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Thread: Pressure Gap

  1. #1
    Join Date
    Oct 2020
    Posts
    16

    Pressure Gap

    Hello everyone,

    Please I need your help to understand the outputs, that our ARBURG machine gives. We have a difference of 200bar between the maximum injection pressure and the switch-over pressure (commutation pressure). My questions are:
    Is that normal to have this difference? if is it not ==> what are the causes of this variation? especially in the switch-over pressure because it is the one that has a minimum value (700bar).

    Note1: I remarque that most of our machines have approximately the same value in maximum injection pressure and switch-over pressure.

    Note2: Injection stroke: 55 mm
    Switch-over point: 15.7

    Anyone can help me, I will appreciate it.
    Thanks in advance.

    BR

  2. #2
    Join Date
    Aug 2011
    Posts
    623

    Re: Pressure Gap

    Hello,

    All 'modern' machines, say in the last 20 years made by reputed makes such as Arburg are closed loop machines. So you may set the value to 2000 bar but the machine will only take what it needs to inject at the speed you have input. So at lower speeds you may need only 400 bar but at higher speeds it may be 700 bar. So if you set the machine value at 2000 or 20,000 it will not matter.

    Your car in cruise control is a closed loop system. Think when you are driving your car, you want to drive at 40 miles per hr, you will depress the accelerator half way, you want to go faster you will depress it a little more. The car will do this automatically in cruise control.

    So all is good with your machine
    -Suhas

  3. #3
    Join Date
    Oct 2020
    Posts
    16

    Re: Pressure Gap

    Thank you, Suhas for your feedback. maybe I didn't make a good explanation, hope that the attached picture makes things clear.

    Thank you,
    Attached Thumbnails Attached Thumbnails Capture.jpg  

  4. #4
    Join Date
    Oct 2014
    Posts
    5

    Re: Pressure Gap

    Normally your peak pressure is at switchover, when cavity is most close to full, it could be an indication of a cold slug or some other restriction in the melt flow path. Check your graphs or do a pressure drop study.
    Regards,

  5. #5

    Re: Pressure Gap

    The setup as you described it is correct and will provide consistent parts shot to shot. Maximum Injection Pressure is the maximum pressure you will have available during the injection cycle. The injection rate or speed is dependent on having enough Injection Pressure available to achieve the desired injection rate that you set. The process may not need the maximum Injection pressure that is available to achieve the injection rate setting but it's there. In a situation where the Maximum injection pressure is set too low to support the injection rate or speed you have set the process would be out of control. The machine knows you want a specific injection rate but without enough pressure available it can't reach the speed and you get whatever you get.
    The switch over pressure is the pressure you want the machine to switch over from Injection High to pack or hold pressure, In your note 2 it appears as you are using the position of 15.7 to switch over. So the switch over pressure you have set may never happen. Once the machine hits 15.7 it will switch over. So I would consider your ARBURG setup as a good setup. Hope that makes sense. Bryan

  6. #6
    Join Date
    Oct 2020
    Posts
    16

    Re: Pressure Gap

    Thank you all, for your explanation, I appreciate that.

  7. #7
    Join Date
    Aug 2011
    Posts
    623

    Re: Pressure Gap

    Sorry, if I misunderstood.
    What are p4072 and p4055? What are the output names?
    Thanks
    Suhas

  8. #8
    Join Date
    Oct 2020
    Posts
    16

    Re: Pressure Gap

    Hi,

    The P4072 is the switch-over pressure (Commutation pressure).
    and P4055 is the maximum pressure (or peak pressure).

    BR

  9. #9

    Re: Pressure Gap

    How do I start a post? A new thread? I'm a new member and it doesn't look as though I can do this. Any help would be appreciated. Thanks in advance!

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