Modeling of heat transfer in rotational molding

Abstract

Rotational molding is a process for manufacturing hollow or open-sided plastic products using a rotating mold subjected to heating and then cooling. The process is attractive for the production of stress-free objects at a competitive cost. In this article, a modified model for heat transfer in rotational molding is proposed, which assumes that the heat transfer at the mold-powder interface is because of convection, whereas the powder particles are heated up by conduction. Heat transfer through the mold-air contact is also included. A source-based formulation is used for modeling the layer-by-layer nonisothermal deposition of plastic. The reduced heat transfer due to warpage is calculated by using a modified heat transfer coefficient. Good overall agreement is found between the cycle times as predicted by the model and the experimental data. The model is then used for calculating the cycle time for particulate composites, based on their effective properties. A reduction in the cycle time is observed in the case of reinforced composites. This is attributed to the increase in thermal conductivity of the particulate composites and the reduced mass fraction of the polymer. Numerical calculations of the cycle time for the glass-bead reinforced composites are found to be in good agreement with the experimental results.

Morphological and Mechanical Properties of Bilayers Wood-Plastic Composites and Foams Obtained by Rotational Molding

“…The PIAT values of layer 1 did not show a significant change with the relatively low amount of fiber used in the present work. Conversely, Mounika et al [27] reported variations of the thermal conductivity as a function of the fiber content, while Banerjee et al [28] reported that increasing the fiber content decreased the heat transfer rates and modified the PIAT values. When the material was added for the second layer, there was a significant increase in its PIAT (Table 1) due of the longer time in the mold (20 min for layer 1 versus 32 min for layer 2).…”

Rotational molding: A review of the models and materials

“…Indeed, this model does not require the application of a melt powder interface; and by extension the boundary conditions that are required in order to define it [8]. The models currently being investigated for RM can be divided into temperature based [10,20,21], source based [22] and enthalpybased [23][24][25][26]. In this instance as well the main difference between them is the manner in which ∆H is represented.…”

“…The numerical melting phase proceeded faster than expected, which could not be accounted for by the layer-by-layer deposition. Banerjee et al [22] incorporated into Equation 1the latent heats of melting and crystallization as a sink/ source term respectively (Equation (2)):…”

“…Among the earliest commercial systems includes RotoSim™, a program developed for the analysis of powder kinematics in a 3-D space [18,28]; following which mold local temperature profiles could be developed and cycle times approximated. Although it is a widely used RM simulator, it has faced criticism for its long computational periods [22] and numerical inaccuracies [8]. Of particular significance was the introduction of Rotolog™ in the early 1990's [29].…”

Effect of oven residence time on mechanical properties in rotomoulding of LLDPE

“…Antonio and Alfonso [1] used statistical and kinetic models for one-dimensional unsteady heat transfer during rotational moulding. Source based formulation was proposed by Banerjee et al [16] for modelling layer by layer non-isothermal deposition of plastic. The proposed method was also used for calculating the cycle time for particulate composites.…”