Re: 34DI ink issues
Hi Al,
When I say positive ink feed, I am basically saying a constant volumetric ink feed. This would be independent of the temperature of the ink or of temperatures in the roller train and independent of water settings. It would also be independent of roller setting differences. So yes, it would be independent of differences in temperature from one side of the press to the other.
Positive ink feed does not mean uniform ink feed across the width of the press. The positive ink feed at each key or zone, still has to match the amount of ink required by the print via the roller train. It is a constant volumetric ink feed but one that is adjustable to the constant rate that is needed for the print.
As an added comment, the ink required is not directly related to the image area on the plate. There are other factors such as wet trapping, the amount of ink that goes to the screens (not dot gain) and the lateral transport of ink due to the oscillator ( vibratory) rollers.
If one has the correct ink key calculation and a properly designed positive ink feed system, then you basically have a "keyless" system. Start the press and the density will go directly to the preset values and stay there for the entire run without the operator making any ink adjustments.
The operator could adjust the water to get the quality they wanted but that would basically not affect the density. You would not be able to wash the print out if you really increased the water a lot but of course there is no need to do that in normal operation.
Actually ink control does not have to be precise. A range of +/- 0.05 density points is about +/- 8% change in ink film thickness or ink volume. The total range is 16%. Hardly a precise target.
As you know, I think this is solvable at low cost.
Edited by: Erik Nikkanen on Apr 29, 2008 7:36 PM