Multicavity blow molding machine for producing hollow bodies

Details Multicavity blow molding machine for producing hollow bodies Multicavity blow molding machine for producing hollow bodies

2000-02-29

2001-04-17

Davis, Robert (Department: 1722)

Plastic article or earthenware shaping or treating: apparatus

Means applying electrical or wave energy directly to work

Electro-static or inductive field

C264S454000, C264S465000, C264S540000, C425S532000

Reexamination Certificate

active

06217308

ABSTRACT:

FIELD OF THE INVENTION
My present invention relates to a multicavity blow molding machine for producing hollow articles and, more particularly, to improvements in dissipating electrostatic charge carried by parisons upon extrusion in multicavity blow molding machines.
BACKGROUND OF THE INVENTION
In the production of bottles, tubes, vials and other tubular articles in multicavity blow molding machines from synthetic resin materials, a multicavity mold can be positioned beneath a row of extrusion heads so that respective parisons can be extruded downwardly into the open mold cavities. The mold cavities can be closed, i.e. by closing the multicavity blow mold, mandrels can be inserted into the parisons in the cavities and the parisons can be blown to the shape of the mold cavities. The parisons can be calibrated in tubular shaping portions of the mold cavity.
The closed blow mold can be displaced to the blowing and calibrating station in which the blowing mandrels are inserted into the parisons and, after blowing, the blow mold can be opened, the articles removed and the blow mold returned to alignment with the extrusion heads to receive new parisons.
Between the extrusion heads and the mold cavities, the dangling extruded parisons or tubes carry electrostatic charge.
Apparatus of this type is described, for example, in EP 0 570 393 B1 and the brochure entitled in English “Long Stroke Blow Molding Machines” published in January 1996 by Fischer W. Müller, Blasformtechnik, GmbH of Troisdorf, Germany.
In these blow molding machines the tubular extruded parisons may hang over a considerable distance between the extrusion head and the blow mold.
Because of the static charges developed on the parisons, the parisons tend to swing pendulum-fashion relative to the vertical and frequently cannot pass uniformly or reproducibly into the respective cavities. As a consequence, the wall thickness distribution in the mold cavity may be nonuniform and the product quality may diminish.
It has been proposed to solve this problem by providing an ionization device along side the extruded tubes or parisons and, for that purpose, a commercially available ionization bar has been provided at a high voltage of say 7 kV to ionize the atmosphere around the tubes or parisons utilizing a relatively low current of 0.25 mA. The bar carries a multiplicity of short electrodes in an insulating body, the electrodes projecting by about 2-4 mm from this body. An individual electrode may thus be turned toward each of the parisons and can develop a high voltage and generates positive and negative charge carriers which, in turn, are picked up by air molecules. In practice, however, this system has not been fully satisfactory since the desired charge dissipation often does not occur and efforts to enhance the charge dissipation by displacing the air forcibly brings about a one-sided cooling of the parisons which itself is detrimental and leads to defective products.
OBJECTS OF THE INVENTION
It is the principal object of the present invention to provide a blow molding apparatus, particularly of the type described, with improved capabilities with respect to the dissipation of charge on the extruded parisons or tubes which are produced in the extrusion heads and which are to be received in the blow-molding cavities.
Another object of the invention is to provide an improved blow molding machine which ensures a better feed of the parison tubes into the blow molding.
Still another object of this invention is to provide an improved electrode system for eliminating electrostatic charge on extruded parisons for the production of blow molding articles.
SUMMARY OF THE INVENTION
These objects are attained, in accordance with the invention in a blow molding apparatus comprising:
a multicavity blow-molding station having a row of cavities for receiving respective parisons for blow molding same;
a row of extrusion heads located above the blow mold for extruding respective parisons in a row downwardly into the respective cavities; and
an ionization bar extending alongside the parisons between the heads and the blow-molding station for neutralizing electrostatic charges on the parisons resulting from extrusion thereof, the ionization bar comprising an insulating holder and an electrically conductive strip mounted in the holder and forming a single continuous electrode extending along the row of parisons and having a longitudinal edge turned toward the parisons.
Thus in the system of the invention the ionization bar is in the form of a single long electrode mounted in an insulating holder and having the configuration of an electrically conductive strip, preferably a copper laminate strip, with a longitudinal edge juxtaposed with and turned toward the extruded parsons, extending transversely thereto and along the row of parisons.
Investigation has shown, quite surprisingly, that drawbacks associated with the individual types of separate and spaced apart wire-like electrodes are eliminated by the use of a substantially continuous edge of such a strip and that the discharge of the extruded parisons is far more uniform. It appears that the greater area of the electrically conductive strip, together with the fact that the edge is turned toward the parisons, ensures an improved field distribution in the region of the parisons that promotes the more uniform discharge thereof. It is also possible that the strip itself provides a greater electrical field strength than is the case with the individual electrodes or wires of the earlier system.
In any event with the invention charge dissipation can be effected to a higher degree and improved efficiency, utilizing the improved electrode construction than was hitherto the case.
According to a feature of the invention, the edge of the strip turned toward the parisons is formed with teeth and especially with pointed teeth uniformly distributed along the edge with the flanks of the teeth converging toward the tips and the parison. The strip can be manufactured inexpensively and tends to uniformly discharge the parisons regardless of the tooth spacing and the distribution of the parisons in the respective row.
The distribution of teeth along the edge, moreover, contributes to the uniformity of the discharge field and at the same time ensures a high density of the electrical field lines or lines of equipotential.


REFERENCES:
patent: 3068511 (1962-12-01), Ahlbeck et al.
patent: 4000233 (1976-12-01), Gilbert
patent: 197 49 320 (1999-05-01), None
patent: 0 570 393 B1 (1994-12-01), None
patent: WO 95/21735 (1995-08-01), None

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