Use of Ductor Roller

[arossetti]

Some of you may have been following my foray into our companies acquisition of an offset printing shop. Please excuse my lack of knowledge as I try to better understand the process.

Now to my question, my operator adjusts the ink ductor roller in and out to control the flow of ink across all keys, is that proper? Looking at GATF/PIA information it appears that the ductor roller should be set to a distance of 3-sheets of paper between it and the fountain roller. Ink flow would then only be controlled by the ink keys. Am I understanding that correctly?

What are the negative affects if any of controlling ink flow with the ductor roller?

 

[arossetti]

No looks like I am wrong. He is adjusting the stroke not the distance between rollers. False alarm.

 

[Deleted member 16349]

What are the negative affects if any of controlling ink flow with the ductor roller?

Well, yes there are negative effects of having a ductor roller. It is not yet accepted but the use of the ductor roller is the prime cause of ink water balancing problems on offset presses that are seen as density control problems. This is not to say the chemistry of the inks and fountain solution combinations are not very important but they are more related to the controlling of the image and not image areas on the plate.

The ductor design is over 160 years old and it is a simple way to bring ink over from the ink fountain roller to the roller train. Unfortunately, it does not do this precisely. Actually ink transfer by the ductor goes in both directions. Some fresh ink goes to the roller train and some ink with water mixed in it goes from the roller train back to the ink fountain. One can easily see this happen when one gets the roller train contaminated with back trapped ink from a previous unit. Some of that contaminated ink will get into the ink fountain. It happens quite quickly.

Anyhow, the inconsistency of ink transfer by the ductor means that it is difficult to have a very predictable result from the setting of the keys in the ink fountain.

It is a weakness in the design of the press but that is what the industry wants to keep. I takes skill to run a process that is poorly designed and skill is valued above all. Many do not want to see the skill requirement, designed out of the process.

 

[Alois Senefelder]

Erik,

The Bar of fresh Ink picked up from the fountain roller onto a 3" Dia. Ductor Roller in contact

for say 180 degrees of rotation -- then transfered into the rest of the inking train --- IS not the same as printed

onto the paper, why ? because it is not a "Micro Emulsion Ink "


Regards, Alois

 

[turbotom1052]

I have seen the term "ink duct" used in reference to the what we in the U.S. commonly call the '"ink ball". It sounds to me that your operator is describing the action of the ink ball. Its the ink ball that turns in the ink fountain. The in and out action of the various zones of the ink fountain is what meters out a hypothetically controlled film of ink across the length of the ink ball. This film of ink is then transferred via the reciprocating action of the ink ductor roller and ultimately fed into the ink train. Erik is correct in saying that this transfer of ink winds up going in both directions. This dynamic only partly accounts for the inconsistencies. The very design of the ink fountain, and how it meters out the precise film thickness of ink, is in my opinion more responsible for inconsistencies. Most of the modern ink fountain designs which control the zonal control of the ink film via multiple segmented adjustment zones, as opposed to a single fountain blade are far superior. Either way the skill set required to control, and make consistent this flow of ink, often on multiple units is one of the biggest challenges to the press operator.