The Problem in Detail
Key Contributors to a Loss of Function
The exact cause of degradation for any particular roll depends primarily on the choice of thermal transfer fluid. Glycols can be corrosive when heated; oils tend to coagulate, especially when combined with water or other chemicals. Even if the roller contains straight water, the damaging effects can be substantial, especially if the water is not perfectly balanced. Corrosion is generally associated low pH water. Mineral deposits and scaling are associated with high pH water.
- The roll is completely replaced. This is expensive and time consuming.
- The roll is left in place. This is the most common reaction. More fluid is pumped through the roll in order to achieve the desired heating or cooling of the web. This wears on pumps, supply lines and fittings. Also, some plant managers will actually slow the roll’s rotation (which affects a plant’s overall line speed) to increase the duration of time the roll is in contact with the web (known as “dwell time”).
- The roll is temporarily removed and shipped to a roll rebuilding company (such as Menges Roller), where the interior chamber is flushed using special chemicals designed to breakdown coagulants and rust. These “acid flushing services” can be effective in removing solid and gelatinous materials that were inhibiting thermal transfer, but it is disruptive because the roll must be removed from the plant.
- The roll is so completely damaged that a complete overhaul of the roll is required. The outer shell is cut away, then its inner walls are re-machined and the entire outer shell is replaced. The spiral baffles on the inner shell are also removed, the inner shell’s outer wall is machined, then new spiral baffles are installed. Usually the roll will also need to be re-chromed and rebalanced. All this is expensive and disruptive, and can only be accomplished at an off-site full-service roller company like Menges Roller.
- shortened roller-to-web dwell times, which increases a converter’s line speed
- longer pump and heating/cooling equipment lifespans
- improved converting process results and better overall product quality for the plant