The Relationship Between the Forming Fabric and the Corrector

Why Forming Fabric Need a Corrector？

During papermaking, the forming fabric will always drift to one side of the paper machine to some extent (deviation), which will cause uneven wear and edge damage. Therefore, a corrector is needed to correct the mesh. As an important auxiliary device in papermaking, the forming fabric corrector can automatically adjust and control the position of the fabric in papermaking to prevent deviation and maintain optimal tracking performance.

Types of Forming Fabric Correctors

There are two main types: manual and pneumatic

Manual Forming Fabric Corrector

The manual forming fabric corrector is installed on the correction roller (the guide roller on the corrector). Its transmission end bearing is mounted on the support seat via a hinge or spherical surface. The operating end bearing seat has a distance of 50-100mm. Rotating the adjustment device can make the correction roller tilt to a certain extent. When the misaligned forming mesh passes the roller, the mesh tends to run in the direction perpendicular to the rotation axis of the roller, causing the forming mesh to return to its normal running position. Furthermore, the sensitivity of the corrector is influenced by the tension of the forming fabric, the wrap angle on the correction roll, and the distance between the correction roll and its adjacent rolls. Typically, a wrap angle of 10°–15° is employed, and the distance between the correction roll and the adjacent guide roll should exceed 600–800 mm.

Pneumatic Forming Fabric Corrector

The sensing element of the pneumatic automatic forming fabric corrector is a small baffle that contacts the edge of the forming mesh. When the forming mesh deviates from its designated position, the position of the small baffle will change, thereby opening and closing the exhaust valve, changing the air pressure inside the membrane executive agency, causing the correction roller to make a corresponding displacement, and completing the automatic correction action of the forming fabric. Since the baffle-type sensor subjects the mesh to a certain degree of wear, it is generally recommended that the edge of the forming fabric remain perpendicular to the baffle and be positioned centrally relative to it.

The forming fabric tensioner can also serve a corrective function; by carefully tightening or loosening one end of the tensioning roll, the forming fabric will drift toward the side with the looser tension. However, this method is generally used when there is no forming mesh corrector.

Working Principle and Adjustment of Forming Fabric Corrector

One side of the correction roll is fixed, while the other is movable. The forming fabric moves towards the side that first contacts the guide roller, while the standard line runs ahead of the side that first contacts the roller. To facilitate the description and memorization of the pattern of the corrector’s deviation in the forming fabric, it is as follows: when the operator is in the position of the corrector mesh, moving the corrector roller in the opposite direction of the mesh’s running direction will bring the net towards the operator; moving the corrector roller in the same direction as the mesh’s running direction will bring the mesh towards the drive side.

The positioning of the corrector is of critical importance; generally, it is recommended that the guide roller be situated at the final stage of the loop. The corrector should be positioned as close as possible to the guide rollers. The wrap angle of the automatic correction guide roller should be greater than 25°. If the forming fabric does not respond much or at all to the correction system, the correction system needs to be checked. If poor contact between the forming fabric and the roller—resulting in slippage—is attributed to low tension, the tension should be increased appropriately. Should all components of the tension correction system be functioning normally, yet the forming fabric continues to drift, it is recommended to verify whether the rollers have deviated from their proper alignment. Prior to this, manual correction (by manually adjusting the tensioning roller) may be performed if deemed necessary.

Factors Affecting the Correction of the Forming Fabric

• When the fulcrum position of the correction roll deviates from one side, the corrector can only correct to one side, and when the forming fabric moves to the other side, the correction roller cannot correct the mesh even when it reaches its limit position.
• The greater the tension of the mesh, the stronger the correction effect, but excessive tension may also cause the forming fabric to keep running to both sides.
• The smaller the wrap angle of the correction roll, the smaller the friction between the forming fabric and the correction roll, and the worse the correction effect. Conversely, the greater the coefficient of friction between the correction roll and the mesh, the better the correction effect.
• The smaller the spacing between the correction roll and the guide rolls positioned before and after it, the less effective the correction will be.
• If the tension on the two sides of the forming fabric is uneven, the fabric may drift toward one side, thereby failing to achieve the intended correction.
• For pneumatic correctors, the opening of the throttle valve should also be checked. The smaller the opening, the slower the corrector roller runs.
• For electric correction, the main environmental factors that affect the measurement are light intensity, which can cause inaccurate measurement positions. Improperly configured PID parameters can lead to oscillations within the control system, while significant deviations in the parameters provided by the process specifications may result in control errors.

The synergistic interaction between the forming fabric and the corrector is crucial for maintaining continuous production, extending the service life of the fabric, and ensuring the stability of paper quality. A thorough understanding of the relationship and operational setup between the two is undoubtedly key to achieving continuous production and improving product quality.