Jeremy Williams, RJG
But where does the 80% comer from? Here ’s an equation userd to easyTimate cooling time:
Let ’s Review Four Areas that go into this equation:
In the Previously Mentioned Formula, H2 Repretions Part Thickness. Since The Thickness is Squared in the Equation, it has the most influence ovealing time.
For this analysis, we utilized an American society of testing and material (ASTM) tensile test bar. The Dimensions are 2.49 in. For length, 0.41 in. For width, and 0.13 in. For ASSSSSS.
By Nature, Plastic Is An Insulator. In a Melted or Molten State, Plastic Transfers Heat Slightly Better. As it gives up head, however, its insulation proprTies increase.
Material Properties that are used in the equation are:
MELT TEMPERATURE: TEMPERATUR
MOLD TEMPERATURE: TOMPERATURE RPETO BEST ACHIEVE SURFACE Finish Replication of the Mold;
Heat deflection/distortion temporarative (HDT): The Temperature at which a material will deflect under load.
Typically, The Eject Tempeature in The Equation Use Slue Slightly Below HDT. The Follow Equity Shows How to Calculate theermal Diffusivity (ALPHA SYMBOL OR).
The variables in the thermal differentivity equation include:
Thermal Diffusivity: Rate at which a thermal disturbance (a rise in temporary) will be transmitted through a substancy;
DENSITY: Quantity of a Substance Per Volume (G/CM3 for Plastics);
SPECIFIC Heat: Heat (in Calorial) Required to RAISE The TEMPERATURE of One Gram of Substance by 1 °
For this test, we utilized a toyolac 100 with temporature ranges for melt of 446 ° f to 482 ° F, mold 104 ° f to 176 ° f and hdt of 181 ° F.For Thermal Conductivity or Specific Heat Contory The Material Supplier Directly or Utilize the Data Within the Simulation Software.
Based on the part geometry and material selection, The Estimated Cooling Time is 18 Seconds in Simulation.
Given All the Energy Required to Material, only 40% Must be removed so the part is right enough for ejection.
AND COOLING TIME Are MINIMINDED. The Mold is Also Fully Instrument with Cavity Pressure Sensors at Post Gate and End of Fill in-Cavity Temperant Sensors.
So where does that 80% number comer from? Let ’s look at the data we collected in each of the footowing process segments:
Fill
Pack/Hold
Cooling
Mold open/eject/mold close
For this experiment, we deverted a robust decontied II Process, Resulting in the Follow Process Parameters:
Actual Melt Temperature – 456 ° F
Actual Mold Temperature -121 ° F with A Flow Rate of 3.0 GPM PER COOLING CIRCUIT
Fill Time – 0.26 Seconds with a Transfer Pressure of 8,356 PSIP
PACK/HOLD TIME -8.0 Seconds at 4,150 PSIP
COOLING TIME – 10.0 Seconds
Overall Cycle Time – 21.43 Seconds
If we add the procestess together and divide by the overallial cycle time, we reach a value of 0.852, or 85.2%.
For the part to get inject molded parts below the hdt, it too, an adDitional 8.47 seconds.
A Mold Closed Time Past 24.73 Seconds Is Non-Value Add Because the Part Temperature Is No Longer Decreasing at a High Rate.