help! sheet fanning

jmeehan

New member
would anyone know why our Sakurai has what is being referred to as sheet fanning only on the back side after turning the sheet. Black and Cyan go down perfect, leaving the transfer cylinder going into Magenta in tower 3 and Yellow in tower 4 the image is 3 lines short across the cylinder on the drive and operator side of the sheet.
 
I'm not 100% sure, I used to run full web heatset, but this sounds like your plate packing may be different from the first two colors. (or check blkt. too)

OR is there an adjustment on the gripper bar ? Like I posted I used to run webs, don't know sheetfed thoroughly just a little bit.

Good luck,
Scott
 
I found this on another thread - should help - good luck :)
member name - "otherthoughts"

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It's been many years since I've run a press, maybe 18 years now. However even back then, our sheet-fed presses had split tail-clamps to address "sheet fan-out". To explain what sheet fan-out is, it's the progressive growth of the sheet's width at the tail end as it travels from the first down unit to the last down unit.

To illustrate, imagine the first down color you are concerned with is the black printer. With each successive "Squeeze" the sheet fans-out like bread dough squeezed by a rolling pin. This 1st down black ink image printed on the sheet is also fanned-out more and more as the subsequent impressions occur. In other words, for a sheet-fed KCMY ink sequence, the first down black ink would seem to grow progressively wider near the tail end with respect to the downstream units, typically with the last down unit seeming to print the most narrow.

The split tail-clamps I mentioned earlier, allowed me to force the tail end of the 1st down
plate inwards slightly and stretch the downstream plates outward slightly as needed to counteract any fan-out.

A web press may have a method of achieving a similar task via cylinder skewing or some other method(maybe not). One thing I suspect is common to both web and sheet-fed presses is that the greater the "squeeze" applied to the sheet, the greater the fan-out. Another factor that i suspect is common to both is that, the thinner and larger the stock, the greater the fan-out.

The best way I can think of to determine if it is indeed fan-out you are dealing with, is to compare the first down ink's plate against the resulting printed sheet. Trim the sheet/cutoff as needed near the tail end and compare it carefully with the 1st down inks plate(you should probably remove the plate from the press in order to determine anything or convince anyone). If a sheet/cutoff's 1st down imprint on the sheet/cutoff has grown in width near it's end when compared against the plate that printed it in the first place, how else would you explain it?

If the very same sheet/cutoff compares accurately to the last down inks printing plate, it is further proof that fan-out occurred between the intervening units. For further proof, carefully trim the 1st down plate as needed near the tail and lay it upon the last down unit's plate and see if they match widths with one another, if they do, why don't they match on the press sheet/cutoff? Finally introduce the sheet/cutoff as well to settle things and see what matches what.

As many have indicated before me, the press-room is the much more likely suspect for this problem. I hope that the tests I suggested will reveal the source of the problem. The tests I suggested will likely require enough skill in execution so that one does not warp the plates or the sheet/cutoff. A scope with a 25x magnification or better would likely be needed as well. I should also mention that the tests I suggested should be considered as evidence only, they are only as good as the person's skill performing them. Regardless, no one in their right mind would consider the results of these tests absolute proof.

A dubious test is better than no test at all, the way I see it.
 
would anyone know why our Sakurai has what is being referred to as sheet fanning only on the back side after turning the sheet. Black and Cyan go down perfect, leaving the transfer cylinder going into Magenta in tower 3 and Yellow in tower 4 the image is 3 lines short across the cylinder on the drive and operator side of the sheet.

The way you stated the question is a bit confusing to me. If what you meant by the "back side" is the "tail end" of the sheet, and what you meant by "turning the sheet" is transferring the sheet further downstream towards the Magenta and Yellow printing units and finally the delivery? If that is true, we are on the same page.

It's been many years since I've run a press, however back then, our sheet-fed presses had split tail-clamps to address "sheet fan-out". To explain what sheet fan-out is, it's the progressive growth of the sheet's width at the tail end as it travels from the first down unit to the last down unit.

To illustrate, imagine the first down color you are printing is the black. With each successive "Squeeze" the sheet fans-out like bread dough squeezed by a rolling pin. The 1st down black image printed on the sheet is fanned-out more and more as the subsequent impressions occur. In other words, for a sheet-fed KCMY ink sequence, the first down black ink would seem to grow progressively wider near the tail end of the sheet with respect to the downstream units, typically with the last down unit, Yellow seeming to print the narrowest.

The split tail-clamps I mentioned earlier, allowed me to force the tail end of the 1st down
plate inwards slightly and stretch the downstream plates outward slightly as needed to counteract any fan-out

If the fan out only occurs between the Cyan and Magenta units, you should inspect the transfer drums dividing these units for any debris, especially near the gripper blocks.

Of course I've assumed that you've already checked your plate and blanket packings and tensions using a packing gauge and set the squeeze settings for the impression cylinders to the minimum required to transfer the ink from the blanket to the sheet.

Lastly, increasing the gripper bite by advancing the head stops might help. If it does then roll the plate cylinders as needed to compensate.

I hope this helps.
Otherthoughts
 
Do you have an IR Dryer?

Do you have an IR Dryer?

Hi jmeehan,

Just quickly.

We run a Sakurai 466SIP 2005 model and I had problems backing up with some crazy stretch a few years ago. Like the stretch was worse than I'd seen on coldset press.

What we were doing is running our IR Dryer very high, to cook the sheet and dry as fast as possible. But when we backed up, the sheet was so dry I believe the moisture hitting it in the first two units were causing the sheet to stretch heaps.

We put fresh sheets in, and the fit would be perfect. Back on to the previously printed sections and it would be miles out.

So the question is, are you running an IR dryer on the first side down? Is it running real hot? (35% plus)

If not, then ignore my post...
 
sheet fanning

sheet fanning

thank you all for the information. we are taking steps for each mentioned. if I was not clear the first pass with KCMY are all registering exact. pack, squeeze and tack have all been addressed at this point. the problem is occurring on the last turn.
 
Fresh Sheets?

Fresh Sheets?

Hi jmeehan,

If you are printing the backup (first side already printed) and it's out of fit (fanning out etc), if you put in some fresh unprinted sheets and print the same thing, does the fit come in perfectly again?

Using any heat to dry the stock at all?
 
sheet fan out

sheet fan out

Thanks dwanehollands,
Sheets register perfect with fresh stock, first pass. As mentioned tower 1 (k), and tower 2 (c) register perfect and register to the underside (previously printed side) after the turn. The problem occurs at tower 3 (m) and tower 4 (y) after the transfer from towers 1&2. Both m and y register to one another but do NOT register to c&k (2-3 lines short across the cylinder).
We are attempting to run 50% or less on the IR dryer, first pass to see how the sheets respond. On a variety of coated stocks (70, 80 & 100 book).
 
Re: register fan out on the back-up 1) are you over packed under the blanket? 2) are you printing with minimal pressure? 3) if using IR dryer check pile temp (don't cook it) 4) if you're running AQ on it check viscosity 5) is the gripper edge of your sheet square. check it before you print the first side. if the sheet edge isn't square you may be able to bow your front guides in or out. 6) can you change the ink lay down?7) when fan out happens twice with the same stock try different stock save samples of everything look for patterns
 
To summarize, jmeehan's problem.

Print the first side - Prints with no register problems

Print obverse side - Prints with a fan out of roughly 3-4 lines width occurring between printing units 2 and 3.

Test - Printed some test sheets on identical unprinted stock using the same backup plates that produce mis-register using the backup stock. Results - no register problems

Summary- No mis-register on first printed side of the sheet, regardless of whether he is using front plates or backup plates.There exists a difference between the way fresh stock and backup stock is transfered between units 2 and 3 that results in the register problems.

Sources
- The categories dividing the 1st run stock from the 2nd run stocks are press effects occurring downstream from the 2nd unit. These include heating elements applied to the first run, sheet curling, press room environment variables like temperature and RH changes etc.

Suggestions - Increase the gripper bite by moving the "front stops" forward. Advance any front lay register sensors as needed to comply with this change. If the backup mis-register is minimized, then roll all the print cylinders forward as needed to accommodate the gripper bite change. Investigate further.

otherthoughts
 
15-22% IR Dryer Temp

15-22% IR Dryer Temp

jmeehan,

The stronger position I make the more likely I am to have egg on my face, but I strongly believe it's the excessive heat in the dryer from the first side which is causing the troubles for the second side. Mainly from our own experience with something very similar

In fact the Sakurai dealership were perplexed as to what was happening.

We have an 18kW Baldwin Dryer on our Sakurai which was up-spec'd. Chances are your dryer is 9kW which is standard.

I would strongly recommend putting your dryer temperature down to 15-22% and trying that. I believe we were running around the 50-60% range when we had our troubles. Obviously the run speed will affect the time the sheet 'dwells' in the dryer section, so if you're running slower speeds it may 'multiply' the effect.

Good Luck, I'm interested in how it turns out!
 

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