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[Alois Senefelder]

Web Offset Press Mechanics

Web Offset Press Mechanics

Hi fellow Lithographers and my friend "otherthoughts"

Hope you find the Information useful - Word doc and the PDFs

Regards, Alois

 

[Alois Senefelder]

Web Offset Press Mechanics # 2

Web Offset Press Mechanics # 2

Some more PDFs - for you - enjoy !!!!!!!!!!


Regards again from Alois

 

[Deleted member 16349]

Hi fellow Lithographers and my friend "otherthoughts"

Hope you find the Information useful - Word doc and the PDFs

Regards, Alois

Alois,

The material presented might be OK for a general introduction to web conditions and tension control but the material is much too simple and is not really technically accurate. Some of it is actually wrong or misleading.

As an example, Dancer Rollers do not measure Tension variations. Dancer rollers do three basic things. One is to set the web tension. The idea of the dancer is that even if it moves, the web tension will be constant. The second thing is to signal back to the unwind to meter more or less web. It controls web feed. This is done by the position of the dancer which is measured by a potentiometer and not a load cell. The third thing is to act as a small accumulator that absorbs small variations in web being fed by the infeed.

Another thing is that nip rollers on infeed systems are meant to prevent slippage but they are not able to isolate the press from tension variations coming from the unwind. One needs a dancer roll after the infeed to take care of that.

My point is that the information is OK for general interest for people who do not have to actually solve tension control problems in presses. Some of it is good and some not so good. If people really want to understand the problem of web tension conditions and related print issues, they would need to go to much more technical sources. This is not so easy to obtain.

 

[otherthoughts]

My compliments to both Alois and Erik for their willingness to illustrate the many differences between web offset and sheet-fed offset presses in this thread. I have found it both provocative and informative.

I suspect that there may be other sheet-fed/web pressman that might find this type of thread stimulating as well?

Perhaps a subcategory of the Sheetfed/Web Offset Discussion in this forum regarding the differences between sheet-fed and web offset characteristics would be of some merit? Maybe not?

Best regards and Thanks Again.
otherthoughts

 

[Alois Senefelder]

"Load Cells"

"Load Cells"

Hello Mr. E. Nikkanen,

I'm sadden that you felt the need to " belittle" the Information, it was posted to enlighten and not for "Peer Review" by TAGA Alumni.

Regards, Alois

Load Cell PDFs

 

[Deleted member 16349]

Hello Mr. E. Nikkanen,

I'm sadden that you felt the need to " belittle" the Information, it was posted to enlighten and not for "Peer Review" by TAGA Alumni.

Regards, Alois

Load Cell PDFs

It was more of a cautionary comment. If material is presented for just light general knowledge then that is OK, but if faulty descriptions are then used for developing or trying to control a process, then that leads to problems that can result in a lot of lost money. I say this from personal experience. I have assumed in the past that generally accepted knowledge in the printing industry was true and that resulted in a very expensive lesson. The lesson is that much of the "technical information" in the industry is useless for developing improvements.

I try to be very careful in explaining issues. That tends to result in seemingly complicated explanations but to state things in too simple terms would in my opinion be irresponsible for me personally.

As far as "peer review" from TAGA, I don't have much value in that. TAGA is a collection of untalented technical people who don't seem to have the ability to analyse the simplest of issues. I have presented two papers at a TAGA conference. One on the topic related to density control and the other related to web tension conditions in offset presses. Even though I have presented these papers, I have no interest to be associated with TAGA. It is a useless organization of members that act more like a social club than a scientifically active group.

 

[gordo]

[SNIP]TAGA is a collection of untalented technical people who don't seem to have the ability to analyse the simplest of issues. [SNIP] It is a useless organization of members that act more like a social club than a scientifically active group.

Erik, quit beating around the bush and just say what you mean. LOL!

BTW, I don't believe that TAGA papers are peer reviewed (I co-authored one on halftone screening and don't remember it being reviewed by any member of the TAGA org)

Things may improve though since Dr. Mark Bohan has become Managing Director, TAGA. As Vice President of Research and Technology at PIA/GATF his hands were somewhat tied as far as objective research is concerned (I don't believe that PIA/GATF does any independent research anymore). Perhaps he will be able to help TAGA fulfill a sorely needed role in the industry.

I say this from personal experience. I have assumed in the past that generally accepted knowledge in the printing industry was true and that resulted in a very expensive lesson. The lesson is that much of the "technical information" in the industry is useless for developing improvements.

Quite true. Not only is much of the "technical information" in the industry useless for developing improvements but it is also results in an inability to address many issues in day to day print shop operations.

best gordon p

my print blog here: Quality In Print

 

[Deleted member 16349]

Things may improve though since Dr. Mark Bohan has become Managing Director, TAGA. As Vice President of Research and Technology at PIA/GATF his hands were somewhat tied as far as objective research is concerned (I don't believe that PIA/GATF does any independent research anymore). Perhaps he will be able to help TAGA fulfill a sorely needed role in the industry.
best gordon p

my print blog here: Quality In Print

Gordon, yes there is no peer review for TAGA papers but there is some kind of peer review for their journal. But what is the point of peer review when the peers don't seem to be able to see. At one time the "peer view" held that the world was flat.

As far as Dr. Bohan being of help, I will not comment. Maybe he will, maybe not. I will say that he comes from the University of Swansea mechanical engineering department that specialises in printing technology. They state that they are world renowned but as far as offset printing goes, I have not seen any meaningful work done there and certainly not at any engineering doctorate level.

Much of it is smoke and mirror research as far as offset goes. They also do work on other printing processes but I would not comment on that since that is not my area of particular interest. I doubt that they can point to any one piece of research in offset printing that has any value or that can withstand a bit of critical review by someone outside their protective peer group.

As I have said before, there is a serious problem in the printing industry with the quality of scientific knowledge. PIA. TAGA, Swansea, etc. have not done a good job but it is easy enough to correct. To keep these groups honest about research, the general printing community can make that happen by questioning their research and also demonstrating conflicting theory. But this does not happen and in general, the industry just follows like sheep and accepts what faulty knowledge that is provided.

People that accept rubbish I guess deserve what they get. The industry has not understood that the areas of opportunity for competitive advantage lay in the region between myth and truth. Take advantage of what is true, while others still are believing in myths, can give one an advantage. Knowing what is true is not enough but acting on it with innovation will lead to an advantage.

 

[Green Printer]

There is vast amount of info in the TAGA papers. Interpretation and reading between the lines is were the value is. Multiple papers on similar subjects has even greater value because of different view points and observations.
There is no single item that makes offset work. It is the cumulation of many technologies that are able to work in harmony. You must look at the whole process with chemistry being the first and foremost prerequisite. Once this is understood the mechanics fall in place.

The offset process has two very different methods or approaches solvent or surfactant based. Each type works and works quite well. If you attempt to mix the two there will allows be problems. One type has environmental and health issues the other virtually none.

 

[Deleted member 16349]

There is vast amount of info in the TAGA papers. Interpretation and reading between the lines is were the value is. Multiple papers on similar subjects has even greater value because of different view points and observations.
There is no single item that makes offset work. It is the cumulation of many technologies that are able to work in harmony. You must look at the whole process with chemistry being the first and foremost prerequisite. Once this is understood the mechanics fall in place.

The offset process has two very different methods or approaches solvent or surfactant based. Each type works and works quite well. If you attempt to mix the two there will allows be problems. One type has environmental and health issues the other virtually none.

There are many interesting bits of information in TAGA papers but why should one have to read between the lines. Although I would agree that one can get information from reading between the lines. It is interesting that one can obtain knowledge from these papers that even the authors were not aware of.

Offset lithography is not a chemical process. There are no chemical reactions in the process and the physical chemistry to separate the image from the non image area of the plate with respect to ink, has been done for a very long time. The consistency and predictability of printing has much more to do with the mechanical design of the press than the physical chemical properties of the ink, plate, and fountain solution.

Yes, of course all the components in the process must work properly. Why not fix the ones that don't. Hiding behind the Myth of offset lithograpy being a chemical printing process is a way that the technical community can continue to have a lack of interest in fixing the problems in the process.

 

[Green Printer]

There are many interesting bits of information in TAGA papers but why should one have to read between the lines. Although I would agree that one can get information from reading between the lines. It is interesting that one can obtain knowledge from these papers that even the authors were not aware of.

Offset lithography is not a chemical process. There are no chemical reactions in the process and the physical chemistry to separate the image from the non image area of the plate with respect to ink, has been done for a very long time. The consistency and predictability of printing has much more to do with the mechanical design of the press than the physical chemical properties of the ink, plate, and fountain solution.

Yes, of course all the components in the process must work properly. Why not fix the ones that don't. Hiding behind the Myth of offset lithograpy being a chemical printing process is a way that the technical community can continue to have a lack of interest in fixing the problems in the process.

Interesting few point. I never new that you could control calcium,picture framing,ink piling,plate blinding,back trap mottle,meter roller feedback,toning,scumming,gas ghosting along with many other problems by changing the mechanical design of the press.

 

[Deleted member 16349]

Interesting few point. I never new that you could control calcium,picture framing,ink piling,plate blinding,back trap mottle,meter roller feedback,toning,scumming,gas ghosting along with many other problems by changing the mechanical design of the press.

Not all but some of these issues can have press design related causes. As an example, toning can be related to the ink, fountain and plate properties but I have also seen it related to the design of the dampener system. Same paper, same ink, same fount solution but different designed dampening systems resulted in different performance. No toning in one type and chronic toning in the other. The believed causes was the shearing of ink from the ink film and into the fount solution liquid film which resulted in small specks of ink surrounded by water. This ink in water solution was then applied to the plate in the non image areas and the form rollers were not able to pickup the specks of ink due to the specks being surrounded by water. Running with extra water could not get rid of the toning and the toning was present from the scum point at minimum water settings to higher levels of water setting. It also cause picture framing.

My point is that the design of the press can have a great influence on the performance of the process. Of course even if one had a perfectly designed press, you could have all the problems above due to poor management of your materials, poor maintenance and poor operator skill. One can't make it fool proof.

 

[Green Printer]

Not all but some of these issues can have press design related causes. As an example, toning can be related to the ink, fountain and plate properties but I have also seen it related to the design of the dampener system. Same paper, same ink, same fount solution but different designed dampening systems resulted in different performance. No toning in one type and chronic toning in the other. The believed causes was the shearing of ink from the ink film and into the fount solution liquid film which resulted in small specks of ink surrounded by water. This ink in water solution was then applied to the plate in the non image areas and the form rollers were not able to pickup the specks of ink due to the specks being surrounded by water. Running with extra water could not get rid of the toning and the toning was present from the scum point at minimum water settings to higher levels of water setting. It also cause picture framing.

My point is that the design of the press can have a great influence on the performance of the process. Of course even if one had a perfectly designed press, you could have all the problems above due to poor management of your materials, poor maintenance and poor operator skill. One can't make it fool proof.

What you have described is quite common. Usually a roller stripe or durometer change will fix such a problem. I have seen the same fountain solution and ink combo work on Heidelberg and all of there dampners type, ABdick,Ryobi,Komori,Sakurai,Solna,Mutilith, Miehle, Man,Roland,Crabtree perfectors,Akiyama,Hashimoto,Harrris,Shinohara,Davidson,KBA,ATF,Webendorfer, with sock type ductor and a 3m sleeve or bareback form,continuous epic or dahlgren bridged or unbridged,delta dampner,spray dampner etc.
The only time there had to be a change was when plastic or polyester plates were used. This required a different type of fountain solution.

 

[Deleted member 16349]

What you have described is quite common. Usually a roller stripe or durometer change will fix such a problem. I have seen the same fountain solution and ink combo work on Heidelberg and all of there dampners type, ABdick,Ryobi,Komori,Sakurai,Solna,Mutilith, Miehle, Man,Roland,Crabtree perfectors,Akiyama,Hashimoto,Harrris,Shinohara,Davidson,KBA,ATF,Webendorfer, with sock type ductor and a 3m sleeve or bareback form,continuous epic or dahlgren bridged or unbridged,delta dampner,spray dampner etc.
The only time there had to be a change was when plastic or polyester plates were used. This required a different type of fountain solution.

Well, when things work then things are fine but when when things don't work so well then the root cause is a bit more difficult to find.

The problem I stated was on a ManRoland Cartoman web press. ManRoland could not correct the problem over a three year period where they rebuilt part of the roller train. I don't think many Cartoman presses were made and I think they were discontinued. The inks were EB inks and the substrate was coated board.

As I stated, on a different designed press with a different designed dampener, there was no problem but on the ManRoland press it was chronic. In this case, it was not so simple and it was related to the design of the press.

Trouble shooting can be a tricky thing.

 

[MikeG]

I remember way back in the day when we would take a piece of final film and put it in the fridge to get it to shrink and our Cromalin proof to fit. Next time, make a new set of plates and tell the pressman to go stand outside with them and lock the door

 

[Alois Senefelder]

Auto-Da-Fe

Auto-Da-Fe

Hello Green Printer,

Thank you and welcome to a small band of "Wizards" that still believe in the "Chemistry of Lithography". Together we shall enlighten those "Heretics" in our midst, including the CtP gang!!! with their abomination "Chemistry Free Plates", I curse them with the magic word

Densensitize !

So remember all "Heretics" the Auto-Da-Fe awaits !!!!!!!!

Regards from a lowly "Sorcerer's Apprentice"

Alois

PS a Chemistry Free Press, PDF

 

[gordo]

In fairness to Erik N, he wrote: "Offset lithography is not a chemical process. There are no chemical reactions in the process"

Strictly speaking he is correct, there are no chemical reactions in the press.
A chemical change requires a chemical reaction, and occurs when the actual composition of a substance changes–that is, when one substance is transformed into another. Water can be chemically changed, for instance, if an electric current is run through a sample, separating it into oxygen and hydrogen gas. If liquid water is boiled, it is still water; likewise frozen water, or ice, is still water. Melting, boiling, or freezing simply by the application of a change in temperature are examples of physical changes, because they do not affect the internal composition of the item or items involved.

best gordo

 

[Alois Senefelder]

Chemistry in the Pressroom

Chemistry in the Pressroom

Hello everyone,

The printer is expected to use a lithographic printing plate, which he has not made, to transfer ink which he has not produced, onto paper which he has not produced. In this process he must use ink rollers and rubber blankets which have been made by someone else.
There is chemistry connected with all of these materials which funnel into the pressroom.

When these materials come in contact with rollers, blankets, and water fountain solution quite a number of chemical and physical changes can occur. Two or three things are often involved in a particular chemical reaction. For example, the tinting of ink on a sheet may be due to the ink, partly to the paper and partly to the fountain solution.

Regards, Alois

 

[Alois Senefelder]

Ispa Scienta Potestas Est

Ispa Scienta Potestas Est

Oh yes 1 PDF



Regards, Alois

 

[gordo]

Alois, With all due respect I think you are using the term "chemical reaction" to mean a different thing than perhaps what Erik was meaning. Kind of how the word "theory" is used in common language - which is different than what "theory" means in science usage.
When we use terms incorrectly, or inappropriately (myself included) it can quickly lead to confusion and misunderstanding, which is what I think is happening in this thread. Many of the examples you've cited are effects of mechanical interactions, ink rheology, etc. From a science point of view, those are not "chemical reactions".

( point 4 in my blog post: Quality In Print: Some things I learned from engineers (that printshop folks might find useful) )

best, gordo