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Injection Molding Machine Hang-up

Injection Molding Machine Hang-up

Injection Molding Machine Hang-up


I was called over to look at a Boy 25Ton injection machine whose part ejector...wasn't. Being an EE i'm not a wiz at hydraulic schematics. Everytime I think I understand one - I don't, but I digress.

The entire hydraulic infested machine works great for the entire shot cycle, mold clamping, screw feed, inject, mold open, etc. The very last action is the ejection of the part done with a small ram, probably about 2 inches dia. The electronics command Y60 to shift and extend the ram ejecting the molded part out but then instead of the ejector ram actually retracting fully it just sort of lackadaisically rebounds about half way.

I assumed the return side coil was not working but when I got there I discovered the directional valve only had one coil and was spring returned. This means the electrical side was OKAY because the eject direction operated normally.

I figured the return spring was broken and to prove it pulled the cap off that end of the valve and there.. was a pristine fully intact spring that had nice action. I pulled the little spool out and it looked fine with nothing wrapped around it or nicks or such.

What do you think would cause the ejector ram to not power back to the stop?
I can't even find the big hydraulic pump on the schematic! The oil reservoir appeared full being only about 3/4" below the filler cap. The tank is probably 35 gallons.

I'm thinking there is something else in the circuitry that's causing this but since I can't figure out if A or B is the pressure side I can't make it out.

I've included the entire schematic for your perusal.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Injection Molding Machine Hang-up

I'm far from a hydraulics expert, but here's a few things I would check:

1. Is the ejector mechanism binding or sticking in any way? Since the cylinder will have a lower maximum force on retract (due to smaller area from the rod) it's possible for it to be able to extend but not retract.

2. What is the pressure during the extend and retract cycles? Ideally, you would measure the pressure directly at the cylinder, but it looks like the gauge M5 should give you at least some idea of whats going on. If the pressure is high (ie close to the system relief setting), then the system is likely dead headed in some way, possibly because the ejector mechanism is bound up, a valve isn't shifting properly or it could be something else (being able to compare the pressure at M5 and at the cylinder would help clarify this). If the pressure is very low, then you're likely blowing over a relief somewhere, so your system isn't able to build any meaningful pressure and therefore can't apply any force to move the ejector.

3. Is ISH7 functioning properly? I don't have time to figure out exactly what it does right now, but it seems to be involved with controlling how the ejector cylinder functions.

Also, it looks like the line you have labeled B1 is the pressure line and A1 is the tank line, at least based on the P and T port labels on Y60.

RE: Injection Molding Machine Hang-up

I agree check ISH7. The cam operating device may not be fully releasing the valve to allow the spring to fully return the valve. Partial valve shift would result in slow ejector return.


RE: Injection Molding Machine Hang-up

The ejector pin in the mold would be actuated by the ram. The ram cylinder may be operating correctly but there is something interfering with the pin moving, like resin flash or a broken ejector retainer.

In the bottom left corner of the schematic it shows a return to the fluid reservoir. It is likely that the line next to it coming from off the page is a hydraulic supply line.

RE: Injection Molding Machine Hang-up

Another possibility is problems with the piston seal in the ram.


RE: Injection Molding Machine Hang-up

Thanks all. I don't believe it's any kind of interference since we can completely remove the mold and its misbehavior doesn't change.

They were running the machine and in the middle of a morning run it started this problem.

I'm not there at the moment but I have them hunting for ISH7 since it seems a good candidate for the problem. They're having problems locating it.

The pump is submerged in the tank...

Keith Cress
kcress - http://www.flaminsystems.com

RE: Injection Molding Machine Hang-up

Perhaps if you remove the Y60, below the P port of the valve in the manifold block you may see a small throttle of dia 1.5mm. Please clean the same and re-assemble and your machine would be as good as new

RE: Injection Molding Machine Hang-up

Stick wins the Kewpie doll!

I told them to check ISH7 (see above) as suggested by Stick. They couldn't find it.... So they hired a hydraulics expert. He replaced the seals in the ejection ram.

No joy and no change in the non-functioning retraction of the ejector ram.

They called me again pleading for ASAP help. I rearranged my week and headed over yesterday. Got there at 3:45 - no one there, placed locked up. Annoyed. They will be charged an annoyance charge.

Went back today. They were there. Problem still present. Tested it several times confirming the ram wouldn't return. Cycled (opened and closed) the large covered-wagon safety cover to check an inductive sensor that wasn't lighting up. Noted the ejector ram was now working...

Stopped to search for ISH7. Three micro switches monitor the safety shroud. Two had cables coming out of them and one was more stout and had no cable leaving it and had exactly the hydraulic symbol depicted on the schematic above stamped on it's plate.

An examination showed that the cam follower wheel was so close to side of the safety cover that sometimes it would hang up on it. If I pressed on the roller I could stop ejector motion in its tracks extending OR retracting. We removed and discarded the non-tamper bolts the idiot factory installed to mount the cover with new standard cap-screws and adjusted the safety cover laterally 1/8" so the wheel cannot be interfered by the side of the safety cover.

Once this was done it was found that the mold could not be opened or closed. Back to the non-lighting of the inductive sensor. Careful comparison with an adjacent machine showed that a coupling block had been installed backwards after the ejector seal replacement. This prevented the electrical controls from declaring the ejector was fully retracted preventing all mold movement.

When help isn't..

I learned about cartridge valves, logic elements, and cam operated directional valves.

Thanks again everyone.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Injection Molding Machine Hang-up

Thank you for the reply back with your resolution.


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