Plastic article or earthenware shaping or treating: apparatus – Means feeding fluent stock from plural sources to common... – Extrusion shaping means
Patent
1992-03-30
1993-10-26
Chiesa, Richard L.
Plastic article or earthenware shaping or treating: apparatus
Means feeding fluent stock from plural sources to common...
Extrusion shaping means
425381, 425467, 425523, 425532, B29C 4706
Patent
active
052560511
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a storage head for a blow molding machine for the discontinuous production of multiple-layer high-volume plastic hollow bodies, comprising: at least two extruders connected to the storage-head housing to feed at least two liquid plastic melts into the storage head; a centrally disposed shaft; and at least two mutually independent distributor elements, concentrically surrounding the shaft to distribute the plastic melts circumferentially and to conduct them into an annular storage space below the ejector piston, which is mounted in the storage-head housing by means of a setbolt so as to be movable axially, and by means of which the multiple-layer plastic melt which is distributed circumferentially and which is stored in the storage space is ejected or co-extruded through an annular nozzle gap which is connected below to the storage space.
A comparable storage head of this type is known, e.g , from the DE-OS 39 02 270. This storage head is used for the discontinuous production of multiple-layer, co-extruded, hose-like parisons of thermoplastic to form high-volume, multiple-layer hollow bodies in a divided blow mold. With this storage head, at least two different annular material melts are brought together centrally within the ring piston, one after the other, in the extrusion direction, to form a multiple-layer material melt. After this, the multiple-layer material melt expands in funnel-like fashion and flows into an annular storage space. Subsequently, it is ejected from the storage head housing, by a ring piston that is movable in the axial direction, through an annular nozzle gap. The streams of plastic melt are conducted individually for each layer - up to five different layers may be present. Each one is distributed over the circumference by a separate ring channel. From there, they flow through a annular gap into the storage space beneath the ejector piston. With this circumferential distribution through a ring channel, a disadvantageous feature is the fact that on the side which is opposite to the infeed point, where the two semicircular partial streams coalesce, a welding seam always results, which later appears in the blown hollow body as a longitudinal seam and thus as a weak point. In the case of co-extruded, multiple-layer hollow bodies, the inner welding seams are indeed always covered up by the outer layer; nevertheless, they remain recognizable in the finished product by the formation of undesirable striations.
For example, ring channels or heart-shaped distributors are known as distributor elements to distribute the solid melt strand of plastic, which is conducted from the extruder into the storage housing, onto a circular circumference. However, various plastic molecules or particles here must traverse flow paths of different length. The coalescence points of the individual plastic streams may be recognizable in the blow-molded article as corresponding coalescence-based longitudinal seams. This reduces product quality.
SUMMARY OF THE INVENTION
It is an object of the invention to specify a novel storage head for a blow molding machine for the discontinuous production of plastic hollow bodies, especially high-volume ones, which has rheologically the same flow conditions for all the plastic particles when the liquid melted plastic stream is conducted to a distributor element, and in the distributor elements themselves, and which makes possible improved overlap and circumferential distribution of the melt streams in the distributor element while simultaneously increasing the throughput power and production speed of the blow molding machine.
According to the invention, this object is achieved as follows: The ejector piston consists of at least two tubular pieces which surround one another concentrically, and a separate distributor element is associated with each tubular piece, each distributor element being designed as a cylinder-shaped spiral-channel distributor.
With the inventive design, the plastic melts are fed in from the extruders b
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Langos Peter
Lehmann Manfred
Chiesa Richard L.
Mauser-Werke GmbH
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