ISSUE 2/2012

/// 01
Chiesa F.; Giguère, N.; Duchesne B.; Baril, J.
Measuring mold cavity filling time in Low Pressure Permanent Mold Casting of aluminum A356 parts 

In the present work a great number of castings were poured by the Low Pressure Permanent Mold Process for a wide range of filling times and pouring temperatures. One casting was a 2 mm-wall (0.080”) cover weighing 0.13 kg (0.27 lb) and the other was a 7 kg (15.4 lbs) bell housing with walls varying in thickness from 6 to 25 mm (0.25 to 1”).
 0.12 mm diameter (0.0045”) type K thermocouple wires (response time of 0.1 s) were connected to a data logger (20 readings per second) to detect the passage of the liquid metal front, allowing an accurate measurement of the filling time (±0.05 s); as the filling time is obtained by substracting the passage times recorded by two identical thermocouples, the time lags cancels out with no detrimental effect on the accuracy.
This allowed to determine a “slowing factor” SF defined as the ratio of the actual measured filling time to the filling time calculated based on the static equilibrium level. SF was found to vary from 1, for very slow rates of filling, to values greater than 2 for extremely steep pressure ramps. For typical industrial production conditions, SF is in the range 1.3 to 1.6 and appears to be closer to 1.0 for thin castings. It was found that the pouring temperature had little effect on SF except for extremely low pouring temperatures (below 700 °C or 1292 °F).




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