Heidelberg QMDI Register Issue

[ammiller]

I have a strange issue with our QMDI. We imaged plates, and ran 7000 sheets through the press, 12x18, 10Pt. Carolina C2S, full color/semi-heavy coverage. No problem. After 7000 sheets, the magenta goes out of register, but only from the leading edge of the sheet down about 5 inches, then from there to the tail end of the sheet it is in perfect register.

Replaced the blanket and packing, no change. Checked the pressure, no change. Imaging a new plate fixes the issue, but I don't understand why it is happening, and it's an expensive fix time after time. It would be understandable if it was out of register the entire length of the sheet, but not just the first 4 or 5 inches of the sheet.

This happens on long runs only.

 

[nhprinter]

It sounds as if the plate material is stretching or coming loose creating a "bow" in the plate material. I'm not even sure it CAN stretch, but it seems the only logical reason.

Is the blanket over packed? Has the impression from the plate cylinder to the blanket cylinder been checked? My thought is that the plate is hitting the blanket too hard.

Maybe you could make a reference mark with a sharpie where the plate comes out of the cylinder and check it when the problem arises to see if it moved.

Very strange problem. Hope you find the answer.

Dave

 

[Ret Heidelberg Instructor]

Ret Heidelberg Instructor

Ret Heidelberg Instructor

Does this happen only on card stock? Is the plate winding clutch holding the material tight? It seems strange that when you re-image that the problem goes away. How far off does the registration move? Check to see if the packing is slipping. Is the register out on every sheet? Are you running a mixed grain of paper stock? Sorry, I am just throwing out these questions. I instructed on these presses in the field for many years from the Classic to the Pro and these are some of the questions I would be asking. Try and eliminate one problem at a time. The one thing I did see in the field was a tightly set cleaning cloth that caused a distortion of the plate. Perhaps you are using the hickey picker function mid-run. These are some things to consider.

 

[ammiller]

Thanks for replying!

So far I have only noticed it on card stock, but only because that is what the longer runs have been. i don't know about the clutch, but it seems if that was not working properly the entire image would be off. The last time I noticed it, I tried a few things to see if they helped, I repacked the blanket and checked the pressure on the press, no help. i am not using the hickey picker function. So I don't think it's the blanket/packing, and I don't think it's anything to do with the pressure.

 

[rbailleu]

if it was the clutch it should be the entire plate moving. I assume also that this has happened on more than one roll of plates. does the image go all at once or is it a gradual thing, like after 2000 it starts getting bad and at 7000 it is too far off to continue. I would put extra marks on the plate and see exactly where the stretch is happening. if a tech comes to visit have them dial indicate the trueness of the blanket and plate cylinders. I have a hunch you have a cylinder out slightly and it is thumping .002 harder on that area. run a full solid on the magenta and back off the impression a little at a time to see if there is a high or low spot. or repack the blanket .005 lighter to see if it is a low spot on the plate cyl

 

[ammiller]

I noticed yesterday that it starts getting bad pretty quickly, and just continues to get worse.

 

[Ret Heidelberg Instructor]

Ret Heidelberg Instructor

Ret Heidelberg Instructor

It sounds like you need somebody to look at it from a mechanical standpoint, you might need a technician.

 

[Paul Cavanaugh]

There are a few things that can cause this issue.

1. If the problem is happening right after you change plate material on the first 5 or so jobs it is because you did not install the plate material correctly. See this post from me on another forum to explain in more depth.: Registration problem after each new plate load - Color Printing Forum

2. There is a one way clutch in the plate cylinder that can fail which will cause the plate material to move. Typically this results in the whole plate moving slightly throughout the run.

3. There is also a tensioning clutch in the plate cylinder which helps keep tension on the plate while loading. It is set by a technician using a scale attached to a new plate roll. If this is not set properly the plate material can move on the cylinder.

4. Registration will change if going from light stock to heavy stock. It is recommended to set your register to 100# text. (We used Centura Gloss on installations.) Even at this if you change to a cover stock slight registration diferences could be seen depending on the ink coverages.

5. Heavy ink coverage will affect registration. Especially if one unit has higher ink coverage then the rest of the units. The ink pulls more on the plate with the higher coverage then the other units.

6. Paper quality also can cause registration issues.

Hopefully one of these will put you on track to fix your problems.