Learn how to tension screens the right way and enhance the quality and efficiency of your work.
By Bron Wolff
The primary influences on achieving adequate screen tension include mesh count, screen size, stretching method/ equipment, and the experience of the screenmaker. The mesh count is an obvious factor--not because of the number of threads per inch, but because usually, as thread counts increase, thread diameter decreases. Will a 330-thread/in. screen fabric support a higher tension than a 380- or 420-thread/in. mesh? Sure it will. But will a 380-threads/in. mesh with a 34-micron thread diameter hold a higher tension than the same thread count using 31-micron threads? In fact, it will--by about 3-4 Newtons (N). So the mesh count alone is really an incomplete indicator of a mesh's ability to support higher tensions; thread diameter is an equally important concern.
Screen or frame size is the next factor. Your 380-thread/ in., 34-micron fabric cannot support the same tension level on a large 71 x 81-in. frame as it would support on a 24 x 24-in. frame, or even a 36 x 48-in. one. The smaller the frame size, the higher the tension you can get. But how high can you go on larger-format frames? One article I read contends that a graphics printer using a 380-thread/in. mesh on a frame 48 in. wide will not be able to achieve tensions above 20 N. We tension 380-thread/in. mesh on 41 x 51-in. frames up to 35 N on a daily basis, and on 41 x 88-in. frames, we use our pneumatic stretching system to get finished screens with tensions in the 25-N neighborhood. If you're ever in Joliet, IL, feel free to stop by and see for yourself.
In terms of stretching method, the big issue to me is how to handle relaxation of the mesh after stretching. If you tension a screen to 20 N and leave it overnight, you'll return to find that it is no longer at 20 N, but probably closer to 17-18 N. Now wash and degrease the mesh, then coat it. You drop another Newton or two. Next, put it on the press and print 100 passes. Two or three more Newtons are gone. Reclaim and re-image the screen, then print again. Tension drops by another 1-2 N. After two press runs and associated handling, your 20 N screen has dropped to 12-13 N.
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