Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – Composite article making
Patent
1990-06-21
1992-01-07
Tentoni, Leo B.
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
Composite article making
264 51, 264101, B29C 6720
Patent
active
050789325
ABSTRACT:
In the production of thin-walled disposable casting patterns of expanded foamed plastic beads for the full mold casting method, difficulty is encountered in that the prefoamed preexpanded beads to be introduced into the pattern mold cavity with a bulk density of less than 20 g/l have a diameter of about 2 mm and consequently a reliable reproduceable complete filling of pattern mold cavities with a cross-section of less than 5 to 7 mm is not possible. It has been found that prefoamed and preexpanded beads nevertheless having adequate foaming agent content for the final foaming expansion in the pattern mold can be produced in that following prefoaming, evacuation of the steam-air atmosphere in the prefoamed chamber is effected and additional foaming agent is introduced. Due to the partial vacuum effected by the evacuation any condensate mist can be removed from the preexpanded beads without appreciable pressure drop in the interior of the beads and without a damaging cooling so that the foaming agent being supplied can diffuse very well into the fine beads having a large surface area. As a result, the entire foaming agent content of the beads can be used for the preexpansion so that a finer screen fraction of the beads can be used as starting product and smaller preexpanded beads are obtained. With these smaller beads smaller cross-sections of the pattern mold cavity can be properly filled and a smoother more regular surface can be obtained. To carry out the method it suffices to attach a vacuum line and a supply line for gaseous foaming agent to a conventional pressure prefoamer.
REFERENCES:
patent: 3853972 (1974-12-01), Berner
patent: 4272469 (1981-06-01), Smith
patent: 4482306 (1984-11-01), Hahn
Bissinger Fridolin
Krzyzanowski Erich
Grunzweig & Hartmann und Glasfaser AG
Tentoni Leo B.
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