Plastic article or earthenware shaping or treating: apparatus – Means feeding fluent stock from plural sources to common...
Patent
1995-05-05
1998-05-12
Timm, Catherine
Plastic article or earthenware shaping or treating: apparatus
Means feeding fluent stock from plural sources to common...
264572, B29C 4523
Patent
active
057501556
DESCRIPTION:
BRIEF SUMMARY
The invention deals with a process for injection molding of objects from plastics material containing hollow spaces or cavities in a mold, whose mold hollow space or cavity has to be fed on the one hand plastics melt through a nozzle and on the other hand has to be supplied with an additional pressurized medium as for instance air, gas or also liquid through a hollow needle at a point different from that of the nozzle, wherein a needle core which is axially displaceable to a limited extent, is disposed in said hollow needle, by means of which needle core the discharge aperture of the hollow needle to the mold hollow space or cavity can be varied in its admission cross-section or can be opened and closed.
A device having this combination of characteristics is already part of the state of the art through the DE-OS 39 36 289. Compared to other known devices of similar construction, for instance, one according to the DE-OS 21 06 546 it is distinguished by the circumstance that blocking of the discharge mouth aperture of the hollow needle can be securely counteracted even if this mouth aperture penetrates only into a portion of the wall thickness of the object at the end of the injection process and in the course of the dwell pressure following thereon, thus, while being still surrounded by liquid plastics melt. According to the DE-OS 39 36 289 the mouth aperture of the hollow needle can namely be adjusted to be so small, that it indeed permits the escape of the pressurized medium into the mold hollow space or cavity, while not permitting penetration of liquid plastics melt into the mouth aperture, at least not if one is dealing herein with thermoplastic material.
In particular those injection molding devices according to DE-OS 39 36 289 have been found to be especially useful for practical application, where the needle core carries an enlarged head or dish upstream of the mouth or aperture region of the hollow needle, whose external diameter corresponds at least approximately to the external diameter of the hollow needle and in which the needle core is axially abutted or supported by spring means relative to the hollow needle; this so that the head or dish of the needle core forms a radially oriented splitting valve together with the mouth end of the hollow needle whose maximum mouth or discharge gap, for instance, less than 0.2 millimeters, is defined by the spring means support or abutment. According to the DE-OS 39 36 289 the mouth slit or gap of the splitting valve can become smaller counter to the spring means support, for instance when the pressure of the medium inside the plastics melt contained in the mold hollow space or cavity of the mold increases to a magnitude, which can overcome the actuating force of the spring means.
When injection molding objects from plastics material having relatively large dimensions, therefore also enclosing large cavities at predetermined wall thicknesses, it is not possible to introduce sufficiently large quantities of the pressurized medium into the mold hollow space or cavity of the mold through only one single hollow needle, because the maximally available admission cross section of the splitting valve of this hollow needle is insufficient for this purpose. Therefore, we are faced with the necessity of equipping molds for fabrication of voluminous plastics objects with a correspondingly large quantity of hollow needles discharging into the mold hollow space or cavity. This naturally increases the expense of the molds which have to be made available, because its own particular medium feed must be allocated to each hollow needle.
Another deficiency of the device for injection molding of objects from plastics material containing cavities, which has become known from the DE-OS 39 36 289, arises from the circumstance that in case of the occasionally occurring contamination of the splitting valve in the hollow needle, the exposure of same required for cleaning purposes has to be performed from the rear end, because there the needle core is fixed in a mounting abutted agains
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Eckardt Helmut
Ehritt Jurgen
Hubel Uwe
Schroder Klaus
Battenfeld GmbH
Timm Catherine
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