Web Movement
Aerodynamic instabilities occur when a thin material travels at high speeds through a printing press or a coating machine. The term substrate flutter describes the rapid, uncontrolled vibration of the paper as it moves between rollers. This phenomenon is caused by the interaction of the moving air and the tension of the web.
Tension Variability
Problems arise when the air pressure on one side of the sheet becomes significantly different from the air pressure on the other. During substrate flutter, the paper begins to ripple and snap, which can lead to wrinkles in the finished print or even a complete web break. This movement is most common in long open spans where there are no rollers to support the material.
To stop the vibration, operators must increase the tension or install air bars that blow a steady stream of air to cushion the sheet. If the flutter is not controlled, it can cause the ink to smudge as the paper hits the drying hood or the side of the press. High-speed machines are particularly prone to this issue because the air currents become more turbulent as the velocity increases.
Registration Accuracy
Consistent positioning of the web is impossible if the material is bouncing up and down. When substrate flutter is minimized, the colors line up correctly and the cutting is more precise. Proper machine design includes many small rollers to keep the paper stable at all times.
