One of our more advanced customers brought to us this observation…
It is interesting that this test does not utilize the pack & hold portion of the cycle; just the fill portion. Experience shows, especially with high 2nd stage pressures, that the screw will drift, and some reflection of that would be a good indication of check ring holding. Your thoughts…?
Every check ring will leak and drift. What is most important in maintaining a consistent fill is the repeatability of this leak. The Dynamic Check Ring Repeatability Test is intended to measure this variability in this leak during fill. In most cases, if the drift is variable during 2nd stage, it will also be variable during fill. Although each process is different… if the screw does not bottom out, and cushion varies less than 5% of the overall shot size from shot to shot, usually the amount of drift is not a major factor.
It is always great to hear someone asking such highly technical questions because it means they are focusing on the finer points of processing rather than subjects of general knowledge.