Severe wear of polyester forming fabrics, which forces their premature removal from the paper machine, is one of the significant factors contributing to the shortened service life of the fabrics. When a polyester fabric operates on the wire table, its weft threads come into contact with the table—this is referred to as the weft wear mode. The wear can be roughly classified into three main types: traction wear, hysteresis wear, and transverse wear.
It is crucial during the operation of papermaking fabrics to quickly identify the wear condition of the polyester fabric, so as to determine the root cause of the wear and address it promptly. After the fabric has been in operation for a certain period, a comprehensive inspection should be conducted. For this in-machine inspection, a straight-handle magnifying glass can be used to carefully observe the fabric surface. The goal is to identify the correlation between the wear pattern and the wear rate, thereby calculating the wear rate and assessing the overall wear severity of the fabric. Meanwhile, such observations enable early detection of potential issues, allowing for the timely implementation of corresponding solutions.
For the inspection of polyester forming fabrics that have been removed from the machine, two key steps should be followed:
First, visually inspect the entire width of the fabric surface to spot obvious problems. Then, use a magnifying glass or a handheld microscopic camera for in-depth analysis to pinpoint the exact reason for the fabric’s removal and take targeted measures to resolve the issue.
For a more thorough analysis, cut a 30 cm-long sample of the full-width fabric from the removed material. Clearly mark the sample with its running direction, and also record detailed information for each sample, including the manufacturer, fabric number, paper machine number, machine speed, service life, and operating conditions during its use.
Next, a microscope is used to measure the wear degree of individual threads. For regular wear analysis and measurement, data is collected from three positions: 60 cm from each side of the fabric and the center of the fabric. The average value of these measurements is then calculated. In most cases, a wear curve is plotted with the average wear value as the ordinate (y-axis) and the number of operating cycles of the fabric as the abscissa (x-axis), and this curve is represented as a smooth line. The formula for calculating the daily number of cycles is as follows:
Daily number of cycles = Paper machine speed (m/min) × 1440 (min) / Fabric length (m)
Regardless of the reason for removing the fabric from the machine, its wear amount should align with the wear-life relationship curve specific to that fabric’s structure. Sudden changes in the wear rate or a regular decline in fabric strength can be observed from this curve. Additionally, the curve can be used to compare the wear rates of fabrics with the same structure operating on different paper machines. However, when the fabric is affected by other external factors, an anomaly may occur: the fabric with a shorter service life might have the same or even a lower average wear rate compared to the one with a longer service life.
Under normal circumstances, the inner side (roll-facing side) of the polyester forming fabric is the primary wear side. Nevertheless, for paper machines equipped with dewatering elements on the outer side of the fabric, the outer side (paper-facing side) must still be carefully inspected during the post-removal examination.
The formula for calculating the wear rate is:
Wear rate = [(Diameter of the thread C - Thickness of the thread after wear A) / C] × 100%
The wear rate is usually expressed by the degree of thread wear, specifically referring to the percentage of the wear amount at the elbow of the weft thread relative to its original diameter.
Wear on fabric threads often causes fibrous burrs to form on the front and rear sides of the threads along the fabric’s running direction. The burrs appearing on the rear side relative to the running direction are called traction burrs; they are caused by fixed components or components that operate slower than the fabric. The burrs appearing on the front side relative to the running direction are known as hysteresis burrs, which result from certain parts of the paper machine running faster than the fabric.
Transverse burrs, by contrast, rarely occur. They only appear under two specific conditions:
When the stretching rolls exert an excessively strong stretching force on the fabric;
When the fabric is sucked and depressed between the small holes on the surface of the water absorption equipment.
Sometimes, the small worn surface of the abraded thread appears smooth. This indicates either that the surface of the component causing the wear is relatively smooth, or that the wear occurs under low pressure. Conversely, if the small worn surface is rough, it signifies that the surface of the wear-causing component is relatively rough, or that there are sand particles present in the pulp.
