This query came in the other day through email...
Emailer
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
mm^3/s).
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.
-Andy
Hello Andy.
I did it exactly you said. But technician said: In first portion of injection, increasing injection pressure is too high and machine start to limit the injection speed due to machine design to avoid problem with electric motor. He said also: Maybe you have problem with electric motor what I can't detect in place.
MJ
Milan,
You should look also check the power consumption to ensure all the necessary power is being supplied to the servo-motor. Also, check your injection settings, some machines have different settings on how it behaves as it achieves the desired injection speed. Some machines will creep up on the injection speed to prevent overshoot.
Since your injection time is only 0.6 seconds, any setting intended to avoid overshoot would hinder your overall injection time. You may be able to step up the injection speed using a profile to help trick the machine into thinking it is not going too fast. This causes the machine to keep increasing the injection speed rather than slow it down.
-Andy
Andy,
I tryed start filling slowly and then increase, but same result. I tryed adjust just 60mm/s. Fill speed on begining was stable but when injection pressure started increase (parts 70% full) then machine decreased injection speed. Over the 60mm/s it was just worse. Maximum injection speed of this electric machine is 150mm/s.
MJ
Milan,
To test the speed of the servo-motor, you can use a large decompression before screw recovery so that the barrel is virtually empty. This will determine if the machine can inject any faster without a load.
-Andy
Andy,
When I did airshot, injection time was 0,6 sec.
MJ
Milan,
Seems like you have a poorly performing, under-rated, or underpowered servo-motor.
-Andy
thanks Andy.
Milan