Single Screw Extrusion process
Bausano Single screw extruders build pressure in polymer melt so that it can be extruded through a die or be injected into a mold. Single screw extruders are usually used for conveying rather than for mixing or homogenizing of polymers.
The Bausano single screw extruder consists of a screw and barrel, drive mechanism, resin feed arrangement and controls. The screw inside the extruder is constantly turning, moving the resin through the heated barrel. Thanks to the high temperatures, the material is mixed and becomes a homogeneous melt. A strong pressure is created which pushes the melt out of the extruder into the mold.
A Bausano hopper is attached to the barrel at the entrance end of the screw and the resin is either gravity-fed (flood-fed) into the feed section of the screw or dosed (starve-fed) through the hopper to the screw. The resin can be in either a solid particle form or molten. If the resin feedstock is in solid form, typically pellets (or powders), the Bausano’s extruder screw must first transport the pellets away from the feed opening, melt the resin and then pump and pressurise it for a downstream process operation. This type of machine is referred to as a plasticizing single screw extruder, namely Bausano E-GO single screw extruder.
Temperature zones and screw
The barrel is usually heated with a minimum of three temperature zones. These different temperature zones are consistent with the three utilitarian functions of the screw: solids conveying, melting, and pumping or metering of the polymer. The single screw plasticizing process starts with the mixing of the feedstock materials. Typically, several different feedstocks are added to the hopper, such as fresh resin pellets, recycled material, additives, and a color concentrate. Next, the feedstock flows via gravity from the hopper through the feed throat of the feed casing and into the solids-conveying section of the screw. Typically, this feed casing is cooled using water. The feed section of the screw is typically designed, from the Bausano technical department, with a constant depth and is about 4-to-8-barrel diameters in axial length. Directly after the solids-conveying section is a section where the channel depth tapers to a shallow depth-metering section. In general, the metering section is also a constant depth, but many variations exist where the channels oscillate.
