Press Felt Misalignment Early Warning and Handling

The press felt often shifts during papermaking. Actually, there is a processing window before folding the press felt.
When the alarm for the press felt going off-track sounds, the most common action on site is to immediately turn up the calibrator to try to pull the felt back on track.

However, an alarm does not necessarily mean the press felt is out of control. Sometimes the sensor signal is abnormal and the edge of the blanket does not actually move significantly; sometimes the paper making felt is indeed continuously tilting to one side, but the corrector can no longer keep up, or it swings back and forth between the two directions.

Although both situations will display a “deviation alarm”, the handling methods are completely different. When the press felts start to wrinkle, fold at the edges, or even risk getting caught in the pressure zone, there are fewer options available on-site. The first few minutes after an alarm is triggered are often the critical stage for judgment and handling.

Determine Whether the Alarm is a False Alarm or If the Press Felt Has Actually Shifted

After detecting the deviation alarm, first observe the edge of the press felt, the running trajectory, and the condition of the felt surface from a safe position. Then compare the following signals on the control screen: felt edge position, deviation trend, edge sensor signal, corrector output and actual action, blanket tension, vehicle speed, and the status of related equipment. The key is not whether the alarm has disappeared, but whether the press felt offset continues, whether the corrector responds, and whether the blanket tension is abnormal. If the paper making felt edge doesn’t move much after the alarm sounds, and the calibrator doesn’t show any obvious action, first check the sensor, signal line, installation location, and alarm settings. Issues such as sensor contamination, misaligned mounting, or changes in detection distance can all lead to false alarms.
If the press felt edge is indeed drifting toward one side and the correction mechanism has engaged, yet the felt continues to shift, simply increasing the correction intensity is not the solution. In particular, if the calibrator is close to its travel limit, or if the movement is inconsistent (left and right), it indicates that the system may not have truly pulled the press felt back to a stable position.
At this point, the deviation alarm is not the whole problem, but rather an early warning given by the equipment.

Determining the Problem By Observing Trends

There are many reasons why press felt might drift off-center, and it’s usually difficult to make a direct judgment based solely on alarm records. It’s recommended to check the paper making felt’s position, calibrator output, tension, vehicle speed, and related alarms for the same time period. And pay attention to two time points:

(1) The press felt starts to shift first, and the corrector then increases its movement.
(2) The guide exhibits abnormal movement first, subsequently causing the paper making felt to gradually shift toward one side.

In the first scenario, the root cause may lie in the press felt tension distribution, the condition of the felt itself, or localized contamination; The corrector is catching up with the offset that has already occurred.

If it is the latter case, it is necessary to check whether the edge sensor, the corrector actuator, the hydraulic or pneumatic conditions, and the control signal are stable. Abnormal operation of the corrector may push the press felt to one side.

Mistracking may also occur following events such as the installation of a new press felt, changes in paper making felt washing conditions, the completion of maintenance in the press section, or recent adjustments to machine speed, tension, or nip loads. It is also necessary to compare these time points with alarm trends, but the cause cannot be directly determined based on the fact that the press felt was just replaced or the equipment was repaired. Further confirmation should be made based on the on-site conditions.

Constant Movement of the Correction Device Does Not Necessarily Mean That the Felt Guiding System is Functioning Effectively

The purpose of a correction device is to adjust the position of the press felt; it is not a substitute for investigating the root cause of the mistracking. If the output of the calibrator continues to increase but the paper making felt still moves to the same side, it may be that the actuator has not reached the commanded position, or that the felt tension, roller condition, or calibration conditions themselves are abnormal. Another situation is that the corrector reacts too quickly, and the press felt swings back and forth between two directions, seemingly correcting itself, but in reality, it does not form stable control. It is recommended to check the following:

Whether the correction device’s commanded position matches its actual position.
Whether it is close to the mechanical limit.
Whether the hydraulic or pneumatic pressure is within the normal range.
Whether the actuator’s movement is sluggish.
Whether the edge sensors are clean, stable, and reliable.
Whether there are any erratic fluctuations in the sensor signals.
Whether there is a discrepancy in tension between the left and right sides of the press felt.
Whether the relevant rollers are obviously skewed or out of sync.

If the position of the corrector changes on the screen, but the on-site actuator does not take corresponding action, the problem cannot be treated as a normal press felt misalignment during mechanical operation.

Press Felt Misalignment May Be Related to the Condition of the Rollers

The press felt is not only controlled by the straightener; the parallelism and alignment of the rollers, the operation of the bearings, the press felt tension, and localized stress all affect the lateral position of the paper making felt. If the press felt always runs in the same direction, especially if it starts to deviate after a certain pressure zone, guide roller, or water absorption element, attention should be paid to the relevant roller system and guiding conditions.

Judge based on the following phenomena:

Whether the direction of the run changes after the change of direction.
Is there more rapid wear on one side of the press felt?
Is there any pulp buildup, structural damage, or localized contamination on the roller surfaces?
Are the bearing temperatures consistent at both ends of the rollers?
Is the press felt tension even on both sides?
Whether the press felt joint will swing noticeably when it passes through a certain position.
Is there any localized clogging in the felt-washing equipment or dewatering/suction devices?

If the deviation mainly occurs due to changes in press felt humidity, the operation of the washing machine, or after a certain pressure zone, simply adjusting the corrector can often only temporarily suppress the deviation and cannot eliminate the root cause.
If the press felt is still within a controllable range, but the deviation trend is becoming more and more obvious, the speed can be reduced according to the machine operation assessment, reducing the press felt running speed and equipment load to buy time for judgment. Even after the speed is reduced, it is still necessary to continue to observe:

Whether the speed of paper making felt offset has decreased.
Whether the corrector has started to respond effectively.
Whether the press felt tension has returned to stability.
Is the deviation trend still getting worse?
Whether the edges of the press felt are wrinkling or folding over.

The fact that the alarm temporarily disappears after the speed is reduced does not mean that the fault has been resolved. When the vehicle speed is reduced, the operation of the press felt and the stress on the equipment will change, and the original problem may just be temporarily less noticeable.
When the following situation occurs, the focus shifts from continued observation to controlling the risk according to the machine’s procedures: The press felt continues to shift rapidly to one side; The calibrator is malfunctioning, sluggish, or oscillating back and forth; The press felt begins to wrinkle, fold, or develop curled edges; There are signs of abnormal friction, vibration, or impact noises; Visible damage appears on the press felt, its seams, or its edges.

When inspecting press felts, rollers, or calibration mechanisms after shutdown, the prescribed shutdown, isolation, and energy control procedures must be completed to confirm that the equipment will not rotate unexpectedly before approaching it.

Seizing the Critical Window for Intervention Is the Most Important Step Before Press Felt Becomes Creased or Folded

When press felt misalignment alarm is triggered, the primary focus should not be on resetting the alarm as quickly as possible, nor on maximizing the range of motion of the correction device. Instead, the priority is to verify whether the press felt is indeed misaligned, determine whether the correction device is capable of pulling the felt back into position, and assess whether the misalignment trend is subsiding or continuing to worsen.

If the edge of the press felt remains stable, first check the sensors and signals. If the paper making felt is indeed drifting, examine the operation of the correction mechanism, the tension, and the condition of the roll system. If the correction mechanism is unable to effectively correct the deviation, or if the press felt begins to wrinkle or fold, measures must be taken immediately in accordance with the established operating procedures: reduce the speed, release the tension, or stop the machine.

The press felt misalignment alarm is merely a warning; a creased or folded felt represents an actual loss. The alarm itself is not the primary concern; the real danger lies in relying solely on intuition to “tough it out” after the alarm has sounded. Once a press felt is creased or damaged, the consequences often extend beyond the simple need for a replacement—they can necessitate a cleanup of the press section, lead to machine downtime, and compromise the stability of subsequent operations.