Having an issue that's driving me nuts.

[moldingppm]

I seem to have issues with the nozzle seating against the bushings of any of my molds.

I will be running jobs, and I will have plastic coming out from around the nozzle tip, almost as if it's not seating correctly. I've gone as far as going to a 1/16th" tip to see if I could at least get a few parts out. Now it seems to be running even worse. It's not even getting plastic into the mold, and yes, I've checked the sprue bushings for clogs. I'm at a loss here, and I'm also deciding on which wall to put my head through due to frustration. I've checked to see if the nozzle is centered in the locating ring, and it seems fine. Also, I have the carriage (or sled) pressure set around 2400 PSI, so it should be seating pretty tight.

Does anyone have ANY ideas?


Sorry for the jumping around with my post, I was typing in a hurry.

Van Dorn ET-80, 2 oz barrel, 25mm screw

[Suhas]

Molding ppm,
Have you checked to see if the O-dia of the sprure bushing is way smaller that the nozzle orifice? In such cases, you are applying plastic pressure on face of the sprue bushing causing the sled to get pushed back and leak the plastic.
Suhas

[moldingppm]

Suhas,

The orface of the mold is 3/16. One thing I did notice is that the sled is being pushed back. Not sure how to fix that..

[Suhas]

And what is the orifice of the nozzle? Is it smaller or bigger?
Suhas

[moldingppm]

And what is the orifice of the nozzle? Is it smaller or bigger?
Suhas

I had a 1/16th nozzle on there and just switched to a 5/32. I'm having the same issue with both sizes.

[rickbatey]

You may build very high carriage pressure, but you need enough volume to maintain the carriage position. So you could have low pump volume.
You could have a leaking (internal) carriage cylinder, valve, hydraulic block or crack in injection housing.
Are you sure the barrel is centered? How did you confirm? Is the radius correct for the mold? Did this just start? What is the sequence for carriage psi build and is the psi maintained by holding pump or locked into cylinder by valving?
Rick.

[rickbatey]

One last thought. Could you be running out of resin and the press dropping the carriage psi while the screw still runs?
Rick

[kelley]

A good check for alignment is to take some transfer paper and place it between the nozzle and the sprue bushing, then run the nozzle forward against the bushing, and then retract the sled and remove the paper and check the impression.

Transfer paper is the kind invoices are written on, the kind where you write on the top copy and it transfers to the yellow copy (usually) underneath.

This will also reveal any defects in the radius of either the bushing or the nozzle tip. Wash outs etc.

[moldingppm]

One last thought. Could you be running out of resin and the press dropping the carriage psi while the screw still runs?
Rick


You may build very high carriage pressure, but you need enough volume to maintain the carriage position. So you could have low pump volume.
You could have a leaking (internal) carriage cylinder, valve, hydraulic block or crack in injection housing.
Are you sure the barrel is centered? How did you confirm? Is the radius correct for the mold? Did this just start? What is the sequence for carriage psi build and is the psi maintained by holding pump or locked into cylinder by valving?
Rick.

Found out the valve that holds the forward pressure was stuck open, just had to tear apart and clean. Seems that was the problem, who woulda known.


A good check for alignment is to take some transfer paper and place it between the nozzle and the sprue bushing, then run the nozzle forward against the bushing, and then retract the sled and remove the paper and check the impression.

Transfer paper is the kind invoices are written on, the kind where you write on the top copy and it transfers to the yellow copy (usually) underneath.

This will also reveal any defects in the radius of either the bushing or the nozzle tip. Wash outs etc.

You're talking about carbon paper? Hm, I never did think about that. I should use that next time I do a nozzle alignment.

[brentb]

Found out the valve that holds the forward pressure was stuck open, just had to tear apart and clean. Seems that was the problem, who woulda known.



You're talking about carbon paper? Hm, I never did think about that. I should use that next time I do a nozzle alignment.

Toilet paper works too, Charmin is best
What you set and what you get in hydraulics are 2 different things, many times

KOM

brent

[Suhas]

Moldingppm,
So the problem is solved now? Let us know. I think that is what Rick was saying. Cool!
Kelly - great idea of the 'invoice paper' - I am going to try it.
Brent, I think Charmin is too soft? :) - We need some commercial grade TP - like the ones you get in our national parks - I think they are meant for the bears to use them too :)
Thanks all again for contributing.
Suhas

[rickbatey]

I just use chip board that we've all used as layer pads. It's normally all around you so it reduces the hunt.
Rick.