Part 3: Five Benefits of Vacuum Rolls

Vacuum Roll Characteristics

Vacuum rolls and belts have a number of characteristics that are potentially useful to converters. What benefits are derived depends on the application, which will be addressed later. A summary list of characteristics follows.

  1. Single Side Contact – A very popular feature of vacuum rolls is the ability to control tension in a web while touching only one side.
    • No nip is used, so a potential source of injuries is eliminated.
    • Vacuum rolls can transport a wet web, coated but not yet dried or cured, without touching the coated side.
    • Once the coating is dried or cured, it can be kept free from damage or contamination because it is not touched by the vacuum roll.
  2. Large Tension Differentials – Vacuum rolls and belts can sustain larger differences between Tension In and Tension Out than other technologies.
    • A vacuum roll between two sequential process steps in a converting line can enable each step to be carried out at its optimal tension level, even when there is a big difference between the two levels.
  3. Extremely Low Tensions – Tensions can be minimal since the holding force from the pressure difference does not depend on tensions.
    • Low line tensions can be achieved.
    • High precision web metering can be implemented.
    • Less slippage means more accurate speed control can be provided.
    • Web accumulation can be done.
    • The web can be held in place when a web break occurs.
  4. Small Wrap Angle – Compared to “S” wraps, the wrap angle required for a vacuum roll is fairly small for a given tension differential. For belts, wrap angle can be very small. Line layouts can be improved, for better use of space.
  5. Boundary Air Removal – At higher speeds, boundary air dragged into the area of a roll wrapped by the web can significantly lower coefficients of friction and thereby compromise tension control.
    • Vacuum rolls help remove boundary air allowing higher speed operation.