Troubleshoot
Rollers related common
problems and suggested solutions
- by Vaibhav Agarwal, director, Modinagar Rolls Ltd

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Problems:

• Scum: This is the appearance of unwanted inked areas in the non-image areas, one of the important reasons being – inadequate supply of water to the plate. To prevent this, ensure that the damping rollers should be soft (22/25 SH) and resilient. They should apply a very thin even film of moisture on non-image areas. The fear of scum makes machines run at lower speed – loosing on invaluable production hours.
  
  
• Skidding streaking: When the roller becomes ‘glazed’ due to accumulations of a dried ink film, it looses its frictional potential and slows down due to poor friction. Thus, when the roller strikes the plate whose cylinder speed is greater than that of the slower glazed roller, a skid is produced. This, in turn, causes a streak across the plate.
  
  
• Stripping: Occasionally, parts of the ink rollers refuse to hold ink. This is known as ‘stripping’. There are two main reasons for stripping – (i) a film of dried ink on the roller and (ii) desensitisation of copper rollers.
  
  
• Image wear: With high speed printing, a hard damping/plate inking roller tends to cause a rapid weakening of the plate image due to abrasion.
  
  
• Belling: The damping hose being made of cotton fabric, it tends to exert a constant pull at the edges of the damper roller as it tends to shrink while drying. Belling of roller edges upsets the pressure distribution and a harder setting is required for the middle portion to transfer sufficient moisture to the plate.
  
  
• Swelling: Rollers which readily absorb printing ink oils and cleaning solvents become tacky and swollen due to lack of low ink absorption rate and resistant to chemicals and solvents.

Solutions:

• Keep rollers clean when machine is not in production.
  
  
• Use anti glazing/cleanser solution time to time.
  
  
• Don’t over exert the roller life limits, change or recoat rollers at regular intervals.