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Published on January 1, 2006

Effect of Thermal Loading and Heater Failure on Thermal Performance

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Date Published January 1, 2006

This Report has been authored by:Eugene Ryzer at Acrolab Ltd.

The objective of this research was to compare the thermal response of standard platen and Isoplaten when they are subjected to different thermal loads and heater failures. These types of electrically heated platens are typically used in the rubber molding industry to maintain a uniform temperature distribution within the molds. The part quality in the molding process is significantly improved when the platen is operated at a uniform temperature. Previous studies have found that Isoplatens can significantly improve mold performance by eliminating hot spots and reduce cycle times. In this study, the thermal response of Isoplaten and standard heated Platen is compared in terms of their temperature distributions and thermal transient response times under different thermal loading conditions. The platen tested included heaters only. The Isoplaten tested contained same heaters and Isobars. The platens tested in this study were 457 mm x 457mm and 63 mm thick, with six 12mm diameter by 457 mm long 1000 W cartridge heaters embedded evenly along the bottom half of the platen. The platens were operated at 150°C, and the thermal loads were applied using a pre-determined amount of water to simulate the loading in a typical rubber molding application. Tests were performed with different thermal load contact areas at several locations on the platen surface. The transient temperature response of the platen and Isoplaten under the thermal load was characterized using a FLIR SC 3000 high-speed thermal imaging system. This system measured the temperature distribution of the whole platen surface to an accuracy of 0.1°C at a frame rate up to 900 frames per second. The transient and steady-state thermal performance of the platens was also characterized with different heaters turned off to characterize the performance of the platen under different failure modes. To obtain direct visualization of the temperature distribution of the heated surface at the point of loading, a hollow cylindrical cup was used to apply the water. In this concept, a hollow cylinder was placed directly on the platen and the platen surface acted as the bottom of the load ‘container’ through an o-ring seal. The infrared camera measured the surface temperature distribution within the load area once the water evaporated. This method of testing provided temperature data over the entire load area.