Dr. Anderson's sage advice still rings true today with this flashback to 2003.
Single-stage versus multistage stretching The greater the tension applied to mesh in a single stretching step, the greater the thread deflection and the higher the tension loss the screen will experience due to fiber realignment. Stretching screens to the desired tension level in one action is possible, but produces highly unstable and inconsistent mesh tensions.
As tension forces on mesh threads increase these forces trigger fiber realignment. The realignment of threads continues until the friction forces at thread intersections are greater than the tension forces acting upon the threads. Any time you introduce higher tension forces, this rapid thread realignment and tension loss recurs. However, when tension increases are applied incrementally, with brief rest periods between stretching stages, more of the thread realignment and tension loss occurs during the stretching process than after the process is complete. In other words, you’ll minimize the overall degree of thread deflection by using a greater number of small stretching and rest cycles as opposed to a single stretching stage followed by a long rest period.
In multistage stretching, the time for each cycle should be short so that the overall stretching time remains the same as a standard single-stage tensioning cycle (Figure 3). Even with this approach, you can expect additional tension loss after the final stretching cycle. But the loss will be much smaller and easier to predict and control than if you had stretched the screen all at once.
[Figure 3: Multistage Tensioning
This graph depicts tension level over time when a multistage stretching procedure is employed. Note that total stretching time with the multistage process is identical to the time required for stretching in a single step. However, the multistage process results in a higher and more stable tension level. The shaded area at the top of the multistage graph represents the small degree of variability in final tension that results from using different mesh counts, frame types, etc.]
A rapid-tensioning study by the Screen Printing Technical Foundation, Fairfax, Virginia, revealed the advantages of multistage stretching with rest time between stages. The addition of the “fiber realignment” concept is further testament to the benefits of short rest periods between small, rapid tensioning cycles.
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