Operation of Forming Fabrics
Stringing
Smoking should not be permitted during installation. Other heat sources should also be removed from the vicinity of the fabric.
All parts of the machine must be inspected to insure that they are thoroughly clean and that no lumps of paper or rust are left over.
When stringing a fabric, take care that it does not come into contact with sharp angles (cover sharp angles with used pieces of felt).
Make sure fabric is centered properly and, if there is slack, tighten the tension.
Slow Running
When the fabric is set in the correct position, it should be run slowly, washing the fabric, to ensure there are no foreign materials on it and to check for wrinkles. After confirming that the fabric runs without abnormalities, adjust to the proper tension and increase the speed.
Proper Tension
Safe running and optimal paper quality can only be obtained when the forming fabric is under the proper tension. The appropriate tension depends on the paper-making conditions, but it is generally in the range of 4－7kg/cm2 (22－39psi). When the tension is low, the following results tend to occur; therefore, caution is required.
When the tension is set by hand, it is best to set a comparatively high tension initially. After the initial elongation has settled, readjustments should be performed as necessary. (In general, the initial elongation settles within 2－3 days, but since it is preferable for it to settle earlier, tension measurements should be performed occasionally for several hours after start up to keep tension at the required level.) After this, the same tension may be maintained as long as slippage and damage do not occur. If the fabric is severely stretched after abrasion has progressed, there is the danger that wrinkles may occur. When the machine is stopped for long periods, the fabric should be thoroughly cleaned and the tension should be relaxed. Our company manufactures and sells tension meters specially designed for plastic fabrics.
Winkles easily occur, leading to a streaky sheet.
Stock jump problems
The drag load becomes excessive, slippage and creep increase, and abrasion is accelerated.
Suction Box Vacuum
It is extremely important to run the fabrics so they do not bend or dip after going over each box. The total vacuum load of the boxes should be less than 100mm (4") Hg. Consequently, it is also important to choose fabrics with good drainage ability. Moreover, in some cases it is effective to decrease the number of boxes, if the total vacuum is the same.
Removal of Contamination
Contamination that cannot be removed by high-pressure showers can be effectively removed with chemical cleaning. Various kinds of organic solvents, or 5% caustic soda, can be used to spot clean. When an overall removal operation is performed, the following methods can be used:
After the treatment, the fabric must be thoroughly washed. Ordinarily, the high-pressure shower is sufficient; when it is not sufficient, caustic soda can be used intermittently.
Spraying over the entire surface of the fabric.
Mixing the agent in the shower pipe.
Applying a felt that has been soaked with the cleaning agent onto the forming fabric surface.
Repairs
Repairing ridges and wrinkles
The simplest method to remove ridges or wrinkles is using an iron or steam. There are differences in the degree of improvement depending on the degree of ridging or wrinkling, but when the fabric is folded on itself, it usually cannot be restored. All treatments should be performed at 130°C (302°F) or lower, and care should be taken that there not be any local stagnation.
Repair of holes
When small holes or short tears occur in the fabric, the following methods can be used:
Patching
This is the simplest method, and has excellent durability. We manufacture and sell specialized forming fabric patch kits, which have provided excellent repair results.
Sewing
This method can be employed for coarse-mesh fabric.
Predicting Fabric Life
The simplest method for predicting the life of a fabric, due to abrasion, is that based on its wear profile. Generally, one can count on using the fabric until its original caliper is reduced by 20－35%. However, for better accuracy, it is necessary to accumulate a number of empirical results. Since there are differences in abrasion at the edges (0－100mm or 0－4") and in the middle of the fabric, one should measure to a depth of at least 200mm (8").
