Viscosity Study

[The Rookie]

Hello all. We acquired an old press and tool from our customer who has asked us to re-qualify the process. Currently working on the viscosity study and having a bit of trouble (maybe machine related). Details below:

Material: Plateable ABS
Cavitation: 8
Hot Runner: Valve Gated
Machine: Van Dorn 300 HT Series (maybe late 90s', early 2000's)

Attached you can see the images from our study.

It appears that we have two areas on the curve that flatten out. When looking at the data, I found that fill time did not change when we adjusted injection speeds between 1.5-2.5 in/sec. Any ideas what could be causing this (not pressure limited).

[Bryan E]

Based on my experience with Van Dorn HT series within the vintage years you mention your comment "maybe machine related" is highly likely. Specifically when you run with the processes in the Closed Loop mode. The Injection Valve calibration plays a critical role in the results that you will see. A quick way to determine if the feedback used in the closed loop setting is out of calibration is to switch over to open loop and review the results. There is a procedure to auto calibrate the injection valve for operating in closed loop mode which may work, but often the age of the machine, valve condition and other factors may not allow the auto calibration process to be completed. Understanding that closed loop process is desired, running in open loop may result in a more stable process with better results. In that case you could use the production monitoring screens to set upper and lower limits to assure the open loop process is stable.

[Jendalf]

Hello,

how many tests have you done?

I would repeat that at least for the middle times 1,5 to 3s.

btw. from theory you are good, its actually "wurst" what speed you will setup, viskosity is not changed - this can be also a result.
Of course you have to believe to the machine and tool (and material)
j

[rickbatey]

For me, a press of this vintage has wear in the pumps, bleed off of pressure through manifold blocks and valve stacks, not to mention leakage of hydraulic oil across the injection cylinder(s). Hence why YOU have an old press and have to RE-QUALIFY a tool that has been running trouble free since the press was built and placed into production. You can get new pumps and controls with eco-friendly servo pumps and VSD......But a new press may be the same cost.
Rick