doubling in printing

[sriraghavan]

hi,
In recent past we are facing doubling in printing this is not in one unit but in all units .No major changes made in in the machine.please can any one explain the reason

 

[Cornishpastythighs]

Not knowing your press or if its sheetfed or web here is something to get you going.

Doubling in sheetfed offset

 

[sriraghavan]

It is a web offset machine manugrhic FRONLINE machine

 

[Deleted member 16349]

It is a web offset machine manugrhic FRONLINE machine

This is one of the possible causes.

With a web press, doubling often occurs when there is variation in the tension of the web going into the first print unit. The transient tension variations going through the press cause transient register variations which result in the doubling.

Also variation with web tensions caused by something just after the last print unit can also cause this due to the fact that all the inked images from all the previous units, are on the last set of blankets. Variations in tension caused after the last print unit will cause variations in register of the last unit and can even affect the one before, depending on the type of blankets used.

Web tension control to minimize doubling, requires the right design and properly maintained infeed section, just before the first print unit and the outfeed section just after the last print unit.

The infeed tends to be more critical since there can be variation in web feed from splices and out of round rolls etc. A proper infeed should isolate tension variations of the unwinding of the roll from getting to the first print unit. Nip rollers on the infeed do not isolate tension variations from getting past the infeed unit. Load cell rollers also do not isolate tension variations but dancing rollers do. But dancing rollers need to be designed properly and maintained. It is also good to have a dancer on either side of the infeed unit. One to provide consistent tension after the infeed and control the infeed speed. The other dancer to absorb tension variations coming from the roll unwinding process and to control the unwind speed.

Look for possible changes in these systems.

Hope this helps.

 

[Alois Senefelder]

Web Offset Press - Doubling !

Web Offset Press - Doubling !

Hello sriraghaven,

Web Offset Press Doubling


1) Check - Infeed tension levels/settings are correct?

2) Are ALL Blankets tension/torque setting correct?

3) Check the Blanket Heights on every unit - are correct?

4) Are all the Blankets the same brand and age - again every unit ?

5) Are the RTF/Folder Nip Rollers - settings correct ?


Regards, Alois

 

[sriraghavan]

Hi alois
my sincere thanks for your tips i will go through all.

 

[sriraghavan]

Hi Thank you very much

 

[jshawy]

Hi sriraghaven,

Which direction does the doubling occur? Circumferential, lateral or both - diagonal?