Dr. Anderson's sage advice still rings true today with this flashback to 2003.
A single clamp securely holds the ends of all mesh threads along one edge of the screen and pulls them evenly. This approach would be perfect if screen tensioning occurred only in one direction. But as Part 1 of this series pointed out, stretching is a two-dimensional process, and the forces and mesh alignment that result in the corners of the mesh will be different than those at the middle of each edge. Because a single-clamp system locks onto an entire edge of the screen, you have no way to compensate for the uneven tensioning forces on the screen. Consequently, single-clamps stretchers maximized fiber distortion.
Multiple-clamp tensioning systems (Figure 2), on the other hand, allow you to vary the pulling forces at different locations along each mesh edge, providing more balanced tension across the screen and limiting thread deflection. The result is slightly lower screen distortion than you would experience with a single-clamp system. The downside to multiple-clamp systems is that small areas of unclamped thread ends may be trapped between adjacent clamps, creating narrow bands of mesh with improper tension levels. To minimize or eliminate this problem, adjacent clamp areas must overlap in some way. Overall, the advantage of multiple clamps over single clamps is small, unless you add another capability to the clamps – lateral movement.
[Figure 2: Multiclamp Tensioning
Multiclamp tensioning systems allow you to vary pulling forces at each clamp to provide more balanced tension over the entire mesh. Some models feature clamps that are free to move laterally, which allows them to compensate for thread deflection and reduces the potential for tension loss after the stretching process.]
Lateral clamp movement The vast majority of stretching systems allow little or no sideways motion of the individual clamps during the tensioning process. But during the last decade, a growing number of pneumatic-clamp units have been introduced that mount the clamps on rails with bearings to facilitate smooth, easy lateral movement during stretching. The later movement of the clamps helps reduce the likelihood of tension loss due to thread deflection because the clamps move the thread ends away from the center of the mesh edge, especially near the corners. The net effect is reduced thread bowing, which means that less fiber realignment will occur and less tension will be lost after stretching.
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