What's the Difference between Doubling and Slurring?

[John Van Hoorn]

Sounds like your transfer cylinder shifted on the transfer gear. If the bite is truly different and consistent that may be the problem. Your transfer point could be shifting due to bad cam follower or incorrect gripper setting. It would have to be drastic to be able to be seen by eye. Carefully have somebody turn the press by hand while you hold tension on the back of the sheet. Pay special attention to the side of the gripper shaft that does not have the cam follower on it. If it breaks hold while transferring from on cylinder to the next you will have found your problem

 

[amp080]

Hi John thanks for your prompt reply. I have just went to the press ad checked by feeding a sheet SRA3 portrate to be able to have some extra to hold on to.
swinging arm clamps & Front lay opens = sheet clamped
swiging arm to impression cylinder first unit = sheet clamped and you won't even notice that the sheet went to anothr set of grippers
impression cylinder to transfer= same as above
Transfer to storage drum = at point of transfer paper brakes hold to both of the pair of grippers on the storage drum
1) At this stage is this normal?
2) Assuming that this isin't normal so why is the sheet released rather than being held longer to the transfer cylinder as by nature the lower the point on the cam the longer the grippers remain closed and more over why is it shifting 1 up and the next spot in relation to the first unit considering there is only 1 comon cam

Thanks

 

[John Van Hoorn]

You have a bad cam follower or the grippers are in need of resetting. If this problem came up quickly the problem is most likely a cam follower.

 

[remoteaccess17]

Many things can cause this, slight slop in our Man Rolland was to costly to repair. So basically something is moving (paper/blanket &cylinder) for the split second while in contact. Because I'm a prepress guy, I created a curve to anticipate the gain from slur. I cheap hack but we had serval other presses that printed fine.

 

[John Van Hoorn]

It does not move while in contact. It moves from one unit to the next. The dot does not hit in the same place on the blanket cylinder of the second unit. The wet 1st unit dot is hitting the second unit blanket in different places due to the movement of the substrate with the first unit dot printed on it in between units. If it is in the gear train or drive the dot will move straight back and forward. A bad transfer point will in some cases move up and down but it will not be perfectly up and down straight across the sheet. Although it may look like it at first glance.

 

[Yorkshire Gripper]

This problem is showing up on a 40" 6/C Akiyama.

Cam followers, worn rubber gripper tips is usually the cause. Have you ever had the tips checked or replaced, how many impressions?

 

[John Van Hoorn]

We have a GTO.52-P age 2002 This is now.
This problem is showing up on a 40" 6/C Akiyama--- This was 9 years ago
Wheather it is a 6 color or a 2 color the facts are the same.

 

[alibryan]

I think what you're seeing is actually doubling, not slurring. And yes there's a difference between the two. Regardless, since you mentioned the issue seems to be with the storage drum, can you be more specific? Is the doubling happening on every sheet, or every other sheet?

 

[saso777]

Two kinds of slurring exist – on the one hand, in the direction of printing (circumferential slurring), and on the other hand, transverse to the direction of printing (lateral slurring). These effects lead to a reduction in quality, and reflect the processing conditions within the group comprising the plate, blanket, and printing cylinders, as well as on other material influences.Doubling often manifest as a problem with the range of tones available in the presswork being compressed and loss of detail, particularly in the shadow areas (a.k.a. muddy halftones). You can read more for doubling here or you can find lot of things about offset printing at offset printing technology.

 

[davidrobin85]

Slurring is the filling in of halftones and at the back edges of solids. Mostly occurs on coated papers and is caused mainly by paper slippage in the impression nip between plate and blanket or blanket and paper.
Doubling is a register problem that mainly occurs between plate and blanket within the unit.

 

[John Van Hoorn]

Sorry David,

You could not be more wrong.

 

[alibryan]

Yep, two different things, for sure.

 

[John Van Hoorn]

I just got this quote from CPF but it is not showing up on this thread for me so I am re-posting it. This Gentleman explains it perfectly.

davidrobin85
"To address your explanation and simplify it:
Doubling does not occur in the printing process i.e., an individual unit, but rather it occurs during sheet transfer and is almost always due to a gripper issue.
Slurring occurs during the printing process and is directly related to a problem within an individual printing unit.
You mentioned that slurring is caused mainly by paper slippage in the impression nip between plate and blanket or blanket and paper. It’s not even possible for paper slippage between plate and blanket because the paper doesn’t travel through there. And it’s also not possible for paper slippage between blanket and impression because the paper is being impressed by the blanket, and cannot slip out of there even if you tried. Distortion, maybe, but that is something entirely different. "

 

[aqazi81]

Hi
We have a GTO52-P age 2002 and it is producing of what i think is slurring.
We had tested the press by printing unit by unit and the first unit always matches spot on; while the second unit is slightly shifting from head to tail of sheet in a synchronised manner of about 1 mm shift each sheet up and down
The slurring we are getting on the second unit is caused by ink migration from the first unit of the press.
We have also noticed that the pair of grippers located on the storage drum is receiving the sheet positioned differently in terms of gripper byte

Does anyone have an idea what is causing the issue?

Did you tried different type of paper/board?
What is the grain direction?

 

[John Van Hoorn]

Check the cam followers on the transfer cylinder.

 

[turbotom1052]

This problem is showing up on a 40" 6/C Akiyama.

This is why an akiyama is affectionately known as in some circles as a "Sloppyama"