Losing pressure on Shut-off nozzle 1

[henks580]

Background:
A complete shot is composed of two injections. The first is the largest amount of plastic (~95%) and the second is the smallest injecting the remainder of the plastic (~5%). This helps to control the molded plastic by allowing the first shot to fill most of the cavity and let the plastic consolidate. The second shot is controlled to prevent excessive flash and over injecting plastic.

Question:
Today, I noticed that the shut-off nozzle on the machine struggles to inject during the 2nd shot (~5% shot). It is as if the nozzle doesn’t have enough hydraulic pressure to push. The first shot seems fine though. Any suggestions, or why this may happen?

P.s the parts look good, no visual anomaly
thanks,

 

[patprimmer]

No where near enough information, but maybe the material from the first shot is frozen in a position that obstructs the flow of the second shot.

Maybe the second shot does not have enough stroke to close the check valve.

I do not like shut off nozzles.

Trapping hot material that might degrade between a check valve and a shut off to my mind is an unnecessary danger.

Melt decompress or suck back is to my mind a better method of controlling drool.


Regards

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[injectionmolder]

We have needed more information however, assuming we are talking about a double barrel press therefore with two nozzles and shut off systems. First check the source of heat for the defective nozzle. A defective heater band near the shut off system could give us that kind of problem. If that does not fix it, swap the hydraulic lines between the shut offs. Perhaps the valve is not delivering the pressure, or volume needed, might not be opening properly. At last, check the internal shut off mechanisms for some source of damage, look for excessive drag marks onto the components.
Note: If accumulators assist the press and those are moving clamp and injection, and the shut offs are in that system, make sure enough pressure is available and built into the tanks for the whole process.

Regards