13 novembre 2015 ~ 0 Commentaire

The effect of melt viscosity on thermal efficiency for single screw extrusion of HDPE

In this work, a highly instrumented single screw extruder has been used to review the result of polymer rheology on the thermal efficiency of the extrusion course. Three different molecular pounds grades of great density polyethylene (HDPE) had been extruded at a range of conditions. Three geometries of extruder screws were used at several set screw and temperatures rotation speeds. The extruder was built with real-time quantification of energy usage; thermal dynamics of the procedure were examined applying thermocouple grid sensors at the entrance to the die. Effects showed that polymer rheology acquired a significant influence on process energy consumption and thermal homogeneity of the melt. Highest specific energy consumption and poorest homogeneity was observed for the highest viscosity grade of HDPE. Extruder screw geometry, set extrusion temperature and screw rotation speed were likewise found to get a direct influence on energy usage and melt consistency. Specifically, specific energy usage was lower using a barrier flighted screw in comparison to one flighted screws at the same placed conditions. These benefits highlight the complex characteristics of extrusion thermal dynamics and offer evidence that rheological real estate of the polymer can substantially influence the thermal efficiency of the process.

Consumption of polymeric supplies has greatly increased over the past few decades due to their use in diverse industrial sectors. Plastics are in high demand in the packaging, construction, automotive, electrical and electronics industries, in addition to numerous other diverse applications. European plastics demand totalled 47 million tonnes in 2011, 21% of the full total world development and generated around annual turnover single screw extruders of 300 billion Euros, employing 1.45 million European citizens. Polyethylene represented 29% of the full total plastics demand (5.64 million tonnes of HDPE) (Plastic – the reality, 2012).

In polymer processing machinery such as solo screw extruders, polymer feedstock is fed in to the machine through a hopper, conveyed across the screw and melted by way of a combination of applied external heat and interior shear heat generation. The pressure generated forces the molten materials through a formed die to form the final product. The quality of the extruded merchandise is highly influenced by the regularity of melt made by the screw. Screw design needs to be matched to polymer type in purchase to minimise melting instabilities and pressure inconsistencies also to optimise pumping regularity through the die (Steward, 2002, Wheeler and lee, 1991,Rauwendaal, 1990). Optimised screw geometry can lead to better thermal homogeneity and heightened output and final product quality with lower energy consumption. It has been demonstrated that extruder heaters eat less energy once the extruders are managed at larger screw speeds (Cantor, 2010). It has also been found that sole screw extruders ought to be operated at the highest screw speeds to maximise efficiency, whilst the screw geometry ought to be carefully picked to optimise melt temperatures (Vera-Sorroche et al., 2012, Kelly et al., 2012).

Polyethylenes are actually semi-crystalline thermoplastics that exhibit non-Newtonian pseudoplastic behaviour found in the molten talk about. The partnership between molecular excess weight, its distribution and rheology plays a significant role and hence ought to be investigated when examining polymer processability in sole screw extrusion (Agassant and Villemaire, 1998, Hoffman and McKinley, 1985, Rohlfing and krishnaswamy, 2004, Craig et al, 1968). The aim of this job was to study the result of HDPE rheology on melt quality and energy intake in sole screw extrusion employing real-time measurement approaches. Thermocouple grid sensors allowed characterisation of the thermal dynamics of the extrusion method which in combination with real-time energy intake measurements facilitated an understanding of the thermal efficiency of the process (Brown et al., 2004,Abeykoon et al., 2012). The position of processing conditions, extruder screw place and geometry extrusion temps was examined, and the result of rheology on measured melt energy and temperatures consumption was quantified, in order to highlight potential strength savings from careful collection of processing circumstances and screw geometry.

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