EXPERIMENTATION AND MODELLING OF THE ANNEALING PROCESS PERFORMED IN A HYDROGEN BELL

摘要

The annealing performed in hydrogen bell furnace can represent a good alternative with respect to the other annealing process structured to reach high productivity rate, because it can grant a good cleanliness and homogeneous treatment. This is a technique known for several years, but in this study a new version, named HICON-H2, has been taken into account. The efficient heat transmission is assured by the high convection devices rotating at 75 Hz and the atmosphere is completely satured by 100 percent H2 during the annealing period. This atmosphere permits a satisfactory cleanliness of the surface which also decreases the time of the annealing process. The annelaing cycles of SAE1006 (tab.1) featured by different parameters has been observed (table 2). The positive convection has been proved by the little scatter of the hardness and ductility data among the different coils (table 3) and within any single coil (table 4). The grain size has been measured for each coil (table 5) and then it has been related to the annealing parameters after the definition of the construction of a mathematical model based on the finite different method to treat the heat transmission in order to define the thermal transmission modality. To define the convective heat transmission coefficients the thermocouples have been placed within the coils (fig.1) during the annealing period and then the heat transmission coefficients have been defined in order to fit the experimental results (fig.6). This permits to simulate correctly the annealing process and by the use of a method recently proposed to describe the static recrystallization, the average grain size of the annelaed grain has been related to the characteristic parameters of the annelaing cycle, giving good results. So the combined use of the ricrystallization model and the determined heat convection can allow a good designing of the annelaing process with great savings of money produced avoiding the expensive trial and error procedure.