Plastic and nonmetallic article shaping or treating: processes – Orienting or aligning solid particles in fluent matrix material
Patent
1987-03-30
1988-12-06
Thurlow, Jeffery
Plastic and nonmetallic article shaping or treating: processes
Orienting or aligning solid particles in fluent matrix material
2642098, 264349, 425206, 425207, 425461, 425466, B29C 4712
Patent
active
047895110
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to materials processing, particularly but not exclusively processing of polymer melts (e.g. by extrusion).
The extrusion technique is well established for the production of plastics articles, e.g. sheets and pipes, but does have certain disadvantages associated with the flow pattern of the molten material in the extrusion die. The production of discontinuous fiber reinforced plastics sheet may be cited as an example. During production of such sheets, the flow pattern of the molten plastics material results in the fibers becoming more or less uniaxially aligned in the direction of extrusion. The resultant sheet is substantially anisotropic.
A further example is the production of tubular material. In this case, the flow pattern tends to align reinforcing fibers parallel to the tube axis whereas it may be desirable that the fibers be aligned at various angles to this axis so as to increase the hoop strength.
An additional problem arises in the production of pipes (whether reinforced or not) due to the formation of so-called weld lines. These lines result from the struts (or `spiders`) used to hold the central core of the die in position. Molten material must flow around these struts resulting at the downstream side thereof in weld lines (or join) where the separated flow lines again meet. The resultant pipe includes a number (depending on the number of struts) of axially parallel weld lines which may or may not be visible but which represent weaknesses in the pipe.
Finally, in the production of sheets and pipes as discussed above, it may be desired to control the molecular orientation within the product (e.g. to give multiaxial, orientation) and such control can be difficult to achieve using the conventional apparatus.
It is an object of the present invention to obviate or mitigate the abovementioned disadvantages.
According to a first aspect of the present invention there is provided a method of extruding a solidifiable material through an extrusion die wherein a pressure differential is established across the die transverse to the extrusion direction thereby to create a flow of material through the die having a velocity component transverse to the extrusion direction.
Preferably the pressure differential transverse to the extrusion direction is continuous thereby establishing a continuous change of velocity component transverse to the extrusion direction.
Preferably also there is at least one reversal of transverse pressure differential (and hence transverse velocity component) during the extrusion of the material.
According to a second aspect of the present invention there is provided an extrusion die having an axially extending extrusion channel wherein, in its cross-sectional plane transverse to the flow direction, the channel is shaped to establish a pressure differential transverse to the axial flow direction. This shaping is preferably such that, in the said cross-sectional plane, the depth of the channel varies in a direction transverse to the axial flow direction.
In addition to the extrusion methods and apparatus defined in the two preceding paragraphs, the invention also provides other methods of, and apparatus for, materials processing which embody the same principles.
The invention will be further described by way of example only with reference to the accompanying drawings, in which:
FIG. 1 is a diagrammatic plan view of one embodiment of extrusion apparatus in accordance with the invention for producing sheet material;
FIGS. 2a-2e are sectional views on the line a--a, b--b, c--c, d--d, and e--e of the apparatus shown in FIG. 1;
FIG. 3 is a detail of FIG. 1;
FIG. 4 is a part sectional view of one embodiment of extrusion die for producing a pipe;
FIG. 5 is a sectional view of the line X--X of the die shown in FIG. 4;
FIG. 6 is a part sectional view of a further embodiment of die; and
FIGS. 7a-c are sectional views on the lines A--A, B--B and C--C of FIG. 6.
Referring to FIG. 1, the extrusion apparatus 1 illustrated therein is intended for producing fiber-reinforced p
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Thurlow Jeffery
University of Manchester Institute of Science and Technology
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