Best practice to conduct ring plunger test on molding machine

[Maheshkumar Hiremath]

Hi friends ,

I just want to know the best practice to conduct ring plunger test in injection molding machine.

[rickbatey]

Is that the same as a check ring repeatability test for a reciprocationg screw machine?

You turn the pack/hold pressure off, but leave the time on. Then collect the next 10 parts from the press. Weight the parts, and the range from lightest to heaviest should be less than 3% (if memory serves correctly). Then you get to turn it over to maintenance to replace the worn parts after they measure the parts.

[Rojan]

Rick,

I am time travelling a bit browsing the old threads.
I think it is a bit dangerous for some machines to leave the time counter on in the pack/hold phase as for some machines it is impossible to turn the pressure off completely.

Robert

[rickbatey]

Robert you must use the timer or add that back as screw recovery delay or the plasticizing portion will push more melt into the cavity skewing your test results. BTW how could that be dangerous? Sounds like some of the European folks I know ALWAYS ramping pack/hold pressure down so they "won't damage the press"!? An injection molding machine is one of the toughest most durable machines ever created by man. Hands down.
Rick.

[Rojan]

Rick,
I think we are on the same page, but to clarify. When I do this test for example on Arburg machines I turn off the pack/hold pressure as well as pack/hold timer, but I need to add appropriate time for screw delay. If I don't turn the pack/hold timer off, the machine generates 25 bar of specific pressure as this is the minimal amount of pressure that I can put on this machine. By 'dangerous' I meant that in the above scenario turning off the pack/hold timer is a must. If I do not do this I skew the test results as you wrote.

Robert

[rickbatey]

Robert- my favorite press, Engel, will allow me to turn off pack/hold pressure. Heck I can even set clamp force and zero. We use lots of valve gates tools. On a a KM, you MUST set one valve gate to open at shot size plus decompression stroke. On an Engel, I can pressurize the melt before I open a gate. That's a good thing when using CFA 's or blowing agents.
Rick.