THERMAL CONTROLS OF SLEEVES FOR QUALITY CONTROL

摘要

In sand casting, the thermal evaluation of sleeves remains nearly inexistent when batches are received and after an extended storage period in workshops. As a result of ageing over time and associated with improper storage or changes in materials attributable to suppliers, the thermal characteristics of the sleeves may deteriorate and limit their thermal capacity and consequently create shrinkages in the parts. Knowing the products'thermal characteristics thus allows us to control the quality of the sleeves and upgrade the databases of digital simulation software in order to improve their predictions. In these conditions, this project aims to develop a battery of tests designed to evaluate the thermal characteristics of sleeves used in sand casting operations. These tests measure the specific heat and the temperature diffusivity of die materials by taking small samples (diameter: 22 mm - height: 19 and 5 mm). The major advantage of taking these small samples is being able to avoid destroying the majority of the sleeves. The thermal conductivity is then calculated using the results of the two previous quantities. The specific heat measurement consists in analysing the heat transmission of the sample raised to 160℃ and cooled in the ambient air. The temperature diffusivity measurement consists in analysing the rate of transfer of a temperature front initially at 100℃, within the sample. The test procedures are simple and guarantee reliable responses. Furthermore, analysing the transfer of a temperature front initially at 400℃ allows us to compare or evaluate the volumic power density released by the exothermy of the sleeves. CTIFlaboratories use these tests to characterise the materials of current and future sleeves.