CA1058366A

CA1058366A - Process and apparatus for extruding thermoplastic material

Info

Publication number: CA1058366A
Application number: CA229,371A
Authority: CA
Inventors: Giancarlo Giannarelli; Walter Movilli
Original assignee: Montedison SpA
Current assignee: Montedison SpA
Priority date: 1974-06-17
Filing date: 1975-06-16
Publication date: 1979-07-17
Also published as: BR7503764A; US4061462A; DK266975A; AR208320A1; DK141495C; DK141495B; ES438614A1; NL7507062A; JPS5112871A; FR2274435B1; GB1508851A; DE2526911A1; IT1015100B; FR2274435A1; SE7506795L

Abstract

ABSTRACT OF THE DISCLOSURE

This invention relates to a machine and process for extruding particular shapes in thermoplastic material, and more precisely, flat plates, corrugated plates and the like or, in general, shapes having one section much larger than the other.
The process is particularly suited to eliminate the uneven feed of the molton material coming out from a die. In the process of the invention, the molten material discharged from an extrusion head is subdivided among a number of separate flow tubes which have cross sections and lengths such that the same pressure drop is created in the material flowing through each tube. The tubes are maintained at a predetermined temperature, and are positioned to discharge material to various zones of a die member, so that material flows into the die member at the same temperature and speed throughout the extrusion sections.

Description

~,~58366 This in~ention relates o extrusion of shapes of thermoplastic materials, and an extrusion machine therefor.
As is known, one of the difficulties connected with the extrusion of shapes in thermoplastic material is the regu lation of the thrusts in the various points of the die outlet section. Such problem is particularly complicated in the case of pla~es or, in general, of sections whose one dimension is much greater than the other.
In fact, the longer dista~ce to be covered by the 10 material in order to reach the section ends causes a greater pressure drop and, by consequence, a thrust decrease. This causes different feed speeds of the molton product which, in the case of extrusion of plates, assume very high values.
The aforesaid drawback is generally obviated by hav-ing recourse to various contrivances, depending upon the type of shape. In the case of plates extrusion the art suggests, for example, to regulate the thrusts by using a bending bar, located transversally to the head and controlled by a set of adjusting screws, which permits a throttling of the flow section in the points where the lton product flow speed is the higher. By operating in this way and after a suitable adjustment, a regular feed of the plate is achieved.
The above described method, unfortunately, presents several drawbacks, that may be summarized as follows:
1. Both design and construction of the head are particularly expensive an~ laborious.

2. Since the bar is subjected to continuous bendings, after a certain time-period it becomes unusable and must be replaced. Moreover, the regulation so attained is rather low.

3. The adjustment operation necessary to attain a regular feed of the plate is oft~n time consuming and complicated resulting in a waste of time and material.

4. The utilization of the bar, although it regulates the thrusts, does not solve the problem connected with the different run and consequently, the different residence time of the material in the various head zones. This is very detrimen-tal to the processing of easily degradable materials (PVC), or - in general - of materials, during the conversion of which the amount of heat yielded to the material and the transmission -speed of said heat are of particular importance, such as light-weight or cellular plastics recently or presently developed.
It is an object of this invention to provide an improved method and apparatus for extruding products into shapes having sections whose one dimension is much larger than the other.
It is also an object of this invention to provide an improved extrusion apparatus for regulating the thrust and fIow speed of molton materials which is simple in design and construction.
It is a further object to provide a method and appara-tus for regulating the flow of molten material to provide equal residence time for all material in the extrusion head and pro-20 viding material of equal temperature and viscosity in all sec- -tions of the parts to be extruded.
Another object of the present invention is to provide an improved extrusion process and apparatus particularly suited to both flat and corrugated plates or, in general, to shapes having one section much greater than the other.
It is also an object to provide an improved apparatus for controlling the material to be extruded into shapes having a section with one dimension much larger than the other dimension which is readily adapted for use with conventional equipment.
These and still other objects, that will more clearly appear from the detailed description given hereinafter, are best attained in practice by means of an improved process in .

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accordance with this invention for extruding thermoplastic materials in the form of large-size shapes, in particular of plates and the like. The process, according to this invention, includes the steps of subdividing the molten material flowing :
from an extrusion head among a number of flow tubes separated from one another, the tubes having preferably equal cross-sections;
said flow tubes passing through a thermoregulated bath and lead-ing to the various zones of the die section, from which a shape :~
in the form of a plate or the like is extruded; getting such flow tubes to cover distances substantially of the same length or, in any case, providing tubes such as to cause the same pres-sure drop in each tube, in order to have the material flow out :
of the tubes at the same temperature and at the same speed all over the shape section. :~
Thus according to a first aspect of the present inven- :
tion, there is provided a process for extruding shapes of ther-moplastic material into a shape having a section with one dimen-. sion much greater than the other, which comprises the steps of: :
subdividing the molten material discharged from an extrusion head among a number of flow tubes separated from one another; saidtubes having cross-sections and lengths such that the same pres-sure drop is created in material flowinq there through; main-taining said tubes at a pre-fixed temperature and positioning the tubes to discharge material to various zones of a die member, whereby the material flows into the die member at the same tem-perature and speed in the whole section of the shape under extrusion.
With a view to practicing said extrusion process, a machine has been designed, that consists - according to this invention - of a conventional extrusion head of the type having the molten material outlet zone in the form of a circular crown, and which one end of a set of metal tubes, having preferably the same lengths and the same diameters, is tight~connected, and the opposite ends of such ~lbes having their centers gathered on a same line and connected with a die (or extrusion device) for flat plates or the like. The set of tubes are passed through a thermoregulated bath or the like, interposed between said extrusion head and the die.
According to a second aspect of the invention, there is provided, in an extrusion machine having a extrusion head of the type having a molten material outlet zone shaped as a circular crown and a die member in fluid communication with the extrusion head and having aAsection in which one dimension is larger than the other, the improvement which comprises a plurality of tubes, one end of each tube being in fluid communication with said outlet and the opposite ends of the tubes being gathered on a line along the median of said section of, and in fluid communication with, the die member, the length and interior cross-section of the tubes being such that a constant pressure drop in molten material is produced in each tube, and a thermoregulated bath interposed between the extrusion head and the die member, said tubes being immersed in said thermoregulated bath.
The present invention is now described in more detail with reference to a preferred and non-exclusive embodiment, as well as to the attached drawings, which are illustrative of a preferred embodiment, and in which:
Figure 1 is schematic, longitudinal section view of an improved extrusion apparatus in accordance with the present invention;
Figure 2 is a schematic view illustrating the ar~angement of the set of tubes, as viewed from the die end of the apparatus towards the circular crown of the head; and ~ 4 ~

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Figuxe 3 is an enlar~ed~ perspect~ve vie~ p~rtially ~
in cross~section, of the apparatus in Figure 1. ;-With reference to the drawings~ the apparatus for ;
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10583~;6 carrying out the aforesaid process utilizes a conventional ex-truder (not appearing in the figures), equipped with extrusion head 1 of the known type. The material reaches head 1 by flow-ing through truncated cone-shaped union 2 (Figures 1 and 3) and into a hollow screw zone 3, also having the form of a truncated cone, defined by an outer tapered surface 4 and the inner surface

5. Truncated cone-shaped hollow zone 3 is connected with circu-lar crown 6.
A plurality of metal tubes 7,7! ,7" etc. are connected ~;
in fluid tight communication with zone 3, which has the shape of a truncated cone, and, more precisely, the tubes are connected with circular sector 3' to receive the material outflow. Metal tubes 7,7',7" etc. are equispaced from one another and, there-fore, their ends are distributed on a circular sector as indi-cated with numeral 8 in Figures 2 and 3 , that corresponds to the centre line circle of the circular sector 3'. All the tubes have the same length and the same inside and outside diameters. The tubes are arranged in such a way, that the centres of their opposite ends are gathered on a line 9 (Figures 2 and 33, corresponding to the median longitudinal axis of a flat die 10 (Figure 1). ~he ends of the gathered tubes are in fluid tight-connection with the hollow zone of die 10.
The various spaces existing among the closer-brought tube ends, both those connected with circular crown 3 and those connected with die 10, are closed or clogged, since the molten material coming from circular crown 3 is conveyed into the tube bundle, where it is made to subdivide among several flow tubes until it comes out, in the form of a continuous plate, from die 10.
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Furthermore, the tube bundle is immcrgcd in a thermo-regulated bath consisting of a chamber 11, into which oil or other fluid 12, at a pre-fixed temperature, is introduced - .

~[)58366 :-through inlet 13 and recovered through outlet 14.
It has been ascertained in practice that by subdivid-ing the molten material flowing from the extrusion head among a number of flow tubes having the same section, through tubes of the same length and diameter, it is possible to accurately control the temperatures and to have available a material out-flowing at the same temperature and speed from all points of the shape section. When extruding non-flat plates, the use of tubes which are equal sections and lengths, and practically rec- :
tilinear, like those illustrated in the Figures, may sometimes fail to cause the same pressure drops, and, as a consequence, fail to ensure the desired results. In such cases, in order to obtain like pressure drops and therefore like thrusts in all tubes, the tubes may have different sections and lengths, for example truncated cone-shaped tubes of different lengths and/or of diameters different from one another. These partic~lar em-bodiments also fall within the scope of the present invention, since they always practice the process described hereinbefore.
Of course, other constructive and technically equiva-lent modifications may be made to the embodiments described,without departing from the scope and spirit of the present invention, as pointed out in the appended claims.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for extruding shapes of thermoplastic material into a shape having a cross section with one dimension much greater than the other, which comprises the steps of:
subdividing the molten material discharged from an extrusion head among a number of flow tubes separated from one another;
said tubes having cross-sections and lengths such that the same pressure drop is created in material flowing therethrough;
maintaining said tubes at a pre-fixed temperature and position-ing the tubes to discharge material to various zones of a die member, whereby the material flows into the die member at the same temperature and speed in the whole section of the shape under extrusion.

2. The process according to claim 1, wherein said material flows through tubes having identical cross sections.

3. The process according to claim 1 or claim 2, wherein the runs of said flow tubes are substantially recti-linear and equispaced from one another.

4. The process according to claim 1 or claim 2, wherein said tubes are maintained at a fixed temperature by passing through a thermoregulated bath of fluid at said fixed temperature.

5. In an extrusion machine having an extrusion head of the type having a molten material outlet zone shaped as a circular crown and a die member in fluid communication with the extrusion head, said die member having a cross section in which one dimension is larger than the other, the improvement which comprises a plurality of tubes, one end of each tube being in fluid communication with said outlet and the opposite ends of the tubes being gathered on à line along the median of said section of, and in fluid communication with, the die member, the length and interior cross-section of the tubes being such that a constant pressure drop in molten material is produced in each tube, and a thermoregulated bath interposed between the extrusion head and the die member, said tubes being immersed in said thermoregulated bath.

6. The machine according to claim 5, wherein each of said tubes have the same length and interior cross-section.

7. The machine according to claim 5, wherein said tubes are rectilinear and have a constant cross-section.

8. The machine according to claim 5, wherein said tubes are substantially shaped as truncated cones and have lengths different from one another.