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ROLLER CARE

 
 
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Proper Setting of Rollers
 
Pressman know that if rollers are not accurately set, efficient operation of the inker units will be partially lost and they will not perform at operating capacity. Ductors, distributors and forms are driven from the surface of power rollers. Improper setting of the rollers may cause damage, adversely affecting the quality of printing. Rollers should be set as lightly as possible to accomplish their intended function of transfering ink to plate.

Press manufactures have made it easy to set rollers through fewer and more accessible adjustments. Great care must be given to the proper setting of rollers.

  • Setting inking rollers:
    Once adjustments have been completed and the adjustment screws locked, nothing further is required, unless the plate cylinder diameter is changed or replacement of the roller is necessary .
  • Irregular roller surface affects ink transfer:
    Except for gear-driven steel rollers, all rollers are driven by contact. Thus, an irregular roller surface will adversely affect ink transfer. Form rollers must contact the plate evenly. Poor distribution of ink will result from least loss of contact between the rollers because of the thinness of the ink film.
  • Accommodate the gap of the cylinder:
    Streaks can be avoided if the inker is timed to accommodate the gaps in the cylinder. Older and worn presses may require an earlier start at the back of the plate if the form permits it. Streaks are most prominent on the gripper edge. By starting earlier, the slack created by excessive wear is taken up before the cylinder reaches the gripper.
  • Worn out parts should be replaced:
    Worn out sockets and spindles, should be built up. Any roller, regardless of the material should be set as lightly as possible in order to effect proper ink distribution. This setting is often referred to as the “Kiss”.
  • Downtime:
    Improper setting may cause a substantial portion of downtime, the cost of which can run into hundreds of dollars per hour. Rollers that are not properly set can cause scum, streaks, filled halftones, filled screens and reverse type, lined page, images, ragged solids, retarded ink drying, variation of print values and set off problems. It also adds to a decreased roller life and increased costs.
  • Setting of ductor timing:
    The ductor timing which times the flow of ink should be set very lightly to both points of contact. For example, it may be necessary on some forms, to have much heavier flow of ink at the back rather than the front half of the sheet. The ductor must be set parallel with the steel roller, usually with the vibrator contact with which starts the distribution chain. If a ductor is set so it strikes too hard on contact, it can send reverberations throughout the inking system and cause rubber streaks. The ink ductor and its action should be set so it contacts the ink fountain roller at the extreme height of its stroke.
  • Check form rollers after inking up:
    Distributing rollers must accept and transfer the ink in a position parallel to the rollers that they contact. Form rollers, at the end of the distribution chain, supply ink to the image of the plate or blanket. To check form rollers after inking up, drop them on the plate and be sure to “stripe up” about ¼ to 5/16 inches wide on larger presses and 1/8 to 3/16 inches on smaller presses.
 
 
 
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