The most prone problem in printing is the "bar". It is very difficult for the master to do anything. This requires calm thinking and try to avoid detours. Here is a brief explanation of how to judge and solve the "bar" problem for reference.
Generally "bar" is divided into ink stick, water bar, roller bar, gear bar and so on.
1. Roller meshing gear side gap is too large
The printing press roller gear meshing helical gear which is basically, large transmission coefficient switching gear engages a smaller backlash space to reduce the chatter in the drive when the printing impact and to maintain stability and accuracy of printing. In actual work, the backlash of the drum gear mesh is changed and adjusted according to the printing of paper of different thickness. The thicker the paper, the larger the center distance adjustment is, the smaller the exchange coefficient of the meshing surface of the drum gear is, and the side gap becomes larger. The greater the difference in line speed of the printed roll surface, the greater the relative slip produced by the printed surface and the more pronounced the bar.
Solution: Under the premise of ensuring proper printing pressure, the center distance between the three rolling screws should be minimized, and the meshing backlash should be properly pressed to reduce the degree of "bar".
Excessive backlash caused by gear wear
After a period of work, the drum gear is worn due to load or foreign matter in the tooth gap, resulting in excessive gear meshing backlash, the gear involute cannot be rolled at a constant speed according to the meshing line, or the foreign object "top tooth" makes the gear in operation. The chattering occurs, causing the friction between the rollers to increase to cause slippage, and the printed image portion produces an ink ribbon equal to the pitch of the gear at the moment of the sliding, that is, the gear bar.
Solution: Strengthen the cleaning and maintenance work of mechanical equipment, clean and remove the debris between the gears, and maintain a good lubrication state; according to the gear wear condition, recalculate the adjustment center distance, properly press the backlash, and replace the new one immediately. gear.
2. Bearing wear
After the offset printing machine is used for a long time, especially the roller which does not go to the roller, the impact shock vibration is large, the bearing is easy to wear, and the gap between the journal and the bearing is increased and the sleeve is loosened. The mouth vibrates due to the deviation, and the sliding friction creates a "bar". Especially when the load is not normal or the lubrication is not good, the shaft head and the bushing of the drum are intensified, and the "bar" is most likely to be generated near the mouth.
Solution: The mouth part of the rubber inner liner can be cut into a trapezoidal shape to reduce the impact force when the pressure is combined. When the roller bearing wears seriously, the bearing should be updated in time.
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