Checking Your Check Ring Performance

All check rings leak, but over time the check ring will wear and leak more. The most important issue is how consistently it leaks during the velocity-controlled injection phase of the process.

Question: I have an issue with a 360 ton machine. Over the last three months, I have had most of my process’ have had their shot sizes grow. Same set process’ as before but as much as 10% more shot is required to fill part. The same tools in different machines are running spot on. Could this be the check ring or the barrel causing this issue?
My Response:I strongly recommend performing a Check Ring Repeatability test on all your machines as a baseline for comparison.
To perform this test:
1. Mold 10 short shots
2. Weigh each shot
3. Perform the following calculation:
100% x (Heaviest-Lightest) รท (Average) = %Variation
Some high precision molders will change the check ring when it exceeds 1 or 2%, while some lower precision molders might wait for it to reach 3 or 4%.
  1. Richard Johnston left a comment on 2013/01/26 at 8:03 pm

    I had a similar fault where increased shot was needed for every mould using the same material in the same moulding machine. It turned out that the stroke lenght on the check ring had increased as the check ring had woren away 2-3mm off the flights on the back of the screw tip. The screw tip had inserts / wear pads on the contact area for the check ring. One had come away then another. Then the check ring started to wear in to the screw tip. As the screw tip had further to travel to seal there was increased material leakage.

  2. bryce2013 left a comment on 2013/01/27 at 3:37 am

    The company I work for now, wants all injection/boost pressures set at max 2,000 to 2,300 psi. I was told that it insured a more consistant shot and was also told that this would blow thru any nozzle tip or gate freezing.
    Wouldn’t this be harder on the check ring? We run alot of nylon and glass filled materials that do tend to freeze off alot. With the high psi it causes the press to try and inject until the fill time has timed out which in some cases causes backing up in the throat. In the 7 years I have been with this company I have seen about 3 times as many check rings and screws get replaced then in the 9 years I was with my previous employer although a few check rings needed replacing after getting broke from material handlers or techs trying to clear blocked throats with screw drivers or brass rods because the company is to cheap to buy some nylon rod to poke thru.
    Am I missing something or what about the max psi. The last factory I worked for taught me to use just enough pressure and shot size to fill the part and not to over work the press. I also think this has alot to do with many of our presses overheating.

  3. Andy Routsis left a comment on 2013/01/27 at 10:38 pm

    Good Question,
    I will address this in the next blog posting.

  4. Andy Routsis left a comment on 2013/01/27 at 11:11 pm

    It is extremely unlikely this ring would have passed such a test as mentioned above.

  5. DaltonGang left a comment on 2013/01/31 at 7:41 pm

    I ended up doing the test and found nothing amiss here. Still had some issues so we pulled screw for measurement and inspection. Found that the barrel was badly worn half way back. (from nozzle) The screw was also worn in the metering section. I have ordered new parts. Now just have to wait see.

  6. Andy Routsis left a comment on 2013/02/01 at 10:39 am

    Interesting Results,
    Thank you for posting them. The most striking part of this is the fact that the ring tested well, and turned out to be OK. This demonstrates the fact that this test targets the performance of the check ring very specifically.

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