Continous production of an extruded section
An object of the present invention made in view of the problems inherent in prior art sheet production extruder is therefore to provide a novel extruder that can apply a sufficient pressure to a raw material in a feed passage so that the a wider range of extrusion conditions may be afforded. Another object of the invention is to provide an extruder in which a higher pressure is applied to the raw material, and at the same time this raw material is heated to melt uniform before flowing through an extrusion die so that this die is protected from any breakage impairing its durability. This object must be achieved in the invention in such a manner that the necessity of heaters softening the raw material is reduced, diminished or excluded to decrease the energy consumption and lower the equipment and production costs.
It is still another object to provide an single screw extruder in which a wire-shaped or rod-shaped raw material is continuously forced through a material feed passage in such a manner that any unsoftened or insufficiently softened raw material is prevented from reaching the extrusion die, so as to protect the die from any damage which would otherwise impair its durability. From a first aspect, the present invention provides an extruder comprising: an extrusion die; a feed passage disposed behind the die and guiding a raw material thereinto; and further comprising characteristically at least one pair of blades which each has a helical edge formed at a predetermined lead angle and protruding into the feed passage from an inner periphery thereof, wherein the blades are driven to rotate so as to force the raw material towards the die.
From a second aspect, the present invention provides an extruder comprising: an extrusion die; a feed passage disposed behind the die and guiding a raw material thereinto; and further comprising characteristically a stationary core disposed in an intermediate region of the feed passage so as to define at least one annular passageways around the core and in fluid communication with the feed passage; and at least one pair of blades which each have a helical edge formed at a predetermined lead angle and disposed in the annular passageway, wherein the blades are driven to rotate so as to force the raw material towards the die.
In the twin screw extruder provided herein from the second aspect, the helical edges preferably protrude into the annular passageway(s) from an inner periphery of the feed passage. A plurality of bridges may preferably hold the stationary core in place in the feed passage, wherein the bridges are arranged at angular intervals. It is preferable that each helical edge is not interposed between any helical valleys, along its entire length. The blades having the helical edges may preferably protrude from the inner peripheries of short columnar or disc-shaped members. Each blade may be a sintered block of a hard metal powder or the like, and the feed passage extends axially of the columnar or disc-shaped members.