Extrusion die
An extrusion die comprises a die body defining a die cavity ( 18 ). The cavity ( 18 ) is shaped such that the die body includes a male portion ( 24 ) and a female portion ( 26 ). A leading edge ( 18 a ) of a part of one side of the die cavity ( 18 ) is out of alignment with a leading edge ( 18 a ) of an opposing part of the die cavity ( 18 ), at rest, such that, in use, when deflection of parts of the die occurs, the leading edges ( 18 a ) substantially align.
1. An extrusion die comprising a die body having a die cavity formed therein, the die body defining a male portion which projects into a female portion, a recess of non-uniform depth being provided on the die body ahead of the die cavity in the extrusion direction, the recess being of non-uniform depth both around and across the die cavity, wherein a leading edge of a part of the die cavity defined by the male portion and a leading edge of an opposing part of the die cavity defined by the female portion are out of alignment with one another when the die is not in use, at least part of at least one of the leading edges being defined at the intersection between the die cavity and the recess, wherein the die body has a leading face wherein the die cavity is formed, and wherein the leading face is non-planar whereby the male portion is raised relative to the female portion resulting in the leading edge of the part of the die cavity defined by the male portion being spaced, in the extrusion direction, ahead of the leading edge of the part of the die cavity defined by the female portion by a distance which is not uniform around the die cavity, the spacing being such that deflection of the male portion, in use, brings the leading edges substantially into alignment.
2. A die as claimed in claim 1 , wherein the die cavity is of zero bearing form, both the male and the female portions being zero bearing.
3. A die as claimed claim 1 , wherein the male and female portions co-operate to produce, in use, an extrusion having at least one channel shaped region.
4. A die as claimed claim 1 , wherein the die body has plural parts, the male and female portions being on separate die parts and co-operate to produce, in use, an extrusion including at least one hollow region.
5. A die as claimed claim 1 , wherein the extrusion die is a flat face die.
6. A die as claimed in claim 1 , wherein the die body is a unitary structure, the male and female portions are on that unitary body.
7. A die as claimed in claim 1 , wherein the non-uniform depth across the die cavity results from the male and female portions being of different depths of the recess on the respective male and female portions, and the non-uniform depth around the die cavity results from the depth of at least one of the portions differing itself.
8. An extrusion die comprising a die body having a die cavity formed therein, the die body defining a male portion which projects into a female portion, wherein a leading edge of a part of the die cavity defined by the male portion and a leading edge of an opposing part of the die cavity defined by the female portion are out of alignment with one another when the die is not in use, the leading edge of the part of the die cavity defined by the male portion being spaced by a distance, in the extrusion direction, ahead from the leading edge of the part of the die cavity defined by the female portion, the distance varying around the die cavity, the spacing being such that deflection of the male portion and female portion, in use, brings the opposing leading edges substantially into alignment.
9. A die as claimed in claim 8 , wherein the spacing varies smoothly and continuously over the face of the die.
10. A die as claimed in claim 9 , wherein the spacing varies smoothly and continuously over the face of the die from a maximum at tips of the male portions to a minimum at ends remote therefrom.