movement during run

[Albert Noel]

ive been having some issues lately with movement during the course of a run on my roland 300.

it seems that the higher the press speed, the more movement i get. problem is, it's only in one unit. (the unit we use for black) at speeds up to and including 10,000 sph, things print normally. i get good crisp dots in the 50% and no slur/doubling. though, as i increase speed, say 1000 sph at a time, it gets progressively worse to the point that by the time i get to 14-15k sph my register marks clearly show the black plate being out of register. not able to produce quality sheets at these speeds anymore and thus taking alot longer on some runs than normal. this happens on all stock weights and sizes.
i originally though it was the infeed head stops but they are fine/zero/calibrated and then focused on the transfer grippers leading from the infeed back to the the third unit and all seem to be in spec using a feeler guage. the only thing i can think of now is that there is either plate movement or the grippers still arent right on the impression cylinder for that unit.
the blanket is properly torqued, packed correctly and the plates a punched properly and as far as i can tell the plate clamp on the press is set correctly.

does it sound more like a gripper issue or a plate issue?

 

[Sfdp2300]

Dont know how much help I may be able to give but here it goes.

How many print units do you have and what units are you running your inks in. Is there a perfector if there is ,is it before or after the perfector.
Is the movement up and down, side to side, or are you getting figure 8's in your slur targets. Is the whole sheet showing slur or is it tail end of sheet only.

 

[Albert Noel]

there are 5 printing units and a coating unit.
we print as follows:
unit 1: open
unit 2: black
unit 3: cyan
unit 4: magenta
unit 5: yellow

theres a perfecter after unit 2. the movement is up and down. it shows up as figure 8's in the star targets but since the registration marks are out at all 4 corners of the sheet , i'd say it's slurring the entire sheet. (again, it's the black only the rest of the units are printing fine at all speeds) that leans me more towards the plate moving, but i dont know for sure at this point.

 

[Albert Noel]

heres some closeup pics of the colour bar. first shot is at 10K the second at 11K the third at 12.5k and the fourth at 14k sph. (please ignore the scuffing on the first shot, i rolled the sheet up a little too soon after i pulled it from press)

 

[Sfdp2300]

Ouch those are bad!

With the speeds your getting Im asuming you run a double transfer. With the whole sheet moving like that Im more inclined to believe it is in the transfer. You may have to check your cam followers. Im sure you guys do routine maint. Lubrication and gripper cleanings and such. If it is plate cylinder you should be able to see the movement by running the black only.

 

[Albert Noel]

Ouch those are bad!

With the speeds your getting Im asuming you run a double transfer. With the whole sheet moving like that Im more inclined to believe it is in the transfer. You may have to check your cam followers. Im sure you guys do routine maint. Lubrication and gripper cleanings and such. If it is plate cylinder you should be able to see the movement by running the black only.

the sheet transfer is:
imp cyl
single transfer
double transfer
single transfer
imp cyl


i do see this when running black only but only at the higher speeds. if it were a transfer shouldn't i see more movement in the sheets in general or in the other colours? aside from the black moving, the sheet to sheet register is bang on except for black.
I'm going to check the cam followers from the in-feed back to the perfecter again in case i missed something. (i did it a little briskly when i checked them last week.)
we do routine gripper maintainance/lubrication so i don't understand where its coming from.

we're taking longer than normal on jobs at this point because at decent speeds, you can see how awful it is. it doesn't fly with the production manager / qc.

i appreciate your help, i'll take a look monday morning.

 

[Sfdp2300]

A couple of things to try:


Not meaning to repeat myself but try this again.
Print 2nd unit only with no other impressions on. Check for movement. If there is movement with only the single print unit on impression. Then it is surely isolated in that unit (plate cylinder, Back cylinder). you may have to call somebody.

If you still have movement try taking the perfector in and then back out of perfecting mode making sure everything moves back to inline print mode properly.

I know that when we print before our perfecting cylinder we get some movement but this is on a press that has over 8 billion impressions and counting. In the end you still may have to get a press tech involved. Hope things work out for you good luck.

 

[qaos]

If the cam follower is well and the grippers are
calibrated. You need to check two things, the play between
cylinders rotation and the register system. These
mechanisms are very sensitive. Maybe a technician can
help you identify the problem.

 

[rich apollo]

You don't have slur - you've got doubling. I don't think it can be due to sheet movement. Is it consistent?

 

[Lukew]

Exact same problem we are having,
Our black is doubling
our grippers have been adjusted, next we are having new cam followers put in.. mind you the maachine is only 1 year old..
only happens on lighter stocks specifcly 130 gsm - 200 gsm coated.

When we start our run the first 20 sheets all colours are out by up to 1mm then they slowly come in without touching anything,,This happes every time you stop and start up again, be it on 350gsm card or light weight stock.. Surley this isn't correct, I've been assured it does and always will happen by the tech..

Then after that the sheet is pulling out of the grippers before it gets to the second unit..

If the cam followers don't fix it, the tech is going to pass some of the blame onto the type of ink we are using (novavite 918 bio ink low tack) saying its too tacky, or that its the quality of paper..

Will be very interested to find out what is causing your doubling/sluring.

 

[akiyama_king]

if its doing it on all stocks (thick and Thin) i wouldn't think you have badly set Grippers but maybe you inp cylinder bearing is stiff and not Moving very easily.
or on the other hand although it may sond like a simpletons answer but if you have recntly changed the blanket, check to make sure it is tight and not slack off the cylinder

good lcuk

 

[gordo]

Doubling is typically caused by:
Gripper settings incorrect
Unstable paper - ink/water balance - too much water
Loose plate
Loose blanket - tighten blanket clamps, adjust packing, or replace blanket

best, gordo

 

[Albert Noel]

ok, so doubling it is. for some reason i was under the impression that it was slur. all these years ive had my terminology wrong, that's embarrassing lol.


anyway, i checked and re-checked all my grippers, cam followers and such from the infeed back to the transfer cylinder after the offending unit and everything seemed fine. it's the third time ive checked them in a week. the blanket is properly torqued with the correct packing. i did however recalibrate my plate clamp to zero setting and ran some sheets at various speeds and the problem seemed to go away. i highly doubt the clamp pressure was the cause but i think it might be possible that the clamp wasn't tightening enough allowing the plate to move while under impression. i cant find anything else wrong. there has to be a better explaination.

 

[gordo]

Slur and doubling are very easy to confuse. With slur the halftone dot looks like it has been smeared usually in the direction of sheet travel through the press. With doubling you'll see a very good faint reproduction of the dot following it usually in the direction of sheet travel through the press.
The photo of your colorbar shows the very clear second ghost image of dot doubling rather than a smear of the original graphic.

best, gordo

 

[jbeniston]

Hello again,
I think you need to get a qualified tech to check your gripper systems. If the problem is every sheet then it must be coming from a single diameter cylinder, most likely culprit is the perfector.

 

[Albert Noel]

Hello again,
I think you need to get a qualified tech to check your gripper systems. If the problem is every sheet then it must be coming from a single diameter cylinder, most likely culprit is the perfector.

yeah i was originally thinking it was the impression cylinder grippers but i found nothing wrong there. i never thought to check the perfector. i'll have to check that first thing tomorrow.

 

[Albert Noel]

well i checked the perfecter grippers and theya re all fine.
havent seen the issue though since ive not ran anything over 10500sph
ive got a larger run coming up so i will see what comes up with it hits press

 

[jbeniston]

Albert,
How is the infeed. Check the front lays for squareness and gripper bite. Even if they are indicating square on the console display, put a sheet in the infeed and check the gripper bite to see if the lays are actually square.
I still think you are going to need some help though. When and if the problem happens again could you send us about 100 samples making sure that they are in sequence and show what happens as you increase the speed of the press. Mark them to my attention and I will find out what is happening on your machine.

 

[Albert Noel]

Albert,
How is the infeed. Check the front lays for squareness and gripper bite. Even if they are indicating square on the console display, put a sheet in the infeed and check the gripper bite to see if the lays are actually square.
I still think you are going to need some help though. When and if the problem happens again could you send us about 100 samples making sure that they are in sequence and show what happens as you increase the speed of the press. Mark them to my attention and I will find out what is happening on your machine.

i will check them again tomorrow and this time also check for infeed bite
as for the sheets, i will most definitely do that the next time it happens.
i think the manager and other operator think i'm out of it since neither of them have seen it happen in real time (only the couple of sheets i saved)

 

[Alois Senefelder]

Movement !!!!!!!!

Movement !!!!!!!!

Its " Doubling " have you checked all you Blankets are correctly "Tensioned "


Regards, Alois