34DI ink issues

[banjoman]

I have been running this 34DI for about 4 months and I have noticed that one side is always light on ink and the other side is always dark. The operator side is always dark and the non op side is always light and it is on all colors, more so on red and yellow but it sure isn't right. I can run a job with the same pattern on both sides and have to turn yellow and red up about 10 to 20 times and down as much on the other side. I checked the fountains at zero ink and it looks good to me but I'm going to have it checked out. Anyone have this problem?

banjoman in NC

[OffsetGuy@presstechnician.com]

Roger,

I have heard of that problem on the 34DI. It is a smart idea on your part to have a tech check the settings on the fountain blades and the ductor timing and roller pressures.

Regards
OG

[Erik Nikkanen]

If I understand your comments, you are getting higher density on one side of the press than on the other side. This is happening even though you seem to have things (roller stripes and zero setting) evenly set up across the press.

I will just make some general comments and this applies to all offset presses whether they be waterless or not or sheetfed or not. It also applies to anilox ink feeds. In general the ink feed on offset presses is not directly related to any mechanical setting on the press. The amount of ink that goes into the roller train is transferred in what I call an equilibrium condition. Goss calls it a passive condition. This means that the ink that actually goes from the ink fountain roller to the roller train is affected by variables such as water or temperature or press speed or even air movements. Lots of things.

If you had a positive ink feed system, then basically the ink transfer to the roller train would not be affected by any of these variables.

So in your case, it may be that one side of the press is hotter than the other side due to the mechanical components of the drive. I have seen this on a web press and it also showed up as a greater tendency to tone on one side of the press than the other.

Or it can be that a roller cooling system, which flows from one side of the press to the other might not have a uniform temperature. I have read that this has been seen on a Karat press (anilox waterless) when the roller temperature control was set outside its normal range (set too low).

I have seen an online density monitoring system record density variations that were induced by the cyclical variations in the cooling system that cooled the ink fountain and vibratory rollers.

So if you can realise that the ink key setting and ductor timing are not directly related to the ink feed into the roller train but that there are several other factors, then it might help you to find which one of them is causing your particular problem.

Good luck.

Edited by: Erik Nikkanen on Apr 8, 2008 9:41 PM

[ian]

We had a similar problem that needed an upgrade kit, but our press is two years old.
Open the guards and see how the ductor ducts, the older models it goes from one side to the other, the side it hits first is always heavy even if the keys are zero. Tower 1 is normally the opposite of tower 2. The new models have changed that and the ductor works for the middle. If that is the problem call service and they have an upgrade kit to fix this problem. You notice this the most when using low tak inks, doesent seen to show up with medium tak inks.

On the other hand it could just be your roller stripes, need to do them every 1-3 weeks for the first 6 months then 3-5 weeks after.

thanks
ian

[offsetguy]

Roger,

Did you get that issue resolved?

[banjoman]

I'm getting a tech out as soon as I get caught up, maybe about the middle of May. I went ahead and opened the fountain keys a hair on the side that was lighter and it helped. May just need adjusting but I'm gonna let them fix it so I'll let you know what happens.

banjoman

[OffsetGuy@presstechnician.com]

Roger,
Get it all fixed while your DI is still under warranty. Once it (warranty) expires you are looking at major $$$$ to repair the thing. The stock holders depend on service contracts after the warranty expires to boost the profits.
FYI there are many independent techs available to work on that machine at a lesser cost and are very good techs that Ptek let go to trim costs. Maybe consider that for future reference.

OG

[Al Ferrari]

>If you had a positive ink feed system, then basically the ink transfer to the roller train would not be affected by any of these variables.

Hi Erik,

Would a positive ink feed system be inherently free of variations due to temperature differences from one side to another of a press? On first thought it seems that the positive ink feed system itself would also need to be temperature stabilized in some way in order to feed ink uniformly across the press if there are non uniform sources of heat from other systems below the ink feed system in the press.

Regards,

Al Ferrari

[Erik Nikkanen]

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

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