for better welding together of the granular synthetic material, due to which the moulded article obtains a smooth surface structure. After this foaming operation, a vacuum is applied to the moulded articles 20 in the steam chamber 2 by way of the nozzle apertures 4.

The vacuum is produced directly after the steam treatment phase. It may thus be appropriateto open the valves 1 6 of the right-hand side wall 7 of the chamber for several seconds, for example for approximately 2 seconds, so that the excess pressure is reduced. In this case condensed water flows from the chamber 2 into the drainage channels.

The vacuum is produced due to the fact that the compressed air valve 18 and the valve 13 in the steam pipe 19 are closed and the control valve 29 of the vacuum system is opened. At the time of evacuation a pressure of -0.5 to -0.8 bars preferably prevails. At the instant when the vacuum is applied, the propellant contained in the moulded article 20, for example butane, pentane and the like is removed suddenly and completely from the chamber 2 due to the resulting suction by way of the nozzle apertures 4. Consequently the moulded article 20 is not able to continue foaming, thus achieving high accuracy as regards dimensions in manufacture. Together with the propellants, the water vapour which is also present is sucked out by the vacuum pump 22.

Consequently the moulded article 20 is cooled in a manner similar to that when using a stabilizing medium in the stabilizing phase of known methods. In order to prevent water from passing into the pump upon evacuation and thus damaging the latter, any existing condensate is drawn off by way of the cyclone separator 27 and the outlet valve 28, in which case the rear control valve 24 and the valve 29 are closed. The inspection glass 23 is used to check whether all the condensate has been separated with the cyclone separator 27. The quality of the moulded article is all the better the higher the vacuum in the steam chamber 2.

After this stage of the method, the valve 29 is re-closed and the compressed air valve 1 8 is opened, so that compressed air is introduced into the chamber 2 by way of the compressed air line 30 and the lines 12. One half of the mould is thus removed from the moulded part 20. Compressed air is blown onto the moulded article 20 through the nozzle apertures 4, due to which the moulded article is then firstly pushed out of the other half of the mould and subsequently discharged.

The release and removal of the moulded articles may also be achieved by an arrangement in which the compressed air lines open directly into the foaming mould, in which case these lines are sealed with respect to the heating chambers of the steam chamber and are connected by way of a valve opening in the direction of the foaming mould to the associated inlet opening, which is in turn sealed with respect to the heating chamber.

With such a construction of the chambers (not shown), it is ensured that any possible residual moisture is not absorbed by the compressed air, so that the foaming mould and the moulded article remain dry.

Claims

1. A method for the production of moulded articles from thermoplastic synthetic material which is capable of foaming, in which the synthetic material is introduced into a foaming mould, the moulded article is steam-treated in a steam chamber and then is stabilized, and in which before removing the moulded article from the foaming mould, a vacuum is produced on the moulded article, characterised by the fact that the vacuum is applied directly after foaming without the intermediate addition of a stabilizing medium such as water, air or the like, whereby the moulded article is stabilized exclusively by the application of the vacuum and the propellant located in the foaming mould is removed.

2. A method according to claim 1, characterised by the fact that water is sprayed into the steam during the steam treatment.

3. A method according to claim 1 or 2, characterised by the fact that before applying the vacuum, the excess pressure in the steam chamber is reduced temporarily.

4. A foaming apparatus for carrying out the method according to any one of claims 1 to 3, comprising a steam chamber with a foaming mould, which is located inside the steam chamber and divides the steam chamber into two heating chambers and which comprises respective inlet openings for the steam-treating medium and synthetic material, characterised by the fact that inlet openings to said chamber for the steamtreating medium are connected to a steam delivery pipe, a compressed air line for releasing and removing the moulded articles and a vacuum line.

5. Apparatus according to claim 4, characterised by the fact that a control valve connected to a pressure regulator is located in the steam delivery pipe.

6. Apparatus according to claim 4 or 5, characterised by the fact that successive parts of a vacuum system are connected to the vacuum line in the suction direction of a vacuum pump of said vacuum system; said successive parts comprising a front control valve, a cyclone separator with an outlet valve for condensate, a cut-off for adjusting the vacuum, a rear control or vacuum-limiting valve, and a checking part.

7. Apparatus according to any one of claims 4 to 6, characterised by the fact that on a side wall which is located opposite said inlet openings for the steam, the steam chamber comprises at least two steam outlet openings opening one into each of said heating chambers, and that the steam outlet openings can be closed off or opened by way of control valves.

8. Apparatus according to any one of claims 4 to 7, characterised by the fact that the compressed air line comprises a control valve for removing and releasing the moulded articles.

9. A method for the production of moulded articles from foamable thermoplastic synthetic material substantially as hereinbefore described.

10. Apparatus for performing the method of claim 9 substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.