How To Prevent The Forming Wires From Mistracking, Wearing, And Clogging
During the operation of a paper machine, the condition of the forming fabric directly affects paper quality and production efficiency. When monitoring from the central control station, one cannot rely solely on a single tension value; instead, it is necessary to make a comprehensive assessment by considering multiple parameters together-such as tension, guiding actions, spray pressure/flow rate, vacuum levels, the water line, fabric speed, and the condition of the fabric edges.
Core Principles:
Maintain stability through tension and monitor frequency for deviation correction; ensure cleanliness via spraying and check flow uniformity; if tracking deviation occurs, first stabilize speed and tension,then inspect the spray systerm,guide rollers,load, and mechanical components.
I. Key Points for Wire Section Tension Monitoring 1. Risks of excessively low tension When tension is too low, the forming wires tends to go slack, leading to issues such as wire mistracking, creasing of the wire surface, wrinkling at the edges, abnormal friction against vacuum box covers, an unstable water line, and uneven sheet formation; in severe cases, it can even cause the wire to crack or tear. DCS Indications: · forming fabrics section tension PV falls below SP · Increased amplitude of tension fluctuations · Frequent operation of the wire guiding device · Noticeably intensified wire oscillation during speed fluctuations · Increased frequency of wire section vibrations or alarms
2. Risk of excessive tension
Excessive tension is not a safe operating condition; it accelerates forming net fatigue, leading to stretching and deformation, edge cracking, seam damage, increased bearing loads on guide rolls, and accelerated wear on vacuum box covers, thereby significantly raising the risk of forming fabric breakage. DCS indications: · Tension consistently exceeds the process upper limit · Tension control output remains persistently high · Drive load increases, resulting in higher current in the forming section · Guide response becomes sluggish
3. Risks Associated with Tension Fluctuations Frequent tension fluctuations pose a greater risk than simply high or low tension levels. Common causes include unstable movement of the tensioning roll, pressure fluctuations in pneumatic or hydraulic tensioning systems, excessively rapid changes in forming fabric speed, contamination buildup on guide rolls, frequent operation of the forming wire guiding system, localized forming fabrics wear or seam irregularities, and fluctuations in vacuum suction loads. Key monitoring points for the central control system: · Whether the tension PV exhibits periodic fluctuations · Whether the tension control OP shows large, rapid swings · Whether the tensioning air/hydraulic pressure is stable · Whether the main drive speed fluctuates · Whether the vacuum level fluctuates in synchronization
Key Points for Monitoring Spray Water Flow Rate The function of the spray system is to clean the forming fabric, maintain its permeability, and prevent clogging as well as uneven local dewatering. 1. Insufficient Spray Water Flow Rate Insufficient flow can lead to forming fabric clogging, a shift of the water line toward the dry end, increased vacuum load, uneven cross-machine direction (CD) moisture, poor sheet formation, and localized heating or wear on the fabric surface; it may even cause paper machine forming fabric mistracking or abnormal localized stress. DCS Indications: · Spray water flow PV below normal range · Drop in spray pressure · Increased filter pressure differential · Abnormal high-pressure spray pump current · Gradual changes in vacuum level · Gradual shift of the water line toward the dry end · Deterioration of QCS CD moisture profile 2. Excessive Spray Water Flow Rate Excessive spraying is equally detrimental; it increases the water load on the forming section, causes level fluctuations in the white water system and increases vacuum load, leading to higher sheet moisture content and excessive mist that affects the working environment, while also increasing energy and water consumption.
Key Points for Monitoring Spray Water Flow Rate The function of the spray system is to clean the forming fabric, maintain its permeability, and prevent clogging as well as uneven local dewatering. 1. Insufficient Spray Water Flow Rate Insufficient flow can lead to forming fabric clogging, a shift of the water line toward the dry end, increased vacuum load, uneven cross-machine direction (CD) moisture, poor sheet formation, and localized heating or wear on the fabric surface; it may even cause fabric mistracking or abnormal localized stress. DCS Indications: · Spray water flow PV below normal range · Drop in spray pressure · Increased filter pressure differential · Abnormal high-pressure spray pump current · Gradual changes in vacuum level · Gradual shift of the water line toward the dry end · Deterioration of QCS CD moisture profile 2. Excessive Spray Water Flow Rate Excessive spraying is equally detrimental; it increases the water load on the forming section, causes level fluctuations in the white water system and increases vacuum load, leading to higher sheet moisture content and excessive mist that affects the working environment, while also increasing energy and water consumption.
