Basic tribological problems of plasticizing systems in processing machines
Polimery 2001, No 2, 107
A plasticizing unit is one of basic units of extruders and injection-moulding machines. In the most commonly used screw plasticizing units the screws and barrels undergo the biggest wear. During these units' work, when a polymer moves in a screw channel, friction between the screw and the barrel and between the polymer and elements of the plasticizing unit is of the main part. Screws and barrels undergo different kinds of wear, which can be divided, according to the reason of its generation, on: abrasive, fatigue, erosive, corrosive and cavitational (Figs. 1-3). These kinds of wear occur with different intensity in particular sections of the plasticizing unit. Wear of screws is several times bigger than barrels, so during plasticizing units' work it should be taken into account that for one barrel using three or four screws are needed. The differences in plasticizing units' wear for single-screw extruders and twin-screw extruders have been noticed. (Figs. 4-7). Wear of elements of plasticizing units depends on a lot of factors, mainly on: type of processed polymer (Figs. 8, 9) processing conditions (mainly temperature) design and quality of work of the plasticizing unit and screw deformation under load.
The capacity decrease, the increase of the number of defective products, the increase of operating breaks and repair costs are the results of plasticizing units' wear. Their making and operating is connected with high costs so it is important to recognise reasons and effects of these units' wear and to work out methods for wear prevention or at least its decreasing.
Keywords: plasticizing system, plastic processing, friction wear, single-screw extruders, twin-screw extruders