Views:252 Author:Site Editor Publish Time: 2020-05-18 Origin:Site
There is a wide variety of extruders produced in the world today. In general, they can be classified into two main groups, that is the single screw and twin screw machines.
Twin screws can further be classified into different categories:
Corotating or counter-rotating
Intermeshing or non-intermeshing
Straight or conical(tapered)screws
The screws themselves can have single or multiple principles, compact (meaning that they are built in a single piece) or modular (when different screw sections are mounted on a grooved rod) construction, they can or cannot be provided with inside oil-cooling circulation, etc.
This twin-screw extruder is manufactured by Feininger, and the heat generated by mechanical work is very small, far below the heat required for the material to reach the temperature required for gas mixing. After the mixing, no more heat is applied, and due to the low shear developed, the temperature of the melt will decrease. Because of the relatively slow movement down the barrel and a reasonable little cooling, the temperature will easily reach the one required for the extrusion.
The very special principle of operation that characterizes Feininger corotating intermeshing twin-screws extruders can be summarized as follows:
The screws can be starve-fed by an independent mechanism so that screws speed setting does not affect output.
Positive forwarding action eliminates problems like the bridging or slipping of solid material in the feed section, allowing the feed of pellets, beads, or powder.
Shear rate is very low, and additional external heat, much easier to control, is added; the shear stress distribution can be adjusted by changing screw speed and/or output.
Stock temperature can be raised to the desired level without exceeding it, and low-temperature extrusion is easily obtainable.
Positive conveying of the melt eliminates surging and promotes better dimensional control of the extrudate.
Mixing is also positive and accomplished without overheating the material.
Better dispersing and homogeneisation.
Self-cleaning is fast and complete without overheating the material.
Lower HP required per rated output, resulting in a lesser stress on the machine.
Energy-saving, as the actual energy consumption is very close to the theoretical value needed.
Therefore, Feininger extruders are especially suitable for the extrusion of heat-sensitive polymers, for products that have to be extruded at low temperature, for the extrusion of uncompounded dry blends and for materials that present difficulty in feeding or have to be thoroughly degassed.
Finally, with the proper screw configuration, foamed products can be produced by mixing additives, melting at relatively high temperature, injecting the blowing agent, and then cooling the melt to the lower temperature required for foaming. All these operations are performed in one extruder.