DescriptionThermoforming is widely-used and well-known in plastics processing. This paper deals with a thermoforming process used in pipe extrusion technology, the manufacture of belled pipe ends of thermoplastic sewer pipes. The process can be subdivided in three basic steps: heating of the pipe end, forming of the belled pipe end, including the circumferential groove for the sealing ring, and the cooling phase. The goal of the heating step is to combine three partly contradicting objectives: the achievement of a nearly uniform temperature distribution, the lowest possible heating time and a minimum of energy use. The optimization of the heating process can both shorten the heating time and enhance the quality of the belled pipe end. A parameter study using of a previously developed simulation tool for the heating step is presented in this paper. This simulation tool solves the transient heat transfer equation, including a wavelength dependent heat source term, using a finite differences method. The numerical calculations provide a radius and time dependent temperature distribution in the pipe end during the heating step. It is characterized by four characteristic quantities: the time needed to exceed the lower temperature limit of the processing window; the time required to exceed the upper temperature limit of the processing window; the minimal temperature difference (in the pipe wall) and the moment of its occurrence. The whole procedure was performed at radiator temperatures Trad between 300 and 1400°C and two different heat conduction coefficients on the inner pipe wall alpha (5 and 30 W/m²K). The times needed to exceed the lower and upper processing limits of temperature define an upper limit of the radiator temperature depending on the heat transfer coefficients. The material parameters of surface reflection, penetration depth, density, specific heat capacity and heat conductivity were varied as a part of the parameter study using four heating situations (Trad = 400, 1000°C and alpha = 5, 30 W/m²K). The variation of the penetration depth gives extrema for the four characteristic quantities. In contrast to that, the variation of the other aforementioned parameters resulted in a nearly linear dependence of the four characteristic quantities on these parameters.
|Period||20 Oct 2009|
|Event title||PPS 2009 - Europe/Africa Regional Meeting of the Polymer Processing Society for 2009: null|