Plastic and nonmetallic article shaping or treating: processes – Treatment of material by vibrating – jarring – or agitating... – Continuously formed or indefinite length article
Patent
1990-08-31
1992-07-21
Tentoni, Leo B.
Plastic and nonmetallic article shaping or treating: processes
Treatment of material by vibrating, jarring, or agitating...
Continuously formed or indefinite length article
264108, 26417716, 2642098, 425327, 425340, 425343, 425392, 425394, B29C 7100
Patent
active
051325497
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to the continuous formation, by extrusion, of a product in which constituent elements, normally randomly oriented, are capable of alignment or other ordered orientation to enhance the strength, formability or other useful quality of the extruded product. The invention applies particularly to the formation of extruded products from composite materials comprising a plastics base, for instance polypropylene or nylon, and a fibrous filler such as glass or carbon fibre or a particulate organic or inorganic filler, for example ceramic particles in the form of platelets. Examples of such compositions are described in our patent specification GB-B-2085461. The invention also applies, however, to the continuous formation of products from homogeneous materials, the molecular or other structure of which is capable of undergoing useful physical orientation. The inventions thus applies, for example, to the formation of products from thermoplastic semicrystalline polymer materials which can be effectively oriented, such as homo- or copolyolefins. It also applies to the removal of unwanted orientation effects which may be produced in conventional extrusions, for instance where a melt has to be separated and then recombined within the die prior to expulsion.
Methods and apparatus for achieving useful alignment of fibres or other constituents within moulded products have already been proposed, for example in our patent specification GB-A-2170142, but the process of continuous formation by extrusion poses problems which do not have to be addressed in the formation of a one-off product within a closed mould. Amongst these problems, of course, is the continuous movement of the product and its change of state as it moves.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is defined by the claims, the content of which are to be read as included within the disclosure of this specification. The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which:
FIG. 1 is a diagrammatic longitudinal section through the first and second parts of an extrusion die as extrusion proceeds;
FIG. 2 is a section on the line II--II in FIG. 1;
FIG. 3 is a section on the line III--III in FIG. 1;
FIG. 4 is a section on the line IV--IV in FIG. 1;
FIG. 5 is a diagrammatic longitudinal section through another extrusion die;
FIG. 6 is a similar section through a die for extruding tube;
FIGS. 7 to 11 are schematic transverse sections through the die of FIG. 6, and illustrate a sequence of operations of such a die; and
FIGS. 12 to 15 are schematic transverse sections illustrating the extrusion of products of yet further cross-sections, and
FIG. 16 is a schematic transverse section through yet another extrusion die .
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A composite product comprising polypropylene filled with aligned glass fibres is formed by continuously feeding feedstock 1, comprising a mixture of polypropylene granules and the fibres, from a hopper 2 to an extruder screw 3. The screw plasticises the polypropylene, mixes the fibres into the resulting melt evenly but with random orientation, and provides the head pressure necessary to extrude the melt through a die in two parts, 4 and 5. In the first die part 4 the cross-section of the melt changes and reduces from the circular diameter of the screw housing 6 at the inlet end of part 4 to a broad but shallow rectangle at the outlet end 7.
Throughout its length, the cavity of the second part 5 has the same cross-section as the outlet 7 of the first part 4. Cooling ducts 8a and 8b, through which cooling liquid flows between a controlled-temperature source 9 and a drain 10, are embedded into the structure of die part 5 so that they run parallel to the extrusion axis 11 and close to the die surfaces 12 that define the longer sides of the rectangular cross-section. In practice it is likely to be important that ducts 8a and 8b are arranged in parallel between source 9 and drain 10, and not in se
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patent: 3535737 (1970-10-01), Hendry
patent: 3555128 (1971-01-01), Schrenk
patent: 4056591 (1977-11-01), Goettler et al.
patent: 4789511 (1988-12-01), Bilgin
patent: 4919870 (1990-04-01), Ibar
patent: 4925161 (1990-05-01), Allan et al.
Allan Peter S.
Bevis Michael J.
National Research Development Corporation
Tentoni Leo B.
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