Comparing Machine Capabilities…

This query came in the other day through email…

Today, I moved a mold from one machine to another. The peak injection pressure was 1450 bar with a 0.6 sec. cycle time. On the second machine, I can only get 1.03 sec. injection time at 900 bar. I cannot fill the mold even though the maximum available pressure is 1800 bar.
My Response
It is likely that your new machine lacks the injection speed in cubic millimeters per second to fill the mold.
The best way to approach this is to first determine the ‘Shot Volume Factor’  for your two machines (see Understanding Shot Volume Factors… for more about this). This factor converts the movement of the screw into the volume it displaces (this is expressed in 


If you multiply this factor by the injection speed used in your old machine, you can determine the volumetric injection rate in mm^3/s or cubic millimeters per second. If you divide this result by the volume factor of the second machine, you can determine the approximate injection speed necessary on the second machine. This will allow you to accurately compare the injection capacity of the two machines.

Additional Thoughts
Many of the newer molding machines are now providing much more helpful information such as the volumetric injection rate and displacement as well as the actual pressure being applied to the plastic during injection, pack, and recovery.


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