Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Corrugating
Patent
1986-11-12
1988-12-13
Thurlow, Jeffery
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Corrugating
264514, 264515, 264167, 264173, 264245, 425190, 425192R, 4251311, 4251331, 4253261, 4253871, 425462, 425467, B29C 4704
Patent
active
047909757
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a method in extruding a double-walled plastic tube.
BACKGROUND
In many cases it is desired to indicate on a tube the correct position of installation of the tube. Such indication may be necessary for example in case of infiltration tubes having slots which are asymmetrically distributed; i.e. they are arranged only on that portion of the tube wall, which shall face downwards when the tube is positioned in the ground, i.e. that part of the tube wall, which then shall form the bottom portion of the tube. The indication at present is provided by applying to the tube a longitudinal colour strip which is produced by means of a spray gun or tape or by extrusion from a separate side extruder. In case of plastic tubing having a corrugated or finned outside surface the last-mentioned method is the only one that can be used. However, this method involves high investment cost for a supplementary extruder and moreover causes some operating problems if the tube is a double-walled tube of the type having a corrugated outer wall and a smooth inner wall, because two separate extruders are required for the two walls.
The method of the invention has been developed for such tubes and other plastic tubes having two layers which are extruded from plastic materials of different colours for the inner layer and the outer layer no matter how the two layers are formed, in order to provide in a very simple manner an indication of the correct position of installation by means of a strip on the outer layer, which has a colour deviating from the colour of the remaining portion of the outer layer.
The invention also relates to a tool for working the method.
BRIEF DESCRIPTION OF THE DRAWINGS
In order to explain the invention in more detail embodiments of the method of the invention will be described below, reference being made to the accompanying drawings in which
FIG. 1 is a plan view of a tube having a position indication in the form of a longitudinal colour strip,
FIG. 2 is a diagrammatic axial sectional view of a tool for extruding a double-walled tube having a corrugated outer wall and a smooth inner wall,
FIG. 3 is a view similar to FIG. 2 but with the tool modified for working a modification of the method of the invention,
FIG. 4 is a perspective view showing an element intended to be located in the tool when the method of FIG. 3 is applied to divert material to the colour strip, and
FIG. 5 is a plan view of an extruder arrangement and illustrates another modification of the method of the invention.
DETAILED DESCRIPTION
The tube shown in FIG. 1 having a corrugated outside surface 10 has a longitudinal colour strip 11 for indication of the correct position of installation of the tube. If it is assumed that the tube is of the double-walled type having an outer layer which forms a corrugated outer wall, and an inner layer which forms a smooth inner wall, the outer and inner walls being extruded simultaneously and being interconnected, and if it is also assumed that materials of different colours are used for the outer and inner layers, the indication strip 11 can be produced in a simple manner without large investments by applying the method of the invention.
Referring to FIG. 2 a tool 14 is connected to an extruder 13 partly shown. Material 15 for the outer layer of the tube is supplied through a passage 16 and is delivered through a nozzle orifice 17 while material 18 for the inner layer of the tube is supplied tnrough a passage 19 and is delivered through a nozzle orifice 20. The outer layer of material is corrugated which can take place in a known manner by using chains of chilled molds not shown herein, and the corrugated outer layer is connected at the inside crests of the ridges to the smooth inner layer. This is a known and well-tried method.
In FIG. 3 there is shown how the tool of FIG. 2 can be modified for working the method of the invention. An element 21 which is shown in more detail in perspective view in FIG. 4, is detachably mounted in the tool 14 to shut off the flow
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Holso Paul
Jarvenkyla Jyri
Oy Uponor AB
Thurlow Jeffery
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