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) ÷ (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%.