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the channel system by switching the status of corresponding control
valves. The control and monitor system was used to control all units.
A 3D thermal analysis of ANSYS on a simple mold plate was first run to check the analysis ability of steam heating. Fig. 3 shows the dimension
In which, ρ, V, μ and Cp are the density, flow velocity, viscosity and the specific heat of cooling water, respectively, and L is the characteristic
and the mesh model of the simple plate. The material of plate was chosen as P20 with the density, specific heat and thermal conductivity at
Fig. 2. Mold temperature control units with steam heating.
Fig. 3. Plate dimension and mesh model.
7800 kg/m3, 460 J/kg °C and 54 W/m °C, respectively. In simulation, the heat transfer mode around all external surfaces of plate was set at a free convection to the air; air temperature is 25 °C and heat transfer coefficient is 10 W/m2 K [15]. Multi cycles of steam heating were done based on this model. At the beginning, all plate was setup at 50 °C, and then in each cycle, 5 steps (as shown in Fig. 1) were setup for the heat convection at the channel wall. The heat transfer coefficient and fluid temperature inside channels are shown in Table 2. In general in simulation, the steam at 150 °C will heat plate until the surface temperature reaches to 140 °C, then, cool water (20 °C) will cool down the plate. Simply, by using the same channel, the plate will be heated by 150 °C steam until the surface reaches over 140 °C, then, it will be cooled down by 20 °C water. The temperature history at the point C and D of the plate was collected in multi cycles. Then, experiment result will be used to verify the simulation prediction at point C, and the comparison temperature between point C and D will show the delay time of temperature history.
It is the same with simulation, a steel plate of 100 × 100 × 42.5 mm3
with 4 cooling channels (10 mm diameter with the center 15 mm beneath the surface) was used for the experiment. By using the steam system as in Fig. 3, this plate was heated by hot steam and cooled down by cool water. Then, the temperature distribution and value at the center of the surface plate were collected by an infrared thermal measurement system. This result will be used to verify the simulated prediction at point C.
After that, a real application case for the TV housing mold was designed. The TV housing with 400 mm × 339.5 mm dimension is shown in Fig. 4. A P20 steel plate of 600 × 500 × 140 mm3 was designed with 8 channels (10 mm diameter and 15 mm beneath the cavity surface) for steam heating and water cooling. Fig. 5 shows the mold dimension, channel layout and the mesh model for the TV housing mold plate. For the operation of this case, the mold will first pre-heat by hot water to 50 °C, then; the cycle with steam heating, as shown in Fig. 1, will be applied. When the cavity surface at point P (Fig. 4) reaches to the
Table 2
The change of the heat transfer coefficient and the temperature of fluid in 1 cycle of steam assisted by injection molding.
target temperature, the mold plate will close and the melt will start to
fill cavity.
For observing the effect of steam heating on heating time, the heating process for the mold plate will be run by steam 150 °C and then water 120 °C, next, the cooling process will be done with the same cool water at 20 °C. In all cycles, the temperature at point P will be measured and compared together. Then, with the same process and parameters, a simulation by ANSYS is done and compared with the experiment results.
Finally, the same with the simple plate above, running coolant is 20 °C to cool down the mold, and steam at 150 °C for heating. By variance in the target temperature of the heating step from 70 to 110 °C, the temperature history was collected at point P for both heating and cooling. These results will be collected together with simulation results to show the effect of steam heating on the cavity temperature and time for heating. Besides that, for observation of the effect of steam heating and water heating on the product quality, the gloss and hardness at point P of the TV housing surface will be tested.