Enhancement of convective heat transfer to polymer manufacturing molds

Many complex and dimensionally stable plastic products are manufactured using processes such as blow molding, thermoforming, injection molding, and rotational molding due to various advantages offered by these techniques. However, in many cases, product cycle times—and hence productivity—are limited by the time required to heat up and cool down the mold and the product. This is particularly true for rotational molding of thermoplastics. Due to the complex rotation of the mold, heating and cooling are most commonly achieved by convection to the external surfaces of the mold using air as the transfer medium. The objective of this work is to achieve substantial enhancement in convective heat transfer to mold exteriors and ultimately to reduce production cycle times. In this paper, the application of extended surfaces and roughened textures to molds is investigated. Extended surfaces have the potential to enhance heat transfer by increasing the surface area. Roughness elements are utilized in conjunction with turbulent flows, also producing significant increases in heat transfer rates. A steady state analysis using well-established techniques has been performed to estimate the heat transfer enhancement, and a series of simple experiments have been carried out. The predicted enhancements to heat transfer are substantial, and have been verified by the preliminary experimental results.