Single Screw Extruder

A spray dryer device for spray drying a sample dissolved in an organic solvent is disclosed, comprising a circulation line in which an inert gas is circulated by a blower, a heater for heating the inert gas to a specified temperature, a main drying chamber provided with a spray nozzle through which the sample dissolved in the organic solvent is sprayed into the inert gas, a collector in which the powdered sample produced in the main drying chamber is collected, and a condenser in which the gaseous organic solvent is condensed and recovered. The powdered sample is obtained in this spray dryer device for spray drying organic solvents by spraying the organic solvent through the spray nozzle into the main drying chamber in which the oxygen concentration is held to a low value by the introduction of the inert gas.

The spray dryer device for spray drying the sample dissolved in the organic solvents is designed to obtain samples in powder form by spraying a sample dissolved in an organic solvent through a nozzle into a drying chamber.

In recent years, single screw extruder being based on the so-called barrier screw concept have gained acceptance to an increasing extent. In a so-called barrier screw, the screw channel is divided in a solid matter channel and a melt channel by way of a further side bar. Compared with the primary side bar, being known from conventional screws, the smaller formed barrier side bar allows a transverse flow of melt from the solid matter channel into the melt channel. The cross-section of the melt channel increases in a downstream direction whereas the cross-section of the solid matter channel continuously decreases in the downstream direction as to maintain the desired conveying effect of the screw. Due to the so-called barrier zone particularly the heat transfer from the barrel and the screw surface to the granulate not yet melted is improved.

From a first aspect, the present invention provides an extruder machine 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 a single screw extruder, the screw typically has an external diameter corresponding to outer edges of the helical threads or flights. The flights may be under sized in relation to the barrel in the feed or hopper area so as to reduce feedthroat friction. Typically, a single keyway in the shaft area of the screw matches a keyway in a sleeve portion of a drive shaft so that a key positioned in the matching keyways is utilized to transmit rotational movement from the drive shaft to the screw. The key is a separate piece of rectangular metal which fits into the matching keyways. A disadvantage attendant with the use of keys is that they may be lost or misplaced. Also, worn keys can contribute to screw wobble.

As the viscosity of the thermoplastic material increases, it has been observed, that in single screws of the above described type, radial screw movement or wobble may develop. Clearance in the feed area between the outside diameter of the screw and the inside of the barrel permits movement of screw. As the screw wears, metal may be removed between the exterior of the screw and the inside of the barrel. This creates additional clearance which may cause even more wobble or radial movement.