How do you get the very best from your twin-screw extruder? Bert Elliott of Leistritz has lots more practical tips in this second instalment of his two-part article
Top tips for twin-screw extruders – part two
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. The first part of this article (Compounding World, June 2012, Page 27) featured eight useful tips for improving twin-screw-extrusion. Here are 10 more practical ways to improve the efficiency and effective- ness of compounding operations.
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Acid flushing of barrel cooling bores
Water-cooled extruder barrels are heat exchangers, and like all other heat exchangers the coolant bores are subject to fouling from scale build-up. Most operators notice that the cooling performance of a new extruder is much better than an extruder after three or four years
of running. This is because the new extruder barrel has smooth, shiny, freshly-drilled cooling bores. The older machine has a layer of crusty mineral deposits lining the bores, that effectively act like a good insulator. If left unchecked, scale build-up can lead to a much
more serious problem. Eventually the cooling bores can become completely blocked, and zero water flow means a lack of cooling ability. If this happens, the only solution is to remove the barrels from the extruder and drill out all the cooling bores (Figure 1), which is a time consuming procedure[1]
. Figure 1:
Drilling out a barrel’s cooling bores is time consuming but can be avoided by using scale-removal chemicals