New here and a PC problem

[3NGLENN1889]

Hello all. I supervise a captive molding operation dealing with automotive lighting devices. I'll outline my issue as simply as possible and address any questions as they come up. We use a large amount of automotive grade PC. Many of our jobs involve unscrewing threaded steel cores from our components, for example a dome you would see on a snowplow,dump truck etc. The dome screws on to a plastic or metal base. I tried running the job automatically (robot picking the part) but over a period of time the threads start "picking up" leaving the threads shaved. Had to resort to going semi auto, operator picking the part by hand, dousing the core threads with mold release. Tried adding mold release pellets to the virgin but no go. Part is unscrewed hydraulically (core pull system) before ejection. Any ideas on what is causing this issue? Again I can answer any questions as thy come up. Thanks to any and all who respond. G.P.

[rickbatey]

I see three root causes: 1-Insufficient cooling of the unscrewing core. 2-Surface finish of core needs polishing or better yet plating with a coating that will provide better part release. Even Dyna-Blueing (sp?) should help. 3-The speed of the unscrewing core is too fast or is starting too fast. If you could start the core slower at first or perhaps you need more psi/speed at the start to break the core loose from the part will help.
Now a few questions for you: Does the unscrewing mechanism have solid stops in both directions? I ran a crane remote many years ago that didn't have stops built into the mold. The core would over travel and bind up in the mold time to time. Lastly how is the core turned? I prefer a hydraulic cylinder over a hydraulic motor. It's easy to add stops in the mold for the cylinder. Are you sure the hydraulic psi from the core shuts off while in the set position? I've seen that to cause issues when the machine can't turn off or the valve sticks.
Rick.

[3NGLENN1889]

Rick -thanks for the reply and suggestions. Mold is out now and we'll be inspecting the thread core and polishing. If there is time plating is in the works too.
Yes cooling is an issue in that region of the mold. The stationary core is cooled but of course the is no way to cool the rotating threaded core. Unscrewing core is driven by a hydraulic cylinder,at a very slow rate. There are stop position switches for set and pull. My maint guy is going to look into some kind of variable valving
for speed control. We'll wait and see what happens... thanks again G.P.

[rickbatey]

The rotating section can be cooled by if nothing else a heat transfer material like BeCu. I've seen enough cooling added with water channels cut into the core very similar to the channels added to rotating plattens that carry water and hydraulic oil through them. Granted that section ended up being straight chill water but it kept the mold running.
If the press doesn't have the ability to run a two step - speed/psi motion, then use two valves on the press with psi/speed controls on each and have one work at the start and the other start after that limit switch turns off. BTW what brand of press and year is it? There might be a way to get it working as you need without doing it yourself.
Rick.

[3NGLENN1889]

Hi Rick thanks for the reply. Tore apart the mold and the rotating threaded core had a very small (but sharp and deep) nick. Of course no one knew how it got there... Sent out for laser welding, polishing and plating. Hopefully I'll be able to get back to my automatic cycle with mold release pellets. I'd love a BeCu threaded core but the big guys say too much $$$$$.
Oh yeah the press is a 95 400 ton Nissei with a new barrel and screw. We'll see what happens.... Thanks again. G.P.