Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – By gas forming or expanding
Patent
1995-04-26
1998-01-27
Kuhns, Allan R.
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
By gas forming or expanding
2491141, 264 53, 264101, 264102, 264334, 425 4R, 425444, B29C 4402, B28B 736
Patent
active
057119058
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for producing molded parts made of expanded plastic and to a mold for performing this process.
2. Description of Related Art
Such a process for producing molded parts made of expanded plastic is VDI-Vedag, Duesseldorf 1984, pages 99 to 103. There it is explained that the filling operation with molding compound made of expandable polystyrene can be performed by vacuum filling. For this purpose, the mold cavity is evacuated before tilting and then the feed valve is opened. As advantages of vacuum filling there are indicated: savings in filling air, rifling without a crack gap, with corresponding material savings, shortened filling time and no air between the beads, air that must be expelled by vapor or warmed, which leads to an expectation of a savings in vapor.
As drawbacks there are indicated a limited packing density of the EPS beads and, because of this, the necessary process step "sweeping with vapor" before the transverse steam treatment. Further, a less attractive surface and, generally, a lower quality result than with pressure filling. Therefore, pressure filling is given preference, especially since, in this way, a vacuum pump with far lower capacity needs to be provided. Further, with pressure filling, fewer filling injectors suffice because of the denser packing.
After pressure filling, it is suggested to perform a vacuum sweeping, instead of a vapor sweeping, to extract the air between the beads. With subsequent transverse steam treatment, the vapor can then flow better and savings in vapor is achieved. Then the steam treatment can be performed in the known way.
To cool and stabilize the expanded material, the mold is usually cooled with cooling water. The so-called condensation cooling is also mentioned, in which, cold cooling water is injected into the steam chamber surrounding the mold and thus a partial vacuum of about 0.2 to 0.4 bars is produced. Using condensation cooling yields molded parts with little residual moisture of about 4 to 5 percent by weight.
Demolding and ejection are supported in the usual way, for example with ejectors.
SUMMARY OF THE INVENTION
The object of this invention is to indicate a process and a suitable mold for it with which molded parts made of expanded foam can be produced economically, with low vacuum and vapor requirements and further having very low residual moisture.
Surprisingly, with the simultaneous use of the process steps used in vacuum and pressure filling technology, in combination with condensation cooling, a considerable energy saving is achieved, in particular because of a limited use of vapor and the elimination of separate cooling media. The use of a vacuum before the filling operation and filling by compressed air results in a very intensive filling with even filling density within a very short time.
By introducing the vapor directly into the evacuated mold cavity, without the usual admission of this vapor into the chambers surrounding the mold, the vapor state is maintained and thus an even distribution of the vapor in the mold is achieved, thus avoiding, to the greatest extent possible, condensation of the vapor on the inner walls of the mold, which conduct heat poorly, or on the mold wall layers, which conduct heat poorly. Supplying the mold directly with vapor yields an even condensation of the vapor and thus an intensive energy output to the molding compound, which is expanding during this process step. During the subsequent renewed evacuation of the mold, with the molded part inside it, the condensate of the vapor evaporates. This causes, on the one hand, a cooling of the expanded molded part and, on the other hand, the removal of moisture on the molded part, so that a rapid stabilization of the expanded molded part and low residual moisture of it are maintained. Finally, because of the ejection of the expanded molded part with the support of compressed air, a rapid and residue-free demolding is possible.
The entirety of the process steps used thu
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Kuhns Allan R.
Ph. Kurtz Eisenhammer GmbH & Co.
Safran David S.
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