Procedure to generate a Viscosity Curve
Set the melt temperatures to those recommended by the manufacturer. If there is
a range, set the temperatures to the center of the range.
Set all the holding phase parameters to zero. This means that there will not be
any holding phase and only injection.
Set the injection pressure to the maximum available.
Set the cooling time to a safe value such that the part will be cool and has
reached the ejection temperature before mold opening.
Set the injection speed to ‘slow’ and make a part. The part should be short. If
not adjust the transfer position to make the part such that it is filled only
Increase the speed in steps and make sure that the parts are still short. Mold
a part with close to the maximum injection speed and make sure that it is still
short. If it is full, then adjust the transfer position, such that it is about
95 % full part. If it is less than 95 % full, then also adjust such that the
part is 95% full. This means that at close to the maximum injection speed you
have a 95% full part with no holding time or pressure.
Make another shot and record the fill time and the peak hydraulic pressure
required to fill the part. Note: The peak hydraulic pressure will be the
pressure required to move the screw at the set injection speed. This is taken
from the available pressure from the machine. For example, the machine is set
to 2200 psi but may require only 1850 psi to move the screw at the maximum
speed of 5 in/sec.
Next, lower the speed by a small amount, for example from 5 in/sec to 4.5
in/sec or from 90% to 80%. Note the fill time and the peak injection pressure.
Repeat the above step all the way till you get to the lowest injection speed
possible. Divide the available injection speed range into about 10 - 12 speeds
so that you get as many data points.
Find the Intensification Ratio of the screw from the machine manufacturer. If
this number is not available, pick it to be 10. It does not really matter since
this is a constant used in the equation and will factor the viscosity
To get the viscosity, use the following formula: Viscosity = Peak Injection
Pressure X Fill Time X Screw Intensification RatioPlot the graph of viscosity
vs injection speed.