Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting – Measuring a weight or volume
Patent
1991-06-13
1995-04-25
Timm, Catherine
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
Measuring a weight or volume
264 401, 264 407, 264540, 264541, 425140, 425145, 425150, 425532, B29C 4904, B29C 4978
Patent
active
054096472
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for the production of hollow bodies from thermoplastic material, in which process firstly preforms are discontinuously produced and are then expanded under an internal increased pressure in the mold cavity of a divided blow molding mold. An extrusion blow molding machine provided for that purpose comprises an extrusion unit and a blow molding unit, the respective operating procedures of which must be matched to each other.
Such an extrusion unit has at least one continuously operating extruder for plasticising the plastic material which is generally in granulate form, and an extrusion head in which there are disposed at least one storage chamber for storage of the plasticised material and at least one means for emptying the storage chamber, said emptying means being reciprocatable with a stroke-like movement between two limit positions. In that arrangement the storage chamber is generally annular and the means for emptying the storage chamber is in the form of an annular piston. Therefore, for the sake of simplicity, reference is primarily made hereinafter to an annular piston, without that being intended to involve a limitation.
In the discontinuous formation of the preforms, it is possible to make a distinction between two operating phases in dependence on the stroke movement of the annular piston within the extrusion head during a working cycle. In the one operating phase, the filling or storage phase, the storage chamber is filled with plasticised material, with displacement of the annular piston, until the annular piston reaches its limit position at the end of the filling operation. In the following operating phase, being the ejection or emptying phase, the stored material is ejected from the storage chamber under the effect of the annular piston which is moved by drive means, and urged towards the outlet opening of the extrusion head, with the plasticised material flowing through a communicating duct which is disposed between the storage chamber and the outlet opening. During that second operating phase the ejected material for the preform is predominantly formed by the material being urged out of the storage chamber by the annular piston. However also added thereto is a portion of material which is conveyed into the extrusion head by the continuously operating extruder during the ejection stroke movement. The volume of the total amount of material which issues from the extrusion head is accordingly made up of a portion by volume which was previously stored in the at least one storage chamber, and a portion by volume which is conveyed into the extrusion head during the ejection period by the at least one extruder. The uninterrupted operation of the extruder for plasticising the material is desirable so that the operating condition thereof can be stabilised. The piston reaches its other limit position at the end of the emptying operation.
The preform which is formed during the ejection operation and which generally hangs vertically at the outlet opening of the extrusion head is received by a blow molding mold which is at least divided into two. In that respect, at least a part of the central portion by volume of the overal portion by volume which forms the preform is expanded under an increased internal pressure within the mold cavity of the blow molding mold. The end portions of the overall portion by volume are squeezed off as waste material by a squeezing-off operation in which the blow molding mold portions are involved so that the waste material remains outside the mold cavity. After expansion of the central portion by volume, the hollow body formed is cooled until it is of sufficient stiffness so as to retain its shape upon being removed from the blow molding mold.
Accordingly the cycle time of a working cycle of such a blow molding unit is essentially composed of a receiving time, an expansion time, a cooling time and a removal time and movement times in respect of the blow molding mold portions, while possibly still further additionally required periods have
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Translation of Kunstoffe Band 70, No. 9, Sep. 1980, R. Hegele et al.: "Gewichtsregelung an kontinuierlich extrudierenden Blasformanlagen," pp. 522-524.
"Conference Proceedings of the New York ANTE'89 Society of Plastic Engineers 47th Annual Technical Conference Exhibits", 1.-4. Mai 1989, H. Schrand: Adaptive control loops reduce scrap pp. 952-953.
Kiefer Erich
Klusener Peter
Krupp Kautex Maschinenbau GmbH
Timm Catherine
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