Colour variation problem in SM 72vp

Dear Freinds,
I manufacture mono cartons on 300 gsm fbb. we often face problems of colour variation. in every start of a printing run first 100 sheets are of different color and rest are of disfferent color. please tell me how ca i control that.

 

Pre damping and pre inking settings?

 

It is normal to have a color variation between the start and the end of printing also at the start and at the change of palette and that is why the manufacturer has put a non-stop option to be able to minimize a little of the variation, after you can also improve the start of printing by passing pass sheets in order to unload the touch rollers in the start of printing and remove them at the reception, as you can manually operate the moistening touch rollers before launching the margin so that the plates take a little water at the start of course with a very good adjustment of the inking and moistening rollers also zn rollers in good condition to make a very good ink transfer, keep the balance between water and ink in a way not to have the emulsion and having a thermoregulation option also helps, but you have to be sure that the variation always exists in offset printing a good driver and adequate options can minimize this phenomenon

 

I've never heard that presses manufacturers invented non stop feeders and deliveries to avoid colour variations during start the production
Properly set rollers and pre/post dampening and inking should make colour steady within 15-20 sheets

 

This is the opportunity to hear that, after each stop to feed the feeder the ink goes down into the ink touch rollers and accumulates after the start the ink is transferred to the plate, the ink stabilization begins after a little time the moment when the Rilsan rollers distribute the ink again

 

Thank you for the information. There is no fixed solution to the problem but ya it can be minimized by appropriate settings and experience.

 

Yes sir that s what i told you ,

 

Good luck

 

In addition to the pre damp and pre ink settings, some model year presses also have the ability to shut off the oscillating action of the rollers when the press is not in actual printing mode. By shutting off the oscillation when not printing the press is now able to hold on to small zonal variations across the ink train. It might be that the 72 presses were a bit too primitive to include that feature.