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The Benefits of High-Pressure Washes and High-Tension Screens

(July 2006) posted on Tue Aug 08, 2006

Find out how using an industrial-grade pressure washer to develop stencils and reclaim mesh will improve the quality of your prints and prolong the life of your high-tension screens.

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By Mark A. Coudray

You need way more than 1000 psi in order to really do some work. My personal comfort zone is between 2400-3000 psi. Pressures this high require the use of a multistage pump driven by a 5- to 10-hp motor. These industrial-grade machines are designed to work hour after hour in continuous operation. The cost range can be $400-4000, depending on the working pressure, duty cycle (how long the unit can be used non-stop before it must be allowed to rest), and the size of the motor being used.

Mesh preparation

The journey begins with stretching the mesh on the screen. Virgin mesh is notoriously unstable during the first round of preparation, imaging, and reclaiming. The tension changes constantly (even with very good low-elongation mesh). In addition, various machine oils and silicones may remain on the mesh from the weaving process. Proper practice dictates that you remove any of this foreign contamination before degreasing and coating the screen with emulsion. How you handle the screen during this phase can permanently affect the life of the mesh and the tension of the screen.

For those of you who use stretch-and-glue static frames, the stability of the mesh tension is directly affected by the use of a high-pressure wash. Mesh tension can only go down once it's glued to the frame. When mesh tension was first studied in the early 1980s, researchers thought the initial drop in mesh tension after stretching was caused by a phenomenon called cold flow. This is a process whereby the polymer molecules align themselves in the direction of the tension vectors. During alignment, they slide past each other, and the tension drops. This phenomenon served as a major argument in favor of retensionable frames, which allow continuous adjustment of mesh tension to maintain a consistent target value.

The development of high-density, low-modulus polyester polymers greatly reduced the initial drop in tension, but they did not cure the problem. Work done at the University of Wales, Swansea in the 1990s led to the observation that mesh tension is not uniformly transmitted across the screen. In fact, researchers found that knuckle friction at the intersection of the warp and weft threads restricted the transfer of force over the screen. Only with time, or additional physical assistance, would the tension be smooth, even, and stabilized.


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