Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting
Patent
1989-07-28
1991-01-29
Thurlow, Jeffery
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
264 405, 264 407, 264508, 2642093, 264167, 425145, 425149, 425163, 425532, 425393, 425396, B29C 4792
Patent
active
049884662
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method for the production of ribbed pipes, in which method a pressurized plastic material is fed through an extruder into a pipe moulding space defined by a mandrel, an end face of an extrusion sleeve and chill moulds moving in the direction of the central axis of the mandrel and defining a mould cavity surrounding the extrusion sleeve and the mandrel, the inner face of the chill moulds being provided with annular grooves.
German Offenlegungsschrift No. 2 362 444 discloses a method for the production of ribbed pipes wherein a plastic material is fed into a relatively small moulding space under a high pressure. The material can be fed into the moulding space by means of a high pressure, because the space is small and closed.
In order to provide the pipe with a desired shape, the feeding speed of the extruder and the speed of travel of the chill moulds have to be proportioned to each other in a determined way. If the feeding speed of the extruder is too high with respect to the speed of travel of the chill moulds, the pressure within the mould cavity rises to such an extent that the chill moulds are drawn apart from each other in the direction of their periphery. Plastic material is thereby squeezed into gaps formed between the chill moulds, which can be seen as axial ridges in the finished product.
The feeding speed of the extruder may also be too low with respect to the speed of travel of the chill moulds. Thereby the moulding space of the corrugating means is not filled up completely, which can be seen as incomplete ribs in the finished pipe.
In order to obtain pipes as flawless as possible, it is known to observe the pipe produced by the apparatus and alter the proportion between the speed of the extruder and that of the chill moulds as soon as deviations in the shape of the pipe are detected, cf. Swedish Published Specification No. 381 001.
A disadvantage of this method is the slow adjustment, because the adjustment cannot be commenced until the apparatus already has been producing a defective product for some time. Furthermore, the extent of the correction is difficult to estimate, wherefore it may take a long time before the apparatus again produces flawless pipe.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a method for the production of ribbed pipes, which enables an accurate adjustment without any delay already at the moulding stage of the pipe. The method according to the invention is characterized in that the pressure of the material contained in the moulding space is measured, and that the feeding speed of the extruder and/or the speed of travel of the chill moulds is adjusted on the basis of the measured pressure.
By measuring the pressure of the material contained in the moulding space, information is obtained about the possible deviations already at the stage of the process when the pipe is being moulded, by virtue of which the adjustment can be effected in good time. For this reason it is possible to completely avoid the formation of defective pipes, which is economically beneficial. Since the measuring of the pressure of the moulding space also gives direct information on the strain exerted on the chill moulds, it is relatively easy to estimate the extent of the correction, so that the right correction can be made immediately.
The invention is also concerned with an apparatus for the production of ribbed pipes, comprising an extruder formed by a mandrel positioned on the central axis of the appratus, and an extrusion sleeve surrounding the mandrel, a ring-shaped nozzle being defined by the mandrel and the extrusion sleeve for the feeding of a pressurized plastic material; and corrugating means formed by a mandrel part positioned outside the extrusion sleeve and chill mould surrounding the extrusion sleeve and the mandrel and arranged to move in the direction of the central axis of the mandrel, the chill moulds, an end face of the extrusion sleeve and the mandrel defining therebetween a pipe moul
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Thurlow Jeffery
Uponor N.V., Emmaplein
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