Top tips for twin-screws | processing feature How do you get the very best


from your twin-screw extruder? Bert Elliott of Leistritz has lots of practical tips in this first


instalment of his two-part article


Top tips for twin-screw extruders – part one


There are many techniques known to operators and plant engineers for increasing the performance of a twin-screw extruder. Because of their informal nature, however, most of these methods do not appear in any equipment manuals. Nor are they generally mentioned in textbooks and technical papers. But sometimes attention to several small details can add up to making a big difference in extruder performance. The tips described in this article fall into three broad categories: processing techniques, machine modifications, and maintenance procedures.


0 1


Install a thermal insulator gasket after the feed barrel


The feed barrel in almost all cases is water- cooled. But because this barrel is bolted flange-to-flange up against barrel #2, which is heated, heat is continuously transferred from the hotter barrel to the cooler barrel. As a result, barrel #2 is often not able to maintain a high enough temperature. In a typical case, the operator has a set-point of 180°C for barrel #2, but it can never get above 135°C because of heat loss to the feed barrel. The easiest way to solve this problem is to install an


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insulator gasket (Figure 1) between the flanges of the feed barrel and barrel #2. These gaskets are typically 1 mm thick, and it’s recommended to stack two together for better insulating performance. There will still be some heat conduction through the bolts, and of course the screw shafts, but not nearly as much as without the insulation. New extruders come as standard with the insulator


in place, but many operators don’t realize the impor- tance of it and throw it away when disassembling the barrels. Also, after several years the insulator gasket should be replaced, as the material tends to degrade and crumble.


Figure 1: Insulator


gaskets should be used to


reduce heat transfer


between the


feed barrel and barrel #2


s


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