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Thread: Injection Pressure

  1. #1
    Join Date
    Aug 2018
    Posts
    2

    Question Injection Pressure

    Hi,

    Does someone know how to estimate "approximately" the injection pressure needed for the mold by the machine by hand calcul ?

    I have every spec of mold and resin.


    Thank you in advance !

  2. #2
    Join Date
    Aug 2011
    Posts
    554

    Re: Injection Pressure

    Hi,

    You will need to refer to the books. There are formulas for pressure drop that you can try and use after simplifying the geometry of the part you have. There are formulas for flow through channels which will differ based on the cross section.
    Just curious - is this an academic study?

    -Suhas

  3. #3
    Join Date
    Aug 2018
    Posts
    2

    Re: Injection Pressure

    Hi,

    No it is not an academic study. I need to develop an application that can match mold and machine in the company. The company have over 200 machines and over 300 molds. We want to know if a machine can use a mold or not with the spec.

    And i know that for clamping, we need the injection pressure.

    I just need a little formula that can approximate the injection pressure that a mold can have. Cause i know that a chart exist with L/T but we have some mold with an L/T of 450 and the chart's maximum is 300.

    Thanks

  4. #4
    Join Date
    Aug 2014
    Location
    Michigan
    Posts
    63

    Re: Injection Pressure

    The equation you are looking for is:

    Delta_P = (8*FlowRate*Length*Viscosity)/(Pie*r^4)

    notes:

    FlowRate is not the same as injection speed.

    Viscosity you are going to have to get from a graph provided by a material datasheet (if you can find it).

    This equation is for a round channel, will have to change if rectangular channel.

    This equation will get you an approximate pressure from the sprue to end of fill of the cavity (if you take the sprue and runner dimensions into account). You are going to want to take the pressure loss through the nozzle and any nozzle extensions you may have, into account (put the nozzle you intend to use on the machine and purge a full shot through the nozzle, record that pressure needed, convert to plastic pressure if needed and add that pressure to the above calculation).

    This is the calculation of the PLASTIC pressure needed and applies directly to electric machines. If you have a hydraulic machine, you will need to convert your machines maximum hydraulic pressure to plastic pressure using your machines intensification ratio to see if that machine has the pressure needed.

    Last but not least, UNITS! make sure you are working in the same units! Convert where and when needed.

  5. #5
    Join Date
    Aug 2014
    Location
    Saint Paul, MN
    Posts
    125

    Re: Injection Pressure

    Quote Originally Posted by MTUHusky View Post


    This equation is for a round channel, will have to change if rectangular channel.
    Hydraulic diameter is 4A/P, where A is cross-sectional area and P is perimeter.

  6. #6

    Re: Injection Pressure

    Hi,

    Sorry for the late response.

    I am unclear as to the benefit of such..... it will only get you an approximate value, at best, but if you record the actual Fill Peak PSI during a run of your existing molds, (or max packing psi if it exceeds the fill peak psi) that is the number you want to record and use as your metric, easily kept in a spreadsheet for example.

    And, if it's a new tool being built, requesting a mold flow analysis will get you closer to your PSI needed, as well as provide other critical info.

    Joel

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