Extruder with a shaping device

Details Extruder with a shaping device Extruder with a shaping device

1998-07-29

2001-09-11

Davis, Robert (Department: 1722)

Plastic article or earthenware shaping or treating: apparatus

Including means advancing continuous length work through...

C425S384000, C425S388000, C264S209400

Reexamination Certificate

active

06287102

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to an extrusion system with a shaping device.
BACKGROUND OF THE INVENTION
Shaping devices are already known by means of which extruded articles, particularly hollow profiles or pipes, emerging from an extruder nozzle, are calibrated to desired outer and inner dimensions and are hardened at the desired outer dimensions or, in order to obtain the desired intrinsic rigidity, are cooled to the temperature provided for that purpose. Such shaping devices are known from the book by Walter Michaeli, Extrusions-werkzeuge für Kunststoffe und Kautschuk”, from Carl Hanser Verlag, Munich/Vienna, second fully revised and expanded edition, published 1991, particularly pages 321 to 329. Shown on page 323 is an external calibration with vacuum, in which the extrudate emerging from the extrusion tool is introduced in the form of a hollow profile at some distance after emergence from the nozzle lip of the extruder tool into a calibrating tool, by means of which the extrudate is passed through in the area of its surrounding outer surface, in contact with the mould surfaces of the calibrating tool. The contact without clearance of the surface of the extrudate on the individual mould surfaces of the calibrating tool is achieved by air passages, particularly slots located in the mould surfaces, and which are connected by supply lines to a vacuum source. In order to cool the extrudate, the calibrating tools are provided with one or more surrounding ducts for a heat treatment agent, and the vacuum can increase in the individual air passages or slots as the distance from the nozzle lip of the extruder tool increases. The temperature of the heat treating agent, in contrast to the mass temperature of the extruded profile, is extremely low and comes to about 20° C. Connecting then to such so-called dry calibrators are usually one or more cooling baths, in which the sufficiently rigid profiles, with partial application of vacuum or wetting via spray nozzles or passage through water baths, are cooled to room temperature. In many cases sufficient surface quality of the extrudates produced cannot be achieved with such calibrating tools over a lengthy service life of the shaping device.
A further device for calibrating extruded profiles, particularly extruded hollow profiles of thermoplastics, has become known from DE 22 39 746 A, in which there is located at a spacing in the extrusion direction behind the extruder tool or injection head of the plastics worm extruder press, a vacuum calibrating device with a cooling device integrated therein. In connection with the vacuum calibration device there is provided a low-pressure calibration tank through which a coolant flows, the vacuum calibrating device being so designed that therein only the outer skin and any present outer profile portions such as fine contours of the profile to be calibrated are shaped into their final form. The residual heat still contained in the profile is removed by the coolant in the low pressure calibration tank. Located in the vacuum calibrating device are individual calibrating plates at a spacing from one another, which thus form cavities in the form of vacuum slots, through which the extruded article is suctioned with the aid of the applied vacuum against the mould surfaces of the individual calibrating plates. In the calibration device proposed here, in all cases of application perfect surface quality of the extruded article and a long service life of a device could not be achieved.
SUMMARY OF THE INVENTION
The object underlying the present invention is to achieve, even at high throughputs, a perfect and constant surface quality of the extrudates produced, particularly of window profiles or pipes or the like, without increasing the outlay on machinery.
This object of the invention is achieved by providing a shaping device for an extrusion system comprising an extrusion tool and a calibrating device having a plurality of calibrating tools arranged one after another along an extrusion direction in which an extruded article from the extrusion tool travels through the calibrating device, wherein a seal device is disposed between an end face of the extrusion tool and an upstream end face of the first calibrating tool, and between the downstream end face of each calibrating tool and the upstream end face of an immediately succeeding calibrating tool, the seal devices being structured and arranged to surround the outer surface of the extruded article and to maintain a space in the extrusion direction between the respective end faces between which the seal device is disposed so as to create a cavity surrounding the extruded article that is closed off from environmental pressure outside the calibrating device, whereby the cavity can be evacuated to a reduced pressure relative to the environmental pressure. The surprising advantage of this solution resides in the fact that, simultaneously with a reduction in the outlay for construction and servicing the calibrating tools, the surface quality can be considerably increased, avoiding air passages or cavities for application of vacuum to the profile in the calibrating tools. In a way which could not be foreseen and was totally surprising to the person skilled in the art, in this way however higher dimensional exactitude of the extrudate could be achieved, as the extrudate, after emerging from the nozzle lip of the extruder tool, is no longer exposed to environmental conditions. By means of the direct transfer of the extrudate from the extruder tool into the calibrating tools, sinking of the outer peripheral surfaces by means of a web located there under or within the profile, is avoided, as the external air pressure cannot become directly effective on the outer surface. This however effects in an unforeseeable way rapid precipitation of lubricants or a condensation of lubricant residues, such for example as the waxes or the like mixed with the raw materials, which, due to the high temperatures in this area, are still liquid. In this way the service life of such tools between the individual cleaning procedures is considerably increased without a disadvantageous alteration in surface quality, as contamination in the inlet area of the calibrating tools is prevented by removal of the superfluous lubricants, and contamination in the mould surfaces of the individual calibrating tools is avoided by the elimination of air passages in the predominant area of the mould surfaces of the calibrating tool.
In addition to the seal from external environmental conditions, vacuum or low pressure is applied directly to at least one of the cavities, and the article is cooled immediately thereafter. In this way lubricant residues and precipitated additives such as waxes can be directly removed by the applied vacuum, when adequate temperatures are maintained. Thus the service life of such tools between the individual cleaning procedures is considerably increased without disadvantageous alteration in the surface quality, as contamination in the inlet area of the calibrating tools is prevented by the removal of superfluous lubricants, and contamination in the mould surfaces of the individual calibrating tools is avoided by the elimination of air passages in the predominating area of the mould surfaces of the calibrating tool.
By providing the cavities delimited by the end faces of the calibrating tools and the seal devices, vacuum slots in the mould surfaces can be omitted, whereby formation of smearing by the smooth continuous mould surfaces is avoided, and the respectively required polished effect can be simply achieved on the surface of the article.
It is also advantageous to make the lengths of the mould surfaces in the extrusion direction at least seven times the distance between the nozzle lip of the extrusion tool and the first calibrating tool and the distance between adjacent calibrating tools, as in this way hardening, shaping and smoothing of the surface of the article and an improved quality and lower build-up of tension in said article can be achieved by the gent

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