I am assuming you find yourself in the manufacturing industry, more to the fact in the plastic injection moulding section. You will find my Bio on the 'My Story' page, where I highlight my knowledge and experiences. The services I provide include books of knowledge or learning materials whereby you can get a deeper (meat and potatoes look) into the realms of plastic injection moulding. The insights I provide include some general knowledge on the subject then other books zone in on specifics, such as diesetting, troubleshooting and die trialling.
I hope you find them useful, they are intended to give a more (insightful) look into why things occur and why we do things a certain way in the Plastics industry. I hope to illustrate a clear explanation on each subject, but if you have any questions please don't hesitate to contact me via the 'Talk to me' page. I will get back to you as soon as I can, also allerting others to your plight and possible solution.
ALSO: Please review a few snippets from my books on this page.
One of the biggest things I look for when trying to combat this type of erratic or no cushion situation is by watching the screw move forward, if it makes changeover and holds for a period of time (possibly 1 or 2 seconds) then slowly moves forward to bottom out, the chances are high that either the check ring is not seating as explained above, or indeed the check ring or smear head is worn. This holding pressure for a second or two is indicating that material is being forced in front of the screw to the point of pack but is not able to hold that position showing a bleed back. Typically if there is a foreign body or higher melt granule inhibiting the seating of the check ring, you won't get that initial holding for a period of time, the screw will stall at changeover and keep moving forward which is purely the hydraulics and moog valve coming into play not the physical seating of the check ring. As a temporary measure if purging as indicated above doesn't help, may be to reduce the pack pressures to ensure a hold pattern.
Splay is caused by volatiles in the melt. This is typically moisture in the material whereby the material isn’t sufficiently pre-dried or it could be that the material is overheated/degraded and the molecules are reacting and giving off volatiles. Splay is the initial formation or first indications of melt issues. Check that the material is dried adequately, then check the barrel temperatures for anything untoward. These are the two biggest causes of this issue. Now being the quick fix section of the book, this is a quick remedy. There may be other underlying issues happening in the background. Make sure that you come back to this issue and find the Root Cause of it, Parameters don’t change without something breaking down or malfunctioning.