Roller life - Specifically Soft duro type

[tkemerly]

Water form speed can be up to 5% reduction, some equipment you can choose if you would like for the form to be reduced for hickeys. Anything over 5% causes dot issues.

See picture of extreme case of circumferential comb cording on pan roller, this prints on the substrate.

Etches the chrome and thus make the problem even worse as time goes on.

OMO....

 

[Dan Roll]

All dampeners that have a speed difference between the chrome and metering roller rapidly damage the chrome rollers due to the unceasing friction on the surface. Even though the fountain solution lubricates this to some extent, even the relatively hard chrome surface shows the wear pretty quickly. I have seen people remove the gear from the metering roller, allowing it to be driven by the pan roller, and when this is done the 'cording' on the metering roller disappears. However, there is nothing that can be done about the speed difference between the chrome and form roller, this is how the dampener regulates the water feed. Reducing the pressure is the only way to reduce 'cording' in the print.

I am reminded of when a major web manufacturer was 'improving' their presses by adapting their sheetfed dampener for use on one of their commercial web models. The prototype dampener was the same as on the sheetfeds and within a minute or two of running at moderate web speeds (30,000 to 40,000 iph) tore the cover off of the metering roller, which fell on the web and ran through the unit causing some serious damage. The thinking was the roller must have been defective, so the roller was replaced and the entire process was repeated, complete with the damage (this was done three times before another approach was tried, according to my source). The dampener was eventually redesigned to have the metering and chrome roller turn at approximately the same speed and the metering rollers now last as long as the other rollers.
It is a popular belief the press manufacturers are experts on dampening system design, but I have met many of these engineering teams and they are quick to admit they know next to nothing about it and are mostly basing their designs on not violating any valid patents held by others, as the royalties are very expensive.

 

[Alois Senefelder]

Some Correct Answers

Some Correct Answers

Hello fellow Lithographers,

Topic: The Mechanics of Fluid Transfer

1) Normal to see beading at the nip, on squeeze roller dampener configurations.

because the Metering Nip operates in -- Fully flooded mode

2) What we are seeing is Ribbing/Corduroying which caused by Hydraulic Instabililty

3) The onset of Ribbing is a product of A) Surface Speed B) Fluid Viscosity C) Surface Tension

4) Increasing the Metering Roller Pressure - reduces the Pumping Capacity


Regards, Alois


Yet again some more PDFs

 

[Alois Senefelder]

******

******

Gentlemen,


I also suggest you read this PDF http://printplanet.com/forums/sheetfed-web-offset-discussion/24611-komori-picture-framing


re Gearing of Compliant Rollers


FAO tkemerly, is the IMAGE 0306 viewed from the INFLOW side of the pan roller ?

Also, has any one read my previous post about - Dahlgern Dampening ??



Regards, Alois

 

[Alois Senefelder]

Chrome Rollers

Chrome Rollers

Hello Dan,


I have never seen Chrome Rollers wear due to friction from a Compliant Roller, from my experience running Web Offset Presses since the 1960s - running Dahlgren System, Duotrol and Komorimatic Dampening Systems - and previous Molleton Covered Dampers -- maybe the Chrome was Car Bumper chrome plating ! - I also include Brush Dampening and Spray Dampening



Regards, Alois

 

[Dan Roll]

Alois,

Your experience is certainly valid, I have never seen damage to the chromes on a web either, just on sheetfeds. Even slow webs run too fast to allow the types of pressure and speed differences that are common on sheetfeds. Attempts at adapting common sheetfed dampeners to web printing have always required modification to reduce speed differences between the rollers. If you took the dampener off of the Sakurai we have been discussing and put it on say a Komori System 20, it would tear the covers off of the metering and form rollers in just a few minutes.

Perhaps you can clear something up for me. It is common in Europe (and in your vast library of PDF's) to see references to 'emulsion' dampening. What do they mean by this? If they are referring to the eventual emulsion of the fountain solution and ink, I do not understand why they (whomever 'they' are) do not refer to all dampeners as 'emulsion' dampeners.

Since the 60's? You must be as old as I am.

 

[Kaoticor]

Dan,

We have reverse slip nips on our Komori dampening systems. This friction does not cause any excessive wear on the chrome that I have seen on any of our lithrones. Is there a different point you are referring do? (just for my own personal reference).

K

 

[Dan Roll]

Kaoticor,

There is no more or less friction in the 'reverse slip' nip on the Komori than there would be if it turned the other way. The four roller configuration used by Komori is the same as the DuoTrol dampener used on most (but not all) high speed webs (Harris, Goss, Hantcho, Baker-Perkins, Komori, but not Mitsubishi or Roland) where the upper unit dampeners turn one way and the lower unit dampeners turn the other. Even at high speeds (greater than 70,000 iph) I have not seen wear on the chrome rollers. These four roller systems are (usually) the lowest friction dampening systems on the market. It is usually the pressure between a metering roller and a pan roller not turning at the same speed that causes the dmage to the chrome roller, not the metering (we call it the slip roller on DuoTrols) roller turning against the oscillator.

 

[Alois Senefelder]

Emulsion Dampening

Emulsion Dampening

Hello Dan,

Yes, I'm a relic from the Stone Age ! and don't I know it, having been shown the errors of my way in another forum.

The terminology " three roller emulsion dampening" was used by Harris Marinoni in the 1990's to describe variations of Dampening Systems.

PDF -


I suggest you view a PDF I posted earlier - Configuration "A"



Regards, Alois

 

[Dan Roll]

The terminology 'film' dampening and the distinction between 'independent' and 'emulsion' dampening must be the result of inexact translation from French into English. If you consider (as I do) the plate cylinder to be part of the dampening system, all dampeners are 'emulsion' dampeners and none are 'independent'.

There was a time many years ago I had a reliable source working at Marinoni, but he retired many years ago and now I know nothing about what goes on there (if anything). My last direct involvement was in the lawsuit between the old Arcada plant in New Canton TN and Marinoni over what turned out to be improperly machined dampeners and I was never able to understand a thing the Marinoni engineers tried to explain to me (I was just as dumb then as I am now).