In the corrugating process three basic components combine to produce Board.
Paper + Adhesive + Heat = Combined Board
The primary source of the heat in a corrugating plant is the steam system. While this is a critical and costly system in any plant, it is often overlooked and poorly maintained. In general, this is because it is also the most poorly understood. The plant steam system is typically an “out of sight-out of mind” process that everyone knows sufficiently well to keep operating. It receives little consideration until a problem develops.
Why Use Steam?
- Steam is easily generated, Distributed and controlled.
- It has a high useable heat content.
- It has constant characteristics so its performance is repeatable.
- It is a clean and odorless.
The Role of Heat
- Heat is added to the corrugating medium to soften the thermoplastic fibers. This enables the flutes to be formed without fracturing or losing their shape.
- Heat is added to the liner to begin the gelatinization process of the adhesive.
- Heat is added to the combined board to evaporate the remaining water from the adhesive. This enables the combined board to be bonded firmly when it is discharged from the corrugator.
- Heat is added to the liners to provide some drying action. This is used to balance the moisture content of the moisture content of the combined board and control warp.
Heat is typically added to the corrugating medium by passing it over a steam-filled drum called a preconditioner, over a steam shower, or a preconditioner and steam shower mounted in series. Cellulose fiber and similar to plastic because they become soft and pliable when they are heated.
As the fibers become pliable, the medium can be more easily formed into the fluted shape by the corrugating rolls. The material will retain the fluted shape as it cools.
While the pre-conditioner can only heat the medium, the steam shower can heat the medium and add moisture. Adding moisture to the medium lowers the temperature requires to plasticize the fiber. Maintaining moisture in the paper aids in penetration of the adhesive.
Heat is added to the liner by passing it over a steam-filled drum called preheater. Preheating prepares the liner for bounding to the medium by adding sufficient energy to begin the gelatinization of the adhesive. The final drying of the adhesive occurs in the doublefacer where the combined board id passed over a series of steam-filled chests. Heat is transferred to the combined board, and the remaining moisture is evaporates from the adhesive. This final drying creates the strong bond required to hold the liners and medium together.