SM74 Scuff?

[Cameron]

Hey everyone.. we had an sm74 installed not long ago. It is not a new machine.. but new to us.. and we are having a really frustrating problem that we cant seem to shake so far.

The press operator is sure its scuffing, but we cant figure out why... the press was installed with orange transfer jackets.. but whether the jackets are on.. or off... we have the same problem.

One of the attached images shows what it is doing to the print, and the other two show what it is doing even with the impression turned off completly and just running sheets through the press.

This job in particular is a pantone screen.. we have had some success running a solid pantone, but when running screens, and process solids, we have real issues with this and hoping someone can help!!

(hope you can see it in the photos, it is not as bad as it gets if we continue.. it gets much worse as it goes.

 

[Ret Heidelberg Instructor]

There are several things that could be causing this problem. Try to eliminate them one at a time
1.Is the suction bar on the double transfer set to hold the tail end of the sheet, and working properly? Try sending some already printed sheets thru the press with the impression off and with the compressor on. After you get the stream of sheets into the press hit the emergency stop and check the sheet travel and see if the suction on the tail is working. If the sheet is not being held at the tail, you could have the sheet moving around as it comes into contact with the transfer jacket. Check to see if all air bars are operational. Compressors might not be turned on from the console.
2. Check the packing under the transfer jacket. It should not be too tight or to loose.
3 Check the sheet travel as it comes up thru to the delivery if it is SM74. The sheet should travel along the venturi guide plate un disturbed.
4. If you are running this jobon a 5 color in the 1st 4 units and leaving unit 5 off. Try turning on the impression on #5 unit. This will stop the sheet from fluttering.
These are a few things that you can try to troubleshoot the problem. By the way what kind of SM74 is it with regards to number of units?

 

[Cameron]

All great suggestions.. unfortunately ones we checked (mostly).. It is a 5 color perfector.

1. suction bars are checked and all seem to be working properly and holding the tail of the sheets.. when the vacuum is turned off(at lack of better things to try) the result is the same...

2. We are at a loss on the transfer jackets, they are PrintGuard jackets? they installed them with the machine, with no packing, and no documentation with them or on the website for packing with these.

3. I think we both were trying to see the travel up the delivery but since its a new style delivery to us we were having a hard time with that, but with card stock i would be surprised to see it fluttering there?

4. We have definitely tried with one or any of the unused units having the impression on.. we had considered that as well..

The packing of the jackets definetely came up as a question between us quite a few times... they also seem to take an impression of the sheet and hold onto it quite a bit which is not what hes used to seeing with superblues...

 

[otherthoughts]

I'm not completely sure what the problem is, based on the images shown ....my apologies if I am off the mark here?

What I've known as and called scuffling ..... occurred as a product and route of the sheet release within the delivery.

For example, in image 2 supplied by the OP. There are two sheets shown in the image. The leading edge of one sheet is shown in this image. This leading edge shows traces of ink on it. No ink should exist on the leading edge of a sheet. It is within the gripper bite and is a non-printing region. So how did the ink get there? Are the grippers so dirty that they are leaving these marks on the leading edge?

So here's my point, ink on the leading edge of a sheet, may indicate that the leading edge of the sheet is being delivered in such a way that it lands on the sheet prior to it, and scrapes/scuffles past the wet ink on the surface of the previous sheet.

A sheet should be brought all the way to the joggers at the end of the delivery, before being released and stacked.

If a sheet is released too early on? Then it strikes/scuffles the sheet beneath it and scrapes upon the ink surface of the sheet beneath it.

There should be a delivery lever that controls the timing of the sheet release. If the sheet release occurs in such a way that it strikes the front joggers prior to striking the sheet beneath it? Then that's the way I believe it should be. Why deliver a sheet in such a way that it strikes the wet ink on the sheet beneath it?

Bring the sheet to the end of the delivery and then blow it down with the fans in such a way that there is a slight upwards bow on the edges of the sheet, dipping in the center.

Scuffling of the type I'm speaking of, always occurs on and within the first few inches of the leading edge.

If you're not perfecting/straight-transfer? then there should never be any ink on the leading edge of a sheet. Gripper marks? Yeah ....ink ...no.

Hope that helps?
Regards

 

[Alois Senefelder]

Puzzled

Puzzled

Hello Cameron,

Have tried a Crash Stop at speed ? then followed individual sheets into the delivery, looking for any

so called "Scuff Marks"


Regards, Alois

 

[Ret Heidelberg Instructor]

Good call Alois,on the e-stop while printing at speed. Note to Cameron, check for any possible oil that may be flying around. Also check for dries ink on the perfector. One other thing I would like to know. The sample that that shows the random color bars looks like a slap off a blanket that is not under impression Does the press have a coating unit?

 

[Cameron]

Thanks for the replies everyone, sorry for the misleading picture 'otherthoughts' it is the tail of the sheet, i was just laying them down to take a photo.

We have been keeping an eye out for oil flying around, I think we are ok there, and we have tried the estop, and checking both the perfector and transfer cylinders/jackets.. the perfector looks good, with the cylinders they are buliding ink on them, with the jackets on they are building ink on the jackets... we are trying to get superblues here asap to try those instead, could be that these orange jackets are just junk?

You are correct about the blanket not being under impression... for those sheets showing the color bar impression..

 

[Cameron]

In case anyone was still wondering, or scratching their heads trying to help with this, we think its solved now. Everything is looking much much better.

We got in some blue glass jackets to replace the orange ones on a couple cylinders... and also the star wheels were almost non existant... the installers left them burried under other supplies in a box. We installed them in two heads with the new jackets as well and the 2 color job we were printing looked perfect. We will install all star wheels in the other heads and replace the orange jackets with blue ones as necessary.

Finally.. and I really appreciate everyones effort to help out.. if anyone else runs into antying like this check your star wheels and I would worry about the orange jackets as well.

 

[Ret Heidelberg Instructor]

Glad you were able to troubleshoot the problem. It probably one of the last things you considered.

 

[Cameron]

Pretty much... we noticed the missing star wheels... but werent aware that we had any.. and assumed the press was running without them.. thats why we are not switching all jackets yet.. we will try with full sets of star wheels in the other heads before switching the other jackets to try and figure whether it was one thing or both things contributing to the issue.

 

[Ret Heidelberg Instructor]

You probably don't need them all in at the same time. New presses used to ship with them already in place in every slot. If you didn't have all of them you could probably skip a row and not see much difference. You will have to remove them on small sheets if you want to use the tail suction.

 

[Cameron]

Appreciate the extra tip, the operator was quite familiar with that, he had us put them in every second slot, and I had asked him if they needed to be removed for small sheets which he had already told me that was the case. Good tips are ALWAYS welcome. Its a big change from a GTO52, to a SM74