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 study the result of polymer rheology on the thermal proficiency of the extrusion plan. Three different molecular fat grades of large density polyethylene (HDPE) had been extruded at a range of conditions. Three geometries of extruder screws had been used at one or two set temperatures and screw 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. Results demonstrated that polymer rheology acquired a significant effect on process energy intake and thermal homogeneity of the melt. Highest specific energy intake and poorest homogeneity was noticed for the highest viscosity quality of HDPE. Extruder screw geometry, set extrusion temperature and screw rotation rate were as well found to have a direct effect on energy intake and melt consistency. Specifically, specific energy intake was lower utilizing a barrier flighted screw compared to solitary flighted screws at the same placed conditions. These outcomes highlight the complex characteristics of extrusion thermal dynamics and offer evidence that rheological houses of the polymer can substantially influence the thermal performance of the process.

Consumption of polymeric supplies has greatly increased in the last few decades due to their use in diverse industrial sectors. Plastics will be in high demand in the packaging, engineering, automotive, electrical and electronics industries, in addition to numerous other various applications. European plastics demand totalled 47 million tonnes in 2011, 21% of the full total world development and generated an estimated annual turnover of 300 billion Euros, employing 1.45 million European citizens. Polyethylene represented 29% of the plastic pelletizer full total plastics demand (5.64 million tonnes of HDPE) (Plastic - the Facts, 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 create the final product. The standard of the extruded product depends upon the consistency of melt produced by the screw highly. Screw design needs to be matched to polymer type in buy to minimise melting instabilities and pressure inconsistencies and to optimise pumping regularity through the die (Steward, 2002, Wheeler and lee, 1991,Rauwendaal, 1990). Optimised screw geometry can cause better thermal homogeneity and heightened productivity and final product top quality with lower energy usage. It has been shown that extruder heaters eat less energy once the extruders are managed at higher 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 should be carefully selected to optimise melt temperature (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 point out. The partnership between molecular excess fat, its distribution and rheology takes on a significant role and hence should be investigated when examining polymer processability in solitary screw extrusion (Agassant and Villemaire, 1998, McKinley and hoffman, 1985, Krishnaswamy and Rohlfing, 2004, Craig et al, 1968). The purpose of this job was to study the result of HDPE rheology on melt top quality and energy usage in solitary screw extrusion employing real-time measurement tactics. Thermocouple grid sensors enabled characterisation of the thermal dynamics of the extrusion method which in combination with real-time energy consumption measurements facilitated a knowledge of the thermal productivity of the process (Brown et al., 2004,Abeykoon et al., 2012). The position of processing conditions, extruder screw geometry and set extrusion temperature ranges was examined, and the result of rheology on measured melt energy and temperature ranges consumption was quantified, to be able to highlight potential energy savings from careful selection of processing circumstances and screw geometry.

Write a comment

Comments: 0